Issues with Danfoss Compressor

[lawrence_craig]

Hi guys,

I have read a number of the Danfoss Troubleshooting posts and I think I know what to do but wanted some advice before I did it.

I have an issue where the compressor (BD35F) is failing to run in the night. You hear it try to start and it shuts down and continues this start/stop loop. There is voltage in the batteries (12.5, 12.6), the batteries are brand new and my freezer which also uses a similar compressor runs fine.

This only happens at night as when my solar panels are charging the batteries, there are no issues with it.

I suspect that I need to change the cable wiring as when the voltage is lower at night, the losses are too great to run the compressor.

Is there anything else I should be looking at or considering?

Thanks.

[lawrence_craig]

Originally Posted by lawrence_craig

Hi guys,

I have read a number of the Danfoss Troubleshooting posts and I think I know what to do but wanted some advice before I did it.

I have an issue where the compressor (BD35F) is failing to run in the night. You hear it try to start and it shuts down and continues this start/stop loop. There is voltage in the batteries (12.5, 12.6), the batteries are brand new and my freezer which also uses a similar compressor runs fine.

This only happens at night as when my solar panels are charging the batteries, there are no issues with it.

I suspect that I need to change the cable wiring as when the voltage is lower at night, the losses are too great to run the compressor.

Is there anything else I should be looking at or considering?

Thanks.

Unable to edit the above. I am having issues with it during the day now. I currently have 12.7V on the battery yet the compressor is definitely going off on low voltage (<10.7V) when it ties to run.

What I don't understand, which someone might be able to help me with, is that I didn't previously have this issue so what causes the degradation? Thanks in advanced.

[Pete7]

There is comparatively high start up load when the compressor tries to start. So guessing that either the connections have some corrosion or the wiring is too small for the wire run resulting in a voltage drop.

Had a similar problem on a previous boat, so when I wired up our conversion kit from cool box to fridge on the yacht, I used 4.5mm wire for both the pos and neg cables. This has worked well for the past 14 years.

Trace the wires from the fridge back to the switches and on to the bus bars or batteries to make sure they are substantial enough for all the loads that are being used, not just the fridge.

There is a calculator half way down this page which might be useful.

https://www.12voltplanet.co.uk/cable...selection.html

[barnab]

If you say "definitely going off on low voltage" - did you connect the troubleshooting LED to + and D/I or what makes you so sure?


To be sure I would connect the LED and also measure voltage at the compressor. Also measure current if you can.


A quick measure to reduce current is to reduce the RPMs by removing the resistor between the terminals C and T (see the documentation at https://assets.danfoss.com/documents/DOC147286416541/DOC147286416541.pdf )

[sailing_gal]

Is it possible that your batteries are losing some of their capacity? I had this happen to me, the voltage was plenty high, but as soon as there was a load, the voltage drops and won't run something like a fridge.

[stormalong]

Measure the voltage at the controller as it tries to start up. That is the test that will prove if it is the wiring.. If it is getting progressively worse it is probably a corroded connection somewhere. Just removing and re-attaching the wiring may be a temporary solution.

[psp2psp2]

I had issues with one of these units and on two occasions is turned out to be the “black box” controller, which is attached to the compressor via a multi-pin connector. If possible, find a refrigeration techie who has a used / spare one on the shelf, and you can swap it out for a test.

myageofsail.com

[cpasquin]

I had that problem on my Beneteau. So to test the connection, I simply connected the compressor directly to the battery bank with an on-line fuse. It solved the problem, and I kept it that way for many years after. I used the thermostat to shut it down.

[bradfordharley]

I have been doing lots of monitoring of our compressors as part of some electronics projects. You shouldn’t see a spike over 6 amps and run between 2 and 5 amps. That shouldn’t drain even very aged batteries. I would start by putting a voltmeter on the compressor and measure the startup voltage. Better multimeters can capture spikes. The led is also a great idea if you have one laying around.
All your symptoms would lead me to believe you have a corrosion issue.

[lawrence_craig]

Thanks for your replies so far.

Reading the voltage at the compressor, before start up it reads the same voltage as at the battery (12.6V). Then when the compressor tries to start, it dips below the 10.7V level before the compressor gets up to speed which I believe is the auto shut off.

[gonesail]

one of the problems I had was as simple as cutting an inch off the end of the 12v power wire and exposing fresh wire .. then securing back into the unit.

[CarinaPDX]

Drawing 6A from your battery shouldn't cause a 2V drop - if that is the case at the battery terminals your battery is toast. More likely there is resistance in the wiring from corrosion causing the voltage drop. Check connections first.

Greg

[hzcruiser]

As mentioned, your best bet is to check the wiring and connectors first.

[David B]

Originally Posted by lawrence_craig

Unable to edit the above. I am having issues with it during the day now. I currently have 12.7V on the battery yet the compressor is definitely going off on low voltage (<10.7V) when it ties to run.

What I don't understand, which someone might be able to help me with, is that I didn't previously have this issue so what causes the degradation? Thanks in advanced.

Unless the compressor is developing a fault, then it is voltage to the compressor. With the high in-rush current at start up, the voltage is dropping too low, and it gives up. Put a meter across the terminals right at the compressor (on the compressor terminals, not the connectors to the terminals) and you will know if this the problem or not. Not running, you should see 12.7V or so, then look at what happens when the compressor cuts in (or try's to). That will tell you the problem. Then look for connection issues - could be right where the wiring goes to the compressor - could be right back at the distribution.

Or - it could be your batteries starting to fail, and not handling the in-rush current (but then I would have thought you would notice this elsewhere, such as your fridge).

I hope that helps.

David

[Uncle Bob]

I am surprised that our galloping guru hasn't jumped in to offer words of wisdom, but my guess would be in the power supply camp, check all connections and cable condition/size.