Hi all,
My '82 HE destroyed its second alternator in two years recently (a high output wospi). Ive now had a new high output alternator and all new belts fitted. I have noticed, however that despite the upgraded alternator, the car drops off charge at idle in D with AC on, and even occasionally when pretty hot in traffic with no AC (but with headlights and I suspect with the aux fan on). When I says "drops off charge" I am taking this information from the voltmeter on the cluster and also from the dimming of the backlighting on the cluster (I have LEDs which are generally pretty bright but are voltage sensitive). For background I have an upgraded Sanden AC and a large mass revotec aux fan which is *always on* with AC activated on my age of car. Is there something amiss in this behaviour - I don't want to zap anotehr alternator- or is the answer perhaps that "they all do that sir"...?!
Thanks

 

Please clarify "destroyed".

Physically fell apart? Stopped working entirely? Mechanical failure, like bearings or such? Overheated/burned up?

Knowing the exact nature of the failure might help determine the cause.

What's the output rating of the alternator? And what's the advertised current draw of your electric fans? Some of those fan set ups draw 35-40 amps!

Cheers
DD

 

Hi Doug, I don't know exactly what the failure was but they each stopped working completely and threw the belt in each case: I think the alternator is either 100a or 115a will need to double check, I can't locate the rating for the revotec fan but it's a pretty standard upgrade for the old "hairdryer" aux fan (C38009), from what I understand.

 

My gut raection is that you have a mounting/alignment problem

That sounds like enough oooomph to carry the loads.

I wonder about pulley sizes and alternator RPM at idle.

Cheers
DD

 

I agree with Doug; sounds like a belt alignment issue, and possibly a pulley drive ratio problem. A lot of the (if not all) 100+ amp alternators use a micro groove belt. If you are running a v belt, your alternator load may be exceeding the load rating for the pulley diameter / belt combination.
Either belt type is sensitive to misalignment because the alternator is relatively close to the damper pulley on a V12.
You can figure backward on the drive ratio if you know the max rpm of the alternator and the redline of the engine….

 

thank you both. I must say I was surprised to see the last (upgraded) alternator fail so quickly, and the car did throw multiple belts at once (ie the AC/water pump belt was twisted through 90 degrees...).

 

What make alternator did you go with? If a WAI Global Chinese knock off of the Marelli, they are junk in my experience.

 

Whatever alternator you use, make sure you have good aux ground wire, same gauge as the red power wire, from alternator case to engine/frame. High output alts need high conductivity grounds. Sometimes the alt mount bracket doesn't give the best ground, though in theory it should. Paint, dirt, corrosion are the usual culprits.

Doug