I was wondering whether it would be possible to have 2 x 12v batteries which are charged in parallel, but then the power is drawn in series to give 24v? I have sketched this using diodes and on paper it works but will diode actually work correctly in this manor?

To give some background, Its for running a 24v diesel heater, in a campervan with 12v circuits and charging.

Thanks

 

Welcome to the forum.
Let's see your sketch, or at least a link to it

 

While you may possibly get this to work the results may be poor to very poor. The reason being ia the charge phase is best done by monitoring the voltage of the battery. With two in parallel you never see either batteries voltage correctly.

Either get a 24V charger and leave them in series, or get two 12V chargers and disconnectof ro charging. </two cents>

(Others may have done this and have better comments.)

 

It takes a DPDT switch or relay to do the switching (cannot be done with just diodes).

Two lead-acid batteries of the same capacity and manufacturer (not other chemistries) can be charged in parallel.

 

Two identical lead-acid batteries charge okay in parallel since, even if one battery would charge up slightly before the other, the rise in its voltage from being charged, diverts the current to the other, which has a lower voltage from not being fully charged.

But, as Mike noted, you can't do the series to parallel conversion just with diodes.

 

What you want is a series-parallel switch. they were common on heavy trucks back in the seventies and eighties. they are still available though not as common as they used to be. I think this is what you want:
http://www.gonefcon.com/trucktcom/parallel_sw.htm
http://www.texasindustrialelectric.com/relays_1119845.asp

 

Thanks for you help everyone.