Using Japanese 100v device on 120v  - Page 1
Forum section: electronics / beginners

author: sairfan1
author_rank: Frequent Contributor
timestamp: May 08, 2023, 11:43:40 pm
content: 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?

author: amyk
author_rank: Super Contributor
timestamp: May 09, 2023, 12:08:24 am
content: 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.

author: CaptDon
author_rank: Super Contributor
timestamp: May 09, 2023, 01:07:45 am
content: 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!!

author: Tomorokoshi
author_rank: Super Contributor
timestamp: May 09, 2023, 01:23:51 am
content: 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/403897297686https://www.ebay.com/itm/234928124502https://www.ebay.com/itm/204330932703

author: sairfan1
author_rank: Frequent Contributor
timestamp: May 09, 2023, 03:05:51 am
content: I was able to open and take the picture of transformer

author: Tomorokoshi
author_rank: Super Contributor
timestamp: May 09, 2023, 03:33:02 am
content: 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.

author: EPAIII
author_rank: Super Contributor
timestamp: May 09, 2023, 06:52:04 am
content: 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.

author: EPAIII
author_rank: Super Contributor
timestamp: May 09, 2023, 06:58:59 am
content: 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.Quote from: CaptDon on May 09, 2023, 01:07:45 am

author: Psi
author_rank: Super Contributor
timestamp: May 09, 2023, 07:01:42 am
content: 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.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 09, 2023, 07:05:19 am
content: 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.Quote from: EPAIII on May 09, 2023, 06:58:59 amAnd as always, ignore EPAIII.

author: Psi
author_rank: Super Contributor
timestamp: May 09, 2023, 07:06:31 am
content: 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.

author: RoGeorge
author_rank: Super Contributor
timestamp: May 09, 2023, 07:39:05 am
content: 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.

author: magic
author_rank: Super Contributor
timestamp: May 09, 2023, 08:36:50 am
content: Quote from: EPAIII on May 09, 2023, 06:58:59 amCore saturation is due to magnetizing current, not load current, and depends on mains voltage and frequency. Lower frequency or higher voltage → worse.

author: Zero999
author_rank: Super Contributor
timestamp: May 09, 2023, 08:49:46 am
content: 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.

author: wasedadoc
author_rank: Super Contributor
timestamp: May 09, 2023, 08:54:48 am
content: 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.

author: Gyro
author_rank: Super Contributor
timestamp: May 09, 2023, 09:17:45 am
content: 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 inautotransformerconfiguration (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.

author: CaptDon
author_rank: Super Contributor
timestamp: May 09, 2023, 02:44:05 pm
content: 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!!

author: magic
author_rank: Super Contributor
timestamp: May 09, 2023, 02:48:30 pm
content: Maybe one could puta stringtwo antiparallel strings of diodes in series with the primary

author: schmitt trigger
author_rank: Super Contributor
timestamp: May 09, 2023, 03:07:46 pm
content: I actually saw that anti parallel diode hack once. Seemed to work fine, but I didn’t perform any measurements.

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 09, 2023, 03:52:02 pm
content: Quote from: wasedadoc on May 09, 2023, 08:54:48 amThat'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.

author: sairfan1
author_rank: Frequent Contributor
timestamp: May 09, 2023, 04:55:47 pm
content: 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 advisedhttps://www.ebay.com/itm/234928124502

author: TimFox
author_rank: Super Contributor
timestamp: May 09, 2023, 05:16:17 pm
content: Quote from: CaptDon on May 09, 2023, 02:44:05 pmThe 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,Vpeak= (2pi) xfxBpeak, and there is a maximum saturation value forB.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.

author: CaptDon
author_rank: Super Contributor
timestamp: May 09, 2023, 05:23:12 pm
content: 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.

author: TimFox
author_rank: Super Contributor
timestamp: May 09, 2023, 05:34:23 pm
content: Sairfan1, the original poster, is in Canada.Both the US and Canada default to 120 V, 60 Hz.

author: james_s
author_rank: Super Contributor
timestamp: May 09, 2023, 06:04:52 pm
content: Quote from: EPAIII on May 09, 2023, 06:58:59 amSorry 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.

author: floobydust
author_rank: Super Contributor
timestamp: May 09, 2023, 06:17:11 pm
content: OP, I would look inside (post pics) to make sure the original power transformer has no taps for different voltages. Japan knew the world has different mains voltages and their consumer electronics was almost always good for at least 2-3 countries. Do not run it on 120VAC it will blow up.Second, if it is 100VAC then use a Hammond169or you can connect an autotransformer connected to lower mains by say 25V like a Hammond166rated at least 25V and appropriate wattage (VA) rating.

author: wasedadoc
author_rank: Super Contributor
timestamp: May 09, 2023, 08:02:53 pm
content: Quote from: floobydust on May 09, 2023, 06:17:11 pmThe OP has already posted a photo. Judging by the brown and grey wires coming from whatever switch or AC input socket is mounted on the panel, the brown and red wires appear to be the primary. The transformer is labelled 100V. No other voltage markings. It was very common for products sold on the domestic Japanese market to have 100 Volt only transformers.

author: TimFox
author_rank: Super Contributor
timestamp: May 09, 2023, 08:06:11 pm
content: Quote from: james_s on May 09, 2023, 06:04:52 pmAs I said above, core saturation is determined by the voltages and frequency. The current rating on a transformer comes from copper and core losses heating the device.Note that if a transformer is rated for 50 or 60 Hz operation, you can operate it at about 20% higher voltage if you only run 60 Hz.In the case of this amplifier, of course, the secondary voltage will then be 20% higher, which may be excessive for the amplifier supply.edit: fixed typo

author: floobydust
author_rank: Super Contributor
timestamp: May 09, 2023, 08:22:04 pm
content: Quote from: wasedadoc on May 09, 2023, 08:02:53 pmOh it's a small transformer label 100V 17V 16VA, like in a tuner or EQ preamp etc. I'd just swap it out for something good for 120VAC. A 16V 1A part would be fine.Amplifiers/receivers I worked on always had taps even JDM but these are much larger transformers and I guess the tap pays off then.I did measurements of primary current vs mains voltage on a bunch of small power transformers. Because some are old rated 115V and I get 122V.I do notice the primary current increase and around >130VAC in the transformers growl and buzz loudly. Saturation is a gradual thing.Note the 166JA12 rated 12VAC 1A puts out about 21% higher at no load, I got 14.6VAC/19.1VDC and at full load it drops to what you'd expect.

author: MrAl
author_rank: Super Contributor
timestamp: May 09, 2023, 09:13:15 pm
content: Quote from: EPAIII on May 09, 2023, 06:58:59 amHi there,Sorry to say but although saturation is due to current the other fact is that current is due to voltage, so the transformer flux would be 20 percent higher with 120v as compared to 100v and the excitation current would be at least 20 percent higher.You can look at this in terms of the primary inductance. If you apply a 20 percent increase in voltage across an inductor (the primary turns) the current will increase by 20 percent.The Transformer Equation for flux has voltage in the numerator, which means when you increase the voltage the maximum flux in the core goes up, and as that goes up the flux gets closer to the saturation level. That can cause excessive heating and also some extra buzzing sounds.In short, it's not a good idea as others have pointed out.DC current is different but has a similar effect. As you increase the net DC in the primary (if there is any) the saturation level also goes up causing problems. We don't usually expect that from a regular power line though.

author: TimFox
author_rank: Super Contributor
timestamp: May 09, 2023, 10:45:29 pm
content: As James_S pointed out above, if you put too much voltage into a transformer with no secondary load current whatsoever, the core can saturate and pull a high primary current.Following my discussion above, the voltage limit is due to the maximum flux the core can carry, and the back-emf induced by that maximum flux varying sinusoidally.

author: james_s
author_rank: Super Contributor
timestamp: May 09, 2023, 10:58:44 pm
content: Since a separate step down transformer has already been purchased it's kind of moot at this point, however as others have mentioned if this transformer was made to handle 50Hz as it almost certainly was, then it should handle a 20% overvoltage at the 20% higher 60Hz frequency without saturating. The secondary voltage will consequently be 20% high but that *may* be fine depending on how the power supply is designed.

author: EPAIII
author_rank: Super Contributor
timestamp: May 10, 2023, 11:09:39 am
content: Boy, what a hard crowd! So, by all means, TEST IT. That costs nothing, just some time. And if it overheats, then get another transformer. I have always been a stickler for safety, but I doubt there is much danger here beyond a burnt-up transformer that needs to be replaced.Do some of you guys have stock in transformer companies? Are sales slow? Stock prices or dividends down? Or perhaps the land fills are begging for more copper and steel?Quote from: Psi on May 09, 2023, 07:06:31 am

author: EPAIII
author_rank: Super Contributor
timestamp: May 10, 2023, 11:12:04 am
content: Well, I am glad you said that and I didn't. It occurred to me after posting. Hope they don't jump on you as they did on me.Quote from: james_s on May 09, 2023, 10:58:44 pm

author: EPAIII
author_rank: Super Contributor
timestamp: May 10, 2023, 12:41:33 pm
content: Some math:Original Design, 100 VAC input to primary:17 VAC secondary VoltageSecondary rating (it looks like the secondary rating on the label) = 16 VASo, secondary current rating = 16 VA / 17 VAC = 0.941 AAnd turns ratio = 100 VAC / 17 VAC = 5.88So current reflected back to the primary = 0.941 A / 5.88 = 0.16 ANow, withSuggested diode assembly in secondary:125 VAC input to primarySecondary V = 125 VAC / 5.88 = 21.26 VACAssume diode drop = 6 X 0.75 V = 4.5 VVoltage to regulator = 21.26 VAC - 4.5 V = 16.76 VACRegulator and rest of device still draws 0.941 A (or perhaps a little less)Since secondary winding, diode assembly, and regulator input are in a series loop, the current in the secondary winding = 0.941 A.Transformer turns ratio is still the same so the current level reflected back to the primary winding is 0.941 A / 5.88 = 0.16 Amps.THE PRIMARY CURRENT HAS NOT CHANGED. THE SECONDARY CURRENT HAS NOT CHANGED. AND, as I said before, since saturation depends on the current, if it didn't saturate before, it will not saturate with the diode modification and a 125 VAC input.So, who is it that should be ignored??And YES, I am well aware that there will be losses in any real transformer. But they were there in the original design and they will be much the same with my suggested diode modification. I^2R is I^2R, no matter what the Voltage is. And if the currents are the same and the physical construction of the transformer is the same, then the eddy currents, hysteresis, and flux losses will also be much the same as well.In short, the diode fix should work. And the diodes that I suggested ARE rated at 1 Amp so there should be no problem there either unless they are prevented from having the needed, cooling air flow.NOTE: In reading this before posting I realized that I used a 4.5 VDC diode drop. But this is AC so that should be multiplied by 1.414 for a 6.4 VDC drop instead. 6.4 VDC / 0.75 VDC = 8.5 diodes. So try 8 diodes each way and see how it works. Or perhaps a pair of 6 V, 1 A Zeners in series. As I said, the operation should be verified before calling it done.Quote from: Siwastaja on May 09, 2023, 07:05:19 am

author: TimFox
author_rank: Super Contributor
timestamp: May 10, 2023, 12:55:00 pm
content: For AC, transformers saturate on voltage but overheat on current.https://www.electricalengineering.xyz/article/why-core-saturation-happens-in-transformer-and-what-are-its-effects/With audio transformers such as single-ended plate output transformers in tube circuits, a DC component can cause saturation in a transformer not designed for DC.In the usual model for a practical transformer (ignoring resistive losses for the moment), there is a "magnetizing inductance" in parallel with, and a "leakage inductance" in series with an "ideal transformer".For AC, in a proper application of the transformer, there is a small parasitic current in the magnetizing inductance and a small parasitic voltage across the leakage inductance.In the embedded ideal transformer, the flux due to the primary and secondary currents (useful currents) cancel in the core.DC is another matter.

author: CaptDon
author_rank: Super Contributor
timestamp: May 10, 2023, 12:58:27 pm
content: Are you certain that transformer VR-10 is 240 in 100 out as stated by the seller?? It is hard to know for sure from the picture of the voltage tag. Also it is a bit strange that the unit features outlets capable of accepting a ground pin but the power cord has no ground? It also appears to have a non-polarized cord that would appear to be for 120vac U.S. input? I am not sure what type of power cord plugs are used in Canada? Verify everything with a meter if you can before plugging in your rare unit. Best wishes. Canada is only 35 miles from me (Straight across Lake Erie) Cheers mate!!

author: wasedadoc
author_rank: Super Contributor
timestamp: May 10, 2023, 01:15:36 pm
content: Quote from: CaptDon on May 10, 2023, 12:58:27 pmThere are voltage selectors for both input and output on the front at the top. Protected from inadvertent changes by those horizontal strips.

author: CaptDon
author_rank: Super Contributor
timestamp: May 10, 2023, 01:19:53 pm
content: Ahhh, good eyes, I see that now. Very versatile unit indeed!

author: MrAl
author_rank: Super Contributor
timestamp: May 10, 2023, 03:50:30 pm
content: Quote from: EPAIII on May 10, 2023, 11:09:39 amHello again,Ha ha, well at least there was no name callingFor myself, i was lucky enough to work in a place that had it's own transformer department so i got to design a lot of different kinds of transformers for various power uses and many of them used the EI lamination type cores typical in power line (120v, 240v, etc.) transformers. Thus i got a lot of experience with these things.One of the things about a regular power line transformer is that the core area and the number of turns and the frequency and the applied AC voltage all play a part in the flux density. The thing is, there is a maximum flux density and if you go over that the core is considered to be saturated.Now saturation may overheat the core after some time, possibly a longer run time. But there are other effects to which are not very pleasant such as more audio noise and also a large distortion of the secondary voltage waveform.The audio noise can really be annoying. It can be a buzzing sound or a low frequency sound that fades in and out and that's really annoying.When you design these things you get a feel for what is required, and you tend to not go over the specification because then the amount of materials that has to go into the construction goes up and that means cost goes up. For one, that means you don't use an oversized core area because that takes more laminations. This means that you want to strike a balance between materials and cost, and that means you design for a set of given operating conditions and just a little overhead for safety. For example, if Bmax is 20kG then you might go for 15kG under normal operation conditions. For one thing, that allows for some room if the line voltage goes up to high line, which is always a possibility. The voltage may not be constant at 120v, but may fluctuate from 108v to 132v and with the extra head room in the transformer it would work ok at any of those voltages; ok in that it does not burn out that is. Now if you design for a max of 132v you consider that to be ok, but that's with a nominal voltage of 120v, and we dont design for 144v because it takes more material which also BTW makes it heavier.If we design for 100vac, then we might expect high line to be 110vac. That's the max it should ever see, and we know that in advance so we design with that goal in mind. The question is, what happens if it goes up to 120vac, which is already far greater. That's not the only problem though, because as mentioned, that 120vac can go up as high as 132vac, so now we are operating way beyond the design point which means there is little doubt that it's not going to work very well.So it's not really a matter of testing, it's a matter of understanding the design process that goes into the making of a power transformer and how that fits into the application such as a rectifier circuit.I suppose if you really want to test it though, you should turn the input voltage up to 132vac and see what happens. It would be wise to turn it up slowly while monitoring the input current from the line. If the current goes up suddenly, it's time to forget that and move to a new design. It is not likely at all that would not happen, but just in case you would have to run it overnight at the least at 132vac to make sure nothing goes really wrong. The other test is the output distortion which would have to be checked and considered. There would be flat topping, but also there could be a reduction in leakage inductance if there was some included in the original design, and that means less filtering in a rectifier circuit.Hopefully the new transformer i think was purchased works ok too.

author: james_s
author_rank: Super Contributor
timestamp: May 10, 2023, 05:06:06 pm
content: Quote from: CaptDon on May 10, 2023, 12:58:27 pmIdentical to what's used in the USA. For the most part Canadian electrical code is the same as the US code. There are minor differences here and there but there are also minor regional differences in the US. They use the same NEMA plugs that we do.

author: james_s
author_rank: Super Contributor
timestamp: May 10, 2023, 05:10:57 pm
content: Quote from: EPAIII on May 10, 2023, 11:09:39 amHe said it's rare equipment that he wants to keep original, so that means preserving the original power transformer and not burning it up.While I think this particular transformer will tolerate 120V, that is because it is almost certainly designed to tolerate 50Hz, if it was a 60Hz only 100V transformer then it very likely would saturate on 120V. As I said earlier, a transformer will saturate with no load at all, and indeed becomes *more* prone to saturating the lighter it is loaded. If you don't believe me then try it, wire up a small transformer with the low voltage secondary (so you can easily go past the design voltage) fed by a variac and the line voltage primary capped off and then monitor the current as you slowly increase the voltage. At some point the transformer will start buzzing and the current draw will begin to increase sharply, this is the onset of core saturation. If you put a load on the other winding, you'll be able to run the voltage up higher before saturation takes place.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 10, 2023, 05:27:27 pm
content: Fundamentally, inductors, including transformers, obey di/dt = V/L. L being fixed, given more input voltage the current rise is faster, so saturation current is reached earlier - this can be compensated by using higher frequency i.e. shorter dt, so that it won't be reached after all. EPAIII's mistake is not understanding the existence and as such ignoring this so-called magnetization current and mixing it up with load current.As numerous others have said, a 50Hz 100V transformer will reach the same peak flux density as designed at 60Hz 120V so in this case this is not a problem at all.

author: EPAIII
author_rank: Super Contributor
timestamp: May 11, 2023, 12:27:28 am
content: Well, I am curious. And I wish I had a similar transformer, perhaps I do in my unorganized junk pile, and the time to play with it a bit. I would love to see at what Voltage a transformer, with no load, goes into saturation.And what other conditions also cause saturation.

author: MrAl
author_rank: Super Contributor
timestamp: May 11, 2023, 03:34:31 am
content: Quote from: EPAIII on May 11, 2023, 12:27:28 amHi there,You could do this with any power transformer if you just have a way raise the input voltage like with a variac or something.Have to be careful though that the power source used for testing does not contribute to the problems at hand.Measure input current at the very least, and use a scope too if you have one to look at the excitation current and output voltage.The excitation current would be the most interesting as that should show signs of saturation sooner as the input is raised.

author: MrAl
author_rank: Super Contributor
timestamp: May 11, 2023, 03:37:23 am
content: Quote from: Siwastaja on May 10, 2023, 05:27:27 pmHi there,That's a good point. The ratio 120/100 is the same as the ratio 60/50 so it will probably work the same. The insulation and all that should be ok since it isn't that high of a voltage.There is one other thing to consider though. I believe that parts of Japan run on 50Hz and other parts at 60Hz. They have a completely independent grid system. If we get lucky, the transformer will be designed for 100vac at 50Hz, but if unlucky it will have been designed for 100vac at 60Hz.

author: floobydust
author_rank: Super Contributor
timestamp: May 11, 2023, 04:11:56 am
content: Saturation is not a digital event, you can see magnetization current increase exponentially with primary voltage after the knee.Power transformers are designed to a cost point which varies widely among manufacturers. chinese go for minimum copper and steel leading to high operating flux and high losses. OP's is likely a decent conservative design though.You don't always know how much flux headroom there is.The graphs in my post#28are for two similar Hammond power transformers 12VAC 1A, both outsourced to china.Older 166J12 is a lemon - it's too cheap, runs hot at no load, and at 140VAC has triple the primary (no load) current 150mA vs 50mA.It also has much less copper than the 166JA12. It was a case of Hammond screwing up the outsourcing, apparently they didn't spec anything as far as conservative design/flux headroom yet the OEM met the spec of "12VAC at 1A". They had to redo the parts to be even close to old Canadian designs.There is an art to transformer design - not wasting flux, copper yet have a competitively priced part that can take some overvoltage/high line.

author: magic
author_rank: Super Contributor
timestamp: May 11, 2023, 06:56:25 am
content: Quote from: EPAIII on May 11, 2023, 12:27:28 amWith open secondary, the primary is literally an inductor plugged into mains.dI/dt = V/LThe only condition which causes core saturation is application of one polarity voltage of too high magnitude for too long.So they have to work on AC, at sufficiently high frequency and sufficiently low voltage.Quote from: floobydust on May 11, 2023, 04:11:56 amLinearly

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 11, 2023, 01:06:05 pm
content: Why linearly? That's non-linear system.

author: magic
author_rank: Super Contributor
timestamp: May 11, 2023, 05:07:26 pm
content: After saturation it behaves like an ordinary air coil, so it obeys Ohm's law for AC. Before saturation it also obeys Ohm's law.It's only the knee where it's nonlinear. And the knee isn't exponential either. Exponential means "growing at a rate proportional to the momentary value". Quadratic, etc. isn't exponential.Look at the plot posted by floobydust, it's two straight lines joined by an arc.Yes, I'm nitpicking. But I'm a computer nerd and this constant abuse of "exponential" triggers me

author: TimFox
author_rank: Super Contributor
timestamp: May 11, 2023, 05:51:00 pm
content: With an ungapped ferromagnetic core, the inductance before saturation is not constant (with respect to applied voltage) since the magnetization curve and hysteresis of the core material are not linear.There is an important break point at saturation, where the incremental inductance drops precipitously, above which the incremental inductance is essentially that of an air-core inductor (far less than the inductance under normal operating conditions).With a non-constant inductance and reactance, the circuit does not obey Ohm's Law, which is a linear approximation to circuit behavior.Misuse of "exponential" is a very common vulgar (apology for the redundancy) error.If I have a bank deposit with 3% compound interest, that is truly exponential, but not very rapid.

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 11, 2023, 05:52:37 pm
content: Quote from: magic on May 11, 2023, 05:07:26 pmBut 'saturation' is not an exact point. That's quite a very large area of about 20-40 % of a rated voltage.

author: floobydust
author_rank: Super Contributor
timestamp: May 11, 2023, 07:23:14 pm
content: Quote from: magic on May 11, 2023, 06:56:25 amIt might be sorta piece-wise linear but overall I thought it looks cubic. Point is it's not really a flat top as people are stating.It seems a popular design goal is around 1.5T (for M4 laminations) with headroom for +10% higher flux.

author: MrAl
author_rank: Super Contributor
timestamp: May 11, 2023, 09:40:03 pm
content: Quote from: floobydust on May 11, 2023, 07:23:14 pmYes that's right.The best way to look at this is to look at the BH curve there. Looking at the slope before the knee and after the knee is the telltale evidence of what is going to happen.Before the knee the normalized permeability is around 0.87, and after the knee it is around 0.50, and that's a big difference. A normal design will be before the knee at a point somewhat close to the knee. That means that after the knee the magnetization current will increase by about 75 percent, meaning if it was 1 amp to begin with it will now be 1.75 amps, although that's not over the entire cycle. This can cause a few different problems including heating, electrical noise, and audible noise. That's not the end of it though the slope will most likely decrease even more than that and so we might be left with a very high excitation current.

author: TimFox
author_rank: Super Contributor
timestamp: May 11, 2023, 10:43:00 pm
content: Quote from: floobydust on May 11, 2023, 07:23:14 pmThe graphs you posted go up to only about B = 2.0 T for the different materials, and use a logarithmic axis for H, so you don't see linear behavior.That is approximately the saturation level for these alloys, so they didn't bother to graph theflatterportion to the right.Even there, for the top curve, B goes from about 1.85 to 1.95 T for H ranging from 100 to 700 A/m, which is quite flat.The curves are also quite non-linear below 0.6 T (not graphed): there exists a value of H that gives maximum permeability (slope) somewhere around there, and the "initial permeability" at H = 0 is noticeably less.

author: floobydust
author_rank: Super Contributor
timestamp: May 12, 2023, 12:41:20 am
content: I don't have much hope for Club y=mx+b.

author: MrAl
author_rank: Super Contributor
timestamp: May 12, 2023, 07:14:38 am
content: Quote from: floobydust on May 12, 2023, 12:41:20 amHi,You can use atan(x) with proper scaling and variation parameters and such.The best model might be the Jiles-Atherton (with possible extensions) although is not as easy to use.