Using Japanese 100v device on 120v

[sairfan1]

I bought an audio device it was previously used in  Japan and back of it says 100v there is no voltage selector for other regions.

Its from 1986 must be based on transformer, I'm in Canada I can see on my dmm mostly we have voltage around 120-125v I want to know before using it should i arrange voltage convertor or 100v devices can run on 110/120v as well?

[amyk]

SMPS should be OK with the ~20% higher voltage as long as components are not too close to their ratings, but be more careful with linear regulators. If it was also available in 110/120V countries and not just a JDM-only device, you could see if finding the schematics to compare would show any differences.

[CaptDon]

Based on its age I would guess it has a transformer in the power supply and linear regulators. I would highly suggest NOT to run it on 120vac. You may be able to obtain something like an 18vac secondary transformer with a 120vac primary and wire it as an 18vac buck circuit to reduce the 120vac down to 102vac. The secondary current rating will have to match or be higher than what your equipment draws, guessing only 1 or 2 amps will be required. I think if your equipment really does have a power transformer you will push it into saturation at 120vac and burn it up. You may also damage the linear regulation circuits due to excess heat or even pop a few capacitors. I have seen 15vdc circuits with 16vdc rated capacitors. Put safety and good sense to work in this case!! Cheers!!

[Tomorokoshi]

Check the VA rating on the device along with anything else you might want to run at the same time.

Using a search like "Japan USA step down transformer" and variations look for things like these:

https://www.ebay.com/itm/403897297686
https://www.ebay.com/itm/234928124502
https://www.ebay.com/itm/204330932703

[sairfan1]

I was able to open and take the picture of transformer

[Tomorokoshi]

Another option is to search on Digi-Key or your preferred supplier for a transformer that is from 16VA to perhaps 20VA with the right voltage ratings and replace it in the device.

[EPAIII]

Since you have it open, I would disconnect one wire/side of the secondary of the transformer and measure the output Voltage with it out of circuit. It says it should be 17 Volts with a 16 VA (Watt) rating so it has about a 1 Amp rating. 125 VAC vs. 100 VAC is a 5/4 ratio so I am guessing the secondary Voltage will be around 17 V x 5 / 4 = 21.25 V. And 21.25 V - 17 V = 4.25 V so you need to drop that Voltage to bring it down to 17 Volts.

1N4001 through 1N4007 rectifier diodes are all inexpensive and rated for 1 Amp. They mostly differ by their reverse Voltage and the lowest Vr is 50 Volts so you can choose any of them. The actual current draw of your device is not known and probably varies so start with a nominal forward Voltage drop of 0.75 Volts. Use 4.25 Volts or your actual drop from your actual measurement: 4.25V / 0.75V = 5.6. So try six diodes in series. You need conduction in BOTH directions so six in series going one way with six more also in series, going the other way in parallel.

That should drop your transformer Voltage to the 17 Volts that the rest of the circuit was designed for. The diodes can stand the current and Voltages so there should be no problems there. And if you provide even a little of air around the diodes, they should be able to dissipate any heat generated. The transformer will be delivering the current it is rated for so it should be OK. Any extra Watts should be dissipated by the diodes, not the transformer so probably also OK.

Hook it all up and measure the actual AC Voltage past the diodes. Adjust the number of diodes as needed to get that 17 VAC number.

Those diodes are around $0.10 each when purchased in 10s so just a bit over $1 US for the mod. Diodes, even a dozen or more of them, are a lot less expensive than a new transformer.

[EPAIII]

Saturation is due to current, not Voltage. So, if my suggestion above is followed, the current in the transformer will stay the same and therefore not be a problem.

Based on its age I would guess it has a transformer in the power supply and linear regulators. I would highly suggest NOT to run it on 120vac. You may be able to obtain something like an 18vac secondary transformer with a 120vac primary and wire it as an 18vac buck circuit to reduce the 120vac down to 102vac. The secondary current rating will have to match or be higher than what your equipment draws, guessing only 1 or 2 amps will be required. I think if your equipment really does have a power transformer you will push it into saturation at 120vac and burn it up. You may also damage the linear regulation circuits due to excess heat or even pop a few capacitors. I have seen 15vdc circuits with 16vdc rated capacitors. Put safety and good sense to work in this case!! Cheers!!

[Psi]

Another option is to remove the brown tape/paper and unwind some of the secondary turns to bring the voltage back into normal range.
A bit annoying but totally doable and cheaper than buying a new transformer.
Might be a bit more annoying if it has more than one secondary winding or a CT. But label implies there's just one 17V output.

The diode idea is probably the easiest to do. Just have to confirm they can handle the amps without getting too hot.

[Siwastaja]

Transformer saturation is a real risk; small mains transformers in cheap devices run usually pretty close to saturation for cost savings. As mentioned by others, extra power dissipation in either linear regulators (if any, many devices use non-regulated supplies!), or other circuitry, could make it run too hot.

Saturation is due to current, not Voltage. So, if my suggestion above is followed, the current in the transformer will stay the same and therefore not be a problem.

And as always, ignore EPAIII.

[Psi]

Yeah, obviously running the transformer at 120V instead of 100V would involve testing it and seeing how hot it gets while operating at max load.

[RoGeorge]

Might work for another 37 years, but I wouldn't dare to let it plugged unattended.

Buy a small SMPS, mains to DC, and replace the transformer with the SMPS.  Leave the original bridge filter and stabilizers in place.  The transformer itself can be sold, or reused in another not-mains project, for example to step up the voltage for a curve tracer.

[magic]

Saturation is due to current, not Voltage. So, if my suggestion above is followed, the current in the transformer will stay the same and therefore not be a problem.

Core saturation is due to magnetizing current, not load current, and depends on mains voltage and frequency. Lower frequency or higher voltage → worse.

[Zero999]

You could replace the transformer with a 120V one, perhaps even 18V wouldn't hurt, if that's all you can get.

Another option is to run off 100V. This can be done by connecting another transformer in buck configuration. Use a 120V:20V transformer with the secondary connected in series with the mains anti-phase. This will drop the mains voltage by 20V.

[wasedadoc]

Half of Japan has 50Hz mains and the other half has 60Hz so equipment there must work on both with or without adjustment by end user. The transformer will have been specced for the more demanding 50Hz. Running it at 60Hz in Canada will help reduce any untoward effects on the transformer from the higher voltage input. The higher voltage from the secondary is another matter.

[Gyro]

As the transformer is only 17VA, it would be reasonably cheap to replace it with a standard 16V (8-0-8V) or 18V (9-0-9V) one of the correct mains voltage - are you sure you don't have one in a parts box?

The alternative would be the smallest available 18V mains transformer (3 or 6VA) wired in autotransformer configuration (why do people always use buck configuration? it's inefficient) to drop the primary voltage. It looks as if you have plenty of space on the panel.

[CaptDon]

Of all the advice in this thread "Ignore EPAIII" is the best!!! Raising the input voltage from 100vac to 120vac DOES increase the primary current and usually these home consumer devices are built cheap without excess headroom or capacity, which includes your power transformer. It will most assuredly run hotter!! How hot would be trial and error, and not worth the damage downline to other components. All those suggested diodes in series is a waste of power and still doesn't address possible destruction of the power transformer from long term overheating. Wiring an external transformer with its 120vac primary and 20vac secondary in series as an autotransformer and then seeing only 100vac across the 120vac primary can indeed work. Only a minor difference at this low of a power level if autotransformer vs. buck circuit is preferred. The most sound advice truly is replace your transformer although 17vac is an oddball with 16vac (8-0-8) and 18vac (9-0-9) being much more common. Cheers mate!!

[magic]

Maybe one could put a string two antiparallel strings of diodes in series with the primary

[schmitt trigger]

I actually saw that anti parallel diode hack once. Seemed to work fine, but I didn’t perform any measurements.

[Vovk_Z]

Half of Japan has 50Hz mains and the other half has 60Hz so equipment there must work on both with or without adjustment by end user. The transformer will have been specced for the more demanding 50Hz. Running it at 60Hz in Canada will help reduce any untoward effects on the transformer from the higher voltage input. The higher voltage from the secondary is another matter.

That's a good point. If it is rated for 50 Hz it is easier to work with 60 Hz, so that help with an additional 20% of voltage. So, I would switch it on for half an hour and test the temperature and output voltage. I mean there is some good possibility it'll work fine as is.

[sairfan1]

Thank you everyone for useful advice, as this product is bit rare and i did not want to take risk I decided to buy a 120v to 100v transformer as advised

https://www.ebay.com/itm/234928124502

[TimFox]

Of all the advice in this thread "Ignore EPAIII" is the best!!! Raising the input voltage from 100vac to 120vac DOES increase the primary current and usually these home consumer devices are built cheap without excess headroom or capacity, which includes your power transformer. It will most assuredly run hotter!! How hot would be trial and error, and not worth the damage downline to other components. All those suggested diodes in series is a waste of power and still doesn't address possible destruction of the power transformer from long term overheating. Wiring an external transformer with its 120vac primary and 20vac secondary in series as an autotransformer and then seeing only 100vac across the 120vac primary can indeed work. Only a minor difference at this low of a power level if autotransformer vs. buck circuit is preferred. The most sound advice truly is replace your transformer although 17vac is an oddball with 16vac (8-0-8) and 18vac (9-0-9) being much more common. Cheers mate!!

The calculation for core saturation should proceed from the voltages.
The back-emf at the transformer primary is due to the rate of change of the core flux:  the maximum flux in the core (saturation B times effective cross-section area) and the frequency determine how much voltage can be induced.
For a sinusoid, V_peak = (2pi) x f x B_peak, and there is a maximum saturation value for B.
If you apply a voltage above the available back-emf, the core must saturate and may well overheat, especially with low power transformers that are designed for low weight.

[CaptDon]

That is a very sound move and good choice. I forgot that you are in the land of 240vac. I have become so accustomed to 120vac these days which is kind of in the minority in the world wide scope of things. The last time I have been on Iceland was 2012 when C.R.T. televisions were still very popular and I forgot about that 50Hz flicker rate of the televisions (Sjonvarpid) which is very noticeable compared to the N.T.S.C. 59.94Hz in the U.S.  Now with LCD T.V.'s flicker is a thing of the past.

[TimFox]

Sairfan1, the original poster, is in Canada.
Both the US and Canada default to 120 V, 60 Hz.

[james_s]

Saturation is due to current, not Voltage. So, if my suggestion above is followed, the current in the transformer will stay the same and therefore not be a problem.

Sorry but that's just wrong. A transformer will saturate with no load on it at all, in fact it will saturate more easily under no load, you'll see a sharp increase in current draw as the input voltage goes up to the point where the core saturates.