3rd Alternator Failed

[pfield69]

I have just returned from camping with another failed alternator. This is my third one in 3 years!!

I can not find any simple electrical faults. The only differance to the standard (transporter) wiring is that I have a smartcom split charger connecting 2 batteries together. I am using 90Amp FRA690 QH alternator.

Are there any typical reasons these should fail so often? I have been told it could be pully size but I am using the pully that came with the van. I can test the alternator rpm with a strobe if I need to but I don't know the operating rpm range.

Any ideas?

[bigherb]

Early failures can be caused by the alternator being loose and vibrating or the electrical connections are loose and causing electrical spikes. A lot of early failures are often due to overheating when the alternator is working at high output at low engine speed and not enough cooling air from the fan passing through the alternator. Leaving the engine ticking over charging a flat battery kills alternators same with sitting in traffic with every thing electrical switched on. Higher output alternators are more prone to failure because they produce more heat. 90 amp is about the limit for the type of drive belts fitted to our vans fitting a smaller pulley increases the alternator speed at lower engine speeds (more cooling airflow) but the higher gearing puts more strain on the drive belt unless you really have to have a 90A alternator consider dropping to the 65A it will still charge the battery the same.

[pfield69]

Thanks bigherb

My logic was 90A would work less hard for the same given output. I have 85a main battery & 110a leisure (ex BMW) battery. I will be running a fridge of 12v when the engine is running too. This on top of the usual usage with high draw ICE

Will 65a satisfy this demand?

[CovKid]

You need to tow a power station behind you by the sounds of it.

Mine is a 90amp but with all the will in the world you're asking a lot of it. Many modern vehicles use alternators of 150amps and above. Not sure what to suggest. I've gone the opposite way and reduced the demand on the alternator as much as I can. Fridge seemed like a luxury to me considering its dormant more than its actually used so I ditched that. I just use dried milk etc.

Even if we did come up with a solution, chances are you'd find something else to plug into it

[bigherb]

Unless your seriously anti social or deaf ICE systems don't normally draw the rated power, you need to check the amps draw that you would normally be using but a 65A would normally suffice with that battery set up.

[pfield69]

stereo absolute power 10a
stereo Amp max 17a
fridge (when running) 11a
lights 11a
total 50a max

battery charge circuit too hard to work out but guess 15a to cover everything else should be good enough?

[kevtherev]

which is failing on the alternator?

brush pack
bearings
Diode plate
windings

or have you just handed it in to swap?

[pfield69]

I think its the rectifier/regulator pack.

I haven't checked as they are under warrenty and just swap it out. My multimetre goes ape anywhere near alternator.

[kevtherev]

I think its the rectifier/regulator pack.

I haven't checked as they are under warrenty and just swap it out. My multimetre goes ape anywhere near alternator.

It would be interesting to be shure what failed
I had a bad batch of rectifier brush packs from a supplier near me a while back. They have been Ok since.
But I guess under warranty the failed part would just be swapped out. If there was an issue with the diode plate or winding causing premature regulator failure it might be worth a second opinion from a repair specialist before you return it once again.