Charge controllers and matching PV wattage to Battey bank capacity.

System
System Posts: 2,511 admin
in General Solar Power Topics #1
Someone recently told me that they ordered a charge controller that is rated for 500W and can take any input up to 100V and give a 12V output. For less than $200.

This sounds like something I could use. Anyone know what brand of controller this might be?

Some time ago there were posts explaning the optimum relationship between battery capacity and PV output. I can't find them now and I've forgotten how it was calculated. Is it something like PV output in amps should be 5 or 10% of amphour rating of battery bank?

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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #2
    Re: Charge controllers and matching PV wattage to Battey bank capacity.

    TC,

    I suspect it's a BZ Products MPPT controller. See: http://bzproducts.net/_wsn/page2.html MSRP is $280. I don't have any first hand experience with this model. I suspect the 45 A spec includes the 125% NEC multiplier for design current, and a 111% conversion from Imp to Isc. If so, the 500 W STC rating looks about right.

    A good rule of thumb for "design" charge current is 5% of battery Ah capacity. For example, A design charge current of 20 A is appropriate for a 400 Ah battery bank. However, large loads present while charging the batteries would require higher charge current.

    Assuming ~80% operating performance from the PV array, the cabling, and the controller, a roughly equivalent rule of thumb is one Watt (STC) of PV for each Ah of 12 V battery capacity. For example, a 500 W (STC) PV array should be a reliable match for a 12 V x 500 Ah battery bank.

    HTH,
    Jim / crewzer
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: Charge controllers and matching PV wattage to Battey bank capacity.

    Just the info I needed.

    Thanx, Jim.
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