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Ralph
Starting Member
Belgium
19 Posts |
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Del
Junior Member
United Kingdom
369 Posts |
Posted - 28/08/2007 : 10:15:38
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Hi Ralph,
Welcome to the Gotwind forum.
I've had a look at your link and there's thirteen different motor options to choose from.
Basically you want a motor that will give you the most volts for the least rpm.
The best motor on the chart is the one that is rated at 48V and 1500 rpm.
To work out what rpm it would need to spin at to give you a charge voltage into a battery bank you can divide the rpm by the volts (so 1500 / 48 = 31.25) which give you the rpm for a single volt and then then multiply this figure by 13 (13 volts) so 31.25 x 13 = 406. So if used as a wind turbine your blades would need to spin at 406 rpm to produce 13 volts and therefore begin charging your battery(s).
This rpm is a bit high so no, this motor would not make an ideal generator. Having said that if you live in a windy location then it could be ok.
The power of the generator is also important, but I'll let you read the other forum entries and you can get a feel for how this all works.
Cheers
Del. |
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ll81
Junior Member
124 Posts |
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Ralph
Starting Member
Belgium
19 Posts |
Posted - 28/08/2007 : 12:11:39
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You see, I'm very new at this.
I've contacted Ben and now I'm looking for a treadmill-supplier in Europe(for that greenmaster DC motor)
I saw that motor on Ebay but the transport costs are to much. Can't they be found in Europe?
Which book or article do you recommend for a beginner? The answers on the forum are good but it isn’t the same as in a book (as you know what I mean) Can I learn from the plans which you can buy here?
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Ralph
Starting Member
Belgium
19 Posts |
Posted - 28/08/2007 : 12:18:06
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| So the Ebay motor needs to spin 255 times to pruduce 13V? (5100/260=19.6*13=255) |
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Del
Junior Member
United Kingdom
369 Posts |
Posted - 28/08/2007 : 12:48:29
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Hi Ralph,
Spot on with your maths.
To be absolutely honest i would not bother with a book - you will honestly gain so much more from this forum. Everything is covered and answered and shared and repeated a number of times and you can ask questions!
If you're in Belgium that could be quite handy as Germany often have some intersting motors that you could look at using. Ebay is probably the best place and do a search in different countries ebay sites and search for "DC motor", "wind motor", "servo motor" "treadmill motor", or if you have the time just wade through all the motors in the appropriate section (not automotive or home & garden etc).
Cheers
Del. |
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Ralph
Starting Member
Belgium
19 Posts |
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Del
Junior Member
United Kingdom
369 Posts |
Posted - 28/08/2007 : 13:45:15
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Hi ralph,
Sorry I wasn't clear - I meant amps actually.
Even a small motor can give you 12 volts but it wont give you many amps so won't charge your battery very quickly. The more amps the better.
At this point you need to understand ohms law.
Volt x Amps = Watts I think Ben has got a good explanation and diagram in "Projects" and then "Electronics" section. See http://www.gotwind.org/circuit.htm
Traditionally we measure volts from a motor when not connected to a battery or another 'load' and we call this 'open' volts. But we measure amps by shorting out the two wires. On DC motors (two wires) if you hold them together and try to spin the motor shaft then the harder it is to turn the better. You can measure the amps produced by an ammeter or a multimeter on the appropraite setting. This is called "shorted" amps.
So "open" volts and "shorted" amps. See http://www.gotwind.org/new_gen.htm
Hope this is vaiguely clear
Cheers
Del.
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Ralph
Starting Member
Belgium
19 Posts |
Posted - 28/08/2007 : 14:12:29
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Thanks for the info.
I've got some more reading to do. |
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Del
Junior Member
United Kingdom
369 Posts |
Posted - 28/08/2007 : 14:19:32
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Hi Ralph,
Ah I see you've added a bit to your original post whilst I was in mid-reply to you.
The motor on the link would appear to be good but unfortunately it isn't so good on two counts:
1) It has a gearbox and the ratio is 12:1 so the motor will turn 12 times for every turn of the ouput shaft. Unfortunately the increased friction this results in makes it not very attractive as a generator as it will slow the blades from spinning well - like driving with the brakes on!
2) It also looks like the motor is only rated at 300MA (3 tenths of an amp) which is not very powerful.
You're best bet is as you were advised by Ben - see if you can find a treadmill motor or something similar.
Cheers
Del. |
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BushWhacker
Junior Member
Canada
329 Posts |
Posted - 29/08/2007 : 07:07:27
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Thanks Del,
You Wrote "1) It has a gearbox and the ratio is 12:1 so the motor will turn 12 times for every turn of the ouput shaft. Unfortunately the increased friction this results in makes it not very attractive as a generator as it will slow the blades from spinning well - like driving with the brakes on!"
You confirmed what I though but wasn't sure of.
I guess it pays to read a lot.
Cheers,
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
Edited by - BushWhacker on 29/08/2007 07:08:07 |
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Del
Junior Member
United Kingdom
369 Posts |
Posted - 29/08/2007 : 08:49:23
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Hi BW,
Yes 12 to 1 is a bit much, although I woun't mind trying using a motor/gearbox combo that had a 3:1 or 4:1 ratio on it just to see if it could be overcome by torquey blades.
One of us will no doubt try it at some point.
Cheers
Del. |
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BushWhacker
Junior Member
Canada
329 Posts |
Posted - 29/08/2007 : 10:26:10
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Thanks Del,
Being a bit dense on HAWT blade theory, and having an unending supply of pvc sewer pipe, (and saw blades) can you define what makes a "Torquey" blade? I have access to mountains of 6", 8", and 12" sewer pipe (new thank god!!!) in lengths up to about 10 or 12 feet. For torque I know that a blade should be longer, but what about weight, width, and curve? That 12" pipe is pretty heavy stuff. (But damn, could it make a big blade!).
Ben, do you want to weigh in on this?
I'll do the cutting, routering, grinding, sanding, ect. Can you give me some reasonable ideas? I also posted about some tested blade ideas... ( http://gotwind.forumco.com/topic~TOPIC_ID~180.asp ) with the leading edge "scalloped" like the leading edge of a whales fin. I think I know how to a achieve this using a router.
I live in a city with a fair breeze from time to time, but it's NOT on the coast of England. Please keep that in mind.
Why do I think I'll hate myself for saying all that? *LOL*
Cheers!
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
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Del
Junior Member
United Kingdom
369 Posts |
Posted - 29/08/2007 : 12:52:05
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Hi BW,
To a large extent it's a trial and error thing.
Firstly you want to set the perameters. What generator are you using? Does it spin freely or does it have a cogging effect? If it's the latter you may need a bit more torque, or put more simply, the blades you have need to catch more wind. The downside of more torque is less speed because of the added resistance the blades have when spinning.
Secondly what kind of rpm do you want your blades to spin at for your generator. If you need a high rpm to get 13V + then you dont want torquey blades you want speedy ones.
You also need to consider your average wind speed. If you're in a built up area then you probabaly don't have much wind so this probably leads us to a more torquey blade set up.
It's all a compromise really. Of course we all want our blades to spin as fast as possible (without going scary unsafe fast) and start spinning in the lightest of winds. Tractor power with F1 speed if you like.
You can increase torque by adding more blades, or having longer blades, or the shape and angle into the wind. And gain speed by doing the opposite of the above.
Superwindy has done a few youtube videos and posted them on the forum here and he's found that although he started with Ben's blade design he's added a blade (so has 4) and then shortened them considerably for extra speed and it's worked for him through trial and error. I think that's actually quite a good compromise as the tip speed of your blades is probably the biggest restrictor on rpm speed so the longer the blades the higher the tip speed would be for a given rpm. If the design of you blades simply wont allow your blade tips to exceed a cerain speed then making them shorter makes sence as they'll still be travelling at the same speed but going a shorter distance so will give you a higher rpm.
Personally I like the five blade set up, but I've just made a second set that's 180mm shorter and I will compare the readings I get soon. I hope that it will still catch loads of wind but will allow the blades to spin slightly faster.
Then there's the shape of your blade. Most people are realising the tip speed thing so are having the shape fatter in the middle and thinner at the ends. Ben's latest blades demonstrate this well, but you can experiment with your own designs and if you have plenty of pipe then get to it my friend.
Another consideration is the balancing of your blades and getting them absolutely central on your hub. I was involved with another forum conversation on this very subject very recently so please refer to that.
And finally, the choice of pipe. I'd stick with the 6" pipe if I were you. I'm not sure of the safety or need for anything bigger.
Ooh, one last thing - leading and trailing edge profiles. I need to do some work on my own blades in this respect. Aerofoil profile will be best here like anything that has to move at speed through the air or water. Think fish like. Rounded at the front and sharp at the back.
Does that give you enough to go on?
I'll take some pictures of my own blades set ups and post them on soon so you can see what I'm up to but my advice is to consider all the factors according to your set up and experiment away!
Cheers
Del. |
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Del
Junior Member
United Kingdom
369 Posts |
Posted - 29/08/2007 : 13:23:35
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Here you go BW,
Here's my latest two sets of blades. The bigger of the two are 600mm blades and the smaller are 430mm. They are both mounted on a circular ply hubs which are temporary as I don't think that wood is up to the task and I prefer to have aluminium plate (from an old frying pan) like the one I had on my three blade set up (also in the picture). But I need more old frying pans to attack!
Cheers Del. |
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Ralph
Starting Member
Belgium
19 Posts |
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Topic |
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Good Motor
Posted - 28/08/2007 : 09:57:55