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Old 19-10-2013, 08:00   #1
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charging batts with genset/charger, wet, lifepo4

Hi all,

Gretchen and I have moved aboard our new to us boat, a 1978 Camper Nicholsons 44 ketch. She has two, 24v banks for house, 24v starter batts and a 12v genset starter bat. All are wet cells. There is a 24v 30a ferro res charger, and a 24v alt on the engine of unknown output. The genset is 4kw.

We are trying to find a slip in Annapolis, where we can stay the winter. I have some long term ideas of simplifying the system to one lifepo4 200a bank, and the starter bats with an echo charger.

We were energy independant on Alchemy, but it will take time to get there. In the meantime, I think the charger is the first upgrade to make. With a 4kw genset, just how big of a charger can we practically get away with? We don't even have an ah meter, so I dont know how much juice we are using.

Any specific recommendations on a charger that can do the wet cells now, and lifepo4 in the future?
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Old 19-10-2013, 08:09   #2
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Re: charging batts with genset/charger, wet, lifepo4

I hope this will help you, we have a 2kw genset Honda and are able to use a 40 amp charger no problem but putting the 60 amp when the genset is on idle mode and the charger starts there isn't enough time and the breaker blows, but when not in idle mode it supports it easily so in your case 60 amp for sure and maybe even an 80 depending on the kind of genset your using and weither it has echothrotle or not.
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Old 19-10-2013, 09:35   #3
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Re: charging batts with genset/charger, wet, lifepo4

A 4kw gen set will produce 30 amps 120 volts, 300amps 12 volts, or 150 amps 24 volts.

the math is

amps X volts = kw. 1 amp 120 volts = 10 AMPS 12 volts or 5 amp 24 volts

4kw /120 volts = 30 amps 120 volts X 10 = 300 amps 12 volts / 2 = 150 amps. 24 volts

You should be able to do the conversion in you head when dealing with different volts a.d amps.
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Old 19-10-2013, 09:44   #4
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Re: charging batts with genset/charger, wet, lifepo4

Also when dealing with different volts remember the wire size has to be size correctly

The higher the volts the smaller the wire size has can be. So if the wire is size has for 24 volts is may not be able to handle 12 volts. So be careful when dealing with different amps and volts.
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Old 19-10-2013, 09:56   #5
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I am familiar with the math involved. I guess I am asking if there are some practical limitations on how big of a charger I should use, given a genset size. Considerations on total fuel used, efficiency of the genset with different loads, wear and tear, etc.
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Old 19-10-2013, 10:19   #6
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Re: charging batts with genset/charger, wet, lifepo4

The Sterling line of chargers provides good value for the money and has a Custom setting as well as the normal battery chemistries and types.
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Old 20-10-2013, 17:27   #7
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Yes, I read about the sterling chargers on Maine Sails pages. I really loke them but wish they had higher amperage models.

Chris
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