Rain - Finally

Late yesterday afternoon it finally rained here.  Oh, there's been slight showers and even a few minutes of real rain, but my area finally got the first real rain since last year.  It started a little after 5PM and lasted a couple of hours.  There was a period of thunder and lightning with heavy, wind driven, rain.  The next morning my rain gauge had recorded an inch and a quarter.  This was a real desert monsoon gully washer.  It was GREAT.

I know, this isn't news to anyone.  This happens reasonably often in the Southwestern desert and isn't considered any big deal - except, this time I was measuring the temperature during the storm.  Below, is a snapshot of the temperatures before and after the storm.  Notice how the temperature was over 110 F when the storm started and dropped to 75 F as the rain progressed.  That's a temperature drop of 40 F, all the way down to something reasonable and comfortable.  I don't remember that kind of fluctuation in other places I've visited.

Of course though, it got up to 105 F today, and as the moisture evaporated from the ground, the humidity shot up.  Now, I remember why I hated Louisiana in the summer...

Battery Charging - Part 3 (Harbor Freight item 42292)

Part 1 of this project is here, and part 2 is here.

Yes, I'm still working on a good float charger for maintaining my batteries.  See my other posts on this here and here for a recap of the project.  I finally gave up on the LM7805 circuitry that comes with these devices.  The Harbor Freight 42292 charger used to be controlled by a LM317 variable voltage regulator a long time ago.  They probably changed the regulator at some point to lower cost or overcome a supply problem.  However, it originally was a much better device; it even had a variable resistor in it to allow the end user to tweak it a bit to fit his purposes.  I got a clue on this during my searches to get ideas on what to do.  Here is the link to a schematic of the original device (link).  Notice how different it is from the current circuitry?  Just so I have a picture to talk about, here is the schematic from that site:

Back in those days, the wall wart was just a transformer so the diodes to rectify the supply were in the little black box.  IC1 is a LM317 and notice how they set up the resistor array to limit the range of available voltage and have a transistor to limit current?  Nice design that you can find all over the web.

I just duplicated part of this on a small piece of protoboard that I cut to match the size of the existing board.  It came out like this:

I still have a diode in series with the output to prevent problems with reversing the connection to the lead acid battery and used different values for all the resistors than the original had.  The reason I changed the values was purely practical; it's what I had on hand.  Notice that the parts count is a grand total of five?  So, why doesn't the manufacturer do something like this?  I don't have a clue.  So, my schematic looks more like this:

The input on the left is the wall wart's 19 VDC (apx) output; VR1 is a 1K, 25 turn potentiometer I picked up on eBay; R2 is 1.2K; and R3 is 180 ohms.  This gives the charger a range of about 9.6 to 16 or so volts.  To calibrate it, I put a 1K resistor across the output, set it for 13.4 volts and then took the resistor off.  When I hooked it to the battery, it floated the battery up to 13.37 volts over an hour or so and just held it there.

I rely on the LM317 to take care of itself.  It has over current and over temperature protection built in and regulates the voltage quite nicely.  If I discharge the lead acid battery by pulling a lot of current such that the voltage drops down to 12.4 or so, the IC will get hot, but not dangerously so.  Then over time, it charges the battery back up to the 13.4 volt level and just holds it there.

So, since I'm only using the wall wart, plastic enclosure, and heat sink of the original device, did I save any money?  Yes.  The wall wart alone is worth the price I paid for the original charger and the rest of it serves as a platform for the charger I ended up with.  

So far, I've converted three of these devices to the new design and they are chugging away keeping batteries charged.  I chose 13.4 V as the float point based on experience and a suggestion from a helpful person on the Arduino forum; this seems to be the best point to hold the battery without losing water to the charge current.  I haven't had to add any water to any of the batteries yet.  Over time, I'll know if I need to make adjustments to this, but at least now I can.  

Thinking about this a bit, it brings up an interesting point.  This wall wart can supply an amp easily and the output seems to be very good, that means I have just made a variable voltage 1 A supply that can serve various general purpose uses around the house.  The next time they have these on sale with a 20% off coupon I may pick up a bunch of them and stockpile them for later use.  Heck, since the LM317 can work as long as the difference from voltage in to voltage out isn't more than 40 V, I could use it to control the voltage from a 24 VAC transformer like I needed way back in the thermostat project.  I needed 5 VDC from a rectified 37 VDC taken from an air conditioner power supply; this would have saved me about $20 in power supply cost.

Acid Pump - Back in Service.....Again

A few posts back I declared that I was done trying to make the Hanna Dosing Pump work.  That was a fact, I've just had too many problems with this device and am totally tired of messing with it.  I did some more research and turned up another alternative.  Since there are only two types of pumps that are used for this kind of thing, peristaltic and diaphragm, and diaphragm had too many problems, I went for a peristaltic device.  I found this one that somehow avoided my research the first time:

This is a Rola-Chem RC-25 and comes complete with everything in the picture.  It can handle either chlorine or muriatic acid in the concentrations used for swimming pools.  I normally try to use 30+ percent muriatic acid in my arrangements, so this thing should do the job just fine.  Notice that they provide a brass fitting for the pool injection?  They explain this by illustrating that the tubing should be pushed way down into the pipe so the water flow from the pool pump should dilute and carry it away from the fitting.  This might just work since the flow rate of pool water is many gallons a minute and the pipe is two inches (usually) in diameter, the acid should dilute and move away quickly.

One of the major problems with the diaphragm pump was the force of the fluid motion.  The diaphragm was solenoid operated and really shoved the fluid out hard.  This wouldn't be a problem except for the operation of the various check valves: they were pounded by the movement of the water and that caused the diaphragms in the valves to wear very quickly.  I discovered this by ripping apart several of the valves after they had failed.  There were distinct wear marks on the internal diaphragms that would leak fluids both directions.  This pump produces a relatively gentle flow that will build up to enough pressure to overcome the pools flow and its own check valve quite nicely.

This pump is made of plastic on the entire exterior.  I couldn't find any place that would dissolve in the muratic, so it should stand up better than the last attempt.  It comes with several feet of vinyl tubing to hook it up with.  This led me to a discovery that I wish I had run across earlier: Vinyl is actually PVC.  Yes, vinyl tubing (if it really is vinyl) should stand up nicely to muriatic acid.  The resistance of PVC is lower than other materials, but the tubing will wear out due to exposure in about a year and need to be replaced anyway, so that shouldn't matter.  Also, vinyl tubing is cheap and easy to get; just go the Home Depot, Lowes, or Ace and pick some up.  The pump also uses standard size tubing and fittings that you can get most anywhere; just avoid nylon fittings, look for pvc or vinyl and you should be fine.  The pump tube (the one inside) comes in two materials: Tygon and Norprene.  Tygon is resistant to most chemicals and is used a lot in the food industry.  Norprene is actually a form of Tygon that is specifically formulated to be UV resistant, flexible, and extremely durable.  Rola-Chem recommends the black Norprene for muriatic and the clear Tygon for HCL.  This is mostly because the acid is extremely corrosive and a little leak will mess things up over time; best to be safe.

So, I modified the box I had on the wall holding the Hanna pump and installed the Rola-Chem pump.  This is after running the Rola-Chem into a bucket for a couple of weeks to be sure it worked and I understood how to use it.  I discovered that the pump puts out about a cup (8 ounces, 225ml) every 8 minutes so I'll start out at 10 minutes and see how the acid level holds up in the pool, adjusting as necessary.  I'm not using the timer control on the pump because I want to control the device from my House Controller; I just turned the switch to 'On' and hooked it up.  It was relatively easy since I already had an injection point I installed for the previous pump and the bucket with level sensing has been working fine.  I ran it for a couple of days on water to be sure it didn't leak and the timer controls were working correctly.  Today, it was filled with acid and put into service.  I was surprised how well it worked.  This little device self primes in about a minute and the just rolls away moving the fluid through the tubes.  Yes, I'll have to replace the pump tube twice a year and the other tubing every winter, but that's not a big deal at all.  The internal tube costs about U$20 and the other tubing is less than that (remember, you can get it at Home Depot).  It also needs lubrication periodically; I checked the label on the O-ring lube I use and it should work great.  Just go out every month or so and put some in and it should be fine.  I'll look at everything each time I clean the filters to be sure it's standing up to use.  Here's a picture of the installation:

This pump was larger than the Hanna, so I had to enlarge the box (thank goodness for waterproof glue), but it should work nicely to shelter it from the hot sun and little rain that falls here.  Notice the bottom is open?  This worked well for the last several months.  If it leaks, it doesn't set in the box and corrode things and it gets plenty of ventilation to keep things dry.  There is the occasional spider though.  Here is the injection point:

Notice the check valve?  It's the gray thing that the clear vinyl tubing slips onto.  This check valve was a pleasant surprise also.  It is acid resistant and has a Hastelloy spring inside.  Hastelloy is one of the few metals that is resistant to muriatic acid and hard to find in devices that normal people use.  I chased down the manufacturer and it is available in several configurations from SMC, but they require a minimum U$100 order.  I may pursue getting some of these to keep around if this works out. I didn't use the brass fitting that was supplied with the pump; I just don't trust brass and acid in proximity to each other.  I've had too any bad things happen with that combination.  

I haven't dressed the tubing or tied it down yet.  I want to try it for a week or so first to see how things work out before making it more permanent.  Also, I need to make sure it is easy to change periodically for maintenance.  I don't have clamps all over the place because the peristaltic pump produces such gentle flow that it doesn't look like I need it.  With the heat here and various weather conditions that may cause problems, I will have to watch it over time to see and learn more.  So, right now, the installation looks like this:

I haven't removed all the old tubing and will have to dress stuff up so I don't stumble over it when I go in there, but it works.

Outdoor Temperature - Holy Cow

It's 9:30AM here and the temperature outside is 110F.  WHAT??  I had no idea it got that hot that early in the day here.  Fine, I've lived here for several years now and lived through 120F plus days and watched the plants shrivel up and die, but 9:30 in the morning and hitting 110 already??

Yes, I checked the temperature against another device with a bi-metal spring and it corresponds.  I also dragged a cooking thermometer out there and put the probe in the shade where it could sample the air temperature - same thing.  So, my outdoor temperature device is working and doing what it's supposed to do; I just don't like the data it's giving me.  That explains why the interior temperature of my barbecue was over 200F before I turned it on yesterday.

I think I'll work on inside projects today.....sigh.

Outdoor Temperature

I've had an outdoor temperature sensor for quite a while now.  It's a simple temperature sensor hooked to an Xbee that gets power from a wall wart I picked up on ebay.  The description of this little device is here.  Well, I decided to make it work like it should and actually start measuring the outdoor temperature.  This means I have to enclose it and find a place to mount it that will allow proper operation.

So, I had to build a Stevenson Screen.  At first I had no idea how to do this, then after a few hours of searching and reading I figured out I simply needed a louvered box, painted white, setting somewhere on a pole.  So, I picked a fence post out in the yard and ran a conduit to it.  I mounted a short piece of pipe and installed an outlet.

Above you can see the wall wart a couple of wires and the XBee with its temperature sensor soldered on the side (click on the picture for full size).  I chose to use a wall outlet and regular wall power because I don't want to have to worry about changing batteries every few weeks.  Yes, I could use rechargeables and a solar cell, but those things wear out here in the desert.  Believe it or not, the coating over the top of the inexpensive solar cells used in yard lights turns yellow and starts to flake off in about a year of exposure.  The batteries cook and die after about 8 months; basically solar lights are annoying.  Yes, I could use a good solar cell (with glass) and a lithium ion battery, but pricing those devices and the charge controller that would be required brings the power supply cost to roughly $75.  Conduit and wire ran me around $8.  Additionally, there's not much information on the lifetime of a lithium ion battery in 100+ heat day after day.  Understand my thinking now?

I found several Stevenson Screen projects on the web; one even used flower pot bases which was an intriguing idea, but the cost of those made the enclosure run around $35.  So, I had some scrap wood left over from anther project and decided the good old wooden box painted with glossy white paint would be the best route.  However,  I didn't have enough scrap wood to build a regular Stevenson Screen so I decided to build it in a triangular shape to save wood.  Don't do this.  The angles and complexity of a triangle over a simple 90 degree box drove me nuts.  It did come out reasonably nice though:

There's enough room inside to eventually mount a sensor for humidity and the top is flat so I could mount a wind sensor as well.  The humidity sensor is a good idea, but I would rather sense wind speed and direction from the roof; that will be a complex project that will have to wait for another day.  Since I don't want birds building nests inside this new installation, I lined the inside with aluminum screen wire.  There should be plenty of air flow and the rain can't get through the louvers.  It has several coats of white enamel paint to reflect the sun and limit heating to the minimum so I should have accurate measurements of the air temperature.

 

This is a chart of my temperature recordings over the last 24 hours.  On day one (today), the readings reflect badly because the sensor was in the house, then in the sun, then in the enclosure, but it will be working properly after about noon on July 7th, 2012.

Charting Things

I was stumbling around the site where I store my data Cosm.com (it used to be Pachube.com) and noticed that they have updated their charting capabilities considerably.  This made the data on my Detail Usage Charts page mess up, but also added capabilities that I didn't know I had.  I edited this page and was able to display a years worth of data (NICE).

There seems to be some kind of bug though because if I ask for a data using months as a parameter, it takes forever to return the data, whereas if I use 30 days, it returns it quickly.  The charts on my detail page use 365 days as a parameter and it only takes a few seconds.  I can live with that.

They have another chart that will allow you to get the actual reading for any point, but I haven't figured out how to use it yet.  Over time, I bet I will.