Melted isolator switch - no idea what electric problem cause it

[aaronwood66]

I have an electrical fault that I can't figure out how or why has happened, and I don't want to make the mistake again by just replacing everything only for something to go badly wrong without understanding why...

 

Last week I was running the engine and noticed smoke and a burning smell coming from the engine bay. I immediately turned the engine off and waited for it to cool down before inspecting. I found 3 places where there was evidence that something seriously had happened:

 

1. The starter battery isolator switch had completely burnt out/melted - I could no longer turn the switch (see photo)
2. The electrical harness for my Beta Marine engine had one melted wire. (It is blue/black wire and it seems to run from the starter battery alternator to the Beta Marine control panel, as far as I can follow it.) (see photo)
3. Where I had a piece of kitchen towel wrapped around my oil dispenser tap, this was touching the side of my starter motor. The paper towel was black and had singned (although not caught alight.)

 

The burnt wire in the electric harness was strange that only one had melted, and in a place just above part of the engine. I don't know if it had touched that part of the engine and the hot engine melted it - but then why only one wire - there was no evidence of even slight melting on the others. 

 

I just don't know which thing caused this chain reaction - a melted harness wire? Did the starter motor overheat and cause this? Was it a dodge isolator switch?

If anyone could help with any suggestions of what might have started this, I would be very grateful.

 

(P.S. The isolator switch was new in Feb, and hasn't shown any problems in the months leading up to this - https://www.amazon.co.uk/dp/B07P8KCV35)

[Tracy D'arth]

I think the switch failure is a quality problem.

The blue/black wire looks like a short to the bell housing due to abrasion, lack of support.

Tissue?  Oil and a hot starter?

[magnetman]

Could have been a bad contact between the ring terminal on the wire and the bolt on the isolator switch. 

 

If the contact is not clean it introduces resistance which means heat if current is flowing. In some cases this can be a LOT of heat concentrated in a small area. 

 

 

What was the isolator isolating? Was this a starter battery isolator? 

 

 

The amazon link is a worrying. As said above quality could well be questionable. 

 

Have you still got the bolt and the ring terminal?

[Alan de Enfield]

10 minutes ago, aaronwood66 said:

The electrical harness for my Beta Marine engine had one melted wire. (It is blue/black wire and it seems to run from the starter battery alternator to the Beta Marine control panel, as far as I can follow it.) (see photo)

 

 

If you look in your manual you should be able to identify exactly what the Blue/Black wire is doing.

 

If it is indeed part of the starter circuit than everything (starter isolating switch, starter motor, starter wire) points to it being starter related.

 

 

I'd replace the isolator with a quality one (not the cheapo 'red-key) and splice in a new piece of wire into the Blue/black lead and get some spiral wrap and protect the harness - unprotected single wires near a 'vibrating source' is never good news.

Then try again.

[magnetman]

ETA I see from the OP it was a starter battery isolator. 

 

So a dodgy contact has burnt it..

Or it has been overloaded by a jammed engine which the starter was trying to turn. 

 

Did the engine start ok? 

 

I suppose it could be something preventing the engine from turning causing a current spike in the starter motor and burning the switch .

[pete.i]

Those wires are quite tight on that sharpish edge of the engine. My guess is that that blue and black wire chaffed against that edge wearing the insulation until it shorted with the engine. Witout knowing where that black and blue wire goes it's imposible to say for sure that that is what caused the isolator burn out but it could have. I would rejoin the black and blue wire and replace the isolator and then keep an eye on things whilst running the engine or whatever it was you did when it burnt out. If all is well then some protection is required between that loom and the edge of the engine.

[magnetman]

It is curious that this particular part of the wiring loom is completely unprotected. Looks like someone has cut the covering orf for some reason previously which is rather bizarre. 

 

 

 

 

[David Mack]

The amazon link lists the isolator switch brand as "LotFancy". That sounds far more like cheap Chinese tat than a reputable brand. All it would take is poor contact or corrosion between the switch contacts to generate some heat, and a low grade plastic surround which could melt and catch fire. Better to replace it with a known brand and quality.

[magnetman]

Some of these Chinese junk brands are very amusing..

 

I remember a Lithium battery called the 'Shunbin'. A real giggle. 

 

LotFancy is a good one also. 

 

[aaronwood66]

 

27 minutes ago, Alan de Enfield said:

I'd replace the isolator with a quality one (not the cheapo 'red-key) and splice in a new piece of wire into the Blue/black lead and get some spiral wrap and protect the harness - unprotected single wires near a 'vibrating source' is never good news.

Then try again.

 

I'm definitely going to replace the isolator switch with a better one - are there any recommendations? (This one perhaps? https://www.12voltplanet.co.uk/marine-battery-isolator-switch-2-positions.html)
 

Also, good suggestion - I have the electrical spiral wrap on order now I never actually considered the vibrations are what could have (most likely) destroyed that blue/black wire. (I'll do a bit of digging later to find exactly what it's for)

 

26 minutes ago, magnetman said:

Did the engine start ok? 

 

I suppose it could be something preventing the engine from turning causing a current spike in the starter motor and burning the switch .

 

Yes, the engine started this last time, but not since the burning smell (when the isolator swich melted so no connection)

 

18 minutes ago, magnetman said:

It is curious that this particular part of the wiring loom is completely unprotected. Looks like someone has cut the covering orf for some reason previously which is rather bizarre. 

 

Agreed - this was how the boat came to me 3 years ago and although I made sure to get wires and stuff out the way of all moving parts, I never considered the vibrations being a factor, especially on angular edges like that one... a good point made

 

Edited October 3, 2023 by aaronwood66

[Slim]

9 minutes ago, David Mack said:

The amazon link lists the isolator switch brand as "LotFancy". That sounds far more like cheap Chinese tat than a reputable brand. All it would take is poor contact or corrosion between the switch contacts to generate some heat, and a low grade plastic surround which could melt and catch fire. Better to replace it with a known brand and quality.

Also if you look at the customer comments on Amazon someone reported a similar switch failure in June? with a couple of photos.  

[ditchcrawler]

I have a theory

The starter motor remained energised thus overheating the blue wire, maybe faulty ignition switch, this in turn put a highish (not to high as no load on the starter motor) through the cheap and nasty isolator switch that melted which is only to be expected. The OP says the blue wire goes to the starter

[Jen-in-Wellies]

The Beta manual says that the wire to position 6 on the multi pin plug is black/blue, rather than blue with a black stripe, but it matches the one in the OP's photo. It looks to be the one between the alternator and the tacho.

[magnetman]

13 minutes ago, Slim said:

Also if you look at the customer comments on Amazon someone reported a similar switch failure in June? with a couple of photos.  

Well spotted 

 

This bit in the description seems to imply they are not that convinced about the current ratings.

 

"Rating: 275A DC Continuous (1hr), 455A DC Intermittent (5 min), 1250A DC Cranking (10 sec); Stud Size: 2x3/8" (10mm); Switch on = Power; Switch off = No power. Recommend to install on the negative side of the battery (lower current in negative, will be more safety)"

[aaronwood66]

15 minutes ago, Jen-in-Wellies said:

The Beta manual says that the wire to position 6 on the multi pin plug is black/blue, rather than blue with a black stripe, but it matches the one in the OP's photo. It looks to be the one between the alternator and the tacho.

 

That definitely sounds right, from the best I could do to follow that wire to where it came from and went.

[David Mack]

2 hours ago, magnetman said:

Recommend to install on the negative side of the battery (lower current in negative, will be more safety)

So where does some of the current from the positive go if it isn't returned to the negative?

2 hours ago, Slim said:

Also if you look at the customer comments on Amazon someone reported a similar switch failure in June? with a couple of photos.  

And another review, autotranslated from German:

"Before I installed the switch, I measured it with the battery tester -> resistance 4.. 5.. 6mOhm. The value fluctuated after each shift, it was slightly different.
So open it, remove the large amount of blue pole grease and clean everything with ethanol. Then apply a quarter of a lens of Wago Contact Paste 249-130 and polish the contacts with a smooth cloth so that they are clean but the surface is permanently wetted with the paste.

Switch reassembled and switched multiple times. Resistance is now in the range of 0.4 to 0.6 mOhm. Perfect
However, since the contact area between the two coated brass screws and the copper connector in the switch is only very very small, the switch still gets hot during operation, as can be seen now."

[magnetman]

28 minutes ago, David Mack said:

So where does some of the current from the positive go if it isn't returned to the negative?

 

Maybe it gets swallowed up by the load. 

I would be a little hesitant to buy electrical equipment from someone who does not understand how an electrical circuit operates. 

 

 

[Tracy D'arth]

So rubbish switch, quality problem and a chaffed wire shorted to ground. Simple, nothing suspicious about it.

[system 4-50]

6 hours ago, aaronwood66 said:

The isolator switch was new in Feb,

Why?

[Sea Dog]

6 hours ago, aaronwood66 said:

I'm definitely going to replace the isolator switch with a better one - are there any recommendations? (This one perhaps?

Blue Sea Systems.