Eliminating the fan in the classic Mantis microscope with GU4 LED lamps

[BreakingOhmsLaw]

I set out to eliminate the fan in my 90s Mantis microscope by replacing the lighting with a modern LED alternative. The original lamp provided by vison engineering is an OSRAM 41890SP, a 20 watt job with an opening angle of  just 10°. I was not able to find a suitable replacement with a 10° angle, bus OSRAM makes another GU4 socket LED Lamp, the LED STAR MR35 36° GU4, part number 075105294. The larger opening angle does not affect the amount of light where you want it, as these lamps have 345 lumen where the halogen one had only 205, so if anything, the image is even brighter.

More importantly, at just 4 watts each, the energy consumption is reduced by 80%, so the amount of heat generated is significantly less as well.
To determine if the fan could be omitted alltogether, i did some measurements.

This unit is not designed for easy service. Replacing the fan normally requires taking the entire thing apart because it is plugged into the PCB in the inside, and as most screw are self-tapping this is not a procedure that should be carried out too often. In order to disable the fan without taking it apart, I just removed the fan cover, cut the cable to the fan and put a Dupont connector inbetween. I extended the cable of the fan a bit so I could put the connector in the airduct to the lamp. Reactivating it only requires removing the lamp cover now.

After replacing he lamps with the new LED ones, and fitting the right lamp with a temperature sensor, it was time to  reassemble the unit.
The lamp temperature eventually settled at 74.2°C after 90 minutes, which is well below the 85°C operating limit in its datasheet. The lamp windows never exceeded 43° and feel colder than before.
I took a thermal image of the vents, which feel cool to the touch, and indeed, the maximum temperature is just above 32°. The air temperature measured in the lamp cavity was around 45°C. You can see the warmer air rising from the vents in the picture. All in all every part feels less hot than before  - without the fan running. I will certainly check again in the summer when the temperature in my lab can exceed 35°. At normal temperatures around 22° the Mantis can now run indefinitely without a fan. Silence is bliss.

[esprits4s]

Thanks for posting this.  I'm going to give these a try in my Mantis!  I'm going to try and find a U.S. source.  All the Google links that came up were in Europe.