IBM 4331 Mainframe 3 phase converter

Guy Sotomayor Jr ggs at
Thu May 4 10:36:45 CDT 2017

> On May 4, 2017, at 8:04 AM, jim stephens via cctalk <cctalk at> wrote:
> On 5/4/2017 7:36 AM, Guy Sotomayor Jr via cctalk wrote:
>> Does anyone know how to convert KVa to 208v 3-phase currents and/or HP?  IBM’s docs all specify power in KVa and most of the 3 phase converters (other than what Bob posted) seem to specify HP.  If I’m going to spend serious coin on a phase converter (I think I found it online for ~$3k…ouch!), I want to make sure it’s sized properly.
>> Thanks.
>> TTFN - Guy
> You will also need to get the motor start information, or you will vaporize a phase converter.
> Another possible approach that a friend is taking is to take three single phase identical UPS system and synch the phases of the three converter output circuits to proper three phase.
> He's made up one from three junk APC units I've got.  I can forward info if you would like on this approach from him.  One thing that helps is he snagged and maintained the drawings of all of the APC and other output circuits over the years and has good info on how to pull this off.
> The quadrature power will be something to deal with on your three phase loads, but you may be able to run quite a bit of single phase hardware directly off of the mains.

OK, that’s not helping.  Here’s what I have (from IBM site planning docs GC22-7064-10 and GC22-7069-2):
3340-A2 DASD: 2.2 kVA 3-phase
3340-B2 DASD: 1.7 kVA 3-phase (powered from 3340-A2)
3803 Tape Control unit: 1.8 kVA 3-phase
3420 Tape drive: 2.9 kVA 3-phase (powered from 3803) (x2)
2821 control unit: 1.4 kVA 3-phase
1403N1 Printer: 1.5 kVA 3-phase (powered from 2821)
2540 card reader/punch: 1.2 kVA 3-phase (powered from 2821)

So I have 3 potential power feeds:
DASD: 3.9 kVA
Tape: 10.5 kVA
I/O: 4.1 kVA

For a total of 18.5 kVA

So the several $1000 question is how do the kVA’s map into 208v 3-phase amps?  Depending upon how that works out I need to figure out if 2/3 converters make sense or just one big one.

My simple minded conversion is to take the 18.5kVA, multiply by 1000 and divide by 208.  That gives me just shy of 90A.  Do I then divide by 3 to get A/phase?  If so, then it’s 30A per phase which seems reasonable.  But I don’t know if that’s the correct formulation.

TTFN - Guy

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