Excessive gear ratios in fan belts 1

[michaelLeeKH]

What does excessive gear ratios mean in belt fans? Many consultants say to avoid them and use direct drive. How do I calculate the savings if changing the pulley to direct drive

 

[macmil]

It means what it says. There is a practical upper limit to the speed reduction that can be achieved by V-belt drive. As you increase the size of the larger ( usually driveN ) sheave, the angle of contact, or wrap, on the smaller sheave decreases, unless you ibcrease the centre distances. This can lead to higher slip and less efficiency.
Yes , direct drive is more efficent, but your load has to operate at motor speed. If you need speed reduction, then you can use a gear reducer, but you have to get the ratio correct. V belt speed reduction is typically less expensive than a gear box, and has the advantage that the ratio can be easily and inexpensively adjusted by changing one sheave.
There are numerous other factors to consider as well including but not limited to ambient conditions ( hot / dirty ) horse power, maintenance access, light or severe duty service, etc.
Another option is using a timing or synchronous belt, where the cogged belt drives a toothed sheave.
However there are literally millions of V belt drives out there working just fine ( virtually every automobile.)
Your local bearing house will be able to help you with your application.

 

[ScottyUK]

...but your load has to operate at motor speed...

...And motor speed is easily made continuously variable, precisely and over a very broad range. The caveat is that the torque multiplication you achieve with speed reduction using a gearbox or belt drive does not happen with a variable speed motor.


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Sometimes I only open my mouth to swap feet...

 

[bogeyman]

If you must use a belt there are poly vee belts that can use a very small motor pulley dia efficiently.