SECOP/Danfoss Fridge Mod - Digital Thermostat

[bdosborn]

I ran across a wiring diagram to add some neat features to a Danfoss BD (now SECOP) compressor controller: digital thermostat, turbo mode, and an error LED. I'm in the process of installing a Truckfridge (rebadged Indel B) 12V refrigerator in our van so thought I would give it a try. Here's my fridge controller:




Here's the wiring diagram:




I also added a relay triggered by the fridge fan. It will control an auxiliary fan for fresh air into the fridge cabinet. Adding a resistor across C-P changes the fridge cut-out voltage. I didn't add one as all my 12V loads go through a Victron Battery Protect. I made triple sure to label all my wires and connectors, future me is going to need it!




I made a control panel for the thermostat and switches:




The turbo mode increased the compressor current draw from 2.5A to 4A and noticeably increased the cooling. I watched the thermostat temp go down by 0.1F every 10-20 seconds. ECO mode will be the normal run position, TURBO will be used to cool the fridge or warm beer down fast. The digital thermostat is MUCH more accurate than the mechanical one that comes with the fridge. The 12v fridge in our trailer runs warm during the day and freezes the lettuce at night. The digital thermostat keeps the fridge between the set-point and 2 degrees (both setable) no matter what the exterior temperature is. I did drill a hole in the fridge for the temperature sender but everything else can be returned to stock condition easily. I think the fridge will use less energy with the digital thermostat as it wont have a large temperature swing during a day or excessive setpoint overshoots.

After I found the wiring diagram I did some more Googling and discovered there are retrofit kits to add digital thermostats to Danfoss BD compressors. I've probably got $30 in parts for this mod, the retrofit kits go for $100's. Here's a manual for a kit that goes into detail on how to install a digital thermostat, basically everything I did with great info on temperature setpoints and resistor selection :
“Do It Yourself” Kit Assembly and Installation Manual
Hope somebody finds this interesting.
Bruce

[Greg M]

I, at least, found it interesting. Thanks for posting.

[bdosborn]

Thanks Greg! I cross posted this on the Transit Van forum and a couple of guys over there added a lot of info...

Ford Transit Van Forum Thread

Bruce

[bdosborn]

Then on mrcelsius I read about bimetallic thermometers used in our thermostats for rooms like vans. Did you know about this?

Yup, a bimetallic strip thermostat is what the fridge came with. They just aren't that accurate, which is why I replaced it with a digital version. It's much more accurate and I can control the temperature differential too. I have it set so that the compressor turns on at 40F and turns off at 38F. A bimetallic thermostat is about as accurate as a wet finger in the wind, the fridge temperature would vary from over 40F to below 32F. My vegetables froze at night and my beer got warm during the day.

Bruce