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Michael A. Terrell

Larry Jaques wrote:
On 4 Apr 2017 02:12:18 GMT, "DoN. Nichols"
wrote:

On 2017-04-03, 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.

With modern rectifiers (silicon ones) that would work out to
about 64 VRMS. But vacuum tube rectifiers would have a lot more series
resistance, so that might work out with 110 VAC (the old line voltage,
which then jumped to 115 VAC, then 117 VAC, and now 120 VAC.) (And the
frequency used to be specified as Cycles-Per_Second (CPS) or '~' instead
of Hz. :-)

Also -- the rectifier was likely not used with filter
capacitors, so the RMS value of a half-wave rectified 110 VAC might be
pretty close to that.

Voltages might have started out (in the Dark Ages?) at 110vac, but
they were 115v in my teens and are 120/240vac nowadays. It has been
that way for a long time.

I was thinking that rectification caused the drop to warrant building
90v and 180v DC motors.

120VAC*.707=84.84V Average, unfilterd DC

--
Never **** off an Engineer!

They don't get mad.

They don't get even.

They go for over unity! ;-)