Horizontal or Upside down Placement of capacitors in Power Supply Unit - Page 1
Forum section: electronics / testgear

author: pascal_sweden
author_rank: Super Contributor
timestamp: April 23, 2015, 08:52:47 pm
content: Why do most suppliers put the capacitors in horizontal position (e.g. Korad KA3005P) or even up side down (e.g. Rigol DP832)?Would it not be better to place them vertical with the PCB on the bottom? Or does it not matter?Here are my 2 cents: After several years capacitors start drying out or could even leak, so from that perspective I believe it would be a better design practice to place them vertical with the PCB on the bottom.But obviously my concern is probably not justified, as almost no supplier seems to follow this design practice, on the contrary. Rigol puts them even upside down in the DP832!

author: IanB
author_rank: Super Contributor
timestamp: April 23, 2015, 09:48:09 pm
content: The main requirement for large components is mechanical support. It is not good practice to support them only by their leads. Usually such electrolytic capacitors are glued to the circuit board with white stuff. If so, this should be sufficient support for normal vibrations and such. However, if an item is dropped on the floor from bench height by accident, then it is possible for heavier components to break loose. There is a limit to how much protection can be provided against such events.

author: pascal_sweden
author_rank: Super Contributor
timestamp: April 23, 2015, 10:21:11 pm
content: Concerning mechanical support, I agree that the requirement to keep them in place can be met by using glue or other methods.But even if their placement is firm, I believe it makes more sense to place capacitors vertical on a PCB board on the bottom, and definitely not upside down for such a big electrolytic capacitor.The same board in the Rigol could be placed upwards in the case, but then of course they would need an additional top cover.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 23, 2015, 10:25:38 pm
content: Because they had space to put the board there.

author: DanielS
author_rank: Frequent Contributor
timestamp: April 23, 2015, 10:32:07 pm
content: Quote from: pascal_sweden on April 23, 2015, 08:52:47 pmI doubt orientation makes much of a difference for the "drying out" and as for leaks, those leaks are usually so slow that the electrolyte dries up as it weeps out of the casing through pressure relief vents, so orientation should not make much of a difference there either.Also, the caps in those pictures have covered tops. Those are usually bottom-vented through the plug.

author: dom0
author_rank: Super Contributor
timestamp: April 23, 2015, 10:49:56 pm
content: Electrolytics aren't filled with electrolyte. There's like a half drop of electrolyte in a large cap ; all the rest is "soaked up" in the coil. Orientation doesn't matter for them.

author: pascal_sweden
author_rank: Super Contributor
timestamp: April 24, 2015, 06:43:57 am
content: Check out page 20 and page 21 of the attached document.1) Mounting PositionDo not mountupside downwith terminals down as this mayreduce the operating lifeand could impair the operation of the pressure-relief vent.2) Horizontal MountingOne maker of high voltage screw terminal aluminum electrolytic capacitors reports thatif mounted horizontally, the positive terminal should be above the negative terminal to avoid corrosion.For high-ripple-current applications of screw terminal aluminum electrolytic capacitors with extended paper,horizontal mounting shortens the lifetime. With heating from ripple currentthe electrolyte in such capacitors may bleed from the winding, and puddle along the side of the can where there is no paper to wick it back into the winding. If the ripple current is low(less than half of rated 85 ºC current), this is not an issue. But if the ripple current is high, the effect is accelerated due both to the increasing temperature driving the electrolyte out fasterand to the drying of the wet paper where it is crushed into the can bottom. The drying of the paper can thermally insulate the element causing it to get hotter and the can bottom to get cooler. This can actually turn into a thermal runaway condition that can greatlyreduce the capacitor lifetime, sometimes by as much as 90%.If the capacitor is upright, the electrolyte is able to readily wick back into the winding, and the thermal contact and ESR do not degrade significantly.Thermal runaway does not occur, and the expected lifetime is achieved.3) Position of the Pressure-Relief VentMount the capacitors with the vents up to reduce the amount of electrolyte expelled if a vent operates.Can someone with close contact to Dave or Rigol ask for feedback on design practise as described in most Electrolytic Capacitor Application Guides?

author: Omikron
author_rank: Contributor
timestamp: April 24, 2015, 06:51:13 am
content: Quote from: pascal_sweden on April 24, 2015, 06:43:57 am

author: pascal_sweden
author_rank: Super Contributor
timestamp: April 24, 2015, 06:54:05 am
content: The show must go on of courseBut 90% seems very high, and that's why I felt it made sense to report and bring it up for discussion.

author: tautech
author_rank: Super Contributor
timestamp: April 24, 2015, 07:59:27 am
content: Quote from: pascal_sweden on April 24, 2015, 06:54:05 amGood stuff, it makes prefect sense, thanks for sharing.

author: rdl
author_rank: Super Contributor
timestamp: April 24, 2015, 08:42:12 am
content: When they say do not mount upside down, they are referring to capacitors with screw mount terminals. If you look at the diagrams on page 2, you will see that they consider the end with the leads to be the top. The way Rigol has them oriented is what that guide considers to be "right side up".

author: DanielS
author_rank: Frequent Contributor
timestamp: April 24, 2015, 12:06:21 pm
content: Quote from: pascal_sweden on April 24, 2015, 06:43:57 amFor bung-vented capacitors, the preferred orientation would be bung-up. In that case, Rigol's orientation would be the best.Either way, unless the capacitors are over-stressed or are defective, the amount of hydrogen getting released under normal circumstances should be able to percolate through the bung without blowing the vent.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 24, 2015, 12:17:29 pm
content: An important note for "big" (computer grade / screw terminal) caps! ^^There are also the kind with dented cases, which I think is done to support the winding better, and provide some conduction as well, but may also help (or hinder?) the suggested wicking effect.I suspect these conditions don't apply to standard through-hole parts, which are always(?!) stuffed to capacity, and so there's nowhere for the electrolyte to run (until it forces its way out under pressure, that is).Tim

author: AintBigAintClever
author_rank: Regular Contributor
timestamp: April 24, 2015, 10:42:38 pm
content: It's an interesting point regarding the caps being mounted sideways. Some brands of flatscreen televisions seem to have a habit of popping or drying out their caps, my guess is that when in the normal operating position virtually every cap on the board is sideways. Not such a problem for the smaller ones but more important for the ones in the PSU.

author: SeanB
author_rank: Super Contributor
timestamp: April 25, 2015, 06:34:12 am
content: Quote from: AintBigAintClever on April 24, 2015, 10:42:38 pmThat is more an indication of using the cheapest ones that will just make it out of the warranty period, as those will always be the caps that were 2c cheaper than the better ones. Save a whole pound on the manufacturing cost, and the sucker, sorry customer, will be back in 2 years to buy the new ones.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 25, 2015, 01:10:48 pm
content: Engineering is a holistic optimization process; the dark side being that cost is absolutely a factor, as anything else. To be fair, electronics surviving 98% beyond the warranty period, then not caring how long they survive after that (usually not much), is a triumph of engineering.Tim