Motor generator

Jon Elson elson at
Tue May 4 19:03:03 CDT 2021

On 05/04/2021 06:06 PM, Donald via cctalk wrote:
> In the deep recesses of my mind I seem to remember something about S/360
> machines using a motor generator.
> If I am right was this to create a stable power source at a certain
> frequency or voltage?
Nope.  I know the 360/50 and 360/65 used a 
"converter-inverter" that converted 208 3-phase
to about 280 V DC, then inverted it with a 4-SCR inverter 
feeding a resonant transformer to
create 120 V 2.5 KHz regulated single-phase sine wave 
power.  All the critical loads in the CPU ran off this 
power.  Notably, the I/O power sequencer and console lamps 
power supply did not run off this power.  The 
converter-inverter made an absolutely HORRIBLE whine that 
could be heard 20+ feet from the back of the CPU even in a 
very noisy machine room.

The only "360" machine I know of that used 415 Hz was the 
Model 195, although I can guess that
the 360/85 used 415 Hz also, as it was essentially the 
prototype of the 370/165.

The 370/145 used an internal motor/generator set in the back 
of the CPU cabinet to produce 120 V 415 Hz 3-phase power.  
Larger 370's generally were provided with UPS's instead of 
M/G sets to create the 415 Hz power.

Also, the 709X series ran off 400 Hz from a motor/generator set.

The 360/50 and /65, at least, were pretty sensitive to noise 
and short dropouts in the mains supply.
The 370's with the MG sets rode through pretty severe power 
dips with no effect at all, until the disk drives and tape 
drives went offline.


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