13.9ohms across each coil pair. the only thing I can think of is when the magnetic field collapses it sends a higher voltage back through the other coils sort of like a transformer.

 

When the magnetic field collapses it will increase the voltage over the two coils , opposite polarity of the voltage applied before, yes.

In order to protect the MOSFETs this voltage is clamped to the power supply voltage via the additional diodes in parallel with them, the electrolytic capacitor should be absorbing that energy.

I don't see a problem neither for the MOSFETs nor for the coils.

However, if the main big capacitor does not absorb all this energy it may be possible that voltage transients appear on the power supply to the logic ICs, would be the only explanation for me why all 3 gates inside the 4025 were affected. This is why I would recommend measuring the voltage on the power supply pins of the logic ICs, triggering on the output signal, with a very short time division on the scope.

 

A better idea:

If you leave coils and power resistors in series and then measure the voltage over the resistors you are actually measuring current through the coils too.

This waveform should go down to zero when the corresponding MOSFETs are off and the inductor is discharged. Can you check this?.

 

I probably can, let me draw up, the way I have to resistors, power resistors and coils in the schematic, so you can see how I will set it up, and also so that I understand what you exactly mean.

It won't be until lunch time, because I'm in meetings all morning though.



Edit: Would it hurt to put the other 1000 uF on the FET's board?

 

This is the easiest way for me to hook up the resistors, the power resistors are hard wired into the T7/T8 drain, the coils can be added and removed by a connector and the resistors will be connected via alligator clips. If I understand you, I would supply power to this configuration and place the scopes probes to J1, J2 and J3, the question I have is, do I hook the ground probe to J4 or to 0V and use the 4th channel to hook up to J4? Or am I completely missing your request?

 

It doesn't matter if you connect the ground probe to the drains of T7/T8 or ground as long as you tell us where it was connected to. Especially when working with different configurations it's always good to inicate which signal was measured where.

1. As far as I understand you replaced the coils with the 4,7k resistors , that's the waveform we saw a few post earlier.

2. Next test is using 1 or 2 power resistors (in series) instead of the coils in series with the 10Ω||10Ω. Measure the voltages again (from drains to drains of the MOSFETs).

3. Then connect the coils and measure the voltage only over the 10Ω||10Ω. Since they are in series with the coils the voltage waveform will correspond to the current through the coils

 

Since I only have 2 extra power resistors, I was only able to test 2 coils but the results seem to point to something. I added another junction point to connect the power resistors to (blue)

What I did was remove the coils completely and added 2 10Ω power resistors in their place, one from J1 to J4 and one from J2 to J4, this was the result:

Before I connected the coils I decided to move the power resistors to the other side of the other 2 10Ω power resistors (wired in parallel) from J1 to J5 and J2 to J5, this was the result:

Now here is one from J1 to J4 and J2 to J4 with the coils hooked up:

and then with the parallel power resistors in line(J1-J5 and J2-J5):

What do you think?

 

What do you think?

1. picture: 20Ohms instead of coils and parallel 10R resistors
2. picture: 20Ohms in series with the 10R resistors, therefore replacing the coils

Correct?


Do these two 10R resistors in parallel still have 10Ohms,i.e. 5Ohms in parallel?

 

1. picture: Only 10Ohms instead of coils and parallel 10R resistors
That's this picture:

2. picture: Only 10Ohms in series with the 10R resistors, therefore replacing the coils coils are hooked up in this picture

That's this picture:

Correct?

The other 2 pictures have the 10Ohm resistors (in parallel) removed from the equation.


Do these two 10R resistors in parallel still have 10Ohms,i.e. 5Ohms in parallel?

Good ppoint, I have to check to see if those resistors are still good.

 

It is still 5 ohms

 

1. It seems the higher the current (the smaller the load resistance) the worse is the effect. Is that correct?

2. Since there IS voltage over the coils, is the rotor turning?

3. Can you put everything together as before and measure:
- voltage over the 10||10 resistors?
- voltage on the power supply pins of the 4049, 4025, 4017?

I want to see if voltage transient are present, to make them visible you will need to measure any output pulse with one channel and trigger on that pulse (ground probe to 0V) and measure with another probe the voltage on the IC. Connect the ground probe as near as possible to the IC pin you are verifying.

Zoom in because if there is a transient it will be very short.

I think I have those 9540/540 somewhere, worst case I build the power part here on a breadboard or I find some MOSFETs with the same gate charge...