Fridge compressor - drawing current without running

[MattS]

I observed some strange behaviour from my Frigoboat compressor.

It was drawing 4-5A as if it were running, however when I checked the compressor itself nothing was running. Killing the 12v supply and then re-enabling seemed to snap it out of it for a while. It’s possible the low voltage cut out had kicked in, but I wouldn’t have expected it to continue drawing significant current in that scenario?

Anyone seen this before?

 

[dancrane]

Schrödinger's Fridge. Unless you open it, you don't know whether the light's burning away inside. And it comes on anyway when it's opened.





Sorry, I really can't explain it.

 

[rogerthebodger]

I have had a Fridge boat compressor for some time and not seen that al all

Could you have a fan running all the time I do have a fam but driven only when the compressor is running

 

[Metalicmike]

There must be a door switch for the light, maybe its stuck in the on position.

 

[Gustywinds]

There must be a door switch for the light, maybe its stuck in the on position.

Must be a hell of a light of its drawng 4-5 amps!

 

[bedouin]

A stalled compressor motor will continue to draw current and get hot without actually compressing anything - it sounds as if your compressor is having trouble starting.

I have seen this with a domestic fridge. I think there is a capacitor in there somewhere and I think that failing can cause this issue.

 

[Gustywinds]

A stalled compressor motor will continue to draw current and get hot without actually compressing anything - it sounds as if your compressor is having trouble starting.

I have seen this with a domestic fridge. I think there is a capacitor in there somewhere and I think that failing can cause this issue.

Was just about to write that - if it was an AC fridge it could be a starting capacitor that is faulty but this is DC. It may still have a starter circuit but on small DC motor it is usually just a resistor that is switched out once the motor is up to speed. Sticking relay maybe?

Or is it an AC fridge running from an inverter in which case, yes, capacitor?

 

[Metalicmike]

Must be a hell of a light of its drawng 4-5 amps!

True I was thinking that about the fan, the light is probably only 5w.Breaking it down we have a Thermostat basically cutting in and out the Fan and Motor. The Motor is DC so no capacitor so there must be a short in the thermostat.

 

[MattS]

It’s a 12V DC fridge, no light, just a compressor and small fan.

When it was drawing the current, I tried changing the thermostat and it didn’t seem to make any difference.

There was no evidence of anything actually running I.e. no sound or vibration on the compressor unit

It does feel like it was struggling to get started or something along those lines, but I’d expect it to give up if the voltage was too low to start it…?

 

[KompetentKrew]

I don't know if this suggestion is stupid or not, but could the motor's brushes be on the way out?

 

[garymalmgren]

no light, just a compressor and small fan.

Disconnect the fan and see what happens.
Disconnect the compressor and see what happens.
Then at least you will know what is pulling those amps.

Next is to figure out why.
Also, check your ampmeter.

gary

 

[bedouin]

It is probably worth starting the engine - or otherwise raising the supply voltage - and see if that helps - but it sounds like a compressor problem so you'll probably need an engineer in to fix/replace

 

[B27]

Some of these 'DC' fridges are something a bit like a 3-phase AC motor driven by a bunch of electronics.
No brushes, just 3 connections going to the sealed motor/compressor unit.
Could be the electronics failed, a bad connection, or the compressor jammed.

I assume the boat hasn't been laid on its side, fridges don't like that!

 

[Metalicmike]

If the fan is cutting in and out then the thermostat is functioning so how can the problem be in the fan or compressor if the supply is cut by the thermostat. So if you are drawing 4 amps with the thermostat de powering the compressor and fan. Then the fault has to be in either the Thermostat or wiring to the Thermostat.

 

[Boater Sam]

If its a Danfoss 12v compressor there are no brushes! There is an electronic module that runs the compressor by sequentially switching, I suspect that is what is drawing the current but not running the motor.

 

[B27]

On my fridge, the fan is not directly controlled by the thermostat which switches the compressor on, it keeps running after the compressor stops.

 

[bedouin]

Anything drawing 4-5A will be getting noticeably warm. If you can try feeling the various components and seeing what is the warmest. My guess is it will be the body of the compressor - indicating that power is being provided to the compressor but it is not operating

 

[Metalicmike]

Some of these 'DC' fridges are something a bit like a 3-phase AC motor driven by a bunch of electronics.
No brushes, just 3 connections going to the sealed motor/compressor unit.
Could be the electronics failed, a bad connection, or the compressor jammed.

I assume the boat hasn't been laid on its side, fridges don't like that!

The three wires are 3phase inductors supplied by a controller that converts 12v dc into an 3 phase AC wave form. This type of Fridge is basically computerized and the said failure would probably mean either a circuit board repair or replacement.

 

[MattS]

It is probably worth starting the engine - or otherwise raising the supply voltage - and see if that helps

I think this does help, although I had to turn the fridge off at the power supply for it to “reset itself”

I assume the boat hasn't been laid on its side, fridges don't like that!

Only through the usual heeling under sail! Although I do always wonder how much heeling these units can cope with whilst running…

If the fan is cutting in and out then the thermostat is functioning so how can the problem be in the fan or compressor if the supply is cut by the thermostat. So if you are drawing 4 amps with the thermostat de powering the compressor and fan. Then the fault has to be in either the Thermostat or wiring to the Thermostat.

The thermostat is a simple on/off mechanism as far as I’m aware, and I think is functioning normally most of the time. I did play with it and it didn’t seem to click off, so I suspect it was warm enough to be on even at the highest temp. Even with the thermostat clicked on, the fridge was not running properly.

On my fridge, the fan is not directly controlled by the thermostat which switches the compressor on, it keeps running after the compressor stops.

The fan appears to run in step with the compressor on this unit, I don’t think it runs separately.

 

[Boater Sam]

Either low battery or too thin cable if running the engine i.e. charging, gets it going. You didn't say this before!