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Powermaster alternator

R

RD400HP

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Location
Fowler, Ohio
I bought a Powermaster 140 amp alt off Summit and the pully is around 3/8 of an inch smaller in diameter than stock, my question is what is the output going to be after I put the stock pulley on? Thank's.

Mark
 
I would call them for verification. I think the output is fairly linear with rpm. I think it should output 140 amps at near 2000 rpm?, 0 amps at 0 rpm (at the crank or what ever rated output rpm is see if says anywhere). Do the math for gear reduction (post the pulley diameters and I or someone can calculate the difference in rpm's of alternator) and that should get a ball park answer.
I think since the numbers are all the same I think you can just say the correct pulley radius pulley is 0.1875" (1/2 of 3/8) larger such that it will turn .1875 % slower. Then 0.1875% less output or about 113.75 amperage vs 140 amps (again at the rated rpm).

But you have to see what the rated rpm is at then calculate what you are really outputting driving around.

Note ...
I am kinda assuming this as I worked on a project and they said if you want more amps just spin it faster and output was linear with rpm iirc so we changed the driven pulley size (this was not on a truck and we had different options for driving pulley diameter.
 
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If I get time I will try to measure the main drive pulley diameter or someone post it.

You will need to give this to them so they can corelate the alternator speed when you call them to get actual output for the application at different crank rpms.
 
A good alternator manufacturer should be able to give you a graph or data of the output versus rpm so you can figure out pulley sizing etc. There was a time when certain manufacturers would supply a graph print out of the output of the actual unit from when it was on the test bed. The plot starts off steep and fairly linear and at the top levels off. Attached is a graph as an example from a manufacturer that I install and supply. Just bear in mind that changing pulley sizes will effect tach output.

Cheers
Nobby
 

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OK so its not linear for the whole range but fairly linear at low rpms and again at high rpms with different slopes. We must have been up into the higher range. Not exactly linear but not bad approximation if you know slope and output at a certain rpm you could interpolate/extrapolate somewhat at different sides of the "knee" of the graph.
 
The pully measures 2.046 the stock pully is 2.411 I hope I'm reading it right. There is a card attached to the alt that says at 2400 rpm its output is 92 amps with stock pully at 7500 rpm output is 143, volts 14.8. This alt is was what was listed for my truck 94 to 95 you would think it would have the correct pully on it. I think thats a pretty cheap way to crank up the output is to put a smaller pully on it. This alt will be the same as the stock 100 that came off the truck after I swap pulles. I could have went to Advance or Autozone and bought a new 105 with a lifetime warrentee for a $120 this one was $181 with shipping.

Mark
 
Hang on its probably not that bad. I interpret that's the alternator rotor rpm.

Such that at

as shipped - alternator pulley dia 2.046 to 7-1/2 is a ratio of 3.666

alternator rpm 2500 crank is 683 rpm output 92 amps
alternator rpm 7500 crank is 2049 rpm output is 143 amps

IF so then ..

With diesel pulley dia 2.411 to 7-1/2 is a ratio of 3.111

alternator rpm 2500 crank is 803 rpm output is 92 amps
alternator rpm 7500 crank is 2410 rpm output is 143 amps


Anyone know the rpm rating of the gm alternator ?

You would have to have the powermaster graph vs GM graph to confirm difference in output at different rpm's


Its a bit fuzzy in my mind but ....
What we did before was put a bigger drive pulley on it and this cranked up the alternator rotor speed to get a bit more out of it. And I heard 2nd hand that it was fairly linear if we wanted more amps we could drive it faster but there was less return after the expected range for rpm increase or something like that but still in did increase with increased rpm.
 
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Yup poor mans way to get the current up.

Just out of interest how much current are you looking for, and there is a reason why I ask?

Cheers
Nobby
 
nobby said:
Yup poor mans way to get the current up.

Just out of interest how much current are you looking for, and there is a reason why I ask?

Cheers
Nobby
Click to expand...



Just looking for a little more than the stock 100 amp, you start looking for more than 140 amp and it starts getting expensive Nobby.

Mark
 
Yep sure does start getting expensive, I should know some of the units I install/sell get over a 1000 dollars. However those suckers will put out 24/7 and not sweat about the heat.

The reason why I ask is this, there is a general rule of using only around say 2/3rds output continuous from an alternator from a longevity standpoint especially automotive style ones like these perhaps even a little less. The true hot rated units that I use I trust at their rated output and give an OK lifespan and yet I still aim to size with that 2/3rds in mind. Just some food for thought.

Cheers
Nobby
 
My 95 GMC had one bad battery and that was a little to much for the alt to handle and burnt it so thats why I bought the Powermaster 140. If Advance or Autozone would have handled a 140 I would have bought it there and got a lifetime warranty.

Mark
 
Does any members know what the stock alternator pully diameter is for a 95? I pulled the alt off and I don't see the Delco name anywhere on it makes me wonder if it has the correct pully on it now.

Mark
 
IIRC the correct size is 62mm. The regular pulley usually is 57mm. Or thereabouts. It is about 5mm difference.

In my case, I am not worried too much. I have the 57mm pulley in my alt (not Powermaster though).
The rpm in the tach is off a little high but not an issue with me.
 
Thanks AK and JMJ for the information I have the larger pully of the 2. How much is your tach off JNJ by using the small pully?

Mark
 
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