Main fuse blowing regulator or not

[Harry64]

Hi all
Just a bit of advice/help needed, my main fuse went and when I tried to change it it blew straight away.I have disconnected the regulator which has enabled me to change the fuse without blowing it
went turning the key. Before I run out and buy one is this what's causing the problem? 

[kwackboy]

If removing the regulator has stopped the main fuse blowing I'd say it's that's your problem. Normally with this issue you would have an electrical burning smell before it blew the main fuse, Smell the the back of the regulator to see if it smells burnt.

[greywolf]

A failed diode in the rectifier will do it. So will crossing polarity in its wiring.

[joderest]

You will need to check a bit further, as disconnecting the regulator may have just isolated the circuit that is causing the fault, as there would be some components after the regulator,  for example, the generator.
It will need to be checked by way of a meter to see where the short circuit is.

[greywolf]

There is electrically nothing beyond a working rectifier. The diodes isolate the DC side from the AC side. If plugging in the regulator/rectifier causes a short, the problem is in the device or its two DC wires being shorted to each other, the live wire to the frame or cross wired.

[Harry64]

Hi all and thanks for the replies. Just a bit more information, after I posted the first post I went out and reconnected the regulator and the fuse never blew, however the battery was low so I connected it up to the car with jump leads and it started. That was about 3pm and I have been out 4 times to try it and it started every time. The battery is new only 4 weeks old. 

[greywolf]

Check the wiring out of the regulator. The black/red wire may be wearing through the insulation against the frame, sometimes shorting and sometimes not. A series of short circuits will drain a battery. Also check the voltage at the battery. At 5000rpm, you want to see between 13.5 and 14.8VDC. You could have run through 2 stages of a failing diode too. The first stage lets current run in both directions instead of just one and causes a short circuit, blowing the main fuse. The second stage completely burns out the diode so current runs in neither direction, creating an open circuit. That will eliminate 1/3 of the charging power.

[Harry64]

Thanks Greywolf does this mean if I check the wires and find nothing I need to replace the regulator

[greywolf]

Do the wiring and voltage checks first. If both are good, it's still a mystery. A bad R/R should fail the tests and lower the voltage. Here's how to check the rectifier diodes. Replace the R/R if it fails the checks below.

[joderest]