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CRT monitor scavenging

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: jackssmirkingrevenge » Mon Jan 24, 2011 10:27 am

Hotwired wrote:Yes the flyback is. Does a good few tens of thousand volts in normal use.


What about the smaller ones?
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Unread postAuthor: Lockednloaded » Mon Jan 24, 2011 10:29 am

I don't know if launchpotatoes.com ships to epoxy land, but for 21$ I got a compact, high-power ignitor that it powered by a single nine volt. I can post some pictures of mine, the website doesn't give a very good scale
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Unread postAuthor: jackssmirkingrevenge » Mon Jan 24, 2011 10:34 am

I know there are ready made options but I'm trying to see if I can make one from the bits I've scrounged first :)

So, after a bit of work with a hacksaw, pair of pliers and a soldering iron :roll: finally got one of the flybacks off.

What's the easiest way to hook them up, possibly with parts I can find on the CRT circuit board itself? The articles I've skimmed through so far are a little confusing.
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Unread postAuthor: Hotwired » Mon Jan 24, 2011 4:54 pm

Hah, turns out I still have mine.

I'll have a fiddle about with it again to refresh my memory.

See if I can get the ozone generator going again.
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Unread postAuthor: motorfixer1 » Mon Jan 24, 2011 7:05 pm

I was toying with the flyback driven ignition source for a while and I found these two sites in my travels: http://www.angelfire.com/80s/sixmhz/flyback.html
http://www.powerlabs.org/flybackdriver.htm
I purchased two of the recomended transistors and played around with the primary winding turns, but wasn't able to get the unit to work. It would be neat to make your own ignition circuit out of a flyback and I will say I havent seen one on here yet, just much talk of them! Good luck!
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Unread postAuthor: Hotwired » Mon Jan 24, 2011 8:16 pm

jackssmirkingrevenge wrote:
Hotwired wrote:Yes the flyback is. Does a good few tens of thousand volts in normal use.


What about the smaller ones?


If there's tiny transformers on your CRT circuit board, say about the size of a fingernail... they are not suitable at all.

motorfixer1 wrote:I was toying with the flyback driven ignition source for a while and I found these two sites in my travels: http://www.angelfire.com/80s/sixmhz/flyback.html
http://www.powerlabs.org/flybackdriver.htm
I purchased two of the recomended transistors and played around with the primary winding turns, but wasn't able to get the unit to work. It would be neat to make your own ignition circuit out of a flyback and I will say I havent seen one on here yet, just much talk of them! Good luck!


Oh I did that, worked fine. I did however use my own transistors and not any of the suggested ones. To be honest most transistors will work if they're the right type and not hugely underspec, details such as the best one for it can be sorted once you have a working circuit.

I bought a lucky dip bag of transistors and almost all worked, to various degrees.

Flyback testing...

The primary coils I found were all on one side. You can check this with a continuity meter or if you don't have one, a battery and a bulb can also check for continuity.

There's more than one coil on the transformer you see, and terminals which are linked together are on the same coil.

Image

You can see the Yellow leads which I had on one winding as the primary winding and the Green leads on another winding for feedback. There's a bit of fiddling about needed to find the best sets of terminals to use for each.

The black lead was on the terminal the HV wire (thickest wire coming off the top) most liked to arc to. There's several it will arc to easily but there's a favourite.



But frankly, those circuits are HIGHLY inefficient for ignition. You can see several references to the transistor roasting itself in there and requiring a massive heatsink.

It's drinking current that's why. You do get a sizzling high frequency spark of course but you have to pay in size, heat and power consumption.

If that's what you want then knock yourself out. But there are more efficient ways to drive the high voltage coil for ignition.

Remember this spark demo?

[youtube]http://www.youtube.com/watch?v=mOpsWctz9wk[/youtube]

There was no mains powered behemoth of a transformer or heat sinked transistor behind it:

Image

Image


The black blob is the mini coil, the yellow is the capacitor and the rest, well that's the driving circuit.


Disposable flash camera circuit charging a 0.22uf metal foil capacitor which jumps a spark gap at a few hundred volts, completing the primary winding circuit for the high voltage transformer which chucks out a few tens of kilovolts on the secondary winding side. All powered by two AAA batteries.


For power consumption, commercial igniters are better but they do it by having weaker slower sparks:

[youtube]http://www.youtube.com/watch?v=LhM_c6YoZkc[/youtube]

Mind you when I say they are better I have had one of mine going flat out for half an hour with plenty of life in the batteries when it was turned off so it hardly drinks energy.


Here by the way is the same flyback but rigged to one of my potted capacitor circuits running on 2xAAA. The slow rate of spark is due to each discharge being manually tapped out with a screwdriver, with a proper spark gap it can be the same high rate as the mini circuit above:

[youtube]http://www.youtube.com/watch?v=sBZ0J23sXzg[/youtube]

I'm afraid it's not best quality - I needed a third hand really and something better than a keyfob camera.

But you can see the capacitor is being discharged into two terminals on the bottom and a wire from the HV output is arcing with help from a screwdriver to its return terminal.
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Unread postAuthor: jackssmirkingrevenge » Mon Jan 24, 2011 10:05 pm

Thanks for all that.

Hotwired wrote:To be honest most transistors will work if they're the right type and not hugely underspec, details such as the best one for it can be sorted once you have a working circuit.

I bought a lucky dip bag of transistors and almost all worked, to various degrees.


So, take out transistors and resistors from the CRT board (I think they are transistors, vague recollections of my physics teacher referring to "three legged beasts" :roll:) and have a play :D

The primary coils I found were all on one side. You can check this with a continuity meter or if you don't have one, a battery and a bulb can also check for continuity.


I actually have a continuity meter, is this what I need to do?

But frankly, those circuits are HIGHLY inefficient for ignition. You can see several references to the transistor roasting itself in there and requiring a massive heatsink.

It's drinking current that's why. You do get a sizzling high frequency spark of course but you have to pay in size, heat and power consumption.

If that's what you want then knock yourself out. But there are more efficient ways to drive the high voltage coil for ignition.


I just want a big enough spark to evaluate the power potential of a 28x mix for static testing, not too concerned about efficiency and bulk at this point. Also, I have heatsinks. And fans :)

I'm afraid it's not best quality - I needed a third hand really and something better than a keyfob camera.


Lets face it, if you had a third hand, you wouldn't be filming high energy sparks ;)
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Unread postAuthor: Hotwired » Mon Jan 24, 2011 10:32 pm

jackssmirkingrevenge wrote:So, take out transistors and resistors from the CRT board (I think they are transistors, vague recollections of my physics teacher referring to "three legged beasts" :roll:) and have a play :D


No harm in it at any rate except to patience if they don't work. Tricky bit with transistors you don't know is which legs are which and if they're npn or pnp types. They have codes on them you can look up though.

The primary coils I found were all on one side. You can check this with a continuity meter or if you don't have one, a battery and a bulb can also check for continuity.


jackssmirkingrevenge wrote:I actually have a continuity meter, is this what I need to do?


Yes, that's a more organised way of going about it, I just checked which terminals linked up personally and then applied voltage until the HV line gave off the best arc.
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 25, 2011 3:03 am

Hotwired wrote:No harm in it at any rate except to patience if they don't work. Tricky bit with transistors you don't know is which legs are which and if they're npn or pnp types. They have codes on them you can look up though.


I'll see what there is before easing them out of the boards maybe you can point me to the most suitable one. I have a couple of modems, PC power supplies and CD drives in the scrap bit, any particular one of those likely to have the right components?

Yes, that's a more organised way of going about it, I just checked which terminals linked up personally and then applied voltage until the HV line gave off the best arc.


Better go the organised way, I don't want to fry anything. Rather there are economic benefits to not frying anything :roll:

As to a more permanent solution, this from LaunchPotatoes.com is what Lockednloaded was referring to, right? I would think the USG offering is pretty much the same thing?

Another question - which may or may not make sense - in the case below, would the spark still prefer to arc across the external gap between the schrader and electrode, even if I was feeding it higher energy than a piezo?
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Unread postAuthor: ilovefire » Tue Jan 25, 2011 4:04 am

jackssmirkingrevenge wrote:Another question - which may or may not make sense - in the case below, would the spark still prefer to arc across the external gap between the schrader and electrode, even if I was feeding it higher energy than a piezo?


you might be able to get away with a few more times mix but i have still had problems with my high energy igniter externally arcing
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why make it if it dosent shoot?
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Unread postAuthor: Insomniac » Tue Jan 25, 2011 4:21 am

JSR, a camera flash does discharge the ~300V from the camera capacitor straight through the xenon flash tube. However, under normal circumstances this low a voltage will not jump the gap.

How it works is this: On your camera flash board, first off a small transformer and transistor plus some other electronics tomfoolery boosts the voltage of the battery to the ~330V or so to charge the main photoflash capacitor. At the same time, it also charges (Via a very high value (megaohm or so) resistor), a very small 0.22uF metal film capacitor.

The main capacitors leads are directly soldered to either end of the flash tube. There's no switching or circuitry between them, there's always a ~300V potential across the flashtube when the cap is charged.

When you tell the circuit to fire, a mechanical switch (in disposable cameras), or a solid-state switch in higher end cameras, discharges the little 0.22uF capacitor through a second transformer. This boosts the voltage from ~300 to several thousand volts. One lead from this transformer leads to a metallic plate (the reflector in disposable cameras) located right behind the flash tube. This high voltage pulse causes the gas in the tube to ionise, which drastically lowers its resistance... meaning that the main charge of the photocap, at ~300V or so, is now able to jump the gap, producing the huge flash.

The high-value resistor between the main cap and the little trigger cap prevents the main capacitor from discharging through the little trigger transformer, which would of course cause problems... :wink:
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 25, 2011 5:05 am

ilovefire wrote:you might be able to get away with a few more times mix but i have still had problems with my high energy igniter externally arcing


Figured, was being mindlessly optimistic as usual :)

Insomniac wrote:JSR, a camera flash does discharge the ~300V from the camera capacitor straight through the xenon flash tube.


Thanks for the clarification I have such a circuit somewhere, will try to retrieve it and see if it's usable.

Any word on whether power supplies (the sort of stuff that converts domestic AC to 6-12V DC) might contain suitable components?

... though to be honest at this point I'm very much leaning towards the "plug and play" offerings from our benevolent sponsors...
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Unread postAuthor: Insomniac » Tue Jan 25, 2011 5:32 am

You can take the transformer out of a standard 'wall wart' power supply, and wire it backwards with some method of pulsing ~6V or so through it, and you can get them to jump up to around a 5mm gap. However they arn't built for this kind of voltage, so I always end up with them arcing internally in very short order. And JSR, remember that while a disposable camera circuit can coax the 300V or so to jump the xenon tube, the best you will get in open air (even with the trigger circuit) will be a couple of mm. Making the issue more annoying is that the very powerful, high-current arc will tend to melt away the electrodes a bit, so you'll have to keep readjusting them. Not ideal for a cartridge.
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 25, 2011 6:20 am

Insomniac wrote:the very powerful, high-current arc will tend to melt away the electrodes a bit, so you'll have to keep readjusting them. Not ideal for a cartridge.


I imagine this will be true of any high voltage ignitor, hmmm... this complicates the issue somewhat given my love for epoxy encased unservicable launchers...
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Unread postAuthor: Insomniac » Tue Jan 25, 2011 6:51 am

No. It's only true if you're also delivering a very high current as well. Well, all arcs are going to wear away at the electrodes to some degree, but, for example, something like a grill ignitor can sit sparking away for a very long time before any significant amount of the electrode wears away... notice that when you spark a piezo, you only see the blue arc, and no bright orange metal sparks? Contrast this with what happens when you allow a camera capacitor to discharge:

Image

See the difference? :D
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