Supercomputers, fishing for information

Paul Koning paulkoning at
Tue Nov 8 11:22:09 CST 2016

> On Nov 8, 2016, at 12:08 PM, Guy Sotomayor Jr <ggs at> wrote:
>> On Nov 8, 2016, at 8:47 AM, Jon Elson <elson at> wrote:
>> On 11/07/2016 10:31 PM, Jon Elson wrote:
>>> On 11/07/2016 07:59 PM, Mark Linimon wrote:
>>>> On Mon, Nov 07, 2016 at 11:23:58AM -0800, Chuck Guzis wrote:
>>>>> But if you're a suburban resident living on Mulberry Street, anything
>>>>> but single-phase is pretty much out of the question.
>>>> Oh, you can get it -- but be prepared for a large hassle.
>>>> A former neighbor had a 440V 3-phase Italian lathe in his backyard shop,
>>>> among other toys.  After he was laid off from his aerospace job doing
>>>> machining it was how he made his living.  He was a very handy person
>>>> to know :-)
>>>> mcl
>>> I have two 3-phase machines in my shop (Bridgeport mill and Sheldon lathe) and run them each off a properly-sized VFD. 2-phase in, 3-phase out, plus variable speed and dynamic braking.
>>> Jon
>> And, of course, that is really SINGLE-PHASE power on 2 wires, just to save anybody the trouble of correcting my error.
> I’m looking to have to do something to get 3-phase for the IBM 4331 gear.  I haven’t quite added up the power requirements yet but I’m guessing its going to be in the 10-15kVA range.  Since the power to all of the gear is really split between 3 loads (string of 4 3340 drives, 3803 control unit + 2 3420 tape drives and 2821 control uint + 1403 printer + 2540 card reader/punch) I need to figure out if it’s best to have one big converter or 3 smaller ones.  It’s unlikely that I’d be running all of the peripherals at once.  The 4331 itself runs off of single phase 220v.

A VFD is a good option and may be quite economical if you get one of the low cost simple ones.  I have one (3 hp model for my lathe) that cost only a bit over $100, though the price has gone up since.  (Westinghouse TECO brand.)  VFDs specified for single phase input tend to stop around 3 hp, as far as I have seen.  Rumor has it that higher power units will also work (possibly with some derating) even though they claim to be 3 phase input, when you feed them just one phase on 2 of the 3 wires.  I haven't tried that (but it matches how my VFD is connected).

The other option is a "rotary converter".  Basically that's a 3 phase motor connected to one phase power (with a start and run capacitor); it generates the missing phase roughtly in dynamotor fashion.  Those can be built (articles on the web) or bought from machinery supply companies such as Enco; they show models up to 20 hp, i.e., about 15 kW.  When I was looking into converters, I found VFDs to be the less expensive option.  The instant reverse and variable frequency features were also attractive for lathe use; for powering computers that would not apply.  Well, not unless you need 400 Hz for your Cyber 6600 -- in which case you'd need to check the VFD will go that high, not all do.

Given that you have a number of smaller devices and that not all might need to run, several smaller converters sounds like a good option, especially if that gets you into the "economy VFD" range.


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