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Altenators for low RPM engines

I currently have the need to replace the Alternator on our Narrowboat Blue Rover, and am looking for some advice.
The Engine is a Beta BD£ Tug, that runs at between 700 & 1200 RPM.
Do I need to take the low RPM nature of the engine into consideration when selecting an altenator. If so, what do I need to look for when selecting the correct alternator?
Any advice would be much appreciated

Asked by: duncan  | 3.27pm, Thursday 14 August

WW says:

The most important factor is to ensure that the alternator is being spun fast enough to generate sufficient power. With a low speed engine such as the Beta Tug, or vintage engines, fitting a large pulley to the crankshaft will provide sufficient step up to drive the alternator. A ratio of at least 4:1 between the diameter of the engine pulley and that of the alternator pulley will ensure that the alternator spins at a minimum of 2800rpm for an engine speed of 700rpm. This should provide a useful output, however it would be as well to look at the speed profiles of your chosen alternator.
It is also important to ensure that the alternator is spinning the right way for the cooling fan to operate, to stop it overheating.

Rupert Smedley  | 7.31PM, Thursday 14 August

Having just re-read your question; measure the pulley sizes fitted to the engine and alternator and work out the step up ratio and hence the minimum alternator speed. Then check that the cut-in speed of your chosen alternator is below this speed.

Rupert Smedley  | 7.36PM, Thursday 14 August

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