FUSE BLOWIN UP!!!

Can you see the fuse filament?

The way the filament opens can give a very good guide as to what is happening, if the filament is vapourised end to end then it was a severe overload many times the rating of the fuse, if the filament appears to have only just opened with a small blob on the filament ends then its a tiny overload...

Its surprising what you can tell from inspecting the filament, it can save a lot of time when the fuse has just failed because it is getting old and has been slightly operating at its rated current or been pulsed at its current etc...

John.

Hold on.... you say the controller can only with stand a 15 volt supply?!!

A car or bikes supply can easily produce over 60 volt surges!!!

When I worked on car electronic control units we had to have massive surge suppresion at every signal and power inlet, everything had to be rated to expect the worst of well over 30 volts spikes on the supply...

That could be your problem! John.

Another thing you could look at in the surges area is watch the fuse wire, sometimes, they will "pulse", not to blowing, but give a definite movement as it heats and cools due to the current flow.

I'm not sure of the source, but some fuses I have had had glowed like a light globe, but not blow, strange.

"slow blow" fuse usually glow emitting light before oppening up (blowing) these actually form a part of current limiter , but high boost pulses can blow them up

Fuses don't care about voltage, they only care about amperage.

On a simple heating load, you can limit the amperage by changing the voltage. A complex load, like a motor for instance, will increase its amperage draw as you lower the voltage. But that is not applicable in this case...you have an intermittent dead short somewhere.

Your "smart controller" might be the problem. Some power supplies have what is called "crowbar protection" which react to certain load conditions by blowing the fuse before the over current will damage the load. By dropping an electronic "crowbar" onto the output of the controller, so to speak. This would be normal for a power supply which is being driven close to the edge...random spikes from the generator might well be interpretted by the controller as "danger", and it will shut down in the quickest way possible. Check the "ground fault interrupter" circuitry of the smart controller.

I am puzzled as in my mind it could still be the drop in voltage as some engines, like the lazy v-twins from Harley, will sometimes have bery low tick-over speeds and the "low charge" light might even come on or flicker. If that is the case could this drop not cause the fuse to blow as the load stays the same. If it is near the edge anyway this could perhaps push it over the edge??? Not sure as it is not my strongest point but could it also have to do with the rating of the fuse, i.e. fast or slow blowing?