VFD design

[star882]

I'm planning to build a phase change cooler for a PC (science fair project) and I need to regulate the temperature. Due to cost reasons, I must use an ordinary compressor - no VFD compressors or other special modulating compressors. About how much capacity control (Hz range) can I expect to achieve with a MOSFET inverter and an ordinary recip or rotary compressor? (The inverter will use a simple PWM modulator to achieve sine wave output and adjust the control voltage to the VCO from the temperature sensor with opamps - no Ashlee Simpson micros or PLLs in this design.)

BTW, before anyone asks what compressor I'm going to use it with, I currently don't know as I'm still looking for a good deal on a used compressor.

[Peter_1]

I think your question is a little bit too m uch electronic related, so don't expect that much answers because we're refrigeration techs and no electronic boys.

How low can you go depends on the brand and sort of compressor.
We've ran Bitzer as low as 10 Hz and as high as 70 Hz.
Bitzer gives a minimum of 30 or 25 Hz I think, Bock goes lower.
A scroll must run a much higher speeds, otherwise the scrolls inside loose contact and they compress not any longer.

Main reason for a minimum speed is lubrication in general and boundary layer lubrication more specific.

I think this will be a trial and error.

Why not use a small hot gas, SV controlled and inject some hotgas? At these extreme low capacities, you don't need that much hotgas to achieve a stable LP.

[chemi-cool]

There is a proportional hot gas valve, 3 way.

Should be helpful.

Chemi

[Brian_UK]

Try a low voltage Danfoss compressor, you can vary the speed very easily.

Check out the BD range
http://www.danfoss.com/Products/Cate...972d837cf1a%7d

[star882]

Then I'll need a 12v power supply that can supply a lot of current, and that isn't cheap.