2. Testing the Genny - The VOC Test

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I brought the body of my newest wind generator project to a guy I know who runs a machine shop. He hooked it into his lathe, and we ran a few tests.

There are two tests that we performed. I'll explain the tests, as well as why they're important, in individual posts.

Test #1 - OC (Open Circuit) Voltage Test.

An VOC (Volts, Open Circuit) test measures how many volts the wind generator produces at a specific RPM. The two numbers (voltage and RPM) have a fixed relationship to each other. In other words, the results of this test gives you a ratio that you use in other parts of your project. Specifically, these results are used to determine how large the blades should be on your finished wind generator.

Here are the results from my test of this generator:

153 RPM - 10.1 Volts
303 RPM - 20.7 Volts
403 RPM - 27.8 Volts
652 RPM - 45.4 Volts

So, what exactly does a person do with these numbers? I'll explain.

The main purpose of this wind generator is to produce electricity that will be used to charge batteries. In order to charge a battery, you have to feed it voltage that is higher than the current voltage of the battery. A wind generator will produce electricity from the moment it begins spinning. But that electricity is only useful to you if it is charging your batteries. The speed at which a generator starts producing useful electricity is called "Cut-in" (sometimes written "cutin.") This test uses only a voltmeter. There is no electricity flowing through a circuit, so it is called "Open Circuit."

My system is a 12 volt bank of batteries. 12 volt batteries actually operate closer to 13 volts. So the wind generator has to produce at least 13 volts to be doing anything useful. Using the information from the VOC test, we have to determine what speed represents 13 Volts.

Remember, the numbers represent a ratio. They vary slightly within a certain margin of error. None of this is rocket science. Close is usually good enough. Let's examine the first and last pair of numbers:

10.1 volts at 153 RPM = 1 volt for every 15.15 RPM. That means 13 Volts equals about 197 RPM.

45.4 volts at 652 RPM = 1 volt for every 14.36 RPM. That means 13 Volts equals about 186 RPM.

For this project, I've used 200 RPM as the measured cutin.

Next Post: Cutin Speed leads to Cuttin' Blades.

yuck yuck. Oh, sweet alliteration.