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Registered Member #3395
Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193
[quote]
OK, I get what you are saying! Yes, the high end of the flyback arced to the table and ended up on the inductor as an attempt to get to ground which was the '-' of the SLA bank, correct? What suprises me though is that nothing went pop as it arced very close to the circuit. Maybe the arc bypassed several components and went straight ground which is likely with 20kV. Although there is another strange thing: when the incident occured I'm sure I was zapped multiple times from the switch BEFORE it was turned off. Taken that the cold end of the flyback is grounded to the SLA bank it shouldn't arc to me and go through my body, should it? I will use a better switch next time but I'm skeptical that the voltage still wants to go to ground through me. I don't see why it would shock me if it's already grounded?
Yes, Xray I guess I am a newbie but I DO know what to do and what not do and I exercise safety precautions wherever possible so I'm not stupid (not that you ever called me stupid). I am open to learn things about HV as I would like to expand my knowledge in electronics.
probably dont have that much wisdom when it comes to complaining haha. Anyway, thanks for the help.
Hopefully I can arc with the ZVS without being stressed or nervous of these problems...:-)
Registered Member #3904
Joined: Sat May 21 2011, 10:32AM
Location:
Posts: 28
Taken that the cold end of the flyback is grounded to the SLA bank it shouldn't arc to me and go through my body, should it?
Did you receive a static shock or did the arc actually land on you? I'd expect to get the odd shock when you first touch ground with so many charged particles flying around. Try touching something else that's grounded after having it running for a while.
After you turn it off, you'll probably also get a minor zap if you touch the high output then ground and also the low output then ground (if the low output isn't grounded). You can tell from this that one is above ground and the other below ground.
Unless you want masses of corona coming from the high output, I'm not sure how much there is to be gained from grounding the low. It's the potential difference between the two wires and the current that determines arc length, not the voltage relative to ground.
Registered Member #1081
Joined: Sun Oct 28 2007, 08:04PM
Location: Minsk Belarus
Posts: 12
Józef C :I've attached a schematic for you here.
You need some fast diode (hot wire)for get +30kV DC. End ground cold wire (- 30KV DC) w'll be posible. Any case - ground cold wire with PP capacity 1KV 0.047 mkF to (-) Power suplay unit.
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
Jamie Cansdale wrote ...
Unless you want masses of corona coming from the high output, I'm not sure how much there is to be gained from grounding the low. It's the potential difference between the two wires and the current that determines arc length, not the voltage relative to ground.
Regards, Jamie.
Standard flyback transformers are wound with one side of the hv secondary winding (the "low" end) physically very close to the core. Because of that fact, the low end must be grounded, or else arcing to the core and to other terminals will occur. His schematic diagram shows some sort of transformer that has both secondary ends as hot leads for the hv output (differential mode). That is very unusual, but I suppose there might exist that type of transformer for some special application. Either that, or it was incorrectly drawn.
Registered Member #3904
Joined: Sat May 21 2011, 10:32AM
Location:
Posts: 28
Xray wrote ...
Standard flyback transformers are wound with one side of the hv secondary winding (the "low" end) physically very close to the core. Because of that fact, the low end must be grounded, or else arcing to the core and to other terminals will occur.
Thanks for the explanation. That probably explains why I've killed or maimed a few flybacks! ;)
If I simply clipped the low of the secondary winding to the core, would that also protect it? Obviously the primary winding would need to be well enough insulated to cope with the core floating below ground. I'm trying to think what other issues there might be...
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
Jamie Cansdale wrote ...
If I simply clipped the low of the secondary winding to the core, would that also protect it? Obviously the primary winding would need to be well enough insulated to cope with the core floating below ground. I'm trying to think what other issues there might be...
If you connect the low lead to the core (and you should) then that would cause the core and the low end of the secondary to be at the same electrical potential, thereby eliminating any arcing between the two, but the core will still be "floating" relative to other parts of the circuit, and to your own body! With an AC type of flyback, you can get by this way so long as the primary winding is sufficiently insulated. If you are using a DC flyback, there is the issue of other windings that may be a problem. Even if you attached the low end of the hv secondary to the core, there still could be a problem with arcing between the terminals of the other windings. With experience, you will learn what works and what doesn't work. And sometimes these lessons can be painful if you get zapped!
Registered Member #3395
Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193
Xray wrote ...
Jamie Cansdale wrote ...
If I simply clipped the low of the secondary winding to the core, would that also protect it? Obviously the primary winding would need to be well enough insulated to cope with the core floating below ground. I'm trying to think what other issues there might be...
If you connect the low lead to the core (and you should) then that would cause the core and the low end of the secondary to be at the same electrical potential, thereby eliminating any arcing between the two, but the core will still be "floating" relative to other parts of the circuit, and to your own body! With an AC type of flyback, you can get by this way so long as the primary winding is sufficiently insulated. If you are using a DC flyback, there is the issue of other windings that may be a problem. Even if you attached the low end of the hv secondary to the core, there still could be a problem with arcing between the terminals of the other windings. With experience, you will learn what works and what doesn't work. And sometimes these lessons can be painful if you get zapped!
If you ground both the secondary and core that eliminates the potential its floating at, doesn't it? If I ground just the flyback cold, will it stop arcing to the core?
Ok, I will use a better insulated switch so I don't get zapped next time. Thanks for your help.
Yes, I usually got the minor zap when I turned it off but I think a better insulated should help prevent the problems. I don't think the flyback was producing 30kV, more like 15-20kV.
Taken that the flyback cold is now grounded to the negative end of the SLA bank, is everything safe now? Or are there parts still floating?
Just thinking of making a high current ZVS out of a flyback core and litz wire before I move back to flybacks.
Registered Member #3904
Joined: Sat May 21 2011, 10:32AM
Location:
Posts: 28
Xray wrote ...
If you are using a DC flyback, there is the issue of other windings that may be a problem. Even if you attached the low end of the hv secondary to the core, there still could be a problem with arcing between the terminals of the other windings.
I've just tried soldering a wire across all the terminals at the base of the flyback and then connecting it to the core. This will remove any possibility of arcing between the terminals. There appears to be some extra capacitance between the high voltage terminal and the base of the transformer now. When it sparks there is quite a pop. I wonder if this is a good sign?
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
Jamie Cansdale wrote ...
Xray wrote ...
If you are using a DC flyback, there is the issue of other windings that may be a problem. Even if you attached the low end of the hv secondary to the core, there still could be a problem with arcing between the terminals of the other windings.
I've just tried soldering a wire across all the terminals at the base of the flyback and then connecting it to the core. This will remove any possibility of arcing between the terminals. There appears to be some extra capacitance between the high voltage terminal and the base of the transformer now. When it sparks there is quite a pop. I wonder if this is a good sign?
Your flyback probably won't work now that you've shorted out those windings. By doing so, you've created a direct short dircuit across those windings which would prevent the transformer from producing high voltage. It will likely draw a lot of current from your ZVS driver and damage the FETs.
If you are getting corona or arcing on those extra terminals, try to insulate them by covering them with heat-shrink tubing, and then coat them with a thick layer of Silicone. Wait until the Silicone is completely dry before powering your ZVS up again.
Registered Member #3904
Joined: Sat May 21 2011, 10:32AM
Location:
Posts: 28
Xray wrote ...
Your flyback probably won't work now that you've shorted out those windings. By doing so, you've created a direct short dircuit across those windings which would prevent the transformer from producing high voltage. It will likely draw a lot of current from your ZVS driver and damage the FETs.
If you are getting corona or arcing on those extra terminals, try to insulate them by covering them with heat-shrink tubing, and then coat them with a thick layer of Silicone. Wait until the Silicone is completely dry before powering your ZVS up again.
That's what I thought initially as well. I'm now wondering whether the sparking was actually due to capacitive coupling and not because the terminals were taps of the high voltage winding. The other terminals are maybe for the original primary winding, the CRT heater and other voltages the monitor it came from needed. I wonder if it's better to have these all tied together, rather than having charge that isn't being used moving around inside the transformer?
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Dangerous ZVS Driver 'floating' at 30kV+ ungrounded - Safety advice please!
