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Question for someone who understands practicalities of AC to DC conversion...

Tez

Graduate Poster
Tez
Joined
Nov 29, 2001
Messages
1,104
Ok I understand the theory on power transformation, but have a practical problem:

A few months ago when I had my notebook computer power transformer confiscated by Israeli security. So when I returned I bought a generic converter from Targus - the one I got was almost identical to this one: http://www.targus.com/product_details.asp?sku=PA160U (I couldnt get a toshiba converter fast enough, but this Targus one worked fine).

Then a few weeks ago I was in London I plugged in the transformer - and BANG. Smoke. Burning electrical smell.

Turns out that while the adapter works fine for 240V AC (as I checked was stated on it before I plugged it in), the detachable plug you can see in the diagram does not. It does have a little red sticker saying on it to use only for up to 120V. From the website I find out that if you're going to Europe, then youre supposed to ask them for a different plug.

So on my return I call Targus up, and they send me a new plug for the supply - it comes with the two round prongs for Europe. I didnt tell them that I'd blown up the US plug - just asked for the European plug.

Now on the European plug there is a little red sticker that says "Attention: 220-240V AC only".

My question is this - how could this new plug possibly not work on 110V AC. i.e. why cant I simply (using an appropriate adapter for changing the round prongs to flat ones!) plug in this new plug here in the US? Can they have rigged it so it blows up for the smaller voltage? The European plug is supposedly ok for up to 2.5 amps, whereas the US one was only for up to 1.2 amps as far as I can tell...

Any ideas?

Thanks
 
Sounds fishy. Where was the smoke ? At the plug, or from the power supply ?

What did they say when they confiscated it ?
 
smoke was at the plug - and I'm almost positive that its simply the detachable plug which has been wrecked - since the rest of the adapter can certainly handle the voltage (according to their claims).

Israeli security went bananas because for some reason I kept setting off the explosives residue swab thingy they use. The pulled my luggage (and me!) apart for hours. The only thing they wouldnt let me take was the transformer in the end..
 
Fishy is right, they must be patting themselves on the back for thinking up that one. I would guess they have some sort of voltage sensing device in the 110 Volt thing, because when it is running off 240 Volts, it should be using less current, not more.

If so, then there should be no reason for not being able to run the 240V from 110V. That is, it is easy to have a device blow on over voltage, undervoltage would be a bit harder.
 
It sounds as if you think London AC power is 115V... it isn't.

It's 230V.

Got any pictures ?
 
Sounds like there was a 110V fuse in the US plug.

But I don't see why the European 220V plug wouldn't work in the US at 110V.

(Edited to add) have you tried the new European 220-240 V plug in the US yet?
 
Wierd, since the plug looks like it is only a simple connection as far as I can tell (i.e. no components and such inside) and also the website says:
Right Angle AC Plug for 120V and 240V Operation. For International use, a separate wall adapter is needed. We suggest the World Travel Kit - PA031U or PA033U - Targus Universal Power Travel Adapter.
Click to expand...
Walt
 
Tez said:
My question is this - how could this new plug possibly not work on 110V AC. i.e. why cant I simply (using an appropriate adapter for changing the round prongs to flat ones!) plug in this new plug here in the US? Can they have rigged it so it blows up for the smaller voltage? The European plug is supposedly ok for up to 2.5 amps, whereas the US one was only for up to 1.2 amps as far as I can tell...

Any ideas?

Thanks
Click to expand...

My guess is that the transformer in your power supply has 2 taps, one for 115V and 1 for 230V. The two different plugs are each designed to supply power to the appropriate tap. When you hooked up the 115V plug to the 230V power supply in London, you probably smoked the 115V winding. When you bought the 230V plug you applied power to the 230V winding and the power supply worked normally.

If you attempt to plug the 230V plug into a 115V circuit in the US, you will be supplying only half the designed voltage, so the output voltage to your computer will be half as well. This will probably be insufficient, although it's not as likely to do damage as the other way around.

I would strongly suggest that you beg, borrow, or buy a voltmeter. When you get back to the US, use the 115V plug and check with the voltmeter to see whether or not you are supplying the correct voltage. If you are, it should be OK to use. If not, you'll probably need to buy another power supply.
 
Mmmmm, ehbowen's explanation sounds possible, except it is a bit unlikely to blow a 115V winding on a transformer without impeding 240V operation as it will normally be just one tapped coil.

It is a bit unlikely that they should have made a part that blew at application of wrong voltage just to force you to buy two devices. Having things go up in smoke is better at chasing customers over to the competition than at making them buy more devices.

Possibly there was some sort of noise filter and/or surge suppressor components in the part. The converter itself seems quite compact for its output rating, so it is likely to be a switch-mode type. In this case, it is not unlikely that it will run fine on 115V, and it should not hurt to try.

Is it heavy? If not, it is a switchmode, but if it appears heavy for its size, it will be a conventional transformer, in which case running it on 115V without the proper adapter will probably not work. And you might have ruined the 115V winding by your "London Experience".

Hans
 
Most of the newer power supplies are switchmode, and a good switchmode will cope with the different voltages quite easily. It was also the plug that blew.

I put this down to some genius in the marketing department.
 
Re: Re: Question for someone who understands practicalities of AC to DC conversion...

ehbowen said:


My guess is that the transformer in your power supply has 2 taps, one for 115V and 1 for 230V. The two different plugs are each designed to supply power to the appropriate tap. When you hooked up the 115V plug to the 230V power supply in London, you probably smoked the 115V winding. When you bought the 230V plug you applied power to the 230V winding and the power supply worked normally.

If you attempt to plug the 230V plug into a 115V circuit in the US, you will be supplying only half the designed voltage, so the output voltage to your computer will be half as well. This will probably be insufficient, although it's not as likely to do damage as the other way around.

I would strongly suggest that you beg, borrow, or buy a voltmeter. When you get back to the US, use the 115V plug and check with the voltmeter to see whether or not you are supplying the correct voltage. If you are, it should be OK to use. If not, you'll probably need to buy another power supply.
Click to expand...

This sounds pretty likely -
However, there is also the chance that mis-tapping the transformer caused the wrong filtering capacitors to be in circuit. Filter caps go bang real good, lotsa smoke and a distinctive smell.

The power supply should be a switching power supply - however, it may still have a couple of possibly vulnerable filter caps.
 
Being British, my portable gadgets are all 240V AC fed. Working on US built rigs and (currently) in the CIS, I need to use both US 110V (flat pin), US 220 (flat pins at right angles) and European 110 and 220V AC (round pin) sockets.
I have an adapter which takes the big 3 pin UK plug on the devices and fits to any of the above outlets. The transformers deal with 108-240V.
These adapters are ingenious, but some designs are spoiled by shoddy materials and poor contacts. the pins bend and as a result have a reduced contact area. I have known these to get very hot, on any line voltage. Could it be simply a bad contact that arced and melted the plug?
 
This to some degree is my field. I am an electrical engineer but I don't know the exact answer to your question. A few comments though.

1. Your power supply is probably a switch mode supply. A linear power supply for seventy watts of regulated power would be larger than the picture appears to be.

2. AUP was right and wrong is his statements about switch mode supplies. It is easier to design them to work over a wider range of input voltages than linear supplies. However there are still tradeoffs associated with making a supply that will work from both 115 and 230 volts, i.e. a supply would need to be larger and more expensive if it was to handle both voltages with exactly the same circuitry. One way of dealing with this is to provide a switch for selecting the input voltage so that different parts of the circuit are used for 115 or 230. Another way is to provide automatic input voltage detection. Even with these, a supply that will handle both input voltages is likely to be somewhat more expensive to manufacuture than a supply optimized for one input voltage.

3. It is conceivable to me that the plug that you use in some way sets the power supply up for a particular voltage. If you use the wrong plug bad things might happen.

4.ehbowen's comment about wrong tap on the transformer would be exacly right for an older, simpler, but bigger linear type power supply. As I said above I suspect that you have a switching power supply. In a linear supply the input AC voltage is connected directly to a power transformer that steps the voltage down (usually). If you connect the wrong input voltage to this kind of supply bad things will happen. Particularly bad is to connect 230 volts to an input designed for 115 volts.

In a switch mode supply there may be a transformer connected directly to the input voltages but often to reduce size, weight and cost the input voltage is converted to DC first and then it will feed a switching circuit that may have a transformer as part of that circuitry. Setting up the supply to work off different voltages may involve selecting inputs for that transformer.

5. It hasn't been mentioned and it's probably not part of the problem but Europe power is generally at 50 Hertz and US power is generally at 60 Hertz. This is of absolutely no consequence for some switch mode power supply designs. It is of some consequence for linear supply designs in that certain components need to be larger for a supply designed to run at 50 Hertz.

Edited to add
I looked in the specifications and faq's for more information. I found several things that suggest that you must use their plugs and not "mechanical adapters" to connect to the wall voltage. In the faq section there was this:
AC Unit 95-250 volts AC
US Plug 90-110
Euro Plug 210-240

This suggests to me that their plug adapter is setting up the supply to work at a particular input voltag range. Incidentally there must be something wrong with the US spec. US power line voltages are usually about 117 volts. I have measured over 122 volts and generally in my work we would design for a voltage range of 105 to 130 volts and somewhat lower if we were designing for a device to be used in Japan.
 
Hey, thanks everyone for the info/ideas.

ALthough the plugs contain 2 prongs that go into the wall, the part of the plug which connects to the adapter body has three input lines. So I suspect that they are really forcing me to do a "manual switch" so that the power supply need not try and detect automatically what type of supply I'm connecting to. The plugs are not that heavy...

Because I'm concerned about my laptop, I have not tried using the European plug now that I'm back here in the US. At the moment I'm borrowing a friends' transformer, and trying to decide if I should (i) fork out >$100 for a whole new converter, (ii) try using the European plug, or (iii) whether I should call Targus and see if I can sweet talk them into sending me another US plug....
 
I've seen quite a few switching power supplies (which your adapter almost certainly is), and I think the 2-prong vs. 3-prong ends is the critical bit of information.

Some universal voltage switching supplies use a switch or jumper to set the input voltage - when running on 110V, the voltage will be doubled before being converted to DC, then switched at high frequency through a transformer and rectified to a lower DC voltage. AT 220V, the input is not doubled, just rectified to DC before being switched.

It would appear that the different plugs do either of two things:
1. The input voltage is fed to different lines for different voltages, i.e. on the 3 lines into the adapter are common, 110V input, and 220V input.
2. The input voltage is on the same two lines for all voltages, but the third is used to select the input voltage (something like shorted to neutral=110Vinput, open=220V input)

In either case, you must use the appropriate plug for the voltage, not just a mechanical adapter.

But I fear you may have already blown up the input stage in your adapter anyway - if you applied 220V to an input that was expecting 110V, the capacitors in the rectifier circuit would have been severely over-voltaged. It's also quite possible that the MOSFET switching transistor(s) were killed as well.
 
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