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rotary speed


strongski
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The car heater resistor will certainly slow the rotary down but the added circuit resistance will cause the battery to drain quicker. The other way is to supply the rotary with a device called a pulse width modulator which is basically an electronic switch which pulses the power on and off at a variable rate causeing the rotary to slow down but without draining the battery. Maplins do a kit or somtimes see these things pop up on fleebay..keep your eyes peeled for a PWM or pulse width modulator but make sure its current ratings within the motor you are using.

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find an old ford car and whip out the heat resistor, located near the heater vent under the bonnet in a small metal perforated cage, witll give you 3 speeds when wired up at the cost of a few pence.

 

 

The car heater resistor will certainly slow the rotary down but the added circuit resistance will cause the battery to drain quicker. The other way is to supply the rotary with a device called a pulse width modulator which is basically an electronic switch which pulses the power on and off at a variable rate causeing the rotary to slow down but without draining the battery. Maplins do a kit or somtimes see these things pop up on fleebay..keep your eyes peeled for a PWM or pulse width modulator but make sure its current ratings within the motor you are using.

 

:lol:

 

Buy a speed controller.

 

ZB

 

:good:

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If you want to control the speed of you magnet you WILL need a pulse width modulation speed controller!!! Those of you that try dash board dimmer etc are going to find out the hard way. They may work for days..weeks...months..until they fail.

This because you are using a large variable resistor. It works by dropping some of the battery voltage across it, therefore reducing the voltage dropped across the motor. This gives three problems, 1st the heat generated in the dash board dimmer is far greater than that generated in the car, as the heat increases so does the resistance, this also weakens the wire in the resistor, so over time it will fail (burn out). 2nd as you are dropping voltage before it get to the motor, the motor will not be able to produce the required torque when needed. i.e with no wind the motor will turn fine, when the wind gusts the motor will start to stall/go slow. 3rd as you have added more resistance across the battery, you will now drain it faster.

 

Pulse width modulation allows the motor to see the full volage, if you want your motor to run at half speed then the pwm is 50% on and %50 off for a set time, if you want the motor to run at 3/4 speed the pwm is on for 75% and off for 25% of the time. This ratio happens many times a second, so the motor winding will see this ratio as an averge i.e 6v half speed and 8v 3/4 speed. This method allows the torque to be maintaned at various speed setting regardless of the conditions acting on it(within reason). As most PWM circuits (speed controllers) use a kind of transistor called a mosfet to switch the power to the motor they are either on or off, when they are on they have a very very low on resistance, when they are off they have a very very high resistance i.e open circuit. Giving very good motor control. All speed controllers sold on any site or shop use this method, they only differ in price and how they look on the outside. Any other claim made is to get you to buy it.

 

I hope this helps some people with their choice of controller. Sorry for the long winded discription!!!

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