H.O. alternator made me LOOSE voltage?

[ghart999 10+ year member]

How can one get their HO alt tested for voltage/amps at idle, cruise, etc? Can I get this done at any auto parts shop?

I have a 200A alt from EA as well.

 

[4frogger 10+ year member]

Yours didn't come with a birth sheet?

Not really sure how you would be able to test that out, good question, sorry for the lack of an answer.

 

[OoMesKoO 10+ year member]

I think some of you were right with the idle thing. My tahoe idles at 500rpm. So i think if I either up the idle, or get a smaller pulley... it'll solve my problem...

 

[OoMesKoO 10+ year member]

Now... where do i get a smaller pulley....?

 

[IgnoreMe 5,000+ posts]

If you go with a smaller pulley you run into the chance that at high rpms it spins too fast which would be a bad thing.
My HO does the same thing and its annoying, but its not like my car is going to stall at idle or anything.

No HO alternator produces much power at idle. When you look at all the alts out there you will see a common issue and thats power produced at idle.

IIRC most alternators as well as HO alternators can take 20k+ rpms. and most are also 2.5-3:1 ratio (if i remember correctly). that means he would have to be revving his motor up to 7k rpm for extended periods of time....and i dont know anyone that does that, now if you drive an import with a high redline and you race it, then maybe...hell my redline is 5k rpm. get a smaller pulley, youll be fine.

heres a quote i found

"Typically, a street driven car should have a pulley ratio of at least 3:1. If the vehicle has an automatic transmission with a low idle and the vehicle spends a lot of time cruising, then a higher pulley ratio - perhaps 3.5:1 - should be used. Alternators can take high speeds up to 20,000 RPMs for short periods, so overdriving the unit is not a problem"

contact the alternator compnay you bought it from to see if they make smaller pulley's for the unit, and ask them the ratio as well.

you can get your alternator benched at autozone. 50% chance they will bench it wrong though and tell you its putting out 25A at cruise. if they give you higher figures then chances are they benched it right.

 

[OoMesKoO 10+ year member]

Hey guys. Just figured id update this. I bought a new pulley. Helped A little. A very little. I need to find a way to up the idle in my Tahoe to around 6-700 or so. Its at like 450-500 now. Anyone know?

 

[Lakota 5,000+ posts]

Small pulleys are nice

 

[Andrizzle 10+ year member]

also make sure the belt is perfect,

any looseness = slipping @ idle = glazing the pulley = more slipping = worse and worse progressing voltage and alt belt squealing eventually if u let it get there.

Agreed, try upping the idle rpm by a few hundred, not too much - give ur brakes and gas mileage a rest, i mean dont crank the idle or anything...

Also, getting a nice batt (kinetik or yellowtop) helps ALOT. so do it.

 

[OoMesKoO 10+ year member]

also make sure the belt is perfect,
any looseness = slipping @ idle = glazing the pulley = more slipping = worse and worse progressing voltage and alt belt squealing eventually if u let it get there.

Agreed, try upping the idle rpm by a few hundred, not too much - give ur brakes and gas mileage a rest, i mean dont crank the idle or anything...

You wouldnt by any chance know how to do this would ya?

Also, getting a nice batt (kinetik or yellowtop) helps ALOT. so do it.

In place of the stocker, or as an extra battery?

 

[4frogger 10+ year member]

If you did both that would help the most.

 

[IgnoreMe 5,000+ posts]

how much smaller was this pulley, whats the ratio on it

 

[Boomin_tahoe 5,000+ posts]

Well... after 180 bucks, I bought a brandy new alterstart 180a alternator for my tahoe. Well, after i installed it, I have worse voltage than i did with my stock 100a alt. I dont get it. I got the big 3 done, on a stock battery.
Its like... when i pull up to a stop light, with foot on the brake, the voltage just drops.... no music or anything. As soon as i drive it shoots right back up though. Someone have an idea?

Thanks!

I had the same exact problem when I bought an Excessive Amperage alt from Nathan, spent 300 for it. I emailed him about it and he says that the alt could be bad and says to go ahead and send it to him when I getta chance. Well needless to say, on my way home from work one day my blzr just died. Wouldn't start and couldnt jumpstart it. I sent Nathan the alt. he tested it said that he couldn't find anything wrong at all. Of course I was surprised. So I explained the situation that I was loosing vlotage at a stop sign or stop light....whenever I was stopped. So he suggested that he redo the guts inside of the alt for 150 bux and says the RPM's could be the problem. Paid him the $$, got the alt back shortly, installed it and havent' had a problem since. BUT....I did notice my battery light would come on all the time when this situation happened. I even had a nice Costco battery but I think Nathan fixed it. And I've had it back since Jan of this past yr.

 

[spoonraker 10+ year member]

This is a very very common problem and very easy to fix. The bigger problem is the lack of knowledge on this issue...

An alternator is nothing but an electrical generator. It spins wires near magnets which move the electrons in the wire, thus creating electricity.

Amperage is simply the number of electrons that are moving. Obviously, faster spinning causes more movement, or higher amperage.

In the case of your alternator, the rotation of the wires varies directly with the rotation of your engine. Meaning, for those who haven't passed 7th grade math, that the faster or slower your engine is rotating, the faster or slower your alternator is rotating.

Now as we all know the rotation of the engine is far from constant, therefore the rotation of the alternator is not constant, and again the amperage produced by the alternator is not constant. At low RPMs your alternator will produce lower amperage than at higher speeds.

This is where people run into problems. Their alternator doesn't produce enough current at low speeds, but they are fine at higher speeds near their alternators peak output.

The alternator is not directly linked to the engine. There is a pulley which connects the engine to your alternator. Think of it like the gears of a bike. When you shift into a higher gear, the chain jumps to a smaller sprocket, and every time you pedal the wheel turns more than it did in a lower gear. The alternator works the same way. If you put a smaller pulley on it, the alternator will turn faster with the same amount of engine RPMs, which will solve 90% of people's high output alternator problems.

 

[DumpinTreos 10+ year member]

Interesting thread my EA alt did the same thing everytime my car shifted gears (auto) the alt light would go on (battery+brake light on my car) Well i'm still gonna save up for a Ohio Gen alt anyways

 

[IgnoreMe 5,000+ posts]

This is a very very common problem and very easy to fix. The bigger problem is the lack of knowledge on this issue...
An alternator is nothing but an electrical generator. It spins wires near magnets which move the electrons in the wire, thus creating electricity.

Amperage is simply the number of electrons that are moving. Obviously, faster spinning causes more movement, or higher amperage.

In the case of your alternator, the rotation of the wires varies directly with the rotation of your engine. Meaning, for those who haven't passed 7th grade math, that the faster or slower your engine is rotating, the faster or slower your alternator is rotating.

Now as we all know the rotation of the engine is far from constant, therefore the rotation of the alternator is not constant, and again the amperage produced by the alternator is not constant. At low RPMs your alternator will produce lower amperage than at higher speeds.

This is where people run into problems. Their alternator doesn't produce enough current at low speeds, but they are fine at higher speeds near their alternators peak output.

The alternator is not directly linked to the engine. There is a pulley which connects the engine to your alternator. Think of it like the gears of a bike. When you shift into a higher gear, the chain jumps to a smaller sprocket, and every time you pedal the wheel turns more than it did in a lower gear. The alternator works the same way. If you put a smaller pulley on it, the alternator will turn faster with the same amount of engine RPMs, which will solve 90% of people's high output alternator problems.

im assuming your just trying to make it easier for most people to understand in the first bolded quote. but alternators dont use magnets. electricity running through a conductor will create a magnetic field. the magnetic field has a north and south pole like that picture, and it induces voltage in the stator.

the second quote, again im assuming your just making it easier for people to understand. however, there is a factor people need to understand. counter EMF. an given alternator design will produce more and more amperage up to a certain RPM until there is counter emf. its basically like a self limiting feature of the alternator....hence people that rev their engines up to 7k rpm trying to show off to friends and ending up with a bottom end engine knock the size of king kong in their car, yet not gaining any worthwhile usable amperage for their system...