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Registered Member #1389
Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
Sheesh, is that 14 AWG? Perhaps soaking your coils in carbon fiber or fiberglass laced gorilla glue would have prevented that? In any case, I can't wait to get my 1kJ photo flash bank together now!
Registered Member #10
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
FastMHz wrote ...
My electrical experimentation last night ended with the cops showing up....apparently, the neighbors thought a 14,000j discharge into a pickle was too noisy :-o I launched electromagnetic induction rockets, accidentally detonated a coilgun with too much energy and laughed uncontrollably as pickles exploded with incredible ferocity The coilgun was so powerful at 3.8kj that it shot a slug through both sides of a 5-gal pale and almost through sheet metal behind it!!! So I decided to try 5kj...and this happened: My capacitor bank is 24,000j fully charged.
I would suggest you get your neighbors onside. Explain in a letter, or preferably personally, that you are a mildly eccentric chap that has an electrical lab and will make some noises. Be clear to explain that there are no guns or explosives and that there will be no noise after 9 pm. They are welcome to have a guided tour or have an open day. Otherwise you risk getting them increasingly pissed off.
I have a little concern if you are "accidentally" doing anything with those energies. Have fun but take care. Also bear in mind that inductive loads plus electrolytics will eventually give cap failure and one of them may go the way of your pickle. I got a bruise from an exploding cap less than 1cm size from overvoltage so your mileage with 14kJ will vary.
Registered Member #179
Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287
I totally agree - letting my neighbors know there aren't bombs or something over here is a good idea. Every time I meet a new neighbor I do tell them of my electrical hobbies and that they might hear it. I just hadn't met *all* of them yet as I only moved in on Apr 1st....I'm getting there!
As for accidentally doing stuff....well...coils die, what can I say? My system is remote controlled so I can be really far away from it in case of failure, as I've explained throughout this thread. I've also noticed that my spark gap stops conducting before the bank is completely discharged or reverse charged by the coils - there's always a few hundred volts left in, in the correct polarity. Methinks this is a good thing!
Not sure about the failure mode...but the coil was scrunched up pretty good - I used to be twice as long. It was 3 layers of 50 turns of 14awg. Perhaps I need more layers...
Hopefully I'll get the video edited soon - Almost everything was caught on camera
Registered Member #10
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
FastMHz wrote ...
I've also noticed that my spark gap stops conducting before the bank is completely discharged or reverse charged by the coils - there's always a few hundred volts left in, in the correct polarity. Methinks this is a good thing!
Not sure about the failure mode...but the coil was scrunched up pretty good - I used to be twice as long. It was 3 layers of 50 turns of 14awg. Perhaps I need more layers...
Don't assume that you have just discharged 99%. What is more likely is that there have been repeated ringing cycles and what is left is a combination of what no longer has the power to sustain an arc and some recovered charge (when caps recharge themselves a bit). This is what I see on my storage CRO even when the coil is disrupted.
In terms of coil failure, the forces are for axial compression and radial expansion. It explains why the coils scrunch up (making interturn shorts develop) and expand and disrupt at the same time.
To provide some physical restraining force, I have placed my coin shrinking coil in a container wrapped in old cloth. Fill with water and freeze. Any coil explosion then has to disrupt that. Easy to do and no cost. These are the results of 5kJ on a coil of 2mm wire which had fibreglass wrapping between turns.
Registered Member #1561
Joined: Mon Jun 23 2008, 07:58PM
Location:
Posts: 25
hey i know this is pretty late with the posting, but I was wondering why you didn't decide to put balancing boards on your cap bank?
It seems like your pretty set on having the gun fire a single massive shot, rather than doing multiple stages and what not, but I was thinking you could set up a sweet chainfun style barrel system, consisting of say, 10 cap barrels, and have a cap bank for each of the barrels, you could have it fire all at once or in rapid sucession.
Anyways this is an amazing cap bank and your works is looking great
Registered Member #179
Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287
Yes, a single shot is the plan because I'm building induction launchers....I'm going to build a gigantic 1 foot+ pancake coil and launch some seriously huge objects, and hopefully get some larger "rockets" flying.
All these caps appear to be matched, and charge relatively evenly, so external balancing wasn't necessary.
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[moved] 24,000j Capacitor Bank (Now Complete)
The coilgun was so powerful at 3.8kj that it shot a slug through both sides of a 5-gal pale and almost through sheet metal behind it!!! So I decided to try 5kj...and this happened:
And anything that makes these suckers safer is a good thing!!
