Refrigerator issue Danfoss bd35

[cr180]

Originally Posted by cr180

May still be useful to connect battery directly to controller (electronic module) to prove converter not messing up the DC input.

If that shows converter ok, maybe OzeLouie or Richard Kollman may be able to provide us with acceptable compressor running currents to determine if compressor pulling excessive current causing high temp in controller.

[cr180]

Originally Posted by OzeLouie

Suggest you re-read my post here #2 especially "Next, continue to monitor the voltage as the compressor starts or attempts to start." Test only with a multi-meter at the MDM + &- terminals as described. This is the industry recognised method of determining failure to start / run due to voltage drop. You could also check terminals for heat after failed run / starts as a bad connection will often get quite hot.

Thanks. But our Tundra units are supplied with a converter with Both AC and DC inputs. The output of the converter feeds the DC input to what you are describing as the MDM. Unless the converter is bad it appears the compressor is drawing high amps. What Is the acceptable range for compressor current and where is it measured?

[OzeLouie]

Originally Posted by cr180

If that shows converter ok, maybe OzeLouie or Richard Kollman may be able to provide us with acceptable compressor running currents to determine if compressor pulling excessive current causing high temp in controller.

Due to several factors effecting the current draw, current draw is indicative but not conclusive of compressor / system's situation. But as a guide expect a BD35 Secop (2cc comp) to operate between 3 and 5A/h while the BD50 (2.5cc comp) will be between 3.5 and 6Ah. If there is a compressor mechanical problem (highly unlikely) the current draw would be much higher and the MDM would shut down on over load or low voltage.
Once you read the voltage monitored at the MDM when / if the comp starts and thereafter, then that information will provide some answers

[cr180]

Originally Posted by OzeLouie

Due to several factors effecting the current draw, current draw is indicative but not conclusive of compressor / system's situation. But as a guide expect a BD35 Secop (2cc comp) to operate between 3 and 5A/h while the BD50 (2.5cc comp) will be between 3.5 and 6Ah. If there is a compressor mechanical problem (highly unlikely) the current draw would be much higher and the MDM would shut down on over load or low voltage.
Once you read the voltage monitored at the MDM when / if the comp starts and thereafter, then that information will provide some answers

Not the question I’m asking. Your response is typical load. I’m asking what is threshold that will cause the 5 led alarm?

[OzeLouie]

Originally Posted by cr180

Not the question I’m asking. Your response is typical load. I’m asking what is threshold that will cause the 5 led alarm?

The trip to fault amperage will vary but generally expect approx double normal run rate to cause a trip. If the compressor was mechanically locked it will fault rather quickly at about two + times normal run rate. To be more specific is difficult as other factors influence current rate.
Suggest your testing be done using a good battery supply as those AC / DC MDMs can have issues with their AC to DC inverting yet work ok on DC only.

[cr180]

Originally Posted by OzeLouie

The trip to fault amperage will vary but generally expect approx double normal run rate to cause a trip. If the compressor was mechanically locked it will fault rather quickly at about two + times normal run rate. To be more specific is difficult as other factors influence current rate.
Suggest your testing be done using a good battery supply as those AC / DC MDMs can have issues with their AC to DC inverting yet work ok on DC only.

Thanks

[Richard Kollmann]

The test normally recommended by experienced tech would not power AC convertor but power 12volt battery DC to BD35 module first eliminate dirty current from convertor. If aborted compressor start displays 5 or more flash codes when wired direct and module is not hot module needs to be tested as wired direct eliminated all other electrical and internal compressor problems.

Starting amperage on the BD35 compressor occurs quickly in less than one second followed by lower pump down amps for as much as ten minutes before stabilizing to normal running amps. Normal compressor speed in less than one second must exceed 1950 Rpm to satisfy safety electrical boot up or compressor sequence pulsus are stopped. Salespersons like to use this one time ten minute pump down as a poor performance argument claiming it occurs at every thermostat cycle.

[smcboating]

Thanks for all the information and helping figure this out. So today I first started out by using the AC converter with the thermostat bridged(t & c ). The fridge would attempt to start the compressor for only a split second. It was hard to see any voltage drop at that point because the duration was so short. Also would provide the 5 led flash

I then switched the power supply over to the DC (battery) as I described above. Like when using the AC converter it would at first on and it would be hard to get readings. But the startup attempts would last a little longer and then longer until the fridge compressor would run for 5 min or so. It would also be cooling at this time. It did this several times and I also noticed it was not giving the 5 led trouble code.

I then switched it back to the AC converter because I had a norcold fridge(0040) wanted to test and use the DC battery on. I save that for another thread.

The tundra went back to the situation I described above only starting for short durations and 5 led trouble light came back on.

I then again hooked the tundra back up to the DC (battery) and it went through the same process starting the compressor for short durations but each time getting longer. The fridge has not run for about 30 min. Durning that time I hooked the thermostat back up and it seems to be cycling on and off and again not 5 led trouble light

The last time I hooked the DC current up and it started running long enough to see the voltage drop and amp(assuming I did the amp test right) it did the following:

Before startup
13.12 volts
0 amps

Startup
Volts Dropped to 12.44
Amps around 3 hard to tell cause it dipped quick

Running for 20 min
Volts 12.26
Amps 2.4

I’m going to run the fridge for a while and see if it runs normal and holds temp.

Not sure what originally kicked it into the 5 led trouble code. It would seem the following up with trying to diagnose it while using the AC converter was not working as you guys suggested and suspected. I will monitor the fridge to see if it continues to cool. Hopefully this is a fix, although I feel like the controller might be compromised in some way. Time will tell. Thanks for all the suggestions. I will report back.

Sam

[OzeLouie]

Originally Posted by smcboating

Thanks for all the information and helping figure this out. So today I first started out by using the AC converter with the thermostat bridged(t & c ). The fridge would attempt to start the compressor for only a split second. It was hard to see any voltage drop at that point because the duration was so short. Also would provide the 5 led flash

I then switched the power supply over to the DC (battery) as I described above. Like when using the AC converter it would at first on and it would be hard to get readings. But the startup attempts would last a little longer and then longer until the fridge compressor would run for 5 min or so. It would also be cooling at this time. It did this several times and I also noticed it was not giving the 5 led trouble code.

I then switched it back to the AC converter because I had a norcold fridge(0040) wanted to test and use the DC battery on. I save that for another thread.

The tundra went back to the situation I described above only starting for short durations and 5 led trouble light came back on.

I then again hooked the tundra back up to the DC (battery) and it went through the same process starting the compressor for short durations but each time getting longer. The fridge has not run for about 30 min. Durning that time I hooked the thermostat back up and it seems to be cycling on and off and again not 5 led trouble light

The last time I hooked the DC current up and it started running long enough to see the voltage drop and amp(assuming I did the amp test right) it did the following:

Before startup
13.12 volts
0 amps

Startup
Volts Dropped to 12.44
Amps around 3 hard to tell cause it dipped quick

Running for 20 min
Volts 12.26
Amps 2.4

I’m going to run the fridge for a while and see if it runs normal and holds temp.

Not sure what originally kicked it into the 5 led trouble code. It would seem the following up with trying to diagnose it while using the AC converter was not working as you guys suggested and suspected. I will monitor the fridge to see if it continues to cool. Hopefully this is a fix, although I feel like the controller might be compromised in some way. Time will tell. Thanks for all the suggestions. I will report back.

Sam

Great report Sam, your meter readings provide valuable information and it can be said that the compressor itself is ok. From your readings I suspect that the compressor is running at minimum RPM and is stalling and defaulting as they will if RPM drops to approx 1800. This will cause shut down and indicate as 5 flashes on the LED fault light.
There can be several reasons for this but the most likely remedy is to simply increase the MDMs minimum RPM drive by adding resistance of 270 to 500 ohms to the thermostat circuit (or bypass wire) This will increase speed to avoid stalling.

[Richard Kollmann]

Smcboating, you confuse me when you say switched convertor off, the test I recommended required not having convertor in the circuit between battery and module. If Louie theory is correct LED code would be 4 flashes and not 5 flashes, but try it anyway.

Another point is in the voltage drop starting and running with proper charge and proper size wire voltage at battery and module will not drop on that BD35 compressor.

If you are sure you followed my instruction correctly and your address is in the US, I will loan a new test module to try but it must be returned with in 30 days as it is not for sale, you will pay only shipping both ways.

[smcboating]

Quick update,

I believe the fridge ran last night and looks to have kept things cold. Its cooler where I'm at in the Pacific North West so it probably didn't have to work to hard but I've checked it a few times today and the freezer is at 20 and the refer is at 33 degrees. It seems to be cycling on and off reasonably well. The voltage when the fan is off and compressor is not running is 12.6 volts when the unit cycles on with the fan its dropping to 12.05 volts.

Some parts of my last reply were a little confusing-I will go back and clean that up when I get a chance but to just quickly clarify for Richard, when I was alternating between the AC and DC power sources I was completely switching over and redoing all the connections. So when on DC the AC was completely removed and not in the circuit.

Ill be out of town the rest of the weekend so wont be around the unit to observe it. I will charge up the battery so I can pick up with this on Monday.

Richard thank you for your generous offer to loan me a known working MCM. I did end up buying a new one in a moment of fleeting frustration. I got a good deal on it and so It will be good to have a spare and/or something to test my current one against.

Quick question for Richard. If I'm understanding you, your saying there should be minimal voltage drop when the fan and compressor cycle on? Mine seems to be having some voltage drop by my readings.

Thanks again for all of your help and input. I now know a lot more about this fridge and hopefully can keep it running with this knowledge.

Thanks

Sam

[Richard Kollmann]

Yes, you have an electrical power problem before it reaches the Danfoss module.

[OzeLouie]

Quick question for Richard. If I'm understanding you, your saying there should be minimal voltage drop when the fan and compressor cycle on? Mine seems to be having some voltage drop by my readings.

Thanks again for all of your help and input. I now know a lot more about this fridge and hopefully can keep it running with this knowledge.

Thanks

[/QUOTE]

There will always be some voltage drop when the compressor starts but should not be excessive. Your reported drop of half a volt is not unusual nor excessive.

[Richard Kollmann]

If you see voltage drop at module on BD35 compressor start normally it is because wiring is too small size for its length. Number 10 to 8 gage is preferred up to 15 feet for Danfoss BD compressors, smaller sizes will defeat the low voltage battery protection.

i

[goboatingnow]

Can I ask what’s the purpose of the resistor in the thermostat switch circuit. Is there a chart of resistance and it’s function