Has anyone seen Lasersabers new motor runs on 1000uf cap

[conradelektro]

I experimented with the "Ossi-Motor 1 Reed 2 transistor circuit" from sMartcreations2010:

It was not very interesting, the motor started to run at 12.5 V and 1 mA. The feedback diodes had no effect whatsoever.

sMartcreations2010 http://www.youtube.com/watch?v=auykiV4Kq68 used different transistors which seem to work better. It is strange that the transistors fire at all.

Greetings, Conrad

[gyulasun]

Hi Conrad,

Perhaps the very low inner impedance of the power supply 'supresses' the back spikes coming from the coils via the two diodes, however small those spikes might be due to the small ON coil current involved. Just place a diode in series with one of the supply rails, perhaps the spikes will appear and increase the DC voltage level a little across the electrolytic cap  (or the diodes' forward voltage losses 'gulp' the small increase).

Why you say it is strange the transistors fire at all, I wonder.

Thanks for your efforts.

Greetings, Gyula

[conradelektro]

1) Perhaps the very low inner impedance of the power supply 'supresses' the back spikes coming from the coils via the two diodes, however small those spikes might be due to the small ON coil current involved. Just place a diode in series with one of the supply rails, perhaps the spikes will appear and increase the DC voltage level a little across the electrolytic cap  (or the diodes' forward voltage losses 'gulp' the small increase).

2) Why you say it is strange the transistors fire at all, I wonder.

Ad 1) I will put a diode between the power supply and the positive rail.

Ad 2) In the "Ossi motor circuit" shown in my Reply #200 no current is flowing into the bases of the two transistors (base to base connection via 1 K resistor and Reed switch). Why do the transistors switch? (I checked with the Scope, they do switch, but not completely.)

Tomorrow I will try a circuit with two IRLIZ44NPbF  [R-DS(ON) 0.022 Ohm, V-GS(th) 1 to 2 Volt] , it should run with 2 Volt. See the attached diagram. Comments are appreciated, may be I there is an error in the circuit?

Greetings, Conrad

[gyulasun]

Hi Conrad,

The MOSFET circuit version looks good to me, it can work, albeit normally a P-channel MOSFET is used at the upper position (where the pnp is connected in your bipolar transistor version).
Perhaps a 10 kOhm resistor would insure a little quicker switch-OFF time instead of the 100 kOhm, it can discharge gate-source capacitors more rapidly (RC time constant is less).

Regarding the pnp-npn transistor circuit why the transistors switch: you can consider the base-emitter junction of the pnp transistor as a diode with its anode at the emitter where the positive supply voltage is connected and its cathode is at the base (the arrow symbol may be seen as a diode symbol pointing towards the base). And this is just the opposite for the npn transistor, its base is the anode of the junction diode and its emitter is the cathode, this latter going to the supply negative rail.

Now the supply voltage appearing across the rails, it "finds" two diodes in series: the positive supply voltage can start to drive current into the pnp transistor's emitter-base diode, biasing it in the forward direction and this current can continue to the base-emitter of the npn transistor via the resistor and the switch, the base current is defined by the 1 kOhm resistor only: base current=[12V-(2*0.65V)]/1 kOhm=10.7 mA whenever the reed switch is ON. (the 0.65V is the base-emitter bias voltages) I edited your schematic to show the base-emitter 'diodes' by the red arrows and the path of the base currents (via the resistor and the switch of course).

Gyula

[mariuscivic]

Made some measurments to my toy; it's oscilating from 0.9 to 1.1 mA at full rpm. Also made another rotor more balanced and with no holes to reduce the air drag