How can I make a transformer so my american kitchen appliance can work in the UK - Page 1
Forum section: electronics / projects

author: VladKEasternTiger
author_rank: Regular Contributor
timestamp: March 06, 2010, 01:50:45 pm
content: Hi everyone, I was given a gift its a kitchen smoothie blender, very expensive the problem is its a 2 pin American/Canada plug and will not work in the UK 230 v outputI was told you need a transformer and if you just put an adapter at the end of the plug you will blow it upThe blender sticker says 120V, Max, 250W, 60HzSo how can I get this thing power up, the transformers in the uk electronic shop maplin go about 70 dollars that is £50, as much as the Item itself, surley they is another way anyone?Thanks

author: djsb
author_rank: Super Contributor
timestamp: March 06, 2010, 02:12:23 pm
content: Hi,Try this place.http://www.voltageconversion.co.uk/store/home.php?cat=260HTH,David,London,UK

author: VladKEasternTiger
author_rank: Regular Contributor
timestamp: March 06, 2010, 02:15:11 pm
content: Hi David thanks for the Link I will get back to you friend

author: VladKEasternTiger
author_rank: Regular Contributor
timestamp: March 06, 2010, 02:19:30 pm
content: Quote from: djsb on March 06, 2010, 02:12:23 pmHi David, Im guessing this is the only one from the list that would work as my appliance is 250W so you have to go above but not under, this is 300W. It looks like the first 4 transformers on the page you sent me would not work for my appliancehttp://www.voltageconversion.co.uk/store/product.php?productid=16373&cat=260&page=2

author: djsb
author_rank: Super Contributor
timestamp: March 06, 2010, 02:37:39 pm
content: Hi,I would go for this onehttp://www.voltageconversion.co.uk/store/product.php?productid=16209&cat=260&page=2As it is a similar price but gives a good margin of extra power and can be used for step up as well.It's your choice in the end. Best to err on the side of safety wherever possible.David.

author: Zero999
author_rank: Super Contributor
timestamp: March 06, 2010, 03:31:47 pm
content: Quote from: VladKEasternTiger on March 06, 2010, 01:50:45 pmThat's the problem, transformers aren't cheap.I found one in Maplin for £30.http://www.maplin.co.uk/Module.aspx?ModuleNo=265288How long does the blender normally operate for?If it's only for a few miniutes at a time with as long a rest in-between then you will probably be able to get away with using a slightly lower power transformer, as 150W which will cost you less but it is a risk.http://cgi.ebay.co.uk/K-E-R-T-POWER-TRANSFORMER-EURO-UK-230V-USA-110V_W0QQitemZ320476667026QQcmdZViewItemQQptZLH_DefaultDomain_3?hash=item4a9de5dc92

author: rossmoffett
author_rank: Regular Contributor
timestamp: March 06, 2010, 05:46:42 pm
content: Might be cheaper to replace the motor?

author: PetrosA
author_rank: Frequent Contributor
timestamp: March 06, 2010, 06:00:09 pm
content: You must get a transformer that's rated for more than your motor is rated. Motors can have an inrush current many times that of their operating current (in your case about 2.1A on US voltage). So when you start the machine, it will be using way more than 150W, more like 800W for a short time. You also need to make sure that you get a converter rated for appliances. They will have a magnetic transformer rather than an electronic one. The voltage will not be exact (possibly about 130-140V) but it will handle the motor load. Another thing to be aware of is the frequency difference. Your appliance will run slower on 50Hz than it would in the US on 60Hz, and will have a little less power.

author: Zero999
author_rank: Super Contributor
timestamp: March 07, 2010, 12:16:56 am
content: I wouldn't worry about inrush current, a transformer should be able to handle many times its rating for a very short period of time and double it's conterminous rating for a bit longer.What normally kills a transformer?Overheating which causes the insulation to fail between neighbouring windings to fail causing them to short and overheat more until it starts a fire unless some thermal protection kicks in.The good thing is, because a transformer is a huge lump of iron it takes awhile for it to overheat, even if it's short circuit for a second or so. The inside of a motor has something in common with a transformer: it's lots of wire wound round an iron core. If the motor's windind can withstand the inrush current drawn when it's started, then a transformer of the same power rating certainly will.Underrating for low duty is also very common - you'll often see 3kW for 15 minutes or 1.5kW continuous printed on the nameplates of transformers. Of course you can get away with overloading larger transformers more for longer simply because they have a higher thermal time constant. I wouldn't expect you to connect a 300W load to a 150W transformer for more than a minute without it overheating.In this case the fuse might be a problem. You might only use your blender for a couple of minutes at a time so you decide that a 150VA transformer will do but if the transformer is fitted with a 1.5A fuse it's almost certain to blow within a couple of minutes of just over 2A being drawn.

author: PetrosA
author_rank: Frequent Contributor
timestamp: March 07, 2010, 03:27:41 am
content: Quote from: Hero999 on March 07, 2010, 12:16:56 amYes and no. I lived abroad for many years and had tons of US appliances working off of 230V. There are two main types of "travel" transformers that step down 230V to 120V for US users. One is a magnetic (often toroidal) for heavier loads that don't care much what the exact voltage is like power tools and mixers, the other is fully electronic or magnetic with electronic voltage regulation built in. Neither type is very fond of heavy inrush currents. The regulated ones are designed for use with delicate electronic devices that can't handle a wide variation in voltage. Many of the low wattage units (up to 500VA) are the regulated ones. If you plug any kind of motor into a regulated transformer near its max rating, you'll probably see smoke.QuoteAgain, you're only taking the magnetic transformers into account. Not all of them will be this type.QuoteFor the 250W mixer, I think a 150VA rated transformer will probably blow the fuse in less than a few minutes

author: Simon
author_rank: Unknown
timestamp: March 07, 2010, 07:42:18 pm
content: Quote from: Hero999 on March 06, 2010, 03:31:47 pmthats a very bad idea, particularly as a recomendation, if you choose to take that risk yourself fair enough, don't suggest it to someone that may not understand the implications

author: Zero999
author_rank: Super Contributor
timestamp: March 07, 2010, 09:27:43 pm
content: Quote from: PetrosA on March 07, 2010, 03:27:41 amI've never seen an electronic transformer, apart from the type used to power halogen lamps and in that case the output is normally a high frequency square wave, not a 50Hz sine wave.Could you please post a link to one?I imagine an electronic transformer would be very complicated. First the AC needs to be rectified to DC, then an inverter is required to convert it to a different AC voltage, The inverter won't be simple, to get a good sine-wave, a class D amplifier would have to be used.I would imagine that an electronic transformer would already have built-in over-current protection so overloading it shouldn't do any damage, the chances are it would just shut down, then try to restart after a certain period of time.QuoteI don't know about an electronic transformer but I know a magnetic transformer won't be damaged, just look at any audio amplfier power supply schematic and you'll see a huge electrolytic capacitor immediately after the rectifier which will short circuit the transformer when the power is first applied. So much so that a large audio amplifier will have inrush protection, but not to protect the transformer but to prevent the fuse from blowing every time it's powered up.QuoteI don't see why you'd ever need a tightly regulated mains supply?Most delicate electronic devices are powered from a switched mode supply which can accept a wide range of mains voltages. Those pesky SMPSes also tend to draw a large inrush current because they have a capacitor connected to the output of a rectifier.Quote from: Simon on March 07, 2010, 07:42:18 pmI disagree because I did warn him of all the possible dangers.There's virtually no risk of a fire because all modern mains transformers are thermally protected - it's a legal requirement.Unfortunately, the trouble is the thermal protection is often also non-resettable so it is a risk but not a fatal risk.I'd rather educate someone so they can make up their own mind up rather than be a nanny and say don't do it.

author: Simon
author_rank: Unknown
timestamp: March 07, 2010, 09:41:55 pm
content: well getting people to do things for themselves is great but I would not recomend running a 250 W motor on a 150 W transformer for any amount of time. The motor will draw a high current to start up so you've not given yourself a good head start then you want to continue to run the 250 W motor with something designed to provide 60 % of the power at the most..... not really a good idea

author: Zero999
author_rank: Super Contributor
timestamp: March 07, 2010, 11:24:13 pm
content: See the datasheet for the range of isolation transformers linked below:http://docs-europe.origin.electrocomponents.com/webdocs/017e/0900766b8017e5d3.pdfNotice how the 1/2 hour rating is 50% greater than the continuous rating?Although it's not mentioned on the datasheet, loading at even more than the half hour rating for a minute or so won't do any harm.The thermal circuit breaker must be a time delay type because the 750VA 1/2 hour unit has a 3A breaker.If the smoothie maker is only operated for a minute or so at a time a 150VA transformer should be enough, a 200VA transformer should be more than adequate.You'll also probably find that the smoothie maker's motor is not rated for continuous operation and probably will burn out if you ran it continuously for half an hour.

author: Simon
author_rank: Unknown
timestamp: March 08, 2010, 07:59:10 am
content: ok point taken but on 150 W your still at 90 % of the required power, I suppose it is doable but would not make it a practice, are those figures meant as normal operation conditions or absolute ratings that cannot be exeeded ?

author: PetrosA
author_rank: Frequent Contributor
timestamp: March 08, 2010, 12:59:42 pm
content: Quote from: Hero999 on March 07, 2010, 09:27:43 pmhttp://www.voltageconversion.co.uk/store/product.php?productid=16214&cat=260&page=1QuoteIt's nothing more in theory than a common wall wart, only it'll output AC.QuoteBecause some of the voltage converters have a much wider voltage output range (especially in the unloaded state) than some electronics are designed to handle. You can hook a drill or heater up to 140 or 150 V and it'll be fine. Some electronic products won't. The unregulated step down transformers can have that high of a voltage when no load is applied. It will fry some delicate stuff. If your electronics have a switched mode supply that can handle 90-230V, you probably don't need the step down transformer in the first place, right?QuoteWhile I certainly understand your good intentions, I think you need to be careful when it comes to electrical advice.You've already suggested that he use a 150VA transformer to run a 250W motor load a few times. That's just wrong. You could power a 150W incandescent light bulb, since it's a linear load with near 1.0 power factor and the watts are more or less equal to the VA, but a motor doesn't have a perfect power factor. He will need a minimum of 300VA and likely more.You don't have to be a nanny. Sometimes the best advice is "Speak to a qualified electrician" or something along those lines. I have to deal with laypeople in supply houses or as customers who would like me to tell them how to do something themselves. For liability reasons, I can't do that unless I know that it's something that they understand and can handle with their level of training/understanding. The warning sign in this thread is that the OP would like to save a few pounds on buying the proper power supply. Unfortunately, the OP doesn't seem to understand anything about electric, so I am very hesitant to give any advice that doesn't cover his (and my) butt.

author: Zero999
author_rank: Super Contributor
timestamp: March 08, 2010, 01:44:22 pm
content: Quote from: PetrosA on March 08, 2010, 12:59:42 pmI think you'll find that's a magnetic transformer, the weight kind of gives it away, 1.3kG is far too heavy for a 100W electronic switched mode power supply, it's more the kind of weight of a 50Hz, 50VA isolating transformer or 100VA 2:1 autotransformer.QuoteThen it'll be a magnetic transformer which will have inferior voltage regulation to a much larger and more efficient magnetic transformer; wallwarts are notorious for having poor voltage regulation.QuoteThat's certainly true which is why you should use a large magnetic transformer to power sensitive electronics, not an unregulated wallwart style transformer like you suggested. A 500VA transformer will have much better regulation than a poor quality 100VA transformer from China.QuoteNot always, my PC has an SMPs, yet it has a voltage selector switch on the back. The MOSFETs and filter capacitors and rectifiers will be rated to 400VDC and are unlikely to be damaged unless the voltage exceeds 280VAC.QuoteAll right, you raised a valid point about power factor, still a 300VA motor is not going to burn out a 150VA transformer, if it only operated for a minute or so. I'd also expect a universal motor to have a reasonable power factor, it won't use an induction motor which will have a poor power factor when lightly loaded.I wouldn't push it beyond double the VA rating even for short periods, simply because the voltage drop will be unacceptable, nothing to do with thermal problems.

author: VladKEasternTiger
author_rank: Regular Contributor
timestamp: March 08, 2010, 02:56:54 pm
content: Quote from: rossmoffett on March 06, 2010, 05:46:42 pmIt was specifically purchased for the high powered motor to grind african and indian solid foods to a paste

author: VladKEasternTiger
author_rank: Regular Contributor
timestamp: March 08, 2010, 02:57:58 pm
content: Quote from: PetrosA on March 06, 2010, 06:00:09 pmThank you for your informativeinformation

author: VladKEasternTiger
author_rank: Regular Contributor
timestamp: March 08, 2010, 03:08:03 pm
content: Thank you everyone for the information, im not goingto buy a transformer as it is expensive and imnot going to make one either as its not abreadboard and my partner would be using the blender in the kitchen

author: PetrosA
author_rank: Frequent Contributor
timestamp: March 09, 2010, 03:42:26 am
content: Hero999,I think we probably agree more than disagree, and I'm sure I'm not using the correct names for some of what I'm talking about. From some poking around on the net, there are lots of different ways that some of these producers make their equipment, some safer, more resilient and more dependable than others. The bottom line is that any decent unit is going to cost more than a junky one. Some form of electronics will be present in most of the better ones if only to control the inrush of the transformer itself (I had a large toroidal transformer for coffee equipment in Europe that would blow the breaker just from plugging it in...).All in all, if anyone's going to spend an extended amount of time abroad, buy local. It's cheaper than all this playing around

author: Unknown
author_rank: Unknown
timestamp: March 09, 2010, 07:43:24 am
content: One option not stated is to look around scrap dealers. In Perth (au) we used to have a company called hi tech scrap, they would be paid to junk old phone systems (from Telstra our main telco) and mainframe computers.I bought (for scrap value) a multi tap mains isolation transformer (0-110-240:0-110-240) I use it to isolate my variac (which in the same case has a bridge, large cap bank, circuit breakers, current meter etc) I need to add volt meters etc and close the case (it needs more front panels, and a side)Was a cheap way to build a 0-~460Vdc 5A PSU

author: Zero999
author_rank: Super Contributor
timestamp: March 09, 2010, 12:09:00 pm
content: Quote from: VladKEasternTiger on March 08, 2010, 03:08:03 pmThen it looks like you're out of luck I'm afraid.The cheapest I could find was £30.I wouldn't consider making it from scratch, what you could do though, is buy an open frame transformer and make your own box for it. The problem then becomes finding the connectors. If you can't get a US socket for a reasonable price, you could replace the plug with a suitably rated connector, which can handle the voltage and current and can't be accidentally inserted into a UK outlet.I've found a 225VA transformer in Rapid for £13.85, the trouble is when you add the VAT, delivery and any other connectors it'll probably work out as or more expensive as buying a slighly more expensive transformer off eBay.http://www.rapidonline.com/sku/Electrical-Power/Transformers/Toroidal/Toroidal-transformers/35506/88-2644Rapid do, free delivery but only on orders over £35 so unless there's something else you want to buy, it isn't really an option unles you're close to Rapid and can pick it up.EDIT:I've found some cheap transformer in Farnell and RS. Farnell has free delivery for orders over £20 and RS gives free delivery for business account holders. You still have to build your own enclosure though.http://uk.farnell.com/multicomp/mcta225-55/transformer-225va-2-x-55v/dp/9532889http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=6719044

author: Unknown
author_rank: Unknown
timestamp: March 12, 2010, 06:33:36 pm
content: Personally I'd try two things:First, I'd crack it open and check out how the windings were laid out. If this model is sold internationally, it's very possible that the windings are set up so that by simply wiring them differently, it can operate from either 120 or 240 volts.As a second option, I might see if it's possible to use an incandescent light bulb in series. This is kind of problematic since when the motor is starting up the light bulb will see more voltage than later, so the amount of voltage on one part will be variable.The first option is definitely something to check into though. 120/240 volt wiring changes are common in the world of motors.

author: Simon
author_rank: Unknown
timestamp: March 12, 2010, 06:47:23 pm
content: will this motor run on DC ? maybe simply putting a diode in series will work by cutting have the power out ? (although not ideal)

author: Zero999
author_rank: Super Contributor
timestamp: March 13, 2010, 12:04:19 pm
content: The motor will more than likely work on DC.The trouble is that the required DC voltage to run is safely will be less than that of he AC voltage because the inductance of the windings will no longer limit the current. So to run a 120VAC motor on DC, you might need 60V which makes it more difficult again.

author: Simon
author_rank: Unknown
timestamp: March 13, 2010, 12:33:49 pm
content: why would that be ? if it is a motor with brushes wouldn't it make no difference ? I ran a drill once off 220 VDC by using a rectifier with no problem, it ran as it did before.

author: Zero999
author_rank: Super Contributor
timestamp: March 13, 2010, 09:21:06 pm
content: It depends on the motor.A universal motor will have a stator winding which will either be in series or parallel with the armature. If it's run off AC, the inductance of the coil and to a lesser extent the armature will limit the current. If the motor is run from DC, the inductance won't matter so the current in the stator coil will only be limited by the internal resistance which is why I suggested reducing the voltage.I've tried reducing the speed of a series wound vacuum cleaner motor by connecting a half-wave rectifier in series and was at first surprised that it didn't reduce the speed as much as I would have thought but I put this down to the coil's inductance.I've never tried running a universal motor from a full wave rectifier but I imagine that I would have to use a lower voltage to get the same speed and torque.I don't know your drill might have a PM motor and already have a rectifier built-in? Or perhaps the inductance limited the pulsed current from the rectifier?

author: Simon
author_rank: Unknown
timestamp: March 13, 2010, 11:39:10 pm
content: Well dosen't the motors brush unit cause the current to be reversed continuosly creating the effect of AC ?are you saying that it "sounded" to you that a motor with a diode in series was not much slower ? you would only really know by actually measuring it.my drill was a standard motor with field and armature windings and the brushes

author: Zero999
author_rank: Super Contributor
timestamp: March 14, 2010, 09:55:55 am
content: I only went by sound, so it might've been running at half the speed, I didn't actually measure it.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 05, 2010, 02:55:31 am
content: just get a big 240V to 120V transformer. goto elec. shop and ask. i used to fool around with transformers (smaller one, but for bigger one i think theoritically the same, it just depend on the transformer power rating). at the very most, when u shorted the transformer output, it will get hot, red and eventually melted away. just dont fool around with the main side (input) of the transformer, u will have a big explosion, even bigger if u dont have circuit breaker protection in your house. if u use underrated transformer, it will heavily loaded and get hot and fail fairly quickly, but if you use larger one, no problem at all. even at the same rated transformer and equipment, transformer will get hot. i used to put fan to cool it down and live longer, thats how high end adapters are doing. if u want to output DC, then you'll have to have support circuitry, rectifier and stabilizer caps. but as the thread owner just simply want to use 130V appliance on 240V main, then a single big 1:2 stepdown transformer will do the trick. for AC motor, pls dont rectify the AC supply, AC motor needs AC supply. same thing with DC motor needs constant voltage supply to work perfectly, its just their design and architecture in amarture and winding that requires those kind of supply. just my 2 cents opinion.