Thread: Alternator fuse - Blown - interesting

I recall that someone drove a D3 in WA for days without an operating alternator, recharging the battery overnight at each motel. Non-critical systems were shut-down but for just a few short runs I'm not surprised that the battery has held-up.

Its possible that the regulator has failed rather than suffered from failed diodes or a shorted cable.

Edit: I should read what's written more carefully...the fuse has blown.

You should Graeme , its the idea I stole off you.


Cheers Ean

Ean, if the alternator itself is capable 150A, then you need a fuse of at least that or greater to prevent the fuse from blowing during normal usage. It is possible that the car has met a condition of normal operation that has required more than the 80A fuse can handle.

Originally Posted by SBD4

Ean, if the alternator itself is capable 150A, then you need a fuse of at least that or greater to prevent the fuse from blowing during normal usage. It is possible that the car has met a condition of normal operation that has required more than the 80A fuse can handle.

I don't think so as the car has run for 6 weeks , its been on the gibb river road fully loaded with fridge/freezer and all the other things that the car gets loaded with whilst camping , I have driven at night with everything running and its still held up, plus , the battery at 12.2v tells me its not trying to charge a battery with a problem , on the Gibb the battery was down to 11.9v several times after a couple of days stopped.


I did this to try and combat the problem that seems to be more and more common on the D3 where the alternator shorts and delivers a big current back to the battery, which has killed batteries and left cars dead in the middle of intersections. The car is built with 1 cable that goes to the starter then to the alternator and the only protection is a 500amp fuse which never seems to blow.


Best case is that the alternator has a fault and the system did as its designed , as there has been much discussion about whether a fuse would work , or , if the battery would be killed before it could blow, as they handle double their rating for up to 2 minutes, hence why I am at 80 amps.


Worse case is I never shielded the new cable correctly and its rubbed thru and is arcing out somewhere after its time offroad.


It could be a waste of my time and effort but it could be an answer to a problem that has happened to several D3 owners on this forum.


Cheers Ean

Fuses selected to carry close to their design load get hot and eventually fail due to vibration. I've seen it plenty of times, it can take a few months sometimes but it's almost a certainty. I'd be using a 100 to 150 amp thermal circuit breaker myself, manual or self resetting.

Hi Ean and thats an interesting result so far.

I think you will probably find bee_utey is on the right track as to what caused the failure, but your use of the 80 amp fuse is as high as you can go to be able to get the protection you are after.

So very interested to see further test/operation with the 80 amp fuse.

Hi Sean, and have a read of this thread, it will explain in detail why Ean is using the 80 amp fuse and not a higher rated one.

http://www.aulro.com/afvb/projects-t...-cable-d3.html

If no shorts anywhere then perhaps try an 80A re-settable CB. My D4's 120A CB hasn't tripped yet but it may be a little high.

Well it looks like bee utey was right, cant find any issues and charging fine with new 80amp fuse in it. I will keep an eye on it and if it keeps blowing i will look at a resettable C/B once i have to install my last spare fuse.

Cheers Ean