Multiplus makes loud noise when switching from generator input back to inverter

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hummingbear asked Jan 29, '21

Multiplus makes loud noise when switching from generator input back to inverter

I have a 24V Multiplus 5000VA connected to my battery system. I also have a 10KW Generator connected to AC Input.

If I'm using the generator to charge my system and afterwards turn it off, the Multiplus makes a very loud hum/vibration that slowly diffuses after 5 or so seconds. This happens almost every time I turn off the generator. I even programmed the multiplus to stop taking AC Input from the generator before powering it down.

Is this sound part of normal operation when switching off AC Input to the Multiplus?

Edit: Video of what I'm describing

MultiPlus Quattro Inverter Charger Generator

pxl-20210130-0143117852.mp4 (77.8 MiB)

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klim8skeptic ♦ commented · Jan 29, 2021 at 05:15 AM

I would hope that you have flipped the generator isolator, before shutting down the generator.

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hummingbear klim8skeptic ♦ commented · Jan 29, 2021 at 07:02 AM

@klim8skeptic "flipped the generator isolator"

Where would I find this and how would I flip it? Is this something that would be on the generator or in my multiplus? My generator only has on/off controlled by a relay or switch.

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alan hummingbear commented · Jan 29, 2021 at 11:04 PM

Turn of the breaker on the genset or on the input cable before you turn off the genset.

What is probably happening is when you turn the genset off the voltage tapers down to 180v before the multi disconnects, this is the stock AC input voltage settings, then the multi has to work hard to get back to 230/40v.

You could also raise the disconnect voltage in the multi.

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hummingbear alan commented · Jan 29, 2021 at 11:35 PM

Thanks for the response @Alan - I have the Multiplus programmed to stop taking AC Input, wait 1 minute and then turn off the generator. The Multiplus has already switched over to inverting for 1min, it's only when the generator shuts off that this noise happens

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hummingbear answered · Jan 31, 2021 at 02:12 AM

@Paul B @Alan

Monitoring the Voltage and Frequency of both AC In and AC Out when the generator shuts down (not using a breaker) it brings the frequency of AC In to 45 and AC Out matches that. That's essentially the cause of the issue/noise I'm hearing, and explains why some of the LED lights in my house would flicker as it brings the frequency back up to 60Hz (North America).

Unchecking the setting Accept a wide input frequency range on the Multiplus fixed the issue.

It's interesting that the Multi is still synchronizing the frequency even though it's not accepting AC Input. Does anyone know if that's expected behavior?

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alan commented · Jan 31, 2021 at 02:39 AM

It makes sense that it would, as it has to sync to the incoming AC before it connects the AC input relay.

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hummingbear alan commented · Jan 31, 2021 at 03:29 AM

@Alan I agree that it does have to sync before accepting power from AC Input, but wouldn't it make more sense for the multiplus to start syncing when the Multi is put into charger mode rather than when it's in Inverter Only mode?

Even when it's in Charger mode and you give it AC Input it takes about 30s before it actually switches over to AC Input. It seems like a flaw that the Multi is still syncing to AC Input when in Inverter Only mode

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alan hummingbear commented · Jan 31, 2021 at 03:58 AM

The inverter mode is bidirectional, the multi can take input and output from either ACin or ACout.

there is only 1 AC bus however so the multi is programmed to sync its output to the input provided to its AC in.
When in charger mode there is nothing for it to sync as the AC output is shutdown.

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hummingbear alan commented · Jan 31, 2021 at 04:10 AM

Thanks, glad you know the ins/outs of the system it's helpful to have an explanation.

Can I push on this a little bit and ask is it possible for the Multi to not sync it's output to the input when in Inverter Only mode? Is this something I can program with VE Configure/Assistant or an MQTT Command or does it require a firmware change from Victron.

In what scenario does it make sense for the Multi to sync to Ac Input when in Inverter Only mode?

I guess I'm poking on this because

1) if I were grid-tied and I had AC Input to my Multi but wanted to draw from my battery system, I wouldn't want or expect my system to sync to AC Input when I've set it to be in Inverter Only mode, especially if AC Input is unstable or unreliable.

2) because of my exact issue above

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alan hummingbear commented · Jan 31, 2021 at 05:49 AM

There isn't really inverter only mode, it's inverter/charger or charger. It's possible to turn off the charger in Inverter/Charger mode via VEconfig or via a charge current control assistant.

The multi may also sync the Sine-Carrier Subsystem to the incoming wave while in charger only mode as well, hence the delay. Not sure.

I'm not aware of any way to set the multi to not sync to incoming AC, it may be possible with a MQTT command. however you would have to ask @Johannes Boonstra (Victron Energy Staff) or @mvader (Victron Energy).

Another way around this could be to set up a external contactor on the AC input, use the programmable relay to activate it when your ignore AC input activates. This would drop the genset while its still running in spec. And your genset start/stop will then drop the genset 1 min later.

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hummingbear alan commented · Jan 31, 2021 at 04:44 PM

Really appreciate your insight into all of this, I'm learning a lot about the Multi.

Victron seems to have defined Inverter Only mode, you can see it here under /Mode.

I would expect Inverter Only mode to not sync incoming AC, but it still does. @mvader (Victron Energy) @Johannes Boonstra (Victron Energy Staff) any insight on this expected behavior? Is there a way I can tell my multi not to sync to AC In over modbus or MQTT?

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Johannes Boonstra (Victron Energy Staff) ♦♦ hummingbear commented · Jan 31, 2021 at 05:33 PM

Hi, The Multi has a bi-directional power pack which works DC-AC or AC-DC. The charge function can be set on/off by setting the charge current to 0 for example, but the powerpc itself want to be ready to go into passthrough. So when there is a AC detected on the input terminals the unit will try sync on that, even though the setting is made to "ignore" the AC input, so not go into passthrough, the unit is ready at the moment the "ignore " state is cleared.

In this case of an overload or such the passthrough so happen immediately instead of the need to then start syncing.

So if you don't want the unit to start syncing on an incoming AC source, make this source invisible for the unit by adding a relay or such.

The is no other way/setting to prevent this.

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hummingbear Johannes Boonstra (Victron Energy Staff) ♦♦ commented · Jan 31, 2021 at 06:27 PM

Thank you. I'll see about putting a high-current relay in place.

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klim8skeptic ♦ commented · Jan 31, 2021 at 03:23 AM

Google generator motoring.

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Paul B commented · Jan 31, 2021 at 05:26 AM

the multi will always try to sync and thus its first course is to get the frequency's to match, so yes it will always try to follow the ac in power.

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Modifications Space

Node Red Space

Answer 1 · 2021-01-30T11:45:15Z

Paul B answered · Jan 30, 2021 at 11:45 AM

As far as I know there is no feature that turns the multi to invert 1 min before you turn the generator off. so please explain how you are doing that

Alans comment is more than likely still correct.

also if you have any motors running then as the gen goes off these will likley restart so there will be a high ac current as the start current for these kicks in.

try increasing the AC low disconnect voltage to 205 volts this may help

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hummingbear commented · Jan 30, 2021 at 05:51 PM

@Paul B Correct, there is no built in feature that supports this out of the box. I'm using NodeRed on my VenusOS device and configured it through there. With MQTT you can tell the inverter to go into inverter only mode which disconnects AC Input. After 1min then I turn off the relay for the generator which shuts it off.

I'm not sure Alan's comment would be correct if I'm not accepting input from AC1 at the time the generator shuts off?

I've uploaded a video to my original Question so you can hear exactly what happens.

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hummingbear commented · Jan 30, 2021 at 07:08 PM

@Paul B so I tested turning the breaker off from Generator to Multiplus before shutting down the generator. You are both correct that it did not make the noise I described.

Though this leaves me with even more questions:
1) If the Multiplus is no-longer accepting AC Input from the generator and there are no other loads on the generator, why would it cause issues (this noise) when shutting the generator down?

2) What actually is this noise, what's going on inside the inverter here?

3) If I have to manually flip the generator breaker on/off, this defeats the purpose of having auto start/stop functionality? What am I missing here, there are for sure others who have a similar setup. My previous inverter charger (and old Trace) did not have any issues like this.

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alan hummingbear commented · Jan 31, 2021 at 12:41 AM

Maybe, while AC1 input is being ignored the multi is still dropping/syncing the output voltage to match? Even though it not connected it would still see the input.

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hummingbear alan commented · Jan 31, 2021 at 01:51 AM

In that case, what is the difference between cutting the breaker from Gen to Multi vs. shutting down the generator?

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alan hummingbear commented · Jan 31, 2021 at 02:36 AM

Turning off the breaker, drops the input while the genset is at its rated output. (230/50?)

Switching off the genset kills the engine which continues to turn the alternator at a lower rev producing a lower than rated output for a very short time before it drops to below the multi disconnect setting/shuts off.

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