Acid Pump - Running Again

Well, it's installed.  I got the clamps in and tried them out.  Everything was fine and I put it all together and installed it.  Naturally, I had to build a new enclosure for it and there were a few problems installing it, but it's working now.  Here's the device on the fence:

I made the enclosure from some plywood I had in the garage and painted it with a thick layer of latex paint to help keep the wood from being attacked.  I may tie down the cables and tubing after it runs a while.  There's no  bottom on it because I wanted plenty of ventilation for later in the summer, also it will help dry things out if something does leak somwhere.  Here's how I hooked it into the pool plumbing:

It's just too bad I couldn't find check valve in Kynar that had threaded fittings; that would make it a really clean installation.  Everything works and doesn't leak; now I just have to watch it a few days before I trust it.

When I pulled the foot valve out of the acid to put in a new check valve, the nut that held the tubing had completely dissolved.  The tubing was still attached, but the nut was just gone.  This validated my diagnosis that the nuts were losing grip because they were dissolving in the acid.  This is really irritating because the pump is advertised specifically for chemical dosing.  It seems that the entire problem set I've been trying to overcome would never have happened if they had used high density polyethylene nuts to hold it together.  Since the nuts are custom to their fittings, they can't be second sourced to eliminate the problem either.

Here's the entire installation in place.  To review, the remote control timer that is on my XBee network is on the left in the gray box and the pump is in the new white box; they are both attached to the fence around my pool equipment.

Now I hope I don't have to mess with it for months except refilling the tank.

Update:  I listed the parts and their numbers at the end of my general write up on the injection system here.

Acid Pump - Getting There Slowly

I got the fittings I ordered and tried them out.  They work very nicely and seem to be just the thing for this particular application.  Here's a picture of the construction so far:

There's a bit of illusion here.  The pipe and elbows are 1/4 inch, not huge like the picture seems to show.  I switched to 3/16 inch barbed Kynar check valves too.  Yes, I know I said they would restrict flow, and they do, however they pass enough water to work OK.  I'll just have to run the pump a little longer.  I have the compression fittings in place and they seal it real nice.

Be sure to put Teflon tape on all the joints.  If you don't the plastic binds up and causes leaks; the Teflon does a great job of lubricating the fittings and sealing any leaks.  I've already tested the Teflon for acid resistance back when I was working on the level indicator.  There are a few things to note about putting this together though.  As I mentioned before, the tubing is a tiny bit large to work with the fittings without doing something.  After destroying a couple of feet of tubing trying to get it to work, I came up with a simple procedure.  First, take the compression fitting apart:

The main body piece has a tapered insert that you should bottom the tubing into, but it won't fit so, break out the heat gun and soften the plastic.

Once the plastic is soft, shove it into the body fitting all the way to the bottom. 

Let it cool and  take the body section off and put the other pieces in place.

Notice the positions of the pieces; this is important.  The one nearest the nut is compressed by the nut and grabs the tubing, the other one slides into the body completing the seal.  So, now just shove the tubing into the body, work the compression nut down and thread it on.

This method has given me an easy to make connection that doesn't leak.  I did this for both sides of the pump and will have to do it for the foot valve and injection valve when I install it.

Now, the only thing holding me up is a set of clamps.  The 3/16 inch check valves need a smaller clamp than I have and I have to wait for them to come in.  The seal on the barb fitting is quite good, but there's a lot of vibration and temperature extremes to deal with and I want clamps on the fittings.  The problem is that the clamps are acetate, and they will react to the HCl that will be flowing.  That's OK for everything except the foot valve, fortunately, that's on the suction side and under the level of the HCl, so if it leaks some, I don't care.  

I hope that I can get this installed and go back to electronic projects for a while soon.  I want a couple of timers and a way of telling the garage door is closed from way far away, but I've been stuck with other things for months now.

Acid Pump - Continuing Drama

I'm still working on the darn acid pump.  I don't mess with this full time obviously, but I keep getting back to it. The latest is that I'm not entirely happy with the new fittings and setup.  The tubing is 5/16 inch OD and 3/16 inch ID; this is an odd size, and of course, doesn't fit the 1/4 ID barb fittings.  3/16 inch barb fitting have too small a hole for fluid to pass easily and reduces the volume too much.  It is possible to expand the tubing, but thick wall polyethylene tubing is tough to work with.  I heated several little pieces of tubing and experimented until I could actually put one on the fitting, but it was a trial and error process.  When I tried the pump out, it didn't leak, but the vibration worries me.  Here is the setup as I tested it:

Notice the clamps I used to hold the tubing and the 3/8 inch MPT fittings?  The Kynar check valves worked great and didn't have any back leakage at all.  They have Viton diaphragms that shouldn't have any trouble at all with acid.  They will wear out over time though so I'll have to replace them periodically.  

My concern is that the vibration shakes the tubing and it could leak over time since it gets hard and soft as the temperature changes and could shake loose.  Now, I'm looking at some compression fittings for plastic tubing.  The problem is that most compression fittings are Nylon, which will dissolve, or have a metal insert, which will also dissolve.  I found some compression fittings that should work and even have configurations that may work for me:

This one only comes in 1/4 inch MPT, so I need reducers and adapters to fit it to the pump and direct the tubing.  I have an assortment of 1/4 inch MPT fittings, nipples, and elbows on their way to accomplish this.  These compression fittings are very different from the ones on the pump originally; they compress from the outside and have a built-in compression ring.  The tubing fits much farther inside as well, and they are supposed to handle quite a bit more pressure than I will be putting on them.  Oh, did I mention that they are solid molded Kynar.  That'll show that stupid acid who's boss.

I still have to use tubing barbs to connect the kynar check valves, but I'll address that problem (if necessary) when the plumbing parts arrive.  Strange, I never even knew there was such a thing as 1/4 MPT fittings.  I'm real familiar with 1/2 and 3/4 inch fittings from working with water and natural gas piping, but the thought of 3/8 inch and below never even occurred to me.  Home Depot and Lowe's don't even pretend to have many of these items; certainly not in materials like Kynar or Viton.  No wonder people don't try to do obscure projects like this.

Acid Pump - Replacement Arrived

I got my replacement acid pump a couple of days ago and just now got to testing my ideas for valves and fittings.  I'm trying these:

 

These are 3/8" NPT x 1/4 HB connectors and thread into the pump head just fine once I removed the valves they shipped with it.  I went with tubing connectors for two reasons, these have really long barbs and should seal well, and I couldn't find Kynar valves in anything except tubing configuration.  The Kynar valves look like this:

Notice how long the barb piece is?  That should stop any leaks if they don't dissolve in the acid like the other fittings.

I wrapped the pipe fittings with Teflon tape and screwed them into place.  The 1/4 tubing didn't want to go on the fittings so I got a heat gun and softened up the tubing.  I was able to slide it on just fine.  Now I've got the valves in place with some tubing pumping water around in a five gallon bucket.  I'll test this for a while before I put the pump in place and test it with acid.  I did notice though that the new check valves work really well.  They have no back leakage at all and open with very little pressure.  This should help a lot with my problems priming the pump.  The lines will have four of these valves in them to prevent backflow and loss of prime just like the original shipment so my cost is greatly reduced for maintenance.  These little valves cost less than a buck and a half while the original ones are more than thirty dollars (and don't work).

The pump will be in test mode for at least a day and then I have to get a couple of 1/4" elbow barb fittings because the tubing is so stiff I can't bend it like I want to.  I'm also going to get some tubing clamps like these:

I'll use these clamps around the barbs to make sure the tubing doesn't get warm and flex off during the summer heat.

Battery Charging Part 2 (Harbor Freight item 42292)

Part 1 of this project is here:

I've worked out my modifications to the little charger. Here is the schematic I ended up with:

I used two 100 ohm resistors to keep from hitting the supply rails on each end.  These aren't strictly necessary, but I had them handy and it seemed a little safer.  The diode on the output is to prevent the battery from discharging if the power is down for a long time; like I kicked the plug out of the wall.  It really isn't a 1N4001, it's some generic 1A 400V power supply diode that I had around.  The pot is 1000 ohm 25 turn and cost about a buck or so off ebay.  It allows me to set the voltage precisely.

Here is a picture of the way I hooked it up:

This will give me the float voltage that I want and won't discharge a battery if the power dies.  That makes it reasonable to put on a solar cell for things that don't have power near them.  A tractor parked out in the back somewhere, a quad setting next to a tent on a hunting trip; things like that.  Notice I got rid of the wires with the clamps on them.  I put a plug on the end and can now just plug it into the vehicle.  Improvements could be made like adding a volt meter to it to tell how it's doing and another light that says everything's OK, but those are for the future.  Now all I have to do is put it back in the case and label it with the voltage I set it to and let it do its job.

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.