On Mon, 03 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

Hmm. That sounds about right if you used the field coil as the inductor
in a choke-input "filter".

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!