Running central heating off a 12v battery!

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I am investigating whether I can run the central heating for a short while off a 12v leisure battery (110Ahr) with a suitable inverter.
The problem will be the load (and the time that the inverter will run for before melting). Has any one tried this? We get a lot of power cuts and the lights and cooking are easy, but the heating is not! The water pump only draws 90W or so, but I can not work out the power for the oil-fired boiler. The ignition unit has 3AV as a rating but my electrical knowledge doesn't do AV :-)
If this might work, then what is the best way of keeping the battery charged and ready to go?
If this can not work, then I am off to by a small generator!! Thanks
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There *might* be a problem if the electronics of the boiler or the pump motor don't like the waveform from the inverter, but it's certainly worth trying in my opinion.
The main load will be the pump. Have you misread the '3AV' on the ignition unit, if it was 3VA that would mean 3 VoltAmps which is, effectively (though not exactly) 3 watts. (It can be anything up to 3 watts, depending on the power factor).
Or it could just be that 3AV is a code of some sort and not a power rating.
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redtag wrote:

This should work, and if it does I'd be interested.
The way to keep the battery charged is to use a simple trickle charger off the mains. One could be constructed with a LV lighting transformer (torooidal) a bridge rectifier and a resistor.
As far as teh boler goes - well it has an air blower motor and an oil pump (assuming oil) and an igniter. That plus pumps and motoruised valves has to be less than 500W. I am pretty sure my whole shebang runs of a 3A fused spur. A cheap clamp on ammeter would probably tell you. Lots on ebay at the moment.
So you probably need a big tractor battery and a 500W inverter. Big tractor battery might be 120A/h, ao assuming draw9ng one amp from 250v, thats 250w. The battery will be 12*120 watt hours = 1440watt hours, so maybe 4 hours of safe running.
YMMV
Another trick would be to have an old MOT failed vehicle parked outside the boiler room, and some jump leads coming in...so you can simply pour petrol in that and run it to keep the C/H going. Most alternators will do 20A or so.

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cheaper for a given capacity.
A car/tractor/lorry battery is designed to cope with high charge and discharge rates so that it can manage starting etc. well but is not designed to be discharged to a large proportion of its total capacity.
Batteries which cope with deep discharge well are those designed as traction batteries or as backup batteries in alarm systems, UPS' etc.
If the battery never gets fully discharged and is trickle charged all the time that the mains is on then a vehicle battery may be OK but a much smaller capacity backup/traction battery would also do the job.
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     snipped-for-privacy@isbd.co.uk writes:

Alarm batteries are not normally deep discharge types. Alarms either contain deep discharge protection circuitry, or expect the SLA battery to be replaced if it was completely flattened. Similarly for UPS's I've used -- they contain deep discharge protection circuitry so the UPS doesn't need more expensive batteries to cope with being completely flattened. Many inverters also include deep discharge protection circuitry.
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Andrew Gabriel

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Yes, I was just realising that too, I should have put only traction batteries in my response.

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On 30 Oct 2003 11:50:28 GMT, snipped-for-privacy@isbd.co.uk wrote:

You don't even need that - just a constant (or temperature dependent) output voltage, but it's lower than that used for trickling. Like I said, it's a two transistor circuit. I once made an 8-headed version of this, for permanent use on a battery storage shelf.
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Good grief. How the other half live...
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*Gaffer tape - The Force, light and dark sides - holds the universe together*

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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I remember an article in Practical Mechanics (yes, a LONG time ago) where someone did this with a large battery and a dynamotor. His first stab at it ran the dynamotor the whole time; the second was more sophisticated and provided power only when needed. If it was doable then (40 years?), it's doable now...
I always remember what he called it - BEBOP.
Battery Energised Boiler Operation Plant!
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Bob Eager
rde at tavi.co.uk
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"Bob Eager" wrote | I remember an article in Practical Mechanics (yes, a LONG time ago) | where someone did this with a large battery and a dynamotor. His first | stab at it ran the dynamotor the whole time; the second was more | sophisticated and provided power only when needed. If it was doable then | (40 years?), it's doable now... | I always remember what he called it - BEBOP. | Battery Energised Boiler Operation Plant!
Ah, how times change. We're up to High Integrity Power Heating Operation Plant these days :-)
Owain
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On Thu, 30 Oct 2003 12:39:03 -0000, "Owain"

Basic Universal Low Leakage Standby Heating Integrated Thermal System.
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A new genny will cost approx 2000. This will do all essential services in the house: lights, CH, energy efficient fridge, etc. I would tend to go that way. Tractor batteries are expensive as are inverters. A genny is also very useful for other tasks.
Although too early, the Microgen Combined Heat & power boiler is due out in Spring, so worth investigating in advamnce, with an LPG version to follow. The LPG version may be cheaer to run "overall" than oil, and no cut in CH or DHW.
http://www.microgendirect.com /
The Whisper gen is out around now, but not sure if an LPG version is available. http://www.whispergen.nz
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Don't assume it will run with no mains power though. When I looked at a couple of datasheets a while back, it was quite clear that the units would not work during a power cut. One of them was thinking about an add-on box (probably a battery and charger to provide power for the electronics) to enable this at some unspecified time in the future.
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writes:

Good point. The literature I looked at (initial release) for the Microgen did say that it would work in power cut. I assumed it would have to be running when the cut came. Starting it in a cut would be a problem.
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wrote:

Why not just use a UPS? That's what they are for, after all.
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The easiest way (possibly not the best or cheapest) would be to simply buy a UPS. (uninterruptable power supply) Battery, charger and inverter in one box. I ran my CH unit of one of mine (A small APC unit) for a short while to test it. Worked OK. (But it's only a pump and a few mW for the gas boiler ignition)
Go to http://www.maplin.co.uk/ and enter UPS into their search box. Their top of the range one is 129 which isn't a bad price for a UPS of that capacity. Watch out for run-time quotes for UPSs though - they are usually quoted at less than half load. The typical run-of-the-mill figures I've seen in the past are about 5 minutes on full load and 15-20 on half load (it's very non-linear above half load due to the discharge curve of the sealed lead acid batterys they typically use)
90W is approx 1/6th of the rated capacity of that Maplin one (give or take power VA -> W conversions), so expect it to last a fair old time.
Gordon
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On Thu, 30 Oct 2003 13:28:22 +0000 (UTC), snipped-for-privacy@unicorn.drogon.net (Gordon Henderson) wrote:

In most cases this should work, but there may be some very cheap & nasty UPSs out there that won't like the somewhat inductive load presented by the pump.
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wrote:

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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indication of how long it can supply that power for. There should be another figure in the spec. that indicates how long it can supply that (or less) power for.
110Ahr indicates the capacity of the battery only if you know the voltage as well. Assuming a 12 volt battery that makes 110 x 12 watt hours, allowing for inefficiency and losses say something like 1kwh, i.e. 1000 watts for an hour.

as well.
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3000AV/2250W information. If I understand this correctly, they are both power ratings - the first being for capacitative loads and the second for resistive loads.
You need to find out how long it will provide power at 2250w. Then, roughly, if you are only using 200w it should last 11 times as long.
Roger
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