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Registered Member #1185
Joined: Thu Dec 20 2007, 04:40PM
Location:
Posts: 17
I know I have the tranformers hooked up correctly schematically. The tesla coil I built was working for about five minutes a shot. But I just blew through my second transformer. So I'm looking for advice.
I built a Tesla coil from a 2 foot long 4 inch PVC pipe wrapping 2 inches(using 20 inches for the winding the other for caps on each end) from each end about 850 windings with 24 gauge wire. My primary is 50 ft of copper pipe for refrigerator hookup wound staring at 6 inch diameter going out to about 3 foot diameter about 0.5 inches between each coil going out to around 13 turns. I used deepfriedneon for most of my calculations.
First off what size transformer should I be using for something that big?
I blew through 2 15000 Volt 30 mA midpoint grounded transformers(only one at a time) costing about $50 a piece this is getting expensive. I'm thinking my Tesla Coils dimensions are too big for the size of transformer I am using.
I built my spark gaps from 6 inch PVC black pipe cut into three 6 inch sections and used 2 inch long pieces of copper that are 1 and a half inches in diameter. I spaced the spark gaps about .028(tried for that was more like .03 or maybe .04) inches apart evenly spaced and hooked it up with just enough gaps to hear a slight buzzing sound without it jumping like it did by removing one gap turned out to be about 11 gaps. I figured the gaps out by themselfs without anything else in the circuit.
I built my capacitor with 10 beer bottles filled to the neck with salt water (6 cups water 8 tablespoons salt) and the neck filled with 10w30 motor oil with 6 inch carriage bolts hanging in them and wrapped with aluminum foil. all placed in a Home depot bucket that we sat them a top an aluminum foil base that we had a 1/4 inch bolt connected to a short piece of steel sheet metal(placed under the aluminum base with screw protruding through) to connect all the bases. and more sheet metal to connect all the tops. Total was .005 micro Farads to meet what deepfriedneon told me to match my transformer.
First try I had the saftey gaps too far I think(It didn't blow at this point but was only run for a minute) the saftey gaps where set for double voltage of the transformer this time. the capacitors kept fireing across themselfs but seemed to hold at .005 mF each time we shut it down and discharged and re measured.
Second try I used a safety gap made with two seperate gaps spaced at 0.3 inches grounded in the middle of the two gaps. It worked for a few minutes then the safety gaps kept firing and shortly after stopped and the transformer was blown. It was hooked up with the capacitor across the two ends of the high voltage and the spark gap off one end of the capacitor to one end of the primary coil and the other end of the primary to the other side of the capacitor. The first time was hooked the same way with a 0.5 inch saftey gap on each side.
Third try with second transformer identical specs. I hooked the spark gap across the high voltage(no saftey gap cause I suspected it the cause of last blown transformer) and on one side of the saftey gap hooked to the capacitor to the inside of my primary coil and the outside of primar was hooked to the other side of my spark gap. As soon as the gaps stopped firing I unplugged the transofmer but it seems this was already too late.
Should I be using a 60 ma 15000 volt transformer for my about 3 foot wide 2 foot high tesla coil? Someone else must have one about the same dimensions I would like to know what others are using.
Registered Member #477
Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546
Hi Jeff! Very sorry to hear of your NST-blowing issue. Here's why they're blowing: You're using the resonant capacitor value (5nF), and your capacitor is placed directly across your transformer. Both of those things are extremely bad for your NST. You should be using the so-called "LTR" (Larger Than Resonant) capacitor value, and your capacitor and your spark gap need to trade places so that your *gap* is across your transformer, not your capacitor. Your current setup virtually guarantees that your transformer will be subject to hideous resonant overvoltages. I haven't looked on deepfriedneon to see where exactly the 5nF figure came from, but that is definitely very, very bad.
Also, consider using an RC filter in addition to a safety gap. You may have heard of a "Terry Filter"? Lots of NST coilers use them and they do a great job keeping your NST safe. Google for "Terry Filter" and you'll find the recipe in no time.
EDIT: Also, your coil dimensions sound ok. It should be no trouble to get 3+ft streamers with a 15/30 NST. Be sure to use a strike rail above your primary, too. Secondary-to-primary flashovers are another great way to toast your NST and other stuff.
EDIT #2: Doh! I have this awful tendency to assume that everybody has 60Hz power If you're in the UK, or somewhere else with 50Hz power, your capacitor needs to be bigger. For 50Hz, the LTR value is 10nF. Resonant would be 6.5nF. Anyway...
EDIT #3: Ah, I see it now. You used this (http://www.deepfriedneon.com/tesla_f_calctranscapmatch.html), right? Yep. That's computing the resonant capacitor value. Very bad. Anybody know who runs deepfriedneon? This cap calculator needs to go! Ouch!!
Registered Member #1185
Joined: Thu Dec 20 2007, 04:40PM
Location:
Posts: 17
J. Aaron Holmes wrote ...
Hi Jeff! Very sorry to hear of your NST-blowing issue. Here's why they're blowing: You're using the resonant capacitor value (5nF), and your capacitor is placed directly across your transformer. Both of those things are extremely bad for your NST. You should be using the so-called "LTR" (Larger Than Resonant) capacitor value, and your capacitor and your spark gap need to trade places so that your *gap* is across your transformer, not your capacitor. Your current setup virtually guarantees that your transformer will be subject to hideous resonant overvoltages. I haven't looked on deepfriedneon to see where exactly the 5nF figure came from, but that is definitely very, very bad.
I tried trading places of spark gaps and caps in try three I have a 12 KV 30ma coming so I should maybe try 10 nF? 5nf came from And I though I was suppose to get the resonant settings for a tesla coil to work? No?
J. Aaron Holmes wrote ...
Also, consider using an RC filter in addition to a safety gap. You may have heard of a "Terry Filter"? Lots of NST coilers use them and they do a great job keeping your NST safe. Google for "Terry Filter" and you'll find the recipe in no time.
EDIT: Also, your coil dimensions sound ok. It should be no trouble to get 3+ft streamers with a 15/30 NST. Be sure to use a strike rail above your primary, too. Secondary-to-primary flashovers are another great way to toast your NST and other stuff.
I will look into getting a filter before I proceed.
To get things straight. So the spark off the toroid hitting the primary would be bad? that is what you are saying correct? And your recommending putting a ground loop above my primary? maybe an inch or two above? I don't think it was hitting I was only getting about 10 inch sparks then again that is one change my brother did was turned my toriod over since the first try which I forgot to mention as a result the toroid was about 4 inches closer to my primary.
J. Aaron Holmes wrote ...
EDIT #2: Doh! I have this awful tendency to assume that everybody has 60Hz power If you're in the UK, or somewhere else with 50Hz power, your capacitor needs to be bigger. For 50Hz, the LTR value is 10nF. Resonant would be 6.5nF. Anyway...
60 Hz is correct
J. Aaron Holmes wrote ...
EDIT #3: Ah, I see it now. You used this (http://www.deepfriedneon.com/tesla_f_calctranscapmatch.html), right? Yep. That's computing the resonant capacitor value. Very bad. Anybody know who runs deepfriedneon? This cap calculator needs to go! Ouch!!
Cheers, Aaron, N7OE
I thought I was trying to get it to resonate so I could get a bigger spark?
Registered Member #1185
Joined: Thu Dec 20 2007, 04:40PM
Location:
Posts: 17
I bought a Terry Filter kit for $80 from the ebay store that sells Tesla coil parts. I will also turn my toroid back over my brother said it looked better with the toroid closer but that could definitely have caused it. Functionality over looks any day.
Registered Member #690
Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616
Yes, I always wondered why we used caps that were larger than resonance on purpose.
However, you have to remember that by "larger than resonance" we don't mean the Primary/Secondary resonance that is the core of any Tesla Coil. We can use any capacitance for this and compensate by tuning the primary.
The resonance we are talking about is the resonance where it takes the capacitor exactly one half-cycle of your mains frequency to fully charge the cap, resulting in maximum possible primary voltage+charging efficiency (thus the 120bps on 60Hz mains, 100bps on 50Hz).
To me it seems all this would do is reduce the primary voltage. I don't know why exactly this is used, but I really cannot argue with results.
Registered Member #1185
Joined: Thu Dec 20 2007, 04:40PM
Location:
Posts: 17
Shaun wrote ...
Yes, I always wondered why we used caps that were larger than resonance on purpose.
However, you have to remember that by "larger than resonance" we don't mean the Primary/Secondary resonance that is the core of any Tesla Coil. We can use any capacitance for this and compensate by tuning the primary.
The resonance we are talking about is the resonance where it takes the capacitor exactly one half-cycle of your mains frequency to fully charge the cap, resulting in maximum possible primary voltage+charging efficiency (thus the 120bps on 60Hz mains, 100bps on 50Hz).
To me it seems all this would do is reduce the primary voltage. I don't know why exactly this is used, but I really cannot argue with results.
OK so that is what that calculator is calculating and We should always go above that I'll re-read the instructions and see if they don't say to go over that. Then I use the bigger caps and ballance the equation off of it.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
If you do the math and determine your phasors it all works out properly:
Here is the transformer article too: that will allow you to calculate your transformer characteristics. However, you do need some kind of Watt meter for these calculations, so things get complicated.
Using an LTR cap does not mean that the capacitor won't charge to the AC peak voltage. Instead, it aims to prevent it from going way beyond that voltage when the gap misfires or is set too wide, etc.
The document provides the resonant and LTR values for many common NST's, both for 60Hz and 50Hz. Actually, the values provided are the nearest value that can be achieved using the indicated number of the popular so-called "Geek Group" caps, but should be close enough in general. The resonant cap values are there just for reference.
Happy coiling!
Jeff, when things are all up and working, please post some pics of your setup!
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transformers keep blowing up for me :-(
So I'm looking for advice.
If you're in the UK, or somewhere else with 50Hz power, your capacitor needs to be bigger. For 50Hz, the LTR value is 10nF. Resonant would be 6.5nF. Anyway...
