Wednesday, February 22, 2012

And Now For Something Completely Different

I guess you've all figured out that I live in the desert by now.  Well, we have a lot of birds and other wildlife wandering around; part of the charm of living out here.  Today, a dove decided to invade the house; this is a relatively common thing and is mostly uneventful except for having to clean the droppings off the furniture after chasing it outside.  However, today my trusted guard dog managed to corner the bird.  This is the debris:

Yes, that's the head of the much feared guard dog.  Here's a picture of the dog with evidence of his bravery clearly visible stuck to his nose:

Just so the more environmentally concerned don't misunderstand, here's a picture of the bird after the confrontation, it's perched about 14 feet up on a pot shelf trying to decide what to do:

And here is a picture of the bird in the yard on it's way to freedom:

No, the bird isn't injured, just tired.  I had to chase it all over the house before it found one of the doors I had open for it to escape through.  After a few minutes it took off for safer territory.  Somewhere that didn't have a dangerous five pound Yorky protecting it.  And, yes, this all happened while I was composing the post below on battery chargers (how do I ever manage to get anything done?).  Now, if I could only get the dog to stop strutting proudly around the house and find all the poop left behind by the scared dove.....

Battery Charging (Harbor Freight item 42292)

Part 2 of this project is here and part 3 is here.

I have a tractor and two older quads in my barn.  Yes, I have a barn.  The problem is that about half the time I go out to use one of them the battery is dead.  I drag out a charger and extension cord from the house, charge it up, and then get to use the vehicle; usually a day or so later than I wanted.  All too often, I find out the battery won't recharge and needs to be replaced.  This is not only annoying, it's darned expensive.  And eventually I want to get a nice big portable generator with electric start; I really don't want the battery dead on that when I need it.

Obviously, I need a float charger on the vehicles to keep the batteries charged.  One that doesn't boil the water out and can run unattended for months if necessary.  I can't find such a thing at a reasonable price.  Yes, there are devices like the BatteryMINDer, Battery Tender, and hundreds of float chargers.  These things can cost a heck of a lot if you need several of them for different machines that have a battery in them.  Sure, it's cheaper than replacing the battery, but you have to leave them plugged in all the time, and some of them just don't work as advertised; if at all.  Wouldn't it be nice if there was a cheap little float charger that could be adapted to a solar cell?  One that I could control the float voltage it puts out so I could use it on the AGM battery in one of the cars as well as the standard small lead acid battery in a quad?  One that wouldn't drain the battery if I kicked the cord out of the wall and didn't notice until a month later?  Such a device would run me at least $40 and I need several of them.  Crap.

Looking around, I found a coupon for the Harbor Freight float Charger, but it has some draw backs.  It will drain a battery if it is unplugged from the wall, it puts out too much voltage to be left alone essentially forever, and the stupid wires on it suck.  But, it also has some compelling positives, it's cheap, it has a DC wall wart for power, it's cheap, it has simple circuitry that can be modified to do what I want, and it's cheap.  The DC wall wart is expecially attractive since it can be cut off and a solar cell substituted to run it where there is no power.  So, credit card in hand, I went to Harbor Freight and bought several of them (I did mention they were cheap didn't I?).

First inspection showed me that the little devices are set to 14.1 volts constant voltage with a current limit of around .9 Amps, it will discharge a battery through a status LED, and the combination of thick clumsy wires with smaller power wires is somewhat hard to deal with.  Time to take one apart and see what's in it.  After prying on the cover for a while unsuccessfully, I gave up and cut it open with a Dremel.  Reverse engineering it gave me the schematic below:
Harbor Freight Charger 42292

So, it has a good old 7805 power regulator set up as a variable supply and a TIP41 transistor to regulate the current.  The S9013 transistor is set up to turn the device off around 9V, because a 9V lead acid cell is probably beyond recovery for a float charger.  The resistors in parallel are to get a specific value out of the various dividers in this thing.  My first question was, "Why do it this way instead of a variable resistor?"  The answer was obvious when I checked the prices of the various components; fixed resistors cost a fraction of a cent in quantity, variable resistors are much more expensive.  But, the question I don't have an answer to is why they didn't put in a diode to stop from discharging the battery if it's unplugged from the wall?  Oh well, I have a few (hundred) diodes laying around that can do this job for me.  

When I cut open a second one I found a different set of components.  The second one appeared to be an older version and did not have the parallel resistors.  It had one resistor in each position and was laid out slightly differently.  The circuitry was essentially the same, it just appeared to have been changed over time.  Same drawbacks and advantages as the first one.

So, I hooked one of them up to an AGM battery I have in my car and let it work for a few days.  Sure enough, it float charged the battery up to 14.1 volts and kept it there.  This is not a good thing.  The specs on the Optima AGM automobile cranking batteries warns against this and tells me to keep it between 13.2 and 13.8 volts.  A little rework should take care of this problem; especially if I add a diode to the output which will cut .7 volts off the top and get me right in range.  It also appears that I can set the voltage by adding a simple little potentiometer and setting it to be what's needed for a normal lead acid battery like my tractor.  This would be really useful since the instructions for float charging a lead acid battery vary by each author I look at.

I've seen instructions that insist I shouldn't charge a flooded lead acid battery to more than 2.1V per cell for a 12.6 volt float.  Then when I look at another site it says the float voltage should be 2.2V per cell which gets me up to 13.2 volts float.  Then, they start talking about surface charge, waiting 24 hours to check it, parasitic current draws from onboard devices, and temperature corrections.  Then some of them talk about how as little as one tenth of a volt will shorten the life of the battery considerably.  Obviously, many of these people are spouting off stuff they don't understand and others are just repeating things they read on some forum somewhere.  What to do?  I'm just going to start with the info from Wikipedia and see how the water in the battery holds up.  I'll set the AGM voltage at 13.5 and the flooded cell batteries at 13.9 for a month or so and see how much water goes away.  I'll adjust down if the flooded cells lose water.  Note that using a constant voltage supply will take care of parasitic devices like the little LED that blinks for the alarm system on my car.  That's why I prefer constant voltage with current limiting techniques.  

One of the interesting items is that various articles say that the float voltage has to be correct to 0.02 volts.  First, I've never seen anything that kept that close a tolerance, and second, how the heck is someone supposed to measure that?  Sure, there are meters that give that resolution, but how accurate are they?  It would be relatively easy to set up a little computer to measure the voltage and adjust the bias on a voltage regulator to keep it right on the money, but how expensive is a meter that is calibrated to be that accurate?  And, how can you trust it to be that accurate over time?  My method is going to be much more pragmatic.  I'm going to measure the voltage I set the devices to on several meters and just average them.  Then I'll set the voltage slightly high and adjust downward to minimize water loss.  I know for a fact (long years of experience) that it's better to overcharge a tiny amount than to undercharge.  Undercharging causes sulfation and one of those sulfate crystals can pierce the lead causing a short that cannot be corrected.  Been there, done that.

Here are the two devices I've messed with so far:

Notice that the top one has a smaller component count than the lower one, but essentially the same circuitry?  This is a result of the parallel resistors to get a particular value that I described above.  The schematic I show applies to both of them, just adjust for the difference in methods.  Also, the various values of the resistors involved are different for the two devices.  A friend of mine suggested that they change the various values based on a particular run of 7805 and TIP41 components involved.  Also, variable resistors can be bumped and change value; an important consideration in something that will be tossed around a garage by people like me.  I also want to point out what, to me, is another shortcoming: the wire sizes and types used.  Notice the wall wart has a nice long wire that is quite small and the part that clamps onto a battery has a heavy coiled wire.

Someone out there want to tell me the logic in this?  The coiled wire is strong, relatively inflexible, and drags the device around in the car.  This thing puts out less than one amp and just doesn't need that kind of cable.  They did use good strain relief techniques though so the cables won't just pull the thing apart when you stretch it out.  The heat sink gets warm, not hot, as does the wall wart, and after reaching the float point, cools right down.  On my car with the parasitic draw from various devices, the device stays a little warm because it is supplying current to overcome this instead of sucking the starting battery down to nothing.

Obviously, this project is going to take weeks, if not months, to complete.  I have to test for days at a time and monitor the voltage and current feed to be sure I have something that will maintain the batteries not destroy them.  Then I want to get a solar cell to power several of the devices at once (in my barn where there is no power) and install a nice permanent solution.  You'll be seeing more on this over time.

Monday, February 20, 2012

Anti-Siphon Faucets (Arrowhead Brass Arrow-Breaker)

Not all technology in use around my house is electronic.  Let's talk about anti-siphon hose bibs.  If you have a water well (I do) and especially if you use a water storage tank (I do) these little things are a must have.  I'll leave it up to you to Google around and find out about the various reasons, but basically when the power goes out and the well shuts off, you run the risk of flooding your water system with dirty water from some hose outside that happens to be on.  Yes, if the faucet is turned off, there is no problem; but you may never be sure someone hasn't left one running somewhere.

This came home to me in a big way when my weed guy came around to spray.  He was filling his tank with water from my hose and mixing in the various chemicals he uses when the power died.  The pump shut off and the back flow prevention device on the hose he was using did what it was designed to do; dumped water on the ground that might have made it back into the house water.  Now, there was no real danger because he had the fill device on his tank set up properly to prevent back flow and I had a vacuum break (back flow preventer) at the end of the hose, however it does illustrate that something can happen when you least expect it.  There's been many times I was filling the pool after doing something that the power could have failed and caused a siphon effect to suck water into the house supply.  So, you need these things.

Where I live you have to have a functioning anti-siphon device on all hose bibs before you can pass inspection to move in.  However, almost everyone uses one of these:
They do the job just fine.....,but (remember, there's ALWAYS a but), they cost around 4-5 bucks and fail in about a month in the desert heat.  There are also plastic ones that cost a little less, but I've had them fail in as little as a week.  The construction is the problem with these.  They have a nylon support, metal spring and soft plastic or rubber diaphragm inside.  The nylon support will dry out and crack, the spring loses tension, and the diaphragm dries out and leaks.  Also, at low flow levels, the diaphragm will vibrate and cause a loud squeal that will drive you nuts.  I have personally changed out about 10 of these things over the last few years and have a couple of faucets that I just left them off of when they darn things failed.  To add insult to injury, many plumbers will attach these to the faucet and tighten up the little set screw so you can't remove it.  They actually break the set screw off so it won't unscrew.  This means you have to force it off with a big wrench probably ruining the threads in the process or replace the faucet and vacuum break device.  I really can't blame the plumbers  for doing this.  They put them on to pass inspection and someone comes along and unscrews it which causes the plumber a call back and costs money.  You can't repair these things, they're cast brass and don't come apart, and plastic ones break when you try to take them apart.  

So, what to do?  There are a number of possibilities including a vacuum break for the whole house, but each of the solutions has a drawback that I hate.  For example, the whole house idea will work, but I'll have to drain my house plumbing if there happened to be a problem.  I think I have found a solution to this.  Arrowhead Brass makes a nice anti-siphon hose bib that isn't too expensive and seems to do the job just fine.  Their web page here shows the different styles, and for you folks that live in cold country they even have the no-freeze designs.  I bought three of these:
Yes, they cost a little less than 14 bucks, but they compare favorably with a hose bib and the vacuum break purchased separately.  What's really, really nice about these is that they don't leak water every time you move the garden hose.  See, the water hose holds water in it and when you grab an end and wander over to water some plant the water flows backwards through the hose and sprays out the vacuum break making a mess on your patio.  This can be a problem if the bib is over a nice redwood deck or next to a patio table.  They don't make noise at low flow levels and only purge water if the valve is actually open.  Just about everything you could want in a vacuum break faucet combination.

One suggestion for you folks that decide to try one of these, use pipe dope instead of teflon tape when installing it.  I used teflon tape and the darn thing leaked at the threads; when I pulled it off, cleaned it and used pipe dope, there was no problem at all.  I don't have enough experience to tell you how long they will last.  Mine have only been in place a week and that's not much of a track record, but they can be dismantled and repaired which is a plus in my book

Thursday, February 2, 2012

Acid Pump - Continuing Drama

I had to give up and send the acid pump back to the distributor.  I say distributor because Hanna Instruments gets the pumps from some company in Romania.  Well, they're not Chinese...they might have worked if they were.  It seems the acid caused the pump electronics to rust up and corrode.  The pump body was nicely sealed except for the potentiometer.  It leaked around the shaft and things went down hill from there.

At any rate, when the new one comes back (still under the 1 year warranty), I'll try it with the new fittings and check valves.  I did find out that the check valves I was wanting to use, see here, fail after a few months.  No, the spring didn't dissolve, the valve seal started to leak.  These little check valves can be taken apart, so I took it out and looked to determine the cause.  They should be fine if you're using them for controlling water, but not acid.  I have a couple of Kynar check valves to try this time.  If they work, I'll retrofit all the valves and see what happens.  These pump systems have valves at the injection point for the pool, both into and out of the pump head, and at the pickup point (foot valve).  Lots of redundancy to make sure there's no single point of failure.  That is if it doesn't melt and leak acid all over the place.

Just waiting for the pump to come back to try again.....