Transformer Primary Gets Hot / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

Transformer Primary Gets Hot

Move Thread

LAN_403

KeeDx3

Sat Mar 18 2017, 02:42AM

Registered Member #61435 Joined: Thu Jan 19 2017, 06:46AM
Location:
Posts: 25

So I have this transformer that was the xenon ignitor module from a cinema projector. The specs are:

.200KVA
10,000V

It draws a nice arc, but after using it to run a Jacob's Ladder for 15-20 seconds, I noticed that the primary side was very warm. I would think that after a few minutes, it would overheat and open-circuit.

I guess my question is; do I need to current-limit this? If so, how? I'm imagining it's similar to a MOT in that it will work unballasted for short runs but won't stand up to more than a few minutes of use.

As an aside, how can I figure out the capacitance of the 20KV caps in the picture? I'm hoping to use this arrangement for a Tesla Coil, but I'd really like to know what I'm dealing with first!!!

Edit: Never mind - I decided to stop being an idiot. My meter puts them at around 2nf each.

Hazmatt_(The Underdog)

Sat Mar 18 2017, 05:12PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

The marking is 242, which is 24 and 2 is x100 so you get 2.4nF

Similarly 241 is 24 x10, 240pF, 240 is 24pF, so the last digit is the multiplier, and you're counting in pF.

For TC's you're going to need at least 6 doorknobs 1 to 2 nF, and 30kv would be better then 20kv.

Nik

Sat Mar 18 2017, 10:23PM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

If this was part of the igniter it may not have been designed for continuous use, once the xenon arc is started the transformer was probably turned off. That doesn't mean it's no good you just have to be mindful of how long you run it. Can a transformer be actively cooled when overdriven?

KeeDx3

Sun Mar 19 2017, 01:00AM

Registered Member #61435 Joined: Thu Jan 19 2017, 06:46AM
Location:
Posts: 25

Nik wrote ...
Can a transformer be actively cooled when overdriven?

I'll bet submerging it in mineral oil would help! Not sure how to figure out how much time a given volume of oil will buy, though. Sounds like a can of worms I'd rather not open. This is going in an experimental/first coil anyway, so I doubt I'll run it for more than a handful of seconds at a time. Might be good for me to invest in a laser thermometer.

Hazmatt_(The Underdog) wrote ...
For TC's you're going to need at least 6 doorknobs 1 to 2 nF, and 30kv would be better then 20kv.

If I have two 20KV capacitors in series, would that give me a total capacity of 40KV? I still have a lot to learn about tank capacitors; it just seems like that's how a lot of MMC's are built. On the other hand, the ~4.4nf I would end up with is too low for my 3" coil? (I could probably use a tutorial on how to use JAVATC).

Nik

Sun Mar 19 2017, 09:57PM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

Oil only increases the time until the xfmr over heats unless you actively cool the oil as well. If it takes 5min to heat up the xfrm alone it might take 10min to heat it up while under oil but it will also take twice as long to cool down.

I agree it may be a can of worms but if you have a way to cool the oil you can use relatively little volume, think CPU water cooling but with oil and a fully submerged heat load. Could be a fun project all on its own.

KeeDx3

Wed Apr 12 2017, 06:29AM

Registered Member #61435 Joined: Thu Jan 19 2017, 06:46AM
Location:
Posts: 25

Hazmatt_(The Underdog) wrote ...
For TC's you're going to need at least 6 doorknobs 1 to 2 nF, and 30kv would be better then 20kv.

Thanks again for the help with these caps. I've decided they're a little risky to use, but I'm still looking in to using doorknobs as opposed to MMC in order to keep my first coil simple.

I'm finding many caps on eBay, and I just wanted to confirm that a pair of 30kv 1000pf would be suitable for this application (SGTC w/10kV, .200kva) transformer. I know you said "at least 6", but I assume you were referring to lower value caps?

Hazmatt_(The Underdog)

Thu Apr 13 2017, 04:23AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

A higher power transformer will need more caps, and I was assuming you would use something like a 12kv 30mA sign transformer to start, that should give you about 18" sparks.

Lower power transformers produce coils with less output.

KeeDx3

Thu Apr 13 2017, 04:49AM

Registered Member #61435 Joined: Thu Jan 19 2017, 06:46AM
Location:
Posts: 25

Yeah, I actually do have a few 15/30's and one 7500/30 sitting around. This was more of an opportunistic thing since I found the transformer and figured it wouldn't need the protection (Terry Filter) that an NST would. I thought I'd try my luck at a small, simple "tabletop" device to help me develop a proof-of-concept before burning up any of my nice transformers or spending money going all out on the eventual "nice coil".

This one is a 5:1 with ~900 turns of #26 wire on a 3.5" form and (currently) 7 turns on a 25' primary. Have no idea if it will work or not (still figuring out how to use simulations), but I'm building as much as possible out of spare parts. Mostly I'm just in the weeds with capacitors. The MMC for a 15/30 seems simple and already well-documented on this site and others, but this oddball transformer is putting the few skills I have to the test. I wanted to try it out with doorknobs since they're robust and easy to use.

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob