Why 400 Hz in mainframes? 3

[peebee]

Does anyone know why IBM used to require 400 Hz power to their old mainframes?

 

[busbar]

One is to get high disc drive speed {for faster access.} Apparently 415Hz is/was used too.

 

[peebee]

The drives are AC, not DC? Hmmm....

Still seems like a lot of money and space required for those power supplies. Doesn't seem like a lot of bang for the buck.

 

[cbarn24050]

Hi, same reason as for aircraft, it keeps the size and weight down.

 

[peebee]

I have trouble buying that, cbarn. It makes sense on planes to generate at 400 Hz, then, yes, all subsequent conversions use small inductors. But with data centers, we already have some perfectly good 60 Hz power coming in. Performing two conversions on that (60-400-DC) just seems like it would require extra space and weight.

 

[cbarn24050]

Hi peebee, in those old days mainframes were huge enterprises taking up complete floors. They had hundreds of power units and ac motors. years ago when i was in the military all the field portable radar units had 50 to 400 converters and 1 60's anti aircraft radar even used 1600hz power.

 

[busbar]

One comment that is open for correction/discussion by readers...for higher AC-power frequencies in aviation, isn’t there a savings in iron but not copper for otherwise similar systems?

 

[peebee]

I think you have that right, busbar. My understanding is that higher frequencies mean smaller inductors as impedance is a function of frequency; higher frequencies mean smaller inductors for the same impedance. If you want to reduce copper, you need to increase voltage, same as anywhere else.

 

[cbarn24050]

Hi, a smaller transformer has less copper as well as less iron than a bigger one. Also with power units you need smaller filter caps as well.

 

[Cubrilo]

About busbar comment..cbarn24050 is right, when you have higher frequency in transformer you have less iron but still large induced voltage. So you can reduce number of winding turns, which means less copper.

 

[benray]

Aircraft instruments contain gyroscopes driven by small 3 phase 400 Hz motors. A 4 pole motor will turn at 12,000 RPM, the required speed for the gyros.

The maximum speed from a 60 Hz. supply is 3600 RPM, with 2 poles, not adaquate for a gyro to function.

Speed of drive must be the reason.

 

[peebee]

If you read closely, you'll see benray's answer was right on the mark, with his reference to "speed of drive."

 

[redtrumpet]

Search for "400 hz" in the advanced search function of this website - there are many threads, although most pertain to use of 400 Hz in aircraft.

 

[benray]

Sorry about my lack of clarity. My technical writing skills need improvement. I am accustomed to writing to myself, and sometimes leave a lot of detail out.

I am new to this forum, and don't know the protocol.

400 Hertz is used on warships for gyro stabilized compasses, gyro stabilized operating rooms, gun turrent fire control, and automatic navigation systems, where high constant speed drive motors are required.

Aircraft use is based on the same conditions and need. The automatic flight control, and navigation systems, depend on gyros for stability.

Whenever I see 400 Hertz in use, I think speed plus weight and space, in that order.

 

[busbar]

Aside from physical size, a 2-pole 400Hz induction motor works out to run at 24,000RPM. That would be a nice disc-drive speed. AC…no pesky brushes and commutator maintenance! {Isn't 10kRPM hot stuff in PCs right now?}

 

[cbarn24050]

Hi guys, i hate to disagre with you BUT there was nothing on those old IBM mainframes that ran at high speed.

 

[benray]

Oh well, back to square one. What is the speed of the drives? Would 60 Hertz present a problem with EMF, that may not appear with 400 Hertz? Does filtering of high cycle play into this application? How about harmonic frequencies?

What phasing and voltage is this 400 Hertz?

 

[peebee]

I have no idea, benray. I just know I've seen a bunch of those old power supplies sitting abandoned around old data centers and have ripped a few out. They are really big boxes, usually at least as big as the 60 Hz UPS systems installed next to them (which are often still in operation), which is why I'm struggling with the proposed idea that they are supposed to be saving space or weight or cost. Drive speed sounded like a reasonable idea, but I suspect those old 12" disk stacks could not have been spinning very fast (although its not clear to me that 12" stacks are the kind of drives they were running at 400Hz).

I'm kind of surprised this post set up such a heated debate, I really thought there would be one simple answer like there is on planes. Maybe there never was a good reason for them in the first place other than IBM marketing (let's lock them in to buying a power supply from us), and that's why 400 Hz is gone now.

Not to get too far off the subject, but does anyone have any info on either 1) how to request a data center forum be set up on this site, or 2) any other links for data center and reliability engineering? This is the best site I've found so far for engineering, but I've found little anywhere on the net that's particularly useful or focused for data center design.

 

[IRstuff]

Note that IBM was famous (notorious?) in the old days for building stuff simply to make it difficult for the "7 dwarves," e.g., Honeywell, Burroughs, Sperry, etc., to compete with.

There may not be a technical reason for the design baseline at all.

TTFN

 

[Lewish]

I don't know what RPM the IBM drives ran at, I do know that the big disk drives built by Texas Instruments for themselves and other brands ran at 3600RPM and from 60Hz.
Hope that info is useful.