Rotational Magnetic Field Driver for Three Reed Relay Coils

Sir Kit

Joined Feb 29, 2012
172
I am building a novelty item that requires current at 6VDC fed to three 500R reed relay coils arranged in a circle (ends facing inward) in such a way as to produce a rotating magnetic field at a variable rate (about 60-6K RPM). What would be the best design approach for this project using minimum components?

I assume a gated function would be simplest to implement, but would also be interested applying sine waves for a more even rotation if that is not too much more involved.

I have looked online but did not find anything suitable. Any suggestions or pointers to an existing circuit design would be appreciated.

crutschow

Joined Mar 14, 2008
33,331
A 3-phase, sinewave oscillator like this should work to generate the signal.

But how would a sinewave help produce a better rotating field if the reed relays are either on or off?
Seems like you just need a 3-phase digital signal driving 3 transistor switches.

Example 3-phase digital generator below:

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Sir Kit

Joined Feb 29, 2012
172
The sine module looks great but is probably more than I need. The CD4013 digital circuit would need a clock and output transistors.

After further investigation, I discovered I should have been looking for a "BLDC driver". This brought up a number of seemingly promising options, a few of which of which I have linked below.

I imagine the MOSFET's specified in all the above would be more than needed to each drive a 500R load. Would something like the following two circuits provide enough current on their own?

Since the RC values are fixed, how can the rotational speed can be changed to another fixed rate? For example 500 RPM.

crutschow

Joined Mar 14, 2008
33,331
Since the RC values are fixed, how can the rotational speed can be changed to another fixed rate?
You likely could use a 3-phase BLDC driver with built-in oscillator such as this.
It doesn't show the speed range, so you would have to contact them about that.

Sir Kit

Joined Feb 29, 2012
172
What waveform would the BLDC driver you linked above apply to each coil?

15A is way more than I need for my 500R coils. Nonetheless, it is a good ready-made solution, but I was hoping to build something "simple" myself as a learning experience. Preferably with sine wave output rather than squarish.

Maybe something like the phase shift oscillator below. If I use an LM324 on 6VDC single rail supply would it drive the 500R coils directly without a power stage? That's 12mA per coil and the LM324 is rated for 20mA minimum source.

crutschow

Joined Mar 14, 2008
33,331
Maybe something like the phase shift oscillator below.
How are you going to get the wide frequency range you mentioned in your first post?