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Tricks for 50 - 60 cycles conversion

Primarily worry - This 1401 system was made for 50 cycle European power A great deal of talk and many e-mails have been concerned with the problem of making this system run in at U.S. standard 60 cycle power.

The goal of this document is to:

a) present some relevent background facts
b) summarize some of the comments/positions

Table of contents:

- Ron Williams letter Nov 8, 2004 HTML, image.
- Common "Iron" Core Transformers - the kind we have.
- "Universal" Motors - as in vacuum cleaners, household mixers, hand drills, ...
- Near Synchronous - all the non-fan motors in the 1402, 1403? and 729?? tape units.
- Ferroresonant Power Conditioners - smooths, regulates the output AC voltage.
- 60 Hertz to 50 Hertz Frequency Converters
Common "Iron" Core Power Transformers the kind we have.

Executive Summary: Raising the applied frequency from 50 Hertz to 60 Hertz is just fine.

I am placing quotes around "Iron" because actually the metal is sheet steel with more than the usual amount of silicon to increase its resistivity. The sheets are insulated from each other with oxide to reduce losses and heating due to "circulating currents". For transformers designed for 50 Hertz, raising the applied frequency 20 percent to 60 Hertz is no big deal. :-)) Actually the "iron" losses will decrease a little due to reduced "iron" saturation and hysteresis loss. :-)) Losses due to "circulating currents" will increase a little.

Going the other way, from 60 Hertz design to 50 Hertz usage, is a *BIG DEAL*. The applied input voltage should be reduced to 5/6 name plate rating or bad things can/will happen. They need about 20 % more "iron" to work at 50 Hertz.

Reference - most any transformer book and also

http://www.sola-hevi-duty.com/products/powerconditioning/pdfs/opchars.pdf

"Universal" Motors as in vacuum cleaners, mixers, hand drills, ... Executive Summary: "No Problem"

This little guys (with brushes inside) run just fine from DC to over 400 hertz with nary a whimper.

Near Synchronous like all the non-fan motors in the 1402, 1403? and 729?? tape units.

Executive Summary: The motor will run OK, :-)) except 6/5 faster than at 50 Hertz. :-(( Correctable by changing diameters of capstans (729) and drive belt pulley ratios (1402). We can check with Frank King about how the 1403 printer works.

Similar to the transformer, a near synchronous motor (some times called "squirrel cage" after the conductor pattern in the rotor) designed for 50 Hertz will work. HOWEVER, the speed will be 6/5 faster than at 50 Hertz. (Due to the low cost of rotor manufacture and their great reliability - no brushes - they are very popular in the speed range of a little below 1000 RPM to 3600 RPM).

Allen Palmer measured the capstan diameter of the museum's 729 tape units, and the diameter of the diameter of the 60 Hertz units was 5/6 of the 50 Hertz units - just like the book would predict :-))

It is very likely that a similar comparison of drive pulley ratios in the 1402 reader punch will have the same comparison.

1403 printer?

Design background: The speed of near synchronous (squirrel cage) motors and true synchronous motors is determined by the way the windings are layed in the part containing the rotating field (always the stator or fixed part in the motors of interest to us today.) They are usually wound with one axises of magnetization (two poles), or two axises of magnetization (four poles) or three axises of magnetization (six poles), , These yield
AC Frequency Two Pole Four Pole Six Pole
60 Hertz near 3600 RPM near 1800 RPM near 1200 RPM
50 Hertz near 3000 RPM near 1500 RPM near 1000 RPM

Actually, the near synchronous motors "slip" a little, and up to about 5% under full load. So the full load speed of a 4 pole motor excited at 60 Hertz is about

1800 * 0.95 = 1710 PRM as seen on many motors.

Motor trivia Three phase motors have high starting torque with no artificial help, the internal field actually rotates giving the rotor a good twist. So called split phase motors, as plugged into the usual wall socket, have an internal field that oscilates back and forth, providing no torque until the rotor gets to spinning to say 15 % rated speed. These split phase motors are started in three common ways,

1) capacitor start - as on hard starting loads like piston pumps,
2) resistor start - as on easier starting loads such as drills, grind wheels, bigger fans.
On the two types above, the starting element is switched out when the rotor reaches about 50% rated speed to save damage of the capacitor or resistive element.
3) A third way is used in small motors as in fans, clocks, ...
where efficiency and starting torque is not a big issue.

Like transformers, a near synchronous motor designed for 60 Hertz must have its input voltage reduced to 5/6 of rated voltage for 50 Hertz operation. The rotational speed will be reduced to 5/6. Rated power and starting torque will also be reduced.

Ferroresonant Power Conditioners which smooth and regulate the voltage of AC.
Constant Frequency, Input vs Output Voltage, varying loads
Percent regulation is less than 1% for +- 10% input voltage variation.

Graph from Emerson Industrial.

Constant Load, varying frequency
"Output voltage varies linearly with a change of frequency of the input voltage. This change is about 1.5% of the output voltage for each 1% change in input frequency and in the same direction as the frequency change."

60 Hertz to 50 Hertz Frequency Converters

There are two major types, rotating (as a motor/generator), and static (all electronic)

Robert Garner, Grant Saviers, and Mike Falarski who have studied the pros and cons of the above choose the static converter due reduced noise, maintenance, and heat.

The following discusses static frequency converters. Robert Garner and Grant Saviers who have also studied static frequency converters report that new devices cost new about one dollar per volt amp (in less accurate terms, watts). The full 1401 with out tapes takes about 5 kilo volt amps (KVA) and the system including the five tapes requires (as per IBM documentation) about 13 KVA. Or currently about $15 thousand dollars. There is a bit of reluctance to spend almost as much to power this interesting artifact at its current requirement of 50 Hertz as it took to buy the artifact -

Anyone got a short or long time "loaner"?