Disabling under voltage protection on Danfoss BD35F

westernman

westernman

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I have a Danfoss BD35F compressor for the fridge. This works very well when on shore power or the engine is running. However, when on batteries, unless the batteries have been recently charged to pretty much 100%, the fridge does not stay cold. The compressor continually starts, immediately stops and after a few seconds starts again.

I suspect this is the voltage protection which is supposed to cut out when the battery voltage is below 10.7V. This is not the case, so it is possible that the wiring is not too good to the fridge, or that the voltage protection circuit is out of calibration.

In any case I would prefer that the fridge not stop working - I can switch it off manually if needed!

So is there any way to disable this under voltage protection circuit on the controller?
 
michaelchapman said:
I suspect this is the voltage protection which is supposed to cut out when the battery voltage is below 10.7V. This is not the case, so it is possible that the wiring is not too good to the fridge, or that the voltage protection circuit is out of calibration.
Click to expand...

Sounds like it has already been over-ridden to a higher voltage. There may be a resistor (R2) between terminals C and P.

See http://www.danfoss.com/businessarea...danfosscompressors/instructions_bd-series.htm but note that there are several controllers.

Also here, may be the wrong controller, but it will explain how it works: http://www.google.co.uk/url?sa=t&rc...i3lOxQJGjgVnc-ZWQ&sig2=jiwg1WEGg0sUkrOTLDcK3g
 
Last edited:
nigelmercier said:
Sounds like it has already been over-ridden to a higher voltage. There may be a resistor (R2) between terminals C and P.

See http://www.danfoss.com/businessarea...danfosscompressors/instructions_bd-series.htm but note that there are several controllers.

Also here, may be the wrong controller, but it will explain how it works: http://www.google.co.uk/url?sa=t&rc...i3lOxQJGjgVnc-ZWQ&sig2=jiwg1WEGg0sUkrOTLDcK3g
Click to expand...

There seem to be quite a few controllers - not sure exactly which one I have. But it looks like I should connect terminal C to P directly. Right?
 
FWIW: I wouldn't connect anything to anything until I was sure which module it was - have you seen the price of them ??

If it is one of the older controllers, then you can't do anything about the voltage cut out.

Note that it only takes a dip in voltage for a few milliseconds to trigger the protection - the actual voltage measured by a meter may well be OK.

Does the module have a diagnostic LED?

Lots of information on how to troubleshoot at Kollmann Marine: http://www.kollmann-marine.com/default.aspx

E.g.:

http://www.kollmann-marine.com/Refrigeration/index.php?topic=110.0
http://www.kollmann-marine.com/tip2.aspx

(But loads more around his site if you go digging for it)
 
I had exactly the same problem with my BD35F several years ago. The problem was the cables to the fridge, somewhere deep in the hidden areas of the boat there must have been a joint that had corroded. Measure the voltage at the BD35F terminals both when the compressor is off and when it tries to start and compare that with your battery voltage. You could also run a temporary feed from the batteries to the BD35F to check.

I know my existing batteries are failing, but even they will allow the BD35F to start with a battery voltage (under the BD35F load) of 11.8v.

I'm betting your problem is the cables. :)
 
Tony Cross said:
I had exactly the same problem with my BD35F several years ago. The problem was the cables to the fridge, somewhere deep in the hidden areas of the boat there must have been a joint that had corroded. Measure the voltage at the BD35F terminals both when the compressor is off and when it tries to start and compare that with your battery voltage. You could also run a temporary feed from the batteries to the BD35F to check.

I know my existing batteries are failing, but even they will allow the BD35F to start with a battery voltage (under the BD35F load) of 11.8v.

I'm betting your problem is the cables. :)
Click to expand...

I suspect the cables could be better - the size is not great and it is a fairly long run.

Also I think the compressor creates a very substantial current draw for a fraction of a second - but long enough to trigger the low voltage circuit.
 
The compressor draws 8A+ when it tries to start.

Worth checking for corroded fuses/fuse holders as well as cable joints, etc.
 
Inside the thermostat housing is a little yellow link which is there to protect single battery installations in recreational road vehicles - you wouldn't want to have an unstartable Motorhome in the Mohave desert, would you? However it cuts the refrigeration at far too high a voltage for marine, deep cycle large capacity applications. Remove this and reconnect the lead back on to the terminal and you will transform your fridge. Did mine three years ago and now it behaves perfectly. My neighbour did his last year and is running around telling everyone he knows. Best mod you can make to a waeco fridge. There is an info sheet provided by Danfoss but it can be misleading. Just take out the link which bring down the voltage to a level your system will cope with. I have that info sheet but in pdf form. If I can get it converted and downloaded here I will do.

Addendum: Seems that someone else has sent you that data sheet. What is confusing is that from the diagram "resistor 9" appears to be at the compressor end of the wiring. It is NOT. It is, in fact in the thermostat housing and actually IS the "little yellow link" of which I spoke earlier. Remove that and you have a proper marine fridge.
 
Last edited:
Steve C Cronin said:
Inside the thermostat housing is a little yellow link which is there to protect single battery installations in recreational road vehicles - you wouldn't want to have an unstartable Motorhome in the Mohave desert, would you? However it cuts the refrigeration at far too high a voltage for marine, deep cycle large capacity applications. Remove this and reconnect the lead back on to the terminal and you will transform your fridge. Did mine three years ago and now it behaves perfectly. My neighbour did his last year and is running around telling everyone he knows. Best mod you can make to a waeco fridge. There is an info sheet provided by Danfoss but it can be misleading. Just take out the link which bring down the voltage to a level your system will cope with. I have that info sheet but in pdf form. If I can get it converted and downloaded here I will do.

Addendum: Seems that someone else has sent you that data sheet. What is confusing is that from the diagram "resistor 9" appears to be at the compressor end of the wiring. It is NOT. It is, in fact in the thermostat housing and actually IS the "little yellow link" of which I spoke earlier. Remove that and you have a proper marine fridge.
Click to expand...

In the thermostat - as in the little wheel thing inside the fridge????
 
michaelchapman said:
I have a Danfoss BD35F compressor for the fridge. This works very well when on shore power or the engine is running. However, when on batteries, unless the batteries have been recently charged to pretty much 100%, the fridge does not stay cold. The compressor continually starts, immediately stops and after a few seconds starts again.

I suspect this is the voltage protection which is supposed to cut out when the battery voltage is below 10.7V. This is not the case, so it is possible that the wiring is not too good to the fridge, or that the voltage protection circuit is out of calibration.

In any case I would prefer that the fridge not stop working - I can switch it off manually if needed!

So is there any way to disable this under voltage protection circuit on the controller?
Click to expand...

I think that your best first step would be to measure the voltage at the fridge. Comparing that with battery voltage should give a fairly clear idea of whether it's a wiring problem. If it is, I would tackle that before adjusting the fridge.
 
Steve C Cronin said:
Inside the thermostat housing is a little yellow link which is there to protect single battery installations in recreational road vehicles - you wouldn't want to have an unstartable Motorhome in the Mohave desert, would you? However it cuts the refrigeration at far too high a voltage for marine, deep cycle large capacity applications. Remove this and reconnect the lead back on to the terminal and you will transform your fridge. Did mine three years ago and now it behaves perfectly. My neighbour did his last year and is running around telling everyone he knows. Best mod you can make to a waeco fridge. There is an info sheet provided by Danfoss but it can be misleading. Just take out the link which bring down the voltage to a level your system will cope with. I have that info sheet but in pdf form. If I can get it converted and downloaded here I will do.

Addendum: Seems that someone else has sent you that data sheet. What is confusing is that from the diagram "resistor 9" appears to be at the compressor end of the wiring. It is NOT. It is, in fact in the thermostat housing and actually IS the "little yellow link" of which I spoke earlier. Remove that and you have a proper marine fridge.
Click to expand...

Steve, I'm sorry to be so dense, and I'm excited by your explanation, but I can't match what you're saying to the diagram in the BD35F documentation. You talk about resistor 9 (the one that controls the battery protection settings) actually being inside the thermostat housing, yet the diagram shows resistor 9 being between the C and P terminals on the controller and there is no connection from the thermostat to the P terminal. So whatever resistor is in the thermostat cannot be resistor 9. I do have a resistor (1.5kohms) in the wire from the thermostat to the C terminal (resistor 8). This controls the speed of the motor, 1.5kohm giving the max 3,500rpm. If I take this resistor out the speed does drop (presumably to the 2,000rpm specified in the documentation).

It seems to me that to disable the battery protection altogether I need to connect terminals C and P together (ie. with a 0 ohm resistor). So what is this yellow tag/resistor that is in the thermostat actually for?

Thanks for your help. :)
 
michaelchapman said:
I suspect the cables could be better - the size is not great and it is a fairly long run.

Also I think the compressor creates a very substantial current draw for a fraction of a second - but long enough to trigger the low voltage circuit.
Click to expand...

I think that you would be better off in sorting out the cables before overiding protection devices imho.
 
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