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Hi Steve. Thanks for your thorough response. That Carel controller certainly looks like the parent of my EBay product range.
I have done a double-check on the power supply and connectivity issues and they all get a pass grade. And I've checked the operation of the peltier itself - it works fine. I've got some spares coming from China just in case - I've cooked them before.
I've just made up a couple of those Oatley Electronics kits (K140B) but confess to being uncertain about them. Their accompanying blurb says they can be optioned to function either a a switchmode continually switching controller for peltier devices where the duty cycle varies according to the temperature differential OR for an occasional switching controller with hysteresis for use with fridge compressors and heaters - the difference is in a few of the resistors.
The only adjustment is in a variable 2K potentiometer - so the adjustments are pretty coarse. The thermistor used is a 100K at 25C so when it is centered, the range of adjustments is between 10C and 60C. To go lower, changing one of the resistors from 1K down to 560 ohms would bering the lower setpoint down to 0C. One of the kits I've just made up has that swapped resistor in it.
Trouble is, with ambient still in the mid 20s here, I can't get this thing colder than about 12C so I don't know if the switching is happening or not. It's a bit of a mystery.
When those extra units arrive from China - probably in the coming week, I will probably switch back to them and scrap the Oatley units.
It's all academic really because the clouds/moon combination are keeping my obs roof closed and likely to stay that way for a while yet.
Peter
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