Battery configuration question

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elesaver
elesaver Solar Expert Posts: 185 ✭✭
in Solar Beginners Corner #1
This question pertains to 6V Trojan 125 batteries @ 240 aH each. I have 12 of these batteries. I would like to use them all for my system to give a total of 720 aH. They will be charged by 6 ea 300W panels through a Midnite solar Classic 200 controller. The question is one of connecting the batteries in series. If 2 strings of 4 batteries are in series, there is one negative post and one positive post remaining to which the inverter would be connected. Now, to add one more string of 4 batteries, would I just connect the positive from the first 2 strings with the positive of the third string and the negatives in the same way...then connect the positive and negative to the inverter? Or, should I have 3 separate strings of 4 batteries and connect the 3 positives and 3 negatives together to wire into the inverter? I have looked over the internet for this type of connection and could not find any information. Perhaps it is not good to have an odd number of strings?

Additionally, are there any adverse problems with putting the batteries, controller and inverter in a crawl space under the dwelling? There is a vertical space of 3 1/2', it is well ventilated, and it would seem this would a good location to keep the temperature from going to extremes of highs and lows for better battery life. The moisture barrier is in good shape to keep dampness to a minimum.

My project is beginning to take shape. Thanks for all the help.
1st system:  24Vsystem with 8 X 300W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 150, Outback VFX 3524 with mate, 2 X 12V  fforklift batteries in series 938 aH,  (Outback PSX transformer, Honda EU3000is...not currently hooked up but available if/when needed)

2nd system:  24V system with 4 X 310W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 200, Cotek 1500W pure sine inverter, Trojan 125 batteries (8 available but "currently" using 4)

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Battery configuration question

    Three parallel battery strings isn't a great idea even on a 48 Volt system.
    If you do it you should use Smart Gauge method #3: http://www.smartgauge.co.uk/batt_con.html
    Ideally there should be separate fuse on each battery string in addition to full power fuse on the inverter line as well as on the charger line.

    You're going to need around 72 Amps to charge them. That would require about 2250 Watts of PV on a Classic 150 (the 200 is not needed unless you are running a high Voltage array to overcome wiring losses). 1800 Watts will only produce about 58 Amps or an 8% charge rate. This may work under some circumstances, but it is cutting it close for most applications.

    There are two potential problems with locating equipment in a crawl space: access and humidity. It can be hard to get at stuff (moving batteries in/out and checking them for example) and it may be damp there which will lead to corrosion. If you have no problem with access and the space seems dry enough then there's no issue.
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  • BoFuller
    BoFuller Solar Expert Posts: 187 ✭✭✭
    #3
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    Re: Battery configuration question

    I was originally planning on utilizing my crawl space also ( on one side it's 6 feet) but many members here talked me out of it. Having to get to them is one issue, then lugging them in or out when necessary, possible fumes under the living area, etc. I'll use my crawl space for canned goods and build a shed on the north side of the house.
    12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)

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