Tech Tip Tuesday: The Single Biggest Killer of Alternators and Bad Charging Systems

In this Tech Tip Tuesday, Doug talks a bunch about alternators and pulleys.

LS 3" OD Billet Overdrive Alternator Pulley 6 Rib 10-10042:

LS 3.5" OD Overdrive Alternator Pulley:

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[stevelong]

This is spot on. Wifes car was eating alternators quickly, Put a big pulley on the alt and haven't eaten an alt since. Been several yrs.

[JWP]

One of the most overlooked products on a car. Great video

[HUBBABUBBADOOPYDOOP]

Don't forget, Folks-
Changing your pulley diameters also mean your belt lengths change,
and an auto-tensioner only goes so far, either way. Don't lose tension,
and don't over stress that coil spring. Belts are usually measured in mm.

[supercoupe]

Life lesson right here boys. Good job Doug and the motion crew.👍

[andrewbradley]

Another thing which can damage an alternator with a manual transmission is banging through the gears. A lot of modern cars (especially ones with DSG type gearboxes) have a freewheel on the alternator pulley so that when you change to a higher gear the alternator can freewheel faster than the engine and slow down gradually rather than being forced to slow down suddenly. This makes the belt last longer too.

[sAirForceBrat]

What's the main failure on the alternator is the rotor when you spin it above it's rating the centrifugal force will rip the coil wires away from the slip ring killing the alternator. But also remember if you going to run an underdrive pulley on your alternator on your daily driver you may occur under charging at idle and cruise speeds.

[jsteganius]

G.M. has made a good drag race pulley for the alternator since the early 70s. Pretty sure the part number is 1942911. Its about 4 inches in diameter.

[b.c]

Trouble with a larger pulley on a dual purpose primarily street driven car is a lack of charging at idle and cruise rpm. Amazed nobody has come up with an expanding pulley. Similar to a centrifugal clutch operation, but that allows the pulley diameter to grow a few percent. Brand x, Mr. Patrick has taken care of my alternator needs for the last few years. The hot rod community can learn from the hardcore audio guys. There are better bearings and stators etc available to custom build bulletproof alts, but they are not cheap.

[james]

Good point and a bigger pulley probably won't matter much at idle since stock idle is like 550 and with a decent cam it will probably be like 900 or more

[kanointhephilippines]

Great job, I learned a few things. I always thought heat was the biggest killer of alternators, heat from going to full field while attempting to charge a severely discharged battery. Alternators are designed to keep fully charged batteries at that level not bring up drained ones. Thanks again Doug and have a great day.

[JerZeyFiveOh]

Great video! I upgraded my pullies on my classic mustang and noticed that alternator wasn't happy. I found a calculator online and bought the right size. I did this about 4+ years ago and the alternator has been happy since. My issue was that my underdrive system was cooking my battery because it wasn't charging the battery at idle, traffic jams use to bring me a lot of anxiety lol.

[chrisobrien]

Thanks Doug. Great info. It’s a bit more critical than people think. Keep up the great work

[fredmitchel]

My Nippon Denso alternator..in a 1994 Toyota it had 286K miles...i never replaced it....with the 1969 IHC...it still has the stock Delco 65 amp baby...I did replace the field brushes...and the ball and needle for prevention maintenence...

Sure if either of those engines were tweaked to rev higher...I would increase the pulley size....

It seems like some like to add additional loads....and then they play fry the alternator game...

[tomtee]

Did this years ago with power master they know how to measure crank pulley x alternator pulley x max RPM's. Tech tip I blue lock tite alternator case bolt, pulley, electrical nuts and more on. I always say do it right the first time and be done!!!

[erickbetancourt]

I am so glad you guys are offering these pulleys. Ive cooked plenty of units and even considered having a pulley custom made because no one made them at 3". Thanks Motion!

[NomadicWubze]

Literally fried a alt on my 450ci C6Z spinning to 8200rpm. First mile of driving it almost lit on fire. Got a bigger alt pulley and fixed the issue over last summer

[docfischer]

What you also have to remember is that unless it’s a “ marine” rated alternator and only certain newer style vehicle with an exciter wire it will only function a above 1200 rpm’s or so.
I always used Mercruiser mini alternators rebuilt to charge at 150-200 amp and with ceramic bearings installed.
Marine alternators charge at idle rpm’s .

[robertheinkel]

The alternator on my Odyssey went bad and was replaced. The second one didn’t last a day, and had to replaced again. So far, so good

[rronmar]

It is not just undercharging at low RPM, the regulator will try and maintain the rated output voltage by increasing the field current. That means max current is being pulled thru the brushes and commutator to drive the field, increasing wear there, heat in the regulator and overall heat in the alternator at low RPM when cooling is reduced…

[davidclark]

I had a problem with my alternator overheating even under light load and I finally figured out my alternator pulley was too large and the internal fan wasn't running fast enough to cool it.