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I need a high voltage power supply for the homemade CO2 laser I am building. I understand that a 15kV 60mA transformer is a thing, but its very big and heavy and its out of phase meaning each lug is only 7,500V and the difference is 15,000V. This would work for most applications but not one where i need 15kV positive and GROUND. I have seen simple arc lighter things that generate a supposed 15kV from a small battery, but the amps must be low? How can i design a simple 15kV high amperage transformer that can be smaller than a neon sign transformer?

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  • $\begingroup$ The output lugs are most likely isolated from input return and from case ground. Whether the output wiring can withstand 15kV from ground (e.g. ground one lug) depends on the overall transformer design. $\endgroup$ – Carl Witthoft Jun 8 '18 at 14:47
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Unfortunately, if you have the high-voltage coils, they must be isolated thickly so that you don't get a short-circuit between loops of the coil. Add a rather thick wire to conduct the current needed without excessive losses, and add plenty of coils, because with fewer coils you generate much less of magnetic field in the transformer (in relation to what goes out through supply wires and the rest of circuitry) - and you have a massive device.

The arc lighters are massively lossy devices. They take a relatively high current on the relatively short primary coiling, and can produce massive voltage on the secondary (which still needs to be isolated well, but can be now much shorter; fewer loops of coil) - but most energy goes 'poof' as heat, induction of wires, and losses in general; the energy efficiency is very poor - but since to create the spark you need very little energy, you can afford these losses, at benefit of small, simple, handy device.

If you want to get reasonably good efficiency, you must retain the primary:secondary loops count ratio, but you need much more loops on the primary, and thicker wire on secondary. And you can't really afford low efficiency, because the puny 3.7V battery of a spark lighter will barely heat up your circuit, while massive losses with much higher current will melt the wires and set things on fire.

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  • $\begingroup$ Ok, so i see that what your saying exactly. But now the question remains, i see people with high voltage and high amperage transformers that they build custom. Would i just have to figure out the math for primary coils and secondary coils to see how many i need to get a solid 15kv output. I have been building my laser from this website and he also has a multi kilovolt transformer i would like you to look at laserkids.sourceforge.net/eng_hv_guide.html $\endgroup$ – Reese Houseknecht Jun 8 '18 at 15:05
  • $\begingroup$ @ReeseHouseknecht: The math for the number of turns is pretty trivial, the voltage shift being directly proportional. Say, primary has 230 turns, secondary has 4000, you feed it from 230V mains, you get 4000V on output. (or primary has 115, secondary 2000, same ratio.) The math for what wire to use and how to fit it all on the core is much more complex. Say, your 4000 turns is 20 layers of 200 turns each, weaving back and forth; first turn is touching directly turn#400 (turn#201 is directly on top of #200), so there's 400V between them - your isolation must survive that. $\endgroup$ – SF. Jun 8 '18 at 16:45
  • $\begingroup$ So in this kit here google.com/… what would you say the amps out is? Also if i attach a huge ridiculous heat sink to the transistor could i still have some efficiency? What would happen if i put 120v to this instead of 3.7v $\endgroup$ – Reese Houseknecht Jun 9 '18 at 1:28
  • $\begingroup$ @ReeseHouseknecht: First off, for making big sparks you don't need any significant amperage. That link you provided has some dubious claims; ~0.4A at 15KV would be 6 kilowatt, which would make this little thing go up in flames and/or explode. And attaching 120V would likely cause a short in the primary resulting in a blown fuse for your house (the page writes it can withstand 12V). The secondary is structured in a way that prevents excess voltages between adjacent coils, but that flimsy wire doesn't look like it could withstand more than a couple watts; microamperes at best. $\endgroup$ – SF. Jun 9 '18 at 23:10
  • $\begingroup$ I need amps for the co2 laser i dont want sparks. I built a wimshurst machine that makes great sparks and a bonetti machine that makes even better sparks! But what about this following tutorial laserkids.sourceforge.net/eng_hv_guide.html $\endgroup$ – Reese Houseknecht Jun 9 '18 at 23:14
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Voltage and Current multiply to give power. 15kV times 60mA is the same as 60Volt times 15 Amps (=900 Watts) You would not expect that to be a tiny thing, would you? And that power is without transformation losses.

Keep in mind that 900 watts a common size for an electric space heater. This is not trivial power you are dealing with.

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  • $\begingroup$ Welcome to Engineering Stack Exchange. This is a good answer, but I would also add a few examples of other 120Volt household items that use 7.5A for good comparison (such as a lightbulb, or fan). $\endgroup$ – Mark Jun 8 '18 at 15:57

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