Moding a 120vAC smps to work with 220vAC

[madan1]

Hello everyone.
So basically the question is in the title - is it possible to mod a 120vAC switching mode power supply unit to work with 220-240vAC?
The particular unit is the one from the photos.

It looks like someone ignored the 120vAC label and plugged it in 240vAC. According to the user - "it every time tripped the fuse".
The only visible damage is the high voltage smoothing cap, which has vented quite energetically ( everything above it is sprayed with goo ), but did not explode.
The thru-hole components on the primary side measure fine ( including the fuse ). The smps ic ( 33010 ) also shows no shorts.
So the first thing which came to mind was "make it from full-bridge rectifier to half-bridge rectifier", but I'm kinda stuck with the calculations ( tried to calculate the peak dc voltage with the circuit simulator, but no joy ), so hope someone can get the numbers.
Also, I guess the smoothing cap value should be adjusted with the half-wave?

[eccerr0r]

Re: Moding a 120vAC smps to work with 220vAC

Luck of the draw: just replace the capacitor with a higher voltage unit and it will work.

If unlucky: need to replace: higher voltage MOSFET, increase voltage rating of yellow capacitor, SMPS IC needs to be replaced with a faster unit, transformers' insulation needs to be improved.

[madan1]

Re: Moding a 120vAC smps to work with 220vAC

Yeah, I thought about just replacing the cap with a higher V one... the switching transistor will handle it ( JCS9N50C rated 500V ), but I couldn't find any documentation on the switching IC ( 33010 ) and that is why i ditched that idea for now.
Also, every other SMPS unit which I have seen has been rated 100-250V and only this one 120.. so I wouldn't be surprised if the 33010 is made to lose its magic smoke if 200+ vDC is applied.

[eccerr0r]

Re: Moding a 120vAC smps to work with 220vAC

Sounds like you(or whoever) have nothing to lose at this point anyway, you/they already blew it?

[madan1]

Re: Moding a 120vAC smps to work with 220vAC

Sounds like you(or whoever) have nothing to lose at this point anyway, you/they already blew it?

Well, it wasn't me who blew it.. not that if I buy this from let's say amazon.co.uk I wouldn't also ignore the 120v label and plug it right in the mains .
At this point I think the unit is still salvageable, so really would like to avoid making any further damage to it.. especially to the parts which can not be obtained from the local electronics shop.

And I'm really curious about converting full-wave rect. to a half-wave.

[stj]

Re: Moding a 120vAC smps to work with 220vAC

the u.k. has 110v equipment.
it's used on construction sites to reduce the chance of killing people if it gets damaged or rained on!

[madan1]

Re: Moding a 120vAC smps to work with 220vAC

the u.k. has 110v equipment.
it's used on construction sites to reduce the chance of killing people if it gets damaged or rained on!

yeah.. always wondered about all that 110v equipment on the uk ebay... by the way how do they power it? Is there something like a service 110v mains power line running parallel to the 240v or each building site deploys a temporary transformer?

p.s. indeed the cooler from which is that skinny 12v 4a psu could be used on a building site... for cooling beers.. but still the cooler capacity is waaay not adequate for a building site with more than 1 workers , so doubt that. Probably the Chinese screwed the orders or the retailer did not really know what was selling...

[petehall347]

Re: Moding a 120vAC smps to work with 220vAC


we use these things .. or the 110v or 120v or 115v off a generator .

[eccerr0r]

Re: Moding a 120vAC smps to work with 220vAC

At this point I think the unit is still salvageable, so really would like to avoid making any further damage to it.. especially to the parts which can not be obtained from the local electronics shop.

Depending on how long it was 'plugged in' the damage is already done, likely not much more can hurt...

And I'm really curious about converting full-wave rect. to a half-wave.

It'll really kill the PF, I thought Europe really frowns upon doing stuff like this?

[momaka]

Re: Moding a 120vAC smps to work with 220vAC

And I'm really curious about converting full-wave rect. to a half-wave.

That wouldn't work.

Remember, 230V AC line peaks at +/- 325V DC (230 x sqrt[2]).

So by converting to half-wave, you would still get 325V peaks, but only on the positive or negative side of the sine wave (depending which way you orient your single diode.) Thus, the primary cap would be charging with 325V pulses, but only at 50/60 Hz (well, 50 Hz in your case) instead of both negative and positive peaks of the wave (100 Hz.)

Therefore, just install a 400V cap and the adapter should be good to go in most cases. The SMPS IC (33010) should be OK too. If it's anything like UC3842 or any other standard current-mode SMPS controller, it charges a "start up" capacitor through a high-resistance resistor connected to (+) DC bus. Bad comes to worse, you may have to change that resistor for one with higher resistance and rated for higher power (due to higher bus voltage now.)

Actually, looking at the pictures of your adapter, it seems that R1 and R2 are used for this function as well as discharging the yellow X2 class cap - kind of a cheap move there combining both pf these functions together. The SMPS IC should have its own resistor for charging up the startup cap, but whatever. In any case, those current resistors might still be OK to leave as is, since they are rated for 510 KOhms each. If they end up cooking themselves with 230V AC, replace them with 1M each.

That aside, these adapters are usually designed universally with 100-240V in mind. Reason they used 200V cap is probably because it was cheaper when they know the adapter will be sold in a country with only 110-120V AC. So all in all, I do expect the adapter to work OK with 230V AC mains.

increase voltage rating of yellow capacitor

That shouldn't be an issue.
X1/X2 and Y1/Y2 safety caps are almost always 250V/400V AC in most consumer devices. So it's probably OK. Doesn't hurt to check the voltage rating, of course, just in case.

SMPS IC needs to be replaced with a faster unit

Most likely not.

transformers' insulation needs to be improved.

That and the primary turns ratio may actually be a legit concern.

And this brings another thing to mind: higher input voltage = more narrow PWM pulses to get the same voltage/current output. Thus, output caps may see higher ripple too... so probably a good idea to use good quality caps there.

It'll really kill the PF, I thought Europe really frowns upon doing stuff like this?

Only for devices above a certain power rating (I think it was something like 40 or 50 Watts.) And in most Eastern European countries (Greece, Bulgaria, Romania, and etc.), the government tends to be fairly "lax" for regulations like that.

p.s. indeed the cooler from which is that skinny 12v 4a psu could be used on a building site... for cooling beers.. but still the cooler capacity is waaay not adequate for a building site with more than 1 workers

LOL exactly! Also depends what region/country the workers are from too. Bulgaria, Romania, Germany, Chech Republic, Ireland - cooler needs to be sized for 1 beer per hour per person, minimum.

[stj]

Re: Moding a 120vAC smps to work with 220vAC

in the EU PF correction starts at 70w

as for the yellow site isolation transformers, they are actually 55-0-55 so 110v centertapped to earth.

so if the worse that can happen is you get a 55v shock.
the real risk is actually losing a leg by slipping while using something like a giant circular saw used for cutting out walls!!!

[madan1]

Re: Moding a 120vAC smps to work with 220vAC

Thanks everybody for the replies.
Installed a 400V rated capacitor and the thing choochoo-ed without losing its magic smoke.
I really don't get it why the manufacturer decided to put a 200V cap and leave everything else capable of working with 220-240 mains... Just checked the price of 200v and 400v caps in the nearby electronics shop - they are almost the same ( indeed the 400v is a little bit more expensive ).

[momaka]

Re: Moding a 120vAC smps to work with 220vAC

I really don't get it why the manufacturer decided to put a 200V cap and leave everything else capable of working with 220-240 mains... Just checked the price of 200v and 400v caps in the nearby electronics shop - they are almost the same ( indeed the 400v is a little bit more expensive ).

When they make something like 5000-10000 of these little adapters, even $0.05 difference can matter, as that will be $250-500 more, which can then be put to make more of these PSUs and turn in even more profits.

Or maybe the parts distributors and manufacturers they ordered from didn't have enough 400V caps... so they also bought some 200V, knowing that some of these adapter would be sold in markets with 120V AC line.

Ah well, who knows.

Anyways, glad to hear it's working well ... though there really wasn't any reason why it shouldn't.

[stj]

Re: Moding a 120vAC smps to work with 220vAC

now you can change the fuse to one rated half as much