Sunday, March 11, 2012

Rainy Day Musings

We had planned to go to the rifle range today - when we went to bed, the forecast called for cloudy and breezy with a "30% chance of rain after 11AM".  When the crazy cat woke me for breakfast at 6:30, I could hear the rain dripping off the roof.  When I got out of bed for good, it was really raining hard.  We need the inch of rain we got, but I could use some range time.  It has rained virtually all day.

Given some unexpected free time, I did a little 3D cad of what I want my solar panel system to look like.  Crude  and lacking in details, but in overview, it will look like this:
Turns out I have a battery that might do well with the proposed solar panel system.  It's a 33AH AGM deep cycle battery that I've had for a number of years.  Old batteries, of course, don't last forever and lose their ability to deliver high currents.  Now that I have a smart charger (runs on AC power) I thought I'd check it out more closely.
The charger would say it charged, but unless you can measure the current it delivers, you aren't sure of its real capacity.  I don't have a metered electronic load that I could set up to draw high currents, so how can I know if it really will deliver 33 AH?  Today it hit me that I could use an inverter and 100W lamp with it to see how long it runs.  A 100W bulb draws (100/120) or 0.833 Amp at 120V.  Just scaling that to 12V is 8.33 Amps, and allowing for 80% efficiency in the inverter (wild-ass guess) is 10.4A out of the battery.  By the way, I was not using the little cigarette lighter with lamp cord on the battery; I was using a set of jumper style cables salvaged from an old broken jump starter box, which you can see attached to the inverter (bottom left - silver and black box).  The lamp ran for over an hour and a half but less than two hours.  The "34" displayed on the charger is the percent recharged when I took the picture.

Today, I found the manufacturer's datasheet for the battery.  DrJim, Quizikle and the other engineers who drop by here will probably understand how I almost let out an audible squee when I found it.  According to the datasheet, a constant current discharge at 10.4A (naturally not on the datasheet) can be interpolated to be around 2 1/2 - 3 hours (probably not as much as 3).  It didn't make it, but I haven't been very nice to this battery and have almost thrown it out before.  Often, old lead-acid batteries can be revived by charge cycles.  We'll see. 

Finally, from the "don't ask me how I know" file, if you need to gather water and you don't have a plastic barrel don't forget canvas.  Canvas can make a pretty effective water barrier to line something with.  It will hold water indefinitely. 

11 comments:

RegT said...

SG,

From my reading, some batteries can be desulphated and reclaim more of their capacity if they have been "pulsed: by a battery conditioner with a pulse mode. I don't know if this unit is any good, but it is along the lines of what I read about:

http://www.batteryminders.com/batterycharger/home.php

It is supposed to vibrate or somehow knock the sulphation products off of the plates. I'm sure there must be other battery chargers/maintainers which have this capability, as well.

drjim said...

Yep, if you nicely recharge them, lots of times you can get them back to ~90% of their original capacity.
And since Field Day is just around the corner, I think it's time I get my solar stuff out and checked.
Plus run the generator for an hour or two to warm it up.

Reg T said...

About water, canvas and "sunbrella" fabric biminis (the sun shade covers over some sailboat cockpits) have often been used to catch rain water to refill fresh water tanks on boats. Like tents, though (if you've ever camped in the rain), touching a canvas surface that contains water will often cause it to leak where you have establish a point of "wicking" (compression of the fabric that allows water to wick through, IIRC).

Dacron sails work better, because they don't tend to wick as easily as canvas does. Living in FL as you do, old used sails might be acquired cheaply. A lot of dacron in even a small jib, let alone a mainsail.

RegT said...

drjim,

Just recharging won't bring back batteries that have developed sulphation on the plates. It requires the pulse mode that only _some_ of the chargers and battery maintainers have built into their circuitry (but only a few of these devices apply the proper voltage and the proper pulsation).

It can be done chemically, too, but it is more convenient when it is part of the charging/maintenance process than adding EDTA to clean the plates.

http://www.magnalabs.com/sulfation1.htm

And here is an old article from Richard Perez, founder of Homepower Magazine, and a real expert on battery technology as it applies to alternative energy systems:

ftp://sunsite.unc.edu/pub/academic/environment/alternative-energy/energy-resources/homepower-magazine/archives/20/20pg23.txt

drjim said...

Yep, very familiar with sulphation. I've lost batteries to it more times than I care to admit over the 50 or so years I've been doing this stuff.
I suspect the batteries I brought back with gentle charging hadn't been abuse too badly, and thus weren't sulphated badly.
As you say, the trick is to not let them get to that point. A 100% "dead" lead-acid battery will never come back, but I've had quite a few that were given to me as ready for the recycle bin that DID come back with gentle charging. Sometimes I drained the electrolyte, flushed the cells with distilled water, and refilled them with fresh electrolyte before I charged them. Of course that won't work with a sealed/gel/AGM battery, but I *have* brought back automotive "SLI" batteries doing that. I'm not saying they're as good as new, but I got another year or so of life out of them.
Sometimes when you're a "Starving Student" (who has a ready supply of distilled water and sulphuric acid courtesy of a Chemistry major girlfriend!) you do things other people wouldn't bother to try.
And I have some doubts as to the 'pulse' chargers being as good as they're hyped to be. *Maybe* if the plates aren't too totally crusted up they can work, but there comes a time when NOTHING will revive a truly dead lead-acid battery.

Zendo Deb said...

Canvas bucket is still standard equipment for a lot a sailors. You can't wad the plastic ones up into a small ball and shove them in a locker.

Graybeard said...

I know to take this as true from someone who has a sailboat in their profile picture!

Graybeard said...

I couldn't tell from reading if the charger pulses, but I think it does. (I should drag the o'scope out here.) But I put the 100W bulb on it tonight and it made it all the way to 2 hours. That ain't bad for a battery I figure at about 7 years old that was charged with Sears 6A "constant voltage" supply for all its life.

Doing another charge cycle as I type.

North said...

At a previous job decades ago I made a set of inexpensive loads by cutting up strings of miniature Christmas lights. LOTS of lights. I could switch in the loads a half amp at a time.

Dave, RN said...

I'd like to make a solar set like you've shown here. Any chance you can post the entire setup... panel capacity, charger type, inverter type etc...?

Graybeard said...

The system isn't done yet, and I will be getting back to that soon. So I haven't picked out some of the details like the charger and battery. More is coming.

The panels I have are UPG 87501 (Amazon lists them here.

They're rated at 40 W (two 20W in parallel); I've measured their short circuit current at 1.2A each.

I'm going to put a permalink to a page on this project on the right bar. Should be there soon.