Is it ok to run a 100V 50/60Hz transformer on 120V 60Hz?

[armandhammer]

I have some Yamaha PA-20 transformers from Japan which are 100V 50/60Hz. Would they work ok in the US at 120V 60Hz? Would the output be the same? It's for equipment that is plugged in a few times a month for 1 hour or less, and a couple times a year for as much as 3 hours.

[jonpaul]

Depending on the design and quality of the transformer,  it may saturate and overheat.

Most USA made transformers are well designed and many Chinese are marginal.

The transformer may have taps you can change or use an external buck to reduce voltage to 100V.

50/60 iHz is normally not an issue.

If you have a wattmeter and variac you can test input current and watts as the input line varies  100>>>120V

Finally in USA the max line can be as high as 128V due to power firm tolerance.

Good luck,

Jon

[rpiloverbd]

I don't recommend.

[Gyro]

... Would the output be the same? It's for equipment that is plugged in a few times a month for 1 hour or less, and a couple times a year for as much as 3 hours.

Unfortunately the output would rise in the same proportion to the change of input voltage (unless it was artificially limited by the transformer going into saturation, with the previously mentioned consequences). That's based on higher input voltage, going to a higher mains frequency isn't an issue. This will place additional load on whatever is downstream of the transformer, linear voltage regulators, for instance will dissipate significantly more heat. 3 hours is ample time to fry a transformer or other parts.

Fundamentally, nobody can give you a definite answer. You might get lucky, but there is a significant chance that something will be damaged.

A small mains transformer wired as an autotransformer (primary and secondary in series) would be the most economical way of dropping the voltage. Its secondary winding only needs to be rated for the supply current of your transformer, so will be surprisingly small in comparison. One rated for 18V - 24V output (2 x 9V and 2 x 12V secondary windings are common) would be about right. Of course it needs to be wired safely - mains insulation, insulated enclosure, mains lead mechanical retention etc.

[wraper]

If you run it for a few hours and it does not become hot, then it should be fine. As already said, it depends on margin transformer was made with. In general, unless it's a cheap borderline design, it should be fine.

Would the output be the same?

No, it won't, it will increase by the ratio the input voltage is increased.

[armandhammer]

Does it matter that this is an AC-AC transformer? It's 100V to 2x 17.5V

Would any of the various 120V to 100V step down transformers on Amazon.com work? e.g. this: https://www.amazon.com/gp/product/B00757NFTO/

[Gyro]

Yes, an off the shelf 120V - 100V step-down transformer would work fine - not necessarily the cheapest solution but by the time you take time and effort (and skill level?) into account...

The other alternative may be just to replace your mains transformer with a 120V primary one - it may or may not be a cheaper option. Photos would help.


P.S. Ok, I took the time to look up PA20 transformers, they are an external power brick. It looks as if US mains ones aren't that expensive.

[armandhammer]

The PA-20 is basically just a sealed black box "wall wart". No screws or any other access without likely damaging it:

https://m.media-amazon.com/images/I/51p4mrYcmCL._AC_SX425_.jpg

[Gyro]

As my 'P.S.' above. I'd just buy a US mains spec one.

[armandhammer]

I can't find a PA-20 for 120V anywhere. Every site lists it as unavailable. Where are you seeing it?

[Gyro]

ebay. I'm not in the US so I can't see accurate price including shipping...  eg. https://www.ebay.com/itm/274971152246?epid=1824635092

EDIT: There are lots of cheap China clones too, but possibly not worth the risk (although at least they're traditional transformers, not SMPS).

[fordem]

Depending on the design and quality of the transformer,  it may saturate and overheat.

<SNIP>

50/60 iHz is normally not an issue.

Actually it is - a 60Hz transformer on 50 Hz will run hotter than it should - you can get away with it if the transformers are small & lightly loaded, but if you're dealing with power distribution, and more than a few hundred VA, it will become an issue.

[Zero999]

The transformer is designed to work up to 60Hz, so the higher frequency isn't a problem.

It's also designed to work down to 50Hz, at 100V.

As the higher voltage is also accompanied by a proportionally higher frequency, which the transformer is also designed for, 120VAC won't be an issue.

The issue is most likely the higher secondary voltage, to whatever the transformer is powering, than the transformer itself.

[BeBuLamar]

I don't know if $69 is too much but I believe this is the direct replacement for using with 120VAC
https://www.parts-express.com/Yamaha-WC704100-Replacement-Power-Adapter-for-PA20-MG12-4-247-6045?gclid=CjwKCAiArOqOBhBmEiwAsgeLmZjWezslokg-6UiSpFmFgw7tCLd9mq6iHe9kNzYi5SeMKgd431d5oBoCfQcQAvD_BwE

[BrokenYugo]

The issue is most likely the higher secondary voltage, to whatever the transformer is powering, than the transformer itself.

That was my thought, 20% more input is going to be 20% more heat in any linear regulators and potentially harmful overvoltage on anything on the unregulated rail.

[wraper]

That was my thought, 20% more input is going to be 20% more heat in any linear regulators and potentially harmful overvoltage on anything on the unregulated rail.

It will be more than 20%. For example voltage regulator is powered by 10V and outputs 5V, therefore drops 5V. 20% increase means 12V input voltage and 7V drop on vreg. 7/5 = 1.4 which means 40% higher heat dissipation on vreg.

[TimFox]

Japan is the only major market where the standard line voltage is 100 V, at two different frequencies:  50 Hz in Tokyo and 60 Hz in Osaka, with the geographic dividing line near Shizuoka.
I successfully used a medical-rated toroidal power transformer rated at 50/60 Hz with a 100 V tap on the 120 V primary, driving the 100 V primary tap with 120 V, 60 Hz, to get a higher output voltage for my application.
The logic behind this operation is a bit subtle:  the maximum voltage on an iron-core transformer results from the time derivative of the core flux density (B-field in Tesla), which has a maximum saturation value.
For a given peak B value, the maximum voltage at 60 Hz is 60/50 = 1.2 times the allowed voltage at 50 Hz.

[Zero999]

That was my thought, 20% more input is going to be 20% more heat in any linear regulators and potentially harmful overvoltage on anything on the unregulated rail.

It will be more than 20%. For example voltage regulator is powered by 10V and outputs 5V, therefore drops 5V. 20% increase means 12V input voltage and 7V drop on vreg. 7/5 = 1.4 which means 40% higher heat dissipation on vreg.

Quite right, it depends on the load. If it's a resistive load, then  the power dissipation will increase by the square of the voltage, so 44% higher power dissipation, but if it's a buck regulator, or PWM motor driver, with speed regulation, then the current will be reduced, giving roughly the same power dissipation, which would be fine, assuming the components can take the higher voltage.