How sensitive are high sensitive relays?

[avajoe]

I know small electric motors (for example one of the ones you get at radio shack for 5 bucks) will generate power when spun by there shaft from an outside source. Are there any relays that are sensitive enough so that they could be hooked up to the motor and than trip the relay when the motor spins at a low rpm?

 

[audioguru]

I doubt it. An electric motor must be spinned fast to make enough voltage and current to (power) activate a relay.

 

[kchriste]

Depends on the motor, relay and finger strength. You can get some pretty sensitive relays. How does 3V@17ma or 1.5V@33ma sound:
**broken link removed**

 

[Externet]

Hi.
From the relays I have and used, the most sensitive is the Teltone M-949-01; works with 20mA.
If your spinning motor can generate such at the speed you spin it, it will work.
It is not easy to find lately; seen it at some surplus stores years ago.
Miguel

 

[Boncuk]

I suggest trying a small unipolar stepping motor, e.g. a floppy disk drive stepper for the read/write head. Without any external circuitry in can drive an LED with just a little twist on the shaft. Using rectifier diodes and connecting the outputs parallel you should get reasonable current to activate at least a reed relay.

Boncuk

 

[avajoe]

I suggest trying a small unipolar stepping motor, e.g. a floppy disk drive stepper for the read/write head. Without any external circuitry in can drive an LED with just a little twist on the shaft. Using rectifier diodes and connecting the outputs parallel you should get reasonable current to activate at least a reed relay.

Boncuk

thats a good idea thanks, Im trying to come up with an old drive to take apart and test it

 

[Boncuk]

thats a good idea thanks, Im trying to come up with an old drive to take apart and test it

... and try a reed relay if you want to switch any device. They are normally rated 12mA, which is below the current used for miniature relays (20mA and more)

Boncuk

 

[Sceadwian]

Mind you if such a relay were fed from a Darlington or modest gain BJT it would trigger a 'sensitive relay' on micro amps. Use a resistor/capacitor low pass filter and you can prevent oscillation and provide moderate latching times.