Author Topic: low speed alternator (Read 14627 times)

ebby1234 · « **on:** October 30, 2007, 06:10:09 PM »

I have designed and built a low speed alternator. At 12 revs per minute It gives me 40 watts at 12 volts. I drive it with a 4ft water wheel. The problem is I loose a lot of power to cogging. Could any one help me to over come this. Does any one know of a alternator running that slow

Resectioned.

Flux · « **Reply #1 on:** October 30, 2007, 12:25:27 PM »

If the thing will not start you have a problem with cogging. As long as it runs then forget it, it will not loose you power. With a waterwheel I would not expect cogging to be of any real significance with a large torque to break it away.

As you give absolutely no information I cant be of more help.

Flux

Ungrounded Lightning Rod · « **Reply #2 on:** October 30, 2007, 02:26:58 PM »

Cogging is like pushing a car on a road with a bunch of equal lumps: Once you get it over the first hump it gets just enough speed from going down the lump to get it up to the top of the next one (or would if there were no friction).

So it's strictly an issue for starting. Once you're moving it does nothing except cause a little vibration.

The problem arises in systems like wind turbines where the incoming wind varies. If there is too much cogging, the mill won't start until the wind is well above a speed that would drive a turning mill beyond cutin. This loses you charging opportunity. But if the cogging is low enough that the mill starts below cutin wind speed you're fine.

Weight-type water wheels tend to have less of an issue, since the buckets fill up and give extra starting torque if the wheel is held stopped. (For some others, like a pelton, it might be an issue when turning on the water or if the stream is intermittent and you want the mill to auto-start when it comes up.)

I take it your mill starts up by itself. So cogging is no problem for you.

vawtman · « **Reply #3 on:** October 30, 2007, 02:50:52 PM »

Hi Ebby

It would be awesome if you could provide a pic or more details on the construction.

Thanks

disaray1 · « **Reply #4 on:** October 31, 2007, 05:45:10 AM »

12 revs= 40 watts @ 12v, there's a bunch a folks here that would like to see that gen....

David

smells like fish.

Bruce S · « **Reply #5 on:** October 31, 2007, 07:14:39 AM »

ebby1234;

Are you sure that 12rpm? and where are you measuring the revs? inside part of the wheel or outside? Also where's the alt attached?

It's one thing to measure the revs and another where the Alt is attached and the revs from there.

Same on windmills, it's one thing to measure the outer most parts of the blades and another to be measuring the revs at the Alt.

Can you give us more info? like wheel diameter,alt design , head , flow rate. A picture would be perfect!!

Bruce S

Tritium · « **Reply #6 on:** October 31, 2007, 07:24:02 AM »

RPM is the same on a disk whether at the middle or at the edge 1 rpm = 1 rpm. The FPS of a point on a disk is less near the shaft and greater the further you measure from the shaft radially. RPM and FPS are not the same thing.

Thurmond

wdyasq · « **Reply #7 on:** October 31, 2007, 08:54:17 AM »

"RPM is the same on a disk whether at the middle or at the edge 1 rpm = 1 rpm."

That just can't be right. And you will probably tell us 12rpm is a rotation of once every 5 seconds. I get 240,000 rpf (revolutions per fortnight), plenty fast ... I wonder how many stone/furlong 40 Watts is.

Ron

disaray1 · « **Reply #8 on:** October 31, 2007, 09:46:18 AM »

240000 revs per fortnight...11.904rpm. That is cranking. And since when did 1 rpm=1rpm? :>{ stone/furlong- I cant fathom.

David

disaray1 · « **Reply #9 on:** October 31, 2007, 09:59:05 AM »

No wait- African stone or European stone?

Tritium · « **Reply #10 on:** October 31, 2007, 10:10:57 AM »

"That just can't be right. And you will probably tell us 12rpm is a rotation of once every 5 seconds."

I will make a bold statement here that in addition to the above insight that 1 rotation every 4 seconds is 15 RPM. :-)

I noticed this when watching a 600KW turbine last Friday. I would estimate that the tip speed at 15 RPM was about 100 MPH.

Thurmond

Bruce S · « **Reply #11 on:** October 31, 2007, 12:29:43 PM »

No!!

Rpm at the tip is certainly different than at the middle. That's why propellers make sub and supersonic sounds.

TomW · « **Reply #12 on:** October 31, 2007, 01:26:14 PM »

Bruce;

Rpm at the tip is certainly different than at the middle. That's why propellers make sub and supersonic sounds.

Damn, I am confused.

It is a solid object how can the # of times it makes a full rotation around the axle be different on different points of a solid object?

RPM:

Revolutions

Per

Minute

Right?

Linear speed of given points at different distances from the axle would be different for sure.

I guess I am either misinformed or the terminology is different down there?

Cheers.

TomW

Bruce S · « **Reply #13 on:** October 31, 2007, 01:45:22 PM »

TomW ;

You got it right.

I think I put my terminalogy wrong, so sorry for that.

Was mainly trying to see where he was measuring his rpms.

I was refering to distances traveled around a given axle.

Darn heat down here :-) Halloween is supposed to be cold and wet not 70F

My apologies to those who were getting my head back on right without ripping it off.

I will now go re-read my math books with w truely redened face:_(

Cheers

Bruce S

TomW · « **Reply #14 on:** October 31, 2007, 02:31:10 PM »

Bruce;

You had me going awhile there. I reread it several times to be sure I didn't misread FPS as RPM since the statement made sense then. I guess I just figure it is important to keep the info as near correct as possible.

I would expect you to correct me, also, when I make a factual error.

No harm, no foul.

Cheers.

TomW

vawtman · « **Reply #15 on:** October 31, 2007, 02:39:44 PM »

PLEASE come back Ebby :>)

Flux · « **Reply #16 on:** November 01, 2007, 01:29:21 AM »

As your other post seems to be closed to comment I shall have to reply here.

You obviously don't have a cogging problem, I think you are confusing cogging with the drag on load.

I suspect your alternator is reasonably efficient if you can light two 50W bulbs easily by hand. I think your 40W output is likely to be the limit of the water wheel rather than the alternator.

At best all you will gain with a dual rotor air gap design is the elimination of iron loss which in your case is probably small and the effect mostly bothers wind turbines on start up. With constant water power you may only gain a few %.

If you make it dual rotor you will need more magnet and copper to reach the same efficiency and even more to bring the efficiency up enough to compensate for the iron loss.

If you want the highest possible efficiency regardless of cost then the dual rotor should do best but it may not be the most economic commercial design.

I assume you have looked at matching the alternator to the wheel, if you have too little open circuit volts or too much resistance you may not be fully loading the wheel. Have you checked the power direct into lamps, which you can keep adding until you slow the wheel to where water spills over the buckets.

If you know the flow of water you can easily calculate the power out, you can take 75% for wheel efficiency and you will be lucky to exceed that on the alternator unless it is a monster with lots of magnets.

Flux

HomegrownPower · « **Reply #17 on:** November 01, 2007, 07:20:24 AM »

Ebby

Hey I'm green as can be myself . Wish I knew more and could help with your problems but learning a few things myself.

I'd sure like to see your wheel though as I may undertake about a 4 ft wheel experiment as opposed to building props and a tower for my PMA . Making the wheel would be a pain but so would building a good tower to get me over the trees here .

Where are you ? Country / state Tenn here

Permits were they a problem ?

Can you experiment with the wheel without permits if theirs no PMA hooked to it ?

How did you come up with the number of coils verses the number of magnets ? I'm going with the 12 mag and 9 coils for the 3 phase PMA just like the (Host ) I think or who ever it is that makes the car rotor PMA . Just going with that number becuase it's tested true and I know it works good .

Only difference I had two machined plates on hand the right dia and used them . More like the desighn in Hugh's book but I didn't like his 5 phase stater so I'm using the 3 phase .

hope you get things straightened out with yours . Post a pic of that wheel if you can .

Lonnie

Bruce S · « **Reply #18 on:** November 01, 2007, 08:26:41 AM »

TomW

In light of my boo-boo I added a little by-line to my sig:-)

When I post info , I try to be as real life knowledgeable as possible, there is so much information out on the web that is either not complete or just plain wrong that around our office we tell people, the "NET" stands for "Not Entirely True"

I lurked for more than a year and read ALL of the old forums info long before I even posted anything. Adding wrong or incorrect info kinda bumms me out and certainly doesn't help.☺

Thanks for the kind wake up.

AND AGAIN to those I yelled at in my post. My bad and I fully apologize!!

Now off to learn terminology 101 , or better yet, re-read commanda's LED classes.

Cheers ALL;

Bruce S

disaray1 · « **Reply #19 on:** November 01, 2007, 08:48:55 AM »

Everybody has off days, Bruce. Maybe you hadn't had enough Java?

Take care.

David

finnsawyer · « **Reply #20 on:** November 01, 2007, 09:33:40 AM »

Since he is in the experimental phase he could drill out some or all of the lamination in each coil and see what the result is. He could then tap the resulting holes and insert screws to various depths to further refine the effects on cogging and efficiency. It does appear that he would like to have a design that would be usable for different types of water wheels. It certainly would require a different regime than wind turbines.

ebby1234 · « **Reply #21 on:** November 01, 2007, 01:18:45 PM »

The laminations are made from plastic coated steel approx 60 100mm long 25mm wide. the magnets are 50x25x10mm very very powerful.the diameter of the alternator is 22 inches

2dumb2kwit · « **Reply #22 on:** November 01, 2007, 05:01:18 PM »

Bruce may have been correct. What if the inner part of the disk approached the speed of light? You can't exceed the speed of light, (so they say) so the outer part would have to turn at less rpm than the inner part.(at those speeds)Right? O.K. guys, have at it!LOL

Bruce S · « **Reply #23 on:** November 02, 2007, 10:56:17 AM »

disaray1;

For the past few days, there's not enough caffiene in Missouri to fix the tech-support problems :-)

We even got one of those "can't find the ANY key" calls.

Man what a week!!

off to inject another 100cc:-)

Cheers

Bruce S

finnsawyer · « **Reply #24 on:** November 03, 2007, 08:40:05 AM »

Hmm, according to the Special Theory of Relativity as the speed of an object approaches near the speed of light it gets shorter in the direction of motion. So the outer parts which are going near the speed of light will contract severely while the inner parts are not affected as they will be going much less than the speed of light. So, you are looking at the wrong part of the disk. Of course, the Special Theory of Relativity only applies for linear motion anyway. From a practical stand point the disk would fly apart long before relativistic velocities were reached. One year when I was working in Milwaukee a company tested a large gear up to 25,000 RPM. It flew apart with one piece going a quarter mile. Fortunately no one was hurt. Note to TomW. I'm just having fun with this. You need not get riled.

TomW · « **Reply #25 on:** November 03, 2007, 02:45:05 PM »

Uhh, leave me out of it.

Cheers.

TomW

2dumb2kwit · « **Reply #26 on:** November 03, 2007, 07:18:31 PM »

I was just trying to spark a little fun thought, and I have to admit that you made me think. All of this being theory, I thought that the responce would be that the inner and outer parts of the disk would be turning the same revs per minute, but time would slow down for the outer point as it approached the speed of light, causing the "minutes" to be a different length of time.( as observed from a stationary point) BTW, I'm nowhere near smart enough to be thinking about this! I hope this is being taken in the fun that it was intended.

Old F · « **Reply #27 on:** November 04, 2007, 06:03:50 AM »

Bruce

2 wrongs don't make a write, but they do make more lively conversations:-)

Yes but two Wrights make an airplane

OldF

DamonHD · « **Reply #28 on:** November 04, 2007, 06:33:21 AM »

And now that cellphones are going to be allowed on planes, that will make for a lot of 'lively' conversations.

Rgds

Damon

Bruce S · « **Reply #29 on:** November 06, 2007, 04:33:29 PM »

Sorry folks with conversion from Windows VOIP to Linux, it's been hit-n-miss to ger here, I surely missed the fun.

Old F

I almost forgot about them:-)

Wonder how many RPMs they got once they took OFF:-)

Bruce S · « **Reply #30 on:** November 06, 2007, 04:41:13 PM »

DamonHD;

Great NOW when I travel, I'll get to hear all those people yaking on phone, right along with those with PDAs watching some movie with the sound up too loud for the cheezy speaker to keep up with.

The trips to London Gatwick just got longer :-(

Perhaps I can load this website into an offline viewer and zone out everyone else?

I find it awesome that I can totaly screw up and we end up making light of it.

Cheers ALL:

Bruce S

PS anyone know an easier way to load ICA client on to red-hat:-(

TheCasualTraveler · « **Reply #31 on:** November 08, 2007, 06:28:13 PM »

Is it in any way possible that we are going to see a picture and complete specs for this 40 watt, 12 volt, 12 RPM alternator.

TomW · « **Reply #32 on:** November 08, 2007, 06:55:31 PM »

Andy;

HaHa.

Maybe he is waiting for you to show yours first?

T

News:

Author Topic: low speed alternator (Read 14627 times)