Batteries-charging

System · April 2007

I am currently using a gas generator for power out of necessity. I have obtained 3 batteries from the scrapyard where I work. These were from a gov installation of some type and evidently were for telecommunications backup as they are C-D Technology High Rate Series sealed lead acid batteries rated at 88AH (20V). Well, I thought I scored and could just buy a solar panel to charge up the batteries during the day and use them with an inverter at night. Hah!! I bought a 1200w/12v inverter which powers my computer/tv/radio/clock and a few other doo dads just fine. I estimate about a 1000watt draw. The water pump/refrig/water heater I leave to the gen. So now I had to figure out how to charge these things and thats when I came upon this forum. Obviously my little 10A auto battery charger is not going to do it. Either is the single solar panel I was going to buy. I was considering a 65 W panel as thats all I can barely afford. After reading your forum I wanted to ask ...how can you tell what the SOC of the batteries are. How in the world do you know its 101% without paying 800 dollars for a controller? I don't want to ruin these batteries right off the bat. So now I'm considering using the money I was going to spend on the solar panel to buy a good battery charger but then I have to ask...is a 15 A charger going to work (the cheapest) or should I consider a 30 A, so that I could charge these 3 connected in parallel. Or should I just give up until I win the lottery and keep paying 3.50/gal (N. Cal)for a lot of gas.

Thanks for any comment. Bob

mike95490 · April 2007

Re: Batteries-charging

If the batteries are from a scrapyard, they may have been abused, and may not recover well.

Since they are sealed, you have to be very careful how you charge them, as overcharging will pop the overpressure vent's and you will loose water, that can't be replaced.

I'll assume you will place these in parallel, so you are looking at a 264A battery. The minimum you need to keep it charged is about 3 amps.( about a 100W panel) To Recharge, you will need much more. Perhaps the Vector series of household/automotive charges can do it for a hundred bucks or so:
http://www.battery-care.com/chargers/VEC1093a.htm Draws less than 700W AC
(40A peak charge, supposed to be a smart 3 state charger)
There may be some better charges others will suggest.

Yikes - I didn't see that 20V rating - if true, take them back to the scrapyard !!

System2 · April 2007

Re: Batteries-charging

actually they are less than 3 years old and are in very good shape. Remember the government threw these away. I wonder if my generator will supply the required current for a 40 amp charger. It is 6200 watts....bob

niel · April 2007

Re: Batteries-charging

you can't always judge a book by its cover. once fully charged a load testing is in order. now nobody should go any further until we know if you really mean they are 12v or are they really 20v as you've stated?

Brock · April 2007

Re: Batteries-charging

And the charger charging at 40A is 40A at 12v or 480 watts or about 4 amps at 120vac, still about 480w not 6400 watts.

Honestly i would look at a 5 amp Deltran. I know it's only 5 amps but they, like Iota, put out the full rated power the whole time. Also this little charger is very forgiving on the input voltage and is a true 3 stage charger (they call it 4 stage).

http://cgi.ebay.com/NEW-Deltran-International-12V-5-amp-Battery-Charger_W0QQitemZ260101554198QQcategoryZ50391QQrdZ1QQcmdZViewItem

If you want a larger unit I would look at the Iota line maybe an Iota 15 with a smart charger plug.

crewzer · April 2007

Re: Batteries-charging

Bob,

Here’s a link to specs for your batteries (they’re 12 V, BTW, not 20 V; the “20” number is the discharge period in hours): http://www.cdstandbypower.com/product/battery/vrla/pdf/12_310.pdf

Here’s additional C&D info: http://www.cdstandbypower.com/product/battery/related/7525.pdf And, here’s a link to a very good AGM battery manual from East Penn, the makers of Deka and MK AGM batteries: http://www.eastpenn-deka.com/assets/base/0139.pdf This manual includes a voltage vs. state-of-charge table for AGM batteries (see page 13).

Connected together in parallel for use with your 12 V/1200 W inverter, the three 12 V x 88 Ah batteries form a bank rated at 12 V x ~264 AH. This is roughly equivalent to a size 8D battery – not bad. That’s the good news.

The bad news, if you will, is that an appropriate size PV array for this battery bank would be ~225 W (STC). Such a bank would require a charge controller rated for at least 15 A. A very good candidate would be the Morningstar ProStar 15M, most likely with the optional remote battery temperature sensor. You could probably get by with an array rated at ~135 W (STC) if there are no loads on the batteries while they're being recharged.

See: http://www.morningstarcorp.com/products/ProStar/index.shtml
and: http://store.solar-electric.com/pros30solcha.html

HTH, and let us know if you have any additional questions.
Jim / crewzer

System2 · April 2007

Re: Batteries-charging

Hey, thanks guys for the excellent information. Now I have a direction to go in and with some good references and recommendations to work with. I was kindof stumbling around in the "dark" for a bit....bob

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