# Simple High Voltage Flyback inverter [without feedback coil]

Intro
In this instructable I will guide you trough all the things you need to do to get your flyback transformer working. I hope everything is explained in the instructable, but if there is anything you don't understand, you can ask it here. It's a very simple project with very few components, and it's a lot of fun to make!

A flyback transformer is a transformer with a low number of primary windings, and a high number of secondary windings. The inductance of a flyback's primary coil (this is the resistance of that coil) is really low when working at low frequencies.
When a voltage is applied to that low resistance coil, it will draw a lot of current. To lower that current, the resistance of the coil needs to become higher. We can do that by using a higher frequency. Xl = 2.π.f.L Where Xl is the resistance of the coil, and f is the frequency. (L is the inductance of the coil, which is constant).
This high frequency will be provided by our transistor. It will switch the coil on, at a frequency around 30kHz. We have now limited the current, but it still isn't perfect, so the transistor will get very hot.
That's why it needs to be cooled with a heat-sink. We will also use a MOSFET (Metal Oxide Screen Field Effect Transistor) because it can switch high currents, and is almost indestructible (it can handle high currents, up to 10A, 30A peak).
The core of the flyback transformer is made out of Ferrite, because ferrite works a lot better then iron when working with high frequencies.

Warning: High Voltage!
This guide is meant for people who have experience with high voltage. I gave a lot of safety instructions in all steps, so that people know what can be dangerous and what is safe. Please read my instructions about safety on every step, it's important. I am not responsible for any accidents.
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Has anybody taken into account the enormous inductive kick (AKA the flyback pulse) that occurs every time the MOSFET switches off? It is this voltage spike that gives the flyback its name. The inductance of the secondary winding, together with its self capacitance forms an underdamped LC circuit that resonates at a specific frequency. When the MOSFET switches on, the inrush DC current through the primary winding is limited by inductance. This current ramps up to the point at which the ferrite core magnetically saturates and that electric energy is converted to potential energy stored in the magnetic field surrounding the ferrite core. Because this magnetizing current is opposed by inductance, the magnetic lines of force cutting the secondary winding increase relative slowly after the MOSFET switches on, limiting the voltage output from the secondary to a fraction of its peak value. After the core saturates, no more energy can be stored in the magnetic field and the inductance of the primary winding vanishes. The MOSFET current is now limited only by its internal resistance (<0.1 ohm) in series with the resistance of the primary winding (again <0.1 ohm) at 12 volts, the MOSFET is passing 12volts / <0.2 ohms or >60 amperes! Of course, this will load a wall wart down to almost zero volts, but a beefier supply such as a car battery will happily supply that current, heating the MOSFET to the point of failure in short order. Adding an ohm or two of ballast resistance between the source terminal and ground will eliminate this overcurrent situation and protect the MOSFET.

The real action begins the moment the MOSFET switches off. At that instant, the device impedance transitions from a few milliohms to an open circuit in just a few microseconds. With no current flowing through the primary, the magnetic field surrounding the ferrite core collapses like a steel bear trap, dumping a large pulse of stored energy into the core. The energy stored in the field couples back into the core, magnetizing it rapidly in the opposite direction and inducing very high voltages of reversed polarity in both the primary and secondary windings. In a no-load condition, such as when the flyback secondary isn't connected to a load, the self-resonance of the secondary winding causes the flyback to ring like a bell at its self- resonant frequency. This happens when the impulse energy couples from the magnetic field if the flyback's inductance into the electric field of it's self capacitance. This current flows back and forth tens of thousands of times per second, losing a little energy on each pass because of the coil's resistance until all of the energy is lost as heat in the coil or in the load connected across the secondary winding. This is how the flyback transformer generates extremely high voltage, high frequency AC.

This is also how under rated transistors can quickly fail in these oscillator circuits. Remember, at the moment the magnetic field collapses, very high voltages are induced into both the secondary windings. These voltages can peak at 5-10 times the voltage switched by the MOSFET during the forward conduction phase and they do so in both directions. Most MOSFETS have reverse-biased diodes called free wheeling diodes connected across the source and drain within the case. These serve to divert the reverse current spikes around the device and protect it from destructive reverse current. The diode can do nothing to protect the FET however on the succeeding half-cycles of the ringing waveform. If the device isn't rated for the high kickback voltage, it will fail in short order. There are several ways to prevent this short of installing an 800 volt MOSFET. The easiest is to shunt the device with a zener diode with a knee at 2-3 times the supply voltage, but less than the MOSFET's breakdown voltage. You can also clamp the reverse energy by wrapping a few turns of 18 gauge wire around the ferrite core and inserting a reversed diode (called a damper or flyback diode) across the winding. The diode should be a fast recovery type (<100 ns). This method has two advantages. First, the diode conducts, shorting the winding acts only during the reverse portion of the ringing, thereby storing energy in the winding's own magnetic field, swamping out the high reverse voltage across the FET. Secondly, during the following forward half-cycle, the damper diode conducts, dumping the stored energy of the winding back into the core. This energy shows up at the output of the secondary, boosting the efficiency of the flyback circuit.

So, I suggest two modifications to this circuit, Source resistance at the MOSFET and a reverseddamper diode across a third winding.

1 month ago

Great comment. Would it be possible for you to create a modified schematic with your suggested improvements?

Kutluhan4 months ago

Hey people this instructable is ONLY for black wired flybacks. Red wired ones not work with this circuit. And this circuitry melts flybacks coat very much. So keep that in mind. :) It's simple but not cheap you can kill your flyback well. I want you to know this so sorry if this comment wasn't nice.

I can get pretty purple sparks if I connect this circuit intermittently, but if I hook it up straight the mosfet will get really hot and stop working (I'm on my 5th one on a large heatsink). I'm using an 18.5V 2.7A transformer with a IRF640A mosfet and the recommended resistors (I was using the same mosfet as you which worked even better but eventually burned out too). Is there any way to shield the mosfet maybe with bigger resistors (or a choke ??) or something? I also only measure about 1v through the HV0 (using 18.5V) could that be part of my problem? Thanks for any advice; it is an interesting project.
What do you mean with the HV0 ?
do you mean the voltage over the primary coil?

I have no idea why it gets so hot :/ Is your heat-sink large enough?
2 years ago
When I am trying to locate the secondary coil with the volt meter I put in 18.5 and only get out about 1v from the one little pin on the bottom of the flyback transformer, no response from the others. If I put in 12v I can't get any reading. 32v in will give me about 13v out but I don't want to use that much since 32v is beyond the mosfet rating. The flyback transformer also makes clicking noses sometimes.

My heatsink is about 8in by 4in and seems pretty big; it had 5 separate mosfets/ transistors on it originally.
Ok... That's weird. Are you sure the schematic is correct?
2 years ago
I'm pretty sure it is correct; I took it apart and reassembled it a few times now. It is partially working but just over heats when it is continuously hooked up. I am using alligator clips so it is a bit of a mess but I don't think I have any shorts. Do the Amps matter on the input transformer? Also does your flyback transformer make clicks/screeches?
My flyback transformer doesn't make clicks now because I'm using my new flyback driver.
I must admit that driver you're creating now isn't the best thing you can do.
It should work though.

The amps of the input transformer won't do anything bad.
If it's too low, you'll get tiny sparks,
if it's too normal, you'll get normal sparks
if it's too high, you'll still get normal sparks. It's not a problem.
6 months ago

Well, if it is too high, (as in 10A RMS or greater) you will have overheating problems that can melt the flyback.

Electorials (author)  Electorials2 years ago
Have you also tried with another flyback?
2 years ago
I have not tried with a different flyback, I will the next time I come across one. Do you have a different circuit suggestion that is more reliable?
Not really, except for this one: http://www.instructables.com/id/The-ultimate-PWM-driver-for-many-applications/
But that's something totally different and a lot more complex.
2 years ago
Ok, thanks for the time and info. I appreciate the quick responses. I did get quite a bit of entertainment out of this with just an old monitor, I will probably try a different flyback or circuit when I can. I also picked up a breadboard today so maybe that will help.
No problem. If there's any information you need, just ask it ;)
6 months ago

If you get it to oscillate, you can bring the output to the different pins to see which pin the output tends to arc over to. Also, I like to just touch 12V to other different pins until I see one that causes a spark, indicating an inductive load.

6 months ago

If you have an oscilloscope, check to see if it is oscillating properly. To me, it sounds like the MOSFET is halfway turned ON, so it is dissipating a LOT of power, but since the oscillation is weak or non-existent (you only have an output by interrupting the circuit) you may need to try different value resistors, and change the windings around, or the amount of windings. Try winding a custom primary if you can.

copyjam1 year ago
I couldn't get this circuit to work. I tried it with two different MOSFETs that I had readily available, the IRF510 and the IRFP260. When I connected/disconnected my power supply, I could hear a sharp click coming from the flyback, but there was no HV on the output. The MOSFET became painfully hot in just a matter of seconds.

Any idea what might be happening here?
8 months ago

hi. it's not like you can use any mosfet like the tutorial says. in your case the IRF510 has maximal current between Drain and Sinc (also called: idss) 5.6 A and the inner resistance of it is 0.54 ohm. and that with 12 vdc gives us 23 amps.

THATS WAY OVERPOWERED.

IRLZ34N should do the trick. just put 1ohm resistor on drain, just to be sure if you're using superconductors as wires :D (no really put one there some wires might have lover resistance than you think.)

6 months ago

There are a few other important considerations, however, it is important to know that the MOSFET is not driving a load with zero impedance (similar to resistance, but more general. Impedance includes AC.) It is driving an inductive load. If the figure of 30KHz as the operating frequency is correct, then the inductive reactance (essentially the resistance (or more correctly the impedance) at a certain frequency) will be higher.

Looking at the schematic for the operation of this circuit, it appears that the transistor will never saturate fully anyway. I beleive the output waveform and/or the feedback waveform will be very erratic and contain many harmonics and junk, and since it is amplifying this, it is never fully switched on, so it is truly semiconducting!

Also, the current rating you have given is for steadystate conditions. The peak pulse currents the device can handle go as high as 20A, so as long as it is not left saturated with 20A flowing through it, things should be fine.

With all these simple HV circuits, especially those utilizing MOSFETs, it is important to note that the killers of the MOSFET as overheating of the junction, high voltage transients on the gate (that DESTROY the thin Metal Oxide layer), activation of that parasitic NPN transistor inside all MOSFETs (leads to overheating and catastrophic failure). So, it is important to add at the minimum, a few voltage suppressor devices on the gate so the voltage does not rise higher than the recommended gate voltages in the datasheet. (zener diodes, TVS diodes, MOVs, etc.)

7 months ago

irf3205 might work it can handle 110amps rms

geckomage3 years ago
actually i did a different set-up. i hooked the positive end of the volt meter to the hv. out. the low end of the volt meter to the low end of the power supply, and then used the positive end of the power supply to test around and find it. i found this on another page and it was described there to usually lower the voltage. but generally the secondary coil has a huge amount of resistance (hence why you must use a voltage and power to find it) because otherwise you would need a fancy volt meter to find it. but this resistance goes down when voltage is increased, and the frequency is increased. and most driver circuits run these at 15-25khz ish (correct me if im wrong) and since both the voltage and frequency is increased it lowers the resistance of the secondary coil while in operation. :)
6 months ago

Also all the HV diodes in there have a forward voltage drop, collectively, of amount 15V! Once the voltage exceeds this, the diodes are brought into conduction, and the remainder of the voltage is then has to go though the high impedance coil!

mgingerich2 years ago
For some reason wall jacks always output way more volts than they say they will. I think it's just shoddy manufacturing. It could be that they're designed for a really specific load though
6 months ago

If the reciprocals are outputting ~169.6 volts, that is perfectly normal. You are measuring the peak voltages, not the RMS (Root-Mean Square) voltage. RMS is essentially the average of the absolute value of the AC waveform. It is literally defined as the equivalent voltage/current/power delivered to a resistive load, such as a heater or Edison lamp. Also they are not designed as labratory power supplies, so they are crude in the fact that they have high tolerances.

-max-6 months ago

You should add a few TVS diodes, MOVs, or at least some zener diodes between the gate and drain of the MOSFET, to prevent a high voltage transient from destroying the fragile Metal Oxide Layer between the gate and the rest of the Semiconductor Field Effect Transistor.

msalko8 months ago

I'm not sure but i think there was one type of these transformers that had secondary coil connected to feedback coil. I can only imagine the guys face when he gets 1kv out of nowhere :D

Liam.great981 year ago
(removed by author or community request)
Electorials (author)  Liam.great981 year ago
do you get a spark just at the moment when you connect the power supply to the circuit?
highvoltageguy3 years ago
Electorials (author)  highvoltageguy2 years ago
What's not working?
2 years ago
the whole circuit won't work
geckomage3 years ago
I know this somewhat defeats the purpose of your instructable (which i will try tomorrow and see how well it works :) then post results) but do you know of any good way to detect a feedback coil in a flyback? im thinking of using a 20 volt 2 amp freq generator to make a square wave at around 20 khz and using an osciloscope to find which set of pins gives me the right wave form for the feedback ( i did get some crazy waves comin off of the secondary, but no arcing :[ )
Electorials (author)  geckomage3 years ago
what do you mean with crazy waves? I hope you didn't connect your scope to the secondary, because it can only handle 400V max!

and I don't really know a good way for detecting the feedback. The only real way I know, is to apply an alternating voltage, of which you know that part is working correctly, to the primary windings. (like you said with the functiongenerator), and use a volt-meter to measure the AC feedback voltage. It should be just several volts, 1 to 3 volts I think.
3 years ago
haha no worries. we have a pretty heavy duty oscilloscope aside from the regular ones and have several special probes for it. from bumping up really small voltages to where you can clearly see the waves to taking up to 30 kv and bumping it back down to see the waves without frying the osciloscope ;) (had a bunch of sponsors donate generously to fund the program) got a full electronics lab, the full autodesk, mastercam, and multisim swuites on some powerful computers. a full wood/metal shop with lathes and mig and tig welding machines included. also a large 3 axis cnc mill, a smaller 4 axis one, a smaller 3 axis prototyping one and a cnc plasma cutter. :) ill only have acess to it till the end of next semester though, so if you have anything you'd like me to try to build for a project that you'd like to test let me know ;D we have a circuit board printer too but thats not quite working yet :( and thanks for your speedy replies and advice! :D
Electorials (author)  geckomage3 years ago
aah that's cool

and no problem ;)
geckomage3 years ago
Electorials (author)  geckomage3 years ago
That is indeed a good way for finding it ;)
3 years ago
lol just thought i'd help anyone that needed it :D then you can see fairly easily which way it is (i dont know if you get arcs when you hook it up backwards) but ive always believed in starting with smaller voltages first ;D
geckomage3 years ago
I do not know if anyone had anything similar occur but with this same setup i applied 24 volts to it (as i found on a different instructable) and only got about 12 volts on the HV 0v pin. but none of the other pins showed any voltage. hope this helps someone!
Electorials (author)  geckomage3 years ago
do you mean with the same setup as in the picture here?
It's weird to get only half the voltage.. Really weird actually!
It would mean that the resistance of the coil would be as large as the internal resistance of your volt-meter, which is several mega ohms.
and that would mean your coil is no coil but an insulator.

Could you explain more in detail what you did there?
Umniscient3 years ago
I don't understand what you mean by "the polarity of the primary coil".
Does it mean which side of the primary is connected to the resistor/12 volts and which side is connected to the Drain?

I've tried both directions, and seen no corona discharges at my HV +. The secondary measures at a few millivolts. In fact, I believe my circuit is inputting DC to the primary coil.

Or is my understanding incorrect?
Electorials (author)  Umniscient3 years ago
in step 6 you can see a yellow tag around 'the primary windings'

That winding has 2 connections. Changing the polarity of that coil means reversing both connections.

You try it once with pin1 connected to +12V and pin2 connected to drain, and after that, you try once with pin1 connected to drain and pin2 connected to +12V.

If none of both seem to make high voltage on the secondary windings, you really have a problem :/
Are you sure your setup is the same as in the schematic?

I suggest you try this:
Connect everything
Measure the voltage over the Primary winding
Measure the voltage over the primary winding while Gate is Disconnected

If there is any change, it means your MOSFET is working correctly.

results should be:
Gate connected -> V-meter: 12V
Gate NOT connected -> V-meter: 0V
3 years ago
I did what you said, and it turns out that my MOSFET was broken.

Would this work well instead, or is the current rating too low?

Electorials (author)  Umniscient3 years ago
That mosfet should be fine. I recently used an IRF630, and that one worked great, so if you could also buy that one on radioshack, that's good. But the one from your link should also work fine.

What were te results of the test? You said your mosfet is broken, but are you really sure about that? there might also be another problem...
3 years ago
I first measured the voltage over the primary coil: 12V
Then I measured it when the gate was disconnected: 12V
There was no drop to zero, so I figured there was something wrong with the MOSFET.

After I realized this, I plugged in another random MOSFET and tried it. No HV on the secondary, but a drop from 12 volts to 2 volts when disconnecting the gate. Does this mean the transistor is working? Or does it have to go to 0V?
Electorials (author)  Umniscient3 years ago
Hello,

The 2v might be normal because the gate is connected to nothing.
Try connect the gate to the source (0v) and measure again over the coil. You should now get 0v there instead of 2v
3 years ago
Yes, that was the result.
I went ahead and purchased the IRF510, and I'm going to try it soon. Just a question: is there a minimum voltage required to operate a MOSFET? That is, can I theoretically use any voltage under 12 and still get an output from the inverter circuit?
Electorials (author)  Umniscient3 years ago
The IRF510 needs 4V (= Vgs) at the gate to work properly.

(x2 for voltage divider + some extra) -> you'll need at least 10V

maybe you could use a 9V battery if that's what you meant with "something lower then 12V" but it won't work so really good. The battery will also drain quickly.
3 years ago
All right.
Well, I read the IRF510 datasheets and connected it into my circuit accordingly.
Measurement on the primary: 12V. Disconnected the gate, still 12V.

Now, I'm not sure if the inverter is even outputting AC, because my multimeter shows 12V AUTO. When I manually switch settings to AC, I only get a few millivolts. Does this mean that the recorded 12V is in DC? It would explain the lack of output on my secondary coil.
Electorials (author)  Umniscient3 years ago
Yes, that indeed means you have 12V DC.

When you just connect the circuit, do you get a small spark then? (I mean really tiny, like 0.5mm)
If you don't get that, I think your flyback transformer is broken.

You better test this without the mosfet, just connect 12V straight to the primary coil at a fast frequency.
(I mean connect 12V and inmediately disconnect it, then connect again, and go on like that. This will create a 'fake' AC - alternating - voltage)
Electorials (author)  Electorials3 years ago
oh, and about your mosfet, you don't have to worry about that if might have gone broken. If your wiring is correct, it won't be broken. There's just something else wrong, as I said, probably the transformer.

You also tried with reversing the primary coil right? (it matters since many flyback transformers have a rectifying diode at the secondary coil).
3 years ago
Also, I doubt the transformer itself is broken.
You see, I have a signal generator capable of outputting 5 volts. When I set it to 40 kHz and plug it into the primary, I get about 600 volts on the secondary, with lots of sparks and buzzing noises.
Electorials (author)  Umniscient3 years ago
That's really weird!

When a 5V AC signal creates nice sparks, a 12V (pulsed) DC signal should also creates sparks..

At least we now know that the flyback transformer is working correctly.

I would say that your 12V supply is broken or the power rating is too low but that's also not possible because you said you measure 12V over the primary coil of the flyback :S

oh, and is there a way we could chat somewhere while you're working on your flyback? it would be a lot easier. Because this way it will take years :)
3 years ago
"oh, and is there a way we could chat somewhere while you're working on your flyback"
Sure... do you have a Gmail account?
Electorials (author)  Umniscient3 years ago
no, I have hotmail. Is that ok?
3 years ago
Sorry for my delay!
Yes, it's okay. I have Hotmail as well.
Electorials (author)  Umniscient3 years ago
No problem ;)
I'll speak to you soon then!
3 years ago
Hey, I managed to get it working using a slightly different arrangement with a 2n3055.
Electorials (author)  Umniscient3 years ago
:D nice
Can you post a picture? I'd like to see it :D
3 years ago
Yes, I've tested the primary polarity each time.
3 years ago
I don't get a small spark, but when I repeatedly connect and disconnect the 12V, there is an output of a few volts on the secondary.
njkl443 years ago
Hey thank you again i can finally play with high voltage EASILY!!! what is the voltage output on this thing (volts?)
Electorials (author)  njkl443 years ago
I think mine gives about 5kV
but I'm looking for what I can do to make it even higher.

I'm sure that a higher input voltage will do that, but I'll check my mosfet first, for the maximum ratings, and I'll have to recalculate the resistors.
3 years ago
usually 100,000 volts is feasible not sure how easily tho
3 years ago
100,000 volts is the opposite of feasible. especially for a flyback alone.
were you thinking of a tesla coil?
Electorials (author)  spark light3 years ago
indeed, it's impossible for a flyback to create such a high voltage.
3 years ago
Maybe not alone, but a voltage multiplier on the output side might work.

http://en.wikipedia.org/wiki/Voltage_multiplier
3 years ago
actually it can, you just have to do it right, im not sure how but look it up online you'll see 100kv sparks
3 years ago
at 100,000 volts, the flyback will internally arc, causing a meltdown. i'm 100% sure it's impossible because the ferrite core will be an instant path between the two ends of the coil. even under oil, it is highly likely that it will arc internally. the most i've ever seen is about 70 - 80kv. anyone who claims they've gotten to 100kv is most likely optimistically overestimating.
Jimmy Proton3 years ago
On the third and fourth picture, the insulation is not conducting, it's just making a bunch of corona around it.
Electorials (author)  Jimmy Proton3 years ago
it is conducting, the electrons go trough the insulation.

it's like my bad screwdriver, when I touch it the electricity goes trough the plastic into my hand.
3 years ago
If it was conducting it would burn a hole through the insulation, trust me, I would know :)

I have also done this with a thick ceramic insulator and got the same effects and I know thats not's going conduct.
Electorials (author)  Jimmy Proton3 years ago
I'm still very sure that it Is conducting :)
I asked a teacher at school.
3 years ago
If it was conduction the electricity wouldn't spread out like that, it would be in a "straight" path like all the other photos.
Electorials (author)  Jimmy Proton3 years ago
electricity doesn't follow the shortest path, it follows the easiest path.
Which is now, spreading over the insulation to get a larger surface (less resistance)
3 years ago
Jimmy is right, it would damage the insulation. They are corona discharges. If you connect it backwards (the alligator clip on the HV positive and the HV negative adjacent to the insulation) then you won't see the "electrons discharging" because the corona will be inside the insulation.
Electorials (author)  aesquivel3 years ago
Ok, I re-checked the defenition of corona discharges, and you are correct.
As long as the insulation doesn't break down, it's called a corona discharge.

But I'm also correct that it's "conducting" in one way, because I'm really sure there will be more current flowing when I move towards the insulation, instead of just holding the wire in the air.
slipknot rules3 years ago
Very nice!
RocketPenguin3 years ago
question, is the arc constant or do you have to turn it on and off for it to keep going?
Electorials (author)  RocketPenguin3 years ago
it is a constant arc.
there is one spark every few microseconds (20-50kHz it should be)
so it looks like a continous arc.
3 years ago
Oh, Ok Thanks i might make it! could you give me a link where i could buy the Power MOSFET?

Thanks
Nicola Tesla
Electorials (author)  RocketPenguin3 years ago
I'm sorry, but I have no idea.

Any MOSFET should be ok, just use a regular one.

You don't really need to buy one, you can also find many of them in CRT screens :)
the last screen I took apart, had 4 mosfet's inside.

Good luck.
Kirbsome!3 years ago
I got this to work on my first try!
Thanks for posting a great 'ible.
Electorials (author)  Kirbsome!3 years ago
no problem :)
NPD27053 years ago
I only see the 15+, where's the cathode ????
Electorials (author)  NPD27053 years ago
cathode of what?
3 years ago
the cathode of the battery, there should be a line that connect to the 15-
Electorials (author)  NPD27053 years ago
We take the cathode of the battery as reference, so we call ot 0v or GND.
There is no -15v if there already is a +15v.

What Is possible, is taking the anode as reference, so the anode will be 0v, and then the cathode will be -15v (15v more negative as the anode)

Now the answer to your question is: the GND (0v) at the bottom of the schematic, that's the other side of your battery ;)
3 years ago
thks, a lot :D
Electorials (author)  NPD27053 years ago
No problem ;)
if there's anything else you need to know, just ask it here =)
NPD27053 years ago
hey can you tell me what the HV- is ? Is it the one with the sucken cup ?, and what's the negative side ? is it the plastic cover ? THKS
Electorials (author)  NPD27053 years ago
the positive side (HV+) is the wire that comes out of the top of the transformer, with the sucken cup.

The negative side (HV-) is just one of the pins at the bottom of the transformer.

The plastic cover is no connection, it's just insulation.
cokebottle tuque3 years ago
HV + vacuum = x-ray
3 years ago
Under 25kV x-rays aren't much of a concern.
static3 years ago
In reference to the warning in step 5. I don't know if you are being overly cautious or not. But applying DC to a transformer will not produce high voltage at the secondary. However like the ignition coil on an engine it will produce a impulse if high voltage when the DC is removed from the primary. The voltage that would be produce with this project in that event may be around what delivered to the sparks plugs in a modern car. Hurt enough to say oh crap, but probably no more. When someone believes they found the secondary they test test it further by making a spark gap on the secondary. Then apply DC to the primary, when the DC is removed from the primary. For those who didn't recognize it' in step 3 electorials made a special purpose ohm meter that use a higher voltage than a multi meter generally use to test resistance, insuring there's sufficient voltage to push electrons through the high turns count secondary so one can find the other terminal. Before someone bust me on it; Yes I know this isn't how ohm meters typically work, that's why I used the word specialized. In the end, I only bring it up because, this is good trick for hackers to remember. In the end a very good, well explained instructable, thanks for posting it.
Electorials (author)  static3 years ago
Thanks,

Yes, I'm being overly cautious, I know it won't kill you, but to make sure nothing goes wrong there, I say that it Is dangeroes, because we are indeed generating a high voltage pulse there.

When applying a DC voltage to the primary, we go from 0V to 20V in a few microseconds. That's when the high voltage is 'generated' in the secundary coil. After that short time, we have a constant voltage of 20V so there will be no high voltage generated anymore. When removing the 20V (change from 20V to 0V) we'll create a high voltage pulse again, but with other polarity as the first one.

The pulse will be very short (serveral micro seconds perhaps), so it's impossible to get killed by it.
it will only give a shock and scare you :)

Static: "I don't know if you are being overly cautious or not. But applying DC to a transformer will not produce high voltage at the secondary"

so that's not really true, it Will produce high voltage (you can actually make a spark with it) but as I said, it won't do any harm. it's like getting shocked by a piezo electric ignition of a lighter.
3 years ago
I guess specialized continuity tester would have been a better description than specialized ohm meter
njkl443 years ago
Hey thank you for this project. i am looking forward to doing this because its so simple. Although i wish you could upload some more pictures of the final circuit ( the whole view of it). Its hard to see what going on and a video or more pictures would make this 10x better.

Good Job :)
Electorials (author)  njkl443 years ago
Hello,

I didn't add a picture of the circuit because it was so simple, but as you say, it might be handy for people to see what's going on ;)

I'll add it after I get home (I don't have time now)