Battery back up - central heating

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Jude
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Battery back up - central heating

Postby Jude » Fri Nov 21, 2008 3:19 pm

We have a central heating system run by wood with a battery back up in the case of power failure.

Can any one tell me how long this will last if the electricity is off (looks like a normal size car battery to me) but I am no expert. Also ours have started to make a high pitched noise rather than a hum when the power has been off the last couple of times - does this mean that they need replacing.

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Postby Slaphead » Fri Nov 21, 2008 4:32 pm

Jude, to answer that you need to know a few other things.
What is the pump power in watts?
What is the capacity of the battery? (Ampere hours)
How much power does your invertor use to run itself?

The whine you speak of is probably the unit itself converting the battery output, 12Volt DC to the pump input voltage, 220/230/240 Volt AC.
Best suggestion i can give is ask the installer.

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xt600
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Postby xt600 » Fri Nov 21, 2008 5:16 pm

It's hard to calculate unless you know the exact efficiency of the UPS.

So, the only way to know for sure is to switch off the power to the UPS and time how long the central heating pump continues doing it's job before the battery runs out. As the battery runs out, most UPS's will give off a warning tone letting you know that it's about to run out. At this point, restore the power to it. Allow at least 8 hours for your battery to fully recharge and repeat the operation....this should give you a good indication in answer to your question...
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Postby croxleydog » Fri Nov 21, 2008 6:18 pm

Hey Jude,
Sorry about the Beatles thing, but to get to the nitty gritty, a 65 amp hour deep charge or leasure battery should give you at least 12 hours of back-up. The sound you hear will be the inverter cutting in. You may have a very posh job with cooling fan, but its nothing to worry about. When the system is working off the mains a cheap volt meter connected across the battery terminals should give a reading of between 12 1/2 and 14 volts. Dont worry, you will not get a shock from this. We run 5 radiators and underfloor heating to two bathrooms a hallway and a very big lounge and ours is good for at least 20 hours. All you need to worry about is the battery being recharged. See above re voltage. Most good UPS work at the astounding 85% efficiency, but without knowing what system you have I cant tell. Your manual should advise this.
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Postby Jude » Fri Nov 21, 2008 6:37 pm

Thank you for all your replys (no problem with the Beatles thing used to it) - best go and do some research - problem - no manual and ne dobre installer - remember somewhere being told we had 20 mins - :? this was way after we had had the system installed - hey ho 8O

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Postby xt600 » Fri Nov 21, 2008 6:44 pm

Jude, there's not much point trying to do the calculations because for them to be accurate the battery would have to be in tip top condition at a given temperature,, the load on the pump would have to be determined accurately...most pumps have 3 different settings...and if you have diverter valves in the system too these will also drain some power.
The only way is to switch power off and time it.... Simple as that!

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Postby croxleydog » Fri Nov 21, 2008 6:52 pm

Hi Jude,
sorry about the beatles thing. We do get to be a bit sad with our humour after quite a few years here. If you have a seperate car type bettery you should get plenty of time with it. My computer UPS gives me at least 1/2 hour back-up covering screen, printer,external drives and of course the computer and has a tiny internal battery. It is a KEBO UPS-500M, so your car type battery should be good for a lot longer. I take it you live here and do a regular run of the pump, which will keep it well charged, and is also a good idea to keep the pipeworks clear. I give a run up every month for about an hour. After 3 years, no problems.
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Postby seathrift » Fri Nov 21, 2008 7:12 pm

The only thing that matters is that the voltage of the battery should not be allowed to go below 50% of fully charged. Temperature will affect the battery's capacity quite markedly and for best results the battery temp should be 25 degrees centigrade. To the best of my recollection which is getting very poor these days the 50% voltage of a 12v battery is 12.5v. It can also be checked, if you have a refillable battery using a hygrometer, but a voltmeter is a lot quicker and simpler. You should be able to get the battery voltage curve off the internet for your make of battery.

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Postby neilmay » Fri Nov 21, 2008 9:26 pm

We have central heating system run by wood with a battery back up.
The back up last for about 2 hours.
Time to let your fire die down.
Ours is 2 years old and working fine.
To check your battery , run your system on battery backup for an hour and a half, recharge for 12 hours and then run again for an hour and a half.
This will test to see if your battery is OK or needs replacing.
Used to be in electronic test before retiring here.
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Postby hopkin » Fri Nov 21, 2008 9:37 pm

The pump should have the power consumption marked on it either in watts or amps (1amp = 220watts @ 220volts) If you read or calculate the wattage of the pump divide it by twelve it will give you the amps required at 12volts(battery voltage) as batteries are normally marketed in amphoures it is easy, perhaps using a calculator, to work out the time available. The purists will point out that there will be power loss through heat and resistance but it is a good rule of thumb. Having said that xt600 has posted the best practical solution.


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