Melted Fuse Cover (Thetford N3000 fridge )

[Trekka]

While reversing out of a parking bay at a Motorway services I noticed my rear camera had stopped working.

After getting home I traced the issue to a melted fuse cover. The fuse had not blown, but the plastic cover had melted into the fuse holder. My suspicion is that the fuse covering has gradually melted, with the build up of plastic gradually reducing the fuse holder contact surface, increasing the contact resistance and therefore temperature. There is also some slight browning around the base of the right hand fuse contact which is just visible in the attached image.

The camera & fridge share a 20A fuse (“Fridge D+”) on the Sargent EM40 board for 12V use when driving.

The Thetford N3000 fridge is rated at 190W on 12V supply …. so I’d expect a draw of 15.83A.

Immediately after removing the melted fuse, I measured the draw from the fridge at 16.8A dropping to 16.5A after a few minutes. After cleaning the fuse holder of the melted plastic (not easy) , the fridge draw was down to nearer what I’d expect …. 16A dropping to 15.85A after a few minutes.

I’ve replaced the melted “MTA” 20A fuse with a “Zeeman” 20A fuse and will monitor it.

Wondering if anyone has had similar issues that may have been related to problems with fridges running from 12V supply, or issues with the EM40 board ?

Also are there differences in fuse brand quality that might make 1 cover more likely to melt than another ?

 

[Lenny HB]

Looks like a loose contact and it has been arcing, the fuse holder needs replacing or it will do it again.
Yes there is a bit difference in fuse quality, Littlefuse is a good brand but I don't think the quality of the fuse is a problem in this case.

 

[Trekka]

Thanks for the reply.

I’ve checked the back of the em40 unit and it looks in good order, so I suspect the poor contact is the fuse holder itself. Maybe the holder was damaged if the fuse was taken out for some reason.

I’ve also discussed it with Sargent, and the vehicle manufacturer who have kindly agreed to check it out and fix it if necessary (…. even though the warranty period has just ended).

 

[autorouter]

Spade terminals like the ones in the fuse holder have a maximum working current of around 16 amps. At that current, if there is the slightest resistance, heat will develop. You need to check that the fuse holder, and the connections to it underneath, are 100%.