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Forum Index : Windmills : Contemplating my first windmill....

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SensibleNick

Newbie

Joined: 16/10/2009
Location: Sweden
Posts: 4

Posted: 08:51pm 15 Oct 2009

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Hi All.

I've just signed up to the forum as I've got my grubby mitts on a few servo motors and as I can't sell them, I figure I should use them.

(I work at one of our company's 12R&D departments, and we tend to create a disturbing amount of potentially useful scrap... I have a very understanding missus ;) and a fair bit of storage space, so I save as much as I can . the only rule is that we're not allowed to profit from it)

I'm a mechanical engineer with a "hobby" background of making RC gliders - I'm no stranger to making foam-cored composite wings - pretty blades are something I'm looking forward to making.

Here's where I'm looking for guidance.

My aim isn't to create regulated power, but to create heat: as much as possible.

As far as I understand things, I need to have a load on the 'mill in order to stop it from running free. That load might as well be a ceramic heating element in a radiator right?

So... please correct me if I'm wrong... but - put crudely - I can simply "short circuit" the motor with a 3 phase heating element and get heat on windy days.

This leaves questions of size. I don't have the figures on the servo motors with me.. the larger (unbraked) ones are rated at 16Nm @ 3000rpm If I recall correctly, and the smaller at 13Nm (I've got to remove the brakes from them though)

In the morning I'll get the full details on the motors.

Gut feeling tells me that it'd easily take 1.5 meter blades.. but I'm kind of hoping that once I've got some figures together you guys will be able to point me in the right direction :D

Looking forward to some fun discussions!

All the best,

Nick

floodrod
Regular Member

Joined: 08/07/2009
Location:
Posts: 70

Posted: 11:36pm 15 Oct 2009

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Hi there,

I too want to make primarily heat with my upcoming mill.. You can't take my assumptions as fact because I am new to this, but I have been asking similar questions.. Allow me to share as I understand.

Shorting out your motor all the time with a heater load rated for your maximum output will stall the blades. They may spin in massive winds, but not much spinning will happen if any at all..

The better approach is to ensure the blades always spin and store any and all the energy you can get into batteries, then run a heater off the batteries..

For instance, if your mill is spinning at 200 RPM's, it will be charging batteries at somewhere between 2-4 amps.. But if the same wind speed was applied to a shorted motor, it wouldn't spin at all.. 2-4 amps of stored power is better than no power..

Say you were generating 250 watts into batteries on a constant basis. Every 6 hours of collected energy could run a 1500 watt heater for 1 hour.. So if the wind blew 24 hours a day at 250 watts, you would get 4 hours of heating at a consumption rate of 1500 watts.. But if you had the heater hooked up directly at all times, the load is much greater than 250 watts and the sucker will probably be stalled all day long..

So a battery bank is needed. With this bank comes over-charging/diversion controls, and a system to ensure your batteries do not over-discharge..

Again, I may be wrong, and if I am, I am sure I will be corrected.. Edited by floodrod 2009-10-17

GWatPE

Senior Member

Joined: 01/09/2006
Location: Australia
Posts: 2127

Posted: 07:27am 16 Oct 2009

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Hi Nick,

Series caps are the way to go with a direct resistive[heater] loading. The caps pass power proportional to the voltage and operating frequency. For a doubling of the voltage, the resistive loading offers 4 times more loading. For a doubling of the frequency, the cap offers double the power transfer. This is right on the money for an optimum windmill loading reigime. Cap sizing becomes the primary requirement, and the caps need to be sized for maximum windmill power.

Check this link for caps I used on my windmill as an example caps link

Without a battery, the cap multipliers would not be required.

Gordon.

PS what is with the milk and toast?Edited by GWatPE 2009-10-17

become more energy aware

SensibleNick

Newbie

Joined: 16/10/2009
Location: Sweden
Posts: 4

Posted: 07:36am 16 Oct 2009

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floodrod said Hi there,

I too want to make primarily heat with my upcoming mill.. You can't take my assumptions as fact because I am new to this, but I have been asking similar questions.. Allow me to share as I understand.

That sounds horribly like perfect sense to me... :(

In my non-electrician-mind I have another alternative... I'm happy to make a simple logic circuit that monitors the temperature of a resistor... if it's getting hot, switch in another one... and another and another until the load is large enough.

I also regularly hear of Frequency converters.... I have a few "old" Omron 3phase frequency converters that are used to control asynchronous motor speeds ... I wonder ıf they're any use?

The other things I've been considering is having an asynchronous motor running a water pump... the faster the windmill the harder the pump works.. with the windmill managing to start up under "no load" as the motor won't kick itself into life until the 'mill is producing enough power...

Just incase I appear to be "stating this as fact", please be aware that these are only MY theories based on my weak understanding of electronics, and what I'm hoping is that someone can set me straight!

Here's the larger of the 2 types of motor I have... but it's beginning to look as though the windmill itself is the easy part.. and the electrics are the challenge... :(

SensibleNick

Newbie

Joined: 16/10/2009
Location: Sweden
Posts: 4

Posted: 07:46am 16 Oct 2009

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GWatPE said Hi Nick,

Series caps are the way to go with a direct resistive[heater] loading. The caps pass power proportional to the voltage and operating frequency. For a doubling of the voltage, the resistive loading offers 4 times more loading. For a doubling of the frequency, the cap offers double the power transfer. This is right on the money for an optimum windmill loading reigime. Cap sizing becomes the primary requirement, and the caps need to be sized for maximum windmill power.

Check this link for caps I used on my windmill as an example caps link

Without a battery, the cap multipliers would not be required.

Gordon.

PS what is with the milk and toast?

Ahhh.. now we're talking.. Thanks Gordon, that's fascinating stuff! (and it looks to be relatively simple too)

I'll give it a thorough read and see if I understand it.

Certainly seems to be the kind of way I'd want to go though.

The Milk-Toast in the Avatar is one I use on another forum I hang out on where I'm one of the guys "in the know" instead of being a newbie (like here). It stems from a newbie turning up there and saying "I know everythign and am a very experienced pilot, so don't milquetoast(/I) me" ... kind of an in-joke.
The face however is me....

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