Is it ok to run a 100V 50/60Hz transformer on 120V 60Hz? - Page 1
Forum section: electronics / beginners

author: armandhammer
author_rank: Contributor
timestamp: January 09, 2022, 05:44:52 am
content: 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.

author: jonpaul
author_rank: Super Contributor
timestamp: January 09, 2022, 09:01:34 am
content: 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>>>120VFinally in USA the max line can be as high as 128V due to power firm tolerance.Good luck,Jon

author: rpiloverbd
author_rank: Regular Contributor
timestamp: January 09, 2022, 10:04:13 am
content: I don't recommend.

author: Gyro
author_rank: Super Contributor
timestamp: January 09, 2022, 10:55:29 am
content: Quote from: armandhammer on January 09, 2022, 05:44:52 amUnfortunately 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.

author: wraper
author_rank: Unknown
timestamp: January 09, 2022, 11:04:10 am
content: 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.QuoteNo, it won't, it will increase by the ratio the input voltage is increased.

author: armandhammer
author_rank: Contributor
timestamp: January 09, 2022, 11:14:54 am
content: Does it matter that this is an AC-AC transformer? It's 100V to 2x 17.5VWould any of the various 120V to 100V step down transformers on Amazon.com work? e.g. this:https://www.amazon.com/gp/product/B00757NFTO/

author: Gyro
author_rank: Super Contributor
timestamp: January 09, 2022, 11:22:29 am
content: 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.

author: armandhammer
author_rank: Contributor
timestamp: January 09, 2022, 11:26:27 am
content: 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

author: Gyro
author_rank: Super Contributor
timestamp: January 09, 2022, 11:39:09 am
content: As my 'P.S.' above. I'd just buy a US mains spec one.

author: armandhammer
author_rank: Contributor
timestamp: January 09, 2022, 11:52:11 am
content: I can't find a PA-20 for 120V anywhere. Every site lists it as unavailable. Where are you seeing it?

author: Gyro
author_rank: Super Contributor
timestamp: January 09, 2022, 12:29:47 pm
content: ebay. I'm not in the US so I can't see accurate price including shipping... eg.https://www.ebay.com/itm/274971152246?epid=1824635092EDIT: There are lots of cheap China clones too, but possibly not worth the risk (although at least they're traditional transformers, not SMPS).

author: fordem
author_rank: Regular Contributor
timestamp: January 09, 2022, 01:00:23 pm
content: Quote from: jonpaul on January 09, 2022, 09:01:34 amActually 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.

author: Zero999
author_rank: Super Contributor
timestamp: January 09, 2022, 01:19:50 pm
content: 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.

author: BeBuLamar
author_rank: Super Contributor
timestamp: January 09, 2022, 01:23:27 pm
content: I don't know if $69 is too much but I believe this is the direct replacement for using with 120VAChttps://www.parts-express.com/Yamaha-WC704100-Replacement-Power-Adapter-for-PA20-MG12-4-247-6045?gclid=CjwKCAiArOqOBhBmEiwAsgeLmZjWezslokg-6UiSpFmFgw7tCLd9mq6iHe9kNzYi5SeMKgd431d5oBoCfQcQAvD_BwE

author: BrokenYugo
author_rank: Super Contributor
timestamp: January 09, 2022, 02:47:15 pm
content: Quote from: Zero999 on January 09, 2022, 01:19:50 pmThat 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.

author: wraper
author_rank: Unknown
timestamp: January 09, 2022, 04:24:07 pm
content: Quote from: BrokenYugo on January 09, 2022, 02:47:15 pmIt 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.

author: TimFox
author_rank: Super Contributor
timestamp: January 09, 2022, 06:59:08 pm
content: 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.

author: Zero999
author_rank: Super Contributor
timestamp: January 10, 2022, 01:25:26 pm
content: Quote from: wraper on January 09, 2022, 04:24:07 pmQuite 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.