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'[EE] SCR trigger'
2007\10\02@230523 by Jinx

face picon face
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


2007\10\02@232056 by Richard Prosser

picon face
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_OUTjoecolquittTakeThisOuTspamclear.net.nz> wrote:
{Quote hidden}

> -

2007\10\03@000422 by Jinx

face picon face
> 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

2007\10\03@044020 by Alan B. Pearce

face picon face
>> 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.

2007\10\03@062850 by Tony Smith

picon face
> 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

2007\10\03@080426 by Jinx

face picon face
> 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

2007\10\03@104313 by Timothy Weber

face picon face
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

2007\10\03@180631 by Jinx

face picon face
> Knife switch! Massive knife switch with a really long handle!  They
> just look so Mad Scientist

Buy 10 knife switches, free Young Frankenstein DVD

"What hump ?"

2007\10\03@184242 by Tony Smith

picon face
> 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

2007\10\03@185008 by Jinx

face picon face
> Ask them for a job -
> <http://www.wowcareers.com.au/wowcareers/DickSmithElectronics/Home/>.  :)

"You work for Dick Smith ? Oh wow. Oh man, sit down,have a drink"

2007\10\04@053627 by Jinx

face picon face
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

2007\10\04@064939 by Vasile Surducan

face picon face
On 10/4/07, Jinx <.....joecolquittKILLspamspam@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}

> -

2007\10\04@084011 by Jinx

face picon face
> > 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 ?

2007\10\04@113158 by Vasile Surducan

face picon face
On 10/4/07, Jinx <joecolquittspamKILLspamclear.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.


>
> -

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