Otherpower blade design speeds

[synovialbasher]

Hi. I'm building a turbine of my own using the convenient tape drive motor design. I didn't want to use PVC blades though and went ahead and made wood blades as explained by otherpower.com. The rotor has a 6' diameter. I'm trying to find a good motor to match with this, but the best motors I can find nowadays usually begin producing 12v + at about 550 rpms. Does anyone know how fast these wood blades will spin? In my area, we have a pretty decent 12mph average wind speed. Does anyone know how fast this thing will go, or if there's a formula to figure it out? If these kinds of RPMs are too much for these blades, can anyone recommend a place to get a decent alternator? Building one of these alternators is too complicated for me, and I can't easily aquire the materials.

Thanks,

Joe

[taylorp035]

Welcome aboard!

I think you are asking the right questions.  550 rpm for a 6' diameter is pretty fast.  I haven't done the TSR (Tip Speed Ratio) calculations, but I think some where in the 250 rpm range would be about right for a 6 footer at ~10-12 mph.  Depending on how your blades are shaped will determine how fast it will go.

Certain DC treadmill motors can be a good choice if you are looking for a relatively cheap option.  Many can be found in the 25 RPM/volt range or lower.

[jlt]

Using Altons blade blade calculator  It shows a 6ft with tsr7 doing 374 rpm at 12 mph.

It also shows a 4ft 2 blade hitting 550 rpm at 12mph.
 Try google for altons blade calculator for more info.

                                                          JLT

[Flux]

Depends whether you have 12mph average or whether your winds average out at 12mph.

I suspect the otherpower rotor of 6ft diameter is capable of just starting to produce power with a generator cutting in at about 500rpm in a wind of 12mph. If you have 12mph average then a lot of the time you will have winds well over 12mph and such a cut in may well be reasonable.

The Lucas Freelite had a 6ft rotor but was 2 blade and probably faster than the otherpower blades. These used to cut in at about 450 rpm and in wind speeds approaching 12mph. Being wound field you had to produce about 15W before you got anything so with a pm motor you would be ahead of this.

Ideally you would be looking at cut in nearer 300rpm for this prop, but you do stand a chance ( which you wouldn't with pvc blades).

If you can get a motor with cut in no more than 500rpm I would give it a try, you could always speed the prop up a bit by reducing the angle at the tips, narrowing the tips if needed and if all else fails by cutting the tips back to make it a 5ft 6" rotor.

If you haven't glued the blades at the root you also have the option of making it 2 blade.

If you can live with the noise I suspect the blades will get up to 1000rpm if you get some decent wind so everythiong really depends on what wind you have.

Flux

[synovialbasher]

Thank you everyone for your advice! I wish I would have joined this site sooner. I guess based off of your advice that it *could* work with a 550 rpm generator. According to Alton's calculator with all my information I would begin producing at 19 mph wind. Is this unreasonable? Reason being is that it's VERY difficult to find a decent generator nowadays. All the good ones ae taken and everyone's trying to get them for their wind potential. Those Ametek motors that work the best cost upwards of $150-$200. I don't want to invest that much into just the motor. There are other costs. Treadmill motors are tricky. There's a lot of snake oil when it comes to them.

I think I'll try and get a 550 rpm motor. It won't get every breeze that goes by, but on a windy day (we have a lot of those) I can easily break 19 mph. Thank you everyone!

[definitionofis]

I think you have to look at how much current the motor can produce, not just the voltage.  I think a 1/2hp produces less current than 1hp, for equal rpm versus voltage specifications.

You might end up with more potential power in that 6ft sweep and not enough physical load by the generator, which I think will be my problem when my furnace fan ECM motor spins up one day. Mine does have good rpm per voltage specification, though.

[sean_ork]

Treadmill motors are tricky. There's a lot of snake oil when it comes to them.

such as ?

given enough wind, and a pair (yes just a pair) of short fast spinning blades a DC treadmill motor is probably the easiest method of making electricity out of thin air

 

[synovialbasher]

Treadmill motors are tricky. There's a lot of snake oil when it comes to them.

such as ?

given enough wind, and a pair (yes just a pair) of short fast spinning blades a DC treadmill motor is probably the easiest method of making electricity out of thin air

Snake oil refering to someone selling a tredmill motor claiming it will make a great wind generator. Deep in the fine print do you realize that motor won't make 12v until 1500 rpms, way too fast for a generator.

I decided on getting one of the (way overpriced) ametek motors highly reccommended by everyone. It will begin producing 12v at an ideal 288 rpm, or 10.5mph wind speed. Having a 12mph wind speed, this isn't a problem for me. Thanks everyone for your advice!

[sean_ork]

Snake oil refering to someone selling a tredmill motor claiming it will make a great wind generator. Deep in the fine print do you realize that motor won't make 12v until 1500 rpms, way too fast for a generator.

pick the right treadmill motor and it'll make a fine low budget mill - one I have flying now produces around 200W at around 500RPM, labels are often misleading, the only way to properly test them is to load and spin them



Attempting to fix up the quote for you: DamonHD