SSTC primary coil specifications
Thomas, Fri Sept 01 2006, 01:46AMNow I recently started a thread bridge input voltage, however, that did not cover everything. So, I just need some clarification. How important is the amount of inductance in the primary coil. I've seen some designs by Easternvolt where his coils have many turns, around 18... or so. However, on the contrary Steve's designs have approx. six or so turns. I don't clearly understand the amount of inductance in the SSTC's case. Does the amount of primary coil turns dictate the amount of current drawn in a coil? I've decided to use about 18 and my coil runs very cool and consumes about 3 amps at 120Vac. I don't clearly understand the amount turns deal, since it's not an LC circuit. Now I figured that the less turns the less resistance present in the circuit, so the more current drawn, therefore, the greater power consumed by the driver circuit (bigger output power fomr secondary). Now how does this low inductance effect my coil's preformace. It should have a greater output current and voltage right? I don't seem to see much of a differnce from removing 6 turns (12 turns present in the circuit). In my case specifications aren't necessary to me. I need to understand the logic behind this. Does anyone have any good sites or short an painless explanations?
Also one last question; what is optimal for the primary coil? Using copper tubing or wrapping 12AWG wire? I've seen people use either for SSTCs, but are there any gains or losses involved with this.
Oh I think this topic should be added in HVWIki
I checked but could find anything, same with google 
no one seems to really include much about this topic.Thanks for all your help,
Tom
Re: SSTC primary coil specifications
..., Fri Sept 01 2006, 02:29AM
I am no expert, but having spent the last 2 days failing at making a decent sstc (it started out well, but as time progressed my sparks got shorter instead of longer ) I can say that removing turns does increase current draw, as does increasing coupling (smaller diameter former, lowering secondary) and of course makes sparks longer. Well at least with the coil I was messing with...
As to the type of wire, so long as it doesn't overheat you should be fine. With only 400w coming in you could get away with 20awg wire before it overheats, you should be fine with 12awg. for normal sstc's the number if turns isn't critical like in sgtc's, vttc's, drsstc's, or oltc's, as you aren't making a tuned circuit, you are only feeding energy to the secondary.
..., Fri Sept 01 2006, 02:29AM
I am no expert, but having spent the last 2 days failing at making a decent sstc (it started out well, but as time progressed my sparks got shorter instead of longer
) I can say that removing turns does increase current draw, as does increasing coupling (smaller diameter former, lowering secondary) and of course makes sparks longer. Well at least with the coil I was messing with...As to the type of wire, so long as it doesn't overheat you should be fine. With only 400w coming in you could get away with 20awg wire before it overheats, you should be fine with 12awg. for normal sstc's the number if turns isn't critical like in sgtc's, vttc's, drsstc's, or oltc's, as you aren't making a tuned circuit, you are only feeding energy to the secondary.
Re: SSTC primary coil specifications
Reaching, Fri Sept 01 2006, 04:45AM
after building several successful sstcs i can tell you that the wire thickness is important too, it has nothing to do with overheating, my coils seemed to perform better with thicker wire on the primary , i think it has something to do with the surface area of the wire, the more the better. the turns ratio is up to you and you have to find it experimentally but youre right, the more turns the less current flows. in many of my sstcs i use around 7-8turns with 6mm² wire on 230volt ac drawing 1,5A with a halfbridge, . for my fullbridge sstcs i use 13 or 15 turns, also doubled the turns for a fullbridge, current draw here is 1,5A but with the doubled voltage in cause of the fullbridge so theoretically doubled sparklenght, but only in theory, the sparks are only 1/3 longer compared to a halfbridge, (this means only halfwave rectified sstcs) i rate my sstcs so that 1/10 current flows through the mosfets as seen in the datasheet, so the mosfets stay alive and very cool. wind some 10 turns on a former and measure the current draw while testing less turns and when you get the 1/10 current then youve found a good compromise between sparklneght and mosfet life
Reaching, Fri Sept 01 2006, 04:45AM
after building several successful sstcs i can tell you that the wire thickness is important too, it has nothing to do with overheating, my coils seemed to perform better with thicker wire on the primary , i think it has something to do with the surface area of the wire, the more the better. the turns ratio is up to you and you have to find it experimentally but youre right, the more turns the less current flows. in many of my sstcs i use around 7-8turns with 6mm² wire on 230volt ac drawing 1,5A with a halfbridge, . for my fullbridge sstcs i use 13 or 15 turns, also doubled the turns for a fullbridge, current draw here is 1,5A but with the doubled voltage in cause of the fullbridge so theoretically doubled sparklenght, but only in theory, the sparks are only 1/3 longer compared to a halfbridge, (this means only halfwave rectified sstcs) i rate my sstcs so that 1/10 current flows through the mosfets as seen in the datasheet, so the mosfets stay alive and very cool. wind some 10 turns on a former and measure the current draw while testing less turns and when you get the 1/10 current then youve found a good compromise between sparklneght and mosfet life
Re: SSTC primary coil specifications
Marko, Fri Sept 01 2006, 12:56PM
For maximum power transfer between primary coil and secondary you need to match their impedances. Impedance of secondary at resonance is equal to it's AC resistance.
Scenically, if you use only one primary turn on big secondary, you will be inducing ''too high'' voltage on secondary impedance with small current, making voltage drop across it small; similary, if you use big number of primary turns voltage induced on secondary impedance will be too low and all available current will not be used.
Coupling and input voltage also plays a role here. Halfbridge SSTC may use 2x less primary turns than fullbridge of same power, or coil with lower Z (thicker wire) secondary) may need more turns for impedance amtch, and etc.
SInce my explanations are n40b you should look at richie burnett's site about this, and here are some useful equations I never use (I just try different numbers of turns until I find the best, if something blows up I replace it etc.)
Marko, Fri Sept 01 2006, 12:56PM
For maximum power transfer between primary coil and secondary you need to match their impedances. Impedance of secondary at resonance is equal to it's AC resistance.
Scenically, if you use only one primary turn on big secondary, you will be inducing ''too high'' voltage on secondary impedance with small current, making voltage drop across it small; similary, if you use big number of primary turns voltage induced on secondary impedance will be too low and all available current will not be used.
Coupling and input voltage also plays a role here. Halfbridge SSTC may use 2x less primary turns than fullbridge of same power, or coil with lower Z (thicker wire) secondary) may need more turns for impedance amtch, and etc.
SInce my explanations are n40b you should look at richie burnett's site about this, and here are some useful equations I never use (I just try different numbers of turns until I find the best, if something blows up I replace it etc.)
Re: SSTC primary coil specifications
Thomas, Sat Sept 02 2006, 02:37AM
I just can't seem to break the 10" barrier, my coil is 3.5" wide and 13" high (1200 turns). I tried 5 turns and the output was much smaller. At 16 turns it was around the 10" range and the same for 18 turns. I hooked up my ammeter and the current drawn was pretty much the same for either 5 turns or 16. It drew around 3A at 18 turns and at 4 turns it only drew 4A at max, but it was mailly around 3A, I even switched my 10A fuse with a 5A and it never blew. I checked the site you posted and I didn't realy understand how to do a impedance match. How are you guys getting 1600W SSTCs. I rated mine for high currents, but I just can't seem to get them. It's also a bit hard to turn with the pots, since when i touch the pots with my tool I tend to act like an antenna messing up the signal.
Anyway thanks everyone
-tom
Thomas, Sat Sept 02 2006, 02:37AM
I just can't seem to break the 10" barrier, my coil is 3.5" wide and 13" high (1200 turns). I tried 5 turns and the output was much smaller. At 16 turns it was around the 10" range and the same for 18 turns. I hooked up my ammeter and the current drawn was pretty much the same for either 5 turns or 16. It drew around 3A at 18 turns and at 4 turns it only drew 4A at max, but it was mailly around 3A, I even switched my 10A fuse with a 5A and it never blew. I checked the site you posted and I didn't realy understand how to do a impedance match. How are you guys getting 1600W SSTCs. I rated mine for high currents, but I just can't seem to get them. It's also a bit hard to turn with the pots, since when i touch the pots with my tool I tend to act like an antenna messing up the signal.
Anyway thanks everyone
-tom
Re: SSTC primary coil specifications
Wilson, Sat Sept 02 2006, 10:30AM
My SSTC seems to be the opposite to yours Thomas....I'm already getting a 4A current draw at 75VDC input. not too sure if that will remain constant til 300VDC in. ...
The coupling on my coil is quite high, and i'm finding there isn't too much difference in current draw between 8 and 4 primary turns. the latter seems to give better streamers too.
Wilson, Sat Sept 02 2006, 10:30AM
My SSTC seems to be the opposite to yours Thomas....I'm already getting a 4A current draw at 75VDC input. not too sure if that will remain constant til 300VDC in. ...
The coupling on my coil is quite high, and i'm finding there isn't too much difference in current draw between 8 and 4 primary turns. the latter seems to give better streamers too.
Re: SSTC primary coil specifications
Steve Ward, Sat Sept 02 2006, 09:32PM
Actually, the plasma at the topload acts like a constant current sink mostly, so it may very well stay at about the same current draw, independent of the voltage input. My largest SSTC draws about max current at maybe 1/4 the input voltage. The current only goes up maybe 2-3A after that (talking 30A draw at 280VAC...).
Steve Ward, Sat Sept 02 2006, 09:32PM
not too sure if that will remain constant til 300VDC in. ...
Actually, the plasma at the topload acts like a constant current sink mostly, so it may very well stay at about the same current draw, independent of the voltage input. My largest SSTC draws about max current at maybe 1/4 the input voltage. The current only goes up maybe 2-3A after that (talking 30A draw at 280VAC...).
Re: SSTC primary coil specifications
Thomas, Sun Sept 03 2006, 03:02PM
Odd thing I ended up going all the way back down to six turns again, but instead of wraping the wire together i left it spaced out over the primary's six inch coil form. This for some reason geatly help. At six turns I seem to get a lot of steamers that are about 13" high and ones that branched outward. I guess this is good, but I want to play around a little more before setting up a permenant primary coil.
Thomas, Sun Sept 03 2006, 03:02PM
Odd thing I ended up going all the way back down to six turns again, but instead of wraping the wire together i left it spaced out over the primary's six inch coil form. This for some reason geatly help. At six turns I seem to get a lot of steamers that are about 13" high and ones that branched outward. I guess this is good, but I want to play around a little more before setting up a permenant primary coil.
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