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Registered Member #2553
Joined: Fri Dec 18 2009, 01:36PM
Location: St Cloud Minnesota
Posts: 97
im planning on building a SSTC. right now im just in the research stage. i know there are many different schematics out there. what im looking for is help finding a schematic for a reliable coil that is not overly complicated and NOT direct mains powered. it would be nice to get feedback from someone who has experience designing and building these solid state coils. thank you!!
Registered Member #2887
Joined: Sat May 29 2010, 11:10PM
Location: Panama City, Panama
Posts: 107
You're going to have a though time, as most of the ones I've seen run on 120v. You could, however, use an isolation transformer to avoid it being connected directly to mains. Don't know if that helps, though.
However, class E tesla coils can run on way lower voltages if that is your goal. For instance,
You can take nearly any of the mains fed SSTC schematics/builds and run them from any voltage lower than mains if you like, I've yet to see one that actually requires full DC buss voltage present in order to operate. You would not get nearly the same output as the builder got if you used less voltage, but that should be common sense. I commonly run my largest 1kW mains-fed SSTC on as low as 15Vac using a $50 variac. Variacs don't give isolation from mains, but they do let you run your equipment on nonlethal voltages.
May I ask what your reason for wanting to avoid mains power is? If it is for safety (don't like working with lethal voltage/current mixes) and large component headroom, I say invest in a variac and choose your input power as you like. If it is to protect your mains from RF, there are many solutions, like isolation transformers and RFI/EMI mains filters.
I have tried a few different schematics so far but none have worked as easily for me as Steve Ward's. I am particularly fond of his antenna to 74HC14 schmitt inverter to UCC37321 & UCC37322 gate drive chip pair to halfbridge topology as it has proven to be cheap, reliable, and robust.
Registered Member #2553
Joined: Fri Dec 18 2009, 01:36PM
Location: St Cloud Minnesota
Posts: 97
EasternVoltageResearch wrote ...
When you say not direct mains powered, is say a 24VAC transformer powered coil okay, even if the 24VAC transformer is powered from 120VAC??
by direct mains powered, i mean rectified mains. i prefer something with a power supply. i have had bad luck with direct mains powered high voltage projects. lots of pops, fire, and exploded mosfets!
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Rectified mains is still directly connected to the mains. There is no isolation with a rectified power supply unless you have an isolation transformer in there.
Registered Member #2553
Joined: Fri Dec 18 2009, 01:36PM
Location: St Cloud Minnesota
Posts: 97
EasternVoltageResearch wrote ...
Rectified mains is still directly connected to the mains. There is no isolation with a rectified power supply unless you have an isolation transformer in there.
thats what im saying. i DONT want direct mains powered.
Registered Member #2553
Joined: Fri Dec 18 2009, 01:36PM
Location: St Cloud Minnesota
Posts: 97
Sigurthr wrote ...
You can take nearly any of the mains fed SSTC schematics/builds and run them from any voltage lower than mains if you like, I've yet to see one that actually requires full DC buss voltage present in order to operate. You would not get nearly the same output as the builder got if you used less voltage, but that should be common sense. I commonly run my largest 1kW mains-fed SSTC on as low as 15Vac using a $50 variac. Variacs don't give isolation from mains, but they do let you run your equipment on nonlethal voltages.
May I ask what your reason for wanting to avoid mains power is? If it is for safety (don't like working with lethal voltage/current mixes) and large component headroom, I say invest in a variac and choose your input power as you like. If it is to protect your mains from RF, there are many solutions, like isolation transformers and RFI/EMI mains filters.
I have tried a few different schematics so far but none have worked as easily for me as Steve Ward's. I am particularly fond of his antenna to 74HC14 schmitt inverter to UCC37321 & UCC37322 gate drive chip pair to halfbridge topology as it has proven to be cheap, reliable, and robust.
my reason is because i have had bad luck with recitifed mains. i built a direct mains powered flyback driver running on rectified 240v. it went up in a ball of fire. it ran for a few seconds. the flyback started on fire and the mosfets exploded. if you are sure this wont happen with a SSTC i will definately build it! here is a link if your interested. could you recommend a sstc schematic that isnt overly complicated?
I can see why that flyback driver failed, it is missing most of the important safety devices.
These are all missing: 1) Gate protection zener diodes / TVS diodes 2) ultrafast body-diode-bypass diodes 3) decoupling caps 4) Gate isolation transformer and DC blocking cap (GDT)
Not having #2 is a BIG issue as whenever the current across an inductor (your primary) stops the inductor creates a high voltage of the opposite polarity across itself. This high voltage can (and often does) exceed the voltage the mosfet or IGBT can handle, and will blow it up. Even if the voltage rating of the transistor is not exceeded, it must absorb this voltage as heat, which can kill it as well. Most switching devices intended for this application have a built in diode, but the diode is too slow to react to the high voltage of the inductor at the frequencies we typically use. The result is a bang and/or fire as the mosfet/igbt shorts out internally and shorts your powersupply to the load, which often overheats it and destroys the load. By placing a very high power ultrafast diode in the same direction as the body diode in parallel with the transistor, we give the high voltage something else to go in to that can safely handle it. Heat is moved away from the transistor, and it is protected from self-destruction.
Also the ratings and values of several components appear to be missing enough headroom for safety. This circuit looks like one that would work but could also just as easily go catastrophically wrong.
I would reccommend you go with Steve Ward's SSTC-5 "mini" tesla coil. Here is the link to it: Just remember that for 240V users you need to use different components for the half bridge side of things. You can leave out the 555 subsection and leave pin 3 of the UCC chips disconnected if you want to cut down on cost and don't care about interuption (doing this makes your coil CW output). I can draw up a "bare minimum" schematic for this design if you like. In the one linked there are still no gate protection diodes, which should always be used if you don't want to blow up your mosfets from inexperience at making gate drive transformers.
240V: Use mosfets with Vds of at least 500V and try to keep RdsON lower than 0.1Ohms. Your bridge (fullwave) rectifier should also be rated for at least 500V (600V is a common value) at >15A and needs to be heatsinked. C12 (filtering cap on rectified mains) needs to be rated for at least 350V (>400 is better). The wire you use for your primary coil needs to also have insulation rated for high voltage use. I use 10AWG 600V hi-temp wire with great success, and it should work fine for 240V as well. All of the wire on your GDT 's secondary side and halfbridge will see the full rectified mains voltage, so it needs to be rated for high voltage as well. I use 600V 22AWG insulated wire.
And lastly, with any halfbridge, you need to use a low-inductance layout, so thick short wires are needed. You don't have to do it "point-to-point" style, it can be done on a protoboard (not breadboard) just as well, but that takes a bit more experience with layout.
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
If you want good performance you're going to need a certain amount of power. If you have that much power, it will be dissipated in a fault condition and start fires, make silicon go boom, etc. It doesn't matter whether you're deriving this power from rectified mains or a car battery or a stack of LiPos (don't do the latter!) Even if you had a $1K+ high-power regulated lab supply, it will be only of limited protection, since your bus capacitors will discharge in case of a bridge failure and probably make your silicon go boom.
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finding a SSTC schematic
