Refrigerator issue Danfoss bd35

[OzeLouie]

Originally Posted by 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

Apologies GBN, I should have explained better. The resistor as described increases the compressor speed.
Without resistor the compressor runs at it's minimum 2000RPM and with the least start / run torque.
The problem is that the MDM can default shutting down if the compressor speed drops to approx 1850 RPM and such a drop can be caused by external factors such as a sudden voltage drop due to another item drawing battery supply (like a winch or another fridge etc) This is not uncommon and the reason why we recommend and fit a resistor to all systems so that the minimum RPM is 2500 supporting cleaner, more positive starts / running.

Suggesting this low RPM could be the problem here is because I have seen many 2000RPM systems with similar erratic symptoms albeit other issues also contribute, such as poor / low power supply etc. Another clue is the report that the fridge works best on DC supply (always test on DC) and it functioned ok in a cooler environment. (Easier work, less load)

Here are the resistor value / speed details:



Cheers, Louie

[goboatingnow]

Originally Posted by OzeLouie

Apologies GBN, I should have explained better. The resistor as described increases the compressor speed.

Without resistor the compressor runs at it's minimum 2000RPM and with the least start / run torque.

The problem is that the MDM can default shutting down if the compressor speed drops to approx 1850 RPM and such a drop can be caused by external factors such as a sudden voltage drop due to another item drawing battery supply (like a winch or another fridge etc) This is not uncommon and the reason why we recommend and fit a resistor to all systems so that the minimum RPM is 2500 supporting cleaner, more positive starts / running.



Suggesting this low RPM could be the problem here is because I have seen many 2000RPM systems with similar erratic symptoms albeit other issues also contribute, such as poor / low power supply etc. Another clue is the report that the fridge works best on DC supply (always test on DC) and it functioned ok in a cooler environment. (Easier work, less load)



Here are the resistor value / speed details:



Attachment 247869



Cheers, Louie

Great thanks

Can I vary the speed or is it just startup. Is there Any benefit to running the motor faster

[rgleason]

Great trouble shooting thread! Wonderful.

[cr180]

Originally Posted by Richard Kollmann

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

Agree, but Sam is powering in his garage with a battery directly connected. Would you agree his AC/DC converter suspect?

[OzeLouie]

Originally Posted by cr180

Agree, but Sam is powering in his garage with a battery directly connected. Would you agree his AC/DC converter suspect?

Yes, always best to operate from a good battery supply as those converters can be a problem. While on battery power, always monitor voltage at the MDMs terminals + & - with a good multi-meter as that will provide valuable diagnostic information.

Note: the 'no-load' voltage prior to start up or attempted start up, is meaningless but note that voltage for comparison. Watch for the inevitable voltage drop on start but at best it should not exceed one volt or drop below 11VDC.
Note also that when the MDM defaults into 'off mode' due to low voltage, it then needs to see approx 12.5VDC to 're-boot into run mode'

'Power supply issues are the greatest cause of problems with DC powered fridge systems, and not the fridge itself'

[Richard Kollmann]

Originally Posted by cr180

Agree, but Sam is powering in his garage with a battery directly connected. Would you agree his AC/DC converter suspect?

A follow up test was done without convertor in line and voltage to unit was readable indicating still power supply incorrect to module. Resetting compressor speed is an unwise Band-Aid like putting a coin under a screw in fuse.

[OzeLouie]

Originally Posted by Richard Kollmann

A follow up test was done without convertor in line and voltage to unit was readable indicating still power supply incorrect to module. Resetting compressor speed is an unwise Band-Aid like putting a coin under a screw in fuse.

Please explain!

[Richard Kollmann]

Originally Posted by OzeLouie

Please explain!

I did explain the facts reported in my posts 15, 22 and 27 by reporting starting voltage drop below 12.5 `indicates a low battery condition or less than normal wiring to module voltage drop. Technautic has a video on u tube explaining the need for correct size wiring on these small compressors. This is also why my instructions warn about volt meter test during start because they will not detect the most common low voltage short duration spike seen by module's boot up circuit. These control modules rely on battery and wire size and length to assist like a very large capacitor, this is why on a normal system start voltage is of so short a duration voltage is not in most cases readable. Volt meters are great for selling new module as occurred in this thread. Of the couple hundred modules I tested in the last thirty years and my guess was 60% were good, for the bad ones I sold over 200 new modules. I hope this answers your request for an explanation, I sometimes get behind on my email questions but any time you need me I will try to help.

[OzeLouie]

Post Resetting compressor speed is an unwise Band-Aid like putting a coin under a screw in fuse.

Originally Posted by OzeLouie

Please explain!

Richard, My request for an explanation (Please explain) of the incorrect statement as above, (bold) was because such a statement only serves to side-track what had been an informative thread. Your statement is wrong and misleading, so why do you bother?
I had hoped that you had simply made a mistake and my questioning would have given you an opportunity to correct.

[cr180]

[QUOTE=Richard Kollmann;3517632]I did explain the facts reported in my posts 15, 22 and 27 by reporting starting voltage drop below 12.5 `indicates a low battery condition or less than normal wiring to module voltage drop. Technautic has a video on u tube explaining the need for correct size wiring on these small compressors. This is also why my instructions warn about volt meter test during start because they will not detect the most common low voltage short duration spike seen by module's boot up circuit. These control modules rely on battery and wire size and length to assist like a very large capacitor, this is why on a normal system start voltage is of so short a duration voltage is not in most cases readable. Volt meters are great for selling new module as occurred in this thread. Of the couple hundred modules I tested in the last thirty years and my guess was 60% were good, for the bad ones I sold over 200 new modules. I hope this answers your request for an explanation, I sometimes get behind on my email questions but any time you need me I will try to help.[/QUOTE

Repect the 30 years experience, but must protest. So we have a machine with at most 6 amps dc full load current and you are saying that a battery in a garage directly connected is suspect? Can’t imagine even a 14 awg to a small battery wouldn’t start this machine. Understand motor is actually an ac motor and electronic controller converts dc input to ac output to motor. Your comment about a very large capacitor makes no sense.

[Dymaxion]

Can't imagine a 100Watt converter having any decent specs at all.... hook it up to a 1000watt pure sine wave one and try again. My Isotherm-65 has a BD-35 compressor but it runs via the (isotherm/Danfoss?) 12/24/120v supply directly. Normally running on 12v directly from house battery. Can hear fan start a moment prior to compressor kicking in, unless low battery voltage when fan only runs, no compressor start.

[gleason99]

Rewire with #8 AWG wire and I bet all your issues will go away!

[Richard Kollmann]

When Sam return and tries the higher speed test those interested will find the solution is either poor battery capacity or there was too much resistance in wires between battery and electronic control module. Also when thermostat energizes power to the pulse frequency generator for armature rotation, power to fan is interrupted for a short time until compressor reaches its control speed of 1950 Rpm. If problem was not power to unit five LED code makes makes sense. If it was voltage drop then there would be a single LED code every 4 seconds not five flashes. Yes these variable speed motors are AC rotation brushless. But so were the fixed speed BD2 through BD3 that run on around 7 volts AC by chopper transistors reversing the DC 2500 times per minutes. That completes Danfoss compressor 102. I will start 103 addressing the open question of why variable speed ask earlier in a new thread.

[Bowdrie]

What's with all this variable speed stuff, and resistors to "fool" the unit, not to mention the "converting this" and "inverting that", with pulses of light to reveal information.
It's all a fools errand.
Lets go back to those real, (1/2HP,) 12V machines made by EBM-Pabst in Germany in the '80s.
Yes, they really ran a hermetic compressor on DC.
Being clever, they used an external rotating brush holder, while the commutator was stationary, the wires connecting to terminals outside the hermetic dome.
An additional brush set ran on slip rings to power the field
They even had an additional winding that generated 16VDC, (why?,) to power the condenser fan.


All of the above, while true, I post in jest.
The units were hard on brushes, troublesome, ahead of their time really, but todays tech could probably make them work reliably.
Maybe it's better they're gone,,.

[OzeLouie]

Originally Posted by Bowdrie

What's with all this variable speed stuff, and resistors to "fool" the unit, not to mention the "converting this" and "inverting that", with pulses of light to reveal information.
It's all a fools errand.
Lets go back to those real, (1/2HP,) 12V machines made by EBM-Pabst in Germany in the '80s.
Yes, they really ran a hermetic compressor on DC.
Being clever, they used an external rotating brush holder, while the commutator was stationary, the wires connecting to terminals outside the hermetic dome.
An additional brush set ran on slip rings to power the field
They even had an additional winding that generated 16VDC, (why?,) to power the condenser fan.


All of the above, while true, I post in jest.
The units were hard on brushes, troublesome, ahead of their time really, but todays tech could probably make them work reliably.
Maybe it's better they're gone,,.

Good laugh Bowdrie. My Dad (and mentor laughed and cringed at reading this thread but said 'we all have to start somewhere!)

Pressed, he told me about having to refrigerate a beer fridge for a 3 mates mid summer trip in a VW Combi, Victoria to Darwin in late 1960's. (Well before my time!!) His quick solution was to place a dead 5cf freezer on its side located on the step up interior above the engine compartment, use 3/8 copper coil for evap and driven with a tiny Kelvinator SG open belt drive. He cut a slot hole in the upper engine compartment to run a belt from the Combi's alternator to the Compressor. He said it worked a treat except that the 'thermostat' (non existent) involved a passenger mate flicking the belt off!! The long run across the Barkley highway (42C) saw the 'thermostat' fail!!! and contents freeze /explode.

This was one of his 'Heath Robinson' early days creations which we get a laugh about today but as he said 'start somewhere, but start'

He went on to create, engineer, build, install and service well over 9000 refrigeration systems of various capacities operating businesses successfully Australia wide but the later three decades focused on DC systems to produce the worlds most advanced in their category to which he is most proud. Me too!