On Mon, 13 Nov 2017 05:06:37 -0800 (PST), whisky-dave
wrote:

On Friday, 10 November 2017 19:55:35 UTC, T i m wrote:
On Fri, 10 Nov 2017 04:31:50 -0800 (PST), whisky-dave
wrote:

snip

Sounds like it's the upper limit stat that is cutting in and out on
the bigger element (only) ... before the main stat cuts everything
out? Do you have a IR thermometer? If so it might be interesting to
see what surface temperatures these clicks and measurements apply to.

We do have an IR thermo... good idea, providing I can find it.

;-)

What temperature would you expect say the half way up the fin should be.
I know it's to hot to hold on to as I tried.

I can't say for your rad but when I was experimenting with mine I
think it was pretty high ... as I think the thermal trip was set at
110 DegC or summat (but that may be wrong).

It seems to trip out at about 98C (halfway up the last fin)
so drops to 700W at that point.

Right, it sounds to me like there is a 100 DegC upper limit stat and
only the heavy heater element is going though it.


So, if you hear something click and the wattage from 2000 to 700, but
turning the main stat down sees the current drop to zero, the thought
is that the upper limit stat is cutting the power to the main element
(because the rad is overheating itself) before the main (room-ish)
temp stat is cutting the power to it all?

That seems to be what is happening.

Ok.


So, with the IR thermometer looking say midway up the rad, and you
monitoring the power drawn, see if you can work out a pattern between
the clicks, lights and temperature.

Seems to drop to about 76C then then the full power comes on 1725W.

Yup, sounds about the right hysteresis range for a thermal limit
switch.


I believe on 2000W and the main (room-ish) stat on max, the rad is
unable to dissipate enough heat to stop it 'overheating' and therefore
it's modulating the power on the 'overtemp stat'.

Seems likes what's happening, but if I were designing a cut-out to stop over heating I'd get the whole thing to switch off to 0W as a safety feature.

Quite.

I thought that's what all cut-outs did.

You would think ... however, it may be that the actual switch they use
can't handle the extra 700W or it was considered that the 700W element
couldn't get the rad into an overtemp condition or it was just badly
designed or incorrectly wired.



If you turn the stat down to just above the current temperature, you
may find that (the main stat) will cut out (0W) before the overtemp
stat (leaving 700W).


If they are keeping them I'd be inclined to open one up and make a
wiring diagram (or see if there is one in there or in the manual).

The manual is on line and has the same details as the one supplied in the box.

Ok.

When you say 'they' it is the estates department I doubt they'd like me taking their new stuff apart and I don't particually want to.

When you say 'apart' you just mean the plastic end cover off. ;-)

What plastic end cover ?

Normally the controls / wiring are in a plastic cover of some sort (so
you don't burn yourself when touching it and it's cheaper to make
etc).


I have an oil filled radiator at home that works as I'd expect it to, but then that one was over £100 rather than £35.

Shouldn't make any difference what it cost to how it works.

I think it does as it does with almost anything else and my home one is 2.5KW.

I'm saying 'it shouldn't'. It may be that this entire batch of heaters
have been designed badly or wired incorrectly ... or that there is a
second upper-limit stat (or more likely a thermal fuse) that would
ultimately protect the rad from a real overtemp situation (like if you
covered it in towels, even when only on the 700W element).

Cheers, T i m