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Old 08-09-2009, 11:45   #1
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Battery Charger Question

from a generator, whats the minimum watts input for a 30amp charger? or what is the equation??
cheers
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Old 08-09-2009, 11:50   #2
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What exactly are you actually trying to calculate?

The formulae derive from Ohm’s Law
Goto ➥ "Ohm's Law & Boats"

Watts = Volts x Amps
Amps = Watts ÷ Volts


A 30 Amp Charger (@ 13.5 V Nominal Output) would be a little more than 405 Watts (inefficiencies).

405 Watts @ 120VAC would be 3.375 Amps.
405 Watts @ 240VAC would be 1.6875 Amps.
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Old 08-09-2009, 13:26   #3
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You would probably want a minimum of 1000 watts from the generator--from the WMP advisor:

Power Factors and Generators: The charger in an inverter/charger presents a large, inductive load for a small generator (under 8kW). Chargers with a high “power factor” are desirable because they are less sensitive to peak voltage and need less AC power. Xantrex recommends that a generator be sized at 2.5 times the power draw of the charger.
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Old 08-09-2009, 14:08   #4
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cheers guys.. i was trying to find the largest charger i could have for my 900w honda gen.. so im guessing by ur comments a 25amp charger would be the largest i could go. the 30amp would bugger the gen...
luke
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Old 08-09-2009, 14:22   #5
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Luke,

I think the 30 amp charger will be fine. To be sure, buy a charger which allows you to change the max output so you can adjust it, and with a "slow start" feature that increases charge current slowly to give the generator time to adjust (increase rpm for Honda's). Victron, Xantrex Freedom etc. do that.

ciao!
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Old 09-09-2009, 08:18   #6
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With the Honda generator, I always turned off the "econo throttle" while I first turned on the charger. It still bogged down when it went through it's cycles but it worked fine.

I found that the 40 amp charger did not work with the 1KVA so I changed to the 2KVA generator. It was very easy to sell the 1KVA at nearly the same price I had paid.
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