I am building a small system that includes two Meanwell LRS-100 series power supplies:


Note the photograph on the first page of the data sheet, and the drawings on the last page showing threaded holes along one edge and on the bottom of the unit. I would like to mount the units standing up vertically (on the flat bottom of my chassis), with the narrow edge (with 3 screw holes) downwards. From Meanwell's documentation, it is unclear if this is permissible, and if so, how performance might be de-rated.

Their one-size-fits-all installation manual:


... states "Mounting orientations other than standard orientation or operate under high ambient temperature may increase the internal component temperature and will require a de-rating in output current. Please refer to the specification sheets to receive the optimum mounting position and information about the de-rating curve."

But the LRS-100 series data sheet (the first link above) contains no such information. Telephone tech support confirms that the unit must be installed within the end-system, and that the system must contain 3X the volume of the PS, and that ANY orientation is acceptable. The agent did not inspire confidence, and I find this improbable: e.g. with the large flat side with ventilation holes facing downward, and the solid side (with two screw holes) facing upwards ?!?

So I seek guidance as to whether my vertical orientation is acceptable, and if so, how much de-rating might be required.

  • 1
    \$\begingroup\$ The best way to mount this supply is on a side wall of your main enclosure, with connectors on left or right side, so the air can flow more freely in vertical direction through venting holes. \$\endgroup\$ Commented Aug 30, 2018 at 18:42
  • \$\begingroup\$ Do you have this power supply in your hands? Are the power FETs heatsunk to the metal enclosure? (It's hard to glean that from the picture in the datasheet.) \$\endgroup\$ Commented Aug 30, 2018 at 19:06
  • \$\begingroup\$ How is air flow controlled? vents? forced air? show restricted air sides what volume is your casde relative to 2 PSU's. Without vents it will heat up and UL "coke spill test" prevents top vents. I have done this before with U 19" rack 180W open frame PSU inside with thermal controlled plenum fans \$\endgroup\$ Commented Aug 30, 2018 at 19:09
  • 1
    \$\begingroup\$ To sum it up - just test it under real-world conditions. \$\endgroup\$
    – rdtsc
    Commented Aug 30, 2018 at 21:07

2 Answers 2


If your enclosure has side and bottom vents then the advice you were given makes sense to me. Inverted with bottom and side vents.

i.e. Convection air intake rising and exiting up past hotspots to vent outside with thermal conduction to top cover from baseplate..

In a design I did with 180W open frame PSU in 1U high enclosure, I used side vents with thermal controlled fans using a thermistor epoxied to the hotspot, ferrite transformer. It ran silently to 45'C up to 100W output to ext. load then fans started slowly to limit sense temp to 55'C but never ran full RPM at room temp.

If you mount it vertically then your convection air flow must not be allowed to rise over the hot spot to exit. Otherwise, a 40mm plenum fan may be needed.

More details


First of all, the derating curve is located on the bottom of page 3 on the left. It states that you need to start to derate if your enclosure may heat up above 40 celsius. You can place a thermometer within your enclosure and start it up for a couple of minutes until you see any noticeable change. Measuring the output current of the power supply will also be important during this process.

If your measured current is below 50% of the rated charge, don't even bother with the temperature, you will be fine unless the temperature is above 70. At 70, you overshoot the max temperature of that particular power supply and you will run in all sorts of trouble with what you're powering too too.

Regarding the orientation, the casing itself is a okay heat conductor and unless you basically enclose it from all direction (thus blocking all holes), you will have no problem at all with heat transfer. If you are feeling a bit uncertain about it, you could put a fan to displace the heat and equalize the temperature inside the enclosure, but it will most likely be overkill.

Keep in mind that these recommendations are specific to your particular case with the information you gave us. In general, it is easier to orient correctly the power supply and read thoroughly the application note.

  • \$\begingroup\$ I was imagining that there would be different de-rating curves for other mounting positions. But I believe what you are saying is that in other mounting positions, the temperature will be higher so it simply shifts you to the right on the one de-rating curve supplied. The only problem with that is that the horizontal axis of the curve is ambient temperature; but it is internal component temperature that Meanwell suggests may be higher in "other than standard" (which they don't define) orientations. \$\endgroup\$ Commented Aug 30, 2018 at 18:41
  • \$\begingroup\$ Your information about derating due to temperature is correct. However, it is not generally correct to say that orientation doesn't matter. In this specific example, it may not matter. But in many cases power supplies are designed to use passive convection as cooling. For example, please see figure 2-1 of this datasheet by NI. \$\endgroup\$
    – bitsmack
    Commented Aug 30, 2018 at 18:42
  • \$\begingroup\$ @RustyShackleford most often, the only accurate data that you will have will be the internal temperature of the enclosure (what you called ambient temperature). The temperature of the components will always be higher than the ambient for the simple reason that it is the components that heat the ambient temperature. But, at some point, you just give yourself enough margin and tolerance so that it doesn't become too much of a problem. \$\endgroup\$ Commented Aug 31, 2018 at 16:10
  • \$\begingroup\$ @bitsmack you are quite right. I used a similar power supply on a system I designed and the way it is built prevent having a really bad orientation. There are orientation that are sub optimal that is for sure. But, you are correct to say that on different context, it could be a really bad thing especially with passive convection. \$\endgroup\$ Commented Aug 31, 2018 at 16:12
  • \$\begingroup\$ Ok, thanks everyone. You've convinced me that I am overthinking this. I will mount it vertically, with those ventilation holes (on one side and one edge) exposed. I'll also put the non-ventilated side against the side of my enclosure (maybe use some thermal-transfer material) so get some conduction there too. \$\endgroup\$ Commented Aug 31, 2018 at 22:02

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