It’s connected to the courtesy circuit that is fused @ 7.5a
Today was my lucky day
- Thread starter Deaky
- Start date
Ok ...
What's the rating of the cable? Something isn't matching up here because it shouldn't be able to start losing magic smoke.
Even a small current can cause enough heat to start combusting if the resistance is high enough. It sounds like a broken solder joint was causing the resistance in this case.
If salt has tracked up the cable insulation, caused corrosion and increased the resistance it could have caused overheating.
It’s worth paying the extra for tinned cable and adhesive heat shrink. If you can’t get the heat shrink in place then self amalgamating rubber tape secured with a blob of superglue does the job.
I used to work at sea and even the slightest salt intrusion causes massive problems with machinery electrics
It’s worth paying the extra for tinned cable and adhesive heat shrink. If you can’t get the heat shrink in place then self amalgamating rubber tape secured with a blob of superglue does the job.
I used to work at sea and even the slightest salt intrusion causes massive problems with machinery electrics
@Deaky Hope you don't mind me continuing this discussion because I think there's something for everyone to learn from this...
Heaters are designed to generate heat and appropriate wires, cables and insulators are used for these. Most cables in a car (or house) are intended just to carry the required voltage and current for the connected equipment to operate. We fuse electrical circuits so that if excessive current is drawn the fuse blows before damage to the cabling occurs - at least that is the intention. There shouldn't be any significant heating in these wires even if a fault occurs.
To me it doesn't look like a solder joint failure - there seems to be too much burnt out wire in the photos for a single hot spot. Insulation on cables does not melt/burn until it's well over 100C. As I read it the lights were actually working at the time the smoke was seen so there doesn't appear to be a short between the two wires either.
I do wonder if there were some AC effects from the LEDs (from PWM drivers possibly) such that a higher than expected peak current was allowed that just wasn't sensed by the fuse. If this was the case then it could mean that we all should be re-thinking how cable (and fuse) sizes are selected.
Heaters are designed to generate heat and appropriate wires, cables and insulators are used for these. Most cables in a car (or house) are intended just to carry the required voltage and current for the connected equipment to operate. We fuse electrical circuits so that if excessive current is drawn the fuse blows before damage to the cabling occurs - at least that is the intention. There shouldn't be any significant heating in these wires even if a fault occurs.
To me it doesn't look like a solder joint failure - there seems to be too much burnt out wire in the photos for a single hot spot. Insulation on cables does not melt/burn until it's well over 100C. As I read it the lights were actually working at the time the smoke was seen so there doesn't appear to be a short between the two wires either.
I do wonder if there were some AC effects from the LEDs (from PWM drivers possibly) such that a higher than expected peak current was allowed that just wasn't sensed by the fuse. If this was the case then it could mean that we all should be re-thinking how cable (and fuse) sizes are selected.
@aferris2 The top and bottom of it is that the 30cm length of 4 core cable I'd used to retrospectively add a switch to the circuit was not as thick as the rest of the cable in the courtesy light circuit and consequently was not protected by the fuse in the circuit.
@Deaky glad it turned out to be such a small amount of damage. It's just the reason that I stress to everyone how simple it is to create a fire damaged write-off! Years ago I bought and restored a Type 4 Variant that had been fired, on investigation it was caused by a badly installed rear fog light cable.
@Deaky Glad you know why the cable burnt out.
It's a lesson for everyone to use the right sized cable. I think it's all too easy for people to think that it's only a low powered light so don't need a thick cable. In reality, the cable has to be able to take more than the fuse current.
A note on soldered connections - I always thought that soldered connections should be avoided in high vibration environments because they can fracture. It's the reason why we use stranded wire instead of solid (as in a house). Soldered connections are OK when both ends are securely fixed but not when one end or the other is allowed to flex. Properly crimped connections with strain relief (heatshrink) are generally more robust.
It's a lesson for everyone to use the right sized cable. I think it's all too easy for people to think that it's only a low powered light so don't need a thick cable. In reality, the cable has to be able to take more than the fuse current.
A note on soldered connections - I always thought that soldered connections should be avoided in high vibration environments because they can fracture. It's the reason why we use stranded wire instead of solid (as in a house). Soldered connections are OK when both ends are securely fixed but not when one end or the other is allowed to flex. Properly crimped connections with strain relief (heatshrink) are generally more robust.
