Isolation transformer buzz with generator

[Jaston10078]

Hi there, 

 

Can anyone fathom a guess as to what is happening to cause the excessive transformer buzz that has recently started happening when we charge with our generator (a cheaper Honda copy) ? Video in link below... 

 

The buzzing gets worse the closer the genny is to the transformer... Is it some kind of interference? 

 

We also get a worrying knocking sound from the transformer under higher loads in bulk charge. 

 

Any help would be much appreciated. 

 

James 

 

 

[Tracy D'arth]

The waveform of the gen is not very pure. A pure side wave has very few harmonics but a square wave has lots of odd harmonics. The transformer expects to get a clean sine wave, modified sine wave can be a mix of square and triangular wave forms.

Its the same reason why microwave ovens demand a very pure sine wave.

Edited January 25, 2021 by Tracy D'arth

[Jaston10078]

I see, thanks... It was fine up until now though ?. Admittedly it's not a great genny. 

[Tracy D'arth]

8 minutes ago, Jaston10078 said:

Hi there, 

 

Can anyone fathom a guess as to what is happening to cause the excessive transformer buzz that has recently started happening when we charge with our generator (a cheaper Honda copy) ? Video in link below... 

 

The buzzing gets worse the closer the genny is to the transformer... Is it some kind of interference? 

 

We also get a worrying knocking sound from the transformer under higher loads in bulk charge. 

 

Any help would be much appreciated. 

 

James 

 

 

It seems that it's only when the charger is working... Any other large load like our immersion heater doesn't cause this... 

The immersion heater is a non inductive load, just resistance. AC current will induce eddy currents and physical stress in inductive loads like transformers, DC does not.

 

Not a daft question but why do you feed the gen into the transformer when you are charging batteries? The gen is either isolated or grounded with an earth spike so you don't have to have a transformer in circuit.

[BEngo]

The transformer is buzzing because it does not much like the output from the generator.  If you look at most small generator output with an oscilloscope there are lots of harmonics in the waveform and it is generally nothing like the pure even sine wave that the national grid delivers.  Cheap inverter generators can be among the worst.  As Tracy says, you don't need the IT on a generator, so if you can, take it out of circuit.

 

N

[Tracy D'arth]

Also your transformer will have bee designed to operate in a certain frequency band, likely 50 Hz to 60Hz and the generator may well be producing current outside this range.
I would think that you are not doing the transformer much good if its honking.

[Jaston10078]

Thanks for the responses ?. I'll avoid that generator for the time being and consider an upgrade to a Honda eu20i when funds allow. 

 

Thanks very much for your help ?

[Richard10002]

What’s the make and model of the genny? No point buying a Honda if it might not solve your problem.

[IanD]

2 hours ago, Tracy D'arth said:

Also your transformer will have bee designed to operate in a certain frequency band, likely 50 Hz to 60Hz and the generator may well be producing current outside this range.
I would think that you are not doing the transformer much good if its honking.

No generator should be more than a percent or two off 50Hz.

 

2 hours ago, Tracy D'arth said:

The immersion heater is a non inductive load, just resistance. AC current will induce eddy currents and physical stress in inductive loads like transformers, DC does not.

 

Not a daft question but why do you feed the gen into the transformer when you are charging batteries? The gen is either isolated or grounded with an earth spike so you don't have to have a transformer in circuit.

If there's any DC it must be appearing by magic, I think you're confusing resistive loads (power factor=1) with partially inductive ones (PF<1).

 

The genny will be 230V AC, this needs to go into the combo to provide 12V DC to charge the batteries.

 

By far the most likely cause of the buzz is poor quality output from the genny with lots of harmonics in, some combos don't like this and complain by buzzing.

[Tracy D'arth]

42 minutes ago, IanD said:

No generator should be more than a percent or two off 50Hz.

 

If there's any DC it must be appearing by magic, I think you're confusing resistive loads (power factor=1) with partially inductive ones (PF<1).

 

The genny will be 230V AC, this needs to go into the combo to provide 12V DC to charge the batteries.

 

By far the most likely cause of the buzz is poor quality output from the genny with lots of harmonics in, some combos don't like this and complain by buzzing.

I never said there was any DC!!!!!!!! And my electrical engineering background makes me well aware about inductive loads and resistive loads.

 

[Martin Nicholas]

I'd check the internal components of the transformer are securely mounted. That's a loud hum!

[IanD]

43 minutes ago, Tracy D'arth said:

I never said there was any DC!!!!!!!! And my electrical engineering background makes me well aware about inductive loads and resistive loads.

 

"The immersion heater is a non inductive load, just resistance. AC current will induce eddy currents and physical stress in inductive loads like transformers, DC does not. "

 

Why mention DC in a comment about the immersion heater being resistive then -- or indeed at all in a discussion about AC mains? And a transformer with a resistive load on the output looks essentially like a resistive load at the input, not inductive -- unless it's a *very* poor transformer with massive leakage inductance, which few mains ones are. Eddy currents and physical stress are nothing to do with the PF of the load, just the current (VA).

 

All this taken together with "Also your transformer will have bee designed to operate in a certain frequency band, likely 50 Hz to 60Hz and the generator may well be producing current outside this range." doesn't suggest an electrical engineering background -- maybe it's the way you tell 'em? ?

Edited January 25, 2021 by IanD

[Tracy D'arth]

1 minute ago, IanD said:

"The immersion heater is a non inductive load, just resistance. AC current will induce eddy currents and physical stress in inductive loads like transformers, DC does not. "

 

Why mention DC in a comment about the immersion heater being resistive then -- or indeed at all in a discussion about AC mains?

 

And you have to admit that "Also your transformer will have bee designed to operate in a certain frequency band, likely 50 Hz to 60Hz and the generator may well be producing current outside this range." doesn't suggest an electrical engineering background... ?

Pardon?   You don't know anything about transformer design Sir, from that comment. Try my experience as IEE trained.

[Tractor]

The generator supply, 230Volts single phase, may be square wave or a true sinewave, if it is a 'true sinewave', this should be ok.

The charger will be making a supply from the generator 230 Volt output by switching transistors, these feed into a transformer coil to make the low Voltage DC; this could be making the laminations in the isolation transformer 'rattle'.

Is the noise there when connected to a shore supply?

If there is no noise from a shore supply, I guess it is the generator causing the problem. The isolation transformer will clean up a poor generator output to a point, but a PC supply may not work too well with a rough supply.

[IanD]

6 minutes ago, Tracy D'arth said:

Pardon?   You don't know anything about transformer design Sir, from that comment. Try my experience as IEE trained.

I suppose playing the "my electrical engineering degree is bigger than yours" willy-waving game isn't appropriate then?

 

Yes if there's any DC in the system it can cause early saturation of a transformer, but there's very unlikely to be any here coming from a generator -- though it's not impossible. If that's what you meant, you didn't put it very clearly.

 

Incidentally I've actually designed transformers for SMPS in the past, which have all the same issues as mains ones except the frequencies are a lot higher and they melt down much faster if things go wrong ?

 

Edited January 25, 2021 by IanD

[Tracy D'arth]

Your ignorance is showing sir. Just let it go, my experience and training though a long time ago is beyond reproach. Do you remember Ferranti's? We built transformers for the national grid systems in 18 countries. Core and winding design is pertinent to the AC frequency range expected in operation. Been there, knitted the tee shirt and printed it too.

 

My reference to DC was to explain to the OP that AC will make a hum whilst DC with which he is maybe more familiar will not. I never said that there would be any DC component in the generator output .

 

Do not wave qualifications at me even in jest, I spent 45 years in the industry eventually rising to a fellowship.

 

No further posts of yours will be responded to so don't waste my time arguing.

[IanD]

Moral : be careful with insults when you're picking an argument with somebody you don't know anything about ?

[cuthound]

Definately the waveform not being sinusoidal. Very common with inverter generators.

 

The attached image shows various waveforms.

[DHutch]

Duplicate topics merged.

 

 

Daniel

[Phoenix_V]

My IT always hums noticeably when I use the (small) laser printer any thoughts on why that is?

[Tracy D'arth]

The printer will have a switch mode power supply containing capacitors and inductors which will have a tuned frequency, This will have an harmonic which is in resonance with the inductive windings in the IT..............At an inspired guess.

[GUMPY]

12 minutes ago, Phoenix_V said:

My IT always hums noticeably when I use the (small) laser printer any thoughts on why that is?

I am scanning this to decide if it's a play on words using IT.

 

If not it's possibly harmonics generated by the printer.

 

[cuthound]

2 hours ago, Tracy D&#x27;arth said:

The printer will have a switch mode power supply containing capacitors and inductors which will have a tuned frequency, This will have an harmonic which is in resonance with the inductive windings in the IT..............At an inspired guess.

 

Switch mode power supplies use transistors to switch the supply on and off at high frequencies thus eliminating the need for inductors.

 

This creates the harmonics which Loddon mentions below and it is the harmonics that cause the humming.

 

2 hours ago, Loddon said:

I am scanning this to decide if it's a play on words using IT.

 

If not it's possibly harmonics generated by the printer.

 

 

[Tracy D'arth]

3 minutes ago, cuthound said:

 

Switch mode power supplies use transistors to switch the supply on and off at high frequencies thus eliminating the need for inductors.

 

This creates the harmonics which Loddon mentions below and it is the harmonics that cause the humming.

 

 

Them be mosfets then? Arr more 3 legged fuses.

[Phoenix_V]

16 minutes ago, cuthound said:

 

Switch mode power supplies use transistors to switch the supply on and off at high frequencies thus eliminating the need for inductors.

 

This creates the harmonics which Loddon mentions below and it is the harmonics that cause the humming.

 

 

Thats interesting though I have lots of stuff with power supplies which nowadays must all be switch mode and its only the printer that does it ( i had slightly worried that maybe the heating element which I presume such printers have was causing a heavy loading somehow)

Edited February 2, 2021 by Phoenix_V