[GreenKeys] Need motor for 50Hz supply (or DC)

Thu Sep 3 17:23:36 EDT 2026

Not true.  Single phase to single phase VFDs exist, I happen to own two of them.  Your certainly don’t want to use an older standard three phase output VFD to drive a single-phase load, though.  Many newer VFDs have a parameter setting for driving a single-phase load.  I also use a single-phase input VFD to derive 120/208, 400Hz wye connected power by placing a delta to wye transformer (surplus airliner 400 Hz lighting transformer) on the output.   This is handy for powering up avionics loads.  The important thing is to make sure the parameter are set properly, and carefully measuring the RMS voltage and frequency, before connecting the load.  After saying all of this, it may not be worth the hassle, I have built inverters and frequency changer for years, there are many pitfalls, but amazingly some of the cheap Asian VFDs are being produced with features that will allow much greater flexibility in operation.  

Finally- the old brute force approach:  find and old Bogen or similar PA amplifier with a 125V line transformer output, pump 50 Hz into the input, and adjust for proper voltage at the output, add an AGC circuit if you anticipate a changing load.  This worked for me for years (I needed 400 Hz, but 50 Hz is withing the power bandwidth of most old PA amplifiers).

I do have one question, though- If it is a governed motor, doesn’t that mean it is a brushed universal motor, and it should not be frequency sensitive, at least 50 vs. 60 Hz?  

Scott V. Johnson W7SVJ

President, Collins Collectors Association

Editor, CCA Signal Magazine

5111 E. Sharon Dr.

Scottsdale, AZ 85254 USA

(480) 550-2358

 <mailto:Scottjohnson1 at cox.net> Scottjohnson1 at cox.net

 <mailto:Scott.johnson at ieee.org> Scott.johnson at ieee.org

From: greenkeys-bounces at mailman.qth.net <greenkeys-bounces at mailman.qth.net> On Behalf Of John Lawson via GreenKeys
Sent: Thursday, September 3, 2026 1:43 PM
To: greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] Need motor for 50Hz supply (or DC)

Unfortuneately no VFD will drive a single-phase motor, only 3ph motor loads.

Depends on the contruction of the motor, but outside of a suitable audio power amplifier with a transformer (filament transformers work well, ‘reversed’) to match the motor impedance, there’s no slick way of reducing induction motor speed and maintaining frequency accuracy otherwise. I’ve used this scheme for 400htz motors. And of course there are lots of ‘bench’ supplies for variable frequency, 50 – 100 – 200W and up, 1 and/or 3ph – but they are not cheap, even on That Auction Site.

I do industrial and aerospace control systems as a business, and this exact subject comes up from time to time. And trust me, we’ve tried. Got the bloody t-shirts to prove it.

There are companies who make specialized speed-accurate drives for 1ph motors, but they’re in the US$2K range and up. We just installed a 75HP 600V DC motor controller for a 15,000 rpm pump test bench. It was north of US$30K.

Many sync motors (60htz) will run on 50 htz, but the heat disspation goes up. If the motor is not running at its torque limits, you might get away with 50 htz and suitable gears.

FYI I have 2 Teletype (GE) 50 htz motors NOS, dual-shaft, model 15/19 perhaps. No one here in the US loves them, and shipping to 50Htz lands is too pricey.

Cheerz

John KB6SCO

Carson City NV

From: greenkeys-bounces at mailman.qth.net <mailto:greenkeys-bounces at mailman.qth.net>  <greenkeys-bounces at mailman.qth.net <mailto:greenkeys-bounces at mailman.qth.net> > On Behalf Of Brenda Gentry via GreenKeys
Sent: Thursday, September 3, 2026 1:08 PM
To: greenkeys at mailman.qth.net <mailto:greenkeys at mailman.qth.net> 
Subject: Re: [GreenKeys] Need motor for 50Hz supply (or DC)

Consider a small Variable Frequency Drive. Most can be set wherever you like  for voltage and frequency, many will accept a single phase power input and load.

   Brenda Gentry

On 9/3/26 2:26 PM, Malcolm Macleod via GreenKeys wrote:

Greetings all.

I have a 115V/60Hz Model 28 KSR that I imported to Australia some years
back.  My aim is to get this working on our local mains supply (230V 50Hz).
I'm happy to use a 230V/115V stepdown transformer if needed.  The bigger
issue is the change in mains frequency, and possibly gear change if the new
motor speed is 3000RPM (rather than 3600RPM).

Wondering if anyone can help with a suggestion as to which motor(s) and/or
gear sets I should be looking for.

The main resource I've been looking at is Teletype Corp bulletin 295B
(particularly page 67) ->
https://www.navy-radio.com/manuals/tty/295B-7012.pdf <https://urldefense.proofpoint.com/v2/url?u=https-3A__www.navy-2Dradio.com_manuals_tty_295B-2D7012.pdf&d=DwMDaQ&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=p4uj4qZVe0q2KIXBEwvZA3BicRkyIOf6Xcp1t9RPVQ0&m=TSkMfCu7jhuIdKTRbA1_CEXlrEp-JdmijZZ87xIShS6op4ED_czMr5wfdO-I0dVU&s=nqT4SS1WIgT0mxAYv6Ys3CfF_da8X-OAKM5rPyltSUk&e=> 

Option 1: Am I able to run the existing 60Hz synchronous motor at 50Hz and
just change the gear set to accommodate the reduced RPM?  If so, what gear
set do I need for 45.4Bd/60WPM at 3000RPM?  I remember trying this a decade
ago on an ASR33 and it wasn't successful due to excessive heating of the
motor.

Option 2: Might I be able to run a 115V/60Hz 3600RPM series governed motor
on 50Hz?  If so, it seems I should be looking for an LMU4, LMU6, LMU41,
LMU57 or LMU61.  If it's acceptable to use an ASR motor in the KSR, then the
additional options (for 115V/60Hz) seem to be LMU14, LMU39 or LMU61.

Option 3: If it's not OK to run a 60Hz series governed motor at 50Hz, then
the 115V/50Hz options seem to be LMU38 or LMU50, though these will run at
3000RPM.

Option 4: I would also be fine of course with an LMU55 (230V/50Hz), though I
don't think I will be lucky enough to find one of these, and a gear change
would be necessary as well.

Option 5: Another alternative seems to be an LMU29 (Series governed
48V/3600RPM).

If you have any of these motors that you might be willing to sell, or
otherwise can shed some light in how to solve this problem, please let me
know.  I'm in the U.S. for the next couple of weeks, so can easily take one
back with me if there's one available there.  Similarly interested in
anything that might be available in Australia or the U.K. for local
shipping.

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