Question About Safety Of Voltage Supply

[Chuck]

On Fri, 21 Mar 2008 03:10:49 -0400, "Paul E. Schoen"
<pstech@smart.net> wrote:

"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:0lu4u3ljlh3oegri93ms0inejo5g19vug5@4ax.com...
On Wed, 19 Mar 2008 14:37:26 -0400, "Paul E. Schoen"
pstech@smart.net> wrote:


"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in
message
news:9rb2u35c4g77fpfi6qf3aio3r97b0eopi7@4ax.com...
On 19 Mar 2008 14:25:19 GMT, et472@FreeNet.Carleton.CA (Michael Black)
wrote:


The 9v batteries in series can be as dangerous as a 45volt power supply
(or
as "safe"), the voltage is the same. The current of the power supply
is
likely more, but then few think about the potential danger of running
12v
through their body at really high current.

How would one go about running 12 volts through their body at really
high current?

John

Use two needles stuck into your veins. You will probably get enough
current
to cause serious shock or even death if placed properly.

Or you could get an infection, and die from that. A 12-volt car
battery can kill you, if dropped from a sufficient height.

And a fully discharged AAA cell can kill you if fired from a gun. Or if you
eat enough of them.


For the OP's circuit, with either batteries or wall-warts (especially
with
a big capacitor), it might be good to rig up a simple current limiter,
for
about 5-10 mA, and enclose the whole thing in an insulated box.

An LTspice schematic follows. It limits short circuit current to about 5
mA, but provides 44.6 VDC into a 10 kOhm load or higher. However, it
draws
a constant 93 uA from the battery. You can fiddle with the values, and
maybe use a darlington (but you need to add an extra diode). It is also
possible to build this with a PMOS transistor with negligible current
draw
with no load, but a little more power in the sense resistor while
operating.


Paranoia.

Not at all. It's a good idea, at least, to know how to rig up a current
limiter, especially when it can be built for less than the cost of one of
the batteries. It could prolong their life in the case of an accidental
short circuit or overload, and it would be very much advisable for Lithium
batteries which can explode if short-circuited.

SNIP

Here's a link to a somewhat technical analysis of low voltage hazards.
It is probably an overkill answer to the OP's question, but it is
readable and provides a scientific basis for its conclusions.

Chuck

http://www.mikeholt.com/download.php?file=PDF/SafeVoltageReview.pdf


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[z]

On Mar 19, 1:42 am, "Dave.H" <the19...@googlemail.com> wrote:

On Mar 19, 3:43 pm, "Bob Monsen" <rcmon...@gmail.com> wrote:





"Dave.H" <the19...@googlemail.com> wrote in message

news:bc083361-8e07-4b96-a1c7-940cb8bc97c3@d4g2000prg.googlegroups.com...

I'm not sure if I should be asking this this type of question here,
but couldn't find another suitable newsgroup, so here goes, I'm
building a power supply for a regen radio that consists of two
wallwarts, in series delivering 23 volts 300 mA each, for a total of
46 volts, 300 mA.  I'm not sure if this type of voltage and current is
dangerous, what would happen if I accidentally touched both the B+
line and the B- line, or ground connection at the same time?  Would I
just receive a small electric shock? If it's too dangerous, I'll just
stick to 5, 9 volt batteries in series.
Thanks

Dave

You might be able to feel it. However, batteries will probably support even
more current than a wall transformer. So, just pay attention when you are
playing with it.

Regards,
 Bob Monsen

I don't mind if it hurts, just as long as it's not lethal, the radio
is only using one tube, I've been told it doesn't use much current.
I'll still be supplying the filament voltage via batteries.- Hide quoted text -

- Show quoted text -

46 volts is about what's on the phone line, IIRC, and nobody really
worries about that. (until you're holding the wire and the phone
rings, ring votage being like 90 volts. whoo hee.)

 

[Paul E. Schoen]

"z" <gzuckier@snail-mail.net> wrote in message
news:f3356871-04ac-4e0b-a419-67044fe9b9bc@m34g2000hsc.googlegroups.com...

46 volts is about what's on the phone line, IIRC, and nobody really
worries about that. (until you're holding the wire and the phone
rings, ring votage being like 90 volts. whoo hee.)

The phone line current is limited to something like 20-80 mA, which may or
may not be below the level of serious danger. See
http://www.sandman.com/telco.html for devices that claim to use the telco
power. The maximum power you can draw is probably at the point where the
line voltage drops to half (about 24 VDC), at which line current would
probably be about half (about 40 mA maximum), so power would be just about
1 watt. There will be a point at which the telco senses an off-hook
condition, and will send voice and tone warnings on the line.

The ring voltage is about 20 Hz, which IIRC is not as likely to cause
fibrillation, and it is applied and removed every couple of seconds. It is
also current limited to about 50 mA. It is based on REN (Ringer Equivalence
Number), which is 8.75 mA, and the phone company generally supplies 5 REN,
or 44 mA. This works out to 2.6 watts. But it is duty cycle limited to an
average of about 1 watt.

See http://www.sandman.com/ringvoltbul.html for some interesting
information. It shows 84 VRMS ring voltage at 1.4 REN. The threshold for
ringing is about 60 VAC, but can be much lower for modern phones. These
numbers were based on the old Bell type 2500 with electromechanical bells.

Any voltage source should be treated with some respect and knowledge of
possible hazards, and one should take any reasonable precautions.

Paul

 

[z]

On Mar 21, 5:06 pm, "Paul E. Schoen" <pst...@smart.net> wrote:

"z" <gzuck...@snail-mail.net> wrote in message

news:f3356871-04ac-4e0b-a419-67044fe9b9bc@m34g2000hsc.googlegroups.com...

46 volts is about what's on the phone line, IIRC, and nobody really
worries about that. (until you're holding the wire and the phone
rings, ring votage being like 90 volts. whoo hee.)

The phone line current is limited to something like 20-80 mA, which may or
may not be below the level of serious danger. Seehttp://www.sandman.com/telco.htmlfor devices that claim to use the telco
power. The maximum power you can draw is probably at the point where the
line voltage drops to half (about 24 VDC), at which line current would
probably be about half (about 40 mA maximum), so power would be just about
1 watt. There will be a point at which the telco senses an off-hook
condition, and will send voice and tone warnings on the line.

The ring voltage is about 20 Hz, which IIRC is not as likely to cause
fibrillation, and it is applied and removed every couple of seconds. It is
also current limited to about 50 mA. It is based on REN (Ringer Equivalence
Number), which is 8.75 mA, and the phone company generally supplies 5 REN,
or 44 mA. This works out to 2.6 watts. But it is duty cycle limited to an
average of about 1 watt.

Seehttp://www.sandman.com/ringvoltbul.htmlfor some interesting
information. It shows 84 VRMS ring voltage at 1.4 REN. The threshold for
ringing is about 60 VAC, but can be much lower for modern phones. These
numbers were based on the old Bell type 2500 with electromechanical bells.

Any voltage source should be treated with some respect and knowledge of
possible hazards, and one should take any reasonable precautions.

Paul

off topic, but what with april fools day coming up: when you're on the
phone with somebody, suddenly say 'hey, what are these two wires
coming out of the phone? AAAAAAHHHHHHHHHHHH!!!!!"