# what force is required to rotate a dynamo or alternator

I am working on an initiative for a new product. The product generates a rotational output force from:

• Input force of 14.73 NM
• Input speed 120 rpm
• Gear ratios from 0.5 - 2

The out rotation is intended to produce electricity so therefore it will need to go into a dynamo, or alternator of some sort to generate the maximum KW output based on the input force and speed.

Can someone help me work out the following.

• What force does the dynamo/alternator need to rotate?
• Any advice on which type of Dynamo, alternator, generator will be best
• What KW output can be expected given the input force and speed?

I look forward to any assistance anyone can offer.

Please excuse me but I am a mechanical person and my knowledge of electronics is very limited.

• power = torque * angular velocity maximum power: 14.73 Nm * 120 rpm * 2 * pi / 60 = 185 W = 0.185 kW Commented Jun 22, 2022 at 11:14
• 120 rpm is very slow for an alternator. You may need a gear ratio of more than 2, may be 5 or more. Don't expect 100 % efficiency for alternator with gear, may be 50 to 60 %.
– Uwe
Commented Jun 22, 2022 at 11:21
• If your product is a radio or similar then have a look at the wind-up radios or torches as design solutions. Commented Jun 22, 2022 at 11:39
• Further reading machinedesign.com/motors-drives/article/21168640/… Commented Jun 22, 2022 at 11:45
• Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer.
– Community Bot
Commented Jun 22, 2022 at 11:57