# grounding & a/d converter

Discussion in 'High Voltage' started by Dr_Doggy, Feb 10, 2012.

1. ### Dr_DoggyWell-Known Member

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i am following this guy:
http://www.rmcybernetics.com/projects/DIY_Devices/plasma-gun.htm
and i notice that he is grounding his secondary through his hand, now when i read up on this everyone says not to ground secondary back to the battery, but since his coil is so small its ok to use like this.
Since i have about 220 watts available to me for my hand gun, plus idk yet the size of my secondary, so I am hesitating to run it through me, is there a better solution for ground here?
could i use a capacitor tripple the value of the toroid on the ground side?

what if i wound my coil so that both leads of secondary were on the same side of the coil, so ground and vcc would spark to each other? would that work?

ALSO i'd like to read the value at primary could i use resistors to divide the voltage and then read it from a PIC a/d, does the a/d converter have a thevenin equivalent value??

2. ### ronsimpsonWell-Known MemberMost Helpful Member

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Where to start. You need lots of help. Lets start at the bottom. Why not use a meter? OK you want to measure with a PIC because don't have a meter. You will need to divide the 100,000 volts down to 3 volts for the PIC. You can not use one HV resistor because you don't have one and you can not afford it. (use many resistors) Across the ACD's input you will need a resistor to ground. (part of the divide down) That resistor will dominate the input impedance of the ADC. The input of the ADC, which is about 1,000,000 ohms and 20pF, will have no effect when parallel with 1k ohm from the voltage divider.

You can also measure the voltage by see how many cm or inches it jumps.

When gun, when boosted up to 200 watts will kill you.

3. ### DerStrom8Super ModeratorMost Helpful Member

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Hi doggy. I followed that project some time ago. His coil is very small, so grounding isn't extremely important for his coil. It runs from a simple ignition coil with very low current, so a low power rating. I believe he says it consumes only 72 watts or so, and probably wouldn't even hurt very much to touch it. However, dealing with 220 watts is extremely risky, and though it is still a small coil, I wouldn't recommend grounding it to your hand. The only alternative I can really think of (unless you want to risk it and don't ground the secondary at all) is to run a wire from it straight to ground. You could wire something up so the ground wire straps to your belt, and from there goes down the side of your leg into a nail or something in your shoe, but that seems a little ridiculous. TBH I wouldn't even attempt making a 220 watt handheld tesla coil. Especially the tank circuit would be extremely dangerous, if not deadly. If you ask me, you only have two choices for this: 1) don't use 220 watts, or 2) build a tabletop coil. A 220W handheld coil is definitely not a very good idea. Do you have a different power supply you can use? The guy on RMCybernetics used a small pencil-style ignition coil, which you can get for very cheap at a scrap yard or on ebay. I would suggest taking a look at your other options.

As always, when working with high voltage, I must urge you to be extremely careful, and take all necessary precautions to keep yourself and others safe. I'm sure you've seen this before, but I can't stress it enough how important it is. If possible, always have a buddy watching to pull the plug if something goes wrong, and most of all, just use common sense.

Best wishes,
Der Strom

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5. ### Dr_DoggyWell-Known Member

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thats what i do now thnx, measure arc, but i like more accuracy, and recently I have used a 2\$ meter needle(like on your avatar) from ohmmeter direct in the circuit divider, yes with lots of resistors,

thankyou i will do my divider with 1k then, i just like to double check on things like this...

200 watt is just wats available @ source, idk my secondary size or V*I/t, but i still dont want to ground it through my body, any substitution im sure would be fine, say vs a steak in the ground

hey just read that,, im using a 4kv flyback from crt, dual2n3055, but may need to change that too to a transformer to support the 220W

Last edited: Feb 10, 2012
6. ### ronsimpsonWell-Known MemberMost Helpful Member

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The 1k value was just off the top of my head. The point is the divider will have a low resistance on the PIC end (or meter) and a very high on the input (HV) side.

Depending on who makes the parts, a 1/4 watt resistor can only handle 200/250 volts. Use many. 10 resistors = 2.5kV

250 v working, 400 to 500 for a short time.

7. ### Dr_DoggyWell-Known Member

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yes, i ll do the math later, right now on the needle im using several Mohms, but i want to go higher so there is less of a drain on the HV, The input of the ADC, which is about 1,000,000 ohms and 20pF, was my main concern here, THNX!

alSo if it helps, naturally, i want the longest spark possible, that you can still see, preferably tight coils, what is a good frequency to run at for that? there was a calc somewhere but i cant find it anymore. i dont think i feel comfortable with a wire down my hip either... what about a tinfoil ball at ground, as a toroid would work, like a capacitor, plus a high value resistor for slowing the drain? what would happen if I left ground bare? would it "Bleed" sparks? what if i left ground bare but on the same side as toroid?

btw...what is the limit of safe past 72WATTS?

Last edited: Feb 10, 2012
8. ### Dr_DoggyWell-Known Member

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if i used a second toroid on my secondary, at the same side as the first toroid but wound the second secondary backwards over the first one &maybe some insulation , so to create a inverse flux on the wire, would that work? am i getting warm with this? I googled it and it would be similar to a bipolar coil

I may forgot to mention, one of the reasons im being so safe with the grounding this time, is because im using a LiPo battery, and iv seen what happens when they get an improper charge. HOw do i calc the size of the spike

its just those little handguns making a 1/2" streamer really isnt that worthwhile, i finally figured out that the reason i like these things soo much is that it discharges to air without need for a ground

9. ### DerStrom8Super ModeratorMost Helpful Member

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I definitely would not recommend using a Li-Po battery in a Tesla coil setup! They are very sensitive to back EMF and do not take much to explode. I highly recommend finding a different type of battery, such as SLA, which can stand the EMF more easily.

10. ### Dr_DoggyWell-Known Member

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could i protect that with a HV diode, at vcc and ground?

im noticing where some sparks jump from the HV wire to ground, but then some just "free fly" in the air, i think i am having trouble establishing why the difference occurs or is this just another power thing?

11. ### DerStrom8Super ModeratorMost Helpful Member

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I don't think a diode will help much. The problem is the RF spikes, especially. One moment it will draw a little bit of current, the next it will require a huge amount. All I can say is to not use Li-Po. Try finding an alternative, for your own safety

The arcs to air only happen if there is not enough energy to jump all the way to ground. Some will be more powerful than others, depending on how you have it set up.

Regards

12. ### Dr_DoggyWell-Known Member

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note taken, but when we say power spikes; is that from the ground on the secondary, or are we talking about current draws on primary?

on another note aside to a tesla coil, iv been charging and discharging hv caps for EM toys, do i need to worry about spikes there too on a LiPo; before i used 2-3 series 9v's to power my 3055 driver for microwave coil, then spark gap it at 1kv-4kv, iv just been charging 0.1uf caps, but also what about the bigger ones? so far im using phone wire as grnd an no heat is noticed,

13. ### DerStrom8Super ModeratorMost Helpful Member

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The high frequency oscillations in the tank circuit can send EMF and RF spikes back through the control circuitry, and even into the power supply. No matter how well you ground the circuit, it still won't prevent this from happening entirely.

What do you mean by "EM toys"? As long as there aren't any high voltage, high frequency oscillations, you should be okay, though I still do not recommend the Li-Po battery for anything other than what it's intended for. They are very sensitive to voltage and current spikes, RF, over charging, under charging, reversed polarity, and many other things. As I suggested a few times before, you'll be better off if you get some SLA batteries. They are much more rugged than Li-Po's and are better for high voltage projects. I most certainly do not recommend putting 9 volt batteries in series in most cases. They are not designed to run in series like AAs and AAAs are. Again, that would be a good use for an SLA battery or a rectified and filtered transformer supply.

As for the wiring, heating isn't the only issue. You will also need to worry about the voltage, especially at 1-4 kv. If you're using wire insulated for 200 volts (off the top of my head, roughly what I think phone wire is), the voltage is high enough to jump through it and arc to something else (even you). You should find some high voltage wire. If you have a relatively high current, neon sign cable would be best, but if it's low current, you could probably use the wire found on old flyback transformers in CRT TVs and computer monitors. Find some with the voltage rating marked on the wire. Generally the wire from CRT screens is rated for about 40kv, so you'll be well within the safety range.

Hope this helps.
Regards

14. ### Dr_DoggyWell-Known Member

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all i meant about that was my ground wire, and ever since repairing that microwave i no longer touch live circuitry EVER, in fact i fully intend to use a double ground shield around any contact points near me.

i was hoping i could do a 2 in 1 thing for my gun, so by em toys i mean a can crusher, with around 1/3 to 1Kj discharge, is my idea for now anyway, however i cannot find a seimconductor that goes to 4Kv either, so i may need to use a triggered spark gap, (would it work like a xenon flash trigger? where a 10kv trigger voltage is used, but how much current do i need for that?

sry buy just tellme one more time no lipos! what if i used a choke to protect battery?

15. ### DerStrom8Super ModeratorMost Helpful Member

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For can crushers, the best sort of trigger I've seen is just a classic mechanical spark gap that you short with piece of metal connected to a long insulated rod. This also protects you from any arc flash. Anything smaller and you'd risk melting the contacts, especially with that sort of high-energy device. Also, rapid heating could cause expanding gases that make the device explode. A xenon tube often requires very little current, so the energy stored by the capacitor is extremely little, compared to the capacitors for can crushers. I would not be at all surprised if one of those exploded when you released that kind of stored energy through it.

A choke would help prevent some of the oscillations from passing through the battery, but I still don't think it's worth it. Though the RF would be blocked, not all of the voltage spikes could be prevented. As I have said, the Li-Po may work, but I strongly recommend against it, and once again suggest some of the lead-acid batteries. They will be able to handle the abuse much better.

Regards

16. ### Dr_DoggyWell-Known Member

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i was actually thinking to use my current spark tube (o2 @STP) and just borrowing the trigger type that the flash uses, the other problem though is that i was going to use 3 stages, so i will be using 3seperate sparks and 3caps which will need millisecond timing,

like this:
http://www.macinhouse.com/tesla/triggered_gap/stsg.html
but it doesnt mention current.

Last edited: Feb 14, 2012
17. ### Ubergeek63Well-Known Member

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OY! gone over and over this one 10W CAN KILL! Voltage and power does not kill - CURRENT kills. Voltage is only an enabler!

"The damage caused by electric shock depends on the current flowing through the body -- 1 mA can be felt; 5 mA is painful. Above 15 mA, a person loses muscle control, and 70 mA can be fatal."

http://hypertextbook.com/facts/2000/JackHsu.shtml

by these standards I would estimate that a fresh 9V battery on your might be a couple mA.

Dan

18. ### DerStrom8Super ModeratorMost Helpful Member

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It's important to note that 70mA is WAY more than enough to kill you. 30mA is enough to be lethal, if you touch it wrong. Especially if your hands are sweaty, or if you create a path through your heart, it can kill you instantly. You must be extremely cautious when working with this kind of voltage and current.

19. ### Ubergeek63Well-Known Member

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true but explaining that to the "voltage is king" class of hobbyist that you run across borders on impossible!

20. ### DerStrom8Super ModeratorMost Helpful Member

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I'm not really sure what that has to do with what we were talking about. We were discussing lethal currents, and it cannot be debated that current is what ultimately kills. The voltage only determines how easily the current can flow through the skin.

21. ### Ubergeek63Well-Known Member

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I know.. i just caught a lot of flack at one point for pointing that out... of course if voltage killed the 20KV hit i took when I was 16 would certainly have killed me!