Blowing Fuse

[wheelysteve]

Todays tester question.

Z650 B1 (i.e separate rectifier and regulator). The main fuse ,20A job, gets red hot, in fact hot enough to melt the fuse box. It will not blow if the engine is running with no other load. As soon as you put other load on the think gets red hot and eventually fails.

I can't find anything obviously wrong with the charging system; the battery is charging. I've been through every connection and checked the whole loom.

Will a new combined reg/rec sort the problem?

[DavidZ1R]

Had the same on my z1r, points no igniter, it's the third fuse box in 7 years, I think that over time the vibrations loosen the fuse holder or just rattle the fuse, causing a short thus making the connection over heat, the fuse on mine blew , had a spare tho.

[chrisu]

Sounds like high resistance somewhere

Clean all connectors and earths?

[kev edwards]

On my old A2 a severe kink behind the coloured plugs behind the side panel, solved by straightening the kink.

[Captain Custard]

There are only two reasons that the fuse will get hot -
1 if you have a sustained overload. I recently had a similar fault, the start button had dislodged and was shorting to the metal switch body. If you suspect an over load unplug the harness plugs one at a time to narrow down the fault. It's worth looking behind the electrics panel for a crushed wire it's easy to crush one against the frame when fixing it back.
2 one or both of the fuse end clips is loose, the problem end will be the one getting warm.

[ZedHead]

As already said make sure the fuse is a tight fit in the fuse holder and the connection is clean. Any poor connections here will generate heat.

[wheelysteve]

My thinking is the same as Captain Custards' post. I have been going through the loom checking connections, plugs, sockets bulb holders etc. I haven't pulled the wires from the bars yet....this looks like a pain in the arse to get back. The loom looks very complete and not butchered at all. I will keep looking !

I wondered if the charging system could be part of the cause but it seems ok from the output and continuity checks I've done.
Thanks for the advice....keep them coming.

Steve

[needaz1100r]

Sounds like high resistance somewhere

Clean all connectors and earths?

You'd think so, but it's a low row resistance, high resistance will resist current flow and prevent excess heat, the ultimate being an open circuit, infinite resistance = no current = no heat.

A short circuit, ie, connection straight to earth = low resistance = high current = high heat = fuse blown.