Where is plasma globe arc arcing to?

[Jun]

Hi. I've taken apart plasma globe and noticed that there is only one high voltage output and and no grounding. Is it from corona discharge? but I don't think so because voltage is only few kv. Is is from capacitive coupling? but there is no proper grounding.

I've tried to run the globe with flyback and DIY ZVS driver, but it did not run. I even tried connecting the ground wire close but no plasma was established. My flyback runs around 25kHz at 15kV and plasma globe works similar frequency as well. What am I missing?

[davekni]

The ground return is through the line cord.  It takes very little capacitance to the line wires to return 1-2mA at 25kHz.

"Glow discharge" is the best way to describe the streamers inside a plasma globe.  They are typically filled with a mix of xenon and neon.  Here's a thread on my little DIY plasma globe, using argon, since I don't have neon and xenon around, in case it's of interest:
https://highvoltageforum.net/index.php?topic=924.msg6187#msg6187

Are you sure your flyback doesn't have diodes on the secondary winding?  Most flyback transformers were built for CRT monitors/TVs, so include internal diodes.  Their DC output won't work for a plasma globe.

[John123]

Yeah stray capacitive coupling is what's doing it, like a tesla coil secondary and top load capacitance to the surrounding environment. Pretty sure the little flyback inside my plasma globe was AC too. The DC flybacks will charge up that stray capacitance once and that will be that.

Is the flyback you're driving on the ZVS driver one from an actual plasma globe or from a CRT?

[Jun]

I just realised that my flyback has built-in rectifier inside.
But if it's completing the circuit by capacities coupling, then shouldn't the circuity have better grounding? Or just PCB trace enough for high frequency?

[John123]

The stray parasitic capacitances are enough, anything is a capacitor at high voltages!

[alan sailer]

Dave is right. DC will not work on a normal commercial globe.

If you look closely at the globe you will see that there is no electrical feed thru on the globe (unlike a neon tube). The globe works with AC because there is a small capacitance between the flyback lead and the gas inside the globe. It is small (pF's) but at the typical operating frequencies of the flyback (>10Khz) is enough to transmit the milliamps of current needed to create the plasma tendrils. Normally a globe has a black conductive coating inside the stem of the golbe. This is one plate of the capacitor.

The vast majority of flybacks you will find today are DC. AC flybacks began to disappear during the late 60s because the increasing voltage requirements of modern color TVs. The availability of cheaper solid state HV diodes  made it easier to integrate the rectifier diode(s) into the flyback.

Cheers.

[John123]

You could always try overvolting it with a resonant bridge driver, with enough reverse voltage the diodes have a habit of shorting.

[Jun]

Thanks John! That's a clever idea. I don't have any use for DC flyback so I might try that. I would also like to know if air ioniser has AC flyback or not.

[davekni]

Frying diodes in DC flybacks is certainly possible.  It's sometimes difficult to get complete frying.  Diodes often "fry" partially - with reduced breakdown voltage, but not a complete short.  Reply 4 of this thread has my experience with flyback diode frying:
https://highvoltageforum.net/index.php?topic=958.msg6504#msg6504

All the air ionizers I've seen use DC.

[ElectroXa]

I would also like to know if air ioniser has AC flyback or not.

Hi
like davekni said, air ionisers are using DC voltage, thus a DC flyback.
I've an other suggestion to find AC flybacks,  it's to look for ozone generators, as they have an AC flyback 

[MRMILSTAR]

There are AC flybacks available on E-Bay if you look carefully. They usually don't say that they're AC. You have to look at their appearance. A lot of them are NOS but are so old that the insulation is cracking which can probably be prepared with wax. There are some brand new ones also. I bought 2 new AC flybacks a few months ago from E-Bay.