condensing oil boiler in power outage

einhorn

power outages i guess are here to stay and possibly get worse. so our nice shiny oil condensing boiler is just junk as is the 5000L oil tank without electricity. so what to do as backup during an outage. thinking of PV and batteries. any thoughts, advice please. cheers

QrizB

PV and batteries are good if you're investing £10k for a decade or more.

If you want something cheap and cheerful, consider a £200 petrol generator and a jerry can. Or a £600 diesel generator and you can (probably) run it on your heating oil too.

Practice before you need it and try not to kill yourself with carbon monoxide or stray electricity.

tacpot12

You need to look carefully and what electrical power you need to run the heating system. It is likely to be very little. A small UPS would cover it. The larger cost would be to install the UPS. 

Just be aware that electronic ignition systems can draw a lot more power than they say they need, albeit briefly. 

QrizB

tacpot12 said:

You need to look carefully and what electrical power you need to run the heating system. It is likely to be very little. A small UPS would cover it. The larger cost would be to install the UPS.

Most UPSes are designed to run for a few minutes to let you gracefully shut things down and/or start up your backup generator.

The circulating pump is likely to be 60-80 watts. Let's say 100 watts for the whole system.

And let's also say you want to be able to run it for six hours.

• A small UPS like this will provide 100 watts for 25 minutes.
• A bigger one like this will stretch that to 1 hr 8 mins.
• To get to six hours you'd need one of these plus an extra battery pack. That's almost £1600 worth.

lohr500

I would second QrizB's suggestion. A cheap 1kW inverter petrol generator would probably suffice if all you want to do is run the boiler and circulation pump.

When we had our boiler replaced a year ago, despite the recommended fused spur fixed wiring setup, I asked that the boiler controller/ circulation pump power supply be wired back to a 13 amp standard plug. This gives me the flexibility to power up the boiler from an extension cable plugged into my small 900 watt generator. I know it isn't best practice, but the old boiler was powered from the same 13 amp plug and socket for 30 years with no drama.

It saves messing around with mains isolation switches and the risk of overloading the generator by feeding the genny output to the main distribution panel. 

I haven't tested the new boiler with the generator, but the setup worked fine several years ago with the old boiler when we lost power for nearly a day in freezing cold weather.

Unless the power is off for many hours, things like fridges and freezers should be OK if you leave the doors closed. I fancy a 2kW generator would have enough umphh to keep the heating running and a fridge and freezer if needed. 

 

Gerry1

I'm not convinced it needs a UPS, that seems overkill.  Assuming you're in residence at the time and don't mind manually switching over from the mains supply when the lights go out, a humble inverter might well do the job.  For a relatively short time you might even get away by using your car as the battery supply, otherwise you'd need a car battery or two in the house and a charger.

You might even get away with an old car battery (or two) that you'd replaced: one that can't supply a few hundred amps to turn the starter motor when it's freezing may well be happy to supply ten amps in a warm kitchen.

Some inverters produce a square wave output rather than a sine wave, so it would be wise to consult the boiler manufacturer and the inverter supplier to see whether the combination is likely to work.  However, it could work out considerably cheaper.

https://www.ebay.co.uk/itm/322269782283

https://mygaragedirect.com/products/mgd5-pure-sine-wave-power-inverter?variant=40235565908148

Reed_Richards

Maybe a Micro Combined Heat and Power boiler is the answer?

matelodave

Reed_Richards said:

Maybe a Micro Combined Heat and Power boiler is the answer?

Are they self sustaining insofar as the the heating generates the leccy to keep the heating going or do they need to be externally powered, so the heating part operates to generate leccy.?

I'd have thought that the easiest answer for the OP is a small inverter generator of about 800-100watts.

Even Gerry's idea of an inverter and car battery may not work as pumps and stuff can be pretty brutal when starting up, taking between three and five times their running current so you need sufficient capacity to cope with it. Dont forget the fan if there's one and the igniter which can impose high currents when firing up an oil boiler. Big spikes from pump starting may also damage the electronics if there's insufficient capacity in the power supply.

I previously had some experience of running pumps from generators and managed to destroy two pumps and a generator before understanding what was going on (admittedly the pumps and generator were a bit bigger but we found that the generator had to be capable of delivering at least 3x the running current to avoid burning out the pumps or overloading and stalling the generators)

this is from Wikipedia 

When an electric motor, AC or DC, is first energized, the rotor is not moving, and a current equivalent to the stalled current will flow, reducing as the motor picks up speed and develops a back EMF to oppose the supply. AC induction motors behave as transformers with a shorted secondary until the rotor begins to move, while brushed motors present essentially the winding resistance. The duration of the starting transient is less if the mechanical load on the motor is relieved until it has picked up speed

FreeBear

matelodave said: Even Gerry's idea of an inverter and car battery may not work as pumps and stuff can be pretty brutal when starting up, taking between three and five times their running current

Car batteries are designed to provide high currents for short periods of times (think, cranking over an engine to get it started). They don't last so long when used to provide constant low(ish) power over an extended period.

For electric motors, you can get soft-start gizmos which reduce the start up load - Well worth fitting if you have big motors.

Rodders53

My Grant oil boiler has a Riello oil pump - start current 5A 240V, running current 0.85A, Igniter is 8kV 16mA.  Total absorbed power 115/125/160W depending on exact burner model.

CH circulating pumps in the boler case are similarly rated 5A inrush and about 90W running at max speed may be lower if slower.
I have just replaced my UFH circulating pump with a Wilo max 33 W one (old one was 90W) and it runs at about 28W it's display claims.

Honeywell 22mm 2-port zone valve(s) will consume 6W each. Mains thermostat / controllers will also use a few watts, I guess? I'll use 4W.

So I make the demand of an oil boiler to be  something in the order of 125 + 90 + 6 + 4 = 225 W with an inrush of 5A twice in fairly short succession (circulating pump followed by oil pump/igniter) with the latter repeating regularly.

Or something thereabouts.

matelodave

Its the inrush current that stops the motor from starting properly or that damages inverters and stalls generators if they cant deliver it, not the running current. So although a battery may be able to handle the current the inverter may not be able to deliver it when its needed during starting.

Microwave ovens are the same, a big inrush current with a much lower running current. Inverter controlled microwaves are a lot better at reducing the inrush than a basic microwave which just pulses the magnetron to control it's power.

Not saying it cant be done but you need to ensure that you specify everything properly to avoid causing some expensive damage.

Interestingly I was looking at a couple of central heating pump specs (Wilo) and those with electronic controls demand a sine wave input rather than the stepped square wave that you usually get from a cheap inverter so it's worth checking whether the  fan, pump and boiler controls can cope with a non-sine wave input.