Alternator - Headlights dim - UD Pulleys

DonMaximo · Jan 12, 2012

I've read through several entries regarding this subject as my car is exhibiting issues in this area.

Specifically, when the car is idling (900RPM+), the headlight brightness is relatively dim.
Alternator voltage output in this RPM range is in the high 12s --> low 13s

If I have the Mrs. hold the throttle at a solid 1100-1200RPM, the Alternator output voltage and headlights stay constant. In fact, measured voltage at the headlight socket is ~14 volts.
The voltage stays constant up through 3000+ RPM.

I've made so many changes to this ride, I can't recall what I have now in the way of the Crank pulley...whether it be a UD or stock pulley.

Would someone be so kind as to tell me what the OUTSIDE diameter of a stock 5.0 pulley should be (inches) ???

If I determine I have a UD pulley, I'll try a stock pulley to see if this provides a remedy to my problem.

FYI: I'm using a PA Performance 240amp Alternator.

Noobz347 · Jan 12, 2012

IIRCC, it's 5.5 inches....

I think.

Justin81 · Jan 12, 2012

DonMaximo said:
I've read through several entries regarding this subject as my car is exhibiting issues in this area.

Specifically, when the car is idling (900RPM+), the headlight brightness is relatively dim.
Alternator voltage output in this RPM range is in the high 12s --> low 13s

If I have the Mrs. hold the throttle at a solid 1100-1200RPM, the Alternator output voltage and headlights stay constant. In fact, measured voltage at the headlight socket is ~14 volts.
The voltage stays constant up through 3000+ RPM.

I've made so many changes to this ride, I can't recall what I have now in the way of the Crank pulley...whether it be a UD or stock pulley.

Would someone be so kind as to tell me what the OUTSIDE diameter of a stock 5.0 pulley should be (inches) ???

If I determine I have a UD pulley, I'll try a stock pulley to see if this provides a remedy to my problem.

FYI: I'm using a PA Performance 240amp Alternator.

I have a Powermaster one wire alternator in mine and notice the same thing with the voltage drop at idle. According to Powermaster this is normal. I'm not sure if your PA Performance is using the same type of setup though. Here's something I found on Powermasters website.

I noticed that my Powermaster one wire alternator has to be "revved up" to get the alternator to come on. Why?

A one wire alternator has a turn on point (sometimes called cut in, which is typically 1200 engine RPMs). This is the speed where the internal sense circuitry connects the battery to the voltage regulator, thereby turning the alternator on. Once the voltage regulator turns on, the alternator will remain on and charging until the engine comes to a complete stop. If the engine idle speed and pulley ratio combination do not allow the alternator to come up to this point during starting, the engine will have to be revved up to turn the one wire alternator on. The sense circuitry in the one-wire regulator can be bypassed to excite the alternator as soon as the ignition switch is turned on. This is called three-wire operation. This means the alternator will not be dependent on reaching a certain turn on RPM.

DonMaximo · Jan 12, 2012

The Crank pulley I have is 4.5". If I recall, this is in Underdrive... it was suggested that the Stock pulley is 5.5" OD

I spoke with the Alternator Mfg (PA Performance), and factoring in the size of my Crank pulley, we determined that I'm only getting 1620 RPMs from the alternator @ idle. The Alternator requires a minimum of 1800RPM -AND- this is why I'm experiencing this problem

Their standard alternator pulley has an OD of 2.5". They recommended a 48mm (1.88") pulley.

Using their equation, my Alt RPM will now be 2151. Since this alternator requires 2000RPM to work effectively, I should be fine now.

I will update this thread next week after the part arrives.

Cheers !

-D

Noobz347 · Jan 12, 2012

So if you divide the circumference by pi and factor in the rotation of the earth then add the wind speed velocity (in knots, not mph) then eventually you’ll end up with the same conclusion I’ve had for years. Under drive pulley’s are junk.

DonMaximo · Jan 12, 2012

Yes, but they're Pretty... Pretty Shetty !

File that one under "It seemed like a good idea at the time".

Thanks for weighing in... have a great weekend !

Gearbanger 101 · Jan 13, 2012

Noobz347 said:
So if you divide the circumference by pi and factor in the rotation of the earth then add the wind speed velocity (in knots, not mph) then eventually you’ll end up with the same conclusion I’ve had for years. Under drive pulley’s are junk.

Correction. Underdrive pulleys are fine. The Fox alternators are junk.

I too had this issue. My car came with a brand new stock alternator. Installed a healthy stereo system, along with a set of under drive pulleys and the guage dropped below charge level at idle and completely out of site everytime it took a healthy hit of bass from my stereo. Went with the smallest overdrive pulley available and still had the same issue. Eventually upgraded to a 150-amp 3G unit and the problem went away.

As I stated above, these stock 75a alternators just plain suck. It doesn't matter how fast you spin them.

1991notchbackLX · Jan 13, 2012

When I had the stock 75A alternator on my old notch I disconnected it from the accessory drive belt all together, coupled the pulley to the drive of a Milwaukee 18V power drill, and hired a Mexican midget to sit in the engine bay and hold the trigger of the drill while I was driving to spin the alternator to the desired RPM for charging. It worked like a charm but the weekly cost of enchiladas and band-aids led me to eventually spring for the 130A PA Performance kit.

Noobz347 · Jan 13, 2012

Gearbanger 101 said:
Correction. Underdrive pulleys are fine. The Fox alternators are junk.

I too had this issue. My car came with a brand new stock alternator. Installed a healthy stereo system, along with a set of under drive pulleys and the guage dropped below charge level at idle and completely out of site everytime it took a healthy hit of bass from my stereo. Went with the smallest overdrive pulley available and still had the same issue. Eventually upgraded to a 150-amp 3G unit and the problem went away.

As I stated above, these stock 75a alternators just plain suck. It doesn't matter how fast you spin them.

Correction to the correction

What good is a set of UD pulleys on a pushrod 5oh? Like 3... maybe. What problems do they cause? The list is long and varied.

IMO... Get dress up pulleys if you're cleaning up under your hood. They're not worth it for HP gains.

RacEoHolic330 · Jan 13, 2012

1991notchbackLX said:
When I had the stock 75A alternator on my old notch I disconnected it from the accessory drive belt all together, coupled the pulley to the drive of a Milwaukee 18V power drill, and hired a Mexican midget to sit in the engine bay and hold the trigger of the drill while I was driving to spin the alternator to the desired RPM for charging. It worked like a charm but the weekly cost of enchiladas and band-aids led me to eventually spring for the 130A PA Performance kit.

I think a full size mexican would have been cheaper (there are more of them), but then he would need to sit on top of your hood. You could alway build a hood scoop for him to sit in while he holds the drill. You should provide him with a holster for extra 18V battery packs for a quick battery change so you keep that alternator spinning on long trips.

Gearbanger 101 · Jan 13, 2012

Noobz347 said:
Correction to the correction

What good is a set of UD pulleys on a pushrod 5oh? Like 3... maybe. What problems do they cause? The list is long and varied.

IMO... Get dress up pulleys if you're cleaning up under your hood. They're not worth it for HP gains.

Correction, to your corrections...um...correction?

The stock alternator is crap even without u/d pulleys. Make the slightest draw on your electrical system beyond stock to your vehicle (electric fan, stereo, additional accesories) and your charging is affected. Even without any changes, the 75a unit is barely adequtate. And once it gets warmed up, its even less effective. As the matter of fact, it's not even that. Try turning up your radio at night while sitting at a traffic light, with your HVac fan set on high and your rear window defroster on. You'd think your alternator quit producing current altogether.

IMO, the alternator upgrade should be one of the first things changed with these cars. It goes right up there with adding sub frame connectors for the "must do" list. These cars don't run right without an adequate amount of power being constantly fed to the ECU.

U/D pulleys aren't big horsepower makers, you're right. But they do free up a little power and mileage and will pay for themselves in a matter of months. At the $60 I paid for mine brand new, I'd say it's about the best bang for the buck of any modification you're going to perform to the car. Even if the output is only 3hp like you estimated.....what other mod can you perform to that'll gain you 3hp for $60? I've seen guys spend a lot more than that and go to a lot more trouble to gain less.

I'll agree with you that U/D pulleys will cause issues with the stock alternator in place...but it's not the pulleys that should be to blame, it's the alt.

Spring for a quality 95a-130a or better 3G/6G unit and a decent wiring kit, add the pulleys and never look back. The 3G even in 95a trim charges better at idle than the stock 75a does at 2,000RPM. And at 2,000RPM, the 3G changes better than the 75a does at WOT.

Noobz347 · Jan 13, 2012

Gearbanger 101 said:
Correction, to your corrections...um...correction?

The stock alternator is crap even without u/d pulleys. Make the slightest draw on your electrical system beyond stock to your vehicle (electric fan, stereo, additional accesories) and your charging is affected. Even without any changes, the 75a unit is barely adequtate. And once it gets warmed up, its even less effective. As the matter of fact, it's not even that. Try turning up your radio at night while sitting at a traffic light, with your HVac fan set on high and your rear window defroster on. You'd think your alternator quit producing current altogether.

IMO, the alternator upgrade should be one of the first things changed with these cars. It goes right up there with adding sub frame connectors for the "must do" list. These cars don't run right without an adequate amount of power being constantly fed to the ECU.

U/D pulleys aren't big horsepower makers, you're right. But they do free up a little power and mileage and will pay for themselves in a matter of months. At the $60 I paid for mine brand new, I'd say it's about the best bang for the buck of any modification you're going to perform to the car. Even if the output is only 3hp like you estimated.....what other mod can you perform to that'll gain you 3hp for $60? I've seen guys spend a lot more than that and go to a lot more trouble to gain less.

I'll agree with you that U/D pulleys will cause issues with the stock alternator in place...but it's not the pulleys that should be to blame, it's the alt.

Spring for a quality 95a-130a or better 3G/6G unit and a decent wiring kit, add the pulleys and never look back. The 3G even in 95a trim charges better at idle than the stock 75a does at 2,000RPM. And at 2,000RPM, the 3G changes better than the 75a does at WOT.

Correcting the correct corrections to the original correction....

Yeah... the stock alt is definitely junk. A whopping 80 amp at full tilt. It wasn't all that long ago though, that I saw another thread about someone having cooling issues. Again... OEM components including the radiator and water pump, and returning to the stock pulleys cured his issue.

I'm also reminded of a dyno comparison where a pull was done with stock accessory drive then done again using no serp belt and electric accessories to pump water and provide DC power. The HP increase over the power band was something like 12 whole RWHP! WOOT! Er... I mean, woot.

So I got to thinking about it a little. A set of under drives is what... 20%? So you figure 2.4 RWHP average over the power band.

I just can't see spending money on the pulleys + money having to upgrade the alt and radiator for an increase of 2.4 HP to the wheels.

Track vehicles? Whole different matter all together. Already have the upgrades? Then I could see it. Otherwise... I think they make the engine bay look better.

I just think that for performance, it's a poor (and I use the term loosely), 'upgrade'.

Gearbanger 101 · Jan 13, 2012

As far as cooling goes, youve got to have a pretty hardcore engine and/or live in a pretty scalding hot climate so see any detrimental effects from turning you water pump all of 20% slower. And if that is in fact the case, then you're in need of a heavier duty radiator, more than anything else.

I've had U/D pulleys on my last 2-Mustangs as well as my current daily driven F150. Not one, single issue with cooling.

Let's be honest, of cooling is that big of a concern, a $10 180-deg thermostat will shelve any concerns.

1991notchbackLX · Jan 13, 2012

Gearbanger 101 said:
As far as cooling goes, youve got to have a pretty hardcore engine and/or live in a pretty scalding hot climate so see any detrimental effects from turning you water pump all of 20% slower. And if that is in fact the case, then you're in need of a heavier duty radiator, more than anything else.

I've had U/D pulleys on my last 2-Mustangs as well as my current daily driven F150. Not one, single issue with cooling.

Let's be honest, of cooling is that big of a concern, a $10 180-deg thermostat will shelve any concerns.

Brian, very surprised that you'd even hint at running a 180* thermostat. You know as well as we all do that 195* is the optimal operating temperature for the 5.0L Ford.

Gearbanger 101 · Jan 13, 2012

1991notchbackLX said:
Brian, very surprised that you'd even hint at running a 180* thermostat. You know as well as we all do that 195* is the optimal operating temperature for the 5.0L Ford.

I only suggested it in the event someone was experiencing cooling issues. Otherwise, I agree...the stock 195-deg thermostat is ideal.

1991notchbackLX · Jan 13, 2012

Gearbanger 101 said:
I only suggested it in the event someone was experiencing cooling issues. Otherwise, I agree...the stock 195-deg thermostat is ideal.

I know you know that I know that you know that I know that you know. Just messing with you a little bit.

Noobz347 · Jan 13, 2012

Meh... who knows?

All I know is that I see more headaches caused by UDs than I see performance gains. For me at least, it's a "Nah... I'll Pass" mod.

Way back when, when I was bone stock, I installed em just like everyone else (OEM alt and all). They worked just fine until I started working the night shift. So more money for an OD alt pulley (kinda defeats the purpose). Then when the mods start, I start having cooling hiccups (no so much problems but little spikes. You guys know the kind... bugs you till you know what it is). Water pump pulley goes back to stock. Rats... Down to 2. Then I decide I want to go with a PD blower and the whole kit comes off.

So initially, they worked just fine. I of course, ended up selling them (like most folks). It wasn't until MUCH later that I discovered how little they really offered in the way of HP. That combined with the associated problems is why I'm not a huge fan. By the time you get done modding everything to accommodate the slow-down, you end up with a lot more than just $60 for that 2.4 HP.

Having said all of that... I may be in the market for another set in the near future. But that is because I'm thinking about going with a over drive crank pulley and will use the acc pulleys to bring them back down to regular speed.

I guess they have their niche... Particularly for folks who have thought it out and planned for them to coincide with other mods. For stock or near stock though... I'd say keep your $60 and apply it toward a TB and spacer.

Boydster · Jan 14, 2012

Noobz347 said:
(no so much problems but little spikes. You guys know the kind... bugs you till you know what it is).

Heh heh heh heh... yeah. I know.

FWIW, I had UD pulleys like you did, back when the car was stock and I didn't know better. Put a stereo in it and there went the charging system.

Alternator - Headlights dim - UD Pulleys

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