Back EMF demonstration (and a peek at a coilgun)

Picture is worth 1000 words, as they say:

So, going counter clockwise from the blue lit power supply: it is producing 7 volts, shown on the gauge at top. the relay at left takes that 7V- the minimum to energize it, and mechanically oscillates on and off very rapidly due to how it is wired. The schottky diodes, wired reverse to the input polarity, deliver the Back EMF spike power to the bottom power rail of the breadboard, where it charges a 630v capacitor. A meter on that capacitor, shows its level of charge.

48 volts! So 7v in, 48 out.

Here's the wiring 'under the hood' of the car relay. The white marked wires are the Back EMF, the unmarked are the power and grnd leads. Notice that the power in doesnt go right to the coil, but to the Common contactor tap. The + side of the coil is jumpered to the NC contact.. meaning that the relay is energized as long as its OFF... see the trick? on then off then on then off then on then off... as fast as this little relay contactor can physically switch.. whicih turns out to be pretty darn fast. The Schottky diodes are wired in reverse, because the back EMF pulse is reversed polarity as well.. we dont want the power supply to add its power to the meter at the end! The giant diodes were 100v schottky ones.. because I didnt know how high voltage the EMF was going to be, and schottky diodes drop less voltage across them than normal diodes do. (.2 instead of .7 V drop)

 

This just amazes me. Why don't we use this power?! 7 piddly volts- less than a full amp of supply out of that little hobby power supply chip, and 50 volts pouring into the capacitor!! Sure its pulses, but even the way I've set it up in the video is so rapidly pulsing it might as well be steady.

This gets me thinking! See, I was building a mini coilgun that would shoot paperclip clippings, and it shoots pretty well with a 9volt powering it. but after some failed experiments to build a 555 chip voltage double to try to boost the power, THIS idea came along!

In fact, while this video is uploading, I'm going to go kitbash it right now!

Hmm didn't work for some reason. Maybe he 650v capacitor didn't have enough power capacity to fully energize the gun barrel coil I set up. Or something. bummer. Good news though: it DOES make an effective voltage tripler!! Those giant 10v 4700 Caps I tried to make my first symet out of were the original battery bank for the coilgun, Arranged in a neat circular frame that the coilgun could be suspended in the middle of in a sort of "raygun" configuration that I liked.

See? Isn't that awesome looking?! I don't bother making something unless it makes the inner child in me giggle with joy a bit.

 Together their capacity was 14100uf.. which.. I don't know, may equal 1.41 Full Farad. But in my initial build, all I could pump into those Capacitors was the maximum voltage my little hobby power supply could provide: 10V. this was the upper limit of the pulse I could send through the coilgun... meaning the 1.4" clip of paperclip only shot about 3 feet straight up.. pretty good for no moving parts and all, but not really a GUN. My goal for this coilgun is to have it punch a hole in a piece of paper in front of it... here's hoping!

Oh (lost track) so anyway, this Back EMF rig I have didn't work as a power bank, so, I tried it on my coilgun power bank seen here, to see if the EMF pulses could pump higher voltages into them. It DID. Sure the buildup was slow, so I guess the EMF spikes were infinitesimal (high voltage)spikes, but nevertheless, the volt gauge I had clipped onto them showed the charge rising, and rising, and rising, the meter slowing down its charge around 23V (remember the starting voltage was 7). I didn't have the patience to let it climb up to 50, to see if it could actually reach that charge, and anyway, the caps were only 10v, so if I pushed them too far, they go POOF- so I've heard.

 

So, if I can start with 7v and end up with 25v+ in a capacitor bank, then the back EMF rig is something I have a real use for; a way to double, triple, even septuple voltage, without any complicated electronics nor timing circuits.. nor reall any other parts at all! And thats cool enough to keep.