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CanDo

Wed Jan 23 2008, 11:31PM

Registered Member #1259 Joined: Wed Jan 23 2008, 09:13PM
Location:
Posts: 3

Hey guys,

Well, I've never done anything related to HV before, and am hoping to not kill myself in the process of learning; looks like a lot of fun though, and will be needing some skills for a project in a few months.

I'm making a Jacob's ladder with a 16" color CRT monitor right now with mixed success. I simply cut the lines from the flyback transformer (one from the top of the tube, and two from the back), and put them on each side of the ladder (nothing else was touched). This was great for about thirty seconds when all worked fine. Then the smoke started - one resistor on the circuit board blew. No problem, I'll bypass it. That worked fine until the next resistor blew, and then I was out of alligator clips.

To make a long story short, can I feed 120 straight into the flyback? If so, does polarity matter? Also, can the flyback store any charge such as when power is disconnected (preliminary experiments say no)? Any other help would be great.

Thanks very much,

CanDo

Shaun

Wed Jan 23 2008, 11:42PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

You need a specialized (yet still simple) circuit to drive your flyback. Just take a look at a few flyback-related threads in the High Voltage forum. The most popular drivers are the classic yet horrible 2N3055 driver, better would be the ZVS "Mazilli" driver or 555 driver.

You may be interested in jmartis's improved single-transistor driver; I'm sure he'll chime in with details, or you could check out his thread.

Andyman

Wed Jan 23 2008, 11:42PM

Registered Member #1083 Joined: Mon Oct 29 2007, 06:16PM
Location: Upland, California
Posts: 256

Well, for starters, you definitely do NOT want to feed it straight from the outlet. You'll trip your breakers and fry the flyback. The flyback runs on high frequency and has 2 small primaries. The primaries have nowhere NEAR enough resistance to withstand the kind of current from the outlet. Also the core is ferrite which works poorly with low frequency ac and has two spacers between the halves which makes it even worse for LF. The transformer runs on a square wave at around 22kHz (I think).
You need the transistor and a few other components from the original board. Do a google search for single transistor Flyback driver and you should get some good results for a schematic of the circuit you need to power it.

CanDo

Thu Jan 24 2008, 12:45AM

Registered Member #1259 Joined: Wed Jan 23 2008, 09:13PM
Location:
Posts: 3

Thanks guys! I'll be checking this out.

In the meantime I stumbled upon this from

wrote ...
The high voltage will come out of the fat wire from the top of the flyback-usually connected to the CRT with a suction cup. You will not be able to locate the high voltage return pin with a multimeter. The only way to do it is to bring the high voltage line down to the pins and whichever one it arcs like mad to is the one yer looking for. Try to stay away from arcing to any of the pins used for coils. High voltage is not so good for your transistor or power supply.

Perhaps I shouldn't be using the "wires from transformer to back of tube" at all, but rather, should connect one side of the ladder to one of these arcing pins on the circuit board. Perhaps my problem could be bypassed. Probably not, be we shall see.

CT2

Thu Jan 24 2008, 02:26AM

Registered Member #180 Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187

If you didn't blow anything up and didn't remove anything, all you need to do is remove the HV lead (big red one as you found out) and then for your other lead use a ground from anywhere in the case. I did this befor but my circuit died after awhile like yours, but no smoke it just started arcing on the board...

Shaun

Thu Jan 24 2008, 03:16AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

That single transistor circuit you linked to is known to be very bad...at any reasonable power level the transistor will get very hot very fast. It is simple, and all the parts are stocked at Radioshack, but when you keep having to shell out over 3 dollars each for new transistors, you get tired of it real quick...

Myke

Thu Jan 24 2008, 06:16AM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

...and that's why you go with the ZVS flyback driver.

This is from the old forum and has lots of usefull information on it

Conundrum

Thu Jan 24 2008, 10:44AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

hehe.. or the less annoying method is to use a small lighting transformer of the switch mode variety. As long as you are careful the 11V or so output at HF will drive the flyback nicely even using the original winding(s).

i did this and as long as you make sure the current stays below a reasonable limit you should be fine.

hope this helps. -A

flannelhead

Thu Jan 24 2008, 12:49PM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

The ZVS circuit is good, but it's also dangerous (and you wasn't willing to fry yourself, right?). If I were you, I would try a 555 driven circuit. It'll give you nice results, it's easy to get working and it's not so dangerous. Here is a good 555 circuit:

(preferably the second schematic from the top, it's more reliable)

Myke

Thu Jan 24 2008, 03:18PM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

If you run the ZVS flyback driver at 12V then it should be fine. Sure it can be dangerous but if you are careful not to touch the HV output then it's fine.

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