Refrigeration Riddle

[gbendaly]

Hi all,

as long as I am hooked on shorepower, my fridge compressor works fine and stops when the required cooling temperature is reached
when I unhook the shore power it works by very small intervals and trips with only the fan cooling the radiator.
I have a multistage smart sterling charger
as well as a 75Watts solar panel which keep my battery bank topped at all times (13.8+ Volts)
someone suggested to connect the compressor's wiring directly to the batteries without passing by the panel swich and fuse
is this logical ??
the size of the wiring is OK by waeco's standards and the length of wire does not exceed the recommended 3 meters
any advice would be welcome
cheers
Georges

[Richard Kollmann]

If you have a boat wiring problem and this is generally the cause of Danfoss BD compressor’s failure to start up and run, the solution is to bypass all of the present boats wiring. And yes the bypass wiring must be of correct polarity and protected with the recommended fuse or breaker size. Danfoss recommends their control module’s power wires bypass all branch circuits in a boat that can cause voltage surges. Compressor’s control module is designed to abort a compressor startup if it sees a low voltage spike. Over time in a marine environment when amperage serge tries to pass through a resistance connection such as an inexpensive circuit breaker, Switch, or a wire terminal end there will be a momentary (millisecond) voltage drop. If a fixed load of 7 amps were applied instead of the control module start load it could be seen with a voltmeter but the module reacts too quickly to detect this low voltage occurrence to see voltage changes.

George, your unit should have a troubleshooting LED installed on it, this would confirm low voltage caused by boats wiring or a low battery. The 3 meter length of wiring between module and main battery buss needs to be at least 10 gauge (6mm3) protected with a 15 amp fuse or breaker for 12 volt system and 7.5 amp if 24 volt battery system.

[Strygaldwir]

My wife always says "Check the connections". This is because often times she hears me say, "^&^&%$$% Connection" in regard to electrical gremlins. Make sure they are all clean and corrosion free. I'd also be concerned about the gauge of the wiring. Not just to the compressor itself, but to the breaker panel too. More emphasis on the size of the wire to the compressor. Most of the modern refrigeration units have under voltage protection. They will shut down when they detect a low voltage threshold. This keeps them from completely draining your batteries if nothing else.

Since your unit is working when connected, I'd think you reaching this low voltage threshold. After check all connections, you should measure how many volts are available at the compressor when you're both connected and disconnected from shore power. If there is significant difference, you will need to find out the source of the difference. Is it batteries? other drains? etc...

75 watts of solar is probably not enough to supply the complete load of your boat's systems. You'll typically see that output only at ideal conditions. Optimal sun, optimal battery charge state, etc. So, where is the 13.8 voltage being measured? Are there no other loads on the system?

[David M]

Check the voltage at the battery with a digital multimeter across the battery terminals with all chargers turned off and the refrigerator compressor motor running. Then check the voltage at the refrigerator while the refrigerator is running. Either the battery is not holding proper voltage or there is too great of a voltage drop between the battery and the refrigerator. Trust only what your multimeter tells you. I suspect a voltage drop.

If this is the case, then check all the terminals and wires for a voltage drop across them. You may need to clean up your terminals or re-crimp your connectors or to install larger diameter wire to reduce the voltage drop.

As has already been stated, 75 watts is pushing it for sustaining a refrigerator and other house loads, unless you are super careful with those loads.

[gbendaly]

Originally Posted by Richard Kollmann

If you have a boat wiring problem and this is generally the cause of Danfoss BD compressor’s failure to start up and run, the solution is to bypass all of the present boats wiring. And yes the bypass wiring must be of correct polarity and protected with the recommended fuse or breaker size. Danfoss recommends their control module’s power wires bypass all branch circuits in a boat that can cause voltage surges. Compressor’s control module is designed to abort a compressor startup if it sees a low voltage spike. Over time in a marine environment when amperage serge tries to pass through a resistance connection such as an inexpensive circuit breaker, Switch, or a wire terminal end there will be a momentary (millisecond) voltage drop. If a fixed load of 7 amps were applied instead of the control module start load it could be seen with a voltmeter but the module reacts too quickly to detect this low voltage occurrence to see voltage changes.

George, your unit should have a troubleshooting LED installed on it, this would confirm low voltage caused by boats wiring or a low battery. The 3 meter length of wiring between module and main battery buss needs to be at least 10 gauge (6mm3) protected with a 15 amp fuse or breaker for 12 volt system and 7.5 amp if 24 volt battery system.

thanks Richard for all the info
I will be on the boat this week end but I am sure there is no low voltage led any where
I will however bypass all connections as you recommendedusing a 6mm wire and 15 amps fuse and see how it goes .

[SV Demeter]

I had the same problem with my unit. When I put a meter at the compressor when it was running I was only getting 10.8 volts and the unit would run for a few seconds then shut down. I had plenty of juice at the panel switch. I would check the voltage drop and connections as others have suggested. Maybe you dont need to run a whole new wire? Has it always worked this way or is this something new?

[gbendaly]

Originally Posted by SV Escape Plan

I had the same problem with my unit. When I put a meter at the compressor when it was running I was only getting 10.8 volts and the unit would run for a few seconds then shuts down. I had plenty of juice at the panel switch. I would check the voltage drop and connections as others have suggested. Maybe you dont need to run a whole new wire? Has it always worked this way or is this something new?

this is exactly what I am experiencing it must be a voltage drop since I read 13.8V at the panel and the compressor runs for a second then shuts down.. I will check all the connections and wiring, instal a led as suggested by kollman and see how it goes , I will be checking the voltage at the compressor to make sure there is a drop ..and if needs be I will be bypassing the connections by a new 6mm2 wire and a a dedicated switch and fuse as recommended by danfos..I cannot tell if this is a new problem since I had the boat only for two years.. I noticed this problem from day one ..I guess my urge for ice cold beer must be the cause ..
cheers