High voltage power supply

[t_ryner]

Hello! The other day in my chemistry class, my teacher was teaching us about the properties of electrons using the cathode ray demo. He had some vintage replica cathode ray tubes, which are worth almost $4K!  The cathode ray experiment uses high voltage DC to create a cathode ray from the cathode plate to the anode plate. He created a high voltage by using a hand held teslacoil, and holding it at one end, while moving a magnet along the sides to show how it attracts the charge. In doing so, he repeatedly shocked himself with the charged coil . I know that a hv generator that utilizes a flyback generator could have a good effect, as the corona discharge is visible in air.(I have two from some old CRT tvs). How should I build one? I know that drivers are available on amazon, but I would like to build my own. Also- its there a better way of doing this? Thank You in advance.
-- Tommy Ryner 
solder fumes= electrical perfume

[calexanian]

Generally in those types of setups they used a high voltage transformer. I have one here. It resembles a Neon sign transformer with typically driven by a big Rheostat. Not a variac as I found out. They want the primary resistance. I actually have one around here somewhere. Cenco scientific made most of that stuff. A company I did occasional work for made tubes for Cenco. Hand held tesla coils were also used and ETP still makes them. http://www.electrotechnicproducts.com/products

I would probably use a Neon sign transformer if I were going to play with that stuff today. They are typically impedance limited to not burn things out.

[@rt]

The same ZVS driver usually used behind a flyback transformer is a free design.

[SeanB]

Neon sign transformer is definitely enough to kill you, typical current is 30mA, but the transformer the teacher was using would probably max out at 1uA of current.  I would suggest going onto fleabay and getting a small gas burner ignitor transformer, used in gas appliances and running off a 3V battery, and using that. Still can shock you, but not quite as lethal as the neon transformer.

[james_s]

Sounds like he was using one of those "Oudin coil" type handheld things.

Personally I would just build a driver for a flyback transformer out of an old TV. I have one I made years ago that is nothing more than a mosfet driven by a 555.

[t_ryner]

Yeah. The reason I'm making this is so that he won't get zapped. I was thinking to use some little alligator clamp wires to connect it to the cathode ray tube. I'll Update you guys on this project as I get to it.( I have spring break next week , so probably then) Thank You!

[jimdeane]

The standard power supply used for these is a mechanically interrupted induction coil, very similar to a spark plug ignition with mechanical points.

If you go a little more upscale, a current limited hv DC power supply in the -2kv range with an upper limit of maybe 10mA is what I've used with larger plasma demos. I have been looking for one of those at a reasonable price for a while. I have a schematic and BOM for one, but it's still very expensive to build.

[Red Squirrel]

I was messing around with some ferrite cores and managed to make a small high voltage transformer.  I don't have any instruments to measure such high voltages but I was getting enough to generate a small arc and also light up some CCFL lights.  Basically I was just switching it at a few 100Khz with a 555 timer and about 5 volts.  I'd get better results with 12 volts but the mosfet would get very hot as the primary was just 1 turn, so basically a short circuit.

Suppose with a larger core you could do a few turns and then a ton of turns with small wire and get decent voltage.  internal arcing was an issue for me so had to layer each winding with kapcon tape and also start each new winding at the same end to minimize the voltage difference between any one wire.  Still get some arcing at the terminals if it's not connected to any load.  "air" seems to actually count as a a load at these voltages.  I'd connect one end to ground and the other end was just loose and I could get arcs just touching another piece of wire to it even if that piece of wire is not grounded.  Ex: holding pliers to it.   Fun stuff.  Just be careful.

[james_s]

You can buy a CRT flyback transformer for a few dollars on ebay, or hang around an e-waste center and snag an old TV. Then you'll have a ready made HV transformer complete with internal rectifier.

[Zero999]

I was messing around with some ferrite cores and managed to make a small high voltage transformer.  I don't have any instruments to measure such high voltages but I was getting enough to generate a small arc and also light up some CCFL lights.  Basically I was just switching it at a few 100Khz with a 555 timer and about 5 volts.  I'd get better results with 12 volts but the mosfet would get very hot as the primary was just 1 turn, so basically a short circuit.

There's a simpler circuit that can do that. It's known as a blocking oscillator and only requires one transistor and another tap or winding on the transformer to drive the transistor.


http://webpages.charter.net/dawill/tmoranwms/Elec_SMPS1.html

To get higher voltages, more turns on the secondary are added. If a very high voltage pulses are required (above 10kV) then another stage is added, consisting of a spark gap, which discharges the capacitor into another step up transformer, to produces short high voltage pulses, at a lower frequency. This technique is used in some ignition systems and stun guns/tasers.

[t_ryner]

I recently saved three working CRT TV boards from being thrown out in my neighbor hood I'll make a post on it. I tested them and all of them work.  I also have three flybacks left over from past adventures, so now I have 6. I'm planning on reverse engineering the power modules and using the audio amp chips from them. one of them had a built in DVD player too! 
Ps. how do I post pictures?
-- Tommy Ryner

[Vtile]

  I'd get better results with 12 volts but the mosfet would get very hot as the primary was just 1 turn, so basically a short circuit.

Congrats yourself, since you just have found out what happens with poorly installed current transformers. 

[HighVoltage]

I would probably use a Neon sign transformer if I were going to play with that stuff today. They are typically impedance limited to not burn things out.

Just a warning:
Neon sign transformer are extremely dangerous!
Anyone using them and not knowing what they are doing, is playing with their life!

[James_EAC]

I have a simple example. https://youtu.be/YZycPXPTzK8
Maybe helpful.

[Red Squirrel]

I was messing around with some ferrite cores and managed to make a small high voltage transformer.  I don't have any instruments to measure such high voltages but I was getting enough to generate a small arc and also light up some CCFL lights.  Basically I was just switching it at a few 100Khz with a 555 timer and about 5 volts.  I'd get better results with 12 volts but the mosfet would get very hot as the primary was just 1 turn, so basically a short circuit.

There's a simpler circuit that can do that. It's known as a blocking oscillator and only requires one transistor and another tap or winding on the transformer to drive the transistor.


http://webpages.charter.net/dawill/tmoranwms/Elec_SMPS1.html

To get higher voltages, more turns on the secondary are added. If a very high voltage pulses are required (above 10kV) then another stage is added, consisting of a spark gap, which discharges the capacitor into another step up transformer, to produces short high voltage pulses, at a lower frequency. This technique is used in some ignition systems and stun guns/tasers.

Interesting, I might play with that.  My next step was to do a push-pull config and use arduino to drive it (as I need to time the two square waves decently so there is dead time and not sure if I can do that with a 555) but may play with that circuit too.  Already wound the transformer, and made it so it can work with mains, but this particular transformer is step down and if I get it working will be for another application.

  I'd get better results with 12 volts but the mosfet would get very hot as the primary was just 1 turn, so basically a short circuit.

Congrats yourself, since you just have found out what happens with poorly installed current transformers.

I was thinking more that it has to do with too little turns as for a higher voltage you need more turns, or higher frequency.  But it was just an experiment.  My method is also not so great because of the back EMF produced by having a single switch so the off time is long compared to if I did a push pull or H bridge.  I kept that transformer though as later on I will probably experiment with a H bridge and a higher frequency.   Though that single transistor method looks interesting too so probably play with that. Saves on needing a brain box too.

[Zero999]

I was messing around with some ferrite cores and managed to make a small high voltage transformer.  I don't have any instruments to measure such high voltages but I was getting enough to generate a small arc and also light up some CCFL lights.  Basically I was just switching it at a few 100Khz with a 555 timer and about 5 volts.  I'd get better results with 12 volts but the mosfet would get very hot as the primary was just 1 turn, so basically a short circuit.

There's a simpler circuit that can do that. It's known as a blocking oscillator and only requires one transistor and another tap or winding on the transformer to drive the transistor.


http://webpages.charter.net/dawill/tmoranwms/Elec_SMPS1.html

To get higher voltages, more turns on the secondary are added. If a very high voltage pulses are required (above 10kV) then another stage is added, consisting of a spark gap, which discharges the capacitor into another step up transformer, to produces short high voltage pulses, at a lower frequency. This technique is used in some ignition systems and stun guns/tasers.

Interesting, I might play with that.  My next step was to do a push-pull config and use arduino to drive it (as I need to time the two square waves decently so there is dead time and not sure if I can do that with a 555) but may play with that circuit too.  Already wound the transformer, and made it so it can work with mains, but this particular transformer is step down and if I get it working will be for another application.

It's also possible to make a push-pull oscillator. This circuit shows the simplest way, but it's more efficient to use another feedback winding to drive the transistors.

[bd139]

I have built exactly that circuit before. Works nicely. You're right about efficiency though; the power transistors burn off a lot of power. I used TIP41C's. Managed to pull +/-2kv out, 2 12v +/-12v rails and a heater winding for a DIY oscilloscope. Never got past building the power supply

[Red Squirrel]

Is there a good site that explains what's going on in these types of circuits.  Like I sorta get that the produced voltage from the transformer is probably being used to turn on the transistor but not more than that.