Dometic Fridge trying to kill me!

[veletron]

Hi

 

My dometic 9 series RML 9335 fridge stopped working on 12V, and then started making a smell before blowing its 20A 12V fuse. I have only just had time to investigate the issue over christmas.

 

The vent outside is tiny so the fridge had to come out inside the van. The issue was immediately evident with a charred control panel which had actually got so hot as to sever the 12V positive wire at the top.

 

Not hugely amused by this - its a safety hazard especially with gas about the place. Will raise it with Dometic as such, but I suspect I am going to end up buying a new control panel @ £loads.

 

Nowt wrong with the 12V element - it measures 0.9Ohms which gives the expected 170W @ 12V - the issue is down to poor engineering, pure and simple - the electrics are not built to cope with the load (I am an electronics engineer by trade).

 

https://photos.veletron.com/_data/i/upload/2017/12/27/20171227173339-79753229-me.jpg

 

Pics: https://photos.veletron.com/index.php?/category/371

 

Nigel

[Brian Kirby]

But, step back a moment, Nigel. :-) How old is the van? How many hours would you estimate your fridge has been running on 12V during its life?

 

I assume it must have been on 12V while you were driving, so what could have caused so high a current to flow if the element is within spec? In essence it is a very simple device with a fixed resistance heating element that should be self-limiting in terns of the current flowing - albeit the voltage wobbles around a bit over time. What could have caused so much heat locally to that terminal?

 

Could the terminal clamp have been left loose when the supply cable was installed, to cause arcing and heat? Any other possible explanations that might suddenly arise?

 

After all, there must be thousands of these fridges in use around Europe, and one would have thought that by now there would have been a safety recall were the engineering fundamentally flawed. I'm not in any way seeking to defend Dometic or their product, and have no interest in Dometic, but it seems odd that the thing would suddenly fail in that way were the design fundamentally faulty.

 

It looks, to my inexpert eye, as though the heat was generated in the area of the fried insulation, as the rest seems in generally good condition. I assume the adjoining brown cable is the return and, when the insulations melted there was a local short that blew the fuse.

 

I think you are absolutely right to contact Dometic first as there appears to be, as you say, potential for a serious fire that, while the van was being driven, could have spread before being spotted. I'd also think it worthwhile pursuing the warranty issue as, even if the warranty has expired, if the fault is a manufacturing defect, it is a potentially serious one for which they should take at the very least some responsibility. If there is a latent manufacturing defect I would expect them to want one of their engineers to inspect and, if possible, diagnose the cause. You had a problem earlier with the door which I think you took to someone local. Is that source still available and do they have a trained Dometic fridge engineer at their disposal?

[veletron]

Hi

 

The heat has been generated around the white (-ve) connector. This is a dometic-installed cable, the converter plugs into the the fridge further down the cable. It could well be that this was always a poor connection. As an electronics engineer myself, I would not have designed it like this... High current connections to a PCBA - especially those that are sustained are always better done with a soldered on stud, ring term and AV washer.

 

Having removed the offending cables, the upper spade connector fell out of the PCB, and the tracking on the PCB is in no way man enough to cope with the constant 15-17A current. The tracking has burnt through. I have no reason to suspect that the current ever went higher than normal except when, due to the tracking failure, and resulting melted plastic, the +ve and -ve 12V connectors came together and blew the 20A fuse in the main fuse board.

 

The tracking leads to a relay such that the 12V element only runs when in motion and when the fridge is also 'ON'.

 

Yes, I use my van alot, 21K miles in 2.5years, most of which is touring so the fridge will have been 'ON'. That, in no way excuses this failure mode, I expect consumables to go (eg the 12V and 240V elements, gas burner etc), I do not expect the control board to melt its-self though, not in 20K miles, not in 100K , not in 200K miles!

 

Given my usage, and the age of the van, I would expect that others have perhaps not even encountered this as yet, and that it might be a problem waiting to hit other folks.

 

I have contacted Dometic, asking that they cover the cost of the repair, included photos and commented that in my opinion as an electronics engineer with some 25 years experience, this occurred due to poor design.

 

As for the door, neither Dometic , nor their local agent was interested in fixing this, so I fixed it myself. The how-to article was published in last months MMM!

 

I am away in the van for NY, so needed a fix ASAP. I have added a voltage sensitive relay, and bypassed the control board for 12V operation. Hopefully I will get a response from Dometic in the new year.

 

Kind Regards

 

Nigel

 

 

[Brian Kirby]

Dometic's handbook for the fridge in ours is unclear as to the duration of their warranty, only referring to the "legal warranty period", which it then fails to define. Helpful - not!

 

However, don't forget your supplying dealer also has some responsibility under consumer legislation. I think Scotland is a little different on this, but the broad principle is, I believe, the same - that the seller continues to be legally liable for up to six years, but the extent of his liability diminishes with time, and also depending on how long it was reasonable to expect the item to have lasted given normal use. The seller cannot rely on the manufacturer's warranty to limit his legal liabilities, irrespective of the duration of the manufacturer's warranty. If Dometic won't play ball it may be worth talking to Trading Standards or Citizen's Advice to see where you might stand.

[veletron]

Cheers, will do. It came from Highbridge in Somerset, and I suspect they will get out of any liability by demanding that the vehicle is delivered to them for inspection! Worth a try though.

 

Have also been in touch with the converter, Campereve (Rapido).

 

Made the fridge safe now, and put it all back together. Still have 3-way via an additional relay I have added, that will drive the 12V element directly No thermostatic control, but my old van simply ran the 12V element continuously so I doubt doing the same in this will do any harm - fine as a temporary measure anyway.

 

While I was in there I serviced the flue, burner and cleaned the 'orafice'. Just a dunking for an hour in some isoprop. Quite a few midges met their maker around the flue area!

 

Nigel

[Alanb]

Nigel,

 

Thanks for your interesting posts, from which I surmise that the connectors in question are of the multipole 0.25" blade variety. These connectors are similar to "Lucar" connectors which are rated at 15A, but this figure seems to be stretched in some applications. As you will realise, at 14V your fridge element will take over 15.5A.

 

I recently researched the current rating of the Mate n Lock connector range which are used on my PVC, including the fridge connection, because I was sceptical about their rating. (Not the same connector but similar loading.) The interesting point is that at the upper end of the current range, there are requirements for PCB track size as well as minimum conductor area and length, this being necessary to conduct heat away from the connector.

 

As regards the 0.25" blade connectors I have experienced several failures in the past. These include thermal failure when used on a domestic immersion heater at less than 13A, cracking and consequent failure of a female receptacle, and inadequate contact pressure which caused the connection to the vehicle battery on my PVC to separate at the fuse. The incident with the cracked connector was I believe due to corrosion cracking, and plunged me into darkness while driving on a twisty country road.

 

Alan

 

 

[veletron]

Hi

 

Yep, we are over 15A here - especially when the leisure and vehicle batteries near full charge and no longer load the alternator, which will then generate 14.4V potentially giving a good, sustained 18A through those 0.25" spade connectors. Not surprising they eventually failed in this way. I suspect they loosened over time creating a higher resistance and therefore more heat, self-perpetuating towards eventual failure.

 

As mentioned above, the connection should be via M5 stud's and ring terms, together with PCB tracking that can cope with the load.

 

Nothing back from Dometic, The converter or my dealer --> will give them to middle of next week to come up with some kind of response before contacting the likes of the NCC, and crafting a warning for the motorhome press.

 

My hack worked just fine over new year - reality is an external relay is the exact way that pre 2015 dometic fridges handled the 12V element switching anyway.

 

Nigel