Alternator overspeed

[Mark Maulden]

I installed a series 7 Balmar and everything works fine. Except I want to slow it down by about 1/2. The pulley dia on the alternator is 2.5". The diam at the drive pulley is about 13 giver or take. The ratio is 5.9 as measured by a laser tach. Redline for the alternator is 15k rpm. At 2500engine rpm, the alt is going 14750 rpm. Seems to me I need a 5" alt pulley. It would keep alt speeds between 2400 7500 and supplying same performance. The math doesn't work perfectly as there was some rounding...thing is nobody seems to have a 5" pulley for a single 3/8 belt. Even the electrical shops are skeptical.. I would just like to operate it further down on the curve for longevity. Any other issues of a larger pulley such as side loads? Suggestions as to where to source a pulley?

 

[dparilla]

You don't need to reduce it by half. A five inch pulley on the alternator sounds huge to me, I can't ever recall seeing one that large, and I would think that the low rpm would reduce the alternator output at idle to an unacceptable amount.

 

[Mark Maulden]

Have to remember my pulley ratio is 5.9. The drive pulley on the crankshaft is only a little smaller than the flywheel. 800 rpm on the engine is 4800 on the alternator. If I go from 2.5 pulley to a 5" pulley, the alternator would go to 2400 rpm. Full output starts at 2000. I know it seems weird to have a big pulley, but the ratio is huge.....at 2500 engine rpm, alternator is at 14750 rpm. Even though it's still within factory spec, (barely) why wear it out prematurely?

 

[Charles Erwin]

Do you need a 13" v belt pulley at the crankshaft? Is is possible replace the present crankshaft pulley with a smaller 5 inch?

If not, then can you fasten the smaller pulley to face of the present larger one and modify the mounting hardware?

Charles

 

[Mark Maulden]

I'd have to pull the flywheel which is heavy. After 34 yrs, it probably won't want to come off. There is no room on the outside for a pulley or a way to mount one. Then I'd have totally redesign the alt mount. The starter ring gear is also in the mix. Volvo MD17c

 

[Stu Jackson]

Mark, why bother? You can reduce the output IF you have an external regulator, by using either amp manager or small engine mode.

 

[Charles Erwin]

Call Balmar and discuss?

 

[kloudie1]

A good machine shop could turn a custom one in whatever diameter you need. My bet is cost would be less than $100 .. Take the old one off and take it to them and ask for the same belt size and shaft size and specify the new belt diameter. Finding a proper belt might be interesting, but if you know the width and measure the circumference around the new pulley and the drive pulley, a good belt place can fix ya up pretty quickly.

 

[Mark Maulden]

Called Balmar and discussed. I was even going to take it to them as they're only 1/2 hr away. They said they only had the 2.5 pulley. They did say it would be good to slow it down for longevity. Stu, it's not a matter of electrical output..it's more like saving the shaft bearings etc.

 

[LloydB]

you might check with these guys
Scholten's Equipment Inc
9534 Green Rd Burlington, WA 98233
(360) 755-0560

 

[tommays]

That is insanely fast

 

[Charles Erwin]

Mark

Looks to me as if Kloudie's solution is best. So assuming no bracket changes why not have one made.

Charles

 

[Maine Sail]

Custom....

 

[woodster]

you may find something in the Browning catalogue that would work won't hurt to look

 

[Mark Maulden]

On a whim I called Electromaax. They called me back in an hr with a 4" direct replacement. Very impressed with the service there especially since I'm not using their products. Why couldn't Balmar do the same?......cost me $125 but that's better than 4 hrs labor for custom..

 

[cptjak]

Go to summit racing (car parts) they have different
size pulleys made by Moroso. I used one years ago on a
Volvo and it worked great.

 

[Mark Maulden]

I looked here earlier and made an inquiry. Problem is, these pulleys are for max of 1/2 " width and they do not specify the belt width on the website. Put a 3/8 belt on it and the diameter drops. With a 4" pulley, I need it all.....