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UndermineBriarEverglade
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Yeah it's kind of a kludge, the charge pump uses a few mA in steady state without a disable. It would be better to use a LTC1044 or something but I
wanted to test it without waiting for new components to arrive.
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UndermineBriarEverglade
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Charge pump works well to trigger relay and safety mechanisms are adequate. But the HV converter is just whalloping this 9V battery. 2-4V most of the
time and ringing to 14V, enough to brown out the microcontroller once it starts charging up the cap. I should have scoped this in the early design
phase, I just assumed the source was sufficient based on the output voltage. Even lithium batteries droop too much. I'll need to use a separate
battery (like Sir_Gawain) or redesign to feed the small circuitry with a boost-buck converter or some nonsense.
I'll do my ETN synth soon. Why does it have to be so difficult to get nitrate salts, ammonia, nitric acid when you can literally buy POUNDS of arsenic
trioxide online.
[Edited on 2024-7-25 by UndermineBriarEverglade]
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UndermineBriarEverglade
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Sir_Gawain, what quantity of ETN are you able to detonate unconfined with your EBW setup? Mine failed to detonate 50mg of loose ETN. I can test
initial voltage, but without a way to measure discharge time or current I can't tell if the wire is actually exploding or just melting faster than a
camera frame.
Also, based on a candle flame below aluminum foil, I do think a nichrome coil around an ETN cap might be a simpler detonator. Maybe with a little
motor to vibrate it.
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Sir_Gawain
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Quote: Originally posted by UndermineBriarEverglade  | Sir_Gawain, what quantity of ETN are you able to detonate unconfined with your EBW setup? Mine failed to detonate 50mg of loose ETN. I can test
initial voltage, but without a way to measure discharge time or current I can't tell if the wire is actually exploding or just melting faster than a
camera frame.
Also, based on a candle flame below aluminum foil, I do think a nichrome coil around an ETN cap might be a simpler detonator. Maybe with a little
motor to vibrate it. |
While testing, I would add some ETN (<100mg) to a piece of tape, add the bridge wire, and fold the tape over. These little detonators were quite
powerful and always fully detonated. 500mg wrapped in tape blew a sizable hole in a steel can.
It’s pretty easy to tell if the wire is exploding properly or just rapidly melting. Set off a bridge wire (about 5 mm long) in air. It should make a
loud crack and produce a brief blinding flash. It should also leave a film of vaporized copper on nearby surfaces.
One of the biggest problems with the cook-off type detonator is the tendency to simply catch fire, possibly igniting the main charge. I’ve had it
happen to me before, and trust me, a slowly smoldering stick of dynamite is not a fun thing.
“Alchemy is trying to turn things yellow; chemistry is trying to avoid things turning yellow.” -Tom deP.
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UndermineBriarEverglade
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It does make a loud crack, brief flash, and metal dust deposits. In slow-motion video I get one frame of complete white and then a spray of sparks.
Hmm, that's a good point.
edit: Successful detonation with a slightly larger amount of ETN in tape. Installed new relay after finding the previous one was stuck closed. Contact
resistance might have been increased in previous attempts, explaining weak bursts. Maybe I will "flicker" the relay after firing to try and shake off
any hot gunk. Reed relays might not be the way to go. Must have been <10 bursts before it died.
[Edited on 2024-8-9 by UndermineBriarEverglade]
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UndermineBriarEverglade
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Sir_Gawain, would you mind posting the model of relay you're using, the approximate number of uses you get out of it, and the resistance of one of
your bridgewires? I get maybe 5-6 shots per relay, and that's after melting it unstuck with high current after each shot. I want to find a relay that
will last longer, or at least be cheaper and fit a standard socket. Unfortunately this use is so far out of the datasheets all I can do is trial and
error with different relays. My bridgewires are about a tenth of an ohm. I found it easier to cut stranded wire down to a single strand instead of
soldering nichrome.
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Sir_Gawain
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I'm not sure of the model, but it's a high amperage relay from an HVAC unit similar to this one. I've fired it probably close to 100 times and while there is some erosion of the contacts, it's not problematic. For the bridgewires, I
use 40 AWG wire from a microwave turntable motor. It's hair-thin, and works significantly better than the thicker wire it sounds like you're using.
The resistance is too low to measure with my meter (<0.1Ω)
[Edited on 11-2-2024 by Sir_Gawain]
“Alchemy is trying to turn things yellow; chemistry is trying to avoid things turning yellow.” -Tom deP.
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fx-991ex
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Wouldn't a capacitor across the relay contact fix the contact arcing/welding problem?.
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UndermineBriarEverglade
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Thanks Gawain. I will try a contactor. I do have magnet wire, but apart from the relay damage I haven't had any detonation problems so I'm probably
not going to change the load.
fx, I think it would cause more arcing when the contacts first close in favor of reducing arcing when the relay opens. I don't know if the problem is
arcing on open or on close, but I suspect it's arcing on close that's the problem since the relay gets stuck closed when it fails. I also don't want
to spend my microwave capacitor's energy charging another cap instead of exploding the wire. (And I don't want to explode an inadequately-rated filter
cap either.)
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