accidental creation of AC power using a 9 volt Battery?!

[t_ryner]

 I was messing around with a few large coils used in CRT Tvs, and was getting brief (tiny) arcs when brushing it against the wire in a incomplete connection. In the past, I did this with a transformer from a 12v power supply. I must have been touching the connections, as I received a mighty tingling sensation caused by ac voltage  . Calculations estimate that shock to be around 90 volts (1:10 ratio transformer). Since  DC voltage doesn't tend to pass through transformers. Has anyone else had a similar experience?

[amyk]

You are causing a change in current, and thus magnetic field, which is how AC power can be coupled through a transformer. That's also how inverters and DC-DC converters work.

[Ian.M]

Yes.  Inductive kickback is a common source of high voltage transients in DC circuits.  Its been known about for 180 years. See https://en.wikipedia.org/wiki/Induction_coil

[Brumby]

You might find that the actual voltage you felt was a bit higher than 90V..... but it would only have been a single pulse for each disconnect of the battery.

This phenomenon has been used in the ignition systems of petrol powered motor vehicles for more than a century.

[james_s]

You've created a manually operated boost converter. I remember discovering the same thing when I was about 10 and decided to play with a transformer and a 6V lantern battery, it was quite a shocking experience.

[macboy]

You've created a manually operated boost converter. I remember discovering the same thing when I was about 10 and decided to play with a transformer and a 6V lantern battery, it was quite a shocking experience.

When I was 12 or 13 we did a unit on electronics in "industrial arts" class in school. I connected the DC power supply through the NC side of a relay then through the coil. So as the coil energized, the relay would turn itself off, then on, off, etc. I connected a couple wires across the coil and dared my classmates to hold one in each hand. A couple of them took turns seeing who could hold on the longest. I didn't take a turn. It looked very painful, and according to them, it was. 

[IanB]

I was messing around with a few large coils used in CRT Tvs, and was getting brief (tiny) arcs when brushing it against the wire in a incomplete connection. In the past, I did this with a transformer from a 12v power supply. I must have been touching the connections, as I received a mighty tingling sensation caused by ac voltage  . Calculations estimate that shock to be around 90 volts (1:10 ratio transformer). Since  DC voltage doesn't tend to pass through transformers. Has anyone else had a similar experience?

For more information, see here: https://en.wikipedia.org/wiki/Induction_coil

[Cyberdragon]

You've created a manually operated boost converter. I remember discovering the same thing when I was about 10 and decided to play with a transformer and a 6V lantern battery, it was quite a shocking experience.

When I was 12 or 13 we did a unit on electronics in "industrial arts" class in school. I connected the DC power supply through the NC side of a relay then through the coil. So as the coil energized, the relay would turn itself off, then on, off, etc. I connected a couple wires across the coil and dared my classmates to hold one in each hand. A couple of them took turns seeing who could hold on the longest. I didn't take a turn. It looked very painful, and according to them, it was. 

Did that with three relays (one dpdt, two power) for 2-phase from a bench supply. Except I didn't put any suppressor/snubber on the primary and it fed AC backwards into the psu making it go nuts. It survived, but probably wouldn't have much longer. Oops...

[james_s]

After my discovery, I remember messing around with schoolmates and getting them to hold the wires out of the transformer. "Come on guys, it's only a battery, it can't hurt you!" These days I'd probably be expelled and go to jail.

[Ian.M]

Heh.  It didn't take me long to realise that a lamp flasher module (complimentry BJT astable) could drive the coil, and for some reason, the frequency was drastically increased.  I know now that it was due to the back-EMF.   Some experimentation to find a transistor that could stand up to the voltage spikes, and heatsink it, and I had something that could drive most small transformer secondaries from a supply between 6V and 12V and sustain a continuous discharge from the former primary.   T then got into Cockcroft-Walton voltage multipliers . . . . . .

I packaged the whole circuit up with a 9V battery in a lantern battery shell and took it to school.  Oddly enough charged HV capacitors (small enough to be reasonably safe) didn't make the teachers very fond of me once they'd made the mistake of confiscating what I was fiddling with and getting a 'bite' off them.
However the Physics master and the rest of the science department were vastly amused, and my detention was IIRC a lecture on practical electrical safety, followed by the return of the offending device with strict instructions not to bring it to school again without written permission from the Physics master, or he wouldn't be so lenient the next time.

[CatalinaWOW]

Now you know how those prank books that shock you when you open them work.  Exactly the same idea.

[rrinker]

 LOL my best friend made something of the sort to keep his (younger) sisters out of his work room in the basement. Made one of those shockers that uses the BEMF from a relay wired as a buzzer, and then controlled it with a 4 button capacitive touch combination lock circuit from one of the big circuit annuals I had. Hit the right combination and you could freely open the door. Put in the wrong combination and you got a nice zap if you tried touching the door knob.
                     

[Kilrah]

A friend of mine used to make use of disposable digital(WTF?) camera flashes on people.

I was more of a "make a show" type than "hurt for fun", so I'd rather short them on random metal objects with a loud BANG surprising everyone.

[t_ryner]

  I guess arcs aren't a good word to describe them. The 90 volts were only resulting from passing a pulse through a transformer. I'll try to get measurement for the voltage. Speaking of flyback transformers, passing 12v through one of the coils in the flyback resulted in a 1cm spark (eventually). 

[Brumby]

A friend of mine used to make use of disposable digital camera flashes on people.

I was more of a "make a show" type than "hurt for fun", so I'd rather short them on random metal objects with a loud BANG surprising everyone.

I've got a couple of hundred of those boards in a box around here somewhere....   

[Red Squirrel]

I remember playing around with a 17v AC adapter once as a kid.  Discharging a capacitor through the low voltage end could give you a nice shock on the prong end. 

[Brumby]

A friend of mine used to make use of disposable digital camera flashes on people.

I was more of a "make a show" type than "hurt for fun", so I'd rather short them on random metal objects with a loud BANG surprising everyone.

I've got a couple of hundred of those boards in a box around here somewhere....   

Found it.  The boards themselves were neatly laid out on sheets of paper - but the box fell.



This seems to have all the same design board.  I know I collected whatever was available and found there were 3 or 4 different boards.

I must have some more somewhere......


Some interesting caps....

[Brumby]

Any project suggestions?

[Kilrah]

Wow, how the heck did you end up collecting that many! 

Parallel all their supplies and outputs to common buses? 

Series-wiring them (with batteries then of course) might end up problematic after a number too small to use up much of the bin...

[Brumby]

Asking a few photo processing places to hang on to them for me ... and then going back to collect periodically.  Some of them refused because they have had other requests to hang on to stuff - like empty film cannisters - but people never came back for them.  Since I was true to my word, those who said 'yes' continued to save them and I continued to collect.

A few years ago, I traded about 1,000 of them for merchandise from Oatley Electronics.  I still have this box - and I think I have another stash somewhere.  Possibly another 1,000 all up.

[Kilrah]

Interesting. I had always thought they were being reused.

[Brumby]

Obviously not with the places I scored from.

There was a bonus, too .... the battery used was an alkaline AA.  After 24 flashes, they still had some life in them.  Didn't buy any AAs for a couple of years... 

Even now, I'm looking at a few 120uF 330V photo flash capacitors that could still be good.

[rrinker]

 Reminds me of the later Polaroid cameras - the kind that you just watched the photo develop, not teh old ones where you waited and then peeled the picture off the backer. The film cartridges for those used a flat pack 6V battery that had PLENTY of life left in it after the film was used, I used to snag up as many of those as I could. After a while they went with a smaller battery - same size cardboard carrier to the same dimensions as the film, but the bulge int he middle where the cells were was smaller - even THOSE had decent life left after the film was used. Everyone was gunning for the empties though - there as an article by Forrest Mims in Popular Electronics about how useful this battery was because of the cost and the form factor

[Kilrah]

I've used the Polaroid batteries too!

Not so much the AAs from disposable cams though - for those I had another very prolific source, namely occasionally working for a theatre that used a lot of wireless microphones - and rule #1 in that world is you change the batteries for every performance even if they're normally still 80% full becasue you never know who might have left their mic powered for who knows how many hours either before or after the show.

[james_s]

Ah yes, the PolaPulse batteries, I remember those. They could deliver very high current due to the flat construction with high surface area. Plenty of energy left in them in most cases after the film was expended.