Self starting pulse motor circuit

Thread Starter

AEgoddard

Joined May 9, 2022
11
Hi all I'm wondering if any of you could possibly help me in my understanding of this circuit.

I am wanting to built this circuit to drive a pulse motor, I like the idea that is it self starting. I have tried to replicate it a number of time but with no success.

I don't fully understand the circuit so am having difficulty fault finding. The video shows the led flashing before any movement in the rotor so with saying that It can't be from bemf. Is that correct, if so, what part of the circuit is causing it to flash ?

Thanks in advance, Arthur.
 

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Thread Starter

AEgoddard

Joined May 9, 2022
11
Not strictly true. You need to get a pendulum (or whatever) with a magnetic bob moving past the coil to activate the circuit.
The magnet wire gauge and number of turns on the coil may be important.
I have built a pulse motor before with a circuit that required me to spin the rotor to activate the circuit but after watching this video and others I was under the impression that this particular circuit itself gave off an initial pulse to get it moving, maybe I am wrong. I'm still very new to this and although understand the concept of individual components, don't understand how they all work in a circuit.
 

Alec_t

Joined Sep 17, 2013
12,897
Even if it does provide an initial pulse, unless the magnetic part is in an appropriate position it won't be attracted/repelled by the coil.
 

Danko

Joined Nov 22, 2017
1,365
I am wanting to built this circuit to drive a pulse motor, I like the idea that is it self starting.
I have tried to replicate it a number of time but with no success.
In simulation circuit generates only one initial pulse,
after that produces HF parasitic oscillations
and does not react on EMF pulses.

With minor modification where value of C2 lowered to 100nF and C3 added,
circuit generates initial pulses while EMF pulses not appear, then works synchronously
with EMF pulses.
1656424275956.png___1656423616206.png
 

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Thread Starter

AEgoddard

Joined May 9, 2022
11
Even if it does provide an initial pulse, unless the magnetic part is in an appropriate position it won't be attracted/repelled by the coil.
Hmm... yeah I've been thinking about that, you're right. It doesn't heavily depend on rotor position. Never thought about that previously...


In simulation circuit generates only one initial pulse,
after that produces HF parasitic oscillations
and does not react on EMF pulses.

With minor modification where value of C2 lowered to 100nF and C3 added,
circuit generates initial pulses while EMF pulses not appear, then works synchronously
with EMF pulses.
View attachment 270329___View attachment 270327
Ñ

Wow thank-you Danko for taking the time to simulate this, this helps me understanding this circuit a little better, much appreciated. What you say makes sense and I can see that now. I must ask, what program are you using ?

I think what I shall do is order some more caps and try that modified circuit and see how I get on.

What are your thoughts on the coil ? How much does coil resistance alter the effectiveness of that circuit. My current coil measure 1.7k ohms.
 

Thread Starter

AEgoddard

Joined May 9, 2022
11
Even if it does provide an initial pulse, unless the magnetic part is in an appropriate position it won't be attracted/repelled by the coil.
I've just tested your theory by directly applying the power source to the coil and tapping it. It does seem that even between two magnets it does repel/attract.


So the coil current will always be less than 1mA. Is that enough to generate a sufficiently strong magnetic pulse?
Does the coil have a ferromagnetic core?
Good question. I wish I could answer that but unfortunately I knowledge is limited so I can't. Although I will say that with one of my failed attempts of building the circuit I posted,after trying it with the coil and rotor it didn't seem to have enough. It was trying to turn but didn't have enough power to successfully turn it enough to another magnetic on the rotor. With this being said, how could I overcome this ?

The coil has an air core.
 

Thread Starter

AEgoddard

Joined May 9, 2022
11
So the coil current will always be less than 1mA. Is that enough to generate a sufficiently strong magnetic pulse?
Does the coil have a ferromagnetic core?
How did you calculate this ? I would like to know so I can do it myself if you would be kind enough to explain ? Thank-you
 

Danko

Joined Nov 22, 2017
1,365
Wow thank-you Danko for taking the time to simulate this, this helps me understanding this circuit a little better, much appreciated. What you say makes sense and I can see that now. I must ask, what program are you using ?
I think what I shall do is order some more caps and try that modified circuit and see how I get on.
What are your thoughts on the coil ? How much does coil resistance alter the effectiveness of that circuit. My current coil measure 1.7k ohms.
For simulation I use free program LTspice. You can download it from
https://www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html
Your coil should be winding by wire about 0.3-0.4 mm diameter, and have resistance 20-50 Ω.
1.7 kΩ is too-too much and coil will not work. :(
See diagram with coil 1.7 kΩ:
1656448572758.png
ADDED:
File for using in LTspice simulator "Pulse_motor.asc"
 

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Thread Starter

AEgoddard

Joined May 9, 2022
11
For simulation I use free program LTspice. You can download it from
https://www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html
Your coil should be winding by wire about 0.3-0.4 mm diameter, and have resistance 20-50 Ω.
1.7 kΩ is too-too much and coil will not work. :(
See diagram with coil 1.7 kΩ:
View attachment 270371
ADDED:
File for using in LTspice simulator "Pulse_motor.asc"
Hmm.... that's a shame. I got this particular coil out of a 415v contactor. I also have a 550ohm coil, again from a contactor but nothing as low that 20-50 Ohm's. I will have to make my own it seems. Unless, could I change the values of particular components to accommodate such high resistance in the coil ?

Thanks for the diagram, although what does that show exactly ? Please excuse my ignorance.

I will download that program, looks like it would be very handy indeed.

Your power supply is 1.5V. The coil resistance is 1.7kΩ. I used Ohm's Law to calculate the static current.
That makes sense thank-you. Based on some trial and error today, it seems the coil current is enough to keep the rotor spinning when up to speed but not for an initial push...
 
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