Reed switches, Hall sensors, trigger coils... discuss

[kEhYo77]

Why not to use a reed switch to apply a voltage to the gate of a mosfet, with a pull down resistor?

[synchro1]

The series bifilar coil no longer even needs a switch over the self acceleration threshold. The "Scalar Wave" increases in power and begins to drive the spinner at a new pitch way over the rated circuit switch speed. The longitudinal magnet wave has a back to back pulse included in it! Take another look at the schematic in the comment above!

[conradelektro]

Why not to use a reed switch to apply a voltage to the gate of a mosfet, with a pull down resistor?

Yes, one can do that and it will help to have a long life of the reed switch.

The main advantage of a reed switch usually is that one does not need any electronic component besides it (just a battery, reed switch and drive coil). If you are prepared to use a transistor (MOSFET) then it costs very little more to add a hall sensor in order to get a reliable and accurately switching circuit.

A reed switch can not switch at high frequency, can not switch a high current and is probably more expensive than the transistor plus the hall sensor.

The modern pulse motor circuit would be a hall sensor and a MOSFET. One could throw in a little microprocessor in order to generate some fancy timing (hall sensor, microprocessor, MOSFET).

A trigger coil (instead of the hall sensor) plus an OpAmp is a nerdy solution just for the fun of it.

A trigger coil plus a transistor is a nice home made solution, but there really is no valid reason not to use a hall sensor.

But if we want to be cynical, there is no valid reason to use a pulse motor in the real world. Use these new three phase brushless motors which you see in quadro copters or model airplanes. Some good drive circuits use hall sensors on the face of the motor.

Greetings, Conrad

[dieter]

Conrad,


I agree, for BEMF harvesting a low impedance and a high inductance is required. Few Ohms, but enough mass to create a strong field. I had problems with too little resistance, at a higher RPM the tip2955 would simply go in a on mode, maybe because the supply voltage dropped, the hall sensor latched? It does so whenever there is a contact interruption, eg. by a loose aligator clip when touched. So a few dozen of ohms should it be at least IMHO.


For a good square waveform, it may be useful to use a nand gate chip like the 4011, that will make 0 and 1 out of an analog signal, it may dissipate less than an OA and can trigger any Transistor easily, and it's cheap.


Harvesting the Back EMF may indeed reduce RPM, but maybe this can be optimized by:


Let the BEMF flow trough the drive coil with a rather high load at the "end", the load should not delay the BEMF as capacitors or inductors do. But finally, the BEMF is not for free, so a certain reduction in RPM is to be expected.


High Voltage peaks of a BEMF may however be used in a Bedini Style Battery reconditioning System, at least.


A quick diode like a schottky should be used to catch the BEMF, as well as a cap with a few hundred volts to be able to collect the preaks, I guess.
As it was mentioned, mercury tipped reed contacts are used... doesn't that evaporate? Could gallium be used instead?


Regards

[TinselKoala]

The motor that probably shouldn't work, but does: the Marinov Slab. (bottom view)

One Hall sensor, one capacitor, one resistor, one mosfet, one battery, no cores, two rotor magnets, one switch. No armature back-reaction. Or so it could be claimed.