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'current (was Car battery power help)'
1999\11\04@193511 by bill

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> changing the SUBJECT line...Tell me if this is correct...It doesnt matter
> how much current your batter or what not can supply...it matters how much
> you are drawing out of it (?)

Exactly.  The amount of current depends on the voltage and resistance.
Having a power source that is capable of supplying huge current will not
alone cause the current to increase. It can, however, do more damage in a
fault situation.  A circuit that shorts when connected to a little battery might
do nothing more dramatic than briefly warming up the battery.  With a big
battery, it might smoke or even catch fire.  The more current that's available,
the more you might want to use a fuse.

I actually once saw a prototype circuit board catch fire inside a PC. The
board had a 5V to gnd short caused by a misalignment of its layers.  The
PC just kept right on working even with the flame and smoke pouring out!
The circuit path on the board was long and thin enough that the PC's power
supply was able to maintain 5V even with the short, creating enough heat to
ignite the epoxy and keep it burning.  The flame extinguished itself when the
power was turned off.
---
                                       Peace,
                                       William Kitchen
                                       spam_OUTbillTakeThisOuTspamiglobal.net

The future is ours to create.

1999\11\04@200900 by Tony Nixon

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"William J. Kitchen" wrote:

> With a big battery, it might smoke or even catch fire.  The more current that'
s available,
> the more you might want to use a fuse.

I tell people who build my ignition controller to keep high current
ground returns seperate from the one that powers the PCB. I have seen
most of the PCB tracks vaporised in a fault condition. It's still got be
beat how they did it though.

--
Best regards

Tony

http://www.picnpoke.com
Email .....salesKILLspamspam@spam@picnpoke.com

1999\11\04@202523 by Dennis Plunkett

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At 12:05 5/11/99 +1100, you wrote:
>"William J. Kitchen" wrote:
>
>> With a big battery, it might smoke or even catch fire.  The more current
that's available,
>> the more you might want to use a fuse.
>
>I tell people who build my ignition controller to keep high current
>ground returns seperate from the one that powers the PCB. I have seen
>most of the PCB tracks vaporised in a fault condition. It's still got be
>beat how they did it though.


Something is confusing me here Tony
I thought that you have had no probelms with the 7805 approch nad over 1000
units
Now you seem to indicate unexplainable faults.

HUMM
Maybe there is something in that for all of us... <GRIN>


As for the question of what is a TRISIL. Basicaly is a bidirectional
crowbar device (Like 2 SCRS) that clamps both rails together (To within
0.6V) one the breakover point is reached. These things come in 0.5kW and
1.5kW (Yep thats correct) versions (surface mount 0805, and SOIC8!). I love
these things


Dennis



{Quote hidden}

1999\11\04@203357 by goflo

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If you'll forgive the OT, a shop I once worked in sold a kit with
.040-over pistons to two guys with a .030 block. Undaunted, they
hammered it together. Phone did'nt ring till they could'nt get it
to start.
There's talent out there.

Regards, Jack

Tony Nixon wrote:
I have seen
> most of the PCB tracks vaporised in a fault condition. It's still got be
> beat how they did it though.

1999\11\04@204653 by Tony Nixon

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Dennis Plunkett wrote:

> Something is confusing me here Tony
> I thought that you have had no probelms with the 7805 approch nad over 1000
> units
> Now you seem to indicate unexplainable faults.

That's the thing I suppose. The leds were on an early version, and the
other problem came from the fact that a kit design can be completely
misused by a constructor. That's something no one has control over.

I actually had someone ask me if it was ok to use one of them in an
airplane. I hastily said no, but you never know what the outcome will be
with some people.

As for the 7805 approach, the zener blew off the board, and the 78L05
had to be replaced, but all else were ok including the PIC.

--
Best regards

Tony

http://www.picnpoke.com
Email .....salesKILLspamspam.....picnpoke.com

1999\11\05@033443 by Mark Willis

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Dennis Plunkett wrote:
{Quote hidden}

DigiKey calls these Transient Voltage Suppressors (TVS) - they come
unidirectional or bi-directional.

 Mark

--
I do small package shipping for small businesses, world-wide.

1999\11\05@054822 by Michael Rigby-Jones

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part 0 828 bytes
<P><FONT SIZE=2 FACE="Arial">DigiKey calls these Transient Voltage Suppressors (TVS) - they come</FONT>
<BR><FONT SIZE=2 FACE="Arial">unidirectional or bi-directional.</FONT>
</P>

<P><FONT SIZE=2 FACE="Arial">&nbsp; Mark</FONT>
</P>
</UL>
<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">If it acts like back to back SCR's, then I'm guessing that this really is a crowbar device, i.e. once triggered it remains conducting untill current is removed?&nbsp; If so not too usefull for spike suppression...</FONT></P>

<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">Mike Rigby-Jones</FONT>
</P>

</BODY>
</HTML>
</x-html>

1999\11\05@130423 by Mark Willis

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{Quote hidden}

TVS's act just like a fast, cheap, very high power Zener, they're a
little sloppy on triggering voltage (not quite as precise as a Zener, or
at least weren't at one time), these work well for Auto circuits.  A TVS
won't clamp down to 0.6V (maybe a Trisil is a different beastie?)  TVS's
are rated by power & Vbr (breakdown / avalanche voltage);  1 pSec
avalanche time for unidirectional units, the bidirectional's are slower,
and at $0.72 in onesies for the 1.5kW units, you can do worse.  General
Semiconductor makes the ones I've looked at, other co's make these;
http://www.digikey.com/EC/V3/250.pdf for Digi-Key's catalog page, FYI.
Other places may be cheaper. <G>

The wattage rating IS, btw, a "Peak power pulse" rating - I wouldn't try
to use one at a steady state power dissipation of 1.5kW, "it wouldn't be
pretty!" - I haven't blown one up yet, I'm sure someone will here <G>

 Mark

--
I do small package shipping for small businesses, world-wide.

1999\11\07@164653 by Dennis Plunkett

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<x-rich>At 09:06 5/11/99 -0000, you wrote:

>>>>

<excerpt>RE: current (was Car battery power help)


<fontfamily><param>Arial</param><bigger><<snip></bigger></fontfamily><color><par
am>0000,0000,ffff</param>

<fontfamily><param>Arial</param><bigger>> As for the question of what is
a TRISIL. Basicaly is a bidirectional</bigger></fontfamily>

<fontfamily><param>Arial</param><bigger>> crowbar device (Like 2 SCRS)
that clamps both rails together (To within</bigger></fontfamily>

<fontfamily><param>Arial</param><bigger>> 0.6V) one the breakover point
is reached. These things come in 0.5kW and</bigger></fontfamily>

<fontfamily><param>Arial</param><bigger>> 1.5kW (Yep thats correct)
versions (surface mount 0805, and SOIC8!). I love</bigger></fontfamily>

<fontfamily><param>Arial</param><bigger>> these
things</bigger></fontfamily>

<fontfamily><param>Arial</param><bigger>>

> Dennis</bigger></fontfamily>


<fontfamily><param>Arial</param><bigger>DigiKey calls these Transient
Voltage Suppressors (TVS) - they come</bigger></fontfamily>

<fontfamily><param>Arial</param><bigger>unidirectional or
bi-directional.</bigger></fontfamily>


<fontfamily><param>Arial</param><bigger>  Mark</bigger></fontfamily>



<fontfamily><param>Arial</param><bigger>If it acts like back to back
SCR's, then I'm guessing that this really is a crowbar device, i.e. once
triggered it remains conducting untill current is removed?  If so not too
usefull for spike suppression...</bigger></fontfamily>


<fontfamily><param>Arial</param><bigger>Mike
Rigby-Jones</bigger></fontfamily>

</color></excerpt><color><param>0000,0000,ffff</param>


</color>This depends on the devie that you go for. Yes the hold current
is low once tripped. If you use a TRANZORB then it will clamp one over
voltage. And release once under.


Dennis

</x-rich>

1999\11\07@165107 by Dennis Plunkett

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At 10:02 5/11/99 -0800, you wrote:
{Quote hidden}

I have <G>
But in an power induced envorionment, where one of the tests was to place
415VAC on a line for 15 minutes


Dennis

>
>--
>I do small package shipping for small businesses, world-wide.
>
>

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