Questions about MC4 connectors and battery charger

tndoug99
tndoug99 Registered Users Posts: 10 ✭
in Solar Beginners Corner #1
I have purchased 9-40 watt 12 volt (2.5 amp) panels (360 watts total) with MC4, inverter, and a 25 amp charge controller so far. It has taken me about a year to save up and buy this stuff, and I still need a battery charger, cables, and batteries.

I'm not sure of the best way to connect all the panels together keeping it 12 volt, and what connectors I need.

How many batteries would my set-up support?

What would be a good charger? If I have 2 batteries, do I need a 2-bank charger?

I would appreciate your comments on this, as I can now afford to get a charger, and connectors.

Thanks Everyone.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Questions about MC4 connectors and battery charger

    You have about two choices for connecting the nine 40 Watt panels together:

    All nine in parallel (which will require one fuse per panel). This can be used either on a PWM or MPPT type charge controller.
    Three parallel strings of three panels in series (which will require one fuse per string). This needs to be used with an MPPT type charge controller.

    Nine time 40 Watts is 360 Watts. With the PWM/parallel connection you can expect about 22.5 Amps maximum charge current. This will work fine with two 6 Volt golf cart type batteries in series (220 Amp hours @ 12 Volts). You would get only slightly more from the MPPT set up (which is much more expensive) and not enough to support a larger battery bank.

    Unless there is a very long wire run from the panels to the charge controller I would go with the PWM/parallel system. A charge controller like this, for example: http://www.solar-electric.com/ps-30.html I think you will need to make your own combiner box, as the commercial units for nine panels would not be cheap. You will at the very least need nine MC4 extension cables (cut in half) to connect the panels to regular wire & fusing.

    Others might have different suggestions.
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  • tndoug99
    tndoug99 Registered Users Posts: 10 ✭
    #3
    Re: Questions about MC4 connectors and battery charger

    I was planning on 3 sets of 3. I was thinking of a using pipe, in a "T", with the panels mounted on the top of the T. with a simple horseshoe bracket in the center. This will be portable. I'll make the base out of pipe too, set low to the ground, and have the 3 panel sets mounted stadium seating style, and so it can be disassembled with not too much trouble. They could be pivoted, but I would need a set screw to keep the wind from moving them.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Questions about MC4 connectors and battery charger

    In that case you would have no choice but to use an MPPT controller like the Rogue: http://www.roguepowertech.com/products/mpt3024.htm
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #5
    Re: Questions about MC4 connectors and battery charger

    One of the other posters here let me know that Marc is bringing out his next version somewhere at the end of this year or early next--Check with Rogue directly for updates:
    Out of stock -- an upgraded replacement with new features will be available shortly. Contact us or subscribe to our Facebook page for updated information.

    -Bill "I don't Facebook" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • tndoug99
    tndoug99 Registered Users Posts: 10 ✭
    #6
    Re: Questions about MC4 connectors and battery charger

    This is basically what I had in mind.

    Attachment not found.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #7
    Re: Questions about MC4 connectors and battery charger

    As a general rule, always go for a series battery configuration rather than a parallel one when both are possible.
    If you needed more AmpHour capacity than you could get in one 6 volt battery, then using 4 volt of 2 volt assemblies would be better. Or else increasing the battery bank voltage to 24 or 48 volts, reducing the AH needed by factors of 2 or 4.
    With a 600 watt inverter, you are still in the range where a 12 volt system is practical.
    SMA SB 3000, old BP panels.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #8
    Re: Questions about MC4 connectors and battery charger

    Just as an FYI--Not all "2 volt" batteries are built the same...

    For example, some (one, several, all?) of the Trojan "2 volt" cells are really three 2 volt cells in parallel (you still have to check three caps for electrolyte levels and specific gravity).

    I guess it was easier to take current production and modify the bus bars to 2 volt parallel from 6 volt series.

    The batteries are, otherwise, very good/solid/reliable cells.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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