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Home / Other I-Appliances / 3Com Audrey wall brick open/240V PSU is the PSU rated up to 240V? - about to find out

wall brick open/240V PSU (modified 0 times) ChiefOik Profile | Email Hello everyone, Audrey comes with a 3com wall brick PSU rated on the label for 100-120V. Now, here in the UK we've around 240V coming out the walls. Sooo, having opened the PSU and looked at the components, I reckon it's actually rated up to 250V - the fuse and (what I assume is an) RF choke across the primary winding of the first transformer are rated 250V and 275V respectively. The PCB's also labelled 250VACT2AL... Now my question: has anyone actually (presumably outside the US) tried it at 240V without either an additional step-down transformer nor blue smoke? Will I be the first? Will it go bang? Will I chicken out and buy (four!) converters for the four Audreys I've just received? Don't change the channel... Matt Chief Oik 10-30-2001 07:31:47

RE:wall brick open/240V PSU (modified 0 times) AudreyMI Profile Hi, It's quite common to use components rated higher than required, this does not necessarily mean ALL components are rated for the higher voltage, or that there hasn't been a modification to a 240V device to make it 120V - such as a change to the windings on a transformer. Without a schematic, or even opening it up, I can't say what would be the case... I'm not sure whether the PSU us a linear or switch mode device... If linear, you'll probably end up supplying double the input voltage to at least one of the regulators, which even if its within the components limits will cause it to generate a lot of heat as it wastes the extra voltage... Hopefully my six parts only Audreys will turn up today, and I may need to crack open a PSU... I'll keep you informed. If there is a simple component change to make it run on 240V then I know what my brother back in the UK will be getting for Xmas... Regards, PJE 10-30-2001 07:46:46

RE:wall brick open/240V PSU (modified 0 times) ChiefOik Profile | Email Hi again, It looks like a two-stage switch mode to me - there's an initial small (isolating?) xformer + full-wave rectifier of 4 diodes, a power regulator and one large capacitor. After that there's an RC network feeding a larger array of inductors (one large w/multiple windings), power transistors + diodes, one tiny IC, one small 4-pin power IC (not a regulator; assume it's another rectifier) and some smothing capacitors on the outputs. If anything's going to pop w/240V, it'll be that first regulator. If it were a linear I'd expect a couple of regulators and a much bigger xformer, in which case w/o modification I certainly wouldn't try it at 240V. But I might be wrong on all this. 10-30-2001 08:25:06

RE:wall brick open/240V PSU (modified 0 times) warbird Profile Chief, My background in electronics suggests that the voltage ratings are just to signify the maximum voltage the component can carry or protect against. For instance, a fuse rated for 240V would protect a circuit running at that voltage or less, but apply 440V to it and it will likely arc across the air gap. Likewise, transformers, capacitors, coils, etc.. will burn up or melt (or just arc and cause the former to happen) at voltages that exceed their ratings. HTH \/\/arbird 10-30-2001 12:53:22

RE:wall brick open/240V PSU (modified 0 times) Aztech Profile I should have a couple of Audrey's arriving tomorrrow. (I'm in the UK). It's not just the voltage, wouldn't the 50hz throw it out too? Anyway... what is the power requirements of the Audrey, around 12v @ 500mA? What is the DC plug like, would it be possible to use a regulated PSU instead? Take care, Andrew. 10-30-2001 19:53:07

RE:wall brick open/240V PSU (modified 0 times) Aztech Profile Found something on the Dixons site (www.dixons.co.uk) that will the trick, "TACIMA USA-UK VOLTAGE CONVERTER" £19.99, just do a search for "voltage converter" on their site, they use wierd session id's so direct linking wont work. Apparently Maplin did one for 15 quid, but it's been discontinued. Damn... all this just becase Edison and Swan couldn't keep their ego's under control. 10-30-2001 20:37:24

RE:wall brick open/240V PSU (modified 0 times) ChiefOik Profile | Email Well, I was wrong. The first thing to go was the 100V 100uF electrolytic after the rectifier across the secondary of the initial transformer. A nice ejection of the electrolyte and some smoke. The regulator I thought would go got very hot but didn't pop. Sooo, now we know this isn't a 120/240V PSU, despite the PCB marking. NB, just FYI, in case anyone is thinking about modding this, the 1st transformer is NOT isolating. This also means it can't be rewound w/ a different primary-secondary ratio to make this work at 240V, which was my plan. In fact, it's in the circuit at "right-angles" to the way a linear transformer would work - like it's two inductors in series w/ the rectifier stage. I'll pass on why this is. Anyone? re. buying a step-down brick: it's got to handle an _inductive_ load (like a hairdryer) - there's some cheap ones which are basically a resistor for lamps, etc: this won't work with those. It's also got to handle 50 watts, which is the input spec of the 3com PSU. I think this makes the transformer pretty big (the Maplin £20 one might just work, the £15 can't supply enough current). re. the PSU output spec: 3.3V dc, 1.5A and 5.0V dc, 2.0A. Ripple + noise on both <50mV, so we're looking at a good *regulated* alternative supply. 10-31-2001 03:44:41

RE:wall brick open/240V PSU (modified 0 times) cubto Profile som einfo on the power supply: It is a single stage switch mode power supply. The first 'transformer' in the circuit is not a transformer it's an inductor, which, along with the caps. forms a filter to prevent noise from the switcher from getting back to the power line. The switching regulator provides 5V DC only, there is a PWM regulator on board which drops the 5V down to 3.3V. I haven't looked closely at this on the audrey power supply yet, but, most switching power supplies that can accept either 120 or 240VAC utilise a voltage doubler for 120VAC operation, and no doubler for 240VAC operation. The audrey supply may be internally jumpered to enable the doubler (for 120VAC) if it is, and you can find it, remove the link and you have a 240VAC supply. hope this helps. 10-31-2001 09:11:21

RE:wall brick open/240V PSU (modified 0 times) Aztech Profile Hrm... £54.99 - Use on appliances - 300va (overkill?) £19.99 - Use on appliances - 30va £24.99 - Use on appliances - 50va I guess I should go for the latter? 10-31-2001 13:19:21

RE:wall brick open/240V PSU (modified 0 times) cubto Profile What the voltage out of those things? You'll need 5V 2A and 3.3V 1.5A = about 15VA 10-31-2001 13:34:46

Success! was RE:wall brick open/240V PSU (modified 0 times) ChiefOik Profile | Email Hello again everyone, Now have it working at 240V, but see the disclaimer at the bottom... 1) Remove either diodes D2 and D3, _or_ diodes D1 and D4. This makes the full-wave rectifier after the mains filter (thanks cobto!) into a 1/2 wave rectifier, reducing the mean V into the next stage by 50% and corrects the power U1 has to dissipate. 2) Replace C2, the one I blew, with a 100uF electrolytic rated at no less than 350V (for 240V) or 385V (for 250V). This *must* be done as the peak V across the original 100uF/200V C2 is 240V*sqr(2)=339.5V with a 240V supply. The RMS V is the same, however. Sorry, there's no jumper to correct this as it's strapped straight across the rectifier output. (I mentioned the 100uF cap was rated at 100V earlier. Until I removed it from the board, I was going on it's size as the label was obscurred by the yellow epoxy. It's actually the smallest 100uF/200V I've seen.) Viola, Audrey now works. Disclaimer: *THIS IS A MAINS POWER SUPPLY WITH HIGH VOLTAGES PRESENT AND CAN KILL IF APPROPRIATE PRECAUTIONS ARE NOT OBSERVED*. IF YOU ARE AT ALL UNSURE ABOUT DOING THIS, DO NOT OPEN YOUR PSU. If you don't know what your Cn is from Dn, don't do this. This may not work for you. You may destroy your PSU and/or your Audrey. This may work but burn you house down when you are out. Your partner may leave you because you've splatted electrolyte on the carpet. Your future karma may be affected. Don't say I didn't warn you. If anyone with so-modded supply and a 'scope could confirm the on-load output ripple, I'd much appreciate it. Good luck, matt 11-01-2001 03:37:40

RE:wall brick open/240V PSU (modified 0 times) ChiefOik Profile | Email Just a clarification (and ignoring my spelling/grammer mistakes): Where point 2 reads "The RMS V is the same, however", it should read "This makes the RMS V the same as the original PSU" - i.e., after the rectifier mod, RMS V across C2 is now 110V with 240V in, the same as the un-modded PSU with 110V in. The peak V is as stated (i.e., potentially double the un-modded PSU when off-load). Can anyone see a problem with this - cubto? matt 11-01-2001 05:20:00

Pictures (modified 0 times) ivor Profile All, I've put some pictures of the modification to a PSU on my site: http://www.ivor.org/audrey Cheers 12-29-2001 02:44:06

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