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

Sun Nov 16 13:36:54 EST 2025

 I bought a VFD to play around with so I have looked into this a little.There are some parameters that you set on the VFD that may seem confusing.Sorry I don't remember the names of the parameters but here is the reason those parameters exist.When you change the frequency input to a motor or a transformer (this applies to both)the inductive impendence changes and you must take that into account.Lower frequency input results in a lower inductive impedance and therefore you must drop the voltage inputby a proportional amount to avoid exceeding the current limit of the device.The inverse is true when you increase the frequency you need to also increase the voltage by a proportionalamount to get the same current BUT you are limited in how much you can increase the voltage becauseyou cannot exceed the voltage rating of the shellac in the windings. There is a hard voltage limit you must not exceed when increasing input frequency.So when you are setting up the VFD for your application and you see odd parameter settings this is why those settings exist.
-Steve Bennett 
    On Sunday, November 16, 2025 at 12:22:19 PM EST, Harold Hallikainen via GreenKeys <greenkeys at mailman.qth.net> wrote:  

 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?aaxitk=8
> 13c48a373c02a87e7fda2054e43b758&tqtoken=AgR48QhKJSyZ88_kP9xWcVxj4qb28Y6KZ
> WM8ipgr57rhTg0AGgABAAlyZWNpcGllbnQAC0FtYXpvbkFkc1RRAAEAEWF3cy1rbXMtaGllcm
> FyY2h5ACRiM2NlMjE3OS0wMzJhLTQ5NTAtOWFlZC00MTczZDMxZmNhMmEAXNl6RXMZCptZ6Ym
> Qri2HvwQpDuoWrd6_BX6KtSXtK8nXMwFE6ZdgvB9GW5UIy9JYq-K_8MIgX7x8AyNba-COmKMR
> GIpIifo2Pg3JQIiu0v-_I-9lU4AZa4S5YVU1AgAAEAD7mwwe168kJaRGEY5hm0W0Ko6_w6S0-
> Zx4pMArUcafOVh_FWuP1wzbvjcdgnKlFGz_____AAAAAQAAAAAAAAAAAAAAAQAAABvlvPRzPi
> 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
>>>>
>
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