# Running central heating off a 12v battery!

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• posted on October 31, 2003, 1:33 pm

A large car battery will be 70 amp/hour or very roughly 1000 watt/hours, but I'd half that in practice.
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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• posted on October 31, 2003, 11:52 am
[apologies if this is a repeat - outlook playing up. Outlook or Lookout?]
wrote:

while
[...snip...]
I have found a possible UPS that is rated as 3000AV/2250W. That is a power rating, but how long could I expect it to realistically last if I draw say 200W? What is 3000AV expressed as Ahr? eg; is it better than 110Ahr?
It looks like a genny is the best way to go!!
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• posted on October 31, 2003, 4:48 pm

It's impossible to tell without knowing the capacity of the UPS, but in my experience of using them over the years, you typically get 5 minutes on full load and 15-20 on half load. (Except for 'extended run' types which have more battery capacity). The discharge curve is very non-linear when they are running over half load, but reasobably linear below that.
So, drawing 200W, thats approx 1/10th of the capacity you might expect it to last one to 1.5 hours... But thats jsut a guess based on what I've used over the past few years.
VA doesn't equate to run-time at all. Amp hours is literally that - 110 Amp hours would be 110 amps for one hour, or 220 for half an hour, or 55 for 2 hours, but look out for the continuous current draw which is usually quoted too. Eg. if it was 110Ah at 55 amps then it would give you 2 hours at 55 amps, but much less than 1 hour if you sucked 110 amps out of it.

Possibly. It does depend on how long you think the powers going to be out for...
Gordon
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• posted on October 30, 2003, 4:08 pm

the
boiler.
do
charged
Talked to someone years ago who lived in the wilds of Derbyshire and had oil fired central heating. He had a 12v pump for the CH so he was covered for power failures. Had a quick Google but only found marine applications - however a CH pump for a large barge might do several radiators. This would avoid all the messing about with inverters - although if your boiler requires 240V then you still have a problem :-)
Cheers Dave R
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• posted on October 30, 2003, 4:15 pm

while
for
doesn't
oil
All the major pump makers do low voltage versions.

I know some makers did have low voltage LPG boilers for boats etc, then no problems. I still say a genny is the best option, in price, less hassle, function given and versatility.
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• posted on October 30, 2003, 4:59 pm

If he's got a 12 volt DC pump, then presumably that means messing about with a power supply for that when running off mains?
The inverter isn't the problem - it's the battery, as lead acid types don't like deep discharge. And this would happen with a 12 volt pump equally.
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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• posted on November 1, 2003, 1:17 pm
wrote:

I presume you would have a battery with an 'always on' charger and take the pump feed from that. Assuming that the 'always on' chargers can supply enough juice to run the pump, you would have a seamless transition from power to no power and back. You could even add 12v lighting circuits and alternative inputs to the battery (or batteries) such as solar panels and wind power. First step to a suistainable lifestyle and selling power back to the grid :-)
Cheers Dave R
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• posted on November 1, 2003, 1:39 pm

You might well for the pump, but the boiler usually has mains electrics too. Also the programmer. Of course, all this *could* be designed for 12 volt DC and incorporated with some form of UPS, but I'd say it would be far too expensive for most, given the relatively rare power cuts in *most* of this country. For those who live in areas - usually very rural - where there is a problem, a standby generator would be the best bet anyway.

Fine as a hobby, but really not worth the effort as a genuine standby.
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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