Who needs chemistry when a little bit of physics will do? Instead of brewing up a batch of weak adhesive to make his own post-it notes, [Valentin] built this handheld device to add an electrostatic charge to bits of paper. Just give them a couple of seconds to charge and they’ll stick to the wall with ease.
The charging circuit is pretty simple, involving a transformer, transistor, resistor, and four diodes for rectification. He walks us through the build process, free forming the circuit using the transformer housing as a base. Once the circuit is fully assembled, a 9 volt battery connector is added and the fragile parts are hot-glued in place. It boosts the output voltage all the way up to 2 kV, but it’s still safe because it’s at a very low current.
The concept is akin to the high-voltage bulletin board seen last month. We wonder how long the notes will stay in place without an active electrical connection to keep the charge?
Don’t taze me bro!
Interesting. But where’s normal schematic? It’s hard to figure out from such photos, but is it just flyback converter made from the simpliest form blocking oscillator?
I actually made one of these (portable high voltage supply, different design though) for the sake of an argument. To prove that car tires conduct electricity :P
Anyway, you can make a piece of paper stick to a wall for about half an hour if the air is fairly dry (30% rH), the scale is probably logarithmic for different levels of humidity, so this could possibly work for hours in extremely dry air.
It may also work better with different types of paper.
They mainly conduct because of the black pigment being used, more commonly a carbon based pigment, which is a weak conductor
they are conductive for a reason though, early tires where not conductive, which led to massive amounts of static charges in larger transportation vehicles, I also believe it lead to fires in fuel tankers. Initially they would use a wire that just scraped the ground, but them tires were purposely designed to get rid of the static charge.
“it’s still safe because it’s at a very low current”
I hate reading that over and over, ohm’s law is still applicable for high voltage. It is not low current, but low energy : it is high voltage with high current and very short time.
Anyway, nice hack, and the step by step tutorial is brilliant, clear, accessible for anyone and uses very common parts.
“ohm’s law is still applicable for high voltage. … it is high voltage with high current and very short time.”
No, a bit different. Such supplies have significant equivalent internal resistance, and when we attempt to load them on a low-resistance load, output voltage drops immediately. So no HV output on (relatively) low resistance loads such as human body, that’s why it’s almost safe. But anyway, don’t use it on yourself or anyone else, respect your safety.
Indeed YS is right! Attached load -> voltage drop
Yeah… that’s true and great. But still…
“The detractors who attempt to answer this question invariably end up quoting figures for levels of current which kill then stating that a battery cannot generate these levels of current. This basically just dodges the issue since we have a fairly specific set of circumstances and it is not claimed that the current actually kills, rather the effect of a DC potential connected directly to the nervous system.”
While it is true that this device could not kill anyone under normal circumstances, find me a large electrolytic that’s rated for 2.5kV, and let me run that 9V dead to charge it up… You get the picture?
High voltage, low current; high current, low voltage, the “perfectly insulated” power system… They could all be considered safe in general, but NASTY deadly with the right conditions…
Looks like 230V RMS to me not 2KV… Even with some sort of self resonance in the transformer the turn ratio gives the voltage increase. I don’t see how the input really is charge pump though it clearly is astable. Basically he says 2KV with nothing to back it up in the actual text as far as I can tell.
If the input was a sine wave i would agree with you, however since the input is a square wave the output will be much higher.
A “perfect” square wave and an ideal transformer would generate an infinitely high voltage, however inductances and capacitances in the transformer prevent this, it will however be much higher than the number of turns suggest.
The ratio of the inductance between the two coils is what steps up or down the voltage. Not the freq it is used at… Unless one side of the coil becomes much more inductive relative to the other at high frequencies, what you say isn’t so. The only other option would be a resonance between a capacitance and primary side inductor, if Q of that is maybe 10 then perhaps it is ~90 V on the primary and 2 KV on the secondary. Still such pages should document how/why and measure such a potential rather than just claiming it without support of any kind.
Have a look at the construction of a boost converter, it uses basically only a single coil, transistor and a diode to boost the voltage.
This acts the same way except it uses a secondary coil with even more turns, making the output voltage even higher.
There is no problem what so ever to get a few kV out of a setup like this.
That said you can think of this circuit as a flyback converter if desired, but that isn’t so much a freq dependence more like a switching/pumping of a capacitance on the output if rectified.
Does anyone see how to incorporate this into an automated book scanning project? Would neighboring pages just stick together?
You risk that, yes. Better is a suction arm pulling the pages up and and little blower from the side(s) to separate sticking pages
Nice-to-know about the Graetz-rectifier at the transformer output:
if you don’t have the required 4kV diodes at hand, you can safely use a series-connection of 1N4007 diodes. No need for voltage balancing resistors at these power levels.
Hard to believe there isn’t a commercial product to do this.
Just think how often you say to yourself “Gee, if only I could electrostatically stick this scrape of paper on the wall for a few minutes, life would be just peachy”?
One of the other uses of the Zerostat, Sold for destaticing a LP before and after brush cleaning them. It can post or remove.
Reminds me of rubbing a baloon on my hair and sticking it to the wall, this would make it so much easier.
Just got home from christmas celebrations and tried my portable HV supply, at 19C 30% Rh a paper will stay on a wall for just over 30 minutes.