Battery Maintenance (long term storage)

LBergman
LBergman Solar Expert Posts: 42 ✭
in General Solar Power Topics #1
Hello all,

I have a couple of small capacity gel-type batteries (MK 8GU1 - 31 Ahr) that I've replaced with a larger battery. I have no real use for at least one of them, but don't want to just let it sit and go bad either. At my disposal is one of those "wall" type chargers that outputs 600ma at 12.0 VDC. My planned charging regimen would be a something like a few hours every couple of months on the charger and monitored by a meter. My question: is 12.0 V good enough to maintain a gel-type battery long-term, or should the voltage be higher, like around 12.5 or 13.0 (or even 13.4)?

Thanks
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: Battery Maintenance (long term storage)
    [FONT=Arial, sans-serif]below you will see the charge and float voltages as set forth by deka for their gel batteries at various temperatures. the whole pdf is somewhat long, but may be more readable than my copying a portion from it and is at this link:[/FONT]
    http://www.eastpenn-deka.com/assets/base/0139.pdf
    you need to be sure of the charge in the battery by giving it a full charge as per the voltages speced at xx temperature. as you can see the voltages are much higher than 12v. i would suggest a dvm or dmm to get more accuaracy on the voltages measured if the charger does not have something to accurately measure the voltage.
    [FONT=Arial, sans-serif]Temp. Charge Float Temp.[/FONT]
    [FONT=Arial, sans-serif]°F Optimum Maximum Optimum Maximum °C[/FONT]
    ≥ [FONT=Arial, sans-serif]120 13.00 13.30 12.80 13.00 ≥ 49[/FONT]
    [FONT=Arial, sans-serif]110 – 120 13.20 13.50 12.90 13.20 44 – 48[/FONT]
    [FONT=Arial, sans-serif]100 – 109 13.30 13.60 13.00 13.30 38 – 43[/FONT]
    [FONT=Arial, sans-serif]90 – 99 13.40 13.70 13.10 13.40 32 – 37[/FONT]
    [FONT=Arial, sans-serif]80 – 89 13.50 13.80 13.20 13.50 27 – 31[/FONT]
    [FONT=Arial, sans-serif]70 – 79 13.70 14.00 13.40 13.70 21 – 26[/FONT]
    [FONT=Arial, sans-serif]60 – 69 13.85 14.15 13.55 13.85 16 – 20[/FONT]
    [FONT=Arial, sans-serif]50 – 59 14.00 14.30 13.70 14.00 10 – 15[/FONT]
    [FONT=Arial, sans-serif]40 – 49 14.20 14.50 13.90 14.20 5 – 9[/FONT]
    ≤ [FONT=Arial, sans-serif]39 14.50 14.80 14.20 14.50 [/FONT]≤ [FONT=Arial, sans-serif]4[/FONT]
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  • LBergman
    LBergman Solar Expert Posts: 42 ✭
    #3
    Re: Battery Maintenance (long term storage)

    Thanks for the reply, Niel.

    That's what I was afraid of. I was hoping to get by with what I already had. It's basically just a transformer with a simple rectifier on it. I have a DMM, which was the meter I was referring to. So it looks like I'll need to find some kind of simple (cheap) charger that'll output around 13.4-13.50v (battery will be kept at around 60-70 degrees). Unfortunately all those "wall type" chargers you get with regular household appliances seem to output almost exactly 12vdc. Otherwise one of those would be about ideal for this small battery.

    Too bad I can't just connect it in parallel with the new battery and use it in my PV system, but it seems connecting a 31 Ahr battery in parallel with a 105 Ahr one isn't a good idea. :D
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: Battery Maintenance (long term storage)

    if you know a little bit of electronics you can wire an lm317t regulator ic up for an adjustable constant voltage source to go along with your transformer and diode arrangement. the transformers dc output should be about 3v higher than the speced voltage you wish it to hold at on the battery. the ic will limit the current available to the battery too as it probably won't allow more than an amp to and amp and a half. you do need to know what you're doing here if you do this.
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