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]

CA Traveler wrote:
It's the pulsed cycling that caused the noise vs a constant voltage.

Voltage sense was a general comment not related to the noise. Voltage sense is a small set of wires that connects from the battery post to the controller. There is vitrually no amps so the controller knows the battery voltage and will adjust the charging for the battery. Otherwise the controller is not aware of the wiring voltage loss and the battery will be charging at a lower voltage.

A remote temperature probe will also allow the controller to adjust the charging based on battery temperature.

Thanks. I have a temperature sensor on the -ve battery post, and the controller is located pretty much adjacent to the batteries through very short leads, so I think I'm OK on that front.

[MEXICOWANDERER]

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!

[CA_Traveler]

It's the pulsed cycling that caused the noise vs a constant voltage.

Voltage sense was a general comment not related to the noise. Voltage sense is a small set of wires that connects from the battery post to the controller. There is vitrually no amps so the controller knows the battery voltage and will adjust the charging for the battery. Otherwise the controller is not aware of the wiring voltage loss and the battery will be charging at a lower voltage.

A remote temperature probe will also allow the controller to adjust the charging based on battery temperature.

[Gerald55]

CA Traveler wrote:

Do you mean it's in standby so it's not off?

I mean it is as off as this inverter can be, without actually disconnecting the DC inputs. The power button is an instantaneous button and you push it to turn the unit on and off. No doubt this means that even when "off" there is a microscopic draw to support detecting the button push (there is also a remote option).

So I'm not sure if thats' what you mean by "standby" or not - I'm definitely not talking about a state where it's ready to turn on when it detects an AC load.

FYI Pulsed type of power has a large number and frequency of power transients and can cause various symptoms, especially the way yours is wired.

Interesting. So there is the possibility that the PWM induced transients cause this issue, but it seems also that even ignoring the transients, the PWM itself will cause current flow to cycle on and off rapidly, and this may induce some voltage changes in the wiring?

It helps to have a controller with battery voltage sense capability however.

Helps with this kind of noise issue, or helps in general? Is this a separate set of leads (distinct from the charging ones) that allow the controller to read the voltage? How would it differ from the voltage the controller sees on its charge output? ISTM they would only differ by the voltage drop along the charging wires (which in my case is very small as they are a couple feet long at the current I get from my panels is moderate).

[Almot]

The inverter is off and yet is making buzzing sound, and the sounds depends on the position of lights dimmer? Interesting indeed.

Not sure Samlex controllers qualify as "good", btw. Their inverters are known to be "acceptable" quality.

[time2roll]

Here is a note from Tristar:

PWM Noise: In some installations, the PWM charging may cause audible noise in certain equipment. If this occurs, the PWM can be changed to “OnOff” solar charging to reduce the noise. This requires DIP switch number 8 to be turned On. However, it is strongly recommended to try to remedy the noise problem with grounding or filtering first, because the benefits from PWM battery charging are significant.

See page 28

Unfortunately no real suggestions for grounding or filtering.

[Gerald55]

Just to clarify, I'm not hearing any sounds from controller, but rather from my inverter. The cause of the sounds seems to be the PWM activity of the controller though. The Samlex controller is known to be a decent example of a good PWM controller.

[Almot]

Gerald55 wrote:
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.

There are no voltage fluctuations in my MPPT at this stage - if sun is shining steadily. It goes into Absorb and stays there until conditions for transitioning to Float are met. Current is gradually tapering during this stage. It never makes any sounds other than soft click when switching between bulk/absorb/float.

Gerald55 wrote:

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

Probably normal for this model/brand.

Gerald55 wrote:

Any ideas to get rid of the noise?

Get a quality controller. RF issues that Mr Wiz mentioned could take place too, you may play with wiring to see if it helps, but like I said I never hear any sounds from my controller.

[CA_Traveler]

Yes it could be RFI radiation related. You could connect the house loads with temporary wire directly to the house battery to see if that makes a difference.

[MrWizard]

Gerald55 wrote:
I should add, although I don't think it matters:

The wiring is such that the inverter is the only thing wired directly to the batteries, via 2/0 cable. The solar controller output, as well as the 12V leads for the rest of the coach, are all wired to the inverter terminals.

Circuit-wise this is all same, but I'm not sure if wiring the controller leads to the battery somehow causes more of the PWM noise to affect the inverter.

Yes it matters
The 2/0 cable is great for controlling voltage drop between battery and inverter
But it doesn't filter the noise that is being applied directly to the inverter and the house wiring, because the batteries are at the other end of the 2/0 cable
What you have done turns all that wiring into an antenna to transmit / broadcast that pulse

[MrWizard]

Gerald55 wrote:
I should add, although I don't think it matters:

The wiring is such that the inverter is the only thing wired directly to the batteries, via 2/0 cable. The solar controller output, as well as the 12V leads for the rest of the coach, are all wired to the inverter terminals.

Circuit-wise this is all same, but I'm not sure if wiring the controller leads to the battery somehow causes more of the PWM noise to affect the inverter.

Yes it matters
The 2/0 cable is great for controlling voltage drop between battery and inverter
But it doesn't filter the noise that is being applied directly to the inverter and the house wiring, because the batteries are at the other end of the 2/0 cable
What you have done turns all that wiring into an antenna to transmit / broadcast that pulse

[CA_Traveler]

Gerald55 wrote:
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.

Do you mean it's in standby so it's not off?

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.

FYI Pulsed type of power has a large number and frequency of power transients and can cause various symptoms, especially the way yours is wired.

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

Yes

Rewiring the controller AND the house wiring directly to the battery may/may not solve the problem. You may have incompatible equipment which sometimes becomes a learning opportunity for a DIY project.

There is normally absolutely nothing wrong with wiring a solar controller directly to the inverter depending with adequate wiring. It helps to have a controller with battery voltage sense capability however. My MPPT controller is wired to the inverter terminals and works great with no noise but with different equipment.

[MrWizard]

X2 what Chris said
You wired it wrong
The solar needs to be connected to the batteries, not the inverter terminals

[Chris_Bryant]

Wire everything to the batteries- they act as filters.

[Gerald55]

Well I'm pretty sure those are used in very, very few text messages 🙂

They are technical terms.

PWM Pulse Width Modulation
MPPT Maximum Power Point Tracking