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

Wondering about a great new energy-saving device
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Sorry. Jeff no longer answers questions online.
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Archive for the ‘Diesel’ Category



Wednesday, October 22nd, 2008

Dear Sir:

I am currently building a house, and read your article on generators used with a battery/inverter system to provide off grid power. This intrigued me.

My question is whether or not it is better to get an LP powered generator, versus a diesel because of the price of fuel. The price difference in my area is almost $2.00 per G. I realize that diesel motors usually have greater longevity than other types, but Guardian has introduced an 1800 rpm liquid cooled 18KW generator, and I’m wondering if that might not be more cost effective.

I would also appreciate any info you could provide that would allow my builder to do the install correctly for a future battery /inverter system.

Thank you.


Mike Jamison


My selection of generator type has to do with how often it will be running each week, month, or year. For example, if I want a generator for backup power for a home on the grid that only suffers a power outage for a few hours or days each year, I would select a propane generator as the fuel (propane) does not go stale or get old, so it can sit in the tank for years until needed. Of course you should run the generator every few weeks to keep everything lubricated and operational.

If I was designing an off-grid solar home and the solar system was large enough that the generator would only be needed to run a few hours each week, I would also select the propane fueled generator for the same reason.

If I was designing an off-grid system that needed a generator to run many hours each week I would select the diesel generator as the fuel costs will be lower and would also allow making my own bio-diesel if needed. Since this generator would go through a fuel tank much faster than an occasional use generator, there is less chance that the diesel fuel would go old. Of course you can add additives to the diesel to make it store better, but most of these additives are expensive and another thing to take care of.

If the home’s location is not accessible for filling the propane tank with a propane delivery service truck, you may have to select the diesel, as it will be easier to deliver the diesel fuel in 5 gallon hand-carried fuel cans.

As you see, all designs are have trade-offs and there is not always a perfect answer.

Hope this helps,

Jeff Yago


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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