Fitting a failsafe thermal cutout / fuse to a compressor

[Allubo]

Hi all,

I’ve got an old Prestcold, all restored, rewired and working as well as could be expected.
The fridge is running from solar in a dry insulated shed but I want to be belt and braces sure that it’s safe should the thermostat fail. (We has a total loss fire at work due to a beko fridge thermostat failing causing the compressor to work overtime until fire broke out).

My thoughts were to wire a thermal fuse in series from live and mount it onto the compressor, however I have a few stumbling thoughts...

Firstly, do I wire it into the main circuit effectively killing all power in the event of a blow, or inline with the relay start and run common, therefore just killing power to the compressor circuit?

Secondly, I can’t for the life of me figure how to mount such a fuse. There are no mount points of any description on top of the compressor, and so I’m stumped. I wondered about magnets but it seems a bit of a ****ty solution for a safety device.

And lastly, I’m unsure about normal operating temps and so what degree fuse to use?

I’ll attach some pics of my circuit and the compressor to see if you had any thoughts....

Thanks

Chris.
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[Brian_UK]

Have you looked at "Klixon" safety cutouts?

Various types and fixings available.

[Allubo]

I haven’t seen that brand but a quick google search yields similar results to what I’ve seen, I’m struggling with mounting holes on them...

[Allubo]

I have one of these which operates at 95°C, if I can find a way to mount it to the compressor could I wire it into the black common line to the compressor or is it best to kill all power? The relay is a supco generic start relay, will it continue to try and start and hence get warm if the black common to compressor is interrupted or not?

Thanks

Chris

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[redroge]

I can’t see why you need to go to these lengths as old fridges are more robust than modern fridges.
In the old days I never saw the likes of Prestcold or Frigidaire etc. catch fire.

[Allubo]

I can’t see why you need to go to these lengths as old fridges are more robust than modern fridges.
In the old days I never saw the likes of Prestcold or Frigidaire etc. catch fire.

Up until we had a fire, I’d never seen any fridge catch fire.... I’m fully aware that they are much better constructed than the modern equivalent but in all honesty for a few pounds and a few hours time I’d rather not have the worry of it happening again...

Don’t mean to be blunt but been there, done that....

One saving grace is that it is powered by solar, if the compressor was on constantly for a few hours I dare say my battery would be flat long before it had got hot enough to catch, I’m also pretty sure that aside from the very basic wiring insulation there isn’t an awful lot of combustible material present.

I did wonder about a lower temp cut off, say 50-60 degrees positioned on the back plate behind the compressor, this would obviously then trip if the ambient temp in the immediate area rose....

[Rob White]

.

A rough guide is if the body is too hot to touch.
For most people that is the 60 - 70Dec range so 150Dec
Is extreme.
That one would be for the discharge pipe of the compressor.
Get a lower temp one
https://www.ebay.co.uk/i/174352347932?chn=ps&norover=1&mkevt=1&mkrid=710-153316-527457-8&mkcid=2&itemid=174352347932&targetid=4585581967827491&device=t&mktype=&googleloc=&poi=&campaignid=398226960&mkgroupid=1311717606582975&rlsatarget=pla-4585581967827491&abcId=2145997&merchantid=87779&msclkid=2a4d0828f4c6157a983d577e93f9b068

And put it on the body behind the electric box but with good surface contract.

Rob

[Rob White]

.

Just another thought.

Check the amp rating and make sure they will take start-up amps

Rob

[Allubo]

.

A rough guide is if the body is too hot to touch.
For most people that is the 60 - 70Dec range so 150Dec
Is extreme.
That one would be for the discharge pipe of the compressor.
Get a lower temp one
https://www.ebay.co.uk/i/174352347932?chn=ps&norover=1&mkevt=1&mkrid=710-153316-527457-8&mkcid=2&itemid=174352347932&targetid=4585581967827491&device=t&mktype=&googleloc=&poi=&campaignid=398226960&mkgroupid=1311717606582975&rlsatarget=pla-4585581967827491&abcId=2145997&merchantid=87779&msclkid=2a4d0828f4c6157a983d577e93f9b068

And put it on the body behind the electric box but with good surface contract.

Rob

So you’re saying to mount to the black body panel that sits in front (behind if you were looking at the front of the fridge) of the compressor rather than the compressor itself?

Thanks

Chris

[Allubo]

Or is the best bet to simple wire in a thermal fuse as linked and simply tape it to the top of the compressor?

https://www.espares.co.uk/product/es644151/fridge-freezer-thermal-fuse

Thanks

Chris

[Rob White]

So you’re saying to mount to the black body panel that sits in front (behind if you were looking at the front of the fridge) of the compressor rather than the compressor itself?

Thanks

Chris

It needs to have a good surface contract with the comp body.
Not too high, maybe 1/3rd up from bottom and the bare electrical connections need protection.
So behind the box but touching the compressor body. Behind the box is purely for convenience and electrical protection.

Rob

.

[Allubo]

It needs to have a good surface contract with the comp body.
Not too high, maybe 1/3rd up from bottom and the bare electrical connections need protection.
So behind the box but touching the compressor body. Behind the box is purely for convenience and electrical protection.

Rob

.


Great, I know for sure that start up current will not be more that 2000w momentarily, the fridge is running through a 1000w inverter which has momentary surge of 2000w for starting motors etc so maximum amps it could possibly draw on start up will be around 9amps if I’m not mistaken...?

Yep I’ll sleeve or otherwise insulate whatever I put there....

Thanks

Chris

[Allubo]

Ok so I have a thermal fuse, from what I can tell it’s rated to blow at 72°C and is suitable for a continual load of 10amps upto 250v. So should be perfect. It’s from a beko defrost system and was obviously a readily available part.
Comes with an epoxy sealed plastic housing so shouldn’t require further insulating.

Think this will be ok? Installed first into the live cable before going anywhere further into the fridge cabling?

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Thanks

Chris

[Rob White]

Well it will definitely do the job.

Regards
Rob

[Allubo]

Thanks, I’ve pulled the cables through some thicker insulation, wired it in and tested operation, just got a 50mm wide silicone band on order to stretch round the compressor with the fuse on the inside to hold it in place.
The band obviously doesn’t conduct heat or electricity and is resistant to vibration by default.
Should hold the fuse snugly to the compressor...
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Chris

[Allubo]

Thanks, I’ve pulled the cables through some thicker insulation, wired it in and tested operation, just got a 50mm wide silicone band on order to stretch round the compressor with the fuse on the inside to hold it in place.
The band obviously doesn’t conduct heat or electricity and is resistant to vibration by default.
Should hold the fuse snugly to the compressor...
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Chris

[Rob White]

.

That looks a nice and tidy job.

Rob

.

[Allubo]

Thanks, all finished...

Thank you all for your help!

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