On Mon, 3 Apr 2017 07:18:05 -0400, "Jim Wilkins"
wrote:

"Tim Wescott" wrote in message
...
On Sun, 02 Apr 2017 22:42:36 -0400, clare wrote:

On Sun, 2 Apr 2017 19:27:38 -0700, MOP CAP
wrote:

Many of such motors with wound fields required 90 volts for the
field.
Why 90 volts and how was it derived?
thanks,
CP
Some had field rheostats for speed control. As for the 90 volts,
likely
the output voltage of a rectified line voltage using the rectifier
technology and line voltage of the time.

90V probably became standard at some time in the dim past for
reasons
that haven't applied since 1920, but has been carried forward
because
it's a standard.

Just a guess, but you stumble across that sort of thing all the
time.

--
Tim Wescott
Control systems, embedded software and circuit design
I'm looking for work! See my website if you're interested
http://www.wescottdesign.com

This describes 90VDC motors as suitable for thyristor-regulated
rectified 120VAC.
http://www.leeson.com/Literature/pdf/b1600IEC.pdf

The mercury vapor tubes used as high power rectifiers before
comparable silicon diodes became available dropped around 15V.

-jsw


Absolutely correct.

Gunner

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