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Get Powered Up! Certified Energy Manager Jeff Yago answers your alternative energy questions

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Archive for the ‘Micro-hydro’ Category


Diesel alternator

Tuesday, September 2nd, 2008


I have several question about diesel alternator. First of all I want build micro hydro system using diesel alternator. That means I just take the alternator and using water to rotate the turbine and the alternator will produce the power. Do you think this system is possible to do?

Before this I use the car alternator, and the problem is before alternator connected to the battery I get about 3000 RPM, but when I connect the alternator to the battery and field current occur, the RPM dropped to 500 RPM. So the alternator can’t produce the current. So I want try using diesel alternator.

Since we know diesel alternator power output in AC, so no field current needed. If I get around 3000 RPM, whether diesel alternator produce the power? Or it same with car alternator.



First we need to clarify that all alternators have an AC output, regardless of being installed on trucks or cars, that is why they are called alternators. Until the early 1970’s all cars and trucks had DC generators, and since the DC output required brushes that would constantly need service, they were finally phased out with alternators which have no brushes to replace. There are different types of alternator designs, but all have a bridge rectifier mounted on the rear which converts the AC output to DC for battery charging. Some inverters “self-generate” their own field current and some more expensive models have permanent magnets which can really generate the amps.

Your main problem will be RPM. Almost all alternators need to operate in the 600 RPM or higher range and their pulley sizes are determined and sized to provide this RPM in relation to the engine speed. It will be difficult to build a hydro system that turns this fast unless you use some form of indirect belt drive to change the RPM. There are many web sites that provide details on how to convert an alternator into alternative energy use although most are related to wind energy. Since you have the same type design issues, check out these links:

Good Luck,

Jeff Yago



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