Tinman's coil shorting circuit

[penno64]

Hi all,

Does anyone have suggestions regarding Brad's coil shorting circuit?

From the videos, we see the coils are feed into the circuit and on the top of vero board,
one transistor, one diode and a resistor seem to make up the coil shorting.

Total output is then feed into a larger smoothing/buffer cap.

Any diagram suggestions are welcome. I am happy to build and test.

Regards, Penno

[gyulasun]

Hi Penno,

I drew these two schematics to someone but it was in early July and then tests have been suspended, I have no further info yet.

I also noticed the diode in the veroboard and I thought it is the diode Tinman also showed in his schematic in series with the switch S1. 
If the diode on the vero board is not that one, then the diode shown on the board could be in series with the drain pin of the MOSFET to defeat the effect of the body diode but I did not show this possibility in my schematics.
I may be wrong but I assume in my schematics that the body diode of the MOSFET (shown between drain-source) has no unwanted shorting effect on the induced voltage of coil B when the MOSFET is in the off state. 
Normally for coil shorting when done with MOSFET, two seriesly connected MOSFETs are used (their source pins tied together and the two drains short the coil when both FETs are driven from the same control signal) so that their body diodes block conduction for any AC polarity.  Tinman may have not used two MOSFETs because there is only one shown (I do not assume there are hidden components under the vero board, though it occurs to me he mentioned he did not include in his schematic all the components he used).
So in case two MOSFETs were used for coil shorting, then later I can draw such schematic too.

The reason for drawing two schematics shown below was to show the polarity for the gate-source control signal is important, meaning to choose the connection version which brings a positive gate pulse with respect to the source pin from coil A.
Tinman did not probably use a potmeter to reduce the spike amplitude below 20V (I use R2 as a adjustable voltage divider with R1, this latter is between the gate-source). Tinman did mention the need for reducing the control spikes to the gate (not to burn the gate-source of the MOSFET), maybe he just used R1 in parallel with gate-source to prevent this,  not sure. Zener diode can also be used in parallel with gate-source.

Gyula

[penno64]

Hi Gyula,

Thanks for that.

I understood that the diode was for rectifying only.

The mosfet mentioned was the irf540

The resistor unknown.

It just seems simpler.

Regards, Penno

[shylo]

Penno64, Thanks for starting this thread.
Gyula, I thought that the little circuit board that penno64 showed was the right side of the of the circuit Brad showed in the attached diagram.
In his he has the shorting  shown as just a block.
Where do the spikes go into the cap?
I'm totally useless with electronics, I've been trying mechanical shorting but with no luck.
Can it be that simple , a diode, mosfet, and resistor?
Creating spikes is easy the hard part is catching them and storing .
Thanks artv

[gyulasun]

Hi Penno,

Yes, the diode on the vero board can be the one connected in series with switch S1 and this diode may steer the spikes into the puffer capacitor placed also onto the board.
It may be simpler but we do not know about components Tinman referred to that he has not shown.

Hi Art,

It is very possible that the right side of the circuit Brad showed in his diagram is the little circuit board Penno showed from the video but in Brad's diagram there is no MOSFET on the right side. Of course the circuit board could host the MOSFET and the wires could lead to the left side where Brad indicated the shorting circuit as a block.
On your question: The spikes can go to the puffer capacitor first by induction and then via the diode when switch S1 is on. Remember that the two stator coils share a common magnetic core and when you short and unshort coil B, the spikes appear across coil A by normal transformer induction. With closing S1, the spikes are steered into the capacitor. Also remember that the rotor is brushed and also part of the magnetic circuit so spikes from the rotor coils should also induce voltage and current in the stator coils.
On your other question whether it can be that simple, a diode, MOSFET and resistor: well, basically it could but experiments can tell this, together with knowing what components are not shown, especially in the shorting circuit block. This block may include two MOSFETs connected in series to do AC shorting where the body diodes cannot shunt any AC cycle but the controlled drain-source channels can.

Gyula