I have an APC UPS model SMT1000i, s/n beginning AS1It has a quiet but rather annoying beep/squeak/buzz (it is hard to describe in words) which sounds every 20 seconds. This is not the alarm sound, that works OK and sounds completely different
I have attached an mp3 sound sample of the squeak
After many weeks of mostly fruitless net searching and experimenting I have formulated a theory for what is happening, but I need someone familiar with the operation and workings of APC UPSs to be able to confirm or deny my version of what is going on
Firstly here are the symptoms:
NB: Having a load makes no difference to the timings or how loud/soft the sound is. I only presented these no-load findings to isolate that as being a cause
SMT models have circuitry to prevent battery over charging which was not present in earlier models and so this behaviour is actually intentional as follows:
So, my question is does my theory make sense and tie up with how a SMT UPS is meant to be behaving or am I completely way off and this unit is just malfunctioning in a random way?
NB: Another user posted an unresolved report for the same model and similar behaviour here: http://forums.apc.com/spaces/6/racks-rack-accessories-cooling/forums/general/8575/new-smart-ups-lcd-1000-buzzing-noise-every-20-seconds-is-it-normal#13527
This unit has now developed an additional behaviour (described below). Could anyone with this same model that uses it outside of a comms room, where you wouldnt be able to hear these noises, confirm if their units do anything like this?
A few minutes after shutting down the unit and disconnecting the mains the unit emits a loud sound which is similar to a compressed spring being released
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