Storms, powercuts and central heating

[reb78]

The weather forecast has got me thinking about power cuts.

My central heating is powered by my solid fuel Rayburn, which heats a thermal store and when the store gets to a set temperature a thermostat triggers two 60W Grundfos circulation pumps.

In a power cut, the pumps obviously won't work and the store will get hot. It could boil but that's not a huge issue as it is a vented system so will 'just' overflow into the header tank.

But @dobbslc and his coffee machine inverter thread got me thinking....

I have loads of 12v car batteries here. 120W isn't that much really. How long would a typical 110Ah lead acid battery run my pumps via an inverter? They aren't on constantly either unless I really have the Rayburn raging so once they've dissipated the heat and cooled that section of the tank they are off again until it reheats.

What size/type of inverter would be needed?

As powercuts arent common bit are a pain when they occur I'd keep it xheap and simple and set it all up as a manual changeover thing so just put a plug and socket on the pump wiring and more the plug to the inverter if there was a power cut.

 

[qwakers]

the maths is simple. 1 amp 110 hours. 110 amps 1 hour. anything in between is easy to figure. 120w is about 1/2 amp. so 220hrs / 24. about 9 days. halve that for inefficiencies and round it down 4 days.

 

[voipio]

For a 120W pump, expect about 5 hours worth of pump run time from a healthy, fully charged 110Ah 12V battery, based on a 50% discharge cutoff point. A true sinewave inverter (not a pseudo sinewave) would be best for running these pumps. An inverter running a 120W pump will be drawing in excess of 11A from the battery.

 

[addjunkie]

The weather forecast has got me thinking about power cuts.

My central heating is powered by my solid fuel Rayburn, which heats a thermal store and when the store gets to a set temperature a thermostat triggers two 60W Grundfos circulation pumps.

In a power cut, the pumps obviously won't work and the store will get hot. It could boil but that's not a huge issue as it is a vented system so will 'just' overflow into the header tank.

But @dobbslc and his coffee machine inverter thread got me thinking....

I have loads of 12v car batteries here. 120W isn't that much really. How long would a typical 110Ah lead acid battery run my pumps via an inverter? They aren't on constantly either unless I really have the Rayburn raging so once they've dissipated the heat and cooled that section of the tank they are off again until it reheats.

What size/type of inverter would be needed?

As powercuts arent common bit are a pain when they occur I'd keep it xheap and simple and set it all up as a manual changeover thing so just put a plug and socket on the pump wiring and more the plug to the inverter if there was a power cut.

Generator, change over switch, have heating, lights, tv, etc

 

[reb78]

the maths is simple. 1 amp 110 hours. 110 amps 1 hour. anything in between is easy to figure. 120w is about 1/2 amp. so 220hrs / 24. about 9 days. halve that for inefficiencies and round it down 4 days.

Blimey. That's a decent run time. It'd be unusual to be without power for more than a day here. I usually have four charged batteries in the shed so could run the pumps for weeks with those!

It wouldn't need a particularly large or expensive inverter either would it?

 

[reb78]

Generator, change over switch, have heating, lights, tv, etc

Yeah but I have batteries and wanted cheap and cheerful for now. I quite like candles and no tv.

One day a generator maybe but don't really need one for the odd powercut.

 

[qwakers]

nope. a 300w one would do fine. or go decently large and run the kettle occasionally too. just bear in mind the bigger the inverter the less efficient it will be running a small load.

the biggest issues is what current the inverter draws on its own. you'd need a clamp meter on the dc side to see what the true draw is and do the maths from there.

 

[reb78]

nope. a 300w one would do fine. or go decently large and run the kettle occasionally too. just bear in mind the bigger the inverter the less efficient it will be running a small load.

Dont need a kettle - the Rayburns on!

 

[sako243]

In slow time it may be worth getting an electrician to wire in a generator change over switch. We've got one in our house basically

Grid -> meter -> Isolator -> change over switch.

When we have a big power cut just flick the switch and fire up the genny. If we cant be bothered with the big genny we just turn off things at the consumer unit to kill the workshops, etc., and just leave lights and central heating on.

A 4kW gennie actually powers most of the house if we don't use the high power loads and we've always got gas and the Aga to boil water.

 

[Fintray]

the maths is simple. 1 amp 110 hours. 110 amps 1 hour. anything in between is easy to figure. 120w is about 1/2 amp. so 220hrs / 24. about 9 days. halve that for inefficiencies and round it down 4 days.

120W is 10A, so much closer to Voipio's suggested run time.

 

[reb78]

In slow time it may be worth getting an electrician to wire in a generator change over switch. We've got one in our house basically

Grid -> meter -> Isolator -> change over switch.

When we have a big power cut just flick the switch and fire up the genny. If we cant be bothered with the big genny we just turn off things at the consumer unit to kill the workshops, etc., and just leave lights and central heating on.

A 4kW gennie actually powers most of the house if we don't use the high power loads and we've always got gas and the Aga to boil water.

In time, yes, but this will be something that gets kicked down the road for years knowing me. If I just have to buy an inverter and change some wiring on the circulation pumps this will happen a lot quicker and keep the house warm in thr event of a power cut which is my main aim currently.

 

[sako243]

the maths is simple. 1 amp 110 hours. 110 amps 1 hour. anything in between is easy to figure. 120w is about 1/2 amp. so 220hrs / 24. about 9 days. halve that for inefficiencies and round it down 4 days.

120W is 10A at 12V, 0.5A at 240V...

You forgot the change of voltage....

 

[qwakers]

howd you get to that?

 

[sako243]

In time, yes, but this will be something that gets kicked down the road for years knowing me. If I just have to buy an inverter and change some wiring on the circulation pumps this will happen a lot quicker and keep the house warm in thr event of a power cut which is my main aim currently.

Honestly I kicked it down the road (putting a plug onto the switch) and then did it in the middle of a storm. Now I just pull the generator out of the workshop into the outside bog (used to be a generator shed), plug it in and fire it up.

 

[qwakers]

correction, i was working it out on the ac side, of course it really matters where it draws on the battery, so 10a is correct.

 

[sako243]

howd you get to that?

View attachment 525974

120W is power. Power = Voltage x Current.

Ergo Current = Power / Voltage = 120W/12V = 10A

 

[reb78]

Thanks folks. Even with the 10A amd 5 hours run time this is a simple solution.

 

[Fintray]

We had a power cut with storm Arwen, 4 days without power is no fun especially as I had a 10.5kW lister generator installed in the garage but had never got round to fitting the exhaust or even starting it in the 20 or so years that I had it!
Needless to say the exhaust was fitted and the generator tested pretty damn quick after that, when we had another 2 day power cut sometime later it was a relief just to switch on the generator and life could go on as normal.

 

[reb78]

Honestly I kicked it down the road (putting a plug onto the switch) and then did it in the middle of a storm. Now I just pull the generator out of the workshop into the outside bog (used to be a generator shed), plug it in and fire it up.

Yeah, but I have other things to spend my money on at the minute Ed. I have the added complexity that if I want to power the holiday cottages they are all on different phases of my 3P supply so suspect that makes it more complex.

This thread was really - how do I simply and cheaply stop my thermal store boiling over in the event of a powercut as that stresses me a lot more than no lights or TV!

 

[sako243]

This thread was really - how do I simply and cheaply stop my thermal store boiling over in the event of a powercut as that stresses me a lot more than no lights or TV!

Until the kids are older and in school and all they want is to sit infront of a screen like vegetables