Post by thread:[EE] SCR trigger

A friend has been given a bunch of 50,000uF 400V caps. They apparently were ripple filters in some big-ass PSU. He wants eventually to use them in a coilgun-type experiment. For his own amusement I hasten to add (he has this thing about HV and sparks !! ;)) and owns some Tesla equipment) http://en.wikipedia.org/wiki/Coilgun Any advice I/we can give him for a suitable and rugged trigger ? ======================== He asks - Do you have any simple SCR triggering circuts? I have 10 x 15A SCRs in parallel each having a 10ms peak one shot current rating of 100A. The resistive load I am using should cause the energy in the caps to be dumped in 1ms. For safety reasons I am only using 150V to charge the caps (hehehe... not for personal safety but for the safety of the cap) At this stage I just need to be able to press a button and have the SCRs fire with a pulse that lasts only 1ms or thereabouts, was looking at using a 555 for a one shot timer. I have a spare MOC3021 sitting here as well so I could use that to decouple the trigger circuit from the HV circuit

Is this the sort of friend to whom you refer when talking informally to a doctor (or priest)? eg "I have a friend who has ......." :-) More to the point, how about a simple toggle switch, a trigger cap and a long piece of string. a) Tie string to toggle switch b) Charge the cap c) retire behind something solid & fireproof d) pull string RP On 03/10/2007, Jinx <spam_OUTjoecolquittTakeThisOuTclear.net.nz> wrote: {Quote hidden}> A friend has been given a bunch of 50,000uF 400V caps. They > apparently were ripple filters in some big-ass PSU. He wants > eventually to use them in a coilgun-type experiment. For his own > amusement I hasten to add (he has this thing about HV and > sparks !! ;)) and owns some Tesla equipment) > > http://en.wikipedia.org/wiki/Coilgun > > Any advice I/we can give him for a suitable and rugged trigger ? > > ======================== > > He asks - > > Do you have any simple SCR triggering circuts? I have 10 x 15A > SCRs in parallel each having a 10ms peak one shot current rating > of 100A. The resistive load I am using should cause the energy in > the caps to be dumped in 1ms. For safety reasons I am only using > 150V to charge the caps (hehehe... not for personal safety but for > the safety of the cap) > > At this stage I just need to be able to press a button and have the > SCRs fire with a pulse that lasts only 1ms or thereabouts, was > looking at using a 555 for a one shot timer. I have a spare MOC3021 > sitting here as well so I could use that to decouple the trigger circuit > from the HV circuit > > > -

> Is this the sort of friend to whom you refer when talking informally > to a doctor > eg "I have a friend who has ......." :-) Nah nah nah. If it was me with the clap I'd say so > More to the point, how about a simple toggle switch, a trigger > cap and a long piece of string. Just a button will do. Just a button

> A friend has been given a bunch of 50,000uF 400V caps. They > apparently were ripple filters in some big-ass PSU. He wants > eventually to use them in a coilgun-type experiment. For his > own amusement I hasten to add (he has this thing about HV and > sparks !! ;)) and owns some Tesla equipment) > > http://en.wikipedia.org/wiki/Coilgun > > Any advice I/we can give him for a suitable and rugged trigger ? You can get (not easily & not cheaply, ymmv) gas-filled reed switches, relays and the like. The gas stops arcing between the contacts. Well, it's supposed to. Current might be a bit of bugger though... Or like tasers work, with a spark gap. Cap charges, arcs at the high volt point, dumps the charge, rinse lather repeat. Down side is you don't get much of a say when it triggers. By sheer coincidence, I encountered this: <http://www.philpem.me.uk/elec/welder/> yesterday. I thought the name sounded familiar. Phil reckons a 50RIA20 SCR would handle the current, he doesn't mention the voltage as he's only using a few volts. (I'm going to parallel a couple of modified microwave transformers instead, 'cause I've got them.) Tony

> Tony Cheers for the input Seems to be an "SCR week" for me. I hardly ever touch them. Also looking into a sound-operated flash. Probably will make something like this, plus a PIC for triggering, maybe, and other functions http://sound.westhost.com/project65.htm Quite some activity re-jiggering disposable camera flashes, eg http://repairfaq.ece.drexel.edu/sam/strbfaq.htm Helpfully there are schematics of some brand-name units. A few summers ago I visited chemists and processors for disposable cameras that had been, um disposed of, and could have got more than a few I notice tonight that DSE is having a close-out sale on yet another line, 5W Xenon tubes this time, for $1. Might have to go urgent shopping tomorrow They should just change the name to Dick Smith Appliances. Better still, sell the West Auckland store to Jaycar

Alan B. Pearce wrote: >>> More to the point, how about a simple toggle switch, a trigger >> < cap and a long piece of string. >> >> Just a button will do. Just a button > > Oh, I dunno, for something like that you need a decent plunger ... at least > then you feel like you are firing something big. Knife switch! Massive knife switch with a really long handle! They just look so Mad Scientist. Your friend might enjoy a look at _Electronic Gadgets for the Evil Genius_ - it has plans for lots of high-voltage weapons, er, experiments. -- Timothy J. Weber http://timothyweber.org

> I notice tonight that DSE is having a close-out sale on yet > another line, 5W Xenon tubes this time, for $1. Might have to > go urgent shopping tomorrow > > They should just change the name to Dick Smith Appliances. > Better still, sell the West Auckland store to Jaycar A while back Russell pointed out that DSE were selling a 10MHz scope for $128. Obviously that didn't clear the stock out, so a few weeks back you could buy one for $99, so I did. No doubt any left will be at $50 one day. A quick look shows they're back to $128. Hmmm, cable is being dumped as well, I guess I'll be going shopping too. Oh wait, the power cable range is looking a bit thin... 6 whole items, and no 4G. Sigh. Ask them for a job - <http://www.wowcareers.com.au/wowcareers/DickSmithElectronics/Home/>. :) Tony

About the circuit here - http://sound.westhost.com/project65.htm Is there any reson why I couldn't use an X2 capacitor instead of a current-limiting resistor ? If so, I would use the impedance of it as the effective resistance to get the charge time for the storage cap ? I have a selection of X2 caps from 47n to 2u2 The set-up I'm planning is fairly small. 240V mains, 5W or less tube flashing at no more than 1Hz (probably) A long time ago I repaired a biggish stage flash, and that had, ISTR, only 4uF in a metal can (cigarette packet size) with screw terminals. It seemed bright enough, so I wonder what type of tube the author is thinking of that needs 200uF Pretty sure the old ETI strobe used only a few uF as well, but can't lay my hands on the article to check the tube wattage

On 10/4/07, Jinx <.....joecolquittKILLspam@spam@clear.net.nz> wrote: > About the circuit here - > > http://sound.westhost.com/project65.htm > > Is there any reson why I couldn't use an X2 capacitor instead of > a current-limiting resistor ? If you're talking about R3, then you've forget everything is happening in DC. C3 is charging with the energy already accumulated on C1/C2 which must be high, so you can't limit the current in AC. If so, I would use the impedance of {Quote hidden}> it as the effective resistance to get the charge time for the storage > cap ? I have a selection of X2 caps from 47n to 2u2 > > The set-up I'm planning is fairly small. 240V mains, 5W or less > tube flashing at no more than 1Hz (probably) > > A long time ago I repaired a biggish stage flash, and that had, ISTR, > only 4uF in a metal can (cigarette packet size) with screw terminals. > It seemed bright enough, so I wonder what type of tube the author > is thinking of that needs 200uF > > Pretty sure the old ETI strobe used only a few uF as well, but can't > lay my hands on the article to check the tube wattage > > -

> > Is there any reson why I couldn't use an X2 capacitor instead of > > a current-limiting resistor ? > > If you're talking about R3, then you've forget everything is happening > in DC. C3 is charging with the energy already accumulated on C1/C2 > which must be high, so you can't limit the current in AC. Hi Vasile. Yes, I realise the current limiting resistor is after rectification, so what about a cap between F1 and D1/D3 or in series with R1 ?

On 10/4/07, Jinx <joecolquittKILLspamclear.net.nz> wrote: > > > Is there any reson why I couldn't use an X2 capacitor instead of > > > a current-limiting resistor ? > > > > If you're talking about R3, then you've forget everything is happening > > in DC. C3 is charging with the energy already accumulated on C1/C2 > > which must be high, so you can't limit the current in AC. > > Hi Vasile. Yes, I realise the current limiting resistor is after > rectification, > so what about a cap between F1 and D1/D3 or in series with R1 ? Yes, should work with a decreasing of the repetition rate flash. > > -