# Help me out with a circuit design

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Hi guys! I know this is a little off topic, but I'm kind of in a bind, and it sort of relates.

I need to build up a high voltage transformer. Basically, I need to go from a 110V wall plug to a high voltage, short duration pulse through a copper solenoid. I may need to do this 2 or 3 times in rapid succession, too. We're thinking in the 1000-2500V range, though I've not completed the calculations quite yet to determine the exact voltage needed.

I'm not going to be building the circuit, so don't worry about me frying myself by being inexperienced, which I am.

Can you guys help me out?

#### korneluk

Basically, I need to go from a 110V wall plug to a high voltage, short duration pulse through a copper solenoid. I may need to do this 2 or 3 times in rapid succession, too. We're thinking in the 1000-2500V range...

Define "rapid sucession". What's the period in between short HV pulses?

Keep in mind there is going to be substantial back EMF generated by the solenoid. Are you prepared to handle that?

-- josé k.

Re: Re: Help me out with a circuit design

korneluk said:

Define "rapid sucession". What's the period in between short HV pulses?

Keep in mind there is going to be substantial back EMF generated by the solenoid. Are you prepared to handle that?

-- josé k.

Well, by rapid I mean probably within a few seconds. It's not that rapid, I suppose.

I feel like we are. The solenoid is going to be contained, with the circuit guts outside the metal box and inside a different metal box. Of course, we won't know for sure until we build it.

#### Merlinb

A neon-light transformer perhaps? They can kick out around 5kV, and are pretty cheap- or free if you find an old shop sign in a skip.

#### Wavebourn

A choke may work well without any transformer.

Oh, do you think that could work? That would be alright...

#### Miles Prower

Hi guys! I know this is a little off topic...

I'll say

...but I'm kind of in a bind, and it sort of relates.

Well, no, it doesn't.

I need to build up a high voltage transformer. Basically, I need to go from a 110V wall plug to a high voltage, short duration pulse through a copper solenoid. I may need to do this 2 or 3 times in rapid succession, too. We're thinking in the 1000-2500V range, though I've not completed the calculations quite yet to determine the exact voltage needed.

Solid state is more suitable for this sort of thing. Power MOSFETs or IGBJTs are much better at switching big currents and doing it very fast than are VTs. I'd ask around in the Solid State forums about this sort of thing.

#### Tubelab_com

I got an old defibrillator from a medical equipment repair guy. Once they get too old to be recertified, they are junk. It has a 15 uF low ESR pulse cap rated at 7.5 KV. These caps are just right for use in monster tube amps (like my 833A experiment). The defib has a solid state power supply that charges the cap up to a predetermined voltage based on the setting of the watt - seconds dial. There is a vacuum relay that applies the charged cap to the paddles through an air wound inductor. Recycle time is 3 to 10 seconds depending on how high you turn the knob.

I used this setup for some simulated lightning strike testing by bypassing the inductor.

WARNING --- This equipment, and anything else that would fit your requirements is EXTREMELY LETHAL!!!!!! You must know what you are doing to even think about going here.

Second warning ---- connecting this device across a banana and pushing the button makes a big mess!

#### EC8010

Yes, we have no bananas...

tubelab.com said:
WARNING --- This equipment, and anything else that would fit your requirements is EXTREMELY LETHAL!!!!!! You must know what you are doing to even think about going here.

Second warning ---- connecting this device across a banana and pushing the button makes a big mess!

First warning: Either something is lethal or it isn't. I'm fairly sure medics don't classify people as "dead" or "extremely dead." Actually, rereading that, and having met a few medics, I'm not quite so sure, but you know what I mean.

Second warning: I'm not even sure where to start. How? Why? Where? Why? (Yes, I know I asked "why" twice, but I'm still staggered as to why an EHT supply might find itself connected across a banana.)

On a more serious note, if you have to ask how to produce high voltages, you shouldn't be anywhere near them.

#### Wavebourn

Oh, do you think that could work? That would be alright...

No, I think theoretically it would be all right. Practically I think you should stay away.

#### Tubelab_com

why an EHT supply might find itself connected across a banana

To see what would happen of course. About 15 years ago myself and another engineer were asked to solve some field failure issues in wireless SCADA equipment. We needed to simulate the impulse created by a nearby lightning strike. I obtained some decertified defibrillators from a friend in the medical equipment repair business. We built a large Lexan box to enclose the unit under test, and the defib was actuated by remote control.

After some considerable experimentation, we succeeded in designing an input circuit and a PC board that could take a zap from the defib across any two inputs or from any input to ground. Field failures were cut in half.

Now that the required work was done, a few "items" were "tested". You thought I only "tested" tubes? The setup was torn down, and I brought the defib home. That monster cap found its way into my 833A prototype, and it is still sitting on the corner of my workbench.

First warning: Either something is lethal or it isn't. I'm fairly sure medics don't classify people as "dead" or "extremely dead." Actually, rereading that, and having met a few medics, I'm not quite so sure, but you know what I mean.

Yes this is true, but as the voltage and stored energy levels rise the probability of death occurring from accidental contact increases. The original poster mentioned 1000 to 2500 volts. At these levels you don't get a second chance.

Some of my experiments may sound unsafe, but I will have multiple barriers between me and the high voltage for tests involving HV or anything that I am not sure of. Usually one of those barriers in a 1/4 inch thick piece of Lexan. There must be two actions necessary to activate the HV. I will turn off a device under test AND remove its power cord to prevent accidental turn on.

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