I've just finished testing mine. I've installed a double pole changeover relay in the output from the FCU that feeds the central heating - the coil of that relay being energised by the mains. If the mains goes off, it connects to a 150 watt invertor I've just made - using a Vellerman kit as the basis. It runs off a car battery. It's been on since about 12 o'clock and the battery is still fine.
At the moment, it's not *totally* automatic, as the invertor has to be switched on even if left connected to the battery. I might add a second relay to switch it on when the mains dies, but that would only be strictly necessary if I wanted the heating to work if I was out when the power failed.
I'm happy to rely on torches and battery radios etc for the duration of the cut, as I have a gas hob for any essential cooking.
Google back. There was a fairly recent long thread on this subject. No firm answer as it depends on a particular installations supply type but basically:
You need a properly installed earth spike connected with suitably sized cable to:
a) The generators frame. b) One of the phases from the generator to create a local "neutral". c) The installations main earth terminal.
It is c) that causes the problems depending on how the "earth" for the main earth terminal is normally derived.
Huge - having a lead lying around under any circumstances with a 13 amp plug on either end is madness. Unless you keep it in a locked cupboard along with your shotgun, and treat it like that gun - never let it out of your sight.
It's neither particularly expensive or difficult to fit a suitable contractor that will isolate the incoming mains in event of a failure, and route a generator output to the house via that. Then you can use appropriate connectors of the right sex.
Bit expensive having a contractor lying around to do this job when you need him isn't it? ;)
PoP
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Once our factory in Switzerland ran out of BS1363 13A panel sockets and shipped a machine to the UK with a continental SHUKO type accessory outlet and included a SHUKO - IEC mains lead. Stupid electrician cut the IEC (female) socket off this lead and fitted a 13 amp (male) plug, so he had a lead with a SHUKO plug > 13A plug. He then proceaded to plug the SHUKO plug into the accessory outlet on the front of the machine and the 13 A plug into the mains and the whole thing worked except for obvious reasons the mains switch on the front of the machine was inoperative! The proper power inlet was an IEC chassis mounted plug at the rear of the machine.
He then phoned us to complain that the mains switch didn't work and the mains inlet connector was unsafe.. It took quite some time on the phone for it to dawn on me what he'd done.
Reminds me of a large notice seen on an Amstrad E-Mailer in a store this week.
"You have ABSOLUTELY NO CHANCE of getting this to work unless you read the instruction manual"
I'm late picking this thread up so if someone's already mentioned this forgive me... Tradex in Huddersfield had small gennies for sale last weekend for under £100 - thought about getting one for the garden shed 'cos the thought of digging out for the mains supply didn't appeal at all and I'd not be using it for anything big. Richard
I noticed on the Screwfix home page that they were doing a small genny too.
You'll have to bear in mind that these small generators provide typically about 600 watts of useful power. So with a couple of light bulbs and an average electric drill you are hitting the limits.
And an electric kettle to give a cuppa is out of the question.
I view my small genny as being able to power my CH system and not much else if the supply company hit difficulties - I'd have to jury-rig the genny into the CH system so this is very much on the "ideas" charter rather than a genny sitting waiting to power up. I'm old enough to remember the electricity strikes of the 70's, and I don't want to go thru that again if I can help it.
PoP
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I've just finished doing something similar to mine, although I've used a car battery and invertor as the standby source. But the method is similar from the safety point of view, and I'd be happy with comments from others on any improvements.
Like most systems, my CH is all fed via an FCU. After the FCU I've fitted a DPDT rocker switch marked normal and emergency. In the normal position, it simply routes the output of the FCU direct to the CH in the normal way. In emergency position, it routes the output of a mains coil relay - I've used a triple pole CO type with 10 amp contacts which is readily available from the likes of TLC or RS etc for about 20 quid including base. With mains still working the coil is energised and simply routes the mains through in the normal way. If the mains fails, the relay drops out and routes the output of my invertor -(or generator) to the CH spur. The reason for the relay is that the output lead from the generator or invertor has to be a plug, and this eliminates any chance of mains flowing back up the lead and making the plug live - or indeed damaging the standby source. The third pole on the relay is used to switch the invertor on. Note it actually just switches the electronics, not the battery feed, which would require a much larger relay due to the current involved. This extra pole could also be used to control the starter on a self start genny set.
I've mounted the rocker switch in a matching blank panel to the FCU, and incorporated the LEDs from the invertor which show working and low battery volts. The relay is fitted in a steel adaptable box behind it - I'm fortunate that the CH controls are mounted in the oven housing unit in the kitched so there's plenty of space behind. The invertor and battery simply sit in an adjacent kitchen unit - I don't intend it as a permanent installation.
On tests, I've had the system running for about 6 hours on a fully charged 50 Ah battery, and it showed no signs of failing. But of course it will depend on the weather and how hard the pump etc is running. A test with a 100 watt bulb showed a life of again about 6 hours before the battery died.
The next thing is whether to fit a battery charger to the system.
Might be a lot cheaper and easier to use a UPS rather than a genny. That way you've got battery backed up CH 24x7 and never need to worry about switching over.
Power the UPS from a 13A socket - and if the UPS battery gets a bit short then unplug and connect the UPS to the genny so that it has an incoming 240v supply from which to recharge - you can run the genny for a few hours to recharge the UPS, then off for another few hours, etc.
And if the leccy companies are still offline then there will be people on the streets.....and I predict it won't be David Bowie and Mick Jagger on behalf of charity collections.....
PoP
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The UPS is a good idea, although I would just stick it inline between the FCU/isolator and the wiring centre, not sure it would consider the genny feed as 'in-spec' power.
One point with the sort of UPS for PCs such as the APC ones, are they won't power something from cold. That is, if you've got one charged up but not plugged in, then just plug an item into one of the outlets you won't get any power provided. If it's receiving a mains input and you subsequently remove it, then the power is maintained at the outlets.
Dave - I was very interested in your solution. Does your inverter produce a sine wave or a square wave output? If the latter, do your boiler electronics seem happy with it? Have you done anything to eliminate spikes? How is the CH supply earthed when powered by the inverter?
If you have read my earlier posts (I started this thread!) you will know that I am planning something similar with a generator - but not with any sort of automatic changeover.
Until a couple of days ago, my CH was fed by a FCU in the airing cupboard. There was a very short T&E cable going from the FCU into a 10-way junction box, into which the boiler, 3-port valve, room stat and cylinder stat are all connected. The pump (although also in the airing cupboard) is connected directly to the boiler - and controlled by its over-run stat. This means that the boiler needs a live connection in addition to neutral, earth and switched live.
It was thus relatively trivial to change the wiring in such a way that the whole thing is now powered from the boiler end rather than the the airing cupboard end of the cable which joins the two. I have now done this, and the whole thing is now powered from a 13A plug adjacent to the boiler. The utility room also houses a couple of freezers - which I wish to power in the event of a prolonged power cut.
The idea is that, when the power fails, I can put the generator in a suitable location (maybe in the conservatory - not sure yet) with a 4 or 6 way extension lead into which I can plug the heating, freezers plus some lighting. As stated earlier, I am looking at the Honda eu10i and eu20i generators as possible contenders. The smaller one (900 watts) appears adequate *unless* SWMBO decides she needs to use the microwave - in which case we shall need the 1600 watt model. Even so, forget electric kettles!
FWIW, I've just invested £20 in a plug-in volt/amp/watt meter from Machine Mart - which is proving useful in determining the consumption of various appliances. However, I suspect it doesn't show peak loads on switch-on. The
2 freezers take about 250watts each (only when their compressors are running, of course) and the heating takes a max of less than 150 watts - so with 900 watts I would still have some leaway for lighting. [Interestingly, the 3-port valve consumes about 7 watts even when nothing is running].
The things which I still need to bottom out are earthing and spike protection.
Clearly, when I unplug appliances from the mains, they are no longer earthed through the mains - even if the electricity board's earth remains intact during a power cut. The central heating pipes are sort-of earthed, by being bonded to a steel gas pipe which disappears underground. What else do I need to do? For example, do I need to connect the generator's earth to a spike in the ground? What about the generator's neutral (it's single phase, of course!) - does that need tying down, and if so, to what?
The generators in question both essentially generate DC and use inverter technology to produce AC. [I presume this is easier than generating AC since it doesn't require accurate speed control]. I have a concern - don't know whether it's real or not - that when, for example, a freezer turns on or off there could be spikes on the AC output and that these might be detrimental to the components on the boiler PCB [MkI Baxi Solo 70/4PF]. Does anyone have any comments about this, and any suggestions on what to do. For example, you can buy extension leads for computer use with built-in spike suppression. Would one of these help?
But Dave's already got the guts of a UPS, in the form of his inverter and car battery. An off-the-shelf cheapie UPS won't have the runtime he's getting - lots more stored energy in a 50AH car battery such as the man says he's already using, than the smaller lead-acids which come with your UPS. Admittedly, the ones in a UPS ought to be rated for deep discharge, which a car battery isn't: but even living where he does, Dave's not likely to run his battery flat all that often.
Course, for "the rest of us", an inline UPS could be a good idea, as it already has much of the safety-relevant considerations applied (for completeness giving it an independent earth might be desirable).
Actually, at least some of the APC ones - the "SmartUPS" range for one - does indeed have this capability, which their marketroids imaginitively call "cold start". Could be that their entry-level "BackUPS" range doesn't.
Exactly. And it was the (not so) Smart-UPS about to cause trouble in a call centre with an almost expired call processor a couple of years back. Looks like the budget Back-UPS CS (Hmm wonder what those initials stand for) would work from cold.
Thanks Stefek for the cold start keyword, knew there was some featurette. Just what sort of power would be need to keep the CH going for a couple of hours? I would assume it's less than 100w flat out.
Just what sort of power would be need to keep the CH
Measurements on my system suggest about 120 watts - pump 70, boiler 40 and
3-port valve actuator 10. With a 100% efficient inverter, you'd need 10 amps at 12v to support this. A (say) 70 amp-hour leisure battery should keep you going for (maybe) 5 hours continuous. In reality, the boiler and pump will keep going on and off on their stats - so the battery will last longer than this.
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