Diversion Load for wind generator [RE-wrenches]

[Charlie Robb, Element Engineering]

By coincidence, I've just done a water heating diversion load for a customer
with an AIR403. He wanted to use the excess power instead of having the AIR
dump it in rage mode.

After a little searching I discovered that I could get immersion elements
made as specials with any rating/voltage (ie resistance) that I wanted, and
a wide choice of fittings and lengths and complete with a thermostat sleeve.
I went for a 300W 24V with standard 2.1/4 inch fitting. It wasn't much more
expensive than a standard a.c. element. We left his a.c. element in place
and added the new one using an Essex flange.

Because the immersion tank is in the house, some distance away from the AIR
and (NiCad) battery, I chose to make a controller which would do sustained
(several minute) dumps to keep the battery voltage down, rather than using a
high speed switching divert controller which might not work so well at the
end of a long wire run with other loads on it. Perhaps not so appropriate
for Lead Acid systems. I used a voltage sensing relay, a delay-off relay and
a 20A power relay for the load. The immersion thermostat is part of the
circuit, to cut the supply to the relay if the tank gets too hot. (Another
system I work on uses a 100kW dump load which is designed to boil! Sounds
like thunder when the wind gets up)

The voltage sensing relay is set to cut in at 1.5V per cell (19 cells) and
the AIR is set a little higher so that it doesn't interfere but acts as
backup if the tank overheats or he blows a main load fuse or whatever.

So far there hasn't been enough wind to make it dump. I'll give you a
performance report in the autumn if you like....

Hope this is some help
Charlie

Charlie Robb
Element Engineering

77 Society Road
South Queensferry
Edinburgh
EH30 9XP      UK

Tel: 0131 331 5835
Fax: 0131 331 5848
Mobile: 07887 991866

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