Convert 110v refrigerator to 12v?

[phorvati]

I am looking into doing something similar. I wanna rip out my Copeland 110V condensing unit but keep evaporator which i believe is a rather large holdover plate. Nobody mentioned the BTU/h. I wish Richard Coleman was here to chime in. Don't the BTU/h have to add up or at least be comparable for the swap to work? Otherwise you will have oversized evaporator or undersized condensing unit. AC condensing units can put out 3-4 times more BTU than BD35/50/80 compressors.
Perhaps on a college fridge you have a thin plate evaporator so it really doesn't matter. It cycles all the time. And the side door really hurts, you loose so much energy every time you open the door. then you wonder where the Amp-hours went.
Sailorchick34, could you give us a reference where it shows that motor inside BD35/50/80 is in fact an AC motor. I cant believe that.

[sailorchic34]

Originally Posted by phorvati

Sailorchick34, could you give us a reference where it shows that motor inside BD35/50/80 is in fact an AC motor. I cant believe that.

Danfoss does not talk about their motors but here is a link to a discussion about them. The motor is a 3 phase a/c motor and the black box is the converter. You can not run a "12V" compressor on 12V without the black box that is the inverter. Danfoss Compressor Speed Controller

If the motor was a 12V dc motor you would not need the spendy blank box to run it.

On a side note, I just ordered a replacement fridge, a 120V edgestar 3.1 CF. two, ok three reasons. First it has a true freezer compartment, the old fridge did not keep the meats frozen and the freeze thaw cycles were annoying. Second it has the lowest power use at <=80 watts (0.6 ah @120v) and third it's only $215 including shipping. The old fridge was a 1.4 amp draw at 110, so 0.6 amp is very attractive. My guess is it will run longer but still reduce overall daily ah load.

My old 3.5 cf magic chef after running continuously for 9 years is starting to make noise in the compressor. As I'm half deaf, I thought that a problem. Plus the amp draw has increased which means bearings are going.

Still 9 years for a $130 fridge running on a $45 MSW inverter is pretty good service.

Pretty excited that I might get to have ice cream aboard and drop ah to 40 ah ish a day. That last based on others who have measured performance. I will of course do my own testing, though the true test is in 95+ degrees F delta temperature this summer.

Still icecream would be a plus. That will be the true test this summer....

[SV THIRD DAY]

Originally Posted by phorvati

could you give us a reference where it shows that motor inside BD35/50/80 is in fact an AC motor. I cant believe that.

It's not just an AC compressor...but more importantly a 3-phase AC compressor. That's used as a engineering mechanism to give a soft start and for efficiency.

The black box controller take the 12/24v DC and converts it to 3-phase AC.

[Lepke]

My old inverter was 2200 watts and easily ran a double door reefer and a chest freezer. At the time I had 2 banks of 2 8dd batteries. One bank would run both and any lights, tv,etc. for about 30 hours. All but 2 lights are 120v ac. I could run with just one of the mains alternator keeping the bank up.
Where the reefer is built into cabinetry, I added extra foam sheets. If the doors aren't opened, it runs about once an hour in cool weather. Same with the freezer.

[ranger58sb]

Originally Posted by sailorchic34

Yes there are efficiency losses running an inverter, but it's not so bad. Lets not forget that the black box on the danfoss is an inverter (DC to AC) so no free lunches there.

Originally Posted by phorvati

Sailorchick34, could you give us a reference where it shows that motor inside BD35/50/80 is in fact an AC motor. I cant believe that.

Originally Posted by sailorchic34

Danfoss does not talk about their motors but here is a link to a discussion about them. The motor is a 3 phase a/c motor and the black box is the converter. You can not run a "12V" compressor on 12V without the black box that is the inverter. Danfoss Compressor Speed Controller

If the motor was a 12V dc motor you would not need the spendy blank box to run it.

Originally Posted by SV THIRD DAY

It's not just an AC compressor...but more importantly a 3-phase AC compressor. That's used as a engineering mechanism to give a soft start and for efficiency.

The black box controller take the 12/24v DC and converts it to 3-phase AC.

Trying to follow this... to better understand how our NovaKool AC/DC fridges work. And with some educational challenges, like "what's 3-phase?"

A few years ago I spoke with the NovaKool folks and their tech said their fridges convert AC, if present, to DC to run the compressor. Or if DC is present but AC is not, they run on DC. Seemed very straightforward at the time; I interpreted that to mean their "AC power supply" is just an AC-to-DC converter...

So fast forward to reading this above, and the link SC included...

This means the "DC" compressor motor actually always works on AC (is there a difference between AC and 3-phase AC?) so... back to the NovaKool saga...

Does that mean the NovaKool AC power supply is simply an AC power supply... and their "DC power supply" is actually a DC-to-AC inverter? Is that the "black box" SC mentions?

Can't imagine it would be as complicated as converting AC to DC when AC is present... and then inverting DC to AC when only DC is present...

Can ya'll maybe point me toward the correct end of the stick?

BTW, I can say our two fridges work pretty well (easily passes SC" "ice cream standard"), and I don't notice much in the way of power consumption. OTOH, they're not frost-free, which would seem to me a good feature if these went south and I were to get a little splurgy with the wallet. That feature is more commonly available on straight AC fridges, and I'm guessing a straight AC frost-free fridge running on an inverter (i.e., including both costs) probably wouldn't be as expensive as the AC/DC marine units... (assuming sufficient battery bank, charging system, etc,). Another reason for my questions...

-Chris

[SV THIRD DAY]

Originally Posted by ranger42c

Trying to follow this... to better understand how our NovaKool AC/DC fridges work. And with some educational challenges, like "what's 3-phase?"

A few years ago I spoke with the NovaKool folks and their tech said their fridges convert AC, if present, to DC to run the compressor. Or if DC is present but AC is not, they run on DC. Seemed very straightforward at the time; I interpreted that to mean their "AC power supply" is just an AC-to-DC converter...

So fast forward to reading this above, and the link SC included...

This means the "DC" compressor motor actually always works on AC (is there a difference between AC and 3-phase AC?) so... back to the NovaKool saga...

Does that mean the NovaKool AC power supply is simply an AC power supply... and their "DC power supply" is actually a DC-to-AC inverter? Is that the "black box" SC mentions?

Can't imagine it would be as complicated as converting AC to DC when AC is present... and then inverting DC to AC when only DC is present...

Can ya'll maybe point me toward the correct end of the stick?

BTW, I can say our two fridges work pretty well (easily passes SC" "ice cream standard"), and I don't notice much in the way of power consumption. OTOH, they're not frost-free, which would seem to me a good feature if these went south and I were to get a little splurgy with the wallet. That feature is more commonly available on straight AC fridges, and I'm guessing a straight AC frost-free fridge running on an inverter (i.e., including both costs) probably wouldn't be as expensive as the AC/DC marine units... (assuming sufficient battery bank, charging system, etc,). Another reason for my questions...

-Chris

The Danfoss or Cubigel compressors that Novacool, Technautics, AB ColdMachine, Frigoboat, and Everyone else uses are ALL 3-phase AC compressors.

The standard black control module Box on ALL of them take 12 or 24v DC and convert it to 3-phase AC.

Now, there is a controller option to take direct single phase 120v AC for when you are plugged into shore power. In this case, the single phase AC is converted in the Box to 3-phase AC to run the controller. I'm personally not a fan of this Option because when plugged into shore power your battery charge will be on anyway...and it will supply the 12v DC power to your system...so why add another level of complexity/switching in the black box controller that is already the weak link in any system?

Now Yes there is a difference between single phase AC and 3 phase AC...but I'm not going to play electrical engineer...so here's a Google link to explain the differences:
Single-Phase Power vs Three-Phase Power | EEP

[sailorchic34]

Weather a motor is single phase or three phase, has to do with how it's wound. A three phase motor like in many dc compressors is wired in a delta configuration. That is three circuits each with one end a hot leg and the other ends all tied together. in 3 phase the phases are 120 degrees apart where single phase is 180 degrees. The advantage over single phase is smaller inrush current and lower run current and smaller conductor diameter (wires). That is, at least in my mind, the reason Danfoss and others use a 3 phase AC motor.

Why not DC.. Efficiency, high inrush, and wire size.

[svlamorocha]

I understand that the 3-phase AC in these boat fridges is not "normal" AC with constant frequency. The frequency varies in order to reduce startup current. Given the need for variable frequency, if you want to run the thing off "normal" 60Hz AC you need to rectify it to DC first and then run it through a special type of inverter with variable frequency.

[SV THIRD DAY]

Before anyone runs off half-baked and starts messing with the electrical on their compressor....take a deep breath and back away. The black box controller mounted to the side of your compressor does everything for you. Just land your 12v/24v DC wires and forget about trying to take the controller apart and re-engineer it. I have to say this because you would be surprised at the crazy S#$! I see people do and try after misreading an internet post.

$295 for a replacement controller....Na...I read on the internet that I could build one myself but now my compressor is dead

Trust me...I've seen it all....

[ranger58sb]

Originally Posted by SV THIRD DAY

The Danfoss or Cubigel compressors that Novacool, Technautics, AB ColdMachine, Frigoboat, and Everyone else uses are ALL 3-phase AC compressors.

The standard black control module Box on ALL of them take 12 or 24v DC and convert it to 3-phase AC.

Now, there is a controller option to take direct single phase 120v AC for when you are plugged into shore power. In this case, the single phase AC is converted in the Box to 3-phase AC to run the controller.

Thanks very much. Very interesting. So I understand...

The Danfoss "DC compressor"... isn't a DC compressor, yes?

Instead, it's a 3-phase AC compressor with a DC-to-AC inverter (conceptually, at least) added on so it is intended to work on DC, yes?

And then it may also have an optional AC-to AC converter (?) so it can run on typical 110V/220V AC shorepower, yes? (Or maybe shorepower AC is first converted to DC, but then that get's inverted to 3-phase AC as above?)

I'd guess that means ours have the option, since they run fine on shorepower, too.

Thanks also (all) for the AC v.s 3-phase AC info, and for the probable why's behind the 3-phase selection...

And I have absolutely no intention of even finding the compressors, let alone messing with them.

-Chris

[masonc]

The issue of the motor being three phase may be a little confusing to the non-electrician participants in this discussion. When people see the word AC as opposed to DC, they start thinking that this is the power they see in their house. That's not the case. All that AC means is the motors are fed a sinusoidal waveform so as to allow for speed control. The frequency of the waveform is varied to effect speed control, faster frequency gives faster rotation. The rotor of the motor follows the rotating frequency of the three phase waveform.
This has nothing to do with the three phase 480V or 208V electrical supply provided by your utility.
The control in a Danfoss compressor is effectively an amplifier. It takes a DC power source and creates a three sinusoidal waveforms, which are fed to the three stator windings. The rotor follows the rotation of the waveforms. Therefore the controller can efficiently control the speed of the rotor by varying the frequency of the waveforms, and the motor will stay at that speed or stall.
In the DC motor, the speed is controlled by varying the voltage and therefore the current. The speed is hard to control accurately as load will have the opposite effect. Three phase wound motors are very efficient, especially when ran at slower speeds.
So don't confused AC waveforms with 110V power.

[JstaRebel]

Originally Posted by TitoSoto

Yup I do see that!

I just always thought that it was more efficient to keep the condenser coils in a separate location since their whole purpose is to get heat AWAY from the fridge.

I agree. I had a solar 12volt grape solar fridge. The condenser coils were wrapped around the insulation just under the skin as Rich mentions and this thing ran all of the time. A very poorly designed fridge box. Something else to consider is that most of the condensers on the fridges are NOT copper, so you cannot solder them. They have to be brazed. In doing my conversion of a 120v to 12v fridge, I used stainless swedgelock high pressure plumbing fittings to make this connection. I can solder fine, but brazing is a different thing all together. I found a chest freezer that used the same gas as the grape solar fridge that had the condenser unit located on the back of the fridge. I also chose a chest freezer to convert because they have better insulation than the little fridges and top loaders are more efficient.

The other issue you may run into is controlling the 12v with the thermostat. I guess on a f keys it may be different but with the freezer unit I converted, I purchased a 12 volt thermostat controller and installed it. All and all, it worked out better than I had hoped it would. Good luck with your conversion.

[ranger58sb]

Originally Posted by masonc

The issue of the motor being three phase may be a little confusing to the non-electrician participants in this discussion.

The control in a Danfoss compressor is effectively an amplifier. It takes a DC power source and creates a three sinusoidal waveforms, which are fed to the three stator windings. The rotor follows the rotation of the waveforms. Therefore the controller can efficiently control the speed of the rotor by varying the frequency of the waveforms, and the motor will stay at that speed or stall.
In the DC motor, the speed is controlled by varying the voltage and therefore the current. The speed is hard to control accurately as load will have the opposite effect. Three phase wound motors are very efficient, especially when ran at slower speeds.

So don't confused AC waveforms with 110V power.

Fair enough, thanks for the amplification.

-Chris

[SV THIRD DAY]

Originally Posted by JstaRebel

I agree. I had a solar 12volt grape solar fridge. The condenser coils were wrapped around the insulation just under the skin as Rich mentions and this thing ran all of the time. A very poorly designed fridge box. Something else to consider is that most of the condensers on the fridges are NOT copper, so you cannot solder them. They have to be brazed. In doing my conversion of a 120v to 12v fridge, I used stainless swedgelock high pressure plumbing fittings to make this connection. I can solder fine, but brazing is a different thing all together. I found a chest freezer that used the same gas as the grape solar fridge that had the condenser unit located on the back of the fridge. I also chose a chest freezer to convert because they have better insulation than the little fridges and top loaders are more efficient.

The other issue you may run into is controlling the 12v with the thermostat. I guess on a f keys it may be different but with the freezer unit I converted, I purchased a 12 volt thermostat controller and installed it. All and all, it worked out better than I had hoped it would. Good luck with your conversion.

Great Job!
That's essentially what we do as well with our EcoFridge units for the conversion, but we do the silver braze rather than Swagelok fittings. Works great. The harder part these days is finding the Box units without the condensing units under the skin of the external walls. They work much better with the rear condensing coils like in your photo.

[JstaRebel]

Originally Posted by SV THIRD DAY

Great Job!
That's essentially what we do as well with our EcoFridge units for the conversion, but we do the silver braze rather than Swagelok fittings. Works great. The harder part these days is finding the Box units without the condensing units under the skin of the external walls. They work much better with the rear condensing coils like in your photo.

The fridge with rear mounted condensers are difficult to find especially in the states. I got this freezer in St. Maarten. It's an "Ocean" brand made in Portugal. The fix for this I guess would be to install a separate condensing unit and do the plumbing. The hard part for me was trying to get someone to charge the darned thing. I ended up buying a cheap auto A/C charge hose kit, cutting off the the hose and adapting it to a piece of 1/4" stainless with a swedgelock ferrel/ nut set up on it. Thats why there is a swedgelock check valve on the LP side. Then I followed instructions for charging it from a gentlemen from this board that was explaining the process to another poster who also had no gauges to check pressures, and it went very smoothly. Even the evaporator lines freezing and melting like magic as everything leveled out was spot on. Also comes in handy working with RO's and having swedgelock fittings around..