Getting the ball rolling... / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

Getting the ball rolling...

first previous 8 9 10 11 next

Move Thread

LAN_403

Blitzorn

Mon Jun 01 2009, 04:08AM

Registered Member #2128 Joined: Thu May 21 2009, 03:17AM
Location: Seattle, Washington, USA
Posts: 58

UPDATE - Alright, looks like there's no capacitance multimeter available. I wasn't imagining things, he did have one, but we looked for it and it was nowhere to be found. it looks to me like it's going to be a lot of trial and error >.>

StevenCaton

Mon Jun 01 2009, 04:38AM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

Its okay that you can't measure the capacitance of your bank. Just plug the parameters of your salt water caps into some calculator and it will give you a rough idea. You'll then have a general idea of where to start with the # of primary turns. If you are way off with the number of primary turns and the coil is way out of resonance, its unlikely that something will get damaged, as long as you don't leave it plugged in too long. If you don't have your variac, then put a sharp object on the toroid when you plug it in the first time. This will take some stress off the system if its out of tune initially.
Calculations will only get you so far with Tesla Coils. To really get that thing into resonance, it will take many many fine adjustments. You seem well aware of this so you will be fine.

I know how you feel right now. I was scared as hell to plug in my first coil, but when I did and it worked, I did that champion hand clench motion (like Tiger Woods did when he holes a shot) and bellowed a deep "Yeahhhhhhh" It was a pretty cool experience.

Blitzorn

Mon Jun 01 2009, 05:21AM

Registered Member #2128 Joined: Thu May 21 2009, 03:17AM
Location: Seattle, Washington, USA
Posts: 58

I'm finished with a number of components, i'm in the final stages of just about everything else, and the stuff i haven't gotten started on yet (like the strike rail stands) will take little time at all. It is entirely possible that everything will be finished up tonight.

I have the variac, two different elements of line filtering (one is a real line filter, one is a special power supply power strip that i'm using for it's emergency cut-off button), and i have all my tuning parameters set. I just have to finish assembly!

This has been a great project, it's not quite done yet, but i would barely be started if it weren't for all the help you guys have provided! THANK YOU!

Herr Zapp

Mon Jun 01 2009, 06:06AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Blitzorn -

(Now how did I know that your multimeter didn't have a capacitance function?)

You might consider revealing the design details of your salt-water capacitor bank for group review.

Go ahead and use the bottle-capacitor calculator at classictesla.com to estimate the capacitance value of the bottles you have selected and at least get a preliminary value for the entire bank.

Design the bank so you can easily connect/disconnect individual bottles to allow "adjusting" the value (if necessary) during tuning.

Also, carefully inspect the bottles you intend to use, and discard any that have obvious molding flaws in the glass like "folds" or especially small air bubbles.

Keep a few pre-inspected "spare" bottles on hand in case any crack during coil testing.

Regards,
Herr Zapp

Blitzorn

Wed Jun 03 2009, 03:55AM

Registered Member #2128 Joined: Thu May 21 2009, 03:17AM
Location: Seattle, Washington, USA
Posts: 58

The good news - the coil is nearly finished!
The bad news - it was supposed to be done by today.

No matter though, i've spoken with the science dept. and although it wasn't ready by the science fair they are more than happy to have me demo it today or tomorrow, so all is well.

Well almost.

Everything is going marvelous EXCEPT the secondary coil - i had a friend helping me wind it and although we both thought he did it great, when i went back later that night i realized there was a tiny bit of slack in it that was causing it to unwind. Attempting to fix it only aggravated the problem, so i broke down and unwound the entire thing. I have enough time and wire to re-do it, it's just a PitA.

Blitzorn

Thu Jun 04 2009, 01:43AM

Registered Member #2128 Joined: Thu May 21 2009, 03:17AM
Location: Seattle, Washington, USA
Posts: 58

Sorry for double post - but there's been a bit of a, shall we say, breakdown. The spark gap i was midway through building has sustained some damage (it fell from a height after a broken drill bit caused a chain reaction of things falling over in a most improbable and comical way) rendering it unusable. The copper pipe electrodes are bent and scratched to the point of being unserviceable. So i need to make a new spark gap, quickly, that will be a fast assembly, work efficiently enough for my power supply demands, and still be able to sustain the wear and tear of tuning and several demos without needing major maintainance.

I'm working on some plans right now, but anyone with info to share would make my day!

Coronafix

Thu Jun 04 2009, 02:33AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

Just cut 4 or 5 bits of copper pipe 3-4" long and screw them onto some of that white plastic chopping board about 1/8 - 1/16" apart. Either tap them to get the spacing you want or throw another bit of pipe on two of them to short them together.
There you have a static spark gap, nothing complex and will work up to 1kW.

StevenCaton

Sun Jun 07 2009, 04:05AM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

So did your coil work?

Blitzorn

Sun Jun 07 2009, 10:04PM

Registered Member #2128 Joined: Thu May 21 2009, 03:17AM
Location: Seattle, Washington, USA
Posts: 58

Alright, well it's not done - but that's alright, i've talked to the science dept. and they'll just have me demo it when it's done. Which i would like to be tomorrow. Every component is done, as far as i know, but in getting things set up i have a few little issues...

i've got the primary circuit all hooked up to see if my spark gap and caps work. When i power up the variac, i start to hear this electrical sounding buzz, but when i get a spark across the gap seems a lot like the one i get off the outputs of transformers, and doesn't feel at all like the hefty sparks i've read about and seen online.

anyone know what's going on here? have i got my outputs crossed?

EDIT: This appears to have been the case, i switched them and got a much more intense spark with a perceptible firing rate - not to mention it was far louder. Construction continues! I used a design almost identical to this

for my spark gap, and it seems to work marvelously. I don't know why i don't see these more often...

Blitzorn

Mon Jun 08 2009, 08:47AM

Registered Member #2128 Joined: Thu May 21 2009, 03:17AM
Location: Seattle, Washington, USA
Posts: 58

Once again, sorry for double post, but the results of the full scale test are in!

As the sunlight vanished my best fried - er, friend - and i got the driveway all cleaned up etc. etc. and ran down my safety and functionality checklist. everything being in apparent working order, i set the tap point at ~4.5 turns (an absolute minimum estimate). Remember, if you had read earlier in the thread, i had only a ballpark estimate of my capacitance, and after some tuning the ballpark now looks more like a national park. I really have no idea how much capacitance i'm working with. But more later.

We powered up and the spark gap roared - but nada on the secondary. Moved tap point in, mostly because i forgot i started at my minimum estimate, partially out of curiosity. Powered up. Spark gap roared. Nada.

At this point i realized i was an idiot and moved the tap point out a whole two turns, and we powered up again. Nada. But i realized the spark gap wasn't firing - i had left my shorting stick (for discharging caps) across the gap. After removing it and slightly narrowing the spark gap, we powered up again. the spark gap roared. nada.

At this point i'm starting to get really worried i screwed up bigtime, but not having lost faith in my ability to do stuff right, i temporarily assumed that my capacitor was FAR more effective than i'd intended. Operating under this assumption, i went to move the tap point out a couple whole turns, and i realized that i had been starting my counting with the very beginning of the primary (like 0.00001 turns) as my 1 turn point, i was counting metal bits and not full revolutions. This was possibly throwing me way off. So i went out to about 6.5 turns. We powered up and WE GOT SPARKS! now, mind you, these were only about 3" sparks. I had a breakout point ~3" from the head of a flexible brass floor lamp that was my guinea pig.

My mom was watching and she started laughing, which was probably just because she was overjoyed i hadn't blown up the whole neighborhood. My friend and i did a lot of high-fiving and whooping and all that, it was a great moment.

Well, hell, i figured, lets move the lamp back to like six inches and see what we get. This time, we got a very dispersed corona-type discharge from the breakout point to the lamp. It was visible, but unsatisfying. I was ready to concede that it just wasn't tuned yet.

I moved the tap point up about half a turn, bringing us up to almost 7 turns exactly. The results were almost identical. At ~3" we got cool, solid sparks, and at ~6" we got fluffy corona. Okay, i'm thinking to myself, if we get about the same result here as we did half a turn ago, then clearly optimal lies about halfway between these two points. So i set the tap at ~6.75 turns and we fired it up. Same result. No matter where we put it above about 6 turns, the result was similar, decaying a bit (in my opinion) as it went up.

I'm in no way done testing, and i'm willing to consider that some confounding variable may have been preventing firing in the first few tests and thus throwing off the rest of the tests. I'm also willing to consider that i missed the optimal point in one of my larger jumps up the primary. Tuning will continue tonight.

Also of note- The following may be a major player in the performance of the coil as yet, and needs to be addressed before any more tuning takes place:

As i was disconnecting some components after the session was done, i happened to rest my hand on one transformer, and found it warm to the touch. Not hot, but warm. I instinctively touched the other transformer, and to my mild surprise it was cool. It hadn't heated up from the latent air temperature. Each of my transformers has a pull-chain switch on the side of it, perfect for turning a neon sign on and off if you own a pub, but a horrible confounding variable in this sort of situation. I was prepared to bet that one of the transformers had been off the whole time, and it was only reasonable to assume that this was the cold one. So i bulled the chain on the cold one, theoretically putting both in the "on" position. I turned on the power. Nothing. This struck me as really weird. I switched the hot one (which i was quite sure had been running) into the position i had to assume was "off" and fired up the thing again. Sparks. So clearly when one of them was on i could tease arcs out of it, but when both were on (or off, but we'll just say "duh" to that one) there were no sparks. So that indicated they were out of phase... I had definitely hooked them up and tested them to see if they were in phase. But then it occurred to me - what if they WEREN'T in phase. And what if i just THOUGHT they were in phase because one of them had been switched off since before i tested them together - therefore rendering the initial test essentially null. If one was switched off then it would put a bit of a load on the other one, but if they both had decent current limiting then it could go more or less unnoticed and not blow a fuse or anything. When i had spliced the input cords, i believe i reversed one of them on accident, messing up the relevance of the color coding on the outputs. I matched them, assuming i had retained the initial state, and got an arc (but only from power from one transformer - the inactive transformer did not add to it, but neither did it cancel it out). Therefore i had hooked up the whole transformer rig so that it was out of phase but not phased out...

EDIT: With only 30mA (one transformer) the recommended LTR cap is something between 17 and 18nF. I conservatively estimate my entire bank at 44nF. Could this disparity alone cause dramatic underperformance? Would an excessive cap size decrease performance even with both running in tandem (60mA demands ~34nF, so i would still be over) and should i try disconnecting a number of my bottles to boost performance?

YET ANOTHER EDIT WOW THIS POST IS LONG: Many of my connections were made by twisting copper wire together and then crimping it - i know it's not the safest thing ever, but it's been working pretty well so far - but it's just occurred to me that all that twisting might be generating a huge amount of inductance. Is this another thing to be tackled to unleash the actual potential of this thing? How much do little twists (or LOTS of little twists) detract from efficiency?

ANYHOW what this all brings me to is... Once i've got them properly phased, is it conceivable that my spark length will improve immediately? I don't need 2 foot arcs coming out of this thing, and i'm being realistic, this setup is by no means optimized. But more than 3" would be nice =/.

first previous 8 9 10 11 next

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