On 2017-04-05, Michael A. Terrell wrote:
Larry Jaques wrote:
On 4 Apr 2017 02:12:18 GMT, "DoN. Nichols"
wrote:

[ ... ]

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


That sounds wrong. The 0.707 multiplier is applied to the peak
voltage (170V) to get to the 120 VAC rating. Applying it again to the
result just feels wrong. :-)

However, if you are half-wave rectifying, with no filtration
capacitors, the RMS (Root-Mean-Square) value of that half cycle,
followed by another half-cycle of time, could be pretty close to the
90V rating for the field.

O.K. -- Looking in this site:

http://www.daycounter.com/Calculators/RMS-Calculator.phtml

gives this for a half-wave rectified value:


================================================== ====================
Half rectified wave Vrms= Vpk/2
================================================== ====================

so -- for the 170 V Peak, we get 85V RMS

so -- 90 V field allows for a surge of 127 VRMS ac -- so a worst-case
value.

Enjoy,
DoN.

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