Hi All,
I live off the grid and just got a chest freezer. In order to reduce night time running I want to set the temperature lower during the day when the batteries are at float and then go back to a normal setting at night. Hard to say how much power that will save, but it will be fun to try. I have a kill-a-watt hooked up to it and I'll keep that logging while I build the new controller. There was a similar thread a while back but as this is a new project I thought I'd give it a new thread.
Firstly, any thoughts as to if this will really save any power at night? As y'all know, the less you discharge your batteries every night the longer they last. So even if it is a modest reduction in run time I am interested. Of course, this needs to be balanced against compressor wear and of course the compressor will be running more in this scenario. How much more is hard to say. Opinions?
The electronic side of it should be pretty easy. My Midnite charge controller has a float output. I'll use a SS relay to hijack the compressor controls, a uC and a temp. sensor. An optoisolator to the compressor motor to determine if it is running. I'll leave the existing controls in place and run mine in parallel, so if my controller craps out the freezer will stay cold. Not that any project of mine ever would! ;-)
One of the things I recall from the other thread is that the compressor should be allowed time off if it has just turned off. It also seems a run time limit is a good idea too. Here is some pseudo code:
main:
if batteries at float AND compressor is NOT running AND has not run in last X mins THEN
turn on compressor
reset run time counter
if temperature = lower set point OR compressor has run too long OR batteries <> float THEN
turn off compressor
reset off time counter
Anything else I should add to the logic? Suggestions for length of off period and max run time? Any other safeguards?
Jonathan - KK6RPX