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# Question About Safety Of Voltage Supply

C

#### Chuck

Jan 1, 1970
0
And a fully discharged AAA cell can kill you if fired from a gun. Or if you
eat enough of them.

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

Z

#### z

Jan 1, 1970
0
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.)

P

#### Paul E. Schoen

Jan 1, 1970
0
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

#### z

Jan 1, 1970
0
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!!!!!"

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