Alt-BEAM Archive
Message #06919
To: beam@corp.sgi.com (mailing list)
From: Benjamin Edward Hitchcock beh01@uow.edu.au
Date: Wed, 20 Oct 1999 13:18:40 +1000 (EST)
Subject: [alt-beam] Re: Someone else's mistake
I think I should step in here.
120V AC WILL kill you, given the right conditions. Here in Australia, we
have 240VAC as our primary domestic power source, and it is lethal. Where
I work, we have been given numerouswarnings about electrical safety (I'm
an electrician) and every week we get a bulletin that documents all the
incidents that have occurred throughout our plants.
Here at the steelworks anything over 32V AC is considered lethal. This
might sound silly, but consider this:
You need about 30 milliamps flowing through you before you can't 'let go'.
You need about 80 milliamps flowing through you before damage starts
occurring.
That's right, MILLI amps. There is a critical part in the hearts cycle
when the pacemaker resets itself, and if you get a boot across your chest
during this period (it is pretty quick, in the region of 10 milliseconds
or so) then your heart can lose its rhythm. This means that although you
survive the shock, your heart might lose its rhythm and stop beating a
couple of hours later.
Another thing to consider is fault current. Where I work, the fault
current is in the region of 10 000A. So if you short circuit something,
chances are that you will be burnt, and burnt badly. A normal wall socket
isn't nearly that high, probably about 3 000 Amps or so, but that can
still cause some bad burns.
So if that person had touched the two paper clips together, chances are
they would have gotten badly burnt.
As an excercise, get a multimeter, and measure the resistance of your
skin. Take the voltage at the wall, (120V in this case) and divide that
by your resistance in K.
This will give you the approximate current that will flow through your
body in milliamps. Remeber that when current starts flowing through skin,
the skin
resistance 'breaks down' so the resistance will decrease. And the human
body is just one big salty water-reservoir. Ever wondered how conductive
salt water is?
Try wetting your skin, and measuring the resistance. How much current
will flow through you when you're wet from the bath?
Please, people, DON'T be careless with mains power. It can, has and will
kill people.
Ben Hitchcock
----- Forwarded message from Jim
Taylor -----
[Charset iso-8859-1 unsupported, filtering to ASCII...]
> 120V AC, which can kill (Not will). I never touch any AC lines or alike
> without checking it with my DMM to see if the lines are hot. I hope you
are
> getting taught MUCH better electrical safety than that.
> Devin
>
Come on, your going to tell me you've never been zapped by 120 AC before! I
was zapped in second grade, and 3 months ago at my place of employment.
Aside from the burns on my fingers and the strange sensation to get my
groove on, no noticable side effects have shown themselves. However your
results may vary
On the topic of really stupid things to do aside from around 500 xacto cuts
( I think I have developed an immunity to such cuts) I REALLY sliced my
chin open from a clutch shoe (a centrifical clutch from an RC heli) flying
out of the heli and slicing my chin. The cut was about 4 inches long! OUCH!
James Taylor
URL: http://fly.to/springmeadows
------------------------------------------------------------------------
Was the salesman clueless?
Productopia has the answers.
http://clickhere.egroups.com/click/555
eGroups.com home: http://www.egroups.com/group/alt-beam
http://www.egroups.com
- Simplifying group communications
----- End of forwarded message from Jim Taylor -----
--
Nothing is foolproof to a sufficiently talented fool.
6920 Tue, 19 Oct 1999 23:29:54 EDT [alt-beam] Removal from list beam@sgiblab.sgi.com Zexan@aol.com I'm not sure if this is where I write too, But I'd like to be removed from
the Beam list...
Zexan@aol.com
6921 Tue, 19 Oct 1999 21:14:59 -0700 [alt-beam] Re: What The...! My Bot Is On Drugs! beam@sgiblab.sgi.com Sean Rigter I know I'm repeating myself Sparky but then you asked for it: HC
bicores are and always have been slower than HCT bicores. Perfectly
predictable and I could tell you exactly why in detail but read it for
yourself in the archive. The motors run longer in each direction and you
get higher "slo mo" steps. So how to speed things up and get the big
steps to boot? Reduce the resistors and increase the voltage.
Now the battery: Was it hot after the 5 minute discharge?
regards
wilf
SG wrote:
> Ok, i was havin a little troouble with an h-bridge that kept
> burning out, so i decided to approach the problem in a
> different way.
> I have been using the 74HCT240 for my Master/Slave Bicore
> (Ian's "Compleate Walker Circuit") and read somewhere that
> the AC or HC was preferable over the HCT. so i ordered a
> few 74HC240's from bgMicro. (couldn't find the AC's)
> well, i popped one in there and WOAAAA MOMMMA!
> what the heck is happinin??!!????! MY BOT IS ON DRUGS!!!!
> the steps were MUCH higher, but the whole bot ran like
> it was in a slow motion movie.... had to adjust a pot i had on the
> front servo to get the walking gait straight. Every few
> strides the bot would stop alltogether for about 2 secs.
> after about five mins of playing around and trying to
> tweak it, the thing RAN DOWN my fully charged battery!
> (I was mad too! cause these things take 14 hrs to charge,
> and now i can't play with my bot anymore tonight cause i
> didn't charge up my spare!)
> What happened? i sure don't know! the new HC's i have are numbered
> SN74HC240N
> (hmmmm.. a few extra letters there...)
> weird man weird. ...bummer.
> -Sparky
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