Domestic Fridge Relay

[Dave Scadding]

Good morning all,
I recently changed the fridge relay in the engine compartment as the old one over heated. It was a 30amp so I replaced it with a 40amp thinking it would solve the problem. The fridge works perfectly on 12v as it should however the replacement relay is still getting very hot and if left is likely to burn out as well? Any ideas why? And is 40amp still not big enough. The supply fuse is 30amp.

 

[Spriddler]

the replacement relay is still getting very hot and if left is likely to burn out as well? Any ideas why? And is 40amp still not big enough. The supply fuse is 30amp.

Are you sure that is the fridge relay and not the split charge one?
The 12v fridge heater element (usually circa 180 watts) should only draw about 15 amps max.
The fridge heater element supply should be fused at an appropriate rating to protect its wiring.

 

[Itsmcb]

Possibly a dodgy connection getting hot at the base of the relay? Maybe some contact cleaner would help.

 

[Dave Scadding]

Are you sure that is the fridge relay and not the split charge one?
The 12v fridge heater element (usually circa 180 watts) should only draw about 15 amps max.
The fridge heater supply should be fused at an appropriate rating to protect its wiring.

Thanks, yes definitely fridge as won’t work on 12v if relay removed.

 

[Dave Scadding]

Possibly a dodgy connection getting hot at the base of the relay? Maybe some contact cleaner would help.

Thanks, I’ll try that now and see.

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[Dave Scadding]

Cleaned terminals but they weren’t dirty anyway, still getting hot even after only 5 mins of engine run. It’s terminal 87 which is getting hot which I believe is the supply to the fridge.

 

[Richard n Ann]

Cleaned terminals but they weren’t dirty anyway, still getting hot even after only 5 mins of engine run. It’s terminal 87 which is getting hot which I believe is the supply to the fridge.

Are the spade terminals tight? They need to be

 

[Dave Scadding]

Are the spade terminals tight? They need to be

I’ll go and check.

 

[Dave Scadding]

Yep good snug fit when relay pushed in.

 

[Richard n Ann]

Yep good snug fit when relay pushed in.

Oh it's pushed into a socket then? Sounds like terminal 87 could be loose and the others are tight. When it's been hot previously the socket female spade can get annealed.
Next thing I'd do is change the socket for what they cost.

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[Spriddler]

I'm guessing that if the switching coil supply to 85 and 86 is fluctuating/intermittent due to a poor/corroded connection (anywhere in its circuit) it could allow the fridge main element power contact on 87 to tremble on/off causing arcing at 87 and heating it up. You could check by removing 85 or 86 and putting a meter between the removed one and its contact on the relay to check that the 12v switching supply is constant.

Here's mine - (a 4 pin one from Halfords):

 

[Richard n Ann]

I think technically it's a voltage drop across the spade that causes an induced wattage. P=VxI

So a 3v drop at 15amps = 45 Watts.. the spade is a 45w heater

 

[Dave Scadding]

Thanks for taking the time to reply, I don’t think it’s a connection problem. I’m drawn to the relay size. Unfortunately I don’t have an original relay to compare as the one I’m replacing was a 5 pin which was incorrect as only 4 cables going to connector. 2 relatively small which I think go to the coil side of the relay and 2 larger cables which are the supply in and out. I really need to know what amp the correct relay should be. Unfortunately the wiring diagram I have doesn’t state the size?

 

[Richard n Ann]

Thanks for taking the time to reply, I don’t think it’s a connection problem. I’m drawn to the relay size. Unfortunately I don’t have an original relay to compare as the one I’m replacing was a 5 pin which was incorrect as only 4 cables going to connector. 2 relatively small which I think go to the coil side of the relay and 2 larger cables which are the supply in and out. I really need to know what amp the correct relay should be. Unfortunately the wiring diagram I have doesn’t state the size?

You should be able to use a 5 pin one, it's just that the normally closed contact isn't used (it's for switching something on when the relay is de-energised)

 

[Richard n Ann]

87a not used...

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[Dave Scadding]

I'm guessing that if the switching supply to 85 and 86 is fluctuating/intermittent due to a poor/corroded connection (anywhere in its circuit) it could allow the fridge main element power contact on 87 to tremble on/off causing arcing at 87 and heating it up. You could check by removing 85 or 86 and putting a meter between the removed one and its contact on the relay to check that the 12v switching supply is constant.

Here's mine:

View attachment 662970

Thanks, my relay is in the engine compartment. Terminals 85 & 86 are small cables and terminals 87&30 are considerably larger.

 

[Spriddler]

Thanks, my relay is in the engine compartment. Terminals 85 & 86 are small cables and terminals 87&30 are considerably larger.

That's how it should be as the fridge element (switched across contacts 87 and 30) will be drawing more current than the switching coil (contacts 85 and 86).

 

[Dave Scadding]

Thank you Richard n Ann and Spriddler, I think I need to get a specialist to sort, I have a lack of testing gear. Thanks for taking the time to provide valuable information and guidance.

 

[pete4x4]

In a lot of motorhomes the split charge relay is also the fridge relay, is there another relay for the split charge?
I say this as 30A fuse is quite large for a fridge supply but not if its combined.
Is your leisure battery ok, ie holding charge?

 

[Dave Scadding]

Yeh I think the split charge is separate and have no issues with leisure battery. In the photo the blank space is the relay I have removed (fridge).

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[Richard n Ann]

That looks suspiciously like it's got too hot and it's pin 87

Anyway I'm out.. Good luck

 

[Dave Scadding]

That looks suspiciously like it's got too hot and it's pin 87

View attachment 662989

Anyway I'm out.. Good luck

Thanks.

 

[pete4x4]

Yes I agree that socket needs replacing or the terminal does

 

[jockaneezer]

Richard n Ann, that's most likely the problem, Dave Scadding have you got a spare Lucar spade connector (see pic) that you could try in slot 87 to see what the fit is like compared to the others, plugging in the relay won't tell you if one of the terminals is too loose ? Sometimes you can get in with a small screwdriver and cinch the female terminal up a bit to make better contact ? I've had those connections burn out on my fridge supply too.