HP Small Form Factor SMPS - Can I Use Extended Leads On Capacitors?

[SgtRock]

Greetings EEVBees:

--I am rebuilding one of those HP small form factor power supplies. My problem is I cannot find adequate capacitors which fit the width and height requirements, plus, they are in the hottest place possible. Could I add 3" insulated extensions to the leads and put larger caps in a cooler area? Your help would be sincerely appreciated. I will post pictures of the project when I get further along.

"He was born ignorant, and has been losing ground ever since."
Fred Allen 1894 1956

Best Regards
Clear Ether

[Psi]

We really need more info, switching frequency, size of capacitor, how hot does this area get?
But assuming general PC powersupply figures its probably fine to move them a little, and 3 inches isn't very far.

The best approach is probably to use the biggest capacitor you can fit and then add to it's capacity with another cap located further away.
But if the area really is hot you will have to spec the close capacitor to handle that temp without lifespan issues.

I wouldn't put an electrolytic cap in an area that gets really hot. Tantalums maybe a better choice as some of them are rated up to 200C, they're not cheap though.

[SgtRock]

Dear Psi:

--Thanks for your rapid response. I do not know the switching frequency. Please see attached pic. How hot? By observation I would say RFH. The caps you cannot read are from left to right 2200uF 10V, 2200uF 10V, 1000uF 10V, and 2200uF 16V. I propose to use all 16V 5000 Hrs at 105C for all. Thanks again for the good advice.

"If you build a better mousetrap, you will catch better mice."
George Gobel 1919 1991
 
Best Regards
Clear Ether

[mikeselectricstuff]

If you do extend, it would be a good idea to add ceramic or film caps (a few uF) close to the original pads to deal with higher frequency currents -  then adding length to the electrolytic leads will have much less effect.

[tom66]

Curious: What manufacturer of caps was used? I see Chemicon KY, and "nondiscript blue capacitor company".

[SgtRock]

To All:

Thank to all. Chemicons, I wish. The brands used are Ltec, Aishi, KY, and Teapo. What appears to be dust is One Hung Low hold down goop. This power supply appears to be less than a year old. It also does not appear to be radically different in design from any other ATX PS. The main difference being it smaller size and long rectangular profile to fit the HP Small Form Factor constraint. These power supplies do not have a good record for longevity, and the replacement cost from 90 to 150 dollars US. HP sticks it to you, because they know you cannot fit an ordinary ATX supply into the case. As far as I can tell the caps used are One Hung Low junk as well. Good luck finding and trusting the specs.

--I think I will just overspec the Caps, and use good DigiKey brands, extend the leads to get to  roomier and cooler place, and glue them down so they will not flop around. Then I will hook up the PS to a test bed computer, making sure to draw at least rated power, and let her rip for a day or two. If no problems then I shall pronounce er fixed. I appreciate Mike's suggestion but there is absolutely no spare room for additional caps in the small box. Also, I do not have a working Oscope to use to follow Ahmed's suggestions, so cut and shoot is my solution. This is just an experiment and a learning experience. The time involved in de-gooping, de-soldering, photographing and documenting is considerable. Again, thanks to all for you good advice. More later.

"Reality is merely an illusion, albeit a very persistent one."
Albert Einstein 1879 1936

[SeanB]

You can just replace them as is, and add extra airflow through the area. Otherwise use smaller value caps with the rest of the value on short leads up in the air above the original place. The only reason the originals fail in my experience is because they are being run beyond ratings, use a capacitor rated for the load will run cooler. I have seen longer capacitors but same diameter that will have more area to dissipate heat, and as well add some ceramic capacitors on the bottom of the board. As large a value as you can get in a 25v rating, and remove the resist to get them in to as many spots as possible. While you are there recapping, change the primary side crapolytics, they probably are nearly open circuit by now. Use a 400V capacitor that is same size, never mind the value - close enough by 50% will work well enough, and bypass with 400V polyester caps as well. You probably will have to put those in in place of the bleeder resistors, and if you leave the leads long you can put the resistors back on the capacitor leads on the top side.

i did do a few PSU's using wet tantalum capacitors - 100uF units replacing 1000uF units with no problems, just added the extra on flyleads to the output connectors.

[NiHaoMike]

After replacing the caps, rewire the fan directly to 12V if it isn't already or preferably replace it with a high power Delta wired direct to 12V. Heat is the most common cause of problems.

[SgtRock]

Greetings EEVBees:

--Dear SeanB: I very much appreciate your suggestions.You seem very knowledgeable in this area. Please consider posting photographs of one of your projects, so that we can all learn from it. Indeed, I am replacing every capacitor as per your suggestion. As an experiment I am going to try insulating and extending the leads on some of the caps to get them to a cooler spot. There is no room to go taller or fatter, and where the cap is within a quarter inch of a massive heat sink with multiple mosfets on it the increased surface area would be as much a detriment as a boon. I have ordered (from Digi-Key) the best caps for SMPS I can find, and where possible (usually not) I have upgraded in voltage. Some of your other suggestions are passing over my head, but I will keep them in mind for when my understanding is more mature. Thanks again for the good advice.

Dear NiHaoMike: I will follow your suggestion and make sure that the fan is hooked directly to the 12 V rail. The fan in the HP SMPS box is a GP is a GP D80SH-12, which I assume is nothing special. I will consider a Delta after, and if I get the thing running, Also, I will try to mount a probe inside some where to get an idea of the operating temperature, and report back.
Thanks again for the good advice.

"È finita la cuccagna!" Translation "No more free lunch"
Fiorello La Guardia 1882 1921

[Psi]

I appreciate Mike's suggestion but there is absolutely no spare room for additional caps in the small box.

...There is no room to go taller or fatter, and where the cap is within a quarter inch of a massive heat sink with multiple mosfets on it the increased surface area would be as much a detriment as a boon.

What mikeselectricstuff, AcHmed99 and myself are recommending is...  If you relocate a cap further away, put a 2nd capacitor in parallel at the point where the capacitor is supposed to be. It doesn't have to be big and wont use up any space but it will really help reduce the negative effects of moving the main capacitor far away.

I'm not sure exactly how hot the area gets, one would assume it was designed to keep the temperate safe for the electrolytic next to it.
But if heat is a real issue you can use a small ceramic or film capacitor for this small cap, (they can handle the heat better than an electrolytic)
It doesn't have to be large but we really want to have some capacity in the correct location. The fact that it's ceramic or film means good ESR, so a little will go a long way to helping the powersupply handle high frequency currents.
A 33-100uf ceramic is is physically much smaller than original cap and can easily be soldered into the same holes or even under the pcb.
Then add your second large cap on wires as normal.

[SgtRock]

Dear Psi, Mike & Achmed:

--Would I be correct in assuming that the voltage of these additional caps would have to match or exceed that of the originals? I which case, I am having trouble finding some of them. Nothing on eBay, and I can find only 10 V and below on Digi-Key. Would you care to suggest a source. I would not mind trying to parallel some SMDs, if I could find something with voltages of 10, 16, 25, 50. I do not know much about this sort of thing, but when I fix things I do like them to stay fixed, if possible. I am only doing this to learn, and I do not charge my friends for my ?repairs?Thanks again for all your help.

"He was born ignorant, and has been losing ground ever since."
Fred Allen 1894 1956

Best Regards
Clear Ether

[alm]

I would probably recommend caps with at least the voltage ratings of the original, possibly more since the high-K dielectrics tend to decrease in capacitance if the DC bias is close to its max. voltage (see datasheet). I can find plenty of large (>= 33 uF) ceramics with voltage ratings of up to 25V on Digikey, most in SMD. They are kind of expensive ($1 or so in single quantities), though. You can even find SMD caps soldered in parallel with endcaps or pins soldered to them by the manufacturer with even higher voltage ratings.