Dual V belts taking different paths?

[Bill Seal]

I don't think V-belts like to be bent backwards. If you can find an automotive V-belt tensioner, you could use the axle and sheave from it and machine from there.
I think the old Subarus used one.

[bcboomer]

Converting to serpentine drive is a lot simpler than trying to cobble up tensioners.

Plus, you can customize the ratios to get better output at the lower RPM's we cruise at.

[Martkimwat]

Originally Posted by Pauls

You WILL need two belts. Belt life with a single belt driving that many amps will be short.

Two belts on two different paths is fine, but you must have a way to tension both. Normally your alternator pivots to tension the alternator/water pump belt. The second belt will need to be long enough to be loose when the alternator/water pump belt is tight. The second belt will have its own tensioner. With this system both belts can be well tensioned and you will have a long life, reliable system.

Not necessarily. The far more common practise is to use a wide multi-V belt as used on a lot of cars these days.( typically 25~28mm wide) You only have one belt tension to worry about. It will need a change in the drive and slave pulleys to accommodate the new style belt.

[vpbarkley]

Some people are of the opinion that multiple V belts are equivalent to a serpentine belt drive. This is not the case when it comes to high output alternators.

Since serpentine belts have a lower height than V belts they can bend around smaller pulley diameters. This makes them ideal for driving an alternator at high speed.

Most alternators have RPM limits above 8000 rpm. You need a serious ratio of pulley diameters to approach anything like that with a slow turning diesel engine.

Operating the alternator at high speed is ideal for several reasons. The first is that alternators don't start producing any significant charge below a certain rpm.

So you will have to fast idle for any type of charging to occur. Secondly the high amp rating of the alternator only happens at high rpm.

Thirdly, cooling strongly favors high rpm. This is because airflow of centrifugal blowers increases with the square of the rpm. So there is much higher cooling air flow at higher rpm.

This is important because air is not dense, engine room temps are high to begin with and alternators output 50% usable energy and 50% heat.

So, a small 100 amp 12 volt alternator producing rated capacity needs to dissipate 600 watts of heat energy.

But it gets worse. Heat increases resistance in the windings lowering efficiency further, producing more heat. Failure to remove this heat causes alternators to fail.

Finally, serpentine belts have higher capacity than do V belts. This translates into long life, no slipping and no belt dust.

For all of these reasons I strongly recommend springing for a serpentine belt drive. This upgrade is necessary to realize the advantage of a high output alternator.

[RaymondR]

I dunno the charge curve seems to fairly well flatten out above 3,500 RPMs to me.

Faster would probably pull more air through though.