Convert 230V only PSU to 115V?

[Pentium4]

Is it possible? If so, what would you need to do?

[kaboom]

Re: Convert 230V only PSU to 115V?

Is it possible? If so, what would you need to do?

If there are two large electrolytics after the rectifier, connect that mid-point to one of the "AC" legs of the rectifier.

This may help:
http://www.pavouk.org/hw/atxps.html

Look at how the voltage selector switch is wired.


If there's only a single cap, it's probably got APFC. In that case, running on lower voltage will depend on the design of the APFC booster.

There are 120V-only supplies which use a single bulk filter cap, but not most (all?) PC supplies.

[c_hegge]

Re: Convert 230V only PSU to 115V?

If it's because it only has half-range APFC, then the procedure will be a little different. You basically just need to beef up the primary side parts to make it capable of sustaining full load at 115V.

[Pentium4]

Re: Convert 230V only PSU to 115V?

Thanks for the reply. It is a voltage doubler. When you say "connect that" mid-point to one of the AC legs, what are you referring to?

Edit: Oh okay I see SW1 and SW2 holes in the PCB, so I could just put a voltage selector switch there and it should work?

[kaboom]

Re: Convert 230V only PSU to 115V?

Those two caps:

(ASSuming you've got a packaged bridge rectifier, like a KBL406)

The positive of one (call it C1) will go to the "+" from the rectifier
The negative from the other (call it C2) will go to the "-" from the rectifier

The negative of C1 will go to the positive of C2. This center-point, in supplies with the "voltage select" switch, is connected to the AC line, when in the "120V" position.

See how the switch works with C5 and C6 in the diagram? That center point does not connect to the line when set to "240V," otherwise, each cap would have ~340V across it!

But for 120V-only use and no switch, you need to run a jumper to permanently "set" it up as a doubler. Connect the jumper from that center point to either outer leg of the rectifier. If you've got four individual diodes instead, trace back and make sure you're going to either line or neutral with that jumper! If you connect the center point to the wrong diode lead, you'll partially short the rectifier out.

Edit: Oh okay I see SW1 and SW2 holes in the PCB, so I could just put a voltage selector switch there and it should work?

No need for a switch, a simple jumper will do. Saves you from having to mount the switch.

[Pentium4]

Re: Convert 230V only PSU to 115V?

Yes it does have a rectifier Awesome, thank you so much!!! I figured I would include a pic anyways Outer leg being one of the ~ leads? Initially I was just going to chuck the PSU

[kaboom]

Re: Convert 230V only PSU to 115V?

Yes it does have a rectifier Awesome, thank you so much!!! I figured I would include a pic anyways Outer leg being one of the ~ leads? Initially I was just going to chuck the PSU

But for 120V-only use and no switch, you need to run a jumper to permanently "set" it up as a doubler. Connect the jumper from that center point to either outer leg of the rectifier.

Well, I was fucking stupid...

That should've been "to either inner leg of the rectifier." One of the two leads with the "~" by them.

Sorry for the bad info...



Just make sure one "SW" point goes to either "~" and the other "SW" goes to that cap "center-link."

[Pentium4]

Re: Convert 230V only PSU to 115V?

No worries man that's what I thought you meant will try it out today!

[Pentium4]

Re: Convert 230V only PSU to 115V?

One thing that I just thought about, do you think it would be a good idea to replace the fuse with a higher amperage? Since it was designed for 230V, it has a 6.3A 250V fuse, would it be a good idea to replace it with a 8A or 10A 250V fuse?

[kaboom]

Re: Convert 230V only PSU to 115V?

No worries man that's what I thought you meant will try it out today!

That's why it's never a good idea to be "Inside a power supply" late at night! If ya followed my advice, you would've pulled a "kaboom," hehe...


The 6.3A should be fine. That's still 756VA at 120V- plenty. Even at .7PF and 65% efficiency, that's still good for ~345W output.

They tend to be sort of overfused anyway, with semis "protecting" the fuses.

It would be great if I could see more of that board, specifically from its AC input up to the line rectifier. There may be a place for a thermistor- it looks like there's a place for one where a jumper has been "substituted."

Quite typical. That thermistor is omitted and a too-large fuse is used, to allow for the surge of those two caps charging.

[Pentium4]

Re: Convert 230V only PSU to 115V?

That's why it's never a good idea to be "Inside a power supply" late at night! If ya followed my advice, you would've pulled a "kaboom," hehe...

Ha!

The 6.3A should be fine. That's still 756VA at 120V- plenty. Even at .7PF and 65% efficiency, that's still good for ~345W output.

Perfect!

It would be great if I could see more of that board, specifically from its AC input up to the line rectifier. There may be a place for a thermistor- it looks like there's a place for one where a jumper has been "substituted."

Quite typical. That thermistor is omitted and a too-large fuse is used, to allow for the surge of those two caps charging.

Wow, good catch. I think this is the first PSU I've seen with no NTC Thermistor! I do have some lying around, should I add one?

[kaboom]

Re: Convert 230V only PSU to 115V?

Wow, good catch. I think this is the first PSU I've seen with no NTC Thermistor! I do have some lying around, should I add one?

Yes.

If this PS doesn't have a line switch, adding an NTC will greatly reduce sparking when you plug it in. It'll reduce the inrush the two caps and rectifier see as well. If it does have a line switch, an NTC will reduce wear on its contacts.

What make/model is this power supply? Or, with the "ChaChang" caps, would you rather not tell?

[Pentium4]

Re: Convert 230V only PSU to 115V?

Can't believe they left it out! It's a low end Zalman that my work got a sample of. It does have a line switch. I'm just going to add an SCK 2R58 to it

[kaboom]

Re: Convert 230V only PSU to 115V?

Can't believe they left it out! It's a low end Zalman that my work got a sample of. It does have a line switch.

Ahh, a sample. Bet you the production units are/will be even worse!

I'm just going to add an SCK 2R58 to it

2.5 ohms at 25 degrees Celcius, and supposedly 8A average. They run hot at their full rating, so it's always better to oversize. At 2.5 ohms, it'll still "thump" a little, but better than no resistance at all.

Is that thermistor 3/4"-7/8" in diameter and about 3/16" thick?

It's "soiteny" an improvement!

[Pentium4]

Re: Convert 230V only PSU to 115V?

Pretty much nailed it, 1/2" diameter and 3/16" thick. Definitely an improvement! I'm also gonna throw two MOV's in there

[Pentium4]

Re: Convert 230V only PSU to 115V?

I was pleasantly surprised to see the 560uF Cheng input caps test 575uF. I don't know a whole lot about MOV's, what are the most important specs? Are 7mm MOV's sufficient or are bigger ones recommended? I have some 7N271K's here http://www.gemkenz.com.tw/Varistor/N7%20TYPE.htm

[kaboom]

Re: Convert 230V only PSU to 115V?

I was pleasantly surprised to see the 560uF Cheng input caps test 575uF. I don't know a whole lot about MOV's, what are the most important specs? Are 7mm MOV's sufficient or are bigger ones recommended? I have some 7N271K's here http://www.gemkenz.com.tw/Varistor/N7%20TYPE.htm

I'd say it's more important to have equalizing resistors across those two caps. 100K, 1/2W; 220K or 330K, 1/4W.

Obviously, in order for MOVs to conduct, the voltage across them must rise above their rating. As the MOVs will be across the caps, guess what have to charge up first?


I'd personally settle for equalizing resistors w/o MOVs rather than MOVs and no equalizers, provided there's some form of an input filter.

I could suggest better if I actually saw that portion of the board.
Add them if you want, but make sure those equalizing resistors are there.

[Pentium4]

Re: Convert 230V only PSU to 115V?

My apologies for not having anymore pictures up, I will take some tomorrow. Thanks for the consistent replies The two slots are labelled ZR2 and ZR3. I don't think it has bleed resistors either so I just unplugged it while it was running and the caps went down to 0.33V

[kaboom]

Re: Convert 230V only PSU to 115V?

My apologies for not having anymore pictures up, I will take some tomorrow. Thanks for the consistent replies The two slots are labelled ZR2 and ZR3. I don't think it has bleed resistors either so I just unplugged it while it was running and the caps went down to 0.33V

You're welcome!

You should also have a "ZR1." Either across the line, or from either + or - of the DC bus to GND/chassis.

They're not bleeders, they are equalizers! When they are connected in series, without the "center link" connected to anything, small leakage currents can cause each cap to have slightly different voltages.

Ex- 240V in, rectified not doubled, with extreme leakage: 340 across both, with one having 140V and the other having 200V. The two resistors even this out. Again, that was an extreme example to illustrate the purpose of those resistors.

Equalizers usually draw a milliamp or so. Or usually ten times the leakage of the particular caps in the ckt. Bleeders draw more current, and are [i]specifically[/i used/sized to discharge x microfarads in y seconds.

Your caps discharged quickly because the unit was running from them.

Usually, you end up with 40-80V left when unplugging-while-running, because of low voltage cutoff. Sounds like this supply will "attempt" to run even with low line voltage- could be stressful to the switchers.

[Pentium4]

Re: Convert 230V only PSU to 115V?

I was just also mentioning that it has no bleeders it's pretty empty there... thanks for the info!! And I know you said a jumper would do but I added the switch anyways because I had some just sitting around, so I figured why not. Added some pics, will try and get a solder shot soon too