The 24-Volt Insurgency: Why Desert Packrats Are Mocking Your Peppermint Oil

There is a specific, primal horror to waking up in the middle of an Arizona summer night in a pool of your own sweat, checking the thermostat, and seeing a crisp 89 degrees staring back at you.

It’s even worse when you grab a flashlight, walk out into the hot, dark, pre-dawn desert air to inspect your air conditioner, and find that a furry, four-legged demolition specialist has systematically snipped your 24-volt control line, converting your life-saving air conditioner into a heater.

If this happens once, it’s an annoyance. If it happens three nights in a row, it’s a battlefield between the primal forces of nature and civilization as we know it.

What was going on?

For the last week, my northern AC unit became the epicenter of a tactical showdown between human engineering and rodent persistence. A huge inconvenience to me, but after a few midnight flashlight repairs and some serious crime-scene analysis, I’ve cracked the code on why they do it, why the internet’s favorite DIY remedies are absolute garbage, and most importantly, how to build a defense grid that actually works.

Add to that the safety factor. The default factor in home AC heat pumps is to heat. It seems better to be awakened to the heater running unexpectedly instead of the cooling. The engineers seem to think that uncomfortable heat is better than freezing to death in the winter from a rat breaking the 24-volt circuit. Living in Arizona, I might argue that, but my relatives in the Northeast would object.

The Soy-Plastic Myth vs. The "Perfect Toothpick" Reality

If you spend ten minutes on automotive or HVAC forums, you will run into the classic urban legend: "The government forced manufacturers to change the insulation to soy-based plastics, and now the wires taste like food!"

Let's set the record straight. While it’s true that modern car manufacturers did switch to soy-based bioplastics over the last decade (creating a multi-thousand-dollar buffet under modern truck hoods), it wasn't due to US regulations. It was companies pandering to environmental concerns.

This new insulation will, over time and exposure, decay—unlike petrochemicals that last forever. It’s lighter, easier to form, weighs less, and fills that niche of environmental awareness that sells so well to city dwellers who seldom actually see, much less live in, the environment they talk so much about preserving. The unintended consequence of this corporate virtue signaling? Your expensive vehicle or outdoor equipment has been converted into a gourmet snack.

However, before you go blaming a corporate marketing department for your broken AC unit, there’s a twist: your standard residential air conditioner thermostat wire isn't soy. It's still old-school, petroleum-based Polyvinyl Chloride (PVC). It smells like chemical garbage, not dinner.

So why did the rats keep coming back to my north unit to slice the exact same wire?

During day three of my investigation, I noticed something critical: The rats completely ignored the thick outer cable sheath. They only attacked the thin, individual 18-gauge colored wires after the sheath had been peeled back for the connections. "But why?" one asks.

It turns out it's a matter of biological imperatives. A rodent’s incisors grow continuously—up to five inches a year. If they don't constantly gnaw on things to file them down, their teeth will literally grow through their own jaws. This provides some clues to why, but also some cautions.

The thick outer jacket of an AC cable is too wide and smooth; they can't get a jaw around it. But an individual 18-gauge strand? That is the exact diameter of a small root or a piece of desert scrub. It fits perfectly into the sweet spot of their jaw mechanics. It's not dinner—it's a precision-engineered toothpick. Something to gnaw on to help grind down their teeth, and a low enough voltage not to roast them into a carbon footprint. 

Why Internet Remedies Fail: The Evaporation Trap 

Before we talk about what works, let’s talk about the absolute sales BS cluttering up the internet. In my time fighting the desert wire-eaters, I have systematically tested the "feel-good" remedies. Here is the field report:

• Peppermint Oil: I once sprayed a literal quart of high-concentration peppermint oil around the engine compartment of my truck. The result? I had the best-smelling, mintiest rodent hotel in Arizona. Once the initial vapor shock wears off in a few hours, the rat’s drive to chew completely overrides any objection the rat has to the smell. Trusting that home remedy cost me $2400 at the dealer having wiring harnesses replaced.

• Bitter Sprays: Products designed to stop dogs from chewing work for about 48 hours. In our brutal desert environment, the intense sun, heat, and ambient dust cause the bitter compounds to volatilize and vanish. Also, remember, the rat has to chew enough of it to taste the bitters. Our own experience with canine bitters has mixed results; some dogs react to it, and others ignore it and still chew off our baseboards and chair legs. How well would we expect it to work on a rodent that eats cactus (thorns and all), chews the bark off our fruit trees, gathers dried dog poop and uses it as a front door to its home, and leaves trails of its scat under our BBQ?

• Predator Urine: Buying fox or coyote urine sounds tactical, but rodents are highly adaptable. A desert packrat has no evolutionary memory of a European Red Fox. Even if you use local coyote scent, if the smell just sits there day after day without a physical coyote ever showing up, the rats figure out within 48 hours that it’s a ghost threat. Renewing the dosage only helps the rat to learn that the smell is not left by a predator simply because the threat never materializes. 

The Real Culprit: The Oasis Effect

While inspecting the unit on day four, I finally found the smoking gun. I noticed a distinct, wet patch of condensation pooling right on the base tray of the compressor housing. Look closely at the dust, and you can see the tiny, muddy footprints.

In the middle of a scorching summer, a guaranteed, daily source of fresh, dripping water is worth more than gold. The copper pipe carrying cold refrigerant into the air handler inside the house condensed the limited humidity of our desert air and dripped into that little reservoir at the bottom of the compressor casing. My AC unit wasn't just a hardware store; it was a five-star desert oasis. The rats were stopping by for a cool drink of AC sweat to beat the heat and then deciding to utilize the local 24-volt toothpicks while relaxing by the pool.

Before your environmental instincts kick in and you comment on how bad for the environment rat poison is, I had been three nights without sleep in a sweltering puddle of sweat, listening to complaints about the AC continuing to fail. What exactly would you have done? Cut me some slack here. Plus, this is some of the incredibly expensive rodenticide that only kills once. 

Even worse? Those green poison pellets I threw down were sitting completely untouched right in the puddle. The rats literally marinated their poison while ignoring it to chew on my wiring.

The Counter-Insurgency Playbook

To win a war, you have to change the environment. Here is the two-phase strategy I used to take back the north wall.

Phase 1: The Tactical Retreat to the High Ground (The Free Fix)

The rats were successful because the 24V lines were sitting on a low-level "lounge deck" right at chest height for a sitting rodent.

The service access to the AC compressor

Close up of the wiring area after two

repair attempts. 

I pulled the thin AC control lines completely out of that bottom open shelf. Then I rerouted the multi-conductor line from the house upward and fed it directly into the side knockout of the upper, enclosed high-voltage metal service area.

The 24VAC wires are on the bottom

And the 240VAC wires are on top.

By making all the wire-nut connections inside a sealed metal box, the target wires were protected. The only thing left downstairs near the concrete pad is a smooth, unbroken stretch of factory cable jacket. They showed up the next night, drank their water, and realized the wire playground was locked and went off to some other rat playground. We are currently four nights in with zero outages.

Phase 2: The Permanent Armor (The Parts List)

Once the immediate crisis is averted, it's time to build a maintenance-free fortress. Because we are dealing with a whole desert ecosystem—from tiny mice to heavy-jawed gophers, ground squirrels, and don't forget, rabbits—your best bet is to armor-plate the entire run from the wall to the chassis.

1. Mechanical Armor (Techflex F6 Heavy Wall Braided Sleeving: Instead of tearing your fresh wiring apart to slide a tube over it, use a split braided sleeve. The heavy-wall version has a built-in lateral overlap that snaps shut around the existing wire. A rat's teeth slide right through the slick woven matrix rather than grabbing and cutting it. Plus, the wire sticks them in their mouth, making it unpleasant enough to leave alone. 
   
   

   
   I've used this on my pool for months. 

2. Chemical Deterrence (Genuine Honda Rodent Tape) This stuff is the gold standard for a reason. Honda bakes micro-capsules of pure capsaicin (chili pepper extract) directly into the vinyl substrate. It doesn't wash away or evaporate in the sun like a spray. When a rodent punctures it, the capsules burst directly into their mucous membranes. It's true that the rodent has to actually chew on the tape to get the burst of capsaicin, but that's what rats do, chew.
   
   

   Safety Note: Always wear heavy gloves when handling the spicy tape, and for the love of God, do not rub your eyes, scratch your privates, or pick your nose afterward. You might also warn a repairman, but that's your choice.

End Result

Here's a picture of the AC unit after I finished it up. It has (so far) held up against the wandering rodents seeking cover and water. 

All the points where wires might get exposed are wrapped with rodent tape and  all the wiring is inside the wire sheath. Yes, those are stainless steel zipties; plastic doesn't last long here. I suspect this will hold up for a long time, but I'll keep an eye on it just in case of sun deterioration. 

Final Lessons from the Desert

If you live out in the rural desert, nature is always trying to reclaim your assets. If you park a vehicle outside, leave the hood up. Rats hate open spaces where hawks can see them, and they hate the sun. I've had reasonable luck with flashing lights; get some flashing Christmas tree lights and toss them under your vehicle to chase rodents away. This method does run the risk of the extension cord from the vehicle to the outlet getting chewed up though. For vehicles I use a combination of open hood and flashing lights that has worked well.

If your AC goes down, look for the water source, move your connections into protected areas, and armor the gaps. Let the neighbors deal with the mint sprays and the ghost coyote urine—stick to solid mechanical engineering and really spicy unexpected treats.

Microwave Trouble: Sometimes a Stupid Question is Just What You Needed

Several times now I've mentioned my microwave oven in passing. It's given me a couple of problems over the years: I managed to explode a coffee cup and the liquid got into the turntable motor, and the entire control board went belly up on me. The turntable motor was easy; I just got a new part and replaced it. The control board was harder, that took a call to GE because I wasn't sure which of the four boards was acting up. I couldn't find a schematic on the darn board to isolate it.

The idea I had was to use the best appliances in the kitchen I could and then not have to ever replace them. The fridge has failed twice; the freezer several times, the range once, the dishwasher four or five. Most of the repairs were done by a real GE repairman using real GE parts except the freezer that had a piece of crap defrost timer in it. So much for the idea of getting top-of-the-line appliances.

But, don't misunderstand, I'm not rich and wasn't rich when I got them. I caught a good sale, the prices were much, much lower then and I had just sold my old house. I was also naive about the actual quality of appliances.

The microwave was working fine with a little fan noise and then the noise got really loud. It still worked, but you couldn't stay in the kitchen with it. Obviously, the bearings in it had failed. Right? Not so, the stupid squirrel cage blower had expanded, rubbed against the fan enclosure and started to get ripped apart. Nice.

Of course, I had to take it apart to find this out. This microwave is a ZSC2001FSS02 and looks like this:

I really like this oven. It's microwave as well as a halogen heated convection oven. It'll do three big baked potatoes in around 15 minutes without waiting for it to heat up. After I got it out of the cabinet and took the lid off to tell what was making all the noise, I looked for the part. No stinking luck; well sort of no luck.

The GE parts web site didn't even list a part number for the blower. It simply wasn't there. Sears listed a part number, but it was shown as "Not Available". Partsdirect showed the number and said the factory didn't supply it anymore. I used the part number and searched for about an hour and couldn't find one. Being a resourceful desert dweller, I went looking for the manufacturer since the name was right on the label, Oh Sung and the part was OBB-2009X1 or maybe m051004.3R. Once again, no luck.

I did find the manufacturer, but I really didn't want to spend a week exchanging emails and then maybe a month getting something from them. So, I went looking for a replacement squirrel cage to put in since the existing motor was working fine. The fan looked like this:

See why it was making noise? Ignore the grease, I didn't bother cleaning it up for the picture. When I pulled the blower assembly apart and looked at the actual squirrel cage, it was worse than I thought:

I found the missing pieces inside the blower cover. I had no luck at all finding a replacement for this. The only squirrel cages I found were for HVAC systems and such and they were waaay too large to do me any good.

OK, fine. I'll get something similar from a different microwave and somehow make it work. I switched over to ebay and started looking. There were a a lot of microwave blowers of different styles and sizes. None of them mentioned how big they were, just the various part numbers from the microwaves they were supposed to fit. It was sort of a order-something-to-see-if-it-works kind of thing. I hate that since it could take a long time and cost a lot of money in mistakes.

But, I did it anyway. I ordered a blower from a GE Advantium Microwave Oven that looked similar to the one I had in the squirrel cage construction:

And, that was a mistake. I took it apart and the squirrel cage was the same diameter, but longer and wouldn't fit inside the old housing. The old housing mount wasn't plastic like this one, it was sheet metal:

So, I just tried to mount the new(er) housing in the same place:

That didn't work out well. See how it protruded above the top of the cabinet? Here look from the side:

At this point I was ready to cut a hole in the microwave cover and just let it stick through.

The fans were longer and wouldn't fit inside the old squirrel enclosure and the new enclosure wouldn't fit inside the oven. The next try involved making room inside the old housing for the fans to stick out through the squirrel cage cover. I had to use the new motor because the shaft was longer to handle the longer squirrel cages. There was enough room and the fans would only stick out about a quarter inch, so why not?

About an hour later I had the modification done and now I could mount the new motor to the old metal brackets and put the thing in place except, the new motor was wired differently. The new motor had six wires and the old one had five. I actually hooked it up though to see what would happen (yes, I was that disgusted by then) and the new motor wouldn't start turning. I could get it going by giving it a push, but it wouldn't start on it's own. The start capacitor was wired differently. These motors all have similar wiring, so I should be able to wire it to match ... somehow.

The plug for the motor was one of those that one could remove the pins and rearrange them, but I couldn't figure out how to do it. Yes, I tried the good old paper clip and small screwdriver trick, but the method evaded me. So, I'm sitting there, on the floor, scratching my head and considering just cutting the wires and using some heat shrink and solder to rearrange them when my girlfriend piped up, "This may be a stupid question, but couldn't you just take the rod out of the new motor and put it in the old one?"

Advice to all men, never, ever tell them that they asked a stupid question. The minute I heard it I said, "No, because it's actually part of the armature and it would destroy the armature to try and get the rod ..." I trailed off because I realized that she didn't have a clue that the shaft was integral to the armature, and she really meant to switch the armature. Crap, why didn't I think of that.

I took the motors both apart; switched the armatures; installed the old housing (with the fan holes modified); the old motor and its correct wiring and newly installed armature with longer ends and it worked like a charm. These motors are mass produced for various companies around the world. The windings in the stator are sometimes different to get two or more speeds, but you can choose to use only one speed if you want. The armatures are all the same and you can move them around as needed. In this case, I needed the longer shaft on the armature combined with the windings from the old stator to match the wiring in the microwave. Really glad she was over watching me flail around.

Never ever tell a woman that she had a stupid idea. Her simple suggestion was exactly the thing I needed to get this to work.

I'm on the watch out for a truly suitable replacement, but don't have the pressure of a dead microwave hanging over me. I may contact the manufacturer for help in sourcing parts to see if I can get any help there. They may even have metal squirrel cages for these, and that would eliminate the problem forever. Failing that, I may go to an appliance store and prowl through their supplies to see what I can turn up. Or a junk yard.

And, what did I learn from this experience?

Mostly, I learned to listen.

Supercooling in the Desert: May 22, 2018 a day that will live in infamy !

This is the day I got clobbered by APS (my power company)

Look just before 8PM (20:00); see that bunch of spikes? My peak billing period lasts until 8, and something was sucking power before the period ended ! Let me expand the little piece that shows the problem:

That little period from about 7:24 to 8:00PM was the clothes dryer.

Yes, just a little before the end of my peak period a guest started the dryer to do some clothes. It wasn't their fault, they didn't know that the fascist power company would be watching to see if such a thing happened.

The peaks run as high as 7.4 kW, and it was doing this for a little over a half hour. The APS chart shows it like this:

And it was almost impossible to find. I looked for quite a while before I noticed it. I put the arrow on there to show you the tiny little green area that resulted. It shows up a little better on a single day chart:

That minor little slope up in the green area is where the meter saw the dryer running. It's recorded as "usage 3.18" during the 7-8PM hour. In theory, this should be my high 'demand' number that is calculated into my bill for the month.

I guess I should do a little calculating to see how this works to help me understand and avoid it even more stringently in the future. Let's look at the detail portion of my bill first:

So, the demand number wound up being 3.17 and is used as a multiplier in several items in billing. Here's the rate sheet for the plan I'm on:

So, my 'On-Peak Demand Charge' is 17.438 * 3.17 for $55.28. But, there's nothing on my bill that says that. Guess what? To make it more complicated and harder to understand, they actually split the $17 charge into two components and calculate them separately. From their tarif sheet again:

Notice how the two numbers, $4.000 and $13.438 add up to the $17.438 they call the 'On-Peak Demand Charge'. OK, fine, I have a calculator and can punch in numbers like anyone else. 4.000 * 3.17 = 12.68 and 13.438 * 3.17 = 42.60, and they add up to the 55.28 I got above. So I should see:

Delivery On-Peak Charge 12.68
Generation On-Peak Charge 42.60

Or something similar on the bill, and indeed I do. Sort of:

Demand charge on-peak - delivery $12.40
Demand charge on-peak - generation $41.66

If you look at the bill, you'll see them on there. The sum of the two charges is $54.06 which is darn close to my initial $55.28. The reason for the difference is that APS made a mistake in the original rate change request and has to use the demand number to one significant digit and they can't round, so the actual demand number they get to use in this case is 3.1kW. That's on the bill also, so I don't even have to do the truncation itself:

Your billed on-peak demand in kW 3.1

That's a good thing because rounding would have put me up to 3.2 and would be paying even more.

Now, I got the cost all figured out, the dryer running cost me some amount, but how much extra based on past performance. To get that, I'm going to look at last month to see; taken from last month's bill:

Your billed on-peak demand in kW 1.5
Demand charge on-peak - delivery $6.00
Demand charge on-peak - generation $20.16

That stuff totals up to $26.16, so my dryer cost me $27.90 last month because I didn't keep it under control. It's actually a little bit higher because the rate per kW during peak is higher ($0.08683 vs $0.05230), but that's only 3 cents per kw, and the dryer only uses 7.5 kW at around a 50% duty cycle for 3.75 kW or $0.32 extra. I'm willing to ignore that.

Now is the appropriate time to talk about how APS gets that demand number. As I mentioned in another post, they average each hour and compare it to the maximum hour during the billing cycle. That gives me 5 vulnerable periods each day: 3-4, 4-5, 5-6, 6-7, 7-8. So, the dryer kicked on and sucked power in bursts like all electrical heating appliances and those bursts pulled 7.5 kW for a short period. The bursts were roughly half the time, so it worked out, on average, to the 3.17 kW number that APS measured. It would be too much to read if I did all the calculations, but you see what I mean. That 3.17 was the highest reading so far that month, so it kept it and continued to look for a higher hour; fortunately, it didn't find one, and that's how the month's bill came to be. Next post I'm going into how to read our smart meter so folk can actually see what is coming. Unless one goes to the trouble of doing what I've done, you can't catch it real time and stop it; you can only see the what's already happened.

This is not going to break me, but it does lose me some bragging rights. Because I didn't keep control, I'm out about 28 bucks. Be warned though, if the hot water heater had kicked on, and the stove was running, this would have been a monetary disaster. Thank goodness it was only the clothes dryer and that close to the end of peak !

There you are, an example of how power can get out of control no matter what you do and how much attention you pay to it. Something will slip in and get you from time to time. Overall though, keeping tabs on my power has saved me thousands over the years. This post is also good for folk that don't completely understand how that 'Demand Billing' stuff actually works, and how to tell if you're messing up.

The parts to prevent this from happening to me again are already on order.

Previous post in this series is <link> then next is <nothing yet>

My Freezer: Right in the middle of installing Grafana

So, I'm installing Grafana on my laptop and pull up a chart that looks like this for my monitored appliances:

What the heck? the freezer in the house is getting hot! About a minute later, an email comes in that I actually check since I'm setting right there and it tells me that the house freezer is over 50 F.

Yes, my freezer sends me email. I set this up about 4 months ago when the door didn't get closed completely and was open for HOURS before I noticed it. It didn't cost me much to replace the stuff that had thawed out, I cooked it instead, but having it happen got me to thinking about alarming that kind of thing. I have a process called 'healthcheck.py' that I run as a daemon (all the time) that monitors the other processes and many of the devices that are reporting around the house. Things like the XBee coordinator process, the thermostats and the septic tank float are watched for problems and an email is sent every hour that they don't perform up to snuff. I just added code to this process to watch the temperature in the appliances to make sure they were OK.

I got up, walked over to the freezer, put the frozen french fries back on the shelf correctly, and closed the door. Problem solved and crises averted. All the scoffers out there that poo-poo'd me about putting a temperature sensor in the appliances ... No, none of the other folk that are automating and monitoring their houses had disparaging comments, it was neighbors and friends that just let the house react to things and then complain wondered why I bothered with that much work.

Really ?

What was really unexpected though was the aftermath of letting the freezer warm up like that. Take a look at this chart of the aftermath:

I suppressed the other appliances and expanded this to show a little normal operation on both sides. The big deal is how long it took for the freezer to return to normal. Because I left the door open for about two and a half hours the temperature went all the way from below zero up to 63 degrees. Then it took over 24 hours for the thing to get back to normal.

Wow, I gotta pay more attention to that door. What the heck was happening with the power usage during this time?

Here's the power chart for the same period, and I see that shortly after I closed the door the freezer went into a defrost cycle. That's a good thing because there had to be a bunch of ice all over the evaporator coil. The compressor was on trying cool a freezer with an open door and humidity from the house was freezing all over the coil lowering its efficiency. Then the ice maker took off to fill the empty ice bucket that I had emptied of sludge. The compressor ran for the entire 24 hour period getting the internal temperature back down where it should be, but the defrost cycles and ice maker ate some of the energy during this time.

So, the power bill will be a little higher this month, but notice that the freezer only uses around 150 watts. It won't cost me much at all. Once I started watching the appliances, it really impressed me how little power they use. A little Honda generator could power the appliances around my house for an extended power failure. That will almost certainly become a project in the future.

There's a couple of other things I want to point out to readers. First, the reason I left the door open was that I was playing with Grafana and got distracted. Second, the graph I was playing with actually told me something useful: the stupid freezer was getting hot. Third, I was immediately able to research the results of my screw up. What went on with the temperature recovery in the freezer and how that affected my power usage.

That is so stinkin' COOL. (pun intended)

So, I really recommend saving data for some period. I've never gone back more than a few months looking for some change or problem, but as shown here, a couple of weeks can really be valuable. I personally carry years of data, but that doesn't mean I have to; it also slows down my database queries. So, balance your own needs to what you want to do. Over time, you'll work it out.

Also, Grafana allowed me to look at different time frames and data really quickly. It took me just a few minutes to prowl through the data to understand what was going on. I could have done the exact same thing with other charting tools I've tried, but it would have taken me way longer. Man I'm glad they implemented MySQL in this tool.

I probably should go clean the freezer now, but at least it's working.

More Adventures With My Freezer

Last post I described how I managed to screw up my freezer defrost controller <link>. This is the latest chapter in that escapade.

I started up Eagle and created a board to hold a higher power relay and XBee to overcome the problems with the small relays that are generally available for Arduinos. The board got overly complicated and the cost of the various parts got to the point where it was just silly to continue. Then I got a brainstorm: why not just use a relay board as a module similar to what I did with the XBee.

I started up Eagle again and took that tactic; it worked really well --- at least on paper. Here's the schematic I came up with:

For those of you that aren't used to Eagle schematics, each of the signal lines has a name and you just match up the names to see where things hook together. It makes for a really simple looking schematic that is a bit hard to follow. The idea is that the set of plugs on the right are the pins on an Arduino, the two modules in the middle are an XBee and a relay module that is readily available all over the place:

These little boards are available for less than $5.00 and can handle motors. It should be exactly what I need for this project. Where I ran into trouble was all the parts necessary to support one of the relays. Things like buffer transistors, optoisolators, LEDs and such are a real pain to keep stock of and you can't really order just a couple. I'd have parts piled all over the place if I tried to build up everything necessary; so I took the easy way out and just mounted the relay on a board I designed along with the pins for the temperature sensor, XBee, some lights and some buttons. Basically, my new board would be a holding device for the stuff I needed for this project.

Cool huh? This is the board layout I came up with:

I added some LEDs at the front of the board so I could see that it was alive at a glance, matched holes on the board to the holes on the relay module and added a couple of buttons to control reset and defrost for testing. Heck, I even put a Saguaro cactus on it as a kind of indicator that it was designed by me.

I sent the gerber files to Seeed Fusion because I haven't used them before. About 4 weeks later the boards arrived. I say boards because you get 10 of them for the same price, but the shipping was high. To offset the shipping I included the rest of the temperature sensors I need for my house monitoring project. So, for around $38 I got ten of the defrost controller boards and ten more of the room sensor boards for later.

Here's what the boards look like:

I chose yellow because I've never messed with a yellow board before. I labeled every stinking thing because I can't ever remember where stuff goes after a few weeks of not looking at it. I also stuck the LEDs on the front of the board so they could be seen by peeking through a vent area on the freezer. My way of showing off that I modified the freezer.

Here's the board assembled:

I pulled the screw connectors for the digital signals off the board and replaced them with pins so I could plug the relay module into the board. I bent the LEDs over for that day when I actually make an enclosure for the board. I used Arduino-like pins for connecting to an Arduino, but that was a mistake. Somehow I thought I might someday mount something above this board. Notice that's not possible. Oh well, they may serve as test points some day.

Here it is mounted to the Arduino:

Yep, it's bigger than the Arduino. I considered using one of the really tiny Arduino devices and just having a board that connects the various modules together, but decided to just use what I already had. It won't matter when I get it into an enclosure because only the wires going in and the LEDs will be visible.

I powered it up and everything worked first try. Amazing. I actually got something like this to work without another hitch.

Some tricks you can use if you decide to do something like this: Print the board on paper and try the various parts on the paper. This is how I managed to get the holes for mounting the relay module in the right spot. First I measured them as close as I could, then I printed the board and put the module on top of it to be sure the holes lined up correctly; they didn't. I was a tenth of an inch off. A little moving of stuff and they lined up perfectly. I did the same thing for the pins for the digital signals to the relay module also. I used the same technique to be sure the Arduino pins lined up as well. When I got the boards in I was almost afraid to try it out for real, but it worked perfectly.

Lining up something like this is a real pain, but using the printed version of the board takes almost all of the anxiety out of the process. Another trick is to label every thing in sight. The values of the components, the direction things point, which way a diode goes in, these are the things you forget while you wait for the board to arrive. Just label them in the silk screen so you don't have to wonder what goes in that hole and which way it points.

This is the third board I've had made for one of my projects and I think I'll do more over time. It's just too easy to mess up a tiny wire from one component to another and it makes the end result very fragile. The other thing I learned is just using the inexpensive components that are available to us for projects. I could use multiple relay modules like this in a project and have a board made to mount and wire all of them making the end result pretty and easier to work with. It should make troubleshooting easier as well; I won't have to follow a wire from place to place to see what went wrong.

Now to install it and watch it work for a while. I also have to figure out what to do with the other nine boards I don't really need.

Edit: After it was installed and tested once, it failed. Seems the relay wouldn't close; it got the signal to close just fine, but the relay just wouldn't activate. I chased the problem to the power line going from the wall wart to the Arduino, and changing that cord fixed the problem.

A lot of us have encountered this problem. We get a USB cable from somewhere and they use tiny wires that can't even carry a half amp three feet; it can drive you nuts trying to troubleshoot the problem because it looks just fine until you try to drive a relay or a set of LEDs. When you try and pull power, the voltage drop through the cable shuts things down.

Anyway, it's working just fine now and the stupid cable has been labeled so I'll know next time.

Adventures With My Freezer (the one in the house)

Over the years I've been doing modifications to the freezer in my kitchen. It all started way back in 2014 when I decided to not only measure the power usage of this device <link>, but to also control when the defroster runs <link>.

A tiny bit of background for folk that haven't been following my silliness for very long: I'm trying to lower my electricity bills here in the Arizona desert, and have a power company that offers a lower rate during off hours. What I do is try to keep all my major usage in the non-peak hours, and having the defroster run whenever it wants to sometimes leads to defrosting in the middle of the peak period. Also, I bought this freezer because it is simple, really simple. There's no huge electronic package in there that is designed to save power, hook to the internet, take pictures, call my Mom, etc. It's just the basic freezer, albeit a high capability, and repairable model that looks really good.

I also added the ability to monitor the temperature inside the freezer <link> after my 'wonderful' defrost controller crapped out. While I was fixing that I decided to combine the two relays on the Arduino shield I was using to parallel the contacts, hoping to extend the life of the relays.

Don't ever do that !!

I totally forgot that doubling the number of components also doubles the possibility of failure, as well as doubling the ways they can fail. This is a great story of doing the wrong thing, so I'm going to teach you a bit about the defrost cycle on a freezer so you understand what I got myself into. Since I have the ability to chart the actual action of my freezer, you get to have real examples of my (seemingly infinite) ability to screw up.

This is what a normal defrost cycle looks like when you can observe both temperature and power usage.

Ignore point A, that's the icemaker running to dump ice in the tray, and the tiny bump next to it is the lights in there when I open the door.

Point B is the start of the defrost cycle, this happens on a timer that closed a SPDT set of contacts that shuts off the compressor and kicks on a heater that is actually attached to the evaporator at the bottom of my fridge.

Point C is where the heater is running, and it will run until a temperature sensor (also mounted on the evaporator) reaches a built-in temperature that the manufacturer thinks is the best to clear the frost away. In my particular case this thermostat is 37F.

Point D is where the heater shut off and the freezer just sits there until the timer runs out after 30 minutes. This is to allow the water to drain out the bottom into an evaporation tray and away from the freezing area of the freezer.

Point E is where the compressor kicks back on, the spike is the usual one you get from the run capacitor letting a lot of power through to get things going.

Point F is the normal compressor run cycle. It runs until the Freezer gets to operating temperature and then shuts off. On freezers the compressor runs a long time, but that's OK because these things only use around 100W. In the days before LED lights in appliances, the lights used a lot more power than the compressor did.

So, the heater pulls around 400W, but should only run for around 15 minutes, however once in a while it because of high local humidity, someone holding the door open too long, trying to freeze a gallon of hot water, or something like that, the heater will run the entire 30 minute cycle time. When this happens, the next defrost cycle will take care of the left over buildup.

Unless something is broken, or you've got someone in the house that messed things up.

I noticed that the temperature in my freezer was gradually rising and the compressor seemed to be running too long. Here's a chart of what I saw when I looked at it:

Once again, the sharp peaks are the icemaker doing its thing, but let me step through the other parts I pointed out:

A is where the defrost heater started. This part appears perfectly normal.

B is where the defrost heater should have leveled off at around 400 watts. Notice it's up around six hundred and climbs after that.

C is the defrost heater shutting off after the full thirty minutes of time allowed by the timer. It didn't shut off early and coast.

D the big spike of power should have shown up, it didn't. The spike there is the ice maker dumping ice.

What was happening? After a bunch of troubleshooting and scratching of my head, I figured it out; one of the relays had a frozen up contact and the compressor was running during the defrost cycle. The other relay was working just fine, but it couldn't stop the compressor with the other one bad.

I gutted the relays to double check (sorry I forgot to get a picture) and one of them had the contacts welded together and was the culprit in this mystery. I pulled it loose and let it go. About two days later, the remaining relay gave up the ghost as well. So much for those relays. I've got my eyes on one of the 30 amp relays now and have an order off for a circuit board that will hold it and an XBEE in my own designed Arduino shield.

Yes, I feel a bit stupid. But, isn't the ability to chart the performance of my freezer cool? Looking at the database of freezer data I was able to tell exactly which day it happened and how much the temperature rose over time as the defroster competed unsuccessfully with the compressor. Even the fancy internet connected freezers can't do that.

Right now, the freezer has the old mechanical defrost control in it that has had to be replaced twice because the mechanical clock in it doesn't hold up over time, and the defroster turns on whenever it feels like it. I had to get out the heat gun and melt the frost off of the evaporator by hand to give it a head start, that wasn't hard, but it did let the ice cream get soft.

More later, I'm not giving up on this.

Interaction of Appliances

One of my readers (thanks Andreas) commented about how controlling the appliances could help me.  For example, not letting the compressors of the refrigerator and freezer go on at the same time could lower my peak demand.  I answered that I was a bit leery about that because it could lead to spoiled food.  But, I decided an exercise in looking at it wouldn't take too much time and maybe it would tell me if such a thing would save me money.

For those of you just stumbling upon this site, I have demand billing from my wonderful power company.  There's a long discussion of this here <link>, but suffice it to say that from noon to 7PM I carefully control the usage of power around the house to reduce the power bill.  A single mistake that lasts for 15 minutes during this period could cost me a LOT of money.  Enough to buy several little computers to control things around the house.

So, I looked at adding the usages and creating a new graph to show the total use from my two freezers and refrigerator over a period of time, but had a brainstorm along the way.  I could simply use HighCharts ability to stack graphs.  It worked, and now I have a better understanding of my usage that I want to illustrate for people out there that are considering (or doing) the same kind of thing I do.

First though, a recap of the appliances and what their power usage profile is.  Here's my refrigerator graph as an area chart:

This appliance runs for short bursts to cool down to around 38-40 degrees.  It gets the most activity, but is pretty efficient.  Now, my freezer:

This thing runs a lot.  It has a good compressor that doesn't use much power, but it runs a lot more than I expected.  Still, it doesn't actually chew up much power.  And last, the garage freezer:

This thing runs about half the time during the summer because the garage is hot.  I don't cool the garage and it's on the south side.  

The little spikes in the charts are an artifact of the way I graph the data.  Yes, I could have hunted down the problem and fixed it, but I wanted to study the data, not spend a couple of hours chasing down a bug and fixing it.  So, just ignore the spikes, they only mean I'm lazy.

And finally, the stacked composite graph:

Spikes aside, this shows that my peak usage for all three devices is less than 500 watts.  Sure, it would be more energy efficient to stop one to allow a different one to run, but it wouldn't change my peak usage much.  The way they (the power company) company calculate this is to take a moving average of 15 minutes over the entire peak period for a month and then they bill me for the highest period.  So, any 500 watt period will cost me for the entire month.  I once messed up and used a couple of kW, so I had the freedom to really eat the power for the rest of the month.  Interesting result of peak demand billing, I wonder if they realize it.

At any rate, it doesn't look like I have to worry much about the combination of appliances getting my usage out of control, but it could be useful to keep this in mind if I add an appliance, or need to modify my lifestyle in the future.  Most people don't want to put up with their A/C units being shut off during the hottest part of the day, or their pool motor not running in the afternoon or early evening when they want to use it.  Fortunately, when relatives visit me, they understand my OCD about keeping appliances shut off, and just giggle about me when they get home, so I don't have to worry about them.

See folk, I actually take your suggestions seriously and even act on them from time to time.  It may take months, but I eventually get there.  Now I still have to think about getting a temperature sensor inside the freezer (thanks badhairday).

Arduino, XBee, and a Freezer Defroster

I have an upright freezer.  Living a ways from town and the climate make this necessary.  I load a cooler in the car, go to the store get my frozen goods and some ice, pack the food in the cooler with the ice and come home.  When it's over 114F outside, you have to take some special precautions to keep the food from becoming a puddle in the back of the car.

A while back I discusssed how my freezer uses power; it's relatively efficient except for one item, the defroster <link>.  A freezer's defroster is a combination of a timer, a heater, and a thermostat to monitor the temperature of the evaporator.  What bothered me was the timing of the defrost cycle.  Every 11 hours or so, it would defrost, and this meant that the heater would be on during peak usage period.  Since I pay a lot for peak usage it would be nice to have better control of the timing of the defrost cycle.  So, an examination of the defrost circuitry showed a clear opportunity for an accurate timer and a simple SPDT relay as a replacement for the conventional method.

So, since I had a couple of arduinos that weren't doing anything, I got one of these:

This shield has both the relays and the XBee socket I wanted to use, perfect.  I have a few XBees that I picked up, so I configured one and plugged it in.  A little code later I was reading my house clock transmissions and setting off a timer every 12 hours.  I chose 08:15 and 20:15, times that are outside the peak period, now all I had to do was wire it in and test it.  Here's an image of the schematic of the circuitry:

I circled the defrost timer to make it obvious.  Notice that it simply switches between the compressor circuitry and the defrost heating assembly.  This makes it simple to wire into the circuitry, so I took out the timer and used the plug that went to it to wire into the relay of the arduino shield.  It was ready to test, and I hooked up a wall wart power supply and plugged the arduino into the same power monitor that I use on the freezer.  It worked like a charm.  Now my freezer goes into a defrost cycle at the programmed times and runs for 30 minutes.  I checked the evaporator pretty often to make sure it was running the heater long enough and everything seems fine.

While I was programming the device I threw in some code to allow me to set off the defrost cycle any time I want to as well as having it report through the XBee the status of the defroster.  This leaves a clear opportunity for installing a temperature sensor, compressor sensor, door sensor, etc.  Over time I may well do some of these things.  I could go nuts and use the arduino to control the entire freezer; these appliances are relatively simple devices and a little arduino and some relays could take over the entire operation.  I'm not sure there's any real point to that since it works well already, but I may get bored some hot summer day.

A temperature sensor would be pretty nice though.  I could send the temp to my house controller <link> and set up a piece of code to check for the temperature getting too high.  A too-high situation could easily send me mail or light up an LED somewhere to alert me to a problem.  Or both.   

Here's a chart of my freezer power usage over a 24 hour period:

The freezer is the black line.  Notice the two humps, one at 08:15 and the other at 20:15?  That's the increased power usage from the heating units (one on the evaporator and the other on the drain tube).  Now I have this power using mode scheduled for the lower rate periods.  With the new LED lights I installed in the freezer to replace the incandescent ones, this device is getting cheaper to run all the time.

Before you tell me that the wall wart and arduino probably use 5 watts continuously, remember my goal was to move the higher usage away from peak billing periods.  I'd rather have 5 watts continuous than 400 watts for thirty minutes during peak.  Peak usage is really expensive in my area.

No, it's not a major savings, but every little bit helps.  Heck, I'll probably get back the money I spent on the shield and arduino in ... what ... 10 years or so.

My Freezer and the Iris Smart Switch, Measuring Power

I went to Lowe's Home Improvement the other day to get supplies for jobs around the house that need to be done, you know caulk needing replacement, some spray foam, wire brush, the things we all have to get from time to time, but somehow, I wound up in front of the Iris display.  Shame on me.

When I got home with the stuff I needed, and my new Iris smart (which was NOT on the list) I decided to hook it to my freezer so I can monitor both big appliances in the kitchen.  Since I was lazy the last time I played with these devices, I had to modify the code to support more than one switch.  That wasn't too hard.  The switch connected first try and started reporting.  I was a bit surprised at what I got out:

I labeled a couple of interesting things; remember I have separate refrigerator and freezer, this is the freezer only.

The spike and drop at point A is the automatic defrost running.  The way these things work is there is an actual heating element on the evaporator in the freezer, and a timer runs it a couple or more times a day.  The timer kicks on and the heater brings the evaporator up to 40°F when a thermostat on the evaporator coil opens and turns off the heater.  The rest of the defrost cycle runs and control goes back to the temperature control system.  Which usually means the compressor kicks on.  This period of time allows the water to drain away into a pan where a fan evaporates it.  My defrost cycle falls in the 'Peak' period of billing, so that's not good.  The timer also runs on a little less than a 24 hour cycle, so it doesn't kick in at the same time each day.

This all means that I have a heater kicking on during the peak period that could be run some other time.  Fortunately, there's a little slot on the defrost timer that allows it to be advanced such that the defrost time can be moved, but since it will eventually move back into the peak period, I'll have to readjust it from time to time.  Notice it runs twice a day, that'll just complicate matters a bit.  This little timer may be a good place to put an Arduino synced up to my house time for absolute control of the defrost cycle.  No, I'm not getting too anal about this ...

Point B is the lights inside the darn thing.  This freezer has 8 stinking lights in it; four on the top, and four on the bottom.  Time to see if I can get a deal on led lights to replace these incandescents along with the ones in the fridge.  I mean the lights actually use more power while they're on than the compressor does.  Granted, they aren't on very often or for very long, but crap, close to 300 watts to light up the freezer?

Point C is the automatic ice maker.  When ice is low, this thing kicks on periodically to roll the new cubes into the tray and opens a valve to let water in for more.  This seemingly simple operation uses over 150 watts.  This is also short lived, so it can be tolerated.

What surprised me was how long the compressor runs.  I was worried that there may be something wrong since low coolant pressure or an air leak can cause the compressor to run too much.  I went to the GE site and looked up their explanation of the compressor cycle and what I'm seeing is perfectly normal.  The compressor on a freezer can run from 75 to 90 percent of the time under normal operation.  This seems excessive, but the motor is designed to take this much use.  It only uses 130 watts, so that's not too bad, and it does cycle somewhat, especially in the late evening early morning period.

What's becoming more apparent over time is the insignificance of parasitic power devices.  Little things like cell phone chargers that are left plugged in, televisions that look for remote control signals, wireless phones, etc.  I'll start checking on these devices, but it appears that all of them are roughly equivalent to a 60 watt light bulb.  You'll get a lot of bang on the power bill by paying attention to the lights and ignoring the small devices around the house.

Now, I have to get the caulk gun and get back to what I'm supposed to be doing.

I Want To Complain about 'Experts'

My refrigerator started giving me trouble.  No, it wasn't the Iris Smart Switch I installed in the power, it was that the darn thing started to get warm.  I opened the door and the little thermometer I have inside said it was 55 F inside.  It usually runs under 45, so something was up.  I checked all the obvious things, the compressor was going, the fan on the condenser coil was running; I couldn't see anything obvious.

Once again, a little bit about the refrigerator:  It's a refrigerator (only) that I've had for some years and it has given me trouble before; I even had to have the evaporator coil replaced.  I got this thing because I wanted it to be the last refrigerator I'd ever buy.  To meet that I got the very top of the line GE Monogram model ZIRS36 in stainless steel (ZIRS36NMRH).  It's a really, really old design that doesn't even have a frost free option.  That's because it has no freezer inside and just doesn't form frost.

Basically, the power comes in, goes to the temperature control, then to a temperature sensor on the evaporator coil (to prevent freezing up) and then to the compressor.  There's three fans: one on the top to cool the condenser and condenser coil, one inside to circulate air from the evaporator coil to the rest of the fridge, and one on the bottom to evaporate any water that drains out of the evaporator.  Then the lights are all that's left.  Not much to go bad, and not much to troubleshoot when it has problems.

However, I couldn't find anything wrong with any of those things, so I went to the web and found this discussion on one of those 'Ask an Expert' sites <link>; basically, the expert said the correct thing first, then corrected himself to the wrong thing.  This fridge is a middle level cooling system.  It doesn't cool below freezing anywhere inside except the actual surface of the evaporator coil.  It maintains a temperature of about 38 degrees and doesn't need a defrost timer or defrost heater at all.  The customer in the discussion tells the expert this, but that doesn't keep the expert from getting confused and messing it up.  I chuckled a little bit and then found this discussion <link>;  once again, the expert changes his mind midstream and messes it up.

The last link is especially interesting because a couple of other repairmen get into it and try to straighten things out.  By the very bottom of the discussion, the actual possible problems finally show up.

So, what was wrong with mine?  The door needed to be adjusted.  Yep, the door has sagged a little bit over the years and was far enough down that it didn't close a switch at the top that turns on the fan for the evaporator.  See, if the fan isn't on, the evaporator goes into freezing range and the temperature sensor I mentioned above, shuts off the compressor to prevent ice forming and breaking the evaporator coil.  I drug out the tools and modified the top hinge to be adjustable and reset the door.  Problem solved.

The reason I had to modify the hinge was because GE made provisions for raising and lowering the door, but not tilting it.  They even avoid the subject in their installation manual (yes, I read it) like a door will never, ever skew a little bit.  The experts out there will tell me that I should adjust the fridge to assure that it's square because that can cause the same problem; I did that first with a nice level, framing square, and all.  Nope, the door actually needed to be adjusted.

But the point of this is that after I found the two discussions listed above, I found several others where the expert just wouldn't listen to the customer, assumed he knew everything, and screwed it up.

I'll never, ever ask a question on one of those sites.

But, there were a few good things that came out of this fiasco.  I moved the Smart Switch back to the fridge (I had it on the freezer for a few days), and took a look at the power usage during the problem:

Notice the small spikes?  It seems the compressor was turning on for a very short period, then shutting off for a very long period.  This was because the evaporator coil got too cold (no airflow) and the thermal protection kicked in and shut the compressor off.  This is very different from the graph I blogged about earlier <link>.  Another thing good about this was that I improved the performance of the appliance:

Now, the compressor is on longer, but off longer as well.  I turned the temperature control down and allowed it to stabilize at 38 F and all seems to be well.  Of course, something else can crop up and cause problems, but it looks like I fixed it.

Edit:  It's been a little over a day since I fixed the door on the fridge and I thought someone out there might be interested in the result.  Yes I fixed it, and I made out like a bandit on this:

Ignoring the couple of bumps in the middle of the chart, notice how it has settled down to a regular rythm?  It's on for about 15 minutes and off for around an hour and a half.  The huge spike in the middle is when I had the door open and the compressor kicked on at the same time; 300 W for the lights and around 400 W for the spike of the compressor starting.  The other bump right next to it was where I finally finished up assembling the fridge.  I put the drawers back in that I had take out to check things and also the temperature controller cover.  

Net, over time I'll get a feel for the usage of the fridge and a simple check every once in a while will tell me if it's working OK, or if it needs some attention.  It would be cool to completely automate the operation of this device with a little computer and radio combination, but not now, I want to take a really close look at the freezer setting nearby.  Then I'll take a look at the chest freezer I have out in the garage.  These appliance have been blamed by many people for using too much power, but my experience is the exact opposite.  The pool is my biggest electrical usage followed by the water heater.  Those I have under control with load balancing to off-peak periods and solar assistance.  Next is the two A/C units I have;  if I left them to run on their own, they would far exceed everything else, but I control when they can run also to minimize their impact on my wallet.

So, you folk that are looking at one of those multi-hundred dollar fancy thermostats to control the temperature in your house, think again.  You won't get nearly as much information from them as I do with my set up, and you won't be able to control it as well.  Sure, you'll have to actually learn something instead of buying the hype they try to sell you, but what's wrong with that?

Smart grid my butt, smart house is the solution.