On Monday, 13 November 2017 15:26:02 UTC, T i m wrote:
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 it's not realy a cut-out more like a cut-back.

So what does a cut-out do.




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.

So is that the new name for a cut-out.


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.

But of course it's not called a cut out but Overheat protection.


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.

So many options to consider one wonders how yuo;d calculate how many heaters would be needed, it;s a problem we're having at this very moment and discussing , how many more to buy and who should pay for them.


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).

thought the plastic would be likely to melt and if I did it would then fail regualtaions as we;d need it PAT tested before it was put back into use.
So another reason njot to take it apart, I'd prefer that we were supplied with working equipment that was up for the job.


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'.

Well it does just like anything else, or at least you should expect it to.



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

Nothing of which help work out how many we need.
Perhaps that's why we have 14 due to arrive this week.