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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
you found on the Internet? Then CLICK HERE!

Sorry. Jeff no longer answers questions online.
This will remain as a searchable
resource for all BHM website visitors.

Archive for the ‘Alternator’ Category


Hydro generator system

Friday, March 6th, 2009

Hi Jeff:

I purchased DC-512 four alternators over the Internet for a hydro project. I’m taking advantage of an existing irrigation system on a farm, which pumps a steady stream of water with great pressure at a very long distance. It’s like a fire hose in action.

This system is running continuously for 12 hours daily. I’ve designed a special, very light aluminum=blades arrangement and I have adapted it to the DC-512 via belt drive to disrupt the powerful irrigation water stream, moving this blade as when cleaning a painting roll with a pressure hose. This creates a speed in the DC-512 of 1150 RPM as measured with a tachometer. The voltage produced with no load, e.g., disconnected from the batteries, is approximately 25 volts, measured with a Flux digital meter.

The DC-512 were all connected in parallel to a single 12 volts Flex-Charger of 100 amps to charge a battery bank, 4 batteries connected in parallel. Three alternators DC-512 were disconnected from the charger to perform troubleshooting leaving just one connected in parallel. This is what happens; when I connect the positive cable to close the circuit, seems like a short circuit is created in the alternator, which slows down the speed to about 500 RPM stopping the blades and disrupting its function to load the battery bank. The charger light turns on indicating that is charging but, producing only 13 volts, which is not really enough voltage to charge the batteries. I have connected everything precisely as per alternator and charger instructions. Finally, I am tired of getting wet like crazy during test and troubleshooting process. I wonder if you can explain what is happening and how can I make this system work. Your help will be really appreciated.

Thank you in advance.

Carlos Echevarria


As it states on the web site, we can not answer specific design questions as we do not know all of the specifics of your installations, and this is a free site and we have limited time to spend on each email question. However, we can provide general answers that may be of some help.

First, I assume this pressure flow is due to gravity head and not from a pressure pump somewhere. Second, if I had this much “free” water flow I would purchase a quality hydro-generator that is designed to maximize the conversion of energy. Most likely a properly sized and designed unit could replace all four of your home-made units and without all the problems you are having.

If things work fine with all four alternators in the circuit and then when you cut out all but one and it does what you describe, it sounds like it is being over-loaded. This would drop the voltage while appearing to be under load. Also, your wiring switching to one alternator could be causing the remaining alternator to be sending power into the alternators not being used which would be a large current drain on the working unit.

Again, you have a great opportunity to power your home with this much hydro power if you bite the bullet and purchase the correct equipment.

Good luck!

Jeff Yago


Charging batteries with car alternator

Thursday, December 11th, 2008

Hello Jeff,

I want to build a small battery backup/inverter system for when the lights go out using 2-4 smaller deep cycle batteries. Is it practical to recharge these batteries from a vehicle alternator with the car running and what hardware would I need to actually do it? Attaching an inverter to the car battery and plugging in an automotive smart charger seems horribly inefficient. Just using jumper cables seems like a good way to burn my batteries up.




Its possible to do what you want to do, but its not very practical. Charging up a bank of deep cycle batteries that have been depleted can require hours of heavy charge time and running a car engine at medium RPMs for 3 hours each day during a power outage is like taking a 200 mile trip each day and you can imagine what the fuel would cost for that.

You can either use a solar array to keep the batteries charged or buy generator in the 8 kW range and power a quality inverter. Most name-brand inverters designed for off-grid service have very robust battery chargers built in and are designed to maximize the charging to minimize generator run time. You are also correct about jumber cables as most are very light duty and only designed to carry a large current for a few seconds then out away. During battery charging with a good inverter, battery charge currents over 100 amps for several hours is not uncommon and that requires #2/0 or #4/0 size copper cables and bolt type connectors.

A small generator will use much less fuel than a car to provide the same charging.

Good Luck,

Jeff Yago


Air conditioning for a pickup camper

Thursday, November 27th, 2008

Hi Jeff.

I would like to put Air conditioning in my pickup truck camper shell to keep my dogs cool in the summer. It would only be in use when I was traveling down the road, not while the truck was turned off. Here was what I was thinking – could you offer an opinion on whether it would work or how to to do it, if it is even possible.

[I want to] put an RV air conditioning unit on the top of my camper shell and run that off an inverter connected to my pickups battery.

I do have a 2500/5000 watt inverter but I wonder if the air conditioning unit would suck so much energy that the alternator could not keep the truck battery charged up going down the road.. My truck has two batteries up front


Hello, MIke.

The problem is not battery size, it’s your alternator capacity. There is no way an RV air conditioner can run off one or two truck batteries for more than a few minutes without draining them. For example, the smallest, newest, and most efficient truck camper AC unit draws 8 amps at 120 VAC. Assuming a 90% system efficiency, this would be a 1,100 watt “run” load on your inverter, and require an inverter that can handle at least 2 kW “start” load since any compressor load is a dead short on the power source for the first few seconds it is trying to rotate.

You said you had a 2,500 watt inverter which should be able to handle a small RV air conditioner, but that is not your main problem. Your inverter will have a constant draw of 88 amps at 12 volts DC while an 8 amp load air conditioner is running, and could draw up to 150 amps for a few seconds every time the compressor kicks in. This means your truck alternator and all related cables need to be large enough to handle these larger current flows and still have enough excess power to operate your lights and other electrical loads in the truck. Each time you stop at a light, there will not be enough amps coming from your alternator even if it is a larger 150 to 170 amp heavy duty model.

This is why the air conditioning unit in an RV is always wired into the exterior shore power or generator panel, and not powered from the batteries. Any 120 VAC electrical load on an inverter will draw 11 times the AC amps from a 12 volt DC battery.

I suggest letting the dogs ride in the back seat!

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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