25 Hz?

[hbiss]

I was watching a guy on YouTube who was repairing a vintage radio from the 40's. He happens to be in Canada and the radio he was working on had an unusually large power transformer. He said that was because it was designed to operate off 25Hz power. That became clearer when someone in the comments said something like his father worked in Michigan and when he looked across the river at Ontario, there was a noticeable flicker in the lighting. He said Ontario used 25Hz until sometime in the 50's. Anybody heard of this and why did they use 25Hz?

-Hal

 

[drcampbell]

25 Hz used to be very common for electric trains. I think a little bit of it is still in use.
It would have been selected because it was a good compromise between electrical inefficiency and mechanical inefficiency at the time.

 

[retirede]

There is a hydroelectric dam on the Mississippi River at Keokuk Iowa. It originally generated 25 cycle power. When it was commissioned in 1913, it was the largest hydro power plant in the world - 142 MW. Much of the power was utilized by streetcars as far away as St. Louis.
After WW2, it was transitioned to 60 HZ.

 

[bwat]

25 Hz used to be very common for electric trains. I think a little bit of it is still in use.

Yes, Amtrak still uses 25 cycle. Kinda neat because it’s rather unique in today’s age, but it can make it more challenging if you are doing projects for them..

 

[zbang]

IIRC the original installation at Niagara Falls was 25Hz and it was the industrial frequency for years (apparently, AC motors commutate better at lower freq's). It is still in use for Amtrak from DC to NYC, Phila to Harrisburg, and for the ex-Reading lines. (And that'll never change due to cost.)

Also, IIRC Bethlehem Steel in Baltimore still generated 25Hz into the 1990s for the older rolling plants (with their "walk-in" motors).

If you search these fora, you'll turn up a few more threads on the subject.

 

[Jraef]

Tesla's first power generator at Niagara Falls was 25Hz, as were most of the big pumps keeping New Orleans dry, up until they flooded out with Katrina. In fact one of the problems after Katrina was that they lost all of their 25Hz generators in the storm, so they couldn't restart the pumps until they changed the motors to 60Hz. Lower frequency was actually better for motors, they only changed to higher frequencies when they went to use electricity for lighting. There was lots of experimentation on the right frequency to use; 40Hz was tried for a while, 100Hz, 133Hz, even 16-2/3Hz. Different levels were tried until they settled on 60Hz (here). The first AC 3 phase system installed in the US was at the Redlands Power House outside of Riverside, California (Tesla's system at Niagara was 2 phase). It was originally 40Hz, then changed to 50Hz.

 

[zbang]

FWIW, some European railways still use 16 2/3 Hz.

 

[hbiss]

In fact one of the problems after Katrina was that they lost all of their 25Hz generators in the storm, so they couldn't restart the pumps...

Yes! I do remember that now that you mentioned it.

-Hal

 

[LarryFine]

. . . the radio he was working on had an unusually large power transformer. He said that was because it was designed to operate off 25Hz power.

Sorta the "reciprocal" of why they use 400 Hz on aircraft.

 

[synchro]

An article that gives some background on how frequencies were selected:

 

[LarryFine]

An article that gives some background on how frequencies were selected:

View attachment 2552261View attachment 2552262

(I'm blinded!)



It kinda seems logical that a motor on a lower frequency, that requires more steel, would result in greater torque.

 

[romex jockey]

interesting article, all sorts of HZ, phases & poles conjecture , seems there was a lot of good ideas on the table a century ago.....some better than what we have now...

but i'm willing to wager a standard had to be agreed upon for martketability

~RJ~

 

[drcampbell]

... they use 400 Hz on aircraft.

Automotive alternators also use higher frequencies to save weight.
They're obviously not constant-frequency devices but do operate near 400 Hz. (when cruising easy)
Most of them are a three-phase ac generator with a full-wave diode bridge, typically ten or twelve-pole machines.

 

[LarryFine]

Of course, automotive alternators are variable speed/frequency, but the rectification makes that point moot.

My bike's alternator has not only three stator phase diode pairs, there is a fourth pair on the output common.

Something like this:

 

[hillbilly1]

Many years ago they made a kit that would convert your car alternator to power a 120 receptacle. Worked pretty decent, though it would eat up the brushes fairly quickly if you used it a lot. Had a light on it that would light up when you got to the correct voltage.

 

[synchro]

Of course, automotive alternators are variable speed/frequency, but the rectification makes that point moot.

My bike's alternator has not only three stator phase diode pairs, there is a fourth pair on the output common.

Something like this:

The extra 2 diodes connected to the wye center tap apparently contribute as much as 15% extra output current, but at the expense of some added ripple.
This is described on page 3 of this article:

https://www.scannerdanner.com/media/kunena/attachments/4419/updatingyourripplevoltagetutorial.pdf#page=3

These "power boost" diodes are also mentioned in this patent:

US3866072A - Power boost auxiliary diode assembly for vehicle alternator - Google Patents

The two diodes of a power boost attachment for a three-phase star connected alternator-rectifier unit of a motor vehicle is provided as a flat assembly to be mounted directly across the d.c. terminals on the casing of the alternator-rectifier unit. The third connection is provided by a hollow...

patents.google.com

 

[GeorgeB]

Many years ago they made a kit that would convert your car alternator to power a 120 receptacle. Worked pretty decent, though it would eat up the brushes fairly quickly if you used it a lot. Had a light on it that would light up when you got to the correct voltage.

Very stale memory here ... one ham buddy, back in the late 50s or early 60s, tapped a Chrysler alternator ahead of the diodes and connected it to a 400 Hz transformer core to step the (probably 15V square wave?) up to operate his kW amplifier. I helped him wind the coils as a pre-teen who hung out in his shack and got to talk to people all over the world.

 

[drcampbell]

... a kit that would convert your car alternator to power a 120 receptacle. ... eat up the brushes fairly quickly ...

They didn't really "convert" anything. They just disconnected the alternator from the vehicle wiring, unplugged the voltage regulator (they were in two different packages then) and put 100% excitation on the rotor winding. Then speed up the engine until 90-plus volts DC appears on the B+ terminal and the neon lamp comes on, then plug in your incandescent lamps or universal-motor AC/DC tools.

Every once in a while, you'd see a service truck with a second alternator permanently installed and a "110-volt" receptacle under the hood.

They put a lot of stress on the diodes, too.

- - -

... tapped a Chrysler alternator ahead of the diodes and connected it to a 400 Hz transformer core to step the (probably 15V square wave?) up ...

A while back, (1980s?) Cadillac did that same thing to provide a higher voltage for a heated windshield. If I recall correctly, it was 96 volts, 48 on either side of ground. Cadillac subcontracted Western Electric to make transformers, told them to prepare for building 100,000 (?) per year, then sold maybe 1,000 (?) cars with that option and dropping it after one (?) model year. There was a big brouhaha when Western Electric asked to be paid for all 100,000.

 

[hillbilly1]

They didn't really "convert" anything. They just disconnected the alternator from the vehicle wiring, unplugged the voltage regulator (they were in two different packages then) and put 100% excitation on the rotor winding. Then speed up the engine until 90-plus volts DC appears on the B+ terminal and the neon lamp comes on, then plug in your incandescent lamps or universal-motor AC/DC tools.

Every once in a while, you'd see a service truck with a second alternator permanently installed and a "110-volt" receptacle under the hood.

They put a lot of stress on the diodes, too.

- - -


A while back, (1980s?) Cadillac did that same thing to provide a higher voltage for a heated windshield. If I recall correctly, it was 96 volts, 48 on either side of ground. Cadillac subcontracted Western Electric to make transformers, told them to prepare for building 100,000 (?) per year, then sold maybe 1,000 (?) cars with that option and dropping it after one (?) model year. There was a big brouhaha when Western Electric asked to be paid for all 100,000.

The one I had used a switch on a box, I had to disassemble the alternator, wire it in between the rectifier and the regulator. So it was sort of a conversion.

 

[Frank DuVal]

I've never seen the "High Voltage" alternator on a Cadillac, but, I have seen several on Ford products (1974 to 1976) to heat the windshield. They carry a big High Voltage nameplate.

The heated windshields of the late 80s onward Fords did it at 12V.