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StephenH View Drop Down
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Posts: 6288 		Direct Link To This Post Topic: Fridge not cooling
    Posted: 09 Jul 2020 at 9:55pm
In my case, my FPSC cooler cost me $100, so it was a no-brainer to purchase. That seemed to be a one-time opportunity as I have not seen any more available at the ReStore locations near me. The biggest advantage is that it will cool in hot temperatures. Once it is cool, the power use is minimal and I have been able to leave it running overnight and still have plenty of battery power available in the morning, totally unlike my one attempt at running the Dometic refrigerator on 12V when we first got the RPod. Now I can run the Dometic on 12V since my new setup provides more than enough power to both charge my LiFePO4 battery and run the refrigerator. However, if we are boondocking, once we stop, the Dometic goes back on LP power since I would need a lot more battery capacity to run that on 12V.
StephenH
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Posts: 5290 		Direct Link To This Post Posted: 10 Jul 2020 at 6:51am
Originally posted by podwerkz

Correct me if I am wrong, but even the Danfoss and other '12V' compressors are not REALLY 12V DC...I am under the impression they have an internal control board (and inverter or switching/buck-boost circuit) feeding the brush-less compressor windings (and possibly a field coil) a 3 phase AC voltage...although I have no idea what that voltage would be. 

Yeah, there are 12V positive and negative wires or terminals, but the windings of the compressor are something else. Otherwise, with typical 12V DC motors, we would need brushes and commutators, and these compressors do not normally have those.

Although, I have not torn into one to verify that.

At any rate, I did the typical solar powered fridge experiment most of last year...I found that to have more compromises than a propane powered fridge. Just sayin.

IIRC (which I might not, it was 35 years ago) the Secop controllers provide low voltage square wave output to the hermetically sealed compressor motor. So they are a kind of inverter, just like brushes and commutator are a kind of inverter. That is what a brushless DC motor design does, it replaces the com and brushes with transistors do the polarity switching, based on a position sensor within the motor. You can't hermetically seal a brushed motor so this was the solution. The variable frequency 3 phase AC motor drive systems were originally developed for big industrial motors and have now made their way into EV's. But for a little bitty fridge compressor those are overkill, at least so far. 
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Posts: 5290 		Direct Link To This Post Posted: 10 Jul 2020 at 7:04am
Originally posted by StephenH

In my case, my FPSC cooler cost me $100, so it was a no-brainer to purchase. That seemed to be a one-time opportunity as I have not seen any more available at the ReStore locations near me. The biggest advantage is that it will cool in hot temperatures. Once it is cool, the power use is minimal and I have been able to leave it running overnight and still have plenty of battery power available in the morning, totally unlike my one attempt at running the Dometic refrigerator on 12V when we first got the RPod. Now I can run the Dometic on 12V since my new setup provides more than enough power to both charge my LiFePO4 battery and run the refrigerator. However, if we are boondocking, once we stop, the Dometic goes back on LP power since I would need a lot more battery capacity to run that on 12V.

You got a steal of a deal. Keep it nice, it might be a collector's item before too long. I don't think you can get a FPSC now, except for high end computer builders who spend big bucks to buy tiny ones to cool their overclocked CPUs to -40C or some such craziness. 

You can't compare the Dometic on 12V to the Danfoss, the Dometic absorption cycle COP is probably around 0.5 vs around 2 for the Danfoss (or FPSC). The absorption fridge is terribly inefficient but there is so much energy content in propane that it more than males up for it RV applications. 
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Posts: 6288 		Direct Link To This Post Posted: 10 Jul 2020 at 7:55am
I wasn't comparing 12V FPSC to propane Dometic, but 12V FPSC to Dometic on 12V. That is why I will continue to use the Dometic on propane when not connected to shore power or towing and use the FPSC to supplement for meats and other things that really do need to stay cold, even in hot weather.
StephenH
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Posts: 3219 		Direct Link To This Post Posted: 10 Jul 2020 at 2:17pm
Back to the OP.  Yesterday with the fridge 1/2 full with water and beverages the temp during the daytime stabilized at 43-44 degrees which is better but the outside temp was cooler as well, only getting up to 88 degrees.  This morning at 6 am temp was sitting at 42 which didn't please me as outside temp was 74. 

Decided to clean combustion chamber yet once again in light of all this fussing.  Turned to electric, causing the fridge temp to drop from 43 to 36 degrees in about 3 hours.  Let combustion chamber sit in mineral spirits for 2 hours and then blew out with compressed air and re-inserted.  At noon I turned off the electric (fridge was at 37) and turned propane back on.  Here it is 3.25 hours later and the temp has not changed, outside temperature is 80.  So things are looking up at this point.  Trying to figure out if there may still have been some crud either inside the combustion chamber or inside the orifice - doesn't seem likely as both had been cleaned out 2 times before doing it again this morning.
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Posts: 5290 		Direct Link To This Post Posted: 10 Jul 2020 at 6:30pm
Once you have a lot of thermal mass in the fridge the coldest morning temp won't go as low. That't the downside of the warm temp in the afternoon not going as high.  Basically the thermal mass makes the fridge temp seek an average. Overall at this point I think your fridge is probably working about as well as its going to. Might want to add the fans as others have suggested to keep the outside air circulating, that's probably about  Hopefully you can get a few more years out of it.....
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Posts: 3219 		Direct Link To This Post Posted: 16 Jul 2020 at 6:42am
Final report is in.  After camping in the UP of Michigan and temps were warm we decided to camp where we would have electricity for a change.  Temps stayed between 40 - 42 degrees regardless of outside temps which varied between 61 - 85.  Traveling down the road in propane mode was pretty much the same for the 7 plus hours of drive time (3.5 hours each way) 40 - 41 degrees.  Thank you all for your kind help and advice.
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Posts: 6288 		Direct Link To This Post Posted: 16 Jul 2020 at 9:15am
Great! I'm glad it worked out for you. Thumbs Up
StephenH
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ouR escaPOD mods
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