I used to have a Multiplus II then 5kVA version. it was fine but too small for my edge cases where some of the loads if all came online at the same time would exceed 6000W. That is why I bought this 10kVA version (future proofing also did a firmware update as soon as i noticed the humming, so its now firmware (v560)). But it came with a strange behavior whereby, every 20 minutes or so it starts humming.
The humming happens independent of what load is there. For example, right now as I type, the load is 656W and the humming just started. and it will go on like this for 20 minutes. and then it will stop and everything will be silent (no humming at all) for the next 20 minutes. In those silent 20 minutes there would be no sound at all unless the load exceeds 1500W, but if it stays below 1000W (which it does for most of the time) there would be no sound for about 20 minutes and the humming comes back again and cycles like that the whole day and night.
My question is, what is causing this humming and is there a way to stop it?
Thank you all for your feedback, I’m hopeful I’m going to get a solution from here.
I think my case is different. I have had a multiplus ii 5000VA for over two years and I know the sound of a fan keeping or getting closer to an overload. This new multiplus ii 10kVA I have had for about 4 days now. it behaves like the 5kVA in most cases (ofcourse with higher thresholds), but this periodic/cyclic hum happening for 20 minutes (even when the load is exactly the same) and then being silent for 20 other minutes (with the exact same load). is strange.
I have attached the two videos (one with humming and one when its silent). both showing the load at the time the humming started and the load at the time the silence started. maybe it can give you a clear picture
It could very well be that one of the loads throws a lot of harmonics. And it does not have to be a big load to be able to get a coil to hum. It could be the fridge with a dodgy capacitor on the compressor. That would also be a good match for the 20 minute period..
The transformer in your 10k MPII has a different electrical characteristic compared to the 5k before. That is why it is entirely possible that you couldn’t hear it before.
Well, my first post was way more informative, but I was advised to make it shorter.
But basically, I have tried all sorts of possibilities to try to understand what is causing it.
The main thing is, this humming and silence cycle, happens every 20 minutes. The question is, why 20 minutes? why not 5 minutes or 2 hours?
At first I thought it was the grid. I switched off the grid, but the cycle kept happening.
Second, I thought it was the inverter-charger. so I set it to inverter only, the cycle still happened.
The i thought it was one of my loads, maybe the fridge or the heater (you know, one of those appliances that go on and off periodically). So I switched those off…but no, the cycle still happened. I have 5 MCBs/breakers for 5 different types of appliances that I have connected to the inverter, and I switched each of them, but the cycle still happened.
And this is not a constant humming as reported in other humming cases. This is a humming that goes on for only 20 minutes… then I get a complete silence for another 20 minutes…then the humming comes back again for 20 minutes, then silence again for another 20 minutes…24/7 non-stop
The i thought it was one of my loads, maybe the fridge or the heater (you know, one of those appliances that go on and off periodically). So I switched those off…but no, the cycle still happened. I have 5 MCBs/breakers for 5 different types of appliances that I have connected to the inverter, and I switched each of them, but the cycle still happened.
I just noticed that, when the inverter is using the grid to power the load, that 20 minute cycle disappears and its replaced with that normal hum (that sounds like a transformer).
so the 20 minute loud hum cycle only happens when the inverter is on battery/solar