[GreenKeys] Why high loop voltages?

[Ralph Mowery]

----- Original Message ----- 
From: "John Nagle" <nagle at animats.com>
To: <greenkeys at mailman.qth.net>
Sent: Tuesday, January 27, 2009 3:28 PM
Subject: [GreenKeys] Why high loop voltages?


>    Something I don't get: why were such high loop voltages used?
>
>    I just got a Model 15, and just finished degreasing, cleaning and
> re-oiling it, but don't have anything to connect it to yet.
> (It was mechanically in good shape, but out of use for years.)
> The magnets are wired in parallel and measure 55.3 ohms at the
> input to the printer.   This is a 60mA current loop device, so
> it should run on 3.3V.  3 D batteries in series will run the thing,
> drawing 75mA; I should put a 20 ohm resistor in to get the
> current right.
>
>    So what is the rationale for huge loop voltages?  I realize
> the drive is supposed to be constant current, but making a

>

For a good explination you can go here:

http://home.earthlink.net/~ku4pt/RTTY/rtty%20loop.pdf

It is all abut the time it takes to reach the steady state 60 ma.  When you 
first apply a low voltage it will take a long time (in miliseconds) to reach 
the 60 ma or close to it that is required for the magnets to work.  The 
higher the voltage , the faster the 60 ma will be reached and the quicker 
the magnets will pull in.

If the coils are rewound with bigger wire and less turns of wire you could 
use a lower voltage and higher current to get the magnets to pull in faster.