# Battery recharging from generator

Discussion in 'The Beginner' started by Phil56, Feb 15, 2014.

1. ### Phil56Read Only Funster

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Anyone know how I calculate how long I would have to run a 3kw generator to recharge two 80Ah leisure batteries? Assuming that once 50% discharged they will have 12.3V and when fully charged they hold 12.7V, then it seems to me that it shouldn't take too long to charge 0.4 volts. But there again, I read somewhere on here that you are supposed to recharge slowly.....as a rule of thumb I thought I read that if you spend 2 days discharging, you should spend 2 days charging. That seems like a long time to be running a noisy generator!

I'm pretty sure I'm making a big mistake somewhere!

Phil

2. ### pappajohnFunsterLife Member

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the generators output has no effect on charging time....thats determined by your onboard chargers output.

A 15amp constant rate charger will take around 5-1/2hrs plus an hour or two for the absorbsion stage to be effective.
A modern electronic charger may take 12hrs or more but is far kinder to the batteries.

Charging directly from the generators 12v output terminals wil take forever..it may only be 5amp to 8amp.
A 50% discharged battery will show 12v....100% charged will be 12.7
12.3v is approx half charged

Last edited: Feb 15, 2014
3. ### JeanLucFunster

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As this is an onboard generator, it is probably wired to charge the batteries directly rather than being the equivalent of a 230V mains input to the charger. If it were a separate portable generator, the usual practice is to plug the 230V output into the Hymer's EHU point. Under those conditions, Pappajohn's comments are correct. I believe yours has a Hymer factory-fitted 3 kw generator but I have no knowledge of how it might be connected, or indeed whether there is any linkage with the EBL. Hopefully there is some documentation / handbook that can help?

p.s. the batteries should be showing 13.8V when they are full and being float charged by the EBL, not 12.7V

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