Gallery, Projects and General > How do I??

Making pulleys (sheaves)

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AdeV:
One of the many projects I'm currently mulling over in my head (whilst I've no access to my workshop...), is a generator for the race car transporter/motorhome.

The engine I want to use for the genset works best at 2200rpm. The alternator needs to spin at 3000rpm. Seems simple enough, right? Ratio is 1-4/11ths (naturally), so pick a pulley size for the alternator such that there's one 1 4/11ths ish bigger available for the engine.

Except.... is it REALLY that simple? I'm aware that Pitch Diameter is the all-important measure. I'm assuming I'll have some engine speed adjustment, so I can wriggle out any minor discrepancy, but can I just match the ODs of sheaves and expect them to be "more or less" right?

OK, second example, assume I slow the engine to 2000rpm, making a nice easy 2:3 ratio. Can I put a 9" pulley on the alternator, a 6" pulley on the engine, and expect it to work at about the right speed?

PS: I ask here because my google-fu is sorely lacking today, for some reason.

AdeV:
PS: The reason for the title of the topic...? Well, if it IS just a case of matching up ODs, then I'll have a crack at casting my own of the exact size(s) I need...

mexican jon:
Provided the engine is of a suitable size then yes  :scratch: I have a Honda generator that is belt driven so it's the same principal  :thumbup:

John Rudd:
The smallest pulley is determined by the minimum wrap of the belt you use as a general rule......

And dont forget, you may need to govern the engine to maintain speed as you load/unload the generator.....

AdeV:
Thanks guys, what I'm after is: Is using the ratio of the OD of the pulleys generally regarded as "close enough" when sizing up?

e.g. if my power source ran at 3000rpm with a 5" pulley, and my output ran at 1500rpm, is it close enough to just ask for a 10" pulley?

Or is it more scientific than that & actually I neeed a 10.25" pulley due to the difference in pitch diameter?

I'm probably not explaining this very well, hence the google problems...

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