360/50 microcode listing

Jon Elson elson at pico-systems.com
Fri May 8 10:39:13 CDT 2015

On 05/08/2015 06:30 AM, Noel Chiappa wrote:
>      > From: Jon Elson
>      > Well, first, rotary converters draw a LOT of imaginary power (in other
>      > words, they have an awful power factor) and so the line current can
>      > become MUCH higher than you would expect.
>      > ...
>      > We tried to rig up a phase converter scheme to run the motor-generator
>      > set on a 370/145 in a guy's house, and it did NOT go well. he only had
>      > a 60 A 240 V service, and the imaginary current was over 60 A!
> Had to Google 'imaginary power'... Not a lot of experience with high-power AC
> stuff! :-) ('Imaginary power' is probably not the best term to use, because
> there are actual currents involved; I like the 'reactive power' name better.)
Yup, that's another name.  The imaginary comes from the real 
and imaginary components of a complex number.
> The article I read said that in reactive load which is high in inductance
> (which is, I assume, the source of the high reactive load in rotary
> convertors - or am I confused - a common happening, I concede :-), judicious
> application of capacitance can reduce the reactive load. Why isn't this used
> with rotary convertors to reduce their reactive load?
Yes, but it takes a BIG bank of caps to compensate the 
current on a 17 KVA motor.  Meanwhile, you are trying to 
generate a reactive current (phase shifted) to drive the 3rd 
leg of the motor.  It gets messy.  Also, the cap bank is 
going to draw a huge current spike when the relays are 
closed, and that could weld contacts in the contactor.  it 
was just a fool's errand to try this on a house with 60 A 
> Any idea what the active and reactive powers/currents were in that attempted
> installation?
Well, the MG system in the 370/145 had delta/wye starting.  
We had to have a guy HOLD the circuit breaker while in the 
wye configuration, so the total current was already over 60 
A.  Then, when we closed the delta contactor, he could NOT 
hold the breaker closed with both hands.  That's when we 
knew we were totally beat. But, you can compute the line 
current for a 17 KVA motor.  Line current should be about 40 
A with real 3-phase power.  If you need to run this off a 
single-phase 240 V mains, then the line current just to 
satisfy the unity power factor requirement would be closer 
to 70 A.  Add in bad power factor from the phase shifting 
scheme, and you could easily end up over 100 A without a 
huge phase compensating cap bank.  Now, the crazy thing is 
the /145 had a DC power dissipation of 1.9 KW, if I remember 
right!  390 A at 4.8 V. (They used +1.3 and -3.5 V I think, 
so it put their ECL terminators at ground.)  I think they 
used the same MG sets for a range of different computer models.

The only sane fix would have been to scrounge up some big 
switching power supplies and replace the whole PS system on 
the machine.  But, then, the guy that had this would have 
been able to load microcode and key in programs to type 
stuff on the console typewriter.  He'd still need a disk 
controller and a com controller at the very least.


More information about the cctech mailing list