Underdrive alternator pulley! You gonna like this!!

[96blak54]

The pulley is from a modular steering pump. It will need minimal machine work to adapt. I.D. needs opened up .040" and a little bit off the hub length. Pulley is 5.5" O.D. Original pulley size is 2.5" O.D.

 

[96blak54]

Original max rpm speed of small pulley put the alternator running 16,000rpm. Now the max rpm will be 7500rpm.

Not sure how well idle speed output will be, but i got a good big, strong battery in the trunk!

 

[DKblue98GT]

Wow, under drive is right. Let us know how it works.

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[96blak54]

Well...i tell you right now, the same size works really well on a particular coyote stock drag car! Only its made of aluminum.

 

[evilcw311]

I can’t imagine the 0.0000125th of a snail power will justify the voltage loss.

But I too am curious. I’d say this is right up there with the 18 to whatever compression ratio you tried. If nothing else it’s fun to experiment.


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[ttocs]

we already know how well udp's do at idle, I don't care how big your battery is this will be a quick one.

 

[evilcw311]

My concern is that even at driving speeds it won’t put out enough to maintain the battery as it’s now spinning at basically half of what it should. It would be like driving around with an alternator that is dying.

It will most definitely:
1) not create enough voltage.
2) run hot cause it’s not spinning fast enough to cool the internals of the alternator
3) burn up the regulator cause it will be overworking to try and make up the difference.


But again, please proceed while we watch and enjoy the popcorn. I’m curious to see how long before it does start causing problems.


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[PinkieT]

My concern is that even at driving speeds it won’t put out enough to maintain the battery as it’s now spinning at basically half of what it should. It would be like driving around with an alternator that is dying.

It will most definitely:
1) not create enough voltage.
2) run hot cause it’s not spinning fast enough to cool the internals of the alternator
3) burn up the regulator cause it will be overworking to try and make up the difference.


But again, please proceed while we watch and enjoy the popcorn. I’m curious to see how long before it does start causing problems.

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"Always with the negative waves Moriarty, always with the negative waves."

 

[ttocs]

are you going to do some dyno runs to see if its worth it or just seat of the pants and see if the battery dies?

 

[evilcw311]

"Always with the negative waves Moriarty, always with the negative waves."

Being a realist doesn’t make me a pessimist.

Scott and I both come from high end mobile electronics backgrounds and we know what problems udp’s normally cause. This behemoth will be even worse. It’s simple mechanics and understanding of such.

Again, I’m curious to see Gary’s results with meters being used to show if it can even keep up with the current drawn during driving. I’m just explaining why it’s unfortunately going to cause problems.


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[lutter94]

Isn't the only load on the alternator whatever the draw from the system is? So trying to slow it down is only going to reduce your ability to charge, and cause issues? I.e. wouldn't shutting electrical devices off reduce alternator load? Seems to me it would be better to reduce weight of extra batteries.

 

[ttocs]

#1)Isn't the only load on the alternator whatever the draw from the system is? #2)So trying to slow it down is only going to reduce your ability to charge, and cause issues?#3) I.e. wouldn't shutting electrical devices off reduce alternator load? Seems to me it would be better to reduce weight of extra batteries.

1.)yes
2.)yes
3.)yes

Problem is that he has not done anything to reduce any load on the alternator and the stock alternator was not made with much headroom to allow for it to be expanded/tested. Not sure why extra batteries came up because if it isn't charging enough he will need more batteries to keep it running, and would need to plug them in when it was not running to charge them as well. As logan mentioned earlier an alt is meant to develop and dissipate a certain amount of heat and it cools itself by spinning and moving air through it. Slowing it down not only increases the heat that builds from reduced output but also takes away its ability to get rid of that heat.

 

[96blak54]

You guys have it figured out!

The idea comes to the trailer queen hard core drag racer. You know, that guy who trailers the car and only runs 2 rpm ranges?...idle and wide open. The intended purpose is to find the extent of the modifications and simplicity for that guy trying to find that edge over the competition.

For everyday driving, you guys nailed every problem that would be encountered. Good thread tho!

 

[01yellercobra]

Years ago I read an article in Hot Rod about one of the race cars that was popular at the time. I can't remember his name, but he was a rival of Pat Musi.

Anyway, I still remember they had an alternator driven off the driveshaft. Apparently the car would slow down half track because the batteries were draining. So they basically had the alternator come on at that point. Always thought it was odd/cool.

 

[evilcw311]

Most drag cars don’t run alternators as much anymore if track only cars. They run big batteries and charge in between rounds.

Glad to know your not crazy enough to try this on your car Gary. You were scaring me for a sec.


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[ttocs]

yes for a track only car it would not matter. I thought it was a little odd looking to look at the cars accessories last time I was at the track as there were nearly none on there or looked like it if they had an electric water pump.

 

[96blak54]

Oh im going to try it!

 

[PinkieT]

Being a realist doesn’t make me a pessimist.

Scott and I both come from high end mobile electronics backgrounds and we know what problems udp’s normally cause. This behemoth will be even worse. It’s simple mechanics and understanding of such.

Again, I’m curious to see Gary’s results with meters being used to show if it can even keep up with the current drawn during driving. I’m just explaining why it’s unfortunately going to cause problems.

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I get it, just 1)pullin' your leg, and 2) see who recognizes the quote from one of my favorite oddball movies.

 

[Silver95bird]

A normal stock setup gets to full charge at what, like 900rpms? So this wouldn't be at full charge til probably double that. For a stock auto trans car I'd never recommend it. For a 4.10s 5 spd car with no big speakers in the trunk, it might not be too terrible. Nobody with 4.10s drives around under 1500 lugging it like the autos do. It'd be a fun experiment. Get a 2ñd stock alt and swap them between runs!

 

[96blak54]

There is also this idea of switching the alt into an electric motor! That tiny pulley would have had no traction.