Relay computers

From: Dwight K. Elvey <>
Date: Fri Sep 24 15:45:08 2004

>From: "Tom Jennings" <>
>On Fri, 2004-09-24 at 07:39, Ade Vickers wrote:
>> If each relay needs, say, 25mA _at_ 6v to operate, then the peak current
>> draw
>> of our R80 (as I shall call it) could be around 600A (I think). And
>> that's
>> before we've added memory, i/o, etc.
>Last things first :-) the place to look for this is telco. They did
>really for real. Most of them are 48V; it lowers current plus higher
>voltages help with the inductive time constant thing (take a look at how
>teletype loops are done; HV, a series resistor shortens the *effective*
>time constant (eg. the time to reach 60mA in the tty case).

 Increasing the resistance doesn't change the power needed
to pull in the armature, all it does is decrease the time
constant for a particular inductance. Higher voltages require
more resistance in the wire, meaning more turns. The pulling
effect on the armature is just ampere-turns. Using more resistance
just means higher voltage. E^2.
 One can do the same thing by adding a resistor in series with
the 6V coil and using a higher drive voltage. Power wise, it is
a loss. You still need the effective 25mA in the coil.

Received on Fri Sep 24 2004 - 15:45:08 BST

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