Danfoss Secop bd35 Scania 24v addon red thermistor electric controller for fridge drawer - want 12V operation

Thread Starter

12star

Joined Aug 29, 2019
5
Hi All,

I have a Scania drawer fridge that has the Secop bd35 compressor and 101N210 controller - this bit works on 12 & 24v (checked by connecting C & T) it runs and gets cold.
It has a red electronic controller that plugs into the Secop controller terminals and is used for On/Off temp control & tilt control, but Only works on 24v and not 12v (not designed for 12V?)
The red controller appears similar to the Isotherm red controller but appears more basic - link Red Electronic Control Unit for refrigerator SCANIA 1894994, 2409029 - P.U.H. HESTA

the top 4 terminals go to the thermistor & on/off switch - this controls the IRF2807 and allows the earth side to connect
bottom 2 terminals go to the tilt sensor - open/closed circuit
Fan=fan
- & + 24v only - what I would like is to know if the circuit can be changed to allow 12v as well - as it is a drawer fridge it would allow me to connect to my car or use as a camping fridge & control it from inside the fridge drawer (ie front), instead of having to buy a temp controller of ebay & mounting (on back) of fridge where accessibility is poor & wiring in the thermistor to it.

I don't know too much about circuits

let me know if better pics/info are needed & thanks in advance

original module, rear spade terminals push onto the Secop controller.
View attachment 231533
front
note the 5 female pinout bottom rh is not used - suspect for programming?
View attachment 231534

Back
View attachment 231536
 

debe

Joined Sep 21, 2010
1,251
Personaly i would not bother spending the time required to alter that unit. Its far easier & cheaper to purchase a ready made Electronic Thermostat from Ebay. Theres plenty of small units avalable. Pick one then go from there. Most of the units use a 10K ohm NTC thermistor as a sensor, so you probably can use the one already fitted.
 

Thread Starter

12star

Joined Aug 29, 2019
5
I thought as much thanks - done 12v sct-1000, and yes will just wire into the thermistor already in place
For 'science' what would need to be done to alter the circuit board?
 

Dodgydave

Joined Jun 22, 2012
10,060
The motor will probably only run on 24V, also the fan too. The micro will work on 5V so looks like a 5V regulator on the board and two zeners to switch the transistors on..
 
Last edited:

Thread Starter

12star

Joined Aug 29, 2019
5
The motor will probably only run on 24V, also the fan too. The micro will work on 5V so looks like a 5V regulator on the board and two zeners to switch the transistors on..
The fridge will work on both 24 & 12V when connected direct to the Secop controller, fan is 12v (feed from Secop controller) - problem is then either to use a thermostat or electronic controller with thermistor (fairly sure this is 5v controlled - but to test I just short C & T terminals)
Secop controller will turn on via C & T terminals if between 0-1600 ohms - various speeds

The Red electronic thermistor controller only works if connected via 24v - it turns on the IRF2807 Mosfet to earth (so completes the earth side of the Secop controller)
when connected to 12v it won't turn on the mosfet to earth out the circuit - controlled via 10k thermistor and 10k pot in series

there is a blue box that looks like a variable pot (set with white paint) - a feed comes from the blue pot to pin 4 then tru the thermistor then back out pin 3 which goes to the switch side of the mosfet & to what appears to be a sml regulator? or switch? (I'll see if I can get an id number off it...)

would this be the issue?
24v circuit design so values on some of the circuit board need doubling to run at 12v - (at the blue box?) - could it be that simple?

the design I'm guessing allows temp & speed setting via the thermistor & pot - so if these are out of range (too high) then won't turn on...
 

Thread Starter

12star

Joined Aug 29, 2019
5
So while waiting for my temp controller from Ebay, I ended up shorting out D & S on the Mosfet - seems to work on 12V with Thermistor & On/Off control sw via the original switching if I do that.
I wired in a sml micro switch & thin control wire which open/closes the short circuit (so could potentially use both 12V & 24V)
Basically shorting out the Earth side out connecting the main -12v input from the control unit to the Danfoss control unit.
Any thoughts on this?
 
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