Hi guys,
I bought recently a 2200VA ups second hand for 40 euros which the seller told me that it's in perfect condition......(nope)
I brought it home, put a pair new batteries and i noticed while it was charging, was making an humming electrical noise for 2-3s for every 7-8s.
After some research i read that it's normal for it while it's charging.
The next day, expecting it will be silent finally (i couldn't stand beside it since it gave me a headache) but again, the humming noise was not over even when the charging was finished.
So finally i opened it, and put my multimeter to measure the batteries and here comes something odd, while the software says batteries 100%, the two batteries (in series x2 12V 9Ah) was fluctuating from 27v-27.7v like saying it's trying to charge it further but for some reason something stops it.

If there is someone with something in mind, which can help would be nice.
Thank you
https://youtube.com/shorts/xvFZQE2vLf8?feature=share

 

Is the noise the problem ?
The behavior and Voltage seems to be reasonable.
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Thank you for your reply.
Yes, the noise is a big problem since i'm in a small room and the noise penetrates and can be heared almost to the next room.
Some folks gave some options to resolve the noise problem:
A. add more epoxy on the inside of the transformer, maybe the coil is loose
B. unwrap the coil and check for any burn or cut
Would be nice if you could explain to me because It seems odd to me the fact that the batteries are charged by pulse instead of constant.

Thank you

 

The percentage of Charge in the Battery can't be accurately determined
while the Battery is actively being Charged,
so the Charging pauses long enough for the Voltage of the Battery to "settle",
so that it can be accurately measured.

I have no clue about the noise, that would have to be determined in person.

If the VA-rating, and Output-Voltage-rating, of the Transformer could be
determined with reasonable accuracy,
the Transformer could be replaced with a new one.
I would recommend a new "Toroidal-style"-Transformer,
as they are usually more compact for a given VA-rating, and are usually more efficient.
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The noise is coming clearly from the transformer as you can see in the video, from what i'm thinking now is the primary problem is not the noise, but why it makes it, i noticed when the batteries were charging from the beginning it was making noise for longer periods so it was trying to provide more current from what i understand, which make me wonder, if there is a controller is responsible for sensing the voltage and start charging from an percentage and under, why does it make it in so shorts of periods.

I asked Powerwalker about the issue and the response was:


Hello,

when the software reads the battery voltage, it actually reads the charger voltage. To avoid this bias voltage, you must switch to battery mode ( simulation of mains failure ). Without AC input, the charger will switch off and the battery voltage will stabilise to your actual voltage in a short time.

 

to resolve the noise problem:
A. add more epoxy on the inside of the transformer, maybe the coil is loose
B. unwrap the coil and check for any burn or cut

it will not help. Apply some epoxy varnish as more liquid as better inside to the winding, as deep as possible. Leave it to dry. Turn the transformer over and repeat the procedure