How important is mains frequency in practice? - Page 1
Forum section: electronics / beginners

author: Sigmoid
author_rank: Frequent Contributor
timestamp: April 20, 2015, 03:31:35 am
content: I am about to move back to Europe from the US after a few years, and have a few appliances I'm thinking about taking with me. I have some pretty nice mains converter boxes, but those only convert voltage.What I'm interested in is what to expect if I run, for example, a motor designed for 120V 60Hz at 120V 50Hz - for example a kitchenaid food processor, those are really expensive in the EU and I got this one for a bargain - or a transformer, say in a soldering station... I know that lower frequency means higher losses - but I'm curious whether that has any significance in practice in this specific case.

author: cs.dk
author_rank: Unknown
timestamp: April 20, 2015, 03:46:17 am
content: 120V 50 Hz - Does any european country run at 120V mains?

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 20, 2015, 03:53:31 am
content: Quote from: cs.dk on April 20, 2015, 03:46:17 amI don't think that is the question. @Sigmoid said he is going to use "mains converter boxes" (presumably step-down transformers?) which will convert the mains voltage to 120V, but of course will do nothing about the 50 Hz mains frequency.There is no general answer to the question. Of course anything with an AC motor will operate at only 83% of the original speed. And some marginally-designed power transformers may run at higher temperatures because of the lower frequency.

author: Smokey
author_rank: Super Contributor
timestamp: April 20, 2015, 04:07:15 am
content: Typically you will be fine. You can't say for sure 100% unless you look at each specific case, but it's not like things are going to typically blow up because of the frequency.If the AC is being rectified then it's essentially irrelevant. The amount of additional ripple from the 10hz frequency difference will be tiny.And like was stated above, if the AC is being used directly then things will run a little slower (either as a clock source like an AC line cycle wall clock, or induction motor speed).

author: Pillager
author_rank: Unknown
timestamp: April 20, 2015, 05:31:15 am
content: Essentially, if the device doesn't have an induction motor, or use the mains frequency for timing, you should be OK.In my experience, kitchen appliances use universal motors, that can be run on both AC and DC (basically). They motor speed with these is dependent on the current. However, because the motors do use coils, the current might be a bit higher, due to the lower impedance.As someone mentioned before, you should check each case. But keep the frequency dependance in mind.

author: richard.cs
author_rank: Super Contributor
timestamp: April 20, 2015, 06:41:02 am
content: The food processor is probably a universal motor, it'll probably draw a bit more current as it's reactance will be lower at 50 Hz and will probably turn faster and run hotter, though the increased cooling fan speed should help. Note that this is the opposite to an induction motor.The soldering station will be similar, but this time only the magnetising current rather than the load current is affected so it's less of a problem unless the transformer is pushed into saturation. Only the cheapest and most marginal transformers will struggle (that does include nearly all microwave oven transformers though, even in expensive microwaves).Give us a full list and we'll comment on each.

author: Zero999
author_rank: Super Contributor
timestamp: April 20, 2015, 08:12:29 am
content: As above, the kitchen appliances should be fine as they have universal motors, so even if you wanted to use DC it shouldn't be a problem.I haven't tested a food processor off DC but I did try a vacuum cleaner motor and it worked just as well off rectified 230VDC as it did off AC so it won't make any difference whether it's 50Hz or 60Hz.It's true transformers run a bit hotter at lower frequencies but for small transformers (under a couple of hundred VA or so) , it's less of an issue because they have a higher resistance.

author: rolycat
author_rank: Super Contributor
timestamp: April 20, 2015, 08:58:05 am
content: Quote from: Pillager on April 20, 2015, 05:31:15 amQuote from: richard.cs on April 20, 2015, 06:41:02 amKitchenaid food processors use induction motors, as do a number of other brands such as Cuisinart and Magimix. Most commercial machines are also fitted with them.

author: Zero999
author_rank: Super Contributor
timestamp: April 20, 2015, 09:49:00 am
content: Quote from: rolycat on April 20, 2015, 08:58:05 amAre you sure? All the domestic food processors I'm aware of use universal motors. No doubt the larger, food processors used in commercial use induction motors but universal motors are much lighter and cheaper and therefore are motor common in domestic appliances.Even if it does have an induction motor, as long as it has variable speed control, the input mains frequency shouldn't matter, as it will have already have a variable frequency inverter to drive the motor at the correct speed/frequency, regardless of the mains frequency.

author: rolycat
author_rank: Super Contributor
timestamp: April 20, 2015, 10:20:09 am
content: Quote from: Hero999 on April 20, 2015, 09:49:00 amYes, quite sure. They tend to be used in the pricier brands, but Sigmoid mentioned that he had a KitchenAid machine. I have owned two Magimix domestic food processors; both had induction motors.QuoteUnfortunately they tend not to have a speed control, usually just on/off/pulse switches.

author: Cherry
author_rank: Contributor
timestamp: April 20, 2015, 11:47:55 am
content: The food processor is probably a universal motor

author: richard.cs
author_rank: Super Contributor
timestamp: April 20, 2015, 12:04:59 pm
content: Induction motors will run off the wrong frequency but may get hot and will definately turn slower. The heating is nasty because as well as drawing more current (sometimes lots more due to saturation) the lower speed reduces the effectiveness of the cooling fans. The correct approach is to reduce the voltage in proportion so a 120V 60Hz motor should be run at 100V 50Hz. Just a transformer but maybe not the same one you'd use for other equipment. Current draw and torque should stay the same, speed and therefore absolute power reduced.It's been stated that universal motors don't care and are also happy on DC. That's not entirely true but close. Any brushed motor looks like a back-emf (dependant on rotation speed) and a series impedance, that impedance is freqeuncy dependant. I have found that small (~500W) 110V 50Hz universal motors draw their rated AC current and produce rated output power at about 80 V DC. They still have a back-emf and some series resistance but the reactive part no longer limits the current. Hence such a motor might be unhappy at on DC at its rated AC voltwage, but in practice they're usually ok. Anything with a universal motor that's marked AC/DC experiences this effect but the designers have decided it's negligable and/or have picked a motor with a larger ratio of R to XLso the reactance matters less. The difference between 50Hz and 60Hz is hardly ever noticeable, but they can be a bit underpowered on 400 Hz.110V angle grinders make nice electric bike motors off 80V DC or so.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 20, 2015, 12:23:31 pm
content: If the device is rated "50/60Hz", that means they have enough turns on enough iron to handle nominal voltage at the lowest (worst case) frequency.If not... I'd suggest caution and an amp-clamp. If it's drawing way more current than usual (>20%), better not to use it!Tim

author: ConKbot
author_rank: Super Contributor
timestamp: April 20, 2015, 01:10:00 pm
content: Quote from: rolycat on April 20, 2015, 08:58:05 amKitchenaid mixers have covers on the side for replacing the brushes. Definitely not induction.5:20, universal!

author: macboy
author_rank: Super Contributor
timestamp: April 20, 2015, 01:20:17 pm
content: Quote from: rolycat on April 20, 2015, 10:20:09 amThe on/off/pulse switch makes sense in your case since you can't easily control the speed of an induction motor. The kitchenaid ones use a variable speed control and have a centrifugal speed governor. They use universal (i.e. brushed DC) motors.It is not wise to use 60 Hz electronics at 50 Hz. The other way around is usually less of an issue. Motor speed problems aside, the main problem with 60 Hz at 50 Hz is the increased magnetic flux in transformers which can cause saturation. That can lead to excessive heat and premature failure, or at worst, catastrophic failure. The magnetic flux is related to the integral of the magnetizing voltage over time; at 50 Hz you have 16.7% more time each half AC cycle, so more flux buildup. You can reduce the likelihood of saturation by reducing the voltage; use 110 V (or 105 V) instead of 120 V. Most devices will work just fine with the reduced voltage and the transformers will be happier.

author: Zero999
author_rank: Super Contributor
timestamp: April 20, 2015, 01:53:16 pm
content: Quote from: ConKbot on April 20, 2015, 01:10:00 pmNo surprise there.How heavy is it? What's the rated power?Most food processors are rated to more than a few hundred Watts and would weigh several kg if they used induction motors so wouldn't be portable.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: April 20, 2015, 04:16:21 pm
content: What about pumps in coffee makers? I know my Saeco has two part numbers for the 60Hz and 50Hz pumps.

author: bitwelder
author_rank: Super Contributor
timestamp: April 20, 2015, 04:56:42 pm
content: Quote from: Alex Eisenhut on April 20, 2015, 04:16:21 pmIf they have specifically listed two parts, I guess the pump may run synchronously with mains frequency, i.e. wrong pump -> wrong liquid volumes.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: April 20, 2015, 05:07:40 pm
content: Quote from: bitwelder on April 20, 2015, 04:56:42 pmThey're funny pumps, they work based on a bit of metal bouncing back and forth inside. That's a coil wrapped around it.I guess that this thing is tuned to work at the power frequency.

author: max666
author_rank: Frequent Contributor
timestamp: April 20, 2015, 05:15:53 pm
content: Quote from: ConKbot on April 20, 2015, 01:10:00 pmI'm sorry to go off topic, but that's not a dab of oil:https://youtu.be/HYZBH2MF2KM?t=5m31s

author: rolycat
author_rank: Super Contributor
timestamp: April 20, 2015, 05:17:29 pm
content: Quote from: Hero999 on April 20, 2015, 01:53:16 pmKitchenAidmixersuse universal motors, but they are not food processors.ManyKitchenAid food processors use induction motors. For instance:KFP750OBKFP740QBF5KFPM771SOB5KFPM775BOBThey can be distinguished from the universal motor type since as I mentioned earlier they typically have three buttons, on, off and pulse.

author: SeanB
author_rank: Super Contributor
timestamp: April 20, 2015, 05:23:17 pm
content: Quote from: Alex Eisenhut on April 20, 2015, 04:16:21 pmDifference is the voltage of the coil. The 60Hz will be 110-115VAC and the 50Hz 220-230VAC. The pump unit inside is the same, irrespective of the frequency, the pump is used to build up pressure, and the flow rate is not really going to vary much with the 20% change in pulse rate, it is more varied by the compaction of the grinds and the back pressure developed by the filter.The 50Hz pump might be slightly larger in diameter to give an increased flow with the fewer pulses, but I doubt that, it would be just the coil voltage that is changed.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: April 20, 2015, 05:36:23 pm
content: Quote from: SeanB on April 20, 2015, 05:23:17 pmI heard that the Saeco Superautomatica won't work at the wrong frequency even at the right voltage. Who knows.

author: macboy
author_rank: Super Contributor
timestamp: April 20, 2015, 06:04:18 pm
content: Quote from: rolycat on April 20, 2015, 05:17:29 pmTouché.

author: SeanB
author_rank: Super Contributor
timestamp: April 20, 2015, 06:06:52 pm
content: That would be the processor board needing a mains frequency input, and if it does not match the programmed value it stops working.

author: ConKbot
author_rank: Super Contributor
timestamp: April 20, 2015, 10:46:10 pm
content: Quote from: rolycat on April 20, 2015, 05:17:29 pmDoh, Didnt even know they made food processors. With all the attachments they make for the mixers, figured that'd bolt onto the front of the mixerDouble Doh, cant even put my reply at the end. Bed early tonight

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: April 20, 2015, 11:19:34 pm
content: QuoteAnother device to watch out for is a Wahl electric hair clippers. I think the motor on these is tuned to work at a specific frequency.A guy I know tried his USA version in Australia with a step down transformer but the vibration was so bad it wasn't usable.Can't remember what this kind of motor is called.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 20, 2015, 11:33:00 pm
content: Quote from: HackedFridgeMagnet on April 20, 2015, 11:19:34 pmSome gadgets like that are simply giant "buzzers". So you can easily imagine that they can gain maximum mechanical work (i.e. displacement) by tuning the mass of the moving part (the "rotor") to the mains frequency.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: April 21, 2015, 03:22:55 am
content: Quote from: Richard Crowley on April 20, 2015, 11:33:00 pmThat's pretty much what I concluded upon hearing those stories. Never tested it though, the risk of losing my espresso machine is too great.