Output inductor replacement on FSP 700 PSU

[badcapsal]

Hi
Have a FSP 700 with a burned out inductor on the output side.
It handles 5v, 12v & -12v with 3, 8 & 8 turns respectively.
It has shorted 5v & 12v together.

I have a FSP 600 dead on the side with a good inductor however it has a different number of turns.
The 600 is a FSP700-80GLC(NEW)
The 700 is a FSP850-80GLN(REV1)

Turns are as follows

rail - 600 - 700
v - turns - turns
---- ----- -----
5 5 3
12 13 8
-12 13 8

Q. will this 600 inductor work in place of the 700?
If yes yipee!
If no, would unwinding be practical? Or perhaps a change in the output filter caps?
My knowledge is about Ohms law and not much more, although I do enjoy a little Giancoli.
Thanks in advance
Sal . . .

[Th3_uN1Qu3]

Re: Output inductor replacement on FSP 700 PSU

That inductor has more turns thus higher inductance, so in terms of filtering it is even better. However, the control loop may not like it. I say go for it, for in any case it will power on, but listen for any weird noise that the PSU makes.

[badcapsal]

Re: Output inductor replacement on FSP 700 PSU

Thanks, will give it try
Sal . . .

[kaboom]

Re: Output inductor replacement on FSP 700 PSU

They may have reduced the number of turns to reduce the I2R heating, instead of using a bigger core/wire.

I'd check the airflow- some FSP 'noise killers' are also power supply killers. If there's just a thermistor on the rectifier heatsink, the fan may not run fast if the heatsink is cool, but that doesn't mean the inductor isn't smoking away.

If the 'fan killer' consists of a small board with a few components attached to the top of the secondary heatsink, like an 'afterthought,' watch out. I've seen such a board with red black wires back to the main board where there was once a header/plug for the fan. This bastard board was 'inline' with the 12v ckt to the fan, the fan's wires coming off this board.

This was 'marketed' to those 'silent computing' idiots. Sure, why not, just take something that works and screw it up so we attract a 'certain' kind of crowd.

The old AT power supplies sometimes had a resistor, which would run the fan on ~9V. The fans were ballsier and unless you used an AT Super 7 board, heat usually wasn't a problem.

I will remove such nonsense from any power supply. Dell-hell got some 'designer' who dared to put only 4.6V to the fan under low heat conditions, with a stupidly weak fan besides. Some Gateways have Hipros with decent fan control, but the case can't supply the makeup air! Even better is when I see a too-large rear exhaust fan and the one in the PS is temp controlled. The big fan puts the case into a vacuum and 'backdrafts' the fan in the PS. The heat removed by the case fan rises up and is pulled into the PS. The warmer-than-ambient air gets hotter as it picks up heat inside the PS and is then pulled into the chassis, to be exhausted and 'recirculated.'

Th3_uN1Qu3, come on in here and make a nice long reply to that- you are in the longest post contest after all.

-Paul

[Th3_uN1Qu3]

Re: Output inductor replacement on FSP 700 PSU

They may have reduced the number of turns to reduce the I2R heating, instead of using a bigger core/wire.

Mm, wasn't that the other way round in this case? Less turns = higher flux = more core loss...

I'd check the airflow- some FSP 'noise killers' are also power supply killers. If there's just a thermistor on the rectifier heatsink, the fan may not run fast if the heatsink is cool, but that doesn't mean the inductor isn't smoking away.

Or you can move said thermistor inside the core of the inductor. That oughta run the fan at the right speed.

Th3_uN1Qu3, come on in here and make a nice long reply to that- you are in the longest post contest after all.

-Paul

I'll pass today - have better things to worry about right now.

[kaboom]

Re: Output inductor replacement on FSP 700 PSU

They probably dropped the turns in the 700 vs the 600 to reduce the I2R losses in the wire and reduce the flux. But knowing that the currents would be higher in the 700, they should've also upsized the wire to get higher ampacity/lower local temp rise.

It's the output inductor, not the transformer primary.

[Th3_uN1Qu3]

Re: Output inductor replacement on FSP 700 PSU

Ah, by I2R you meant resistive losses. I have a hard time translating acronyms sometimes.

Last time i checked my textbook, any inductor follows Faraday's law regardless if it's a choke or a transformer primary... less turns for the same voltage = higher flux.

[kaboom]

Re: Output inductor replacement on FSP 700 PSU

While reducing the turns in the output inductor increases the pk-pk current swing for a given DC output, it reduces the DC bias on the core- fewer amp turns. Further away from saturation, the higher flux swings would be of less consequence, since the lower bias has 'made the core bigger.'

And of course, with powdered iron cores, the saturation would be 'soft.' Put ferrite in there and the supply would eat itself. The nasty spikes from the hard saturation would blow the semiconductors.

Of course, you can 'cheat' and never, ever allow the ferrite to saturate, or gap the core, one may be able to use it for the output inductor.

My problem was it sounded like FSP cheeped out and simply dropped the turns. You can put higher current through 8 turns and get the same dissipation as lower current through 12 turns, but now we have more amps/circular mil. Hence local heating of the windings and a 5-12 short in the inductor.

No- keep the turns the same (within flux limitations) and truly increase the ampacity with larger wire or more 'filliars.'

[Th3_uN1Qu3]

Re: Output inductor replacement on FSP 700 PSU

True. I had forgotten that -26 and -52 materials have significant changes in inductance with DC bias.