# DC Motor used as a generator determining output.



## Windy in Kansas (Jun 16, 2002)

Sort of thinking out loud and wonder if you could help me.

When looking at surplus dc electric motors how do you go about determining output when they are used as a dc wind generator? 

Examples: https://www.surpluscenter.com/electric.asp?UID=2009072000344143&catname=electric

I know that volts X amps= watts but of course that can only be used when they are given in the description.

Does VxA=W still apply when converting a motor draw to output? Are they 100% efficient or true to formula IF turned at the rated RPMs?

On the ones rated in horsepower or fractional horsepower is it somewhat safe to use the normal watts per horsepower rating?

Does a person need any sort of charge controller if using a 12 VDC motor as a 12 volt generator or can they tie directly to a bank of batteries?

Am I correct in saying that a person should always use a permanent magnet motor IF they don't wish to rig a field activation switch to prevent battery run down?

Any good books that you can recommend for such conversions and systems?

Thanks.


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## wy_white_wolf (Oct 14, 2004)

Windy in Kansas said:


> ..When looking at surplus dc electric motors how do you go about determining output when they are used as a dc wind generator? ...


If the manufacture or someone hasn't tested the motor as a generator and published the specifications than the only way is to test it yourself. Output of DC motors used as gennies varies to much for any standard formula.


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## artificer (Feb 26, 2007)

Take a look at: http://otherpower.com

Lots of good information there. Also go to their commercial site for books:
http://www.forcefieldmagnets.com

Getting a DC motor to produce power is the easy part. You need the turbine blades, furling/safety system, charge controller to have a functioning system.

I guess it comes down to what you want to do. Do you want to use a DC motor and some PVC pipe blades, and be able to say you're making power, or do you want a system that can produce a significant/useable amount of power. Either is really cool, its just a matter of goals.

Good luck

Michael


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## roachhill (Jul 8, 2009)

If you want an efficient wind turbine you will need a permanent magnet alternator/motor a self excited motor (one that creates a magnetic field with electromagnets) needs to much start up torque for use with wind. Thats why the old systems using auto alternators were so inefficient. How much does it cost to build your own? You can buy a kit for a pretty nice turbine that's already tested and has the bugs worked out for about $450. I'm sure that's more than it cost to build but if you fail on your first try you have the cost of trying again (you know testing different motor and blade combos) and if a turbines not balanced properly it will shake and rip it self apart in high wind. Improperly designed and build wind turbines can be dangerous and destructive. I'm not trying to sell anything just realize it's not hard to build a wind turbine but making one safe, efficient and long lasting can be tricky.


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## damoc (Jul 14, 2007)

i used on several wind and hydro experiment a 30 v dc motor 
amtek an old tape drive motor.

it was very good for experimenting but the most ever produced from it
was 8 amps into 12 volts almost 100w with a wind turbine.

i would recomend to someone for projects but not for long term energy production.


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## damoc (Jul 14, 2007)

roachhill said:


> If you want an efficient wind turbine you will need a permanent magnet alternator/motor a self excited motor (one that creates a magnetic field with electromagnets) needs to much start up torque for use with wind. Thats why the old systems using auto alternators were so inefficient. How much does it cost to build your own? You can buy a kit for a pretty nice turbine that's already tested and has the bugs worked out for about $450. I'm sure that's more than it cost to build but if you fail on your first try you have the cost of trying again (you know testing different motor and blade combos) and if a turbines not balanced properly it will shake and rip it self apart in high wind. Improperly designed and build wind turbines can be dangerous and destructive. I'm not trying to sell anything just realize it's not hard to build a wind turbine but making one safe, efficient and long lasting can be tricky.


very good advice as i have destroyed several home made ones which i was
to lazy to build in protection


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## Windy in Kansas (Jun 16, 2002)

Great! This was just the kind of information I was looking for. I really don't need any serious production I more or less just want to play around. I live in town and want to experiment out at my farm with it. Power a little lighting maybe just enough to show from the county road that the place might be inhabited which might tend to ward of burglars. 

I had forgotten about seeing a YouTube video showing how to make PVC blades from pipe. I'll view it again, thanks for reminding me. 

Thanks to each of you for the information.


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## mightybooboo (Feb 10, 2004)

Some really nice blades and hubs on ebay at very reasonable prices.


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