Feasibility of Battery Backup/Generator for Boiler/CH/Hot Water etc

molerat

It is pretty straight forward to replace the FCU with a twin single back box, single DP switched  socket, 20A flex outlet plate. 3 pin plug fused as FCU and a bit of flex.

grumbler

knightstyle said:

inverters £2k each. 

£2K inverter for a 50W motor!?

motorman99

Re using a car battery with an inverter….you’re converting 12v to 240v so that means a 1amp draw on the 240v side means a 20amp draw from the battery.
I guess 1amp is enough to run say the boiler plus a table lamp, maybe a small tv.
but a 20amp draw on a car battery will soon flatten it.

so is there any reason you wouldn’t be able to have the car running on tickover and let the alternator keep you going without flattening the battery?

Bendy_House

molerat said:

It is pretty straight forward to replace the FCU with a twin single back box, single DP switched  socket, 20A flex outlet plate. 3 pin plug fused as FCU and a bit of flex.

Why would you need all that? 

Surely just replace the FCU with a single socket with a DP switch. Boiler/CH cable terminated in a plug top. During power cut, unplug from socket, and plug into inverter.

Have I missed something?

Bendy_House

motorman99 said:

Re using a car battery with an inverter….you’re converting 12v to 240v so that means a 1amp draw on the 240v side means a 20amp draw from the battery.
I guess 1amp is enough to run say the boiler plus a table lamp, maybe a small tv.
but a 20amp draw on a car battery will soon flatten it.

so is there any reason you wouldn’t be able to have the car running on tickover and let the alternator keep you going without flattening the battery?

You'll find car batteries will have an Ahr ( ampere-hour) figure, probably around '100' or so. That's its capacity, and means - roughly - that it can deliver 100 amps for one hour. Or 50 amps for 2 hours. Or 20 amps for 5 hours - you get the idea.

If you have a couple of batteries to hand,  then one could theoretically be charged as you use your car, even via a cigarette socket, I think?, and them swapped. Or have it charged using a small portable generator. Using a battery and inverter would certainly give a clean supply, I think. But, using a small petrol generator directly might/should be fine too - I can't imagine that boilers/pumps are that sensitive?

FreeBear

Bendy_House said: But, using a small petrol generator directly might/should be fine too - I can't imagine that boilers/pumps are that sensitive?

The electronics in many boilers cab be sensitive to spikes & brownouts depending on how well they are designed. I'd be wary of using a cheap petrol generator. And if you have one of those fancy "smart" controls....

royalmike

From experience 40 years most gas boilers with electronics all of them these days wont work of generators you may even damage the pcb.
May work with a  ground spike but trial and error on that one.

Apodemus

My need is to power my Rayburn, so it is mainly old technology but comes with three motors to run - 1 for the boiler fan, 1 for the cooker fan & oil pump and 1 for CH circulation.  Adding in five solenoids and two igniters, it still works out at about 1 Amp draw.

My Grundfos CH circulation pump certainly recommends being on a clean supply and suggests that it might become noisy and wear out quickly on a partial sine wave.  From what I've seen the cost difference between a pure sine wave inverter and a cheap one is about the same as a Grundfos pump.  Since the pump is 23 years old, it owes me nothing but even so, I would rather ensure I have a pure sine wave so that I can use the inverter in other situations.

My car battery is 80Ah and being an AGM battery it can probably cope with a higher depth of discharge than a standard battery.  My old battery is running my pond pump, with a 30Amp solar charge controller set to 10.7 volt minimum remaining charge.  During winter the pond pump is off, so I could either move the charge controller over to the car/inverter set-up, or use the old battery on the inverter and recharge the old battery off the car, when needed.

 

Bendy_House

Sounds as tho' a battery-powered option might be best, then? This will seemingly require regular recharges.

Might not be ideal, but recharging using, say, a diesel vehicle on tick-over as mentioned before might be required if the outage is prolonged.

Keep an eye on local Fb Marketplace for good batteries? You might pick up a couple (or more) of near- new ones for ~£50 each? In parallel, they should also reduce the deep-cycle requirement.

How efficient are DC/AC inverters? Are more powerful ones more so than small ones? Best to have a 75W jobbie running flat out, or a larger one coping with ease?!

Apodemus

The inverter I am looking at is 600W and claims to be greater than 90% efficient.