Room thermostat with 'heater'

[88v8]

Not sure if this should be in the Electricals board, anyway...

So, being a fan of electrical antiquities, two years ago I installed this NOS Ekco room stat to run a 1kw kick heater.
Probably 1960s.
Used it with a clockwork Horstmann time switch.

The wiring options for the stat were with and without internal heater, and as the load is below 8A, I chose with.

In operation, it cycles a lot. Switches off for a few moments then back on. Sparking across the points. Does that several times before it decides that it's done and really switches off.

Would it be less sensitive if I didn't use the internal heater?

 

[stem]

Probably it would be less sensitive. When the thermostat is 'on' the little heater (aka an accelerator) also comes 'on' to warm the thermostat slightly. This switches it off earlier to improve its operating accuracy due to the inaccuracies of a mechanical mechanism.

With higher loads some natural heating occurs due to the higher current flowing through it so using the heater as well can make it switch off too early. A 1kw heater is approximately 5A so will probably provide some additional warming. There wouldn't be a problem if you wanted to try it without the accelerator in circuit.

The arching you refer to is because the mechanical parts of the thermostat are worn, either the mechanism is not 'snapping' open fast enough or the contacts are pitted. Nothing to do with the use of its internal heater.

 

[88v8]

OK, thanks, I'll try that.
There should be no wear in the stat as it was new, but perhaps it needs some lubrication. I'll take it off and have a look.
Yesterday I bought an even older one on eBay so I have that as a reserve....

 

[stem]

Ah OK, I've not come across a recent thermostat made by EKCO so I'd assumed that the thermostat was as old as the heater and the mechanism had deteriorated and weakened with age. If it's new then it shouldn't be doing that is it still under warrantee?

It shouldn't be arching, provided that the contacts are suitably rated for the appliance. I'm not familiar with the the old heater, so I assume back then it would have just a resistive load and not inductive load, because sometimes contacts are de-rated for inductive loads.

 

[88v8]

The kickspace heater is a Myson KSU500E, with fan of course, 2kw but I disabled the second element and run it at 1kw because the time switch is not rated for 2kw.

The stat was NOS, so new but not as we know it. I guess 60s from the design.
It might be faulty of course. Sometimes stuff is NOS because it came back faulty and sat on the shelf.
Anyway, I'll try it without the internal heater and let you know.

 

[stem]

Just had to Google NOS

To me it meant either an abbreviation of the word Numbers, or Network Operating System. However, I'm guessing you're using it to mean 'New Old Stock' (and not Nitrous Oxide ) So, if the thermostat is old but has never been used, you may find that it will improve with use...... Or maybe, because of its age the spring that snaps the contact open has lost its zeal, in which case it won't.

 

[Harry Bloomfield]

Would it be less sensitive if I didn't use the internal heater?

Yes. The idea of the heater is to get the stat to react a little faster than it normally would, and switch off sooner than it would without. Idea was to reduce the mechanical hysteresis. Without the heater, it would rely entirely on ambient air temperature to switch it.

With the heater, it will hold the ambient temperature more closely to the set temperature, without the wild swings.