On Tue, 29 Nov 2005 10:54:31 +0200, Nicolas Boretos
wrote:


I live off-grid, and my main problem is that the leadscrew drive system
has a gearbox, and sucks down ~ 20 amps (@12v) off my battery bank, with
no load, and with the simple on-off control, the leadscrew (burner) is
mostly on. The thermostat has only a few degress hysterises, so the
boiler comes back on ~42 degrees...

What I'd like to do is have the burner "sleep", and come back on when
water in the return line reaches ~ 25 degrees instead. This is not
considering lags, etc...

Anyone have any ideas on doing this in an easy way, outside of using an
programmable boiler controller..dont need the expense, nor the hassle. I
wonder if they make thermostats with adjustable hysterises-differential?

One not so smart option is to use a programmable timer here, the octal
plug type, that has adjustable TIMEon, TIMEoff, but this does not take
into consideration temperature, the thermostat is simply wired in series
with it and the motor/blower...


You could do this using two thermostats and a relay.

Use one thermostat set to the low temperature to energise the relay.
Use the pair of contacts on the thermostat which close below the set
temperature to do this.

A spare pair of relay contacts is connected to latch the relay on.
THe second thermostat is wired in series with the latching contacts
and using the thermostat contacts which open above the set point.

You don't say what type of thermostat is needed for this. Does it
need to be submersible or in contact with a surface?

An electronic temperature controller and probe is not going to be that
expensive (about €70) e.g. rswww.com part no. 250-0079



--

..andy