giga fet
science_geek
Posts: 247
i need a fet or several that can handle 400 to 500 amps that can be switched with the propellor, do any of you guys know of anything that will do. could i run a bunch of small ones in parallel and have them all switch at once, any info is helpful
Comments
You might want to leave the lab and push the button over the internet.
You haven't mentioned how many times per second you want to do this and I don't understand why you don't just use relays, but
please proceed and get it on video!!!
There is absolutely nothing wrong with blowing things up as long as you get it on video... and no-one gets hurt
Rich
I hooked up a piddly little FET wrong and nothing happened except that I melted the plastic on my jumper and zapped my Prop in a way that hasn't yet been described in this forum[noparse]:)[/noparse]
Other issues: When you switch that amount of current quickly, you create huge magnetic fields that can induce currents all over the place, frequently back in the control circuitry that's very sensitive to small voltages and currents ... again part of the art involved ... trying to avoid trashing the rest of the system.
Only 31nF gate capacitance. $54 from DigiKey.
Post Edited (Mike Green) : 9/15/2008 3:22:12 AM GMT
You'd probably need one for each of the 220A power FETs. Again, I don't have the experience to suggest how to make sure the timing would work out so they'd all switch quickly enough. You really want them to turn on and off quickly to minimize the power dissipation.
Frankly, I wouldn't touch this topic with a ten-foot pole.
-Phil
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'Still some PropSTICK Kit bare PCBs left!
Thanks. Well said. I was trying to illustrate with real world examples, that this sort of thing is complex, expensive, with many hidden pitfalls and, absolutely, extremely dangerous. I have no idea what sort of power source he may be thinking about. Currents on this order of magnitude are commonly found in large arc welders, larger home power distribution panels, not to mention commercial and industrial power distribution systems. The lower voltage systems can produce spattering molten metal, dangerous amounts of localized heat. The arc heat can cause blindness without appropriate protective gear. Higher voltages can kill instantly. We're talking large amounts of energy here.
Phil is absolutely correct.
I'm guessing here that you are looking into a do-it-yourself EV (Electric Vehicle) options.... If that is the route that you are going, then there are several controllers out there designed to do what you want. Still dealing with that much current can kill you if you don't know what you are doing. Even if you do know what you are doing, a slight mishap (working late hours, etc.) can be lethal to yourself or someone else. If you are dealing with an EV controller, I haven't even mentioned the voltage levels.... typically 144 Volts @ 500 Amps.... You've got 72,000 Watts to deal with when something goes wrong !!!
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
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It might be the Information Age but the Eon of Ignorance has yet to end.
Even at 480v its nasty, it will vaporize your tools and you can imagine what it would do to a human.
It was plain *** dangerous to work on hot starters and required complete concentration because you do not mess around because you either die or get horribly maimed should you make a mistake.
Did you see the cables that are used in cars to power the starter motor ?, well you will need thicker ones, and with better insulation, that kind of stuff... 35um copper does not cut it.
Be careful, train yourself. It is possible there are courses at the university that you can take. Electricity is treacherous because you do not see it.
Ken Whitten is a personal friend of mine, and I encourage you to read his story at the link below.
http://www.scottsabolich.com/KenWhitten.html
What the article does not say is that the 7,620 Volts was only carrying 2 Amps of current.
Please be extremely careful and think about what you are doing.·
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 9/15/2008 2:38:33 PM GMT
But, with a coil gun, your biggest danger isn't the projectile travelling through the coils. It's the capacitors, and to a lesser extent, the switchers and coils.
Coil gun capacitors are known to explode, particularly those which are in undamped guns. If you do damp them, the damping diodes are liable to explode. The switches are also known to die - sometimes explosively. The coils also get hot - and often exert enough pressure on themselves to crush the barrell.
If you really were serious about making a coil gun, you would know that FETs are less than ideal in the first place, and you would also know that what you want is not lots of amps.
And even when you do finish it, the results will be completely underwhelming (I should know - I built one, which was pretty much useless. And the whole time I kept the capacitors in a steel box with large resistors to bleed them, and a voltmeter to tell me when they'd discharged. One thing you learn is that coil gun caps don't fully discharge - you can watch the voltage going back up afterwards)
I have had a 3phase 200amp service panel blow up in my face(i was wearing saftyglasses thank god)..... I could not see for 10secs.....and that was just 200amps 240v
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·"I have always wished that my computer would be as easy to use as my telephone.· My wish has come true.· I no longer know how to use my telephone."
- Bjarne Stroustrup
second, i need the fet to handle 24v i probably wont even be able to get much more than 100 amps and with the way i decided on my design shouldnt need any more than 50, and its to control a motor yes for a go kart, and i know its dangerous, but i do have help, i·have ideas on·how to handle switching but i dont get speed control with my ideas, i just need speed control which is why i was looking at gigafets
and last, its not for my gaussian rifle, and obviously some people seem to think im just another stupid teenager, my gaussian rifle used a lot more than·500 amps, try closer to 3000 amps at 330 volts, i have a 1ft by 1ft 1/4in steel box built around just a "couple" flash camera capacitors, my coil has brass tubing running through it(which i know decreases efficiency) to cool it to about 40 degrees before firing so that the coil doesnt melt, the bullet im using is way to small so it slows from the coil still being on when the bullet goes all the way through, i dont use a heavier bullet because i dont NEED to know just how far or fast it can shoot so long as it works, to switch it i use a home made knife switch which is 1/2 in thick copper bar slamming down on a copper plate via a pnuematic ram, when i use it for demonstrations i just use a 400 amp relay and im only using 300 amps only 15 caps in parallel, no cooled coil and a very small bullet.
From what i can tell from R&D,·there's a fundamental problem with paralleling FET's, it's not really the turn on times and syncronization but having that many matching FET's, the caracteristics have to be within 1% of one another or you'll end up with a fancy and expensive smoke show when the FET's die domino style because there was one weaker one or a couple turned on a few mS faster than the rest in the bunch.
There are schematics on discover circuits for a 10KW amplifier but i would recomend ALOT of caution if considering something that dangerous.
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E3 = Thought
http://folding.stanford.edu/·- Donating some CPU/GPU downtime just might lead to a cure for cancer! My team stats.
Post Edited (RinksCustoms) : 9/26/2008 3:49:23 PM GMT
Because you're quite qualified to be lecturing most senior electricians and engineers who do this stuff for a living.
Proceed as planned.
True, gasoline engines kill thousands of people a year, but think of how many there are out there: lawnmowers, leaf blowers, edgers, cars, trucks, generators, boats; the list goes on and on. Now think of how many high power electric (personal) devices out there: one or two lawnmowers, a couple of go carts, and maybe a bicycle or two. The gasoline engine has been in development for over a hundred years now, while electric motors much less than that and with a lower priority.
How much is your life worth, anyway? Personally, I think life is worth at least paying $4 a gallon for reliability and ease of use.
Why do you want to have instant torque? All it would do is spin the wheels, and that's no good.
When you circuit is done, and works, and it is safe, you can go to the motor test. You anchor the motor to a test bench used for testing motors, and make all the relevant tests: no load, half load, full load, short-circuit. Once the circuit passes all tests... the kart comes. Testing the circuit in the kart directly... is not safe. When you test the kart, it should not lay on the floor, so it does not move when the motor spins. There you test coupling, light load and so on, and then you move the kart.
Disclaimer: I'm not liable for any of this advice, use it at your own risk.
But, I've used a 600 IGBT module rated for 600 V from Powerex (like the CM600HU-12F). You need a special driver board, but that board (BG1) takes TTL input.
You'll also need some kind of snubber circuit if your load has a lot of inductance.
I was amused with the fact that those fuses aren't blowing under normal impulse operation even though the pulse length is consistently a good 10 cycles long.
PS: Operating voltage is a rectified 10 Vrms transformer. And has a decent lump of copper bar sticking out of her.
I have some 100amp rated cable here, which is 1cm in diameter multistrand copper.
100A at 24V is 2400W. The average hosue in the UK gets a feed of 60A at 230V, thus 13800KW. You are proposing a power level one fifth of the average house' peak demand. The only people I have seen putting that much power into a motor are combat robot builders. To give you an idea of the power, these things can pull landrovers at ~40mph. You do not need anywhere near this much power to the motors of a go-kart. At that much power, a short circuit will weld steel. This is more power than some arc welders use.
At that power level, any components which fail short circuit will explode. At that power level, any switching component will generate masses of heat unless both adequitely cooled and switched very well.
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·"I have always wished that my computer would be as easy to use as my telephone.· My wish has come true.· I no longer know how to use my telephone."
- Bjarne Stroustrup