[GreenKeys] Variable Frequency Drives for synchronous motors 50/60Hz

Sun Nov 16 15:26:04 EST 2025

These are commonly termed "on-line UPS", the inverter always drives the load, either powered by the line to DC converter, or the battery, which is always in the circuit.  These are typically used for critical loads, such as life support, or for loads that have no hold-up time built in.  I have in the past built MO-PA style inverters for small synchronous motors using a sine wave oscillator driving an audio amplifier with an output autotransformer to set the voltage, AGC can be used for feedback voltage regulation.  Keep in mind that these old motors don't like non-sinusoidal waveforms, and the spikes from VFDs and square wave inverters can undermine the insulation.
Regards,

Scott W7SVJ

-----Original Message-----
From: greenkeys-bounces at mailman.qth.net <greenkeys-bounces at mailman.qth.net> On Behalf Of Harold Hallikainen via GreenKeys
Sent: Sunday, November 16, 2025 10:21
To: greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] Variable Frequency Drives for synchronous motors 50/60Hz

Some dual conversion uninteruptible power supplies have a frequency converter mode. They have a batter charger, a battery, and an inverter where you can set the output frequency. I have not researched this deeply, but I did find some. They are more expensive than variable frequency drives, though. Most of the VFDs I've seen have 3 phase outputs, and I don't know if they would drive single phase loads.

My father had an electronic manufacturing company in the 1950s through 1970s. The local power was 60 Hz, but they had to test equipment designed for 50 Hz. They built an interesting frequency converter. Two three phase motors were geared such that one ran at 1/6 the RPM of the other. The second motor became a 3 phase transformer with a rotating secondary. The rotating secondary subtracted 10 Hz from the 60 Hz on the field windings.
Not super practical for running a Teletype, but I always thought it was clever.

Good luck!

Harold
https://w6iwi.org

On Sun, November 16, 2025 8:48 am, Windows XD wrote:
> I've heard of using US 60 hertz battery powerbanks for using 60hz 
> stuff but I don't know how long that would power a teletype.
> Something like this
> <https://www.amazon.com/dp/B082TMBYR6/ref=sspa_dk_offsite_brave_1?aaxi
> tk=8 
> 13c48a373c02a87e7fda2054e43b758&tqtoken=AgR48QhKJSyZ88_kP9xWcVxj4qb28Y
> 6KZ 
> WM8ipgr57rhTg0AGgABAAlyZWNpcGllbnQAC0FtYXpvbkFkc1RRAAEAEWF3cy1rbXMtaGl
> lcm 
> FyY2h5ACRiM2NlMjE3OS0wMzJhLTQ5NTAtOWFlZC00MTczZDMxZmNhMmEAXNl6RXMZCptZ
> 6Ym 
> Qri2HvwQpDuoWrd6_BX6KtSXtK8nXMwFE6ZdgvB9GW5UIy9JYq-K_8MIgX7x8AyNba-COm
> KMR
> GIpIifo2Pg3JQIiu0v-_I-9lU4AZa4S5YVU1AgAAEAD7mwwe168kJaRGEY5hm0W0Ko6_w6
> S0- 
> Zx4pMArUcafOVh_FWuP1wzbvjcdgnKlFGz_____AAAAAQAAAAAAAAAAAAAAAQAAABvlvPR
> zPi LdbE3XGyuT_tcEtclAQeQ4TizDGmyJu38pYKKXBAb1GWxgsdzs&offsiteFlag=1>,
> charge it with DC then use it for AC.
>
> On Sun, Nov 16, 2025 at 1:57â€¯AM Peter Leonard <peter at lencom.com.au>
> wrote:
>
>
>> Hi All,
>>
>>
>> We in the 50Hz 240V world have a problem with machines fitted with 
>> 60Hz  synchronous motors. Machines originally used here are fitted 
>> with governed 110V motors but I have acquired two with 60Hz sync 
>> motors. The 240/110V problem is easily fixed with a transformer. But. 
>> Has anyone experience with using Variable Speed Drive Units, 240V 
>> drives are readily available but would have to power the motor via a 
>> transformer. Any suggestions.
>>
>>
>> Thanks.
>>
>>
>> Kind regards,
>>
>>
>> 73 Pete VK5XP
>>
>>
>>
>>
>>
>>
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>>
>>>>> Jordan Spencer Cunningham's GreenKeys Search Tool:
>>>>>
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>>
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>>>>>
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>>
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>>>>>
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>>
>>
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>
>>>> Jordan Spencer Cunningham's GreenKeys Search Tool:
>>>> https://teletype.net/gksearch
>>>> 2002-to-present greenkeys archive:
>>>> http://mailman.qth.net/pipermail/greenkeys/
>>>> 1998-to-2001 greenkeys archive:
>>>> http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
>>>> http://comcents.com/tty/greenkeyssearch.html
>>>>
>
> This list hosted by: http://www.qsl.net Please help support this email 
> list: http://www.qsl.net/donate.html Message delivered to 
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>>> Jordan Spencer Cunningham's GreenKeys Search Tool: 
>>> https://teletype.net/gksearch 2002-to-present greenkeys archive: 
>>> http://mailman.qth.net/pipermail/greenkeys/
>>> 1998-to-2001 greenkeys archive: 
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>>> http://comcents.com/tty/greenkeyssearch.html

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