Tinman's coil shorting circuit

[Vortex1]

Dear Gyula

I am in agreement with your thoughts in your last post. The schematics you and penno64 offered look viable and are somewhat similar to what I posted elsewhere. In light of the new info of the second coil, I am working on a few new schematics which I will post when I am satisfied that they seem reasonable.

Another thing to ponder is Brad's use of the words BTDC and ATDC. These are terms used for IC engines to denote timing, but how do they apply to a universal motor when each small angular advancement of the rotor to a new commutator contact represents a new reset of conditions, unlike an IC engine?

As an example, a rotor with six poles would achieve magnetic TDC every 60 degrees of rotation, while an IC engine achieves mechanical TDC every 360 degrees of shaft rotation.


It would be better to speak of a timing diagram based on degrees of rotation, unless the terms "Before top dead center" and "after top dead center" can be made meaningful to us.

If the terms BTDC and ATDC refer somehow to one complete revolution of the shaft as in an IC engine, then how  is the timing alignment point to be understood with respect to the stators and rotor?

Kind regards, Vortex1 / ION

[poynt99]

I'm pretty sure he means this:

BTDC=before top dead center
ATDC=after top dead center

"TDC" being when the magnet and armature are in alignment.

[gotoluc]

I also understand it like poynt has posted above but would explain TDC as below.

"TDC" would be where each rotor core section locks to the stator magnet.

Luc

[Vortex1]

Just wanted to clear that issue up, I also agree that TDC is when the rotor flux for a given rotor segment is in complete alignment with the stator flux.

This occurs X times per one shaft revolution, x being the number of rotor poles (or commutator segments).

Thanks for your input guys. We are on the same page so now it's back to getting the timing for the shorting transistor and the actual shorting circuit.

I'll attempt a few schematics that might address what was meant by "shorting" i.e did Brad mean "connecting " one coil to another at a specific time (with an FET) or did he mean providing a low resistance path (FET) for the induced voltage in one or both coils at a specific time.

With only one FET switch as seen in the videos, it could get tricky.

Here is a first cut schematic which just shorts the "second coil" to stator B coil.

I straightened out some of the "tangle" to make the schematic more readable from an electronic schematic conventional viewpoint.

[gyulasun]

Hi Vortex1,

Thanks for the schematic, looks good to me.  This version connects the second winding in parallel with stator coil B   i.e. I would say the second coil quasi shorts stator coil B because I assume the second coil has less L inductance in practice than stator coil B (winding space for the second coil is limited).  Nevertheless the 'short' does not represent a really low impedence like a MOSFET's on channel would insure for instance but this may not be a drawback.
Of course, some protection means are to be provided for the gate-source electrodes of the MOSFET to limit any control voltage within +/- 20V (spec for most MOSFETs including the IRF540 Brad used),  though these means are not needed to include in the first cut schematic. 

Gyula