In an earlier contribution to this discussion,
Dave Plowman wrote:


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.


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?

TIA.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is Black Hole!