On Fri, 27 Nov 2020 18:00:48 +0000 (UTC), Peter Burke
wrote:

Caecilius wrote in
:


My plan is to put this temperature controller between the timeclock
and the heater, and set the heater thermostat to something like 25C as
a fail-safe.

Has anyone found or built something like this? I'm sure I can't be
the only person who want a constant overnight bedroom temperature
without running the main house heating.

In a similar application I found my 2kw convectors had 2 paralleled
elements and disconnected one to make them 1kW only and less agressive in
their heat output.

You're the second person who's mentioned de-rating a 2KW heater. I
initially thought this was pointless, but perhaps it would help reduce
overshoot.

I certainly don't need anywhere near 2KW as the duty cycle is below
10%.

For control, honeywell have been forcing P+I control and multiple switching
cycles per hour on us in their room stats for years (wearing out over
cycled zone controls in the process).

I assume P+I is like a PID controller without the derivative term?
What's "multiple switching cycles per hour" mean? The DT90E datasheet
shows a "Cycle rate" parameter with a default of 6 and possible values
of 3,6,9 or 12 so presumably that's cycles per hour, but the datasheet
doesn't explain what that really means.

Their programmable stats (eliminating the time switch) are a bit overpriced
but this one has all the P+I, default 6 cycles per hour (programmable up to
12 if desired) and is 8A rated (selectable prog option) so will direct
switch. The mag assisted batt powered internal relay should be quiet
enough.

36.50 is not that bad, but I note this comment on the screwfix site:

"I have marked it down on performance as the "click" when it turns on
and off can be heard all over the house"

So maybe not that quiet.


https://www.screwfix.com/p/honeywell-home-dt90e/41365

Instructions downloadable from the spec tab of that page for a preview.

Could save a bit of faff in rolling your own.