Loud UPS fan

[JohnLeslie]

I have a Tripp Lite SU1500RTXLCD2U UPS. Very loud 80mm fan. Tried to replace with std. 80mm computer fan and it doesnt like it. Apparently there is a tachometer feed from the original fan that does not square with the new fan. Wondering if I can defeat this tachometer input somehow. New fan is almost completly silent. Old one is pushing 30db

[james_s]

I think there was another thread almost exactly like this a few months ago, that person eventually gave up and installed the UPS in the basement.

If you want to replace the fan, use an oscilloscope to examine the tach signal. Also make sure the new fan moves as much air as the old one or the UPS may overheat, unless you are sure you will never run it near its full rating.

[Jeroen3]

Have you used an 555 before?

[coromonadalix]

https://electronics.stackexchange.com/questions/396881/using-timer-555-to-obtain-a-frequency-multiplier

??

you have to know the pwm pin freqency with the loud fan,  replace the fan with a lower speed / noise  and add the circuit to match the need pwn sensing ....   

[TruslowPJ]

I know this is an old topic, but figured I'd post an answer

my SU2200RTXL2UA appears to be manufactured by Delta, and uses delta fans with the R00 suffix, which means the third wire isn't for tachometer at all, but instead a locked rotor signal that it pulls down to ground when the fan is operating normally. my unit has two fans and as long as I short the third wire to ground on at least one of the two fans, it's happy. if left floating or connected to the RPM sense of the fan, it triggers a fan fault.