Load of pump and boiler say 100 W, at 80 % invertor effciency 125 W from the battery at 12 V is about 10 A. 50 AHr battery might sustain that for four hours. It's a reasonable draw and the heavier the draw the less of the rated capacity you get.
But even a brand spanking new (bog standard not one the fancy modern things) car battery would proabably only do it a few times and old one maybe only once. Car batteries really do not like being deep discharged. That's why you can get leisure batteries that are designed for deep discharge,
those figures apply if teh CH is running flat out all the time. If it runs 25% of the time you can quadruple that. Maximise run time by turning the primary circuit temp up high.
Still only going "to run an oil fired CH system" for four hours. If it ain't on, it ain't running. B-) With the battery being given a bit of rest you may get closer to the rated battery capacity.
How ever I assumed a gas boiler for my 100W not an oil fired one, I think 150W for an oil boiler and circulator would be closer. So 190 W or 15 A from the battery or 3 hours ish.
So, probably not worth the effort. We could live without the heating, although washing may be a bit uncomfortable! As we're talking about something that may not happen, I'll accept the risk. I have just spent a tenner on a Calor lantern, though.
You can work it out. Once you have a plug and socket, run the boiler through a plug-in power meter - for running from an inverter or generator, you want to take the VA rating, not the power rating.
The Potterton Profile is 158VA when firing, dropping to 100VA with just the pump running. If we assume 80% efficiency of the inverter, the power draw from the battery will be 25% higher, which is 200W, or 16A. A Morris minor probably has a 40AH battery, so that would be 2.5 hours. In practice, you don't want to run a car battery flat as that knackers it, so 1.5-2 hours max.
However, I wouldn't try to run a boiler normally from a battery. The boiler doesn't use any more electricity when running the heating at low or high flow temperature, but the heating output is higher at high flow temperature, so crank the flow temperature up high. That way, you get more heating power for same electrical consumption. Also, I wouldn't bother running the pump when the boiler isn't firing (although don't cut out the pump run-on). If you combine these two, set the flow temp to max, and when the boiler burner cuts out due to reaching that temperature, kill the demand for heat (turn the room stat right down) so the heating stops running (after any run-on timer), your electrical power consumption should be as low as possible for heat output. When the radiators cool down, repeat the sequence, and the battery will last longest.
If we start getting regular power cuts, I might program this into my home automation. So far, I've only had to do it once.
I said pull start and I mean pull start as in bit of string, T handle and rachet attachment to engine.
Essential there is no way to pull this a diesel through compression at anything like fast enough to cause it to fire.
Hand crank with a valve lifter that latches open until you trip it closed I think I'd agree. Easier to get the engine spinning on the flywheel the trip the valve lifter.
The valve lifter on this one does latch but automatically trips as the engine rotates. To get enough spin into the engine requires repeated and fast pulls of the cord whilst holding the valve lifter open(*). Considerably harder work that the 4 stroke petrol mower or even the two stroke strimmer.
(*) I guess there maybe a method to start on a single pull but I haven't found it yet. Perhaps pull it to compression, open the valve lifter and then pull as hard and as fast as you can. Electric start is much easier if the battery isn't flat. B-)
Didn't you say you had a camping hob of some sort? Hot water doesn't have to come out of the tap marked "HOT". B-)
A battery and invertor solution isn't very viable but a "little stinky" 750 W two stroke petrol genset might be worth it to keep fridges/freezers cold and the heating system running but probably only one thingat a time. May also have other uses besides back up.
You won't be disappointed don't forget to get a few cyclinders. B-)
We now have LPG hob so hot water is not a problem. Just not as convenient as jumping in the shower.
Indeed. I'll grab one if ever available as a 'bargain'.
We already have a matching single burner camping stove - I was careful to choose a lantern that uses the same cylinders, so only one set of spares required :-)
Andrew, thanks for the explanation. As said to Dave, a cheap and cheerful generator may be the answer, if I happen to find a cheapie. Not worth investing in a big, new genset that may never be used. That could all change, I suppose, if we return to the early 70s with rolling blackouts.
Have not looked at home automation, as the house is very rarely empty.
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