why does my inverter 'sing' when batteries are charged?

[StarUKKiwi]

Forgive me, I have searched and I cannot find the answer.

We have three leisure batteries, we have a Victron inverter, which is used to charge laptops, phones (one a smartphone), the MiFi unit and a couple of lamps.

Last night, we had my smartphone and OH laptop plugged in and the inverter started singing. So turned it off - it had been on for about four hours - this morning, when we turned the engine on, it started and the charge in the batteries was 13.5, so, is it the batteries not holding charge (the alarm going off due to.low power) or something wrong with the inverter?

We do not have microwave or TV (from choice) and washing machine & vacuum cleaner I use when engine is running only. Just puzzled really & looking for some ABC answers

[Arthur Brown]

Most modern chargers are switched mode types, these can impose their switching frequency on the supply, maybe that is what you are hearing. Sometimes a moderate tungsten lamp load would absorb the electrical noise.

[StarUKKiwi]

So I am now confused - this is really electricity for dummies - what does that mean? And how do I fix it?

[John V]

is the "singing" noise the same or different to the low battery alarm sound ?

[Chalky]

A switch mode power supply contains small coils / transformers and switches the power through these on and off at high speed to change the voltage from one voltage to another (huge over simplification). When power goes through the coil it causes a magnetic field to be formed in the centre of the coil and the windings. This magnetic field causes movement in the windings and this can be heard as the whistling sound. (either the fundamental frequency of some of the harmonics).

 

You can stop the noise by:-

 

Designing the circuit to use a frequency above what can be heard

Encapsulating the windings in epoxy resin so they can't move

 

Most people just live with the noise .

[jelunga]

My Victron "sings" when the cooling fan is in low speed. It is resonating a little. Hold the fan cover grill when it is singing and see if that changes.

[StarUKKiwi]

My Victron "sings" when the cooling fan is in low speed. It is resonating a little. Hold the fan cover grill when it is singing and see if that changes.

I'll try that next time, it's not the same sound as the low battery sound,

is the "singing" noise the same or different to the low battery alarm sound ?

Slightly different sound (I think)

[John V]

If the sound is not from the "low volt sounder" or from vibrating fan (post#6) I don't know. Have you tried putting a resistive load on the inverter and listening to hear if the noise changes as per #2 ? ( a bedside light with an old fashioned filament lamp fitted would do) other than that I have no suggestions....sorry