Bypassing Danfoss Controller 3-pin compressor

[Jon Phillips]

Hi everyone,

I hope someone with expertise or experience can help answer this question instead of just getting a bunch of stabs in the dark.

The controller for my Danfoss 35/50 compressor is out. It should be possible, in theory, to directly connect power source to compressor via 3-pins on compressor and wire in an external thermostat to +. The compressor would run at full RPM (not variable as it would with the controller) when on, but other than that, I don't see why this wouldn't be possible. I just have to figure out which pin on the compressor in what...

Anyone ever try this?

[sneuman]

Good question. I am in precisely the same situation.

[accomplice]

I believe the Danfoss uses a brushless Dc motor. If so, it will require both a wire and a motor controller. The controller does some signal processing, usually Kalman filtering, to rotate the field in the compressor's motor. For almost everyone, it is impractical to try to design your own. If you like to tinker you could make a project out of it, but I'd rather go sailing.
,

Sent from my SM-G930V using Cruisers Sailing Forum mobile app

[Frankly]

Afraid you are SOL. The motor is 3 phase AC and one of the functions of the motor controller is to convert DC to 3 phase AC. Richard K was offering a repair service once if my memory is correct (often it aint). RPARTS if they are still around also had the controllers.

If you are running the compressor on maximum speed a small blower is suggested to keep the controller from over heating.

[Jon Phillips]

Thanks Guys,

Already ordered the controller and will put it in. Was more of a thought experiment as I couldn't find the electrical info for the compressor online. Without claiming any expertise with these compressor myself, I'm actually suprised to hear the motor runs 3 phase AC. If you look at the self-contained dometic/waeco units on Amazon they often sell with AC to DC converters... In these applications then, AC is being converted to DC just to be converted back again. Anywho, thanks for the info =)

Cheers,
Jon

[senormechanico]

What comes out of the controller is actually 3 phases of pulsed DC.
Each pulse is 120 degrees out of phase from the next one.
The motor acts as if it's AC.

[Jon Phillips]

Thanks again,

Out of curiosity, what would be the protocol to bypass the thermostat to troubleshoot? I have a hunch that the thermostat may be suspect too

[maine50]

On mine I followed the wires from the thermostat and just connect those two posts with a short piece of wire. That duplicates the thermostat calling for cooling. (turns it on) . You might want to google Kollman Refrigeration. He has retired ( more than once) and has put up trouble shooting guides on his web site.

[boatbod]

Thermostat bypass: join C to T.
Note that this also bypasses any speed control (compressor runs at slowest speed).

http://files.danfoss.com/TechnicalIn...aWvWD3nL7YNM5A

[Stu Jackson]

Originally Posted by Frankly

RPARTS if they are still around also had the controllers.

They were as of August 2016. Great folks, quick shipping & delivery. Had exactly what I needed to replace my 29 year old module. Been working fine ever since.

Adler Barbour Replacement Electronic Modules

If you're indeed in Grenada, this may still help. If your module is truly fried, like mine was, bypasses will only prove that for you. You still need a long term solution.

[a64pilot]

Originally Posted by senormechanico

What comes out of the controller is actually 3 phases of pulsed DC.
Each pulse is 120 degrees out of phase from the next one.
The motor acts as if it's AC.

I believe this to be correct, motor may in fact be three phase AC, but pulsed DC emulates AC

Originally Posted by boatbod

Thermostat bypass: join C to T.
Note that this also bypasses any speed control (compressor runs at slowest speed).

http://files.danfoss.com/TechnicalIn...aWvWD3nL7YNM5A

This is also correct, I have done it myself to get around a hard start situation

[Dougtiff]

The question is why did the module fail, they are expensive and replacing the blown one, could do the same to the replacement, i don't have a answer the it, i do know the older modules would fail due to the hard start over time, unlike the newer design that has a soft start and is not being slammed with full voltage.

[belizesailor]

Originally Posted by maine50

On mine I followed the wires from the thermostat and just connect those two posts with a short piece of wire. That duplicates the thermostat calling for cooling. (turns it on) . You might want to google Kollman Refrigeration. He has retired ( more than once) and has put up trouble shooting guides on his web site.

Richard also sells a very good book on his web site too.

There usred to also be lots of good troubleshooting info on the Danfoss sight too. Not sure if its still there after the change in ownership.

[belizesailor]

Originally Posted by senormechanico

What comes out of the controller is actually 3 phases of pulsed DC.
Each pulse is 120 degrees out of phase from the next one.
The motor acts as if it's AC.

Interesting. Ive often wondered about that, but found no tech detail. Pulsed/phased DC makes more sense to me than inverting.

Have any reference for this?

[belizesailor]

Originally Posted by Dougtiff

The question is why did the module fail, they are expensive and replacing the blown one, could do the same to the replacement, i don't have a answer the it, i do know the older modules would fail due to the hard start over time, unlike the newer design that has a soft start and is not being slammed with full voltage.

The electronics module, or thermostat, are the most common failures...the compressors are pretty bullet proof. Heat, moisture, vibration all take their toll.