Generators & battery chargers

Submitted: Wednesday, Apr 21, 2004 at 21:18
ThreadID: 12268 Views:1905 Replies:6 FollowUps:3
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Hi All,
I am considering buying a generator for charging aux battery when staying in one spot for a few days. I have read the archives & understand the limitation of the 240vac units as they mainly only provide around 8amps on 12v, I have also considered the christie unit but would like to use 240vac at times for other jobs. Anyway back to my question, if say I get a Honda EU10 & plug a normal battery charger of around 20amp's into the 240vac output would the 1000watts be sufficient. I saw a 12amp 240vac - 12volt charger that specified an input requirement of 280watts, this is what got me thinking, I was always under the impression that in order to get 12amps out you would have to put at least 12amps in which would require over 2200 watts at 240VAC Am I missing something ?
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Reply By: Eric Experience. - Wednesday, Apr 21, 2004 at 22:34

Wednesday, Apr 21, 2004 at 22:34
The recognised maximum charging rate for a battery is what is called the 10hour rate. That is if you battery is 70AH [amp hour] then the charge rate is 7 amps, that is why most battery charges are about 8 amps. If you try to charge at a higher rate you have to riase the charging voltage to more than the recomended max of 14.8 volts. The life of the battery is reduced if you do this. Honda has done its homework and has produced the best compromise of charge rate and battery life. You statement about 240 volt charges is wrong, the way you calculate the input power is to ad about 10% to the input power, IE 12volt 10 amps= 120 watts, input power aprox 132 watts. Happy camping. Eric
AnswerID: 55409

Follow Up By: Member - Cruisin (QLD) - Thursday, Apr 22, 2004 at 06:57

Thursday, Apr 22, 2004 at 06:57
Hi Eric

So whats the go with the Generators that are attached to an Alternator.
Are they any better or quicker at charging batteries than a standard Genset ???

Cheers Cruisin
FollowupID: 317271

Follow Up By: Eric Experience. - Saturday, Apr 24, 2004 at 21:27

Saturday, Apr 24, 2004 at 21:27
I assume you mean a alternator connected to a motor. The type of charger makes no difference it is the battery that determins the charging rate, if you read the adds for a well know unit you will note they say the alternator is rated at 50 amps, the wording is designed to make you think you can charge at 50 amps, but you can not unless you want to reduce the life of the battery. You can run a load and charge at the same time but that is not the question you asked. Eric.
FollowupID: 317648

Follow Up By: Member - Cruisin (QLD) - Tuesday, Apr 27, 2004 at 21:31

Tuesday, Apr 27, 2004 at 21:31
Makes sense what you say Eric. Is a Generator like the Honda EU 10 your prefered unit over the Motor connected to an Alternator unit ???
It would seem a bit more versatile. I guess its all just horses for courses as with everything.
FollowupID: 318034

Reply By: Rosco - Bris. - Wednesday, Apr 21, 2004 at 22:40

Wednesday, Apr 21, 2004 at 22:40

Apart from Eric's good advice, you will also need a battery charger as I understand the 8 A output from the genset is unregulated, hence it will still keep pumping 8 amps into the battery whether it needs it or not. end result ... one cooked battery.
AnswerID: 55410

Reply By: Member- Rox - Thursday, Apr 22, 2004 at 00:14

Thursday, Apr 22, 2004 at 00:14
I have a EU 10 as well and a 100amp Deep/c bat. I use a 20 amp smart charger from 12 volt shop(3 stage) not cheep but if i put in 2x100amp bateries its fine, I am thinking long term traveling 4+days before a charge.
AnswerID: 55426

Reply By: Member - Nigel (QLD) - Thursday, Apr 22, 2004 at 00:29

Thursday, Apr 22, 2004 at 00:29
a 12 amp charger at say 15 volts max (for ease of calculation) would
require 12 x 15 = 180 watts

180 watts at 240 volts is 180 / 240 = 0.75 amps @ 240 volts

now chargers aren't ever 100% efficient so if your charger was
80% efficient you'd want 225 watts available to run it.

Hope that makes it easier to understand
AnswerID: 55431

Reply By: Mark - Thursday, Apr 22, 2004 at 21:38

Thursday, Apr 22, 2004 at 21:38
Thanks Guys for all the replys. I guess its safe to say a 1000w generator would have no trouble providing powerto a 12vdc charger of around 20 - 30 amps providing the battery was capable of accepting the high charge current.
AnswerID: 55587

Reply By: Eric Experience. - Tuesday, Apr 27, 2004 at 21:59

Tuesday, Apr 27, 2004 at 21:59
Yes i would go for the honda, its costs a little more but you will get on a lot better with your fellow campers because it is not as niosy as the others. Niose carries a long way when you are out in the scrub. Eric.
AnswerID: 56290

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