Dimming at idle.

[jdawg 5,000+ posts]

take your alt off and go to advanced, they have boxes of pulleys, they switched one for me

 

[MmatsDude 10+ year member]

What kind of new pulley does the alt need and where can I get one?

auto zone

thats were i got mine

 

[Sarthos 10+ year member]

how do I determine what kind it needs? Does it need a smaller or larger one?

 

[jdawg 5,000+ posts]

smaller one because you slowed it down so it needs to spin faster

 

[Sarthos 10+ year member]

A smaller one will spin faster, but it will have smaller revolutions, so will that make a difference in some way?

 

[snb778 5,000+ posts]

you need to change the pulley on your alt, my buddy went thru this about a month ago. The problem is your alt just isnt spinning fast enough. A volt reg WILL NOT help. You alt doesnt spin fast enough to make good voltage.

im having the same issue though (factory pulley on H.O. alt), but my Voltage still stays @14V... he shouldn't be droppin that low.....and on my car, it sounds like the car is about to die @idle because its not givin much power.... lights kinda flicker a little bit

also get a smaller belt just in case your factory one doesnt fit once you go smaller on the pulley

 

[Sarthos 10+ year member]

It's not just the pulley on the alternator, it's the underdrive pulley and the fact that I also idle below the low power level on the alternator (I idle at 600 RPMs, it gets 80 amps at 800 RPMs)

But isn't there some disadvantage to changing the alternator pulley size? I mean like if you change the tire size on a car and get shorter tires they spin faster and you get better acceleration but less top end, and if you get taller ones they spin slower but get better top end so does anything like that happen with an alternator pulley or should I just get about as small of a pulley as I can?

 

[Sarthos 10+ year member]

So how much smaller should I go? Half-diameter maybe?

And I'm confused. By running a smaller pulley, there would be less weight on the crank pulley, allowing it to spin easier and also the smaller revolutions would let the alternator spin faster too? This just seems contradictory that you would gain alternator power and technically a tiny bit like it must be against the laws of physics //content.invisioncic.com/y282845/emoticons/eek.gif.771b7a90cf45cabdc554ff1121c21c4a.gif Also, couldn't a smaller pulley mean spinning the alternator too much at higher speeds or would that not be a problem thanks to the regulator or something like that?

 

[nuugen 10+ year member]

Let me shed a little light for you...Some alternators don't start charging until they are spinning above a certain rpm..I have dealt with this for many years on German cars with Bosch alternators, it is a normal occurence.Let the idle drop too low even with a stock pulley and the alt stops charging... The tire analogy doesn't translate to the charging system---once the alternator is charging you are not going to lose any "top-end" performance.

It is a very simple solution: Either bump your idle up to where it should be or a little higher, or go get the proper pulley(just get the OEM one)..

Underdrive pulleys are more suited to cars used at the track--since they spin slower, idle speeds can cause the alt to undercharge, the car can tend to overheat if you have one on the water pump, and one on the ps pump can cause hard steering at idle..Also, 5hp will probably never be seen on a street car with basically no other mods..

 

[snb778 5,000+ posts]

Let me shed a little light for you...Some alternators don't start charging until they are spinning above a certain rpm..I have dealt with this for many years on German cars with Bosch alternators, it is a normal occurence.Let the idle drop too low even with a stock pulley and the alt stops charging... The tire analogy doesn't translate to the charging system---once the alternator is charging you are not going to lose any "top-end" performance.It is a very simple solution: Either bump your idle up to where it should be or a little higher, or go get the proper pulley(just get the OEM one)..

Underdrive pulleys are more suited to cars used at the track--since they spin slower, idle speeds can cause the alt to undercharge, the car can tend to overheat if you have one on the water pump, and one on the ps pump can cause hard steering at idle..Also, 5hp will probably never be seen on a street car with basically no other mods..

this is exactly why my lights are FLICKERING @idle (at the same rate the alt is spinning), but my voltage is holding at 14+

just go to your local parts store... ask them for a belt for your car, and get 1 smaller than that... it will only be like an inch or 2 smaller... there is a pulley tensioner on your alt to tighten it.... with your stock pulley, stock belt, its probably as tight as it can get, but still to loose

 

[on1wheel01 10+ year member]

Let me shed a little light for you...Some alternators don't start charging until they are spinning above a certain rpm..I have dealt with this for many years on German cars with Bosch alternators, it is a normal occurence.Let the idle drop too low even with a stock pulley and the alt stops charging... The tire analogy doesn't translate to the charging system---once the alternator is charging you are not going to lose any "top-end" performance.It is a very simple solution: Either bump your idle up to where it should be or a little higher, or go get the proper pulley(just get the OEM one)..

Underdrive pulleys are more suited to cars used at the track--since they spin slower, idle speeds can cause the alt to undercharge, the car can tend to overheat if you have one on the water pump, and one on the ps pump can cause hard steering at idle..Also, 5hp will probably never be seen on a street car with basically no other mods..

good info man

 

[Sarthos 10+ year member]

Does the alternator not start charging because it's not getting enough power or because the car's ECU tells it not to charge? Also, not sure why I was thinking 600, but the car does idle at 800 which it's supposed to. If I up the idle speed it would just make the car sound like I'm revving it up all the time, which would be somewhat annoying and above the specs in the manual. But if the alternator does need a new pulley to spin faster as snb said, how much smaller does it have to be? I noticed that while my car has low voltage at 800 RPMs, it regains it as low as 11-1200 RPMs, so would a pulley 2/3 the size mean it would spin 3/2 as fast, so when the car is at 800 RPMs the alternator would spin like it's at 1200?

 

[snb778 5,000+ posts]

as i said... just get 1 belt smaller than the stock one in your car. This is your problem, get it done......most HO alts pull more power, so you may see a little drop in gas mileage (3-4mpg)

 

[Sarthos 10+ year member]

Losing 3-4 MPG would be a lot for a HO alternator to pull. That'd be like over 10% of my mileage. But the pulley can be measured as one belt smaller? I thought they were measured by diameter?