Mystery power supply

[Behemot]

Re: Mystery power supply

to prevent splatter if it should blow.

Or to set your balls on fire?

[everell]

Re: Mystery power supply

What do you think that thin wires taped on the pcb at the bottom is about?

You are correct. The fuse was blown when I got the power supply. I soldered a thin wire across the fuse holder and wrapped tape around the wire to prevent splatter if it should blow. So far it has not blown. Known as my "economy" fuse!

When I wiggle the green wire on the 20 pin ATX power connector, the power supply intermittently turns on and off. That may have been the original problem.

Anyone ready to take a guess at who the manufacturer might be?

[Behemot]

Re: Mystery power supply

Yep, the thin wire inside transparent tape

I have lately seen similar fuses…original blown 25A car fuses inside UPS were soldered over with thin wires. I am curious how precise that was, +-10 A?

tom66: I got 85W PSU in old Compaq, and as you see lti has even just 75W one

[mariushm]

Re: Mystery power supply

What do you think that thin wires taped on the pcb at the bottom is about?

[ben7]

Re: Mystery power supply

Hi, I got a question!

Did ANYONE see a fuse on the PSU? I didn't!

[budm]

Re: Mystery power supply

The POWER SUPPLY with PFC will have PFC + Voltage booster circuit, it will boost the DC supply from 169 DC (120VAC input voltage x 1.414 = 169) and boosted it up around 400VDC to feed the switcher driving circuit that drives the step-down power transformer.

[mariushm]

Re: Mystery power supply

Capacitors in series:

1 / Ctotal = 1/C1 + 1/C2 + ... + 1/Cn



On this power supply like it was already said, the capacitors are in a voltage doubler circuit :



Ignore the actual values.. btw got this from https://cdn.badcaps-static.com/pdfs/...44a9724ffd.pdf which is pretty interesting

In this power supply above, the psu is set to 110v input using that yellow wire.

On Active PFC power supplies, the voltage can go up to about 350-400v.

Depeding on the power supply topology, even with active pfc it's possible to need 2 capacitors, because of how the psu works.

Rather than simplifying and screwing the explanation, see this app note: https://cdn.badcaps-static.com/pdfs/...4fc807c47b.pdf

You'll find the half bridge converter at page 19 - that's one of the topologies that works fine with two primary capacitors.

[Wester547]

Re: Mystery power supply

Oh, right, the same reason why APFC PSUs don't have a voltage switch. ^^; Does using 400V primary capacitors as opposed to 200V capacitors in a non-PFC design help the overall capacitance much then (if the microfarad value is the same)?

EDIT: Oh, not much of a difference if a non-PFC PSU can only go up to 230V-240V and if an APFC PSU doesn't go past 400V.

[budm]

Re: Mystery power supply

The two caps are in series is setup as voltage doubler setup for 120/230v Operation, or part of the Half-bridge drive setup.

[Wester547]

Re: Mystery power supply

A 4A rectifying bridge is more than enough for 100-200W, assuming that the secondary rectifiers are up to par.

Those two caps are in series, so 100uF caps would have a total capacitance of 50uF.

Does that apply for all input capacitors no matter the voltage (IE, two 400V capacitors in a series as opposed to the usual 200V)?

[everell]

Re: Mystery power supply

If you don't mind me asking, what's its rectifying bridge rated at?

Bridge rectifier marking is RS405L

[lti]

Re: Mystery power supply

My 75W Hipro power supply has 220uF primary caps. Those two caps are in series, so 100uF caps would have a total capacitance of 50uF. I have only seen caps that small in low-power devices like DVD players.

I don't think any major manufacturer would be using a power supply like that. That 75W Hipro is in my old Compaq, and it is extremely overbuilt.

[mariushm]

Re: Mystery power supply

Based on the number of wires coming out of the secondary side, the power supply was probably rated for 80-120w output.

It doesn't even have a lot of extra holes for 5v and 3.3v wires, the main voltages that were used on this psu (I see a '94 date code on the pcb).. and the wires that are there seem to be AWG20 or some other thin stuff.

So 100uF is probably not really that bad... my Delta 100w psu has a single 220uF 400v cap.

The transformer is also big enough, much more than needed. Overall, it looks good to my not so experienced eye.

Maybe it's from some small factor Compaq / Dell system from those times, that had no options for video cards or hard drives?

[Wester547]

Re: Mystery power supply

If you don't mind me asking, what's its rectifying bridge rated at?

Most cheap, generic, no name PSUs I see look desolate like that and use heatsinks like that, as well as being half bridge. It only has 100uF/200V primay capacitors but it makes me wonder how much primary capacitor specs affect the overall wattage in non-PFC/non-APFC PSUs - a review of the Antec VP-350, which has 470uF/220V Capxons as its primaries rated at 105C, has it doing 350W continuously, albeit at 75% efficiency as it exploded at 475W. c_hegge's review of a 460W Coolermaster confirmed that it could do 460W and it only had 560uF/200V Elite primary capacitors rated at 85C. There's even a review of a PSU at X-bit labs that claimed 300W on the label but only had OST, 85C 330uF/200V primaries (a "Tsunami Hercules A300M-C", with puny heatsinks), and only a medium speed 80mm sleeve bearing fan from ADDA (thermally controlled as that PSU didn't hesitate to get hot judging by the review)... and it looks like it too could do its rating.

My guess is that primary capacitors affect the efficiency (if not only that and the input rating?). You could probably cut corners there but then you'd increase heat output, lower efficiency, and make the rest of the components work harder and further breach their limits. All said, though, seeing how "well built" the PSU everell posted is, it probably couldn't do more than 70W safely, as stated before me.

[tom66]

Re: Mystery power supply

Well, at only 100uF per primary cap... I'd rate it at maybe 50-60W output, possibly a little more but you'd be squeezing it. So either a really cheap crappy PSU or one for very low power computers, I'm betting on the first as I've never heard of a 50-60W ATX PSU (and I'm pretty sure it's ATX - it's got a standby transformer.)

[everell]

I removed this power supply pc board from its case because I was going to part it out. I didn't think it was much of a power supply. Then I noticed it was a little different. It has 100 Mfd/200 volt Nichicon CE capacitors for mains. The pwm chip is a KA7500B. The switching transistors are C2553 rated for 400 volts 4 amps. So now I am wondering which case I pulled it out of several months ago. Anyone want to venture a guess as to who made it?