Why Did My Electrics Just Burn Out?

[solomon]

It's melted on the kill switch circuit, in headlamp shell...

This ignition circuit is anyway permanently 'shorted' at contact switch when ignition is on. Pushing the switch breaks the circuit, killing the ignition. A short between the wires lower down wouldn't make any difference, other than the switch not stopping engine?

The ignition circuit is protected by it's own 7.5A fuse.

There's no earth (negative) fuse. It melted at negative battery wire too...

There are four positive line fuses, protecting different circuits. Having a negative line fuse would defeat having individual circuits.

Might the fuse be faulty, and the wires somehow shorted between themselves? Seems unlikely.

Last night, I had the headlamp shell open, so must have disturbed something, but still don't see how that would affect kill-switch circuit.

 

[solomon]

It all seems to work with the kill switch wires pulled. Once rain stops, will see if it sparks, ignition box okay.

Would like a kill switch though. And to know what's wrong...

 

[Rudie]

Why Did My Electrics Just Burn Out?

Unable to inspect the whole bike in 3D, it will be difficult for anyone else to say. However:-

Having a negative line fuse would defeat having individual circuits

... is a dubious principle to the point of being wrong:-

. Bike without an electric starter should ALWAYS have a fuse in the solitary wire connected between the battery earth/ground terminal and the rest of the harness - your bike is made mostly of metal, metal conducts electricity, you cannot eliminate every possibility of something metal connected to battery -ve coming into contact with something else metal connected to battery +ve and making a short-circuit.

. "four positive line fuses", each should be rated just higher than the total Amps drawn by only the electrical resistance/s (coils, bulbs, horns) it protects.

. Because the solitary wire between the battery earth/ground terminal and the rest of the harness conducts all Amps drawn by all electrical resistances in the harness, fuse in that wire by definition has a higher rating than any of the "four positive line fuses".

. Short in a circuit protected by one of the "four positive line fuses", the lower-rated "line fuse" should blow before the higher-rated fuse in the solitary wire connected between the battery earth/ground terminal and the rest of the harness (nevertheless, we carry spares for both fuses for the time when Murphy sticks his oar into a given situation ... ).

. Otoh, short in a 'circuit' - however formed - not protected by any "line fuse" is what the "fuse in the solitary wire connected between the battery earth/ground terminal and the rest of the harness" is there for, it is the last resort.

Any vehicle with an electric starter always requires more thought about fusing, primarily because starters always (ime) earth/ground through their mountings, therefore the connection between the battery earth/ground terminal and the starter's mounting becomes the earth/ground connection for all electrical circuits on the vehicle, the connection cannot be fused sensibly to protect electrics other than the starter because all starters draw high Amps.

Vehicle with an electric starter, only one wire connected between the battery "not earth/ground terminal" and the rest of the harness, fuse in that wire will provide almost as much protection as the above-mentioned fuse in a solitary wire connected between the battery earth/ground terminal and the rest of the harness. The one common situation the latter protects against but the former cannot is something metal coming into contact between the battery "not earth/ground terminal" itself and another part of the bike, the latter by definition potentially ultimately connected to the battery earth/ground terminal.

There's no earth (negative) fuse. It melted at negative battery wire too.

Above:-

. "Bike without an electric starter should ALWAYS have a fuse in the solitary wire connected between the battery earth/ground terminal and the rest of the harness";

. "Vehicle with an electric starter, only one wire connected between the battery "not earth/ground terminal" and the rest of the harness, fuse in that wire will provide almost as much protection".

I rest my case, m'lud ...

melted at negative battery wire too...
four positive line fuses,
Might the fuse be faulty, and the wires somehow shorted between themselves? Seems unlikely.

More like impossible ... - both ends of all "line fuses" are connected to battery positive; otoh, a short circuit connects battery negative to battery positive, without a resistance in between.

This ignition circuit is anyway permanently 'shorted' at contact switch when ignition is on. Pushing the switch breaks the circuit, killing the ignition. A short between the wires lower down wouldn't make any difference, other than the switch not stopping engine?

As posted, this does not appear to make any sense. Care to post a different (clearer?) explanation?

 

[solomon]

Unable to inspect the whole bike in 3D, it will be difficult for anyone else to say. However:-

... is a dubious principle to the point of being wrong:-

. Bike without an electric starter should ALWAYS have a fuse in the solitary wire connected between the battery earth/ground terminal and the rest of the harness - your bike is made mostly of metal, metal conducts electricity, you cannot eliminate every possibility of something metal connected to battery -ve coming into contact with something else metal connected to battery +ve and making a short-circuit.

. "four positive line fuses", each should be rated just higher than the total Amps drawn by only the electrical resistance/s (coils, bulbs, horns) it protects.

. Because the solitary wire between the battery earth/ground terminal and the rest of the harness conducts all Amps drawn by all electrical resistances in the harness, fuse in that wire by definition has a higher rating than any of the "four positive line fuses".

. Short in a circuit protected by one of the "four positive line fuses", the lower-rated "line fuse" should blow before the higher-rated fuse in the solitary wire connected between the battery earth/ground terminal and the rest of the harness (nevertheless, we carry spares for both fuses for the time when Murphy sticks his oar into a given situation ... ).

. Otoh, short in a 'circuit' - however formed - not protected by any "line fuse" is what the "fuse in the solitary wire connected between the battery earth/ground terminal and the rest of the harness" is there for, it is the last resort.

Any vehicle with an electric starter always requires more thought about fusing, primarily because starters always (ime) earth/ground through their mountings, therefore the connection between the battery earth/ground terminal and the starter's mounting becomes the earth/ground connection for all electrical circuits on the vehicle, the connection cannot be fused sensibly to protect electrics other than the starter because all starters draw high Amps.

Vehicle with an electric starter, only one wire connected between the battery "not earth/ground terminal" and the rest of the harness, fuse in that wire will provide almost as much protection as the above-mentioned fuse in a solitary wire connected between the battery earth/ground terminal and the rest of the harness. The one common situation the latter protects against but the former cannot is something metal coming into contact between the battery "not earth/ground terminal" itself and another part of the bike, the latter by definition potentially ultimately connected to the battery earth/ground terminal.


Above:-

. "Bike without an electric starter should ALWAYS have a fuse in the solitary wire connected between the battery earth/ground terminal and the rest of the harness";

. "Vehicle with an electric starter, only one wire connected between the battery "not earth/ground terminal" and the rest of the harness, fuse in that wire will provide almost as much protection".

I rest my case, m'lud ...


More like impossible ... - both ends of all "line fuses" are connected to battery positive; otoh, a short circuit connects battery negative to battery positive, without a resistance in between.


As posted, this does not appear to make any sense. Care to post a different (clearer?) explanation?

There's not yet an electric starter installed.
It's been running fine until this morning.
I've isolated the kill switch and put a negative 15A fuse in. Downgraded largest positive fuse to 10A.
Now sparks, everything works. Except of course kill switch.
Mystery remains why kill switch wires shorted. And why fuse didn't blow. If I pull ignition circuit fuse, it kills circuit, so fuse is wired in.

 

[DaveM]

Did you check the kill switch with a meter to see if it actually works?

 

[solomon]

Did you check the kill switch with a meter to see if it actually works?

The kill switch would be permanently on. So it can't short out. It could at worse not pass current.

 

[grandpaul]

Sure looks like a lot more wires than those bikes came with originally...

 

[Rudie]

View attachment 55415

fuse in the solitary wire connected between the battery earth/ground terminal and the rest of the harness
the solitary wire between the battery earth/ground terminal and the rest of the harness
fuse in the solitary wire connected between the battery earth/ground terminal and the rest of the harness
what the "fuse in the solitary wire connected between the battery earth/ground terminal and the rest of the harness" is there for, it is the last resort.

If you Google "solitary", one returned definition of the adjective from the OED is, "single; only" ...

How is four wires connected to the battery -ve terminal "solitary"? Short circuit can bypass the fuse through any one of the three unfused wires ...

 

[solomon]

fus

How is four wires connected to the battery -ve terminal "solitary"? Short circuit can bypass the fuse through any one of the three unfused wires ...

Thanks for explaining the definition of solitary. Not that I was using it.

There's indeed four wires connected to battery earth. Battery tender, totally separate. Earth to electronic clocks, separate circuit, earth to e.i. box, and earth to bike frame. The newly installed earth fuse protects everything else.

I'll investigate further another day.

 

[Rudie]

earth to bike frame. The newly installed earth fuse protects everything else.

"earth to bike frame" is most likely to bypass the newly installed fuse. The frame is likely to be earthed by an earth wire connected to a component that earths through its mounting on the frame. Even if the bike really needs a discrete earth connection specifically to the frame for some reason, it should be through the newly installed fuse.

Earth to electronic clocks, separate circuit, earth to e.i. box

Reason for these to be separate wires connected to the battery terminal?