Alternator fuse keeps blowing

[3sfe]

The car will run fine until i give it a boot to about 5000rpm and as soon as i back off the fuse blows but the engine is the only thing still working, lights, radio everything is dead.
Seems very strange that it blows after i let my foot off. Anyone have any ideas?
these fuses aren't cheap $5 each. Not sure if it matters but is a GT4 running gear - rear diff

[love ke70]

considered the reg is not working?
im not sure if that would be the case, but it wouldnt hurt to check.
just put a multimeter across the battery, then get someone to rev it and see what voltage goes to.
if your getting 15 + id be worried.

short in the wire to/from the alt maybe?

[LeeRoy]

Bad ground?

- LeeRoy

[worldwalker]

I'd say it'd be your regulator.

[3sfe]

Ok finally got round to getting another fuse, also i change the reg last week and it was still doing it. I did as love ke70 said i revved it to 2k then 3k and even on the rev limiter(the stick slipped) but all where reading 14.5v. As for a short how would you find it as the car runs i can drive all day so long as i don't rev it out?

[WeekendWarrior]

check the wiring to the coil and alternator and just check that nothing is touching where it shouldnt. if it only doing it when u rev it right out then i think it would be related to ur ignition system, because its most likely going to be the only thing that would cause a short in this situation. i once got a capasitor from the coil stuck between the bell housing and the motor and it was fine until i got it past about 3000rpm then it would blow the main fuse. try bypassing the alternator and setup a fuse seperate with the bypass setup and try it then and see what happens if it still does it u know its got nothing to do with alternator


cheers

[oldcorollas]

wire that is shorting out depending on amount of decel...

does it happen when you brake heavily?

look for busted/worn thru wire from alternator to battery...

[maddog]

+1 with oldcorollas.....a wire has worn thru and only touches when the engine rocks back under decel....testing it at night and looking for sparks might help too.

[sideshow]

the alt fuse runs thru the ight si if there is a short between the fuse and alternator it would just bring the light on

from how i think the wiring works on them is the wire from fuse to glode is shorting to 12volts and causing a short to positive
maybe the charge light glode has a prob

one way to test it is find wire that goes from fuse to glode
then cut it and join it to new globe then join other side of glode to ignition
so u have a temp charge light setup and see if it still blows

[bansheebuzz]

sideshow - i think he is talking about the main alternator fuse block that protects the b+ feed to the alternator.

[The Witzl]

what if the brushes in the alternator were worn and she was arc-ing out under the high RPM decell conditions?

maybe the battery isnt bolted down?

[BradW]

what if the brushes in the alternator were worn and she was arc-ing out under the high RPM decell conditions?

maybe the battery isnt bolted down?

Alternator brushes only carry rotor current (~3A). The charging current (output from alternator) comes from the stator via the rectifier (diodes). The rotor current is controlled by the regulator. It all depends on wether the reg is switching the rotor current by the positive supply or the earth. If it is switching the earth then it is possible that a short in the rotor may cause the fuse to blow.
How are your engine mounts. If they are worn or cracked the engine could have excessive movement under hard accell/decell. This extra movement could be putting strain on the wiring and causing it to rub on something it shouldn't. Have a good look at the wiring harness around the engine. Also if you have access to a wiring diagram, have a look and see if anything else is powered off this fuse and check the wiring for it.

Hope this helps.

[The Witzl]

how could i forget the rectum-frier diodes!!????!!??

im going to put money on a short out too....