On Tue, 14 Nov 2017 05:29:29 -0800 (PST), whisky-dave
wrote:

On Monday, 13 November 2017 17:21:04 UTC, T i m wrote:
On Mon, 13 Nov 2017 08:19:36 -0800 (PST), whisky-dave
wrote:

snip

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.

Well, same thing in this case.

No it's not.

Aren't you the one who seemed to have no idea about any of this?

I am describing the electrical device as being what it is, whilst you
are trying to conflate that and the function you (you believe) you see
it having.


So what does a cut-out do.

What it says. It's a thermal switch that cuts out (in this case) when
the temperature reaches a certain point and cuts back in again when
the temperature has dropped back to a certain (lower) point again
(just like a thermostat). You can get them that are wired in reverse
to control cooling fans etc.

So is it a cut-out or a thermostat, you seem to be saying tehy are the same.

Electrically, in this case the result of either 'activating' are the
exact same thing, eg, cutting off the flow of electricity through the
element(s).


snip

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.

Not new (other than to you possibly and in this specific message),
just 'another'.

So you can't tell the differnce between those labels is that it. ?
Thermostat, cut-out, resettable fuse.

What? As you don't want to open a unit up and without recourse to a
wiring diagram you would (normally) have no idea which one had
operated if the unit had gone off (as they are all usually in series).
ITRW, if you adjust the main thermostat and it all comes back on, of
leave it to cool down a bit and it comes back on, then the thermal
fuse hasn't blown.



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.

Yes, where the 'overheat protection' is provided by an overtemp /
thermal / cut-out / switch *and / plus* a one way (non-resettable),
thermal fuse.

As I thought you can;t tell teh difernce between these terms a thermostat is the same as a cut-out.

Are you now just trolling mate?


So many options to consider one wonders how yuo;d calculate how many heaters would be needed,

Not really ... once you have taken the measurements you just need to
do the sums.

What measurements, most situations you decide what you want before taking measurements, because yuo buy based on teh specifications of the product.

Not in this case you shouldn't (tail wagging the dog) and John has
explained the process clearly enough elsewhere.



What you can measure (and it seems like you have been
able to do that bit) you can manage. ;-)

Yep, far better than those using theory.

But only as an 'observation'. You may now have a large quantity of
useless heaters on your hands.

You bought a car to tow a trailer but with no idea how big the trailer
was.


it;s a problem we're having at this very moment and discussing , how many more to buy and who should pay for them.


You would have to decide that based on other factors that you haven't
yet covered (less I missed or forgot), like the need / usage,
environment (building type, thermal characteristics etc).

Yes and those were prettyy much fixed when it was built,

Indeed?

so how would an engineer predict what sort of heater and what power would be required ?

See Johns replies for an answer on those.


Like, my mate used a waste oil burning space hearer (blown air) in his
garage but it got old and I think they banned them (or were going to
if not heavily updated etc). He got the gas board in and (long short),
much to my mates questioning, they fitted two blown air gas heaters
that were never going to be up to the job. The sales rep suggested he
set the timer to come on at say 6am so the place would be warm for
8am, completely ignoring that the first thing my mate typically did
was open up the end of the garage to move cars in and out (and in so
doing losing any heat). So, they eventually ripped out the new units
and fitted bigger ones that were up to the job.

Suppose he was told that 10KW heater would be required to do what he wanted and then on installign them, he found that after a while the 5x2KW were no longer 2KW but reduced in power to 700W, would that change any calculation,

Of course?

I'msuggesting if that is the case he'd need 13-14 of thse heaters wouldn't he.

Possibly not, (because if I remember your statement correctly), the
heaters cycle between 700 and 1600W on the upper limit stat and so the
average energy may be able to eventually get the space up to temp.


So, to 'feel the affect' of the heating effect you might be better of
with industrial fan / space heaters or IR heaters etc.

Neither of which are allowed in the teaching lab due to H&S.

Then you are fcuked mate. That or you buy lower wattage rads with a
greater surface area.


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

Never seen a plastic handle on a hot air gun or soldering iron?

Yes but it's insulated from the heat part.

By ... ?


and if I did it would then fail regualtaions as we;d need it PAT tested before it was put back into use.

See above. Not all 'plastics' are created equal mate. ;-)

and I doubt the best plastics are in use in his cheap heater.

So are they melting in front of your eyes?

But in the manual they do list things like the carry handle adn everything else the seem to have missed out the section on how to get to the wiring.

Of course?

Perhaps it;s not user accesable like changing the oil.

Indeed it isn't typically user accessible and will probably to have
some security screws on it to deter you from doing so. Doesn't mean
someone couldn't open one up and work on it though.



So another reason njot to take it apart, I'd prefer that we were supplied with working equipment that was up for the job.

But 'a reason' to take it apart would possibly to prove that it wasn't
wired correctly?

I don;t care. I have 5 of them and of the 3 I tested they all do the same.

So contact the supplier to confirm they are working correctly.


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).


Nothing of which help work out how many we need.

That wasn't what I was talking about and couldn't without you telling
us more about the entire scenario

you don't need to know more that is the point.

And that my friend simply highlights your ignorance on the matter. ;-(

It's pretty basic maths and even simplier if you think before calculating.

Then why ask us for help?


(including the thermal values for
the rooms / building etc). I gave you most of the tools, costs and
options within my first few posts and I couldn't do much more without
more information (you know, like knowing the likelihood of us leaving
the EU to be likely to be a 'good thing' or not before deciding to do
it). ;-)

No wonder you can't work it out.

Quite. No one can 'work out' anything without the facts. If you can,
you should be rich.


Perhaps that's why we have 14 due to arrive this week.

It might just be a few more to send back. ;-(

They seem to be working as indicated why would I send them back ?

Because they may not have been designed to work that way?


Maybe they could get a 2-3kw garage / workshop fan heater in to try?

Not allowed in a teaching lab .

Ok.

would be handy as my brother works for clarke and he'd get a 10% discount IIRC.

Ok.

But how do you know what power they are ? in order for your calculations to work.

Stamped on the plate and a function of the supply voltage mate.

See, what you have isn't working as expected.

What you have done is buy a cheap compressor that says it can do X but
you have failed to take notice that it's rated duty cycle is only
50:50 and what timescale's that actually is. My compressor for example
has a 50:50 duty cycle with a 60 minute (max) cycle time.

If you bought a 2kW oil filled radiator that could dump the full 2kW
into it's surroundings at all temperature differentials without
overheating itself, we wouldn't be having this discussion right now.

Cheers, T i m