AC vs DC Refrigeration

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dereckbc

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OK guys I am always in the learnng mode and looking for new opputunities. For the last 7 years I have done a lot of of off-grid Solar PV designs for the telecom sector.

Most of these applications are outdoor cabinets that do not require any cooling other than fans. So everything is straight 24 VDC with an inverter to power tower and ground lighting.

Well now I see an opputunity to design off-grid solar for consumers like cabin owners who need a refrigerator and maybe a window shaker AC unit.

I am thinking that a DC unit maybe more effecient by eliminating the inverter, especially an expensive True Sine Wave inverter usually reuired to run motor loads.

So my question is generic, am I smoking crack? Are there good effecient DC powered refers and window shakers out there, and how do they compare to their AC cousins assuming single phase operation?

What is throwing me is my inside the box thinking, especially with Electric Vehicles. EV's use a battery and convert to 3-phase AC for effeciency, rather than a DC motor. But window shakers and refers are single phase?
 
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winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
My engineering hunch ignoring the _cost_ of hardware is that the right way to do this is with refrigeration units that have built in inverters that use your DC system voltage as their input.

The things that you are calling 'DC motors' are really AC motors, where the AC is produced by a mechanical commutation arrangement inside the motor, and the over-all power input is DC. For small scale applications, the efficiency king is the 'brushless DC motor', which is again really an inverter fed AC motor.

Using a large, fixed frequency inverter, combined with 'across the line' starting of the various refrigeration motors, means that you will have to oversize your inverter (to handle starting current) and you will obtain no benefit of variable speed that might be possible with an inverter fed motor.

Putting a small inverter fed motor in each refrigeration unit would mean no inrush current, ability to use brushless DC machines, and potentially the ability to adjust motor speed for best efficiency given current operating conditions.

I don't know if anyone actually builds and sells refrigeration units that work in this fashion. I know that it is an active area of research.

-Jon
 

wireguru

Senior Member
i just got a new GE fridge, and it has a variable speed compressor. I dont know how theyre accomplishing that though.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
winnie said:
My engineering hunch ignoring the _cost_ of hardware is that the right way to do this is with refrigeration units that have built in inverters that use your DC system voltage as their input.

The things that you are calling 'DC motors' are really AC motors, where the AC is produced by a mechanical commutation arrangement inside the motor, and the over-all power input is DC. For small scale applications, the efficiency king is the 'brushless DC motor', which is again really an inverter fed AC motor.

Using a large, fixed frequency inverter, combined with 'across the line' starting of the various refrigeration motors, means that you will have to oversize your inverter (to handle starting current) and you will obtain no benefit of variable speed that might be possible with an inverter fed motor.

Putting a small inverter fed motor in each refrigeration unit would mean no inrush current, ability to use brushless DC machines, and potentially the ability to adjust motor speed for best efficiency given current operating conditions.

I don't know if anyone actually builds and sells refrigeration units that work in this fashion. I know that it is an active area of research.

-Jon
Winnie thanks. I have done some research in this area. For Refers there are a lot of units available in DC. From what I have read Danfoss makes the best DC brushless compressor and the only one that should be considered. Some Refer manufactures that use Danfoss compressors include:

  • Sun Frost
  • Sun Danzer
  • Tundra
  • Norcold
  • Polar Power

I understand DC brushless motors are the way to go and have a psuedo inverter built into them. What is throwing me are window shakers. Can't seen to locate any worth a darn
 
dereckbc said:
Winnie thanks. I have done some research in this area. For Refers there are a lot of units available in DC. From what I have read Danfoss makes the best DC brushless compressor and the only one that should be considered. Some Refer manufactures that use Danfoss compressors include:
  • Sun Frost
  • Sun Danzer
  • Tundra
  • Norcold
  • Polar Power
I understand DC brushless motors are the way to go and have a psuedo inverter built into them. What is throwing me are window shakers. Can't seen to locate any worth a darn

You should check the Marine area some do have on low voltage DC supply but I can't really comfirmed if that kind of beast { window shaker } is out there but central unit yeah .,, there is some around.

The Norcord is one of them it do ring the bell someway and ThermoKing { common commercal truck / Bus /RV system } is the other AFAIK i know there are few more on the market.

Merci,Marc
 
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