Smaller than stock alternator pulley for more charge current

[twopointsevenone Lurker Find all posts View Profile Close twopointsevenone]

Hi

I have a 1997 KZJ95 (Diesel with the 1KZ-TE motor). I've already increased the charge system voltage with a diode, it's about 14.6 V when cold and about 14.2 V when hot. This is fine for my AGM batteries.

I'd like more charge current at idle. The charge is fine when driving but in city traffic the car idles a lot and the charge current is meager if I got the lights on, which is always.

My trusted mechanic says that the solution is a smaller alternator pulley. It's ok, I hardly ever rev the motor more than 3000/min.

Has anyone ever seen a smaller than stock alternator pulley for this motor? I can have one made but buying would be better.

Thanks & greetings from Switzerland

[croozza Avid PP Poster! Find all posts View Profile Close croozza]

Re: Smaller than stock alternator pulley for more charge current

Adding an extra alternator is a big job, plus you have to change all your drive belts to suit the new arrangement, the easiest thing to do is change the pully for a smaller one on the original altenator, reason being is this will make the altenator spin at a higher revolution which will increase the charge given to the batteries.

[twopointsevenone Lurker Find all posts View Profile Close twopointsevenone]

Re: Smaller than stock alternator pulley for more charge current

I'm looking for a smaller than original pulley for the stock alternator, making the alternator run faster. Where can I buy one?

[tassie tiger Advanced Member Find all posts View Profile Close tassie tiger]

Re: Smaller than stock alternator pulley for more charge current

If you have no luck you can always pull the alternator, pull the pulley and head off to the local auto electrician. They should have something even off an old alt.

Getting cold over there yet?

[Derb Senior Member Find all posts View Profile Close Derb]

Re: Smaller than stock alternator pulley for more charge current

Hi twopointseven. Do the math before fitting a smaller pulley. Sooner or later you are going to bump the rev's and then it will be copper everywhere. Centrifugal force is pretty impressive stuff. You will also be reducing the belt contact area. Find an auto electrician who knows his stuff and can tell you the max rpm of your alternator, work out your vehicle theoretical max rpm and do the math. You may well find that you have not got much to come or go on. Might be easier and cheaper in the long run to fit a higher output alternator. No doubt one of our fellow members has already gone up this road and can help. I have seen cars idle for hours with their lights on and still start in the morning! could even be cheaper to simply fit another battery somewhere. Cheers, Derb.

[Matty80 Avid PP Poster! Find all posts View Profile Close Matty80]

Re: Smaller than stock alternator pulley for more charge current

I am unfamiliar with the complexities of the 90 series alternator so a few questions...

• 1. Does it have a self-regulating voltage circuit?
  2. What is the alternators rating (will be in Volts and amps, ie 14.4Vdc, 70A)?
  3. Is anyone able to provide a wiring diagram for the alternator in a 90 series?

Please note the following points about AC power generation using alternators & generators...

The speed of a generator/alternator does not in anyway affect the current output, slowing it down or speeding it up will not change the fact that an alternator is only capable of producing the maximum number of amps as stated on its name plate.

The only condition that will change the amount of amps the generator/alternator outputs is the load applied to it. That being attributed to the state of the battery (fully charged - no load, flat - high load) and additionally the load generated by the cars electrical system - computers, lighting, radio, etc.

Test this if you like! (Prove me wrong maybe?) At idle speed (say 700-1000rpm) your alternator output will be 14.4Vdc (or your equivalent alternators output as stated by the name plate), but at 3000 rpm the ouput will still be 14.4Vdc (or equiv.)! Check it with your multimeter...

However, if you apply more load (use more current - not to be confused with voltage), the alternator has to work harder and wants/tries to slow down!!! It doesn't, because it is so small when compared to the machine driving it... However, this means that the voltage wants to drop {insert complicated electrical formulae here}, this is where the self regulating voltage circuit comes in and increases the excitation field which brings the output back to the correct voltage. if the load then drops (you switched the lights off) the alternator doesn't have to work as hard and the voltage wants to increase in which case the AVR reduces the excitation feild thus reducing the generated voltage back to the correct value.

Please note that in some alternators the excitation field does not become self sufficient until and increased number of revs as produced over and above idle speed, however, once this is done, the alternator will then work at the lower idle speed.

So what am I saying, reducing pulley size to increase alternator speed will cause excess stress on the windings, brushes, springs, rotor and bearings that it was not originally intended for. It will not increase current - cos it is not affected by speed but rather design. And any voltage changes will be negated by the regulating circuit.

In short, if you want more current to power more/larger systems then invest in a bigger alternator and use the correct sized pulley for which it was designed!

Cheers Matt

[twopointsevenone Lurker Find all posts View Profile Close twopointsevenone]

Re: Smaller than stock alternator pulley for more charge current

Thanks guys (mates :-)

@tassie tiger: I was hoping to have a solution before removing parts and disabling the car. And I wouldn't know where to go within bicycling distance. Yes, it got cold now, here in the lowlands its just below freezing and there's a bit of snow not melting away.

@Derb: Good point about the max. rpm of the alternator. We have bi-annual pollution tests and they have to rev the motor without load at full throttle for about 15 seconds several times.

@Matt: It's pretty well known that most alternators don't reach their rated power at idle. I have permanently installed Volt meters for both my batteries. Indeed, when nothing is switched on, the voltage is constant regardless of rpm, about 14.3 V when the engine bay is hot. When I switch on the lights and the seat heater, the voltage drops to maybe 13 V already at idle. The batteries might still charge slightly but the point is I'd like a bit more voltage and charge current at all times. Above 1200/min or so, everything is fine.

1. Does it have a self-regulating voltage circuit?
2. What is the alternators rating (will be in Volts and amps, ie 14.4Vdc, 70A)?
3. Is anyone able to provide a wiring diagram for the alternator in a 90 series?

1. Sure!
2. I'm pretty sure that there's no rated Amps at idle speed. And I'm not worried about the maximum Amps.
3. I think I have a file somewhere. What should I look for, I'm an electrical engineer?

from http://www.alternatorparts.com/FAQ.htm:

How do I get more power at Idle?
Improving Output at Idle Speed

There are several ways to get more power at lower engine speeds. If you only require a little more power at lower engine speeds you may be able to use a smaller pulley. The smaller pulley turns the alternator faster at lower speeds thus making more power. When using a smaller pulley care should be taken not to over rev the motor. If you over rev the alternator with a smaller pulley the alternator can fail.

The best way by far to obtain more power at lower engine speeds is to install an oversize alternator. The physically larger alternators produce more power at lower engine speeds and are much more reliable at higher outputs. Installing a higher output alternator that is the same size as your original alternator will not give you more power at idle.

Conclusion: There is no conclusion yet :-). I think if I can find a smaller pulley that's known to work without removing the original one, I'll go for it. If not, I'll abandon the project.

[croozza Avid PP Poster! Find all posts View Profile Close croozza]

Re: Smaller than stock alternator pulley for more charge current

One thing I found when I had to replace the alternator on my old 80 series (when I had it), was the max amp rating was 120 amps, but this was at 9000 rpm, now i'm sure if you do the math and see how fast your max rpm is with the motor and the different size of the pully on the alt, it was not possable to acheive that 9000 rpm at the alt, and this was for a diesel motor too, a petrol may have a different max rpm at the alt though, so you may need to find out the rating of the alt before you proceed.

[Matty80 Avid PP Poster! Find all posts View Profile Close Matty80]

Re: Smaller than stock alternator pulley for more charge current

I'm not doubting your profession or your knowledge base... But the simple fact of the matter is - an alternator will provide the same voltage regardless of its speed (so long as its speed is withing the confines of what it is designed for), and current supplied is solely dependant on the load you apply to the alternator not the speed of the alternator.

Simply spinning it faster wont change anything, unless the voltage regulation circuit is faulty, or the rectifying diodes are faulty.

My trusted mechanic says that the solution is a smaller alternator pulley

He's a mechanic! Not an electrician. If you want correct advise go to the correct people, someone trained in Electrical Generators & Motors, Power Generation, Distribution Systems and a few years of experience. That can be at the automotive level or industrial electrician level - its all the same stuff.

I'd like more charge current at idle. The charge is fine when driving but in city traffic the car idles a lot and the charge current is meager if I got the lights on, which is always.

I must admit, you have your relationships between voltage, current and load are mixed. Electrical relationships: "Frequency & Speed", "Current & Load", "Voltage & Excitation (Magnetic Field Size)"...

If you choose to go ahead with this mod that is entirely your choice, I personnally would not even think of it. I'd fit a larger alternator, but why would you need to? This idea of increasing speed ot get more charge current is not based on a correct understanding of power generation or consumer loading, and is agasint the fundamentals of basic electrical principles.

But I'm not here to stop you doing whatever it is you think you need to do to your car! Just offering a little professional advise...

Matt

[croozza Avid PP Poster! Find all posts View Profile Close croozza]

Re: Smaller than stock alternator pulley for more charge current

I'm not doubting your profession or your knowledge base... But the simple fact of the matter is - an alternator will provide the same voltage regardless of its speed (so long as its speed is withing the confines of what it is designed for), and current supplied is solely dependant on the load you apply to the alternator not the speed of the alternator.

Simply spinning it faster wont change anything, unless the voltage regulation circuit is faulty, or the rectifying diodes are faulty.

My trusted mechanic says that the solution is a smaller alternator pulley

He's a mechanic! Not an electrician. If you want correct advise go to the correct people, someone trained in Electrical Generators & Motors, Power Generation, Distribution Systems and a few years of experience. That can be at the automotive level or industrial electrician level - its all the same stuff.

I'd like more charge current at idle. The charge is fine when driving but in city traffic the car idles a lot and the charge current is meager if I got the lights on, which is always.

I must admit, you have your relationships between voltage, current and load are mixed. Electrical relationships: "Frequency & Speed", "Current & Load", "Voltage & Excitation (Magnetic Field Size)"...

If you choose to go ahead with this mod that is entirely your choice, I personnally would not even think of it. I'd fit a larger alternator, but why would you need to? This idea of increasing speed ot get more charge current is not based on a correct understanding of power generation or consumer loading, and is agasint the fundamentals of basic electrical principles.

But I'm not here to stop you doing whatever it is you think you need to do to your car! Just offering a little professional advise...

Matt

Sorry Matt, but the graph that I was provided with at the time I installed the new alt, showed the amps at different rpm, and the faster it spun the higher the amps were. It went something like this, 0 rpm = 0 amps, 1000 rpm = 20 amps, 2000 rpm = 30 amps, 3000 rpm = 45 amps, 4000 rpm = 60 amps, 5000 rpm = 80 amps, and so on. i worked out that when the motor was doing 4500 rpm (which was redlining it in the 1HZ) the alt was doing around 9000 rpm which gave the full rating of the alt. If you were to check the amps at the alt at idle and then again at different rpm the amp rating will be at different levels.

[twopointsevenone Lurker Find all posts View Profile Close twopointsevenone]

Re: Smaller than stock alternator pulley for more charge current

Matt, please don't take this to a personal level, it's annoying. "My" mechanic works at a local auto electro shop and he's qualified just fine. I don't like being accused of "you have your relationships between voltage, current and load are mixed" either. I disagree with most of your technical comments too. And look:





And I realize that alternator rpm is higher than engine rpm. But at no rpm the current vs. rpm curve is horizontal which is essentially what you claim.

[Matty80 Avid PP Poster! Find all posts View Profile Close Matty80]

Re: Smaller than stock alternator pulley for more charge current

[quote="twopointsevenone"]Matt, please don't take this to a personal level, it's annoying.[/quote}

Its not personal mate, and I apologise if I came across that way... Certainly not my intention...

I'll take the hit on the curves you have provided - and only say that I have probably given the regulating circuits used for alternators more credit than they were due. That is the efficiency of their ability to maintain voltage levels though a given rpm range.

As for the theories behind ac power generation (incluside of conversion to dc), my comments are correct as these principles are how the 11kV 42MW diesel electric power plant operates not 200m from where I sit now. I also spent time with the electricians and electronic techs that work for me formulating as simple explainations as possible - still, it appears we all over estimated efficiencies in the smaller machines.

I have since located some information that the alternator due to size (and don't quote me - as I do not trust the source) is only around the 60% efficient mark, however the machines I have out here are up toward the 98% mark - this would help explain the differences in voltage over the alternator rev range also.

So I take the correction... Stress free!

Matt