RPM circuit

[Wanabee]

I am building a wind generator and am looking for a circuit that will close a relay to energize a 12 volt linear actuator to stop the wind mill. I need this circuit to close the relay at 300 RPM's. I mounted a magnet on the wind generator that sweeps past a pickup coil and at 300 RPM's, I get a 20 volt pulse and 200 ms between pulses. I can vary the amplitude of the pulse be changing the distance between the magnet and the pickup coil. I looked at using a 555 with a RC circuit, but not sure if this would be reliable enough. I was also thinking about using some kind of counter circuit. If the circuit counts more than 5 pulses per second, which equals the 300 RPM's, the circuit would energize the relay and actuate the brake. The counter circuit would also have to reset every second. Not sure if all this makes any sense, but if anyone has any questions, I will try to answer them. Any comments or ideas are appreciated.
Wanabee

 

[chemelec]

You could just have the coil Charging a Capacitor through a diode to prevent reverse loss.
Also a somewhat high value resistor across the cap, to slightly bleed it off when it slows down.
Than have a Comparator Monitoring the Rise in Voltage on the cap, with a set voltage TRIP-POINT to trigger your relay.
But It Might be better with 2 or 3 Magnets to create a more even rise in voltage.

Very Simple circuit and should work good.
Needs a little Expermentation on Distance between Magnets and coil, as well as capacitor value and Trip point on the Comparator.

 

[birdman0_o]

Well, if wanabe wanted to make his circuit using digital logic:

Use a 4 bit counter, the input being your sensor. Use a 555 to reset the counter every second. If bit 2 and 1
(0110) are set we have 6. So AND these 2 bits, the output would turn on the relay.

How would you undo the brake though?

Just playing around with his idea

 

[StudentSA]

Look into using the LM2917 or LM2907 Frequency to Voltage convertors.

 

[bryan1]

If the wind generator outputs wild AC as it should then measuring the hertz will give an accurate rpm reading. Now why in the world would you want to stop the wind generator at 300 rpm when 99.9% of them are used for battery charging. Having a swinging tail that furls is the best option to stop a wind generator running away and self destructing and is the best option. A dumpload SHOULD be incorporated to divert the power and be sized with a minimum ratio of 3X.

Try to energise a 12 volt linear actuator into a wind generator doing 300 rpm is asking for it to do it once then having to replace it everytime it energizer's. Go and do some research on wind generators and re-think your whole design.

Regards Bryan

 

[MikeMl]

This should work. The first 555 is set up so that its output pulses if the period of the input PULSEs is >260ms. The second 555 acts as a pulse detector, such that if the first 555 stops pulsing, it times out, making its output low. SPEEDOK is high if the pulse period is >260ms; low if they come too frequently.

If you use good capacitors, it should be stable enough. You can convert R2 into a 200K trimpot in series with a 330K to make the speed threshold adjustable.

 

[Diver300]

How do you know when the wind has dropped enough to restart to wind generator?

As Bryan1 said, measure the frequency of the AC from the alternator. Even if you are charging batteries with DC, the actual electrical machine is likely to be an alternator with rectifiers. The frequency of the signal before the rectifiers is proportional to speed.

 

[Wanabee]

Well, if wanabe wanted to make his circuit using digital logic:

Use a 4 bit counter, the input being your sensor. Use a 555 to reset the counter every second. If bit 2 and 1
(0110) are set we have 6. So AND these 2 bits, the output would turn on the relay.

How would you undo the brake though?

Just playing around with his idea

Birdman
I plan on using a DPDT switch to manually reverse the actuator and release the brake.
wanabee

 

[Wanabee]

If the wind generator outputs wild AC as it should then measuring the hertz will give an accurate rpm reading. Now why in the world would you want to stop the wind generator at 300 rpm when 99.9% of them are used for battery charging. Having a swinging tail that furls is the best option to stop a wind generator running away and self destructing and is the best option. A dumpload SHOULD be incorporated to divert the power and be sized with a minimum ratio of 3X.

Try to energise a 12 volt linear actuator into a wind generator doing 300 rpm is asking for it to do it once then having to replace it everytime it energizer's. Go and do some research on wind generators and re-think your whole design.

Regards Bryan

Bryan
The windmill does have a tail that furls and the excess power goes into a water heater. This circuit only will shuts down the windmill if something goes wrong with the controller, rectifer, heater elements, wiring, or anything else that will cause runaway conditions. The actuator applies a band brake which stops it easily. The reason I don't want to use the generator output for the circuit signal, is that if something goes wrong with the generator wiring, and lose voltage, the circuit won't work. That is why I want to use a pickup coil for the signal.
Wanabee

 

[Wanabee]

Thanks everyone for the replies! It will run the ideas through Spice and see how they work.
Wanabee

 

[bryan1]

G'day Wannabe,
First thanks for that explanation and it is good to see you've got the right setup. Now the general way to stop a genny is simply short the phases together and depending on the strength of the magnets shorting should stop it dead. Even in a high wind the blades will turn slowly but no harm will be done. The problems I see with using a band brake is in time the thing will rust unless you use stainless steel and when the time comes to use it the water has already done the damage. I do assume that your wind genny is a dual axial flux and some pictures would be great.

Cheers Bryan