APC Back-UPS RS 800 cooling fan modification

After my UPS went end-of-warranty, I decided to try to extend it’s life by improving it’s cooling. Like many consumer-class UPS’s, this one also has solid plastic casing with only a few small ventilation holes, so UPS runs quite warm even in standby/online mode and would most likely fail after few years. Lead batteries also suffer from higher temperatures and their lifetime decreases.

APC Back-UPS RS800

Do note that RS 800 sends temperature information among it’s diagnostics data, but apparently there is no temp sensor inside the UPS, because every RS 800 I have seen, reports 29,2 degrees Celcius continuously as their temperature.

I’m using UPS to supply my home server, which is located in my storage room. Because of that, fan noise wasn’t problem, so I decided to make a hole into right side cover and install 80mm fan in it. Fan I bought is standard 80mm Zalman case fan which rotates 2000 RPM. There is some space between side cover and heat sinks, so using slim type fan one could possibly install the fan inside the casing. I didn’t measure the space though.

First thing to do is shut down the UPS and remove it’s batteries. For some reason, even hours after detaching batteries, there remains voltage in some of the UPS’s capacitors. I noticed this when I pressed the power button with no batteries or power cord plugged in and still, UPS’s relay clicked.

So be careful not to drop anything conductive on a circuit board.

APC Back-UPS RS800

There is only four screws visible in the back of the RS 800, but there are more screws hidden under the front cover. Front cover is only snapped on it’s place, altough quite tight. Front cover has five fasteners, two on the each side of the cover and one on the bottom. Take a flatbed screwdriver with wide tip, preferably five (5) millimeters or more and stick it between the front cover and body cover. Now just twist the screw driver and fasteners should pop off. one by one. When detaching the cover, be careful not to rip off the ribbon cable controlling front LED’s and power button.

APC Back-UPS RS800

Now one finds three screws holding the side cover. Remove these screws and also the four screws on the back cover, if not already removed. Now pull back cover a bit back and lift right side cover a bit. It has battery connectors in it, so detach them from the circuit board. Make sure to remember cable order, which from up to down is red, yellow and black. Connectors may be a bit tight, but they can be detached by swinging connectors little bit back and forth with fingers and pulling them up. Be very careful if you decide to use needle nose pliers. Now just lift off the right side cover.

First, align the fan on the right place. The exact positition is not important but of course, there is not much room because of battery compartment and transformer. First drill just one hole and put screw in it. Make sure not to drill too big holes. I used 4,2×38 millimeter screws (diameter 4,2mm and length 38 mm), si I drilled three (3) millimeter wholes.

APC Back-UPS RS800

Ups cover is plastic, so threads are formed when screw is first time screwed in the hole. Afterwards when putting screws, turn them always first counter-clockwise so that they drop on threads and then tighten them. When fan is in place, take narrow-tip marker pen and draw a circle between fan blades. Then remove the fan and make a hole with your favorite tool. I used Dremel with a disk blade to make the hole and then finished the job with milling blade and circular grinding blade. Remember to wear safety goggles, just in case. Fan is installed outside UPS and it covers the hole, so it doesn’t matter, if it looks a bit robust. Of course, feel free to use hole saw, if you want perfectly circular hole.

APC Back-UPS RS800

I didn’t have 80mm fan grill at home, so I took square shaped industrial steel grill and cut fan sized part out of it. Finally I spraypainted the grill and screw tops black.

Fan is blowing air out from UPS casing and even though there are ventilation holes in top cover and side covers on the bottom, I wasn’t sure if they are enough for air intake. Just in case, I drilled few dozen five (5) millimeter holes on the bottom cover beneath the transformer. Holes ruin the techical specs (voltage, current etc.) written on the bottom, so if you wish to save them, take a picture of them. After this, when placing UPS somewhere, put small sticks or something under it to raise it few millimeter from the floor to ensure the air flow.

APC Back-UPS RS800

If everything is set, assembly the UPS and install the fan. If front cover was difficult to remove, it is also difficult to put back. I just taped it on it’s place with transparent tape so it’s easier to remove in case I need to open UPS again.

APC Back-UPS RS800

Fan can be powered with 12VDC wall power supply which can be connected to UPS output. I however made an extension cord and powered the fan from server’s power supply

Hopefully this modification brings few years more life time to my UPS. At least now, it only feels a bit warm on the left side. Before the mod, casing was noticeably warm thoroughly.