Hi Peter,
not sure if I can help in your progress any more but I managed to
source a very similar unit to yours through my work.
I dug up two types of units, both 'Carel' temp controllers, typically used
in refrigeration units and cold rooms.
http://www.actrol.com.au/Global/Asse...tion-guide.pdf
http://www.systemcontrol.com.au/prod...ure-controller
Carel units seem to be the units that the 'clones' on eBay mimic.
Main difference in mine to yours are they are 240v mains powered
and simply control a relay within the unit, with relay contacts rated at 10A.
all good, except I don't like mixing 240v and probe/sensor/peltier wiring
in the same vicinity whether in a sealed controller box or whatever.
Your unit would be the better option, because it runs from 12V and controls
the peltier with the same 12V.
But to demonstrate the concept of the controller ( which can't
be too different in performance surely) I set it up on my
cooled DSI II mono camera.
Tonight was a bit warm with ambient at around 28C so I set the setpoint
of my pelt cooler to 17.5C
In the controller menu I set the differential ( the kick in temp and kick out
temp or delta T) to 1C. Default was 3C.
With that differential I managed to get the cooler kicking out at 17.5C and kicking in at about 19.3C
With a pattern that repeated over a few minutes, this set of temps were
stable.
Note that while the controller differential was only 1C and there was
clearly a range of about 1.8C that is because of the thermal inertia of
my heatsink and cold finger setup.
If I wound down the differential to under 1C, say 0.5C I would probably
get a smaller delta T, hopefully as low as about 1C, which would be great
as a sub taken at only 1C difference should stack well.
Stay tuned...testing this right now.....
edit: result of diff set to 0.5C gave an actual differential due to the thermal
inertia of 1.3C
Result of differential set to 0.2C gave an actual differential of 0.7C!!!
I like it, Pete!
(subs at 2C difference from experience with this cooled DSI II stack fine
but it improves signal to noise if lower)
Now back to your setup.
I think there are a few more things you should check if it doesn't seem to be
working right, that is, before you send it back, but I see you have another
on the way.
Check that your power supply 12V DC can supply at least 4-5A for the peltier. I'm assuming you have anyway.
Check the peltier is still ok on a battery, cold side works, hot side works etc. Sometimes brute force DC can kill peltiers. Sometimes pulse width
modulated DC (as I use) can kill peltiers.
Most importantly, check there are no shorts between hot side and cold side electrically.
By this I mean, the peltier sits as a sandwich between a heatsink and
your camera CCD cold finger.
If the cold finger shares ground with the camera casing then NO part of
the heatsink/ fan assembly can share the same ground. That would be
a short across the peltier.
Some pics attached of my testing tonight.
As a straight out of the box solution to pelt control, I think your
controller will be fantastic, especially as it may demonstrate very fine
control of temp and hopefully a very small differential.
I'll do more testing and see if I can wind down that delta T even more.
Steve
