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Old 02-10-2019, 16:05   #1
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Danfoss thermostat resistors values - how accurate??

Hi, I have a Danfoss BD35f compressor with the 101N0210 controller module.


As the manual says, you can use different resistor values in the circuit from the thermostat to control the compressor motor speed. 0, 277, 692, 1523 ohms (slower to faster for the motor ). I have sort of cobbled these values together by joining resistors but it is a bit of a mess as you need to join lots to get close to the exact values. It works but seems very messy.


My question is, how accurate do these resistor values have to be? Does it have to be right on the value? Or is the motor speed controlled variably across as a range depending on the amps allowed through by the resistors. (low to high, rather than steps).


It's been bugging me for a long time



Anyone know?
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Old 02-10-2019, 16:21   #2
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Re: Danfoss thermostat resistors values - how accurate??

As a former electronics tech (30 years) I'd just go with standard values.
270, 680, 1500 ohms.
I can't imagine it making significant (if any) difference.
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Old 02-10-2019, 16:33   #3
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Re: Danfoss thermostat resistors values - how accurate??

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Originally Posted by Warby12 View Post
Hi, I have a Danfoss BD35f compressor with the 101N0210 controller module.


As the manual says, you can use different resistor values in the circuit from the thermostat to control the compressor motor speed. 0, 277, 692, 1523 ohms (slower to faster for the motor ). I have sort of cobbled these values together by joining resistors but it is a bit of a mess as you need to join lots to get close to the exact values. It works but seems very messy.


My question is, how accurate do these resistor values have to be? Does it have to be right on the value? Or is the motor speed controlled variably across as a range depending on the amps allowed through by the resistors. (low to high, rather than steps).


It's been bugging me for a long time



Anyone know?
I believe that the motor speed is variable across the range and the resistor values do not have to be exact, and correspondingly the speeds will not be exact. They will be close.

I had a small detachable circuit board that was on one of refers previously, it had four resisters and spade connectors so you could choose any one of them. The values were approximate. Right now I can't find the diagram I did showing that.
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Old 02-10-2019, 16:45   #4
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Re: Danfoss thermostat resistors values - how accurate??

You guys are legends!

That's what I thought, that it can't be super precise and possibly variable. Now I can fit the resistors on a tiny circuit board.

It's cool here now but as summer approaches I can turn the fridge compressor up. Last summer it would be on continuously (on the lowest compressor speed).

Cheers Stephen
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Old 03-10-2019, 09:08   #5
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Re: Danfoss thermostat resistors values - how accurate??

I don't think the values matter as long as within specified range. This is supported by our experience having a potentiometer on ours so we can adjust motor speed if/as needed. It works great.

Probably better would be one of the Fridge Optimizer controls- on our future upgrade list...

In case this is useful.

Cheers! Bill
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Old 04-10-2019, 09:23   #6
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Re: Danfoss thermostat resistors values - how accurate??

Darby, I’m glad you got that off your chest. Just teasing you. I’m impressed that you had the skill level to even attempt such a thing. Good on you.
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Old 04-10-2019, 15:38   #7
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Re: Danfoss thermostat resistors values - how accurate??

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Darby, Iím glad you got that off your chest. Just teasing you. Iím impressed that you had the skill level to even attempt such a thing. Good on you.

Refrigeration fascinates me! It's like magic. (I like heaters too)
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Old 05-10-2019, 08:05   #8
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Re: Danfoss thermostat resistors values - how accurate??

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Refrigeration fascinates me! It's like magic. (I like heaters too)
The neat part is when I tell folks I can take the heat energy from 55f seawater cause the refrigerant to absorb it and then use it to make the discharged air 110f in the boat...
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Old 05-10-2019, 08:13   #9
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Re: Danfoss thermostat resistors values - how accurate??

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The neat part is when I tell folks I can take the heat energy from 55f seawater cause the refrigerant to absorb it and then use it to make the discharged air 110f in the boat...


Think about your statement.
You take the heat from inside of the refrigerator and move it either into the air or water. Or both.
However the heat output of the average marine refrigerator is about half that of a resting human, so your heating the boat by the amount of what half a person would sitting on the settee.
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