chest freezer / fridge conversion

[StressMan79]

So I want to run my chest freezer at 40 degrees... this thread will document that process. I think I need a 12 v thermostat and a 12 v wall wart, I hope my inverter can provide the start up current. Got 8 amps.

Total of 4.50 (eBay)+3.50 (dealextreme). You might have a wall-wart already.

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[StressMan79]

Total of 4.50 (eBay)+3.50 (dealextreme). You might have a wall-wart already.

Or you could go with an all in one system... lots on sale on eBay... like this
http://m.ebay.com/itm/171411831133?nav=SEARCH

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[loghousenut]

What's the difference between Bill Clinton and Peter Stressman?

[loghousenut]

Well, Peter is gonna make a chest refer....


Bill Clinton never inhaled, so the refer never went anywhere near his chest.

[rreidnauer]

Does your inverter have a remote on/off option? I don't think trying to switch the full load of the inverter through the 12v thermostat is a good idea.

[StressMan79]

here is the wall wart I bought

http://www.dx.com/p/replacement-5-0mm-2-1mm-dc-12v-1a-power-adapter-supply-100-240v-2-flat-pin-plug-66682#.U_wb6WPp8r0

Here is the thermostat.

http://www.ebay.com/itm/400677190587?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

Rod, you can see that the relay is 12VDC or 120VAC. I suppose I could switch 12VDC from the wall wart, then run an auxilliary relay to switch the load. I think that a new relay will cost half what the thermostat runs. I'm inclined to take my chances.

I don't know what the inverter is, I do know that it is 900W modified sine @ 24VDC. I think the power factor is around 0.8. I suppose I could get a 1200 W one. Looked and they can be had for ~$50. http://www.ebay.com/itm/261551395515

I've read that startup current(~10s) is as much as 8-10A. Running is around 2A. Standby power for an inverter is around 1% of the rated power. The power cycle (for freezing) is ~20%. I suppose at fridge temps would be around 10%

Average power = .9 * 9W + .1 * 2A * 115V= 8.1+23W. I would like to put a timer relay on the inverter to turn it on every 5 minutes, and only turn off if on standby... there would reduce the loss of the system by around 35%. Anyone have any bright ideas on how to do this? Also any mods to motors to lessen the startup current, even if it takes twice as long to start.

-Peter

[StressMan79]

I think I know how to do it. I'll run 2 relays in parallel. Then in series through the factory on switch. Ill still be able to shut off the inverter. Anyway, 1 will be a feedback relay, NO, shuts off if there isn't juice on the output

The second, which'll take some figuring, are two timers.say the first is the off timer say 5 min. The second starts (30 sec) the on cycle.

If the fridge needs cooling the relay on the thermostat closes, then the timer relay closes and turns on the inverter. The feedback relay then holds the inverter on until the fridge thermostat turns off demand.

1) I don't know how to make that timer work. I'm a structural engineer. HELP!

2) I know I'll need a battery on the fridge to run the thermostat. Good thing I have a trickle charger. I'll use the wall wart to be the feedback sensor, that runs that relay.

I'll work up the energy cost in a later post

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[StressMan79]

30sec/(5 min x 60sec/min) x 9w + 23w, or 23.9 watts, I suppose I can live with 0.9/23 or 4% loss

[StressMan79]

30sec/(5 min x 60sec/min) x 9w + 23w, or 23.9 watts, I suppose I can live with 0.9/23 or 4% loss

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[rreidnauer]

I'm afraid that I can't quite picture what you're trying to do with all that.

[loghousenut]

He's talking metric.

[StressMan79]

Rod,

IDK what you don't get. It makes perfect sense to me! I'll draw something up in visio in 3 weeks or so... off for fla with the fam for 2 weeks starting tomorrow... then the peter project... I'll be away from the comp till at least the 26th.

LHN,

don't know how to design electronics in standard... maybe candlepower/fortnight and ft-acres?

(yes, I realize the second is an actual unit for the volume of lakes...usually "acre-feet")

-stressman

[StressMan79]

Okay I'm back, but Visio 2003 has half the electrical items I want to build the schematic. Don't know what to do...

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[loghousenut]

Buy more fuel for the generator or learn to like warm beer.... The British seem OK with it.