Has anybody dumped a lot of energy into surfmount resistors, fast? I'd like to discharge about 35 joules of energy from some electrolytic caps, in a couple tenths of a second maybe, and it would be cool to use a few 2512 or some such resistors.
I suppose I could try it...
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com
Not into SMT but thru-hole. Ohmite has Joule ratings for some but I'd contact them because 200msec is long:
Example: Page 141 bottom left
Usually high pulse load calls for carbon resistor types.
-- Regards, Joerg http://www.analogconsultants.com/
Put it in LN2 i.e. IRC.
Test: 2512, thickfilm, 0.2 ohms 1%, soldered to lots of copper.
Dumped 10,000 uF at 10 volts, 0.5 joules.
Blew it open first try. Guess I'll try some wirewounds.
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com
I did that. No good idea. The 2512 develops hot spots which burn out.
Vladimir Vassilevsky DSP and Mixed Signal Designs
Joules assume more or less equilibrium state. For surge, I^2 x T rating is more appropriate.
Vladimir Vassilevsky DSP and Mixed Signal Designs
Why don't you start out on the low end and see where it fails?
tm
Welcome to Learn by Destroying(tm). You get to have all the fun blowing up resistors. I'm jealous.
A really rough estimate of what could be expected in the size of the resitors could be calculated from the specific heat of ceramic. This doesn't include hot spots, uneven radiation, conduction to the PCB, differences in material, current density (fusing), and whatever else I forgot, but should be in the ballpark as far as the phyical weight of the device that you're trying to vaporize. I'll guess(tm) that a resistor can tolerate a 70C temp rise and that the specific heat of ceramic is 1050 J/kg-C. kg = 1 / (70 * 1050) = 0.0136 grams A 2513 resistor is about 0.0513 grams so it should be possible. Therefore the problem is probably hot spots or current density causing the resistor material to act like a fuse. If you can find a chip resistor that uses bulk resistivity instead of a surface painted trace, I think it might work. Something like this (which I've never used or tried): I've used such chip resitors in RF dummy loads with good success.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com
Get a wirewound and make it into a MELF or get a bulk carbon comp and snip and form the leads to make a standing, leaded MELF thingy.
35 joules into a surface mount resistor even slowly would likely open it up.
I think we use a big zener diode to soak up energy from a coil.
George H.
Oops. Bad example as it's too low resistance. Nothing in bulk resistivity here: Foil is too low resistance, thick film can't handle the current density, so I guess it has to be wirewound.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com
Tomorrow maybe. Had to leave at 5:30.
Higher resistor values might do better, but it looks like there's no way I'm going to dump 35 or so joules into any reasonable array of regular surface-mount resistors.
I may have to stand up a leaded wirewound part, roughly 0.25" dia x 1" long. Inelegant.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com
You can blow up resistors too!
We're also designing a power mosfet exploding circuit.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com
How about a manganin ribbon? How much space do you have? 35 J is a lot of energy to dump. Maybe a lamp (or several) of some sort might be able to do it.
Make that 0.0136 kg = 13.6 grams. 250 resistors should be enough.
If the dumping is done relatively infrequently, the heat capacity and pulse power capacity are the limiting factors, the smallest solution is probably a few carbon/ceramic composition resistors like Ohmite OX/OY series.
-- Mikko OH2HVJ
surface-mount
-- http://www.globar.com/ec/bulk-ceramic-resistors
El 23-05-13 1:42, John Larkin escribió:
Hello,
Try to locate the chip resistor datasheet (introduction thick film) on
This shows data for pulse handling for SMD resistors. It may be helpful.
-- Wim PA3DJS
You could use the better thermal coupling of an active part, like the SI8445 FET:
A quick glance reveals thermal impedance, single shot, of 15K/W for 1s pulse. So you should be able to drive about at least 6 Joule into that device.
If you can couple very good thermally to the foot, you can get up to at least
20JouleMost likely there is other parts with better specs than that.
Regards
Klaus
FET:
So you should be able to drive about at least 6 Joule into that device.
20JouleThis one is even better:
Cheers
Klaus
Thanks. I erred, but not where you pointed out.
kg = 1 / (70 * 1050) = 1.36*10^-5 kg Converting to grams g = 1.36*10-5 * 1*10^3 g/kg = 1.36*10^-2 g = 0.0136 g For 35 joules g = 35 * 0.0136 = 0.48 g For a 0.05 gram 2513 resistor 0.48 / 0.05 = 10 resistors required.
As I mumbled, this was an approximation.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com
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