Re: Battery vs Ultracapacitor

[Allen C. Ward]

Surely some out there have read Philip Jose Farmer's "River World" series.  Mark Twain ran his "Fabulous Riverboat" from an ultracapacitor.
Can you imagine what would happen if you accidently shorted a ring across a fully charged ultracap of 20,000 Farads?  Goodbye finger(s).

Allen KA5N
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Ron D'Eau Claire-2]

Allen, KA5N wrote:

 ...Can you imagine what would happen if you accidently shorted a ring
across a fully charged ultracap of 20,000 Farads?  Goodbye finger(s).

--------------------------------------

That's a legitimate concern with our present 13.8 supplies as well. Twenty
or thirty amps can be very dangerous if you get a piece of jewelry across
the contacts. If you're unlucky enough to fail to make good enough contact
to trip the crowbar or blow a fuse, you'll be frozen there as the ring (or
bracelet) melts into your flesh.

Almost everyone who has worked around aircraft knows someone missing a ring
finger and sometimes a whole hand from just such mishaps. Working on a
fighter one night at Lockheed Aircraft, I heard a power cart groan and
looked at the next plane sitting wingtip to wingtip with the one I was in
and saw smoke billowing from a partially-opened canopy and a tech
unconscious inside. It turned out he had tried to replace a breaker without
disconnecting power and dropped this screwdriver where it contacted the
power bus bar and the side of the airplane. The metal shaft of the
screwdriver literally exploded into globules of molten metal that caused him
to jump up, smash his the back of his head on the canopy and knocked himself
out. Other than a concussion he wasn't seriously hurt but the plane was a
mess.

That's one very good reason to be sure that 20 amp fuse Elecraft specifies
for the K2/100 is in the power line.

Ron AC7AC






_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Don Wilhelm-3]

And I will add that we should be very cautious around batteries and battery
sourced power supplies too.  Batteries will produce a LOT of current if
shorted.  I once tested an 8 cell pack of AA sized NiCad batteries in a lab
for their short circuit discharge current - yes the current dropped off
rapidly, but was still sufficient to vaporize the copper in the #16 wire
leads attached to the battery pack.  Keep those battery terminals adequately
covered and safe from accidental contact.  The voltage may not hurt but the
results from the current can certainly maim and even kill.

73,
Don W3FPR

> -----Original Message-----

>
> Allen, KA5N wrote:
>
>  ...Can you imagine what would happen if you accidently shorted a ring
> across a fully charged ultracap of 20,000 Farads?  Goodbye finger(s).
>
> --------------------------------------
>
> That's a legitimate concern with our present 13.8 supplies as well. Twenty
> or thirty amps can be very dangerous if you get a piece of jewelry across
> the contacts. If you're unlucky enough to fail to make good enough contact
> to trip the crowbar or blow a fuse, you'll be frozen there as the ring (or
> bracelet) melts into your flesh.
>
> Almost everyone who has worked around aircraft knows someone
> missing a ring
> finger and sometimes a whole hand from just such mishaps. Working on a
> fighter one night at Lockheed Aircraft, I heard a power cart groan and
> looked at the next plane sitting wingtip to wingtip with the one I was in
> and saw smoke billowing from a partially-opened canopy and a tech
> unconscious inside. It turned out he had tried to replace a
> breaker without
> disconnecting power and dropped this screwdriver where it contacted the
> power bus bar and the side of the airplane. The metal shaft of the
> screwdriver literally exploded into globules of molten metal that
> caused him
> to jump up, smash his the back of his head on the canopy and
> knocked himself
> out. Other than a concussion he wasn't seriously hurt but the plane was a
> mess.
>
> That's one very good reason to be sure that 20 amp fuse Elecraft specifies
> for the K2/100 is in the power line.
>
> Ron AC7AC
>

--
No virus found in this outgoing message.
Checked by AVG Anti-Virus.
Version: 7.0.323 / Virus Database: 267.8.5/32 - Release Date: 6/27/2005

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Tom Hammond-3]

At 08:55 AM 6/28/2005, Ron D'Eau Claire wrote:

>That's a legitimate concern with our present 13.8 supplies as well. Twenty
>or thirty amps can be very dangerous if you get a piece of jewelry across
>the contacts. If you're unlucky enough to fail to make good enough contact
>to trip the crowbar or blow a fuse, you'll be frozen there as the ring (or
>bracelet) melts into your flesh.

You're certainly right there, Ron... UN-limited current from a big honkin'
battery, or power supply really CAN be extremely dangerous.

Fortunately (as I can attest, from several almost unfortunate experiences)
most of the 'modern' AC power supplies offer foldback current limiting
which, if the output is shorted, will reduce the output current (and
voltage) to nearly ZERO, helping to protect against such catastrophes.

UNfortunately, this is not the case for storage batteries, and I'm sure,
some older power supplies as well, which will supply almost unlimited
current until they either run out, blow up, or melt through the power
cable. In fact, a local friend just very recently managed to short out the
power cable on his fully-charged 80AH gell cell... not only melted almost
all the insulation on the DC cable, but actually began melting the THICK
LEAD terminals build into the battery itself. Fortunately, there was no
harm done to my friend... but he got a really QUICK education is the power
of a low internal impedance current source.

As you noted, ALL DC power sources should be adequately (and appropriately)
fused, and fairly close to the DC source itself, if at all possible... it
doesn't have to be the far end of the DC cable that shorts out... could be
anywhere along its length that becomes accidently stripped of insulation...
BAD THINGS CAN HAPPEN.

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com