Fiddy
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its from a desktop pc hey? ive got one very similar.
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ArcticMyst Security by Avery
Tesla Coil Build Thread
- Thread starter Sigurthr
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Speedy78
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Yeah. Small cage fan. You should be able to see it aimed at the spark gap in that mock up picture.
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That won't need a very big heatsink at all. Most 78XX are internally current and temperature limited
anyway, so they are almost bulletproof, especially if the fans are also blowing on it. I would however
instead recommend going down to Goodwill™ and picking up an old 12V SMPS wall adapter. The one up
here has like 3 baskets full of them for $2-3 each. Some of them do upwards of 2A. Also, quite a few 12V
fans will run just fine at up to 24V. This has the added benefit of higher speed and more airflow. They will
make a lot more noise, but I doubt that is going to be an issue on a SGTC.
anyway, so they are almost bulletproof, especially if the fans are also blowing on it. I would however
instead recommend going down to Goodwill™ and picking up an old 12V SMPS wall adapter. The one up
here has like 3 baskets full of them for $2-3 each. Some of them do upwards of 2A. Also, quite a few 12V
fans will run just fine at up to 24V. This has the added benefit of higher speed and more airflow. They will
make a lot more noise, but I doubt that is going to be an issue on a SGTC.
Speedy78
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That would be easier. What is a smps and how do i know it's one and not something else?
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SMPS stands for Switch Mode Power Supply. They are much lighter than the old wall transformers. It is
very easy to tell the difference because they are so light.
very easy to tell the difference because they are so light.
Sigurthr
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I'm not sure a SMPS is a good idea; noise from the SG will trip any internal protection circuits on the SMPS. This happened when I tried to use one to power a SG blower fan on an early coil.
1.2A per fan is a heavy load for a 7812, yes they're internally protected but I'd rather the cheap 7812 fail (or better yet put a modest Heatsink on it) than $300 of expensive caps because the 7812 shut down and the fan stopped. At 19v on the input you're burning 7.14Watts of heat in the 7812 drawing 1.2A, and that's for ONE fan. That's a small soldering iron of heat for two fans. Use a modest 'sink and call it good.
1.2A per fan is a heavy load for a 7812, yes they're internally protected but I'd rather the cheap 7812 fail (or better yet put a modest Heatsink on it) than $300 of expensive caps because the 7812 shut down and the fan stopped. At 19v on the input you're burning 7.14Watts of heat in the 7812 drawing 1.2A, and that's for ONE fan. That's a small soldering iron of heat for two fans. Use a modest 'sink and call it good.
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Well, he was going to power the 7812 with . . . an SMPS. Maybe he should just go with one of the heavier
but noise immune iron core wall warts, though it is more difficult to find them above 1A. Or maybe if he can't
find one of those, remove the cord on one of the SMPS and use really short wire runs to help keep
the noise out. Maybe twisting the wires and/or a common mode choke would also help keep the noise out
of the PS. If that doesn't work, maybe a metal enclosure around it or just give up and use 120V fans from
old microwave ovens.
but noise immune iron core wall warts, though it is more difficult to find them above 1A. Or maybe if he can't
find one of those, remove the cord on one of the SMPS and use really short wire runs to help keep
the noise out. Maybe twisting the wires and/or a common mode choke would also help keep the noise out
of the PS. If that doesn't work, maybe a metal enclosure around it or just give up and use 120V fans from
old microwave ovens.
Last edited:
Sigurthr
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Well, he was going to power the 7812 with . . . an SMPS. Maybe he should just go with one of the heavier
but noise immune iron core wall warts, though it is more difficult to find them above 1A. Or maybe if he can't
find one of those, remove the cord on one of the SMPS and use really short wire runs to help keep
the noise out. Maybe twisting the wires and/or a common mode choke would also help keep the noise out
of the PS. If that doesn't work, maybe a metal enclosure around it or just give up and use 120V fans from
old microwave ovens.
It's a lot harder than you think to keep RF out at such close proximity to a classic TC. I used a fully faraday shielded SMPS with lots of input and output side RF bypassing and it still failed. It's why you can't use solid state NSTs for SGTCs. If you want it to work you've got to go full EMI suppression with multistage RLC input mains filtration and series output RLC filtering. With that much iron you're better off just using a stepdown tranny. Curiously I've never had a laptop psu fail even though they're unshielded.
But yeah, I suggested AC fans a while back. Still, there's no reason to not use the DC fans and laptop psu he has already.
Speedy78
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I do have a 3rd AC but they are both just air movers which is fantastic for cooling the large surface of the mmc. I could duct the fan to the spark gap but I still don't think it will be as much or or as fast moving as the air from that little dc fan. It will literally spin itself until the leads from the psu unclip and blow things weighted down of my desk 8 feet away. It's almost strong enough to use as a turbine for a model plane lol.
Now when these devices "fail" what happens?
Now when these devices "fail" what happens?
Sigurthr
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Which devices in particular are you asking about the failure modes of?
Speedy78
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Smps.
Sigurthr
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Ohh, it'l just think there's an over voltage or short and turn off until it is rebooted. Though I've heard of cheap ones misreading the noise as output and cranking the internal oscillator that controls the output to maximum causing it to fry itself and the load. Never had that issue with any of mine but mine are all shielded with failsafes.
Speedy78
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I wonder what's so special with the laptop charger. I plan on using the one from my oneTesla since I have it. It does just fine in the em field.
Sigurthr
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I think the laptops use a fixed frequency oscillator for the Buck and then perhaps a linear regulator for the end output, just an unfounded guess, but they're not very efficient and they do put up with noise very well.
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The ones I've had apart are similar to ATX power supplies. They use more complex (fault tolerant) circuitry
on both the input and output sides. There is usually a PWM chip driving the main switch, such as a
UC3842 or one of the newer ones, plus lots of failsafe circuitry. The little phone chargers are nothing more
than an LC oscillator with a TL431 providing feedback through an opto a lot of the time. If you could find
the right resistor inside the laptop charger, you could probably get it to reduce output down to 12V.
on both the input and output sides. There is usually a PWM chip driving the main switch, such as a
UC3842 or one of the newer ones, plus lots of failsafe circuitry. The little phone chargers are nothing more
than an LC oscillator with a TL431 providing feedback through an opto a lot of the time. If you could find
the right resistor inside the laptop charger, you could probably get it to reduce output down to 12V.
Speedy78
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BGS update.
Got a lesson in series vs. parallel circuits today. Tried to run 3 fans in series and there was enough voltage to spin any of them. Ooops.
Two wires in the back, left wire goes to the nearest NST terminal, right one goes to my tap wire. Two wires up front, the one that crosses in front of the fan goes to the second NST terminal, the second goes to the bottom of the MMC.
Here is a semi better view. Feel free to jump in if any of this is wrong.
Here is the back of the MMC. Front with all the caps is in front of the two fans for cooling. That bottom wire is visable going to the bottom of the MMC.
Top wire from the MMC goes right up through the plywood and is soldered to the very inner turn of the primary.
SO many capacitors!
Got a lesson in series vs. parallel circuits today. Tried to run 3 fans in series and there was enough voltage to spin any of them. Ooops.
Two wires in the back, left wire goes to the nearest NST terminal, right one goes to my tap wire. Two wires up front, the one that crosses in front of the fan goes to the second NST terminal, the second goes to the bottom of the MMC.
Here is a semi better view. Feel free to jump in if any of this is wrong.
Here is the back of the MMC. Front with all the caps is in front of the two fans for cooling. That bottom wire is visable going to the bottom of the MMC.
Top wire from the MMC goes right up through the plywood and is soldered to the very inner turn of the primary.
SO many capacitors!
