Burning up belts

[Steve Firebird]

I have had problems with my alt pully slipping and put in a deep grove pully and now the belt is just plain buring up slipping and finally broke. I am running a 140 amp one wire alt and a Mark VIII fan. When the fan turns on the slipping starts. It is ok when the fan is off. The pully alinement is right on so thats not the problem. I think the alt just gets harder to turn when the fan is on. Will the fact that is a 140 amp one wire cause that? I am thinking about changing to a three wire one if it will help. What do ya think.
Steve

[Steve Firebird]

I realized after talking to one of my friends that is was most likley a loose belt that caused it. I went and checked the PS belt and it was pretty loose. A new belt is on and very snug. I am going to order a belt tension tester just to be sure from now on. I found out I was not running them tight enough. Some belts need to be as high as 80 lbs tension. I bet I was running less then 40. The tester will tell all. Hopefully this thread will help some ones else down the road. Steve

[GetMore]

Glad you figured it out. Here's some info for you anyway:

Yes, the more electrical power being produced the more drag the alternator applies. When the battery is charged and there is no electrical draw the alternator is almost freewheeling. Turn on the headlights, run the fan, operate power windows, and the alternator takes some decent power to turn.

It does not matter if it is a one wire or a three wire alternator, it's the actual output that causes the drag. One or three wire will have the same drag. The real difference between the two is that the one wire will not turn on until it hits a certain minimum rpm, while the three wire turns on once power (switched by the ignition switch) is applied to it.
A one wire alt. usually needs you to rev the engine just a little bit for it to turn on, shich means there's just a little bit less of a load on the engine when you start it.

Belt tension is a bit tricky to set. There is supposed to be a certain amount of deflection, but that amount depends on the distance between the pulleys. Too loose and you get slippage (any you may have glazed the pulleys, which will help it slip). Too tight and you will wear out bearings in the accessories, or most common the water pump.

[Jim Nilsen]

You might try a cogged style v-belt from Gates or one of the other belt makers. The contact area helps the grip due to the easier ability to conform to the pulley and the added contact psi.