Ac battery charging

no-carrier
no-carrier Registered Users Posts: 13 ✭
in Off Grid Solar & Battery Systems #1
I understand that my trojans, 225ah, should be charged at aprox 10%..22a...What I understand, thats 22adc...What would be the equivalent in ac charging? Thanks
Dennis
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #2
    Re: Ac battery charging

    There is no equivalent. Batteries are DC.

    A DC charger will draw a certain amount of AC to convert to DC.

    For instance, the Iota 15a DC charger draws up to 3.5a of AC:

    http://www.iotaengineering.com/dls15.htm

    The Iota 30a DC charger will draw up to 7a AC.
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  • no-carrier
    no-carrier Registered Users Posts: 13 ✭
    #3
    Re: Ac battery charging

    So when charging with ac I should chg at the same 23a?
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #4
    Re: Ac battery charging

    You can't charge a DC battery with AC. You have to have a battery charger that converts AC to DC.

    10% is a rule of thumb. I'd go with a 30a charger.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Re: Ac battery charging

    Assuming you want ~22 amps charging your 12 volt (?) battery bank with a standard AC charger (~80% efficient, power factor = 0.6 poor but common, and 117 VAC nominal line voltage):
    • 22 amps * 14.5 volts charging * 1/0.80 eff * 1/0.6 power factor * 1/117 VAC = 5.68 amps AC @ 117 volts
    You can also get a Kill-a-Watt meter to measure your own loads (is not quick enough to measure starting surge current--but is about the best thing for the lowest cost out there for use around the home to measure your various plug in AC appliances).

    If you are looking for the appropriate sized genset--The ratings would be:
    • 22 amps * 14.5 volts charging * 1/0.80 eff * 1/0.6 power factor = 665 VA (volt*amps)
    • 22 amps * 14.5 volts charging * 1/0.80 eff = 399 Watts
    For the most part, you need to size the genset to the VA rating of the load... The 0.6 Power Factor can be near 1.0 for "Power Factor Corrected" Battery Chargers--but there are not too many of those, and they tend to be more expensive. For example:

    Iota DLS-15: 12 Volt 15 Amp Battery Charger Price: $129.00 (non-pfc)
    Iota DLS-30-M 12 volt 30 amp regulated battery charger Price: $133.50 (non-pfc)
    Xantrex Truecharge2 12-Volt, 20-Amp Battery Charger Price: $264.00 (non-pfc)

    For the most part, gensets are more fuel efficient at >50% of rated load.

    So the difference between 399 watts of fuel usage vs 665 VA of sizing (wire, alternator, fuse/breaker, etc.) can make a big deal if fuel is expensive and difficult to transport/store. Paying the extra $130 for a PFC type battery charger and a small ~900 watt genset (like the Honda eu1000i) can be a nice combination.

    Of course, even in this case, the eu1000i can support either a 20 amp non-pfc or a 20 amp pfc.

    However, a non-pfc 40 amp battery charger is too large for the eu1000i (you would need an eu2000i or equivalent in that case).

    If you want to know more about PFC and what is it--Please feel free to ask more questions. Also here is good reference source:

    Wiki: Power Factor Correction

    Hope that all made sense.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • no-carrier
    no-carrier Registered Users Posts: 13 ✭
    #6
    Re: Ac battery charging

    Thanks guys, I now understand....
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Ac battery charging

    A couple of observations after reading this thread:

    The 10% current rate (22.5 Amps) is a peak rate. As the battery charges that current will go down. A generator like the Honda 1000 like Bill mention will have no trouble handling this with even a not-so-good PF charger.

    It may be that the OP is trying to program an inverter/charger which has the charge rate given in AC Amps and he needs to know how to adjust for the equivalent DC output (Outbacks function this way). In which case the starting point is the factor of system Voltage to 120 VAC, as in: Amps @ 12 VDC / 10 = Amps @ 120 VAC (not including losses and PF of charger). So if you have an OB inverter and you're trying to find the right AC Amps for 22.5 on the DC side set the number at 3 Amps - should be fine.

    Or that may not be what he's trying to do, in which case the above paragraph is not applicable. :p
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #8
    Re: Ac battery charging

    I can state that a Honda Eu1000 will not run a Xantrex TC 40 because of the PF. It will run a TC 20 without breaking a sweat.

    I don't know about the PF of the new generation of Xantrex chargers.

    That said, the IOTA 15 would probably be a reasonable fit for the 225ah battery. I use the TC 20 on my 450 ah bank, and it works well.
    Tony
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Ac battery charging

    Tony;

    That is good to know about the Xantrex charger! One would expect better from them.

    My aged Honda 1000 will run my Schumacher 30 Amp commercial charger - PF of 0.63.

    There's probably some kind of joke in all this: When is a Watt not a Watt? When it's a Volt Amp!

    Okay, that's not actually funny. We'll keep working on it. :p
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #10
    Re: Ac battery charging

    What the older version of Xantrex TC series chargers lose in PF correction, they make up for in their ability to run fine on whacky AC voltage. I think the specs say ~90-165 vac, 40-70hrz. Ideal for cheese ball gennies. (Not that any of mine would qualify as that!)

    Tony
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