/ Campervan Electrics

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Hope someone can help me...
I have an Erberspacher heater for my van, but it requires 24v power to it. It needs 40W for running, but 500W (+/- 10%) at start up.
I'm trying to work out how best to do that, and have come up with the following ideas, could someone suggest if they'd be likely to work?

1 - buy a 12v to 24v transformer, rated at 500w. Run power from my 110Ah 12V batteries to the transformer, plug in the heater...job done.
2 - Buy 2x 12v to 24v transformers rated at 250W (cheaper than above) - some how wire them up to give 500w power? is that possible?

With either of the above two options, would the transformers always create 500W, thus draining my battery pretty quickly, or would they drop to the 40W as soon as the demand from the heater drops?

Option 3 - Wire two batteries in Series to give 24v power, linked to heater...job done - but would the batteries produce sufficient power for the start up? If not, with some funky wiring, could I set it up so that the Engine is on for start up, and then the continual running can be done off the batteries?

Sorry if I'm being really thick, or missing anything really obvious, I'm not a spark, and have very limited knowledge of electrical theory!

Cheers,

Matt

EeeByGum - on 31 Jan 2013
In reply to carrot_boy (North East Wales MC): Can you not just get

x1 electric hook up lead

?? :-)
In reply to EeeByGum: yea...great, at a campsite.

so - new question - assume I'm nowhere near an electric hook up...
RCC - on 31 Jan 2013
In reply to carrot_boy (North East Wales MC):

> Option 3 - Wire two batteries in Series to give 24v power, linked to heater...job done - but would the batteries produce sufficient power for the start up? If not, with some funky wiring, could I set it up so that the Engine is on for start up, and then the continual running can be done off the batteries?

How would you charge a 24V battery bank?

Would it not be simpler just to put the eberspcacher on ebay, and buy a 12V version?



Hairy Pete on 31 Jan 2013
In reply to carrot_boy (North East Wales MC):
> (In reply to EeeByGum) yea...great, at a campsite.
>
> so - new question - assume I'm nowhere near an electric hook up...

? So where are you getting the AC from?

Transformers are AC devices. The won't work well on DC batteries. Any electronics conversion will probably cost much more than buying an appropriate heater; not to mention all the conversion losses.
Adam Lincoln - on 31 Jan 2013
In reply to carrot_boy (North East Wales MC):

Why did you buy a 24v version?!
Hairy Pete on 31 Jan 2013
In reply to carrot_boy (North East Wales MC): I'd go with option 3, but have the batteries separate from campervan battery - so that you don't flatten your engine starter battery.
3leggeddog on 31 Jan 2013
In reply to carrot_boy (North East Wales MC):

It is possible if you have 2 batteries (van and leisure). With a few relays you can supply the 24v required for the heater and charge from the alternator using a split charge relay. Try bongofury.co.uk some one posted the wiring diagram on there.
quirky - on 31 Jan 2013
In reply to carrot_boy (North East Wales MC): i would have thought the500w start up Will only be for a few seconds probably for a glow plug to start it. you could use a couple of relays to create separate 24dc supply from you existing batteries. as for the power supply you would need 1 500w rated supply, it Will only run at the power demanded from it.
EeeByGum - on 31 Jan 2013
In reply to carrot_boy (North East Wales MC):

> so - new question - assume I'm nowhere near an electric hook up...

<Still being devils advocate> Why would you be anywhere other than a nice comfortable Caravan Club recommended caravan site? :-)

I am afraid I can't help on the electics other than suggest that the more expensive option seems simpler and less likely to spontaneously burst into flames.
RCC - on 31 Jan 2013
In reply to 3leggeddog:

> It is possible if you have 2 batteries (van and leisure). With a few relays you can supply the 24v required for the heater and charge from the alternator using a split charge relay. Try bongofury.co.uk some one posted the wiring diagram on there.

It isn't a great idea to connect forced air heaters like the eberspacher ones in such a way that the power could be inadvertently cut (e.g. by an isolating switch or turning the engine on) before the unit has powered down.

beth on 31 Jan 2013
In reply to carrot_boy (North East Wales MC): You could do some funky wiring to charge two batteries in parallel but switch over to series for running the heater... but it's rife with problems and only needs one little mishap for a big oops to happen. Or have a 12 -> 24 converter of some description, but the efficiency will be poor, meaning you'll need bigger batteries/etc. Two car batteries in series will give you the 24v necessary for start and running no problem. You could charge them entirely separate from the van electrics/etc. But really the sensible thing to do is sell it on the bay of E and get a 12v Eberspacher.

RichardP - on 31 Jan 2013
In reply to carrot_boy (North East Wales MC):
> Hope someone can help me...
> Option 3 - Wire two batteries in Series to give 24v power, linked to heater...job done - but would the batteries produce sufficient power for the start up? If not, with some funky wiring, could I set it up so that the Engine is on for start up, and then the continual running can be done off the batteries?

connect in series when the heater is in use,
and connect in parallel when you need to charge the batteries.

I suppose you could have it set-up in series the whole time and just take it in turns which battery you charge at a time
RichardP - on 31 Jan 2013
In reply to beth:
>get a 12v Eberspacher.

that's the best answer

quirky - on 31 Jan 2013
In reply to RichardP: As others have said, sell it and buy a 12vdc version!!!
Cuthbert on 31 Jan 2013
In reply to quirky:

Aye, or just get a propex.

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