Propex burn out

[CovKid]

Please do. I need an audience and others prodding about.

Thin black wire connected to nut goes to relay. Burnt one to right of that is the one that goes back to thermostat. I'm assuming it must be the earth given that theres a red that also goes to thermostat (intact). If (and only summising) the earth for unit was insufficient, would this cause the wire it to heat up and burn out? If so, perhaps all thats needed is to replace it and ensure earth is good. Nothing else appears damaged or burnt - only that one wire.

[CovKid]

Another view. The copper wire sticking up on the extreme right is the burnt line and normally terminates under the nut seen in photo.

[CJH]

Localised heating due to broken strands (and therefore too high a current in the remaining strand(s))? How far along was the sheath melted?

[CovKid]

Well the cable from thermostat to heater has a four-prong connector about halfway. I'd say the damage was limited to heater to plug section (all of it) but little or no evidence of heat damage after the plug to thermostat. Its somewhat tempting to just fit a completely new cable to replace damaged one, bypassing plug altogether, seal the heater up and simply put it all back, ensuring there a good connection to chassis.

Clearly I'll need to inspect all these four wires beneath the sheath (red, black, orange, white) to check that the heat build up hasn't melted those too.

It could be that this cable was already breaking down or coming loose from nut connection - that might do it but you'd think damage would be greater there if that were the case.

[Oldiebut goodie]

First thoughts are that it is a switched live from the thermostat, evidenced by the red to it, so the black wire is a live not an earth.
I'll search the net later for a decent wiring diagram as we really need one here. Which model is it?

[CovKid]

1600 compact (later type with cool-down cycle)

Its definately black wire in this diagram:



I would say that the nut on the component (spark generator) is a general internal earthing point - not a switched live. Red goes straight to relay - nowhere else.

Given that the damage is limited to length up to four-prong plug and not beyond (or anywhere else), could it be that plug connection was weak/faulty, causing this whole length to heat up? After all, the ground wire has to be at least as good as the 12v positive connection.

Would it not make better sense to just run cable from nut on spark generator direct to chassis closeby?

[Oldiebut goodie]

All I can find is this post on the Brickyard:
http://www.brick-yard.co.uk/forum/prope ... 73141.html
From that the black is an definitely an earth.
The current draw on these heaters isn't very high so it must be a serious short to melt the insulation but I can't see how without blowing the fuse (5Amp only) -what fuse was in there?

[CovKid]

Not convinced it was a short. Mostly because the rest of that line was fine. No sign of trouble beyond the four-prong plug. All I can think is it built up high resistance in that one (first) section due to bad connection - probably at plug itself. Anyway, tomorrow I'll refit with better more substantial earth, run and test properly, checking for heat in the cable.

Fuse was 7.5amp. Didn't blow but warmed up by look of it. I guess the heater itself intervened and switched burner/ignitor off before fuse actually went, which is no bad thing. They're quite sensitive things.

Its not beyond the realms of possibility I suppose, for a bad section of wire to heat up before fuse actually blows. If heater intervened before fuse. wire would cool down (without actually creating a short), and fan cool-down cycle continued as normal it was then drawing very little.

Its the only theory I have so far. I just have a feeling it will be fine with new cable and sound connections. Will fit a 5amp fuse and see how we go.

E D I T: What I don't understand is why Propex didn't earth the case itself - which after all is in direct contact with the bodywork and screwed down. There appears to be an unused post (see pic below). It serves no other purpose. Strange.

Instead they chose to run the earth all the way up to the thermostat and ground from there. Perhaps this is because they get fitted in caravans and boats where there might not be a chassis to fix it to? When I run new cable I'll ground case on the way - makes more sense as a good ground is absolutely assured then.

I think Ghost mentioned in another thread that he grounded his out close to the heater too. Incidentally, stumbled across this for those that find the thermostat range annoying: http://www.thesamba.com/vw/forum/viewto ... ?p=6633445" onclick="window.open(this.href);return false;

[Oldiebut goodie]

It does make sense to ground the case and other grounds via that post. I just can't see how just that section of wire has fried up to the connector only other than as mentioned above most of the strands had broken but the current is quite low which makes it difficult to fathom out. I would put a lower rated fuse in on the next test after the wire replacement. Was the 7.5A fuse put in by you or was it already there? Just thinking of the possibility of someone found that the 5A was blowing previously due to an undiagnosed fault.
What a conundrum!

[CovKid]

No, it was me. 7.5 was lowest I had. I recently fitted new cupboard in the van and had to rewire everything. Ran fine for weeks until I had this. Does seem odd that it appears to have a grounding post thats unused.

Anyway I've cleaned that post and will fit a short length with ring connectors each end, from nut to post, plus an extra to chassis to make sure. That way I can forget original earth and put everything back. Definately a 5amp fuse though - if theres a prob it should blow this time. May take a couple of days though - constant rain predicted tomorrow.

I really miss the heater. Not been anywhere for a week and its been a bit grim seeing ice all over it first thing.

Still, I can fit the remote while I'm at it which will cheer me up no end in the mornings.

Will take more pics of Propex internals though. Be useful for downloads section I'm sure.

[Oldiebut goodie]

There seems to be a dire shortage of any proper info on the Propex internals - they do seem to be quite simple which is maybe why there isn't. Everyone appears to be searching for more info.
The newer models do have more electronics though. A bit like the diesel heaters in that they have evolved from clockwork timers for the glow plug to multi=talented electronics that are far too complicated for easy repair. That's the way of things now though unfortunately.

[CovKid]

Agree. Theres nowt really. I think for the vast majority of owners any maintenance (other than blowing unit free of dust) is best left to Protex or at least someone who knows what they're doing. In this instance it wasn't overly complex to fix but even if a fault developed on a control board, its probably simpler to just fit a new board, even if soldering isn't overly difficult to do, or just get Protex to check it. They are very reliable units to be fair, and not a lot to go wrong (something Propex mention).

Lets also not forget that repair work is important to their business model, and what we don't want is people bypassing safety features trying to get a faulty one running. Major work should be carried out by someone qualified to do so.

The cases can rust out over time through neglect and I imagine their lifespan on a boat isn't quite so long given the moisture around. Keeping on top of corrosion is a good idea and you can open the case to do that if needed. However there are quite a few with compact 1600 models so additional photos wouldn't go amiss.

My separate spark controller box is different from others I've seen. Most seem to have LED indicators but mine is just a sealed plain box. Whether that was due to design or because mine originated from something commercial (Royal Mail vans?) I don't know. Like my 85 Caravelle - it may well be on a changeover year.

I tend to agree with Ghost that their sensitivity isn't great although who wants a heater that keeps going on and off every five minutes - it would soon run the leisure down and not be as efficient to run. In the end, it does what it does. The link I gave about replacing a resistor to move the controllable range was interesting though.

Finally, conversion to a timer and/or remote is definately dooable, doesn't interfere with the operation at all and is a great upgrade. That seems an acceptable project to tackle, even if you have limited skills. With an old unit, I think you have to decide if a Propex rebuild is worthwhile or whether you can find the money for a brand new one. I've started a small savings account with my local credit union to cover the cost of a new one should the worst happen. That heater is just TOO important to me and the lad.

Anyone living without a Propex is indeed missing out.

[ghost123uk]

What a conundrum!

Indeed !

I hate having to guess at faults. It's much better to suss out exactly what is going on and properly sort it isn't it.

Mind you, I have "fixed" my left hand door pin switch "properly" 3 times now in a week and it still ain't right Thinking now it might be another case of one of your (Ralph) faves, ie black wire corrosion. Maybe that was the cause of the decay in that shortish length of earth wire on the Propex,

[CovKid]

For now, its a complete mystery why this particular length of earth wire heated up. I would have thought for it to happen it would have needed to make contact with live. The other possibility (although I can't see how) is for something conductive to have bridged the red and black at the multiplug. That would do it for sure although I'd expect the live to also have shown sign of heat damage, and even with a 7.5amp fuse it would have blown immediately. As Oldie says, the heater is normally only drawing two amps.

The plug is there so you can remove thermostat or heater independently but for now I'll run a complete length to thermostat with new cable. The other colours in the sheath didn't burn through but I'm not taking a chance with it. Unfortunately I don't have cable with the same colours (obviously) so all I can do is use mains flex, use the red, black and green as the red, orange and purple. ground the earth and fit a sticker inside thermostat with new colour arrangement. Bah!

Bit annoying but seems the only solution for now. I imagine Propex stock it but I suppose as long as I know what denotes what, it doesn't matter....

[BOXY]

For now, its a complete mystery why this particular length of earth wire heated up. I would have thought for it to happen it would have needed to make contact with live. The other possibility (although I can't see how) is for something conductive to have bridged the red and black at the multiplug.

Could condensation have caused water to track down the cables and cause a short?