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In Reply to: RE: Step Down Transformer posted by Awe-d-o-file on August 25, 2011 at 14:19:38
You misunderstand the issue.
There is risk of FIRE when running a 60hz transformer on 50hz.
If the transformer is rated for 60hz you can run a higher frequency into it (as you are doing), just don't run a lower frequency into it.
Follow Ups:
The transformer, not the devices connected to it. Gotcha. I must admit however I've never seen a transformer have a frequency rating and all the commercial 220/110 stepdown transformers listed for use by travellers make no mention of frequency. So..............
ET
Edits: 08/26/11
"So.............."
So youn have been warned, and now know better that to try this.
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Introduction
Initially, it all seems simple enough. You buy a piece of equipment from an on-line seller in another country, and expect that it should have the necessary switching to allow you to set the voltage to suit the mains supply where you live. With globalisation being the key term thrown around these days, you'd naturally expect that there should be few (if any) problems.
If the country you bought the gear from is Australia, Europe or the UK (but the equipment was built elsewhere) you might get lucky, but if it's equipment that's made in the country of origin you may not. Buying from the US or Canada will often cause problems, because the "export model" is generally not sold locally, so it will be made to operate only with the US mains voltage and frequency.
While the common answer is to just get a step down transformer to reduce your local mains (say 230V) to 120V, this may not solve the problem at all, and may introduce serious safety risks as well as the possibility of transformer failure. Unfortunately, the simple (and common) answer fails to consider many different possibilities, some of which may place the user and/or the equipment at considerable risk. One of the most common requirements is that people want to be able to use equipment from the US in Australia, Europe, etc.
The step-down transformer is not straightforward, although it initially seems that nothing could be simpler. Very few people seem to appreciate the various things that can go wrong, even those with technical training. "Information" from forum sites is almost always either wrong, overly simplistic or misguided. A small number of forum posters will understand the risks, but it's impossible for the average person to determine who is right and who's not.
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4 - Frequency
Now comes the real can of worms. Many people believe (and will tell you) that the small frequency difference (50Hz vs. 60Hz) is insignificant, but this is not true. Many products intended solely for the US markets will have the transformer made for 60Hz. This has the advantage of making the transformer smaller than it would be if it could also handle 50Hz. Indeed, an advantage of 60Hz mains is that all transformers and induction motors are smaller than the 50Hz equivalent. The alternative is that in some cases, a 60Hz and 50Hz transformer may be the same physical size, but a 60Hz only version can use lower grade (and therefore cheaper) steel laminations.
If a transformer is designed specifically for 60Hz, and understanding that this makes for a smaller and/or cheaper transformer than would be the case if it could also handle 50Hz, why would anyone assume that this 60Hz tranny will work fine at 50Hz? The answer (predictably) is that it will not. An initial quick check will usually not show the problem ... it may need to be left on for a while before anything shows up. The problem is heat - the transformer will get (much) get hotter than normal, and may easily reach a dangerous temperature that will cause failure.
Some years ago, a company I worked for (in Australia, a 50Hz country) took delivery of six very large and expensive 48V power supplies for telecommunications use. These were made in the US, and used ferro-resonant transformers that were designed for 60Hz. I discovered the problem and advised management, but it was decided that I was being "alarmist". The first unit burnt out within 2 weeks of being installed, filled a large computer room with smoke, shut down a call centre and caused great deal of embarrassment for all. After this, management listened when I said there was a problem!
Part of the design process for a transformer is to ensure that there are enough primary turns to prevent the steel core from saturating. This depends on the voltage and the frequency. If the frequency is reduced (and 10Hz or 16.6% makes a big difference), there are no longer sufficient turns to prevent saturation. When the core saturates, the primary winding of the tranny draws much more current from the mains than normal - not just 16% more though, it can easily exceed 100% more.
The result is that the transformer overheats, and will eventually fail. Even most technicians will be unable to tell you that the transformer is saturating, because they either don't know what to look for, or don't have the equipment needed to look at the current waveform. There is actually no difference between decreasing the frequency or increasing the voltage by the same ratio. This is shown in Figure 3, where the voltage was increased from 240V to 270V - a mere 12.5% change.
Figure 3 - Magnetising Current at 240V and 270V
The oscilloscope shows voltage, but this is the output from a current transformer. At 240V, magnetising (idle) current is 32.3mA (which reads as 3.23V RMS), and the transformer will dissipate about 7.7W. A 12.5% increase to 270V increases the magnetising current to 69.6mA, or 18.8W - well over twice the normal idle current and power. Reducing the frequency by 12.5% will have almost exactly the same effect. Any transformer designed specifically for 60Hz will draw far more idle current than normal at 50Hz [2].
Since many modern products will already be operating right at the very limits (smallest possible transformer, etc.), a reduction of mains frequency will almost certainly push them beyond the point where failure is inevitable. It's no longer a matter of "if" it fails, but "when". Large 60Hz transformers may also growl with a 50Hz supply, and this can be loud enough to make a hi-fi amp unusable because of the mechanical noise. Electrical noise is also possible (i.e. noise from speakers), because stray magnetic flux can become a major problem because the core is saturated.
There is no cure for the above-mentioned issues, other than replacing the power transformer with a 50Hz version. The replacement will be expensive - assuming that the transformer is even available from the manufacturer. If not, you have an expensive paperweight that's of no use to anyone. It might be possible to operate the transformer from a lower voltage to avoid damaging saturation, but this approach cannot be recommended because it often leads to quite unacceptable consequences - serious loss of power (for an amplifier), internal supply voltages that are no longer regulated, etc., etc.
Note that operating a transformer designed for 50Hz mains at 60Hz reduces the idle current and power, so the transformer should run a little cooler. Therefore, products that are designed for 50Hz operation (destined for anywhere in the world apart from the US and Canada) will rarely have a problem with mains frequency, provided the supply voltage is correct. Inadequate design can still cause failure though.
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Conclusion
First and foremost, avoid auto transformers. Make certain that the step-up/down transformer that you select has separate primary and secondary windings, is earthed properly, and has a VA rating of about double the maximum expected power drawn by the appliance. As described above, this may not be necessary, but is usually a good idea for most products.
Regarding the possible importance of frequency, it depends a great deal on the product and how it was originally designed (with/without a safety allowance for example). I would have liked to show the difference in idle current by changing the frequency, but unfortunately it requires a great deal of time and effort to set up. If anyone doesn't believe that the results shown here are real, then feel free to ignore this article in its entirety. You might be lucky, you might not. It is important to understand that some products will tolerate a lower frequency while others will not, and it's not usually possible to know beforehand those that will survive and those that won't. This can generally only be determined by testing the product.
There is no simple answer to the common question "Can you make it work?", when someone wants to know if it's alright to import product 'X' from overseas. There are simply too many possibilities for anyone to give a definitive answer - guesses are just that, and cannot be relied upon. This is especially true if the imported equipment is expensive and the seller doesn't know enough to be able to provide useful answers. In such cases, it may be better to avoid the item altogether because the cost of modification may make it more expensive than the same thing purchased locally.
There are some products (especially vintage), where modifications are simply not an option because they will devalue the item. In such cases, the best you can do is hope that it will be alright. Otherwise it becomes a rather expensive display product that can't be used.
For those for whom money is no object, motor-alternator units can be purchased (they are no longer as common as they once were though), or high-power electronic frequency and voltage converters also exist. These units range from a few hundred Watts to many kW, but are typically very expensive ... the mere fact that suppliers seem to never publish any prices gives you a good idea of the price range [3].
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You've got to ask yourself one question: Do I feel lucky? Well, do ya, punk?
Thanks! Great post/link. I have no experience in a 50hz environment/country. That explained a lot of it. Do you think there is as much of an issue as posed in your link/text as with the clock radio that likely draws 40W @120V 60hz? Not saying there isn't just wondering your opinion on that. The original poster did not state the model number or current consumption.
ET
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