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Registered Member #3076
Joined: Fri Aug 06 2010, 07:45PM
Location: San Francisco CA
Posts: 18
hi all, As for ceramic caps...I hope they work ! When I use enough they seem to keep from blowing up.... They must be lossy, but better than home made ? I made a cap by sandwhich-ing Al foil between heavy brownpaper bag paper soaked in olive oil...haven't tried it yet...not expecting too much...the plastic cup/Al foil thing looks better...
I'll post some pics of my whole setup...I think there are a few things wrong...
For one, isn't a flyback TC a DC TC ? There are diodes in the output....the pulsed DC made me think of it as AC, but Duh....20KHz DC is more like DC ....so I am thinking that reading regular AC tesla stuff is kinda dumb because my primary isn't gonna be tuned right ? It just has to charge to 5 RC's in less time than the secondary's resonant freq....(unsure)
I wrapped a new 5cm by 10cm secondary from AWG 30....
I also plan to read the theory of operation more from friedneon....the whole top load cap is weird since I've done the theoretical calculation in E&M class for a spherical cap with one side at infinity but never was given a reason to use such a thing...I am thinking it is for reactance to bring down the res freq and/or cancel conductance besides just avoiding loss from corona discharge....
thanks for reading ! will try to post pics soon...
Registered Member #1408
Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679
500 turns is rock bottom minimum...some may disagree, but I have yet to be able to tune a coil as well as many here and 500 turns is the lowest I would ever go.
Also - remember you my just stumble into a beautiful AC source (a NST or whatever). However DC TC do exist & preform well. Here is the CAP portion of the JAVATC to get you started in the right direction: Use the appropriate caps: CDE's are the favored items, frankly the best. (illustrated in that little PDF above).
A pretty sharp guy here once wrote the you shouldn't get too hung up in theory to the exclusion of bringing it together and seeing if you get it running. That's NOT to say don't do as much studying as you can - but having the thing in it's physical format will allow you to examine the issues AS YOU LEARN. The corrections will instantaneously lead you down the right road; instead of wondering if you need to go into a direction that entails more work or money than necessary.. That has helped me a great deal because the tuning process MAY make more sense if you have the example in front of you.
Again, just my opinion: if you get a breakout without a top-load you're on the right track. Too much emphasis on a top-load when the coil itself is not functional may not lead you to success & become a exercise in frustration..
I have seen some GREAT coils that had some corona. As long as it doesn't do damage, you can correct that as you learn more & tune as well as design in accordance with what materials you have. Attempting perfection with a project as potentially involved as a TC is not a walk in the park. Once that thing works, no matter it's idiosyncrasies, you'll be fine. Those caps you illustrated are not what you want. The parts for a TC can be free if you hunt them down from existing junk materials. I have made one that cost me zero and worked fairly well for the very low input of power I had on hand.
When asking questions from the more experienced members: have on hand, the specifics of most all dimensions you will see illustrated on JAVATC web site. That way they can provide answers to things that will be necessary for them to know prior to making a determination of weak or missing system elements.
Registered Member #3076
Joined: Fri Aug 06 2010, 07:45PM
Location: San Francisco CA
Posts: 18
hey thanks for the great advice...
I tried the JAVAMMC page, however it only calculates if all data is entered, so I can't just use it for the MMC... :( However, I'm gonna try the cermaic caps i ordered since I spent the $ already and get this thing working. I have seen caps in the computer monitors I harvested my flyback from and will try to swap out when time permits...
I definitely need to check the turn directions on primary and sec .... !!
***Question*** I wasn't grounding my sec in the past attempts. I just had the sec in the middle of the primary and had both leads about 1 cm apart. I am concerned about grounding to the mains ground since I am working in a school lab and don't want to blow anything out due to HV. Any thoughts ?
I am thinking of using a pipe passing through the wall which probably comes from the bathroom next door, as my ground for secondary. My bench power supply is floating and I may tie it to the 3rd prong ground, but that seems not so important.
As well, I'm thinking of using a choke at some point to protect the PS from FB back emf....I don't have a diode tough enough to do HV...
Registered Member #1408
Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679
I'm simply giving you opinion of a newbie: I really want to be clear on that issue out of respect to you & the reality that I am just a hobbyist & learn as I go.
A great deal depends on the power / size of the coil. I have built coils that were small and low powered and didn't ground that outside of the mains. I also built a very small one that I didn't ground the secondary at all (& all was well). When dealing with higher current levels / overall power of the coil I would ground them outside of the household mains; unquestionably. I have ran a little 6kv 20ma coil with no secondary grounding and (IMO) it was safe and functioned well. I believe a great deal depends on the current used and the system as a whole. I would make these decision base on danger to people and items; in that order.
A classic example would be a Vacuum tube Tesla coil (VTTC)* utilizing a MOT. (Or a MOT system in general) Here you may have less than 4000v initially but lethal levels of current. When that sweetheart hits the Primary; you have a very serious issue. Careful, appropriate grounding is a MUST. From both a safety standpoint for both YOU and the household (you don't want to fry your computer, so keep that ground away from the mains ground) & functionality. The responsibility & fun go up proportionately.... Plumbing grounding is a tough call. My gut says make a separate ground as the plumbing is likely to contain elements of the mains ground. In a school situation you have additional responsibilities and there is a chance that even a light level of current could do some damage to a delicate instrument. The decision would be to use an outside ground OR if the level of power is truly small & light; keep the matter contained as is. With a very small display coil, there are methods of containment (a whole subject in itself) without the need to give the coil access to the school's grounding system. Consider the "Terry Filter" if "emf / choke issue" is a concern. I once made a coil and it may have messed up a neighbor's reception. I'll never really know because I stopped taking it outside near his house (& I parted it out anyway)....some of them are just too damn loud.
*My present project; a lot of fun and substantially different from a basic SGTC to be a really new experience.
Registered Member #3076
Joined: Fri Aug 06 2010, 07:45PM
Location: San Francisco CA
Posts: 18
wow thanks QuickSilver for the thoughtful response....I think my coil is gonna be pretty low power overall, but I plan to use a stake in the ground, since I moved my coil Home !
School gave me the power supply since it is old and nobody ever used it but me!!!
I got a spark today off of the secondary so I am excited...it was really small and poor and went away when I disconnected the top load. I think this means that the res freq is pretty hi up. On the Oscope, it was 1.6 MHz, but I don't fully trust that since I'm not sure I took the measurement right...but it probably is too high and I was hitting an 'under tone' so to speak..
Gonna try wrapping a longer secondary when caps come and experiment with top loads and total capacitance. It would be nice to measure my flyback's inductance. I tried a bridge circuit and could not quite line up the two phases. Somewhere around 1.5 mH is what I estimated...if X_C = 1/(wc) and X_L = -wL, assume I get my sec. res freq down to 75KHz... X_L = 707 mho so c = 1/(706*w) => 3nF (w = omega) I haven't thought about phasers in a while if this is wrong feel free to point that out...I forgot how to calculate the cap charge time, hyperphysics web site says time constant at 20KV input is 4ns ...so 20 ns is 50 MHz....no problem charging them fast enough...
these coils grow on people...some professors I told think it is a noise maker and a bane to any HAM operators and squid users trying to get their data...Only one professor thinks it is cool that I do this...I think a master's in engineering may be my calling if I can get my stuff together...
Registered Member #1408
Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679
wannabegeekTC wrote ...
Gonna try wrapping a longer secondary when caps come and experiment with top loads and total capacitance. It would be nice to measure my flyback's inductance. I tried a bridge circuit and could not quite line up the two phases. Somewhere around 1.5 mH is what I estimated...if X_C = 1/(wc) and X_L = -wL, assume I get my sec. res freq down to 75KHz... X_L = 707 mho so c = 1/(706*w) => 3nF (w = omega) I haven't thought about phasers in a while if this is wrong feel free to point that out...I forgot how to calculate the cap charge time, hyperphysics web site says time constant at 20KV input is 4ns ...so 20 ns is 50 MHz....no problem charging them fast enough...
There are some very gifted Electronic Engineers on the Board who would be the better source than me or determining if the calculation of capacitor charge time in your setup is spot on & it's significance to performance. Frankly I don't know of a method to determine a flyback's inductance other than to use a meter. But I do know that you are not alone with the challenges of bridge circuity.....
My personal opinion is that as long as you're responsible & having an enjoyable learning experience, you're on the right track. -=A most sincere "good luck" to you!=-
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flyback tesla coil issues
