Note: For best results, read these posts in order. See menu on the right.
Between the two tests, there is one glaring difference. The relationship between voltage and RPM that we determined in the first test all but disappears in the second one. In the first test, 652 RPM produced 45.4 volts. In the second test, 602 RPM produced 12.41 volts. And at 702 RPM, we measured 12.40 volts!
This demonstrates a phenomenon known as voltage regulation. I call it "natural" regulation because there are no gimmicks involved. No fancy circuits or expensive devices. The 45 volts is regulated naturally and automatically to 12.41 by the battery itself!
Voltage regulation is an important concept for a wind / solar builder. When you understand that the battery regulates, or limits, the voltage in your system, you realize that your generator's output voltage doesn't have to match your battery's voltage. In other words, if your generator produces 10, 15, or even 100 volts, you can still hook it up to a 12 volt battery. The battery, in general, doesn't mind. Generally speaking it "converts" the extra voltage into amperage. Notice on the second test, the Charging Voltage doesn't rise, but amperage does. We're producing power now, which is wonderful - but there is a catch.
Regulation comes at the cost of presenting a load to your generator. In other words, the more your battery is regulating the voltage, the harder your generator is working. If you make your generator work too hard, it spu-spu-sputters to a halt. Those of us who learned to drive a vehicle with a manual transmission know what happens when you let the clutch out too fast and present too much of a load to your transmission. Your engine stops immediately.
With wind generators, stall doesn't necessarily mean that your blades (which are the engine of the generator) grind to a halt. What they actually do is something much harder to see with your eyes or instruments.
Imagine pedaling an exercise bike. This bike is configured so that the faster you pedal, the harder it becomes to turn the wheel. You can pedal slowly all day long with nearly zero resistance. But as soon as you really try to pedal fast, the bike seems to "push back" at your feet. As you continue to accelerate, you will reach a point where you know you can move your legs faster, if you could only muster up the strength to pedal harder. Get it? At that point, you've stalled.
Back up on your wind generator tower, a system that is "in stall" is spinning as fast as it possibly can, but there just isn't enough wind (strength) to push it any harder against the resistance. This is a bad place to be, because you are not making good use of the wind. And if you're not putting the wind to good use, what's the point of building a wind generator?
Remember, the more your batteries have to regulate the voltage, the easier it is to stall. That is why people design their systems around all kinds of different "bus" or "system" voltages. Twelve, 24, and 48 are the most common.
So if my generator produces over 40 volts, wouldn't a 48 volt system be less likely to stall? Yes! But remember the concept of cutin. If I had a 48v system, I wouldn't produce any useful electricity until my generator was spinning over 700 RPM. That's pretty fast! At lower speeds, it wouldn't stall, but it also wouldn't be doing anything useful.
My generator actually would probably make a good machine for a 24v system. I chose to stick with 12v because of the wide adundance of inexpensive 12v electronic items. Inverters are cheap for 12v, and any Wal-Mart, auto parts store, or RV dealership has everything from fans to coffee makers to televisions that run straight off a 12v battery.
Also, because a 12v system starts being useful at a lower RPM, I am better prepareed to take advantage of the low winds where I live. I have chosen to compromise between the possibility of stalling at high speeds and squeezing every last watt out of slower winds.
Next Up . . . Taking this information and actually DOING something with it.
Warning - Get out your pocket protectors and slide rules. We's gon' be doin' some math.
Friday, November 28, 2008
Thursday, November 27, 2008
3. Testing the Genny - The Amperage Test
Note: For best results, read these posts in order. See menu on the right.
Test #2 - The Amperage Test
The second test is completely different than the first. This one actually causes electricity to flow from the wind generator into a battery. How much electricity is flowing (measured in Amps) is what we determine here. The first test measured voltage. This one measures voltage and amperage. Therefore there are 2 meters to observe.
The other fundamental difference between the tests is that this is not an "open circuit" test. And because electricity is flowing, there is more potential for danger. Specifically, this test simulates the work performed by the actual, finished wind generator. The faster it spins, the harder it's working, the hotter it gets, etc.
There are valid results from this test, but the best part is from vanity's perspective. Since this test mimics the finished generator's abilities, it is a chance for you to see your project actually working. A little positive feedback never hurt anyone, right?
I was very happy with the results. Here they are:
This time, the RPM and Amperage numbers don't have a fixed relationship. Generally, they are supposed to follow a rising parabolic curve. In the first test, the faster it spun, the higher the voltage climbed. In this test, as RPM increases, the amperage climbs. And as the RPM increases, the amperage climbs at a faster rate. At some point, that curve "levels off."
Compare 200 and 300 RPM. That's only a 50% increase in speed, but represents a 1000% (10x) increase in power production! Near the top, the curve isn't so extreme - twice the RPM equals approximately twice the power. If we tested higher speeds, we'd eventually reach a point where large increases in RPM would represent very small increases in power.
For this test, 702 RPM was about as fast as we wanted to go. My cheap Harbor Freight multimeter is only rated for 10A. We were feeding nearly twice that amount through it. I've fried these meters before - it's pretty stinky. Luckily we didn't fry this one.
Remember that we figured cutin at 200 RPM. As a confirmation, this test shows 540mA flowing into the battery at just over that speed!
Notice that in each line, the Charging Voltage is higher than the Resting Voltage. This is because a battery's voltage rises temporarily while it is being charged. At periods of rest, when no electricity is flowing, the voltage will settle to a lower number. Naturally, this means when you charge a 12v battery, it is not sufficient to stop once the charging voltage reaches exactly 12 volts. Once you stop, it will settle to a lower number.
The Resting Voltage is displayed to check the consistency of our results. It shows that we are putting varying amounts of current into a (relatively) similar battery. If we charged our batteries for too long during the test, the Resting Voltage would rise, meaning the Charging Voltage numbers would also rise, and we'd have skewed results.
Using the Charging Voltage, we can determine Wattage. Power (Watts) is measured by multiplying volts and amps. Doing the math, we come up with these numbers:
203 RPM - 6.5 Watts
353 RPM - 66 Watts
602 RPM - 175 Watts
702 RPM - 212 Watts
How many watts are produced at specific RPMs is information we will use to determine the size of our blades.
Coming up Next - Natural Voltage Regulation and "Stall"
(and I promise we'll tie this all in to cutting blades soon, too.)
Test #2 - The Amperage Test
The second test is completely different than the first. This one actually causes electricity to flow from the wind generator into a battery. How much electricity is flowing (measured in Amps) is what we determine here. The first test measured voltage. This one measures voltage and amperage. Therefore there are 2 meters to observe.
The other fundamental difference between the tests is that this is not an "open circuit" test. And because electricity is flowing, there is more potential for danger. Specifically, this test simulates the work performed by the actual, finished wind generator. The faster it spins, the harder it's working, the hotter it gets, etc.
There are valid results from this test, but the best part is from vanity's perspective. Since this test mimics the finished generator's abilities, it is a chance for you to see your project actually working. A little positive feedback never hurt anyone, right?
I was very happy with the results. Here they are:
| RPM | "Resting" Voltage | Amperage | Charging Battery Voltage |
| 203 | 11.98 | 0.54 | 12.05 |
| 353 | 11.00 | 5.48 | 12.05 |
| 602 | 11.05 | 14.11 | 12.41 |
| 702 | 11.06 | 17.12 | 12.40 |
This time, the RPM and Amperage numbers don't have a fixed relationship. Generally, they are supposed to follow a rising parabolic curve. In the first test, the faster it spun, the higher the voltage climbed. In this test, as RPM increases, the amperage climbs. And as the RPM increases, the amperage climbs at a faster rate. At some point, that curve "levels off."
Compare 200 and 300 RPM. That's only a 50% increase in speed, but represents a 1000% (10x) increase in power production! Near the top, the curve isn't so extreme - twice the RPM equals approximately twice the power. If we tested higher speeds, we'd eventually reach a point where large increases in RPM would represent very small increases in power.
For this test, 702 RPM was about as fast as we wanted to go. My cheap Harbor Freight multimeter is only rated for 10A. We were feeding nearly twice that amount through it. I've fried these meters before - it's pretty stinky. Luckily we didn't fry this one.
Remember that we figured cutin at 200 RPM. As a confirmation, this test shows 540mA flowing into the battery at just over that speed!
Notice that in each line, the Charging Voltage is higher than the Resting Voltage. This is because a battery's voltage rises temporarily while it is being charged. At periods of rest, when no electricity is flowing, the voltage will settle to a lower number. Naturally, this means when you charge a 12v battery, it is not sufficient to stop once the charging voltage reaches exactly 12 volts. Once you stop, it will settle to a lower number.
The Resting Voltage is displayed to check the consistency of our results. It shows that we are putting varying amounts of current into a (relatively) similar battery. If we charged our batteries for too long during the test, the Resting Voltage would rise, meaning the Charging Voltage numbers would also rise, and we'd have skewed results.
Using the Charging Voltage, we can determine Wattage. Power (Watts) is measured by multiplying volts and amps. Doing the math, we come up with these numbers:
203 RPM - 6.5 Watts
353 RPM - 66 Watts
602 RPM - 175 Watts
702 RPM - 212 Watts
How many watts are produced at specific RPMs is information we will use to determine the size of our blades.
Coming up Next - Natural Voltage Regulation and "Stall"
(and I promise we'll tie this all in to cutting blades soon, too.)
2. Testing the Genny - The VOC Test
Note: For best results, read these posts in order. See menu on the right.
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.
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.
Tuesday, November 18, 2008
1. Welcome to BYOE
This is a generic Welcome post.
Welcome to B.Y.O.E. - Bring Your Own Electricity (Energy, Everything!)
This is an Alternative Energy and Self-Sufficiency blog that strives to give you useful information about how lessen your dependence on "the grid."
This blog is about real experiences and real projects from people who have actually done it. Perhaps it will be easier to tell you what will NOT be on this blog:
No theories that "should" work because they do on paper.
No environmental or political propaganda.
No unnecessary emphasis on lingo and jargon, and
No B.S. articles claiming to do things that can't be done.
I don't expect that this blog should be world-renowned or even moderately famous.
But I DO expect that people looking to ease their lives toward the American ideal of rugged individualism can get started with the information they find here.
Later, once I start posting articles, I will update this post to include tips on navigating through various posts and subjects.
Welcome to B.Y.O.E. - Bring Your Own Electricity (Energy, Everything!)
This is an Alternative Energy and Self-Sufficiency blog that strives to give you useful information about how lessen your dependence on "the grid."
This blog is about real experiences and real projects from people who have actually done it. Perhaps it will be easier to tell you what will NOT be on this blog:
No theories that "should" work because they do on paper.
No environmental or political propaganda.
No unnecessary emphasis on lingo and jargon, and
No B.S. articles claiming to do things that can't be done.
I don't expect that this blog should be world-renowned or even moderately famous.
But I DO expect that people looking to ease their lives toward the American ideal of rugged individualism can get started with the information they find here.
Later, once I start posting articles, I will update this post to include tips on navigating through various posts and subjects.
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