STEORN DEMO LIVE & STREAM in Dublin, December 15th, 10 AM

[k4zep]

Hi Ben,
could you please put a graetz bridge rectifier bridge across your toroidal coil and charge up a big cap with it during the motor runs ?
Would like to see the produced voltage and the cap uF capacity.
Many thanks.
Regards, Stefan.

Hi Stefan,

Its not quite that simple, IF I simply put a Graets Bridge (FWBR) across the coil, I will also be switching the power supply into the cap along with any other induced/produced voltages. You would end up with the Cap charged to PS voltage minus diode voltage drop, but then the voltage would slowly integrate up from that value from any other transients/spikes that was there. I would have to put a SS switch/gate to disconnect the FWBR while the coil was powered if I wanted to see actual output without the power supply reflected in the picture!!  Timing gets to be tricky when you do that.....On before off, off before on, and on and on.....Remember the amount of power in the inductive kickback pulse (Low inductance, hence no current or power) and the 60mV pp of the back EMF is insignificant.  Also, that kickback is already integrated into the coil via the diode across the coil. 

Oh, hand drawn schematic of driver attached.  IF anyone feels free to make it "pretty" go ahead, I don't have time.  Oh, forgot to label the top line.  It is 5 to 25VDC, with heat sink, can handle most anything.  Love that IRF1405. It doesn't even get warm as used.

Respectfully
Ben

[interestedinou]

Hi Gang,

Photos of waveform on 12.4 VDC battery supply

First photo JPGxx415:

Bottom trace is voltage across coil, top trace is total system current in .1 ohm resistor.  Hence 12+ V pulse across coil and .8 amps current in coil give or take.   Average power determined by duty cycle of pulse.

Bottom voltage trace is @ 5VDC/div and top current is .5 amp div. inverted trace.  So down is current flow. Remember this is NOT precision measurement!!!!  Note short coil charge up time due to a small amount of inductance not trimmed out in coil.  Also note the integrated voltage at the trailing end of the voltage pulse @ turn off due to diode across coil.

xx416.JPG Below:

Second picture shows same but bottom traceis 20V/div now to show 50v pp giver or take, back emf pulse at turn off with diode across coil removed,  Very fast ringing pulse @ cutoff  but does not show up in current as the diode across coil keeps it in the coil.  Just the current back feeding into diode and circulating around coil.  As you can see, virtually no energy in back emf.  That is the long and short of it.  I could show the current in the coil by putting the .1 ohm resistor in series with diode but haven't bothered.

That's it.

Respectfully
Ben

Your voltage scope trace makes me think that voltage/current does flow backwards when the circuit is opened.

[lumen]

k4zep,

If you want to fuss, go in set down with your wife (bettery half)  and try to have a conversation about FREE ENERGY!!!!!

Yes, I do understand this exactly...... tried that ONCE!
I like your hand drawn circuit! very simple.

[hartiberlin]

Hi Ben,
many thanks for the circuit diagram.

Could you remove the diode across L1 and instead use a graetz bridge
rectifier across L1 and use your boost cap at the output of the graetz bridge ?

Will be interesting to see, how fast this boost-ultracap will charge up.

Probably pretty fast.

Many thanks.

Regards, Stefan.

[k4zep]

Current actually flows from the negative but that is something for another point.

In your case, If you have one side of a coil connected to ground or negative, then you connect the other end to positive for a short pulse, the instant the connection is broken.
The end of the coil, that was positive will (fly back) toward ground but will surpass the ground point and move even more negative to a point that can damage electrical components.
This is exactly why a diode is usually placed across the coil to short this spike and prevent damage to components.
This is what they mean when the say recover the fly back in a way that can be used to recharge the battery.

I cannot understand why anyone would think the current continues to flow forward.
It may be something above me and I just don't see how at this time, but I'm always open to another view.

You are absolutely correct.  The problem is there are resistive losses in the core/windings and diode voltage drop and reversed fields fighting each other with resultant energy used so you can NEVER recover enough back EMF to make it OU. You can make a circuit more efficient if there is a HIGH level of backEMF but it is a no win situation.   

In my circuit, coil is tied to POSITIVE and pulled low, so when FET turns off, that points goes VERY high or higher than the positive rail, .7 VDC later as it rises, the diode turns on/conducts and it then becomes a current supplying device to the coil or external cap or battery if so wired.......