Quote:
Originally Posted by Drake
OK, the question was referring to some of the technical electronics discussed earlier in thread...
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On the electronics front, there are a few things that really need to be addressed in order to protect the compressor from destroying itself...
The most important is a delay period that begins when the compressor is powered up...
The scenario is this:
The compressor has been running for a while and there is a brief power loss of maybe a few seconds, to maybe 30 seconds. It is easily possible for the 'compression chamber' (if there is such a term) to become filled with liquid. If power is applied at this moment, the compressor will be trying to compress an incompressible liquid, and lock up with full power being applied to the compressor motor windings. This could burn and ultimately short out the windings, it is also conceivable that mechanical parts of the compressor could be damaged.
The power-up delay fixes this condition by allowing enough time (usually a couple of minutes) for the liquid in the 'compression chamber' to 'bleed down'.
I knew about the delay thing and only later learned why the delay is there. But on my prototype unit, I bypassed the whole delay circuit and wired power directly to the compressor (the starting cap was there, of course). During my testing, and experimenting with the unit, I accidently did replicate the scenario above, and the compressor locked up under full power, at which time my hand was instinctively flying to the power cord to turn the damn thing off... no harm done. But the scenario is real and it can kill your carefully crafted heat pump.
I have also had the experience, as has probably anyone who is reading these words, where I was sitting in a room, and for no apparent reason, the lights blinked, went off for some small fraction of a minute, then came right back on... this is the killer scenario.
This is what the power-up delay is there for. There is probably some cheap 'off the shelf' component that will do this for you, but I don't yet know what it is.
So, if you are building your own heat pump, and you wire directly to the compressor (with the starting capacitor in place of course), you need to know that there is a risk of intermittent power taking out your compressor..
I have made and used an Arduino-like microprocessor to do the delay task for me, and it's working just fine. If there's anyone interested, I can put the schematic and code on line. The Arduino has plenty of spare processing power so I'm still working on that part of the Arduino controller project.
Quote:
Originally Posted by okpiddler
...My under pressure on the low side protection and over pressure on the high side is all mechanical...
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Can you tell me more about this? What are they called, and where do you get them?
-AC_Hacker
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