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Art

Fri Feb 26 2016, 08:18AM

Registered Member #57369 Joined: Fri Sept 18 2015, 01:24PM
Location:
Posts: 66

Hi Guys :)
The LOPT I was waiting for arrived today, and Iâ€™ve had some success with an arc across the air,
maybe a bit over 7cm with a 12V SLA battery powering a ZVS driver.

My questions...
It makes much lesser an arc from itâ€™s â€œfocusâ€ wire which is actually the stronger HT cable.
When using the â€œscreenâ€ wire a couple of pins under the LOPT were also arcing,
so I bridged them for a better result straight from the screen wire.
Why would the heavy duty focus cable be carrying the lower voltage?

Are the â€œscreenâ€ and â€œfocusâ€ adjustment screws some sort of pot, or variable capacitors to tune the
resonant frequency of their associated windings? I assume the latter because they change the nature of the arc
from a sharp streamer, to something more glowing and not as tight... unless Iâ€™m imagining things!

Is any filter required to protect a flyback transformer as is done with neon sign formers?
I have read these flyback transformers are DC output so must contain some rectifier within them?
This should mean I donâ€™t need extra high voltage diodes to complete a spark gap tesla coil.

Cheers, Art.

Patrick

Fri Feb 26 2016, 08:40AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

these are good questions new people often have. so...

1) the fact you've gotten 7cm spark or arcs is good. I'm not sure if your running it in ZVS mode, others can tell you that.

2) we usually epoxy or in some way prevent the underside pins from arcing/sparking.

3) there are in the cylinder transformer type, with the little box on the side pots, I believe there are LR changes that the TV maker tunes in on for good picture.

4) be careful with short circuits. even though we all like to do it. remember the wire in side is hair-thin, a little to much current and its poof !

5) look here at mine :

ive made some primary side measurements. And here :

there are diodes in series with those HV coils. they divide the windings up to prevent any one section from seeing to much voltage and breaking down. with the diodes you get a pulsing DC output. My oscillograms show a wobbly positive output.

6) Also, the transformers were meant to be part of a SMPS to supply other circuits in the TV.

7) Fiddy has done a great service by sourcing flybacks with just a secondary. no mystery windings or voodoo components epoxied inside. so you can wind your own primary and get AC out.

Art

Fri Feb 26 2016, 10:05AM

Registered Member #57369 Joined: Fri Sept 18 2015, 01:24PM
Location:
Posts: 66

I just got the biggest new LOPT I could find on eBay.
When using the screen wire , which occurs to me the higher voltage (although thinner wire),
every time it arced to the anode, there was also an arc between two of the bottom pins,
so I permanently soldered the two pins together with 1mm copper wire.
Thatâ€™s when I got the bigger arcs from the screen wire to anode.
I presume that joined a couple of secondaries together and improved the turns ratio.

GrantX

Fri Feb 26 2016, 11:02AM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

It sounds like you aren't using the grounded end of the HV coil? One of the pins on the bottom will be connected to one end of the secondary, with the full output between this pin (which can be connected to earth directly) and the thick output wire with the suction cup. There's usually too much resistance due to the HV diodes to measure with a DMM, but I have successfully used a resistor and LED with a 12V battery to determine the ground end of the secondary.

I removed a LOPT from its circuit board recently, multiple pins were earthed for the HV coil, core and internal smoothing cap (or possibly voltage doubler, I've yet to make any measurements).

Art

Fri Feb 26 2016, 01:38PM

Registered Member #57369 Joined: Fri Sept 18 2015, 01:24PM
Location:
Posts: 66

What I think is the other end of the anode coil (the pin at the bottom)
is connected to what I think is the other end of the screen coil.
So I think the turns of both coils are summed for a higher turns secondary.
I could be wrong about that.
Approximately what frequency do these run at?

The focus adjustment on the flyback has some effect on the arc.

Here is is with two batteries in series. I think Iâ€™ve ruined one of the SLAs though by discharging it too much.

Patrick

Fri Feb 26 2016, 07:58PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

That's good. but how many centimeters does it first breakdown at ? those arcs look hot.

Always buy the biggest flyback you can find, that's a good general rule.

jdub1581hv

Fri Feb 26 2016, 08:19PM

Registered Member #55219 Joined: Tue Jun 09 2015, 11:21PM
Location:
Posts: 80

A great overlooked source for lopt's are 'free' projection tv's from Craigslist and other such sites...
They also (most of the time) do not have the "pot's" for adj., are of a good size, and you get an added bonus of the 3way hv splitter, and all the other magnetics/transistors/heatsinks.

The only thing I am unsure about is the internals.. Multiple windings, yes .. but other than that no idea..
I was able to pull 12" FAT white arcs on mine using a Mazzilli ZVS @ 40vdc :)

Also to test, you could put 2 9v bats in series and using diode tester ( put + bat terminal to test pin, neg lead to neg terminal, and pos lead to hv out... helps get over the diode fwd voltage)

Ash Small

Sat Feb 27 2016, 01:10AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Art wrote ...

Approximately what frequency do these run at?

I think it's ~16 kHz, it's a while since I've played with them. PC monitor flybacks possibly run at higher frequencies.

EDIT: running them from a ZVS driver with smaller gap(?) may be different, they are designed for a flyback driver, ie one that gradually rises, then flies back to zero.

Patrick

Sat Feb 27 2016, 03:15AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

The low voltage output winding mirrors the sawtooth of the primary current and, e.g. for television purposes, has fewer turns than the primary thus providing a higher current. This is a ramped and pulsed waveform that repeats at the horizontal (line) frequency of the display. The flyback (vertical portion of the sawtooth wave) can be a potential problem to the flyback transformer if the energy has nowhere to go: the faster a magnetic field collapses, the greater the induced voltage, which if not controlled can flash over the transformer terminals. The high frequency used permits the use of a much smaller transformer. In television sets, this high frequency is about 15 kilohertz (15.734 kHz for NTSC), and vibrations from the transformer core caused by magnetostriction can often be heard as a high-pitched whine. In modern computer displays the frequency can vary over a wide range, from about 30 kHz to 150 kHz.

I don't know what the PWM looks like though.

Art

Sat Feb 27 2016, 01:32PM

Registered Member #57369 Joined: Fri Sept 18 2015, 01:24PM
Location:
Posts: 66

When you say â€œFirst break downâ€ You mean what furtherest distance away? That is about 7cm,
and thereâ€™s a maximum position where sparks will jump and it gets louder.

First results with a spark gap and Tesla coil are not so great,
itâ€™s gets very loud though!
The capacitors are just the quick ones made from foil and OHT transparency for now.
It lights neons in the air at the moment and makes lots of noise,
but not much spark in the air.

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