Annoying PWM sound from Xantrex inverter

[Gerald55]

I finally got my Xantrex ProWatt SW 2000 installed into my rig.

Functionally, everything seems great. I can run the hair dryer (on 800W setting anyway) and microwave at the same time.

I finished setting it up after sundown and did my initial testing in the dark. The next day, sun shining on entering my rig, I could hear an annoying buzzing sound coming form the inverter. The inverter is completely off at this point.

A bunch of testing seems to indicate that the sound occurs when my PWM solar controller (Samlex 30A) goes into current limiting mode (i.e,. absorption aka CV stage) the noise starts. The controller uses PWM at this stage and it seems that the fluctuating voltage/current causes some kind of resonance in the inverter.

I'm not entirely sure if this is normal, but I'm certainly loathe to try to send this guy away for repair.

It's worth noting that when I turn on the dimmable lights in the coach, I can also hear the PWM noise and it varies with the dimmer position (it's a PWM type dimmer). On one of the two dimmers, even the top (fully on) position still has some noise.

Any ideas to get rid of the noise? Do MPPT controllers have PWM-like/switching behavior when they are limiting current?

[Gerald55]

CJW8 wrote:
Think of a battery sense line as the same as a meter lead. Meter leads are very small wire and yet the meter reads very accurately. This is because there is no current flow. Some better charge controllers use this to sense the realtime battery voltage rather than just pull the voltage reading off of the controller output.

Right, that makes sense. In some respects thought the controller-battery system is self correcting when it comes to voltage readings: when the battery is approaching float, the current is slowing and so the readings become more accurate even when taken from the controller output (since the main distortion in the voltage at the controller output is current induced voltage drop, as far as I know).

While not ideal, my MPPT controller is connected to the inverter input for convenience. I have the same inverter as you and there is no noise...ever, no matter what stage the controller is in.

Thanks for the data point! My noise may be related more to my particular wiring setup, than the inverter. I do notice a small amount of noise from the same battery/inverter area when I have my LEDs on PWM, and the solar controller is off.

I even bought an oscilloscope to help narrow this down (and, well, because it was an excuse to buy an oscillscope). Then, I put the bed back on - I had to remove the bed in the back of my van to get at the installation area - and that muffled the noise to the point where I just don't hear it. Occasially when I open the back doors, which have a direct line of sight to the inverter, I hear the noise and am reminded of this thread I started and the oscilloscope I haven't unboxed yet 🙂

As a final note, I installed an toaster oven in my rig as well. When I leave the oven plugged in, I often hear a buzzing from it, even though it is off. That seems to happen even when my solar is off, so I guess there is yet another noise source on the 120V lines.

[CJW8]

Think of a battery sense line as the same as a meter lead. Meter leads are very small wire and yet the meter reads very accurately. This is because there is no current flow. Some better charge controllers use this to sense the realtime battery voltage rather than just pull the voltage reading off of the controller output.

While not ideal, my MPPT controller is connected to the inverter input for convenience. I have the same inverter as you and there is no noise...ever, no matter what stage the controller is in.

[MEXICOWANDERER]

" Well I have an oscilloscope on the way arriving tomorrow, so that may help me investigate the noise more"

A scope diagnostic is by far the best way to tackle this. Straightedge traces are the hot setup.

[Salvo]

You're not making any sense to me.

Say you have 3 battery charging sources: alternator, converter and charge controller;

and 2 battery loads: inverter and dc power center.

All 5 (positive) cables should go independently to the fuse (or fuses) located next to the battery. Likewise the grounds should go independently to the battery chassis connection or independently to battery ground.

In other words, do not daisy chain any power cable!

Almot wrote:

Salvo wrote:
A good design has all battery charging sources connected directly to the battery.

Through the Pos bus is the correct way.

[grizzzman]

Almot wrote:

Salvo wrote:
A good design has all battery charging sources connected directly to the battery.

Through the Pos bus is the correct way.
Controller-> breaker-> Bus-> battery fuse ->battery.
Same for loads, same for inverter, all on the same bus.

Though, this is just for safety. The circuit remains the same, in terms of parallel connections of battery, chargers and loads. If inverter (or controller?) is poorly shielded and PWM pulses are causing this noise, I don't know whether this "better" layout with help with noise. Going MPPT will help 😉

So...... are you saying that MPPT does not use PWM during Absorb???? How is it that it dosent use PWM????

[Almot]

Salvo wrote:
A good design has all battery charging sources connected directly to the battery.

Through the Pos bus is the correct way.
Controller-> breaker-> Bus-> battery fuse ->battery.
Same for loads, same for inverter, all on the same bus.

Though, this is just for safety. The circuit remains the same, in terms of parallel connections of battery, chargers and loads. If inverter (or controller?) is poorly shielded and PWM pulses are causing this noise, I don't know whether this "better" layout will help with noise. Going MPPT would help 😉

[Salvo]

You already have a filter in place. Before doing any other mod, I would connect the charge controller directly to battery.

A good design has all battery charging sources connected directly to the battery.

[Gerald55]

Well I have an oscilloscope on the way arriving tomorrow, so that may help me investigate the noise more.

[MEXICOWANDERER]

Your inverter but not solar controller is not conducting the inverter to "Sing Along With Mitch?".

A Pie Filter is not the answer because of the size. Experiment with electrolytic capacitors across the inverter battery connections. .01 - .1 - .47 - 10 or 100 uf ought to nail it down. Caps are cheap. Just don't connect the electrolytic ones backwards. They are clearly marked.

GOOOOOOOOGLE this...

200-ampere pass-through filter.

When Xan-Ax bought out Trace I dropped the line like a hot rock.

[CA_Traveler]

Try 5uf capacitor.

[Gerald55]

CA Traveler wrote:
Filters are worth a try. See if you can locate someone with some in is junk box that you could try out.

Is that something I can buy off the shelf, or do I have to build it? I've been googling "DC filters" and "low pass filters" without seeing much available to buy beyond some audio centric stuff.

Whatever I put inline with the inverter/battery connection would have to be able to handle 200A.

[CA_Traveler]

Filters are worth a try. See if you can locate someone with some in is junk box that you could try out.

[MEXICOWANDERER]

Ah geez with my deafness, it could have sounded like an F-111 using third stage afterburner. It MUST have been both. Ruben told me "Both noises went away". I take it electronics had nothing to do with the second noise.

[Gerald55]

MEXICOWANDERER wrote:
I just snapped a giant DC line filter around a controller to battery line plus connected a 5uf electrolytic cap right at the controller to battery line. Things got awful quiet. Done at a rancho with panels and batteries. Now the lady is off Ruben's case and my case and she can watch her soap operas. Ojala gracias a dios!

Thanks! Did you have audible noise, or was it interference showing up on your TV or elsewhere?