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Old 31-08-2008, 23:39   #1
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Drive belts

Hopefully the more mechanically experienced may offer suggestions.
I have a pair of 20 Hp Lombardinis and am intending to make one into a DC generator come desalinator. I will use a large frame alternator of about 150 amps and a cat pump with electric clutch.
The pulley on the motor has 2 grooves which are, I think, the small A type V belt. I don't like the idea of one belt for each as the load would be too great for one small belt and the tension required would be a big pull on the crank. I am intending to replace the front pulley and use a different style but there in lies my question.
What style belt would have the lowest loading on the crank for a given amout of power transfer. Would it be the multi groved flat belt that is now common on cars or would a toothed belt be better. Then all that remains is to find the bits that will provide the appropriate ratios.


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Old 01-09-2008, 12:59   #2
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Toothed is the lowest load, highest power, biggest noise. Ever here the blowers on drag cars wind up as they run own the track. The whine out does the engine. That is the noise from a toothed belt under load. A flat ribbed belt does pretty well. But the pulleys are hard to find, at least here anyway. A "V" belt is still the most common easiest and cheapest method IMO. But times are changing and others may have more informed opinions.


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Old 01-09-2008, 13:03   #3
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I have toothed belts on a couple Cummins B series turbo diesels. I don't hear any noise from them.

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Old 01-09-2008, 15:12   #4
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David - toothed belts can be very noisy as Alan says - it depends on the belt speed and configuration so is designed out of "normal" engines. I think the noisy speeds are called idiosyncratic or similar. Our engine has a toothed timing belt and a peculiar very low level whine at some speeds which I attribute to the belt (I hope ).

For the original poster I too think Vee belts are the best for the application described and while it is dependant on engine speed (belt handling kW decreases with lower engine speed), pulley configuration and the loading up characteristics of the pump and alternator you may find an A section belt is ok for each of them. Under normal conditions a properly designed A section belt should handle 7 or so kW at idle engine speeds (but see below re design, don't take my word for it).

Also, Vee belts are always readily found and one should use a good make such as never use anything other than Gates .

There is a common belief among amateur yachtsmen that for 100A plus 12v alternators that 2 belts are required but that is not so. As an example some recent big boats I was involved in had 2 150A 24v alternators (so twice the power of a 12v alternator) on each and they were driven by a single belt (but maybe a B section not an A, I cannot recall) with no problems. In fact the belt was so small looking in comparison to the alternator that I asked the ship yard mechanical engineers to recheck it - it was fine and as far as I know has proved so in service.

But whatever you should get the design of the belts performed by a design engineer experienced in drives and not by some backyard "mechanic". You should also ensure that your engine's bearings are rated for the overhung load of the added belt drives.

As an aside on belt tightness, there has been a big move to flat ribbed belts in the auto industry - I am surprised at how tight these are set up on new cars even though there seems to be little lifetime stretch in them but I am sure they know what they are doing .
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Old 01-09-2008, 15:53   #5
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HI Mike, For my money, a toothed belt will handle all the power you can produce in your application. You might look at pulleys and belts from Harley-Davidson that easily handle 80 to 100+ horespower with trouble-free reliability. The set-up on the H-D Sportster is thinner and slightly lighter. They are not that noisy (as observed while coasting with motor off) when well-adjusted.
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Old 01-09-2008, 15:56   #6
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Coming from a backyard mechanic, you might want to oppose the alternator and Cat pump to help even out bearing side loading. I'd check with your engine manufacturer first to determine the designed side load capabilities. Depending on the RPM and size of the Cat pump it probably will require a two belt clutch. A 150amp alternator has a heck of a pull as well. If you can't buy a two groove bolt on PTO you might need a lathe to cut a custom PTO to match the alternator and Cat pump. Send pics.
PS if you decide on a two belt clutch for a Cat let me know I have two. One's older and the other is new. Depending on which model Cat frame you use. I also have a few used watermaker parts that might save you some.
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