PSU Primary cap question

[Almighty1]

I have a question concerning PSU Primary caps as I was looking at reviews of different PSUs and the Corsair AX1200i for example runs on a pair of 450v 470uF caps, am I correct this can handle 900v combined?

http://www.hardocp.com/article/2012/...3#.VByPkFXMTyc

On my PC Power & Cooling Turbo-Cool 450ATX, it uses a pair of 200V 1000uF caps but it auto switches between 115VAC and 230VAC so would this mean the pair of caps can handle 400V combined since if it was just each cap, then 230VAC would have blown the 200V rated caps.

Then the next question is what is the purpose of putting in a pair of 450V caps since wouldn't just one be able to handle 230VAC without issues?

[budm]

Re: PSU Primary cap question

Well, it depends how the caps are connected, in parallel or in series, you need to find that out. The highest DC Voltage feeding the SMPS circuits in the primary side will be about 400VDC.

[Pentium4]

Re: PSU Primary cap question

I have a question concerning PSU Primary caps as I was looking at reviews of different PSUs and the Corsair AX1200i for example runs on a pair of 450v 470uF caps, am I correct this can handle 900v combined?

They are connected in parallel to equal more capacitance for input filtering. When you have such a high wattage PSU like that one, you need quite a bit of bulk capacitance. Together they equal 940uF. It would be much more difficult to fit a 1000uF 450V cap in there, so that's why they decided to use two 470uF instead.

On my PC Power & Cooling Turbo-Cool 450ATX, it uses a pair of 200V 1000uF caps but it auto switches between 115VAC and 230VAC so would this mean the pair of caps can handle 400V combined since if it was just each cap, then 230VAC would have blown the 200V rated caps.

The two 1000uF 200V caps are connected in series. In this configuration, the voltage is doubled and the capacitance is cut in half. They're essentially the same as a single 500uF 400V capacitor.

[Almighty1]

Re: PSU Primary cap question

Interesting, I never knew the DC voltage can exceed the incoming 230V AC voltage. Thanks both budm and Pentium4 for the insight, always good to learn how things work!

[Pentium4]

Re: PSU Primary cap question

This is why the older designed PSU's come with a voltage selector switch. All the switch does is switch the primary capacitors from being in parallel (115V) and series (230V) That's why 200V caps can be used on 230V

Interesting, I never knew the DC voltage can exceed the incoming 230V AC voltage.

I believe the voltage is stepped up so that the switchers can pulse the current to the main transformer, which likes to run around ~375V

[retiredcaps]

Re: PSU Primary cap question

Interesting, I never knew the DC voltage can exceed the incoming 230V AC voltage.

The AC voltage gets rectified into DC voltage.

In North America, we have 120V AC. This gets rectified into about 170V DC.

That is, 120V AC x 1.414 = 169.68V DC.

If you have PFC involved, that DC voltage can reach nearly 400V DC.

For 230V AC, we get 230 x 1.414 = 325V DC.

This is why the big filter capacitors are rated at 400V or more.

[retiredcaps]

Re: PSU Primary cap question

Wiki explanation ...

http://en.wikipedia.org/wiki/Switche...ectifier_stage

[Almighty1]

Re: PSU Primary cap question

If I am reading the wiki correctly, 115VAC will have a 163VDC max while 230VAC is basically twice that. As for switching power supplies, I do remember the very old power supplies from 2000 and earlier had them but I thought those were only in the cheaper power supplies because it was probably cheaper to put in the selector switch than to put in something that did autoselection of the input voltage. Although on the Oppo BDP-105/BDP-105D Blu-Ray Disc Players which are recent models, they still do the selector switch on the back.

Now I have another question, I haven't seen this discussed on the forums but would changing the any of the capacitors to either a higher voltage or higher capacitance actually increase the AC input Amperage current or does that depend on things other than the capacitors since I sure don't want my 115VAC 10A input to turn into 15A.

[Pentium4]

Re: PSU Primary cap question

Now I have another question, I haven't seen this discussed on the forums but would changing the any of the capacitors to either a higher voltage or higher capacitance actually increase the AC input Amperage current or does that depend on things other than the capacitors since I sure don't want my 115VAC 10A input to turn into 15A.

Changing the values of the caps would have no affect on this. However higher voltage caps can do better over time since they can handle the inrush spike better than lower voltage, but input capacitor failures are extremely rare under normal operating conditions, even the worst brands do okay here.

Thanks both budm and Pentium4 for the insight, always good to learn how things work!

Yeah, PSU's are very fascinating

[budm]

Re: PSU Primary cap question

If it has active PFC Votage booster, then the voltage will be in 360~400VDC range.

[budm]

Re: PSU Primary cap question

"Now I have another question, I haven't seen this discussed on the forums but would changing the any of the capacitors to either a higher voltage or higher capacitance actually increase the AC input Amperage current or does that depend on things other than the capacitors since I sure don't want my 115VAC 10A input to turn into 15A." Higher capaictance will increase the inrush current when the power is applied to the unit, once it is running, the load will determine how much current it will draw on the AC input side.

[wa2ise]

Re: PSU Primary cap question

If I am reading the wiki correctly, 115VAC will have a 163VDC max while 230VAC is basically twice that. As for switching power supplies, I do remember the very old power supplies from 2000 and earlier had them but I thought those were only in the cheaper power supplies because it was probably cheaper to put in the selector switch than to put in something that did autoselection of the input voltage. ...

...would changing the any of the capacitors to either a higher voltage or higher capacitance actually increase the AC input Amperage current or does that depend on things other than the capacitors since I sure don't want my 115VAC 10A input to turn into 15A.

The supplies that are rated to accept 100V to 250V AC don't really do an "autoselect" like the switches on PC power supplies had. These supplies will just adjust their switching duty cycles to convert whatever the rectified input voltage to the desired output voltages (via the transformer).

Replacing the caps won't change the power supplies' average current demand off the powerline.

[Almighty1]

Re: PSU Primary cap question

Good to know that changing the value of caps would have no effect on the input current.

I'm looking for a replacement for the 2x200v 1000uF Teapo 85C capacitor pair 25mm and it seems that the Panasonic TS-ED at 200v has higher ripple current and lower ESR than even something higher than 200v's so probably staying with 200v seems to be a safe bet. I noticed that some people on other Power Supplies seems to ask to replace caps with a higher capacitance rating such as 3300uF replacements for the 2000uF caps but I was advised with the PC Power & Cooling Turbo-Cool 450ATX, the same capacitance is fine as PCP&C Turbo-Cool's are over-built when they were designed. My only issue is the PSU is 14 years old being used 24x7x365 and there is this Sanyo OS-CON 2.2uF 25v polymer capacitor which seems to have no replacement available as it seems like my options are Sanyo OS-CON 2.2uF 25v in a 10 pack on Ebay from someone in China which is highly likely to be fake or getting one of the Panasonic branded OS-CON's 6.8uF 25v polymer capacitors as Panasonic bought Sanyo and rebranded Sanyo OS-CON under their name, would there be anything bad about going with the 6.8uF as it's 3.4x the original capacitance since I'm trying to replace all the caps at one shot unless the Sanyo still has a long life, I measured capacitance of the Sanyo using a Multi-meter and it still reads 2.2uF.

Speaking about capacitance in Power Supplies, what would be considered a acceptable ESR range as I noticed that people would say the ESR is too low for a PSU but suitable for a motherboard, exactly where is the line for ESR distinguished if it's suitable for a PSU or not when looking at specs?

What does PFC do exactly since I know my PC Power & Cooling Turbo-Cool 450ATX does not have PFC as I remember PFC was added in newer models and it's usually mentioned in the product model number. Is PFC only for 115VAC or also for 230VAC since it would seem 230VAC with PFC if it exists would be higher than 400VDC.

[Almighty1]

Re: PSU Primary cap question

Forgot to ask but what is the proper way to discharge the primary capacitors in a power supply?

[budm]

Re: PSU Primary cap question

Forgot to ask but what is the proper way to discharge the primary capacitors in a power supply?

Through a resistor which the value and the Wattage will depend on the Voltage on the cap and the capacitance, the time constant (R*C) will determine what the Voltage will be after first TC which the Voltage will go down by about 63%.

[Almighty1]

Re: PSU Primary cap question

Hmmm, is there another way to do it? Like if it's unplugged from the AC, will it just discharge on it's own and how long will it take?

[budm]

Re: PSU Primary cap question

Hmmm, is there another way to do it? Like if it's unplugged from the AC, will it just discharge on it's own and how long will it take?

Yes, you can, all you have to do is just check the Voltage on the cap to see if it goes down below 50VDC. The discharging rate will depend on the load connected to the caps.