Rectifier Input Range

[synatrol]

Hi Badcap members.

This is a question on switch mode power supplies found in household appliances such as TVs, monitors and computers and the possible problems of sustained over voltage conditions on the rectifier. I have read the FAQ on switch mode power supplies which talks a bout selectable voltage inputs and the affects of connecting 240Vac when selected for 115Vac. But this question is on self sensing switch mode power supplies.

I live in Australia which has a nominal line voltage of 240Vac at 50 Hz. My house utilizes 3 phases with one phase a few volts higher than the other two phases. During the day it is quite normal to have 260 Vac on one phase and 257 Vac on the other two.

Looking at all my appliances all have a rated voltage input of 100-240Vac. Doing a quick search on the internet I do find some switch mode power supplies rated for 100-260Vac. I'd be more comfortable if appliances sold in Australia had such an input voltage range.

Is sustained over voltage something to be concerned about? Manufacturers are selling appliances in Australia with 100-240Vac SMPS so I must assume that they consider possible over voltage as a non-issue. I'm looking to get an in-line UPS for some of my more critical appliances such as computer and monitor which is about a $400 investment. I believe Australia has one of the highest line voltages in the world?

Thanks,
James.

[mariushm]

Re: Rectifier Input Range

The rectifier won't have a problem, some have rectifiers that work up to 400-600v.

In power supplies, the rectified input goes to capacitors which are usually rated for a maximum of 400-450v. The rectified voltage will be Vin x √2 so in your case it would be 260 x 1.4142 = 367 volts. So there should be some room for the capacitors.

Not sure what would "hate" the 260v input -- maybe the transformers could overheat, or efficiency would decrese.

My two cents... I think they list so small range so that the power supplies would do well in EMI tests and have an excuse if they fail tests when going over a specific voltage.

Here in Romania the voltage is 230v but I think the EU standards say all electronic devices should work in the 220v-240v range. The voltages are frequency are pretty stable where I live but sometimes I see 232-235v when measuring.

It's implausible they would make these power supplies to fail when going even less than 1% over the permitted input range or that they would make special power supplies just for the Australian market.

[synatrol]

Re: Rectifier Input Range

Thanks Marisushm,

The EMI hypothesis sounds plausible for the specifications put on the label. I'm assuming the rectifier diodes would also have a rating well over the peak voltage of 367 Volts as is the smoothing capacitor (400-450 Volts).

Sounds like I'd need well over 240 Vac before damage may occur. About 5 years ago under voltage was the issue at my house (I've got a 300m main supply cable run). But at some point the main line voltage has increased to the point that I'm getting 260V when I'm not pulling too much current. So I shouldn't be to concerned with the voltage specifications on devices.

Thanks for your reply.

[japlytic]

Re: Rectifier Input Range

In most switching power supplies, the bridge rectifier at the AC input is rated for at least 600V, as far as I have seen.

[tom66]

Re: Rectifier Input Range

I have seen cheap CFLs with 350V input caps. At 253V (max. nominal in UK), assuming a 1.5V diode drop, that gives 351V across the cap. Although it's barely exceeding the rating, it's still a crap way of doing it. At 260Vac... maybe that might be more of a problem, and add in surges/spikes/transients...

[Behemot]

Re: Rectifier Input Range

That is speaking of crap PSU's. Quality one wont have a problem.

Also the thing is efficiency rises with voltage so you are lucky man:-)

[synatrol]

Re: Rectifier Input Range

I have seen cheap CFLs with 350V input caps. At 253V (max. nominal in UK), assuming a 1.5V diode drop, that gives 351V across the cap. Although it's barely exceeding the rating, it's still a crap way of doing it. At 260Vac... maybe that might be more of a problem, and add in surges/spikes/transients...

That's exactly what I've experienced. I was getting the cheapest CFLs I could find which were still $5 a pop but a lot of them were only lasting weeks.

[synatrol]

Re: Rectifier Input Range

So an expensive On-line UPS for clean power may be a bit of an overkill if I'm purchasing devices with very high quality switch mode power supplies. The efficiency of an on-line UPS is a killer. I remember protecting all my equipment on the power side of things to have a lot of it damaged through the CAT5 cabling via the Ethernet switch which in-turn was connected to my ADSL modem which was in-turn connected to my phone line - Ouch.

I'm probably going away from my original topic but the concern for my equipment was the driver for my original question.

Thanks for sharing your knowledge.