Re: Variac nonsense

On Tue, 17 Feb 2009 13:05:41 +1100, Sylvia Else
<sylvia@xxxxxxxxxxxxxxxxxxx> wrote:

John Fields wrote:
On Mon, 16 Feb 2009 17:57:29 +1100, Sylvia Else
<sylvia@xxxxxxxxxxxxxxxxxxx> wrote:

Phil Allison wrote:

** It's sooo simple.

A variac can work with DC too.
How's that?

---
Voltage divider: (View in Courier)


E1
|
[R1]
|
+----O<---E2
|
[R2]
|
+----O
|
.
.
.
|
[Rn]
|
0V

The voltage at E2 would be equal to the sum of all the resistances
belowe the tap multiplied by E1, then divided by the sum of all the
resistances in the string.

A trifle fanciful though, considering a 300 turn Variac wound with
#10AWG magnet wire and a 12" length of turn would yield a 300 foot
winding with a resistance of 300 milliohms and turn-to-turn resistances
of 0.001 ohm.

I'll grant you that theoretical possibility, but I'd question whether
it's properly called a variac in that context, even if that's what the
gear was designed to be.

---
In the same sense that a variac remains a variac when it's being used as
a variable DC voltage divider, a hammer remains a hammer when it's being
used as a doorstop.


JF
.

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