Shorting the gen coil with PWM? .. and other things.

[AlvaroHN]

Thank you RS I will try to join that forum.
I looked the google site of the coil shorting when you post it the other day, I learned that I need to use 2 transistors/FETS to shot the coil /because of the positive and negative sine wave.

[RS_]

it takes 2 mosfets to short the coil on ether pos or neg peak, and use a diffrent set of mosfets for pos and neg peaks..... study my coil shorting SCH........ and make one for the pos and one for the neg peak with a trigger timer pulser for each
like shown here
https://sites.google.com/site/altern...coils-circuits

[RS_]

you know, after thinking about it a bit, it may only take one set of mosfets to short eather pos or neg peaks.... but a different front end on the timer circuit to see the neg going zero crossing, as well as the pos going zero crossing to short both peaks using the same timer circuit and set of mosfets.

When i was doing this, the magnets on the rotor were all north out, and i only shorted the north peak......

[AlvaroHN]

RS_ I want to do the same but simpler (for now), but don't want to use a pickup coil or HALL or anything to sense the peek of the waves, I just want to short multipletimes but not only in the peeks, I want to short the gen coil also in the medium between the peeks and 0. I am attaching a picture that just made to show what I want to do.

[RS_]

because their is not much voltage built up in the coil from zero crossing to about 3/4 of the way up to the peak, and if any current flows during this time, it will create drag on the rotor/prime mover, wait till just after TDC, and there is no drag

if you build a coil shorting circuit like i show, and use your reed switch to trigger it at the peak, it is the same as using a hall sw to trigger that coil shorting circuit.......

use 2 reed switches setup to trigger on pos and neg peaks

and if you want to test shorting all through the wave form, than 1 555 timer circuit can trigger my coil shorting circuit as many times during the full wave form as you adjust it to......

[AlvaroHN]

Ok RS I will see what I do, ur circuit scares me a little (to many components), why mosfets and no transistors? I thought that transistors switched on/off harder.

[RS_]

the TI LM555 micro power timer..... very nice 555 circuit with a very low power consumption compaired to the older models or other brands of LM555 timers, good for many kinds of projects..............
http://www.ti.com/lit/ds/symlink/lm555.pdf

Use circuit 4 "independent variable timing for both portions of the output cycle" ie: a fully adjustable PWM
http://home.cogeco.ca/~rpaisley4/LM555.html

[RS_]

for this application mosfet's work better

[AlvaroHN]

THANK YOU!!! that was what I was looking for, a simple pwm adjustable circuit using 555. Question: what values of pots resistences and cap should I use? since the diagrams don't have values, sorry to be suck a pain in the a..

[RS_]

use 50k to 100K pots, with a 1K resistor in series with each. Start with a 0.1uF cap, and try 1.0uF, 0.01uF and 0.001uF to see what happens on your scope. On the output, put a 470ohm resistor from the pos rail to the not flat side of a LED lead, then hook the flat side lead of the led to the output pin #3, then another led's non flat side lead to pin #3, then the flat side lead to a 470ohm resistor, and that resistor to the gnd rail.... the led's will flash on and off alternately at the speed and duty cycle that the R1, R2 and C values are set to........ some times it helps to have a 5K pot in series with each of the other pots, for fine tuning.....

Carlos, the 13y old local boy, just build this same 555 timer circuit on a bread board a few days ago, and when he watched the LED's and watched it on a scope to see what it was doing as he changed things, he was grinning ear to ear.......


ps... you can also use a 50K to100K pot, with a 1K resistor in series with it, in place of R1

[Bradley Malone]

Has anyone tried the coil shorting on a transformer. I am just thinking if there is no current used until the peak then short it would it do the same thing as is not use current to set up the field then short to create a back pulse that will help the current in the primary on the downside of the peak. From my understanding if you hook up a transformer with open secondary then the only current used is because of the resistance of the coil (wich is not much) therefore it sounds like it may perform the same taking very littole current to set up the voltage then connect and use it???

[RS_]

i think in theory that works too.... your paying for a small AC current on a low voltage primary to make the voltage peak on a high voltage secondary, that you only short on the peak, so no current flows during the ramp up to peak, and the fall down from peak, and you harvest the ringing into a cap......

[Faraday88]

for this application mosfet's work better

I remember, Aviso Ismeal got special High-Power MOSFETS/IGBT designed for his Coil shorting experiments...

[Bradley Malone]

I cant remember where but i saw a video of someone talking about shorting and they said it had to be a short of less than .005 ohms or something similar. he stated that it would take like 8-10 mosfets in paralel to short the coil with such little resistance because of the internal resistance. even if its .2 ohms its still to much. I have been looking an only ever see two or four mosfets 20 for one peak two for another....but this guy said 8 for one side. or are the mosfets people are using below .005 ohms?

[AlvaroHN]

use 50k to 100K pots, with a 1K resistor in series with each. Start with a 0.1uF cap, and try 1.0uF, 0.01uF and 0.001uF to see what happens on your scope. On the output, put a 470ohm resistor from the pos rail to the not flat side of a LED lead, then hook the flat side lead of the led to the output pin #3, then another led's non flat side lead to pin #3, then the flat side lead to a 470ohm resistor, and that resistor to the gnd rail.... the led's will flash on and off alternately at the speed and duty cycle that the R1, R2 and C values are set to........ some times it helps to have a 5K pot in series with each of the other pots, for fine tuning.....

Carlos, the 13y old local boy, just build this same 555 timer circuit on a bread board a few days ago, and when he watched the LED's and watched it on a scope to see what it was doing as he changed things, he was grinning ear to ear.......


ps... you can also use a 50K to100K pot, with a 1K resistor in series with it, in place of R1

Thank you RS_, the other day I put together a 555 circuit from the link you gave me. thank you!, I made it changing resistors and caps manually because I didn't have any potentiometer in hand.
But Yesterday I went to my parents’ house and found 2 old radios, and inside I took the volume potentiometers, and also, those variable capacitors that are used to tune am and fm.

So maybe using those variable capacitors I can change frequency in my 555 timer. I read on internet that are low capacitance, but also read that those variable caps from radios are 4 in one case, so maybe I can put all 4 in parallel to get higher capacitance?, I also have 2 of them so maybe all 2 in parallel.

I am still waiting for a little scope that I ordered from china to see the frequency at high speeds.

Does anybody knows the frequency limit of a 555? and eventually 555 --->opto--->2n2222 ??? can I switch in Mhz with that???