Multiplus II generator charging problems

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jdenergy asked Apr 16 2024 at 2:54 PM

Multiplus II generator charging problems

Hi,

I've a 20kW battery pack including 2x multiplus II inverters, only one is used for charging and inverting to and from the batteries, and the other one only converts to 230VAC.
A machine including a PLC is powered by the Multiplus II (sensors and a CAN-bus system are inside).
It is an off-grid machine and to charge the batteries I use a generator capable of charging 4000W continuously.
The problem is when the consumption is higher than the continuous charge limit, the Generator stops working and the machine gets a power dip. It looks like it takes a few milliseconds to change to the batteries instead of the generator. According to the Victron expert, it should not be an issue at all, the multiplus II should change the operations of charging to inverting within a quarter sinus. It should be so fast the machine can not recognize the power dip.
Does anyone have an idea to solve this problem?

Thanks in advance!
Kind regards.

Multiplus-II battery charging Generator

2

Alexandra ♦ commented · Apr 16 2024 at 7:20 PM

To clarify here.

One inverter only ever inverts from battery to loads? This is the unit where the power dip is happening on the AC output?

The other inverter is charging only nothing on its output?

And the two are not combined on the ve bus at all?

And a Victron is not a certified UPS which is what it seems you actually need there.

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jdenergy Alexandra ♦ commented · Apr 17 2024 at 7:00 AM

So there are two inverters connected to the battery separately.

Both are connected to a BMS Master LV and behind it are the batteries.
Normally the machine consumes only power from the batteries and supplies the power to two separate machines (the machines need to work together), but sometimes the machine must be charged during operation.
To charge we use the generator connected to one multiplus inverter that is connected to the AC In and Out at the same time when there is a peak consumption from the machine the generator stops (the input current limit is already set to 17A, that means 3910W).
Still not the 4000W continuous power supply that the generator can handle, the max peak supply is 6500W.

The multiplus that is connected to the generator is also connected to the VE.bus.
This design is setup together with a big victron dealer.

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Answer 1 · 2024-04-17T03:55:22Z

JohnC answered · Apr 17 2024 at 3:55 AM

Hi @JDenergy

This should be seamless.

You say "Generator stops working", what's that, an overload? Set an Input Current Limit in the Multi to stop that happening. Power Assist (if you haven't disabled it) will pick up any deficit by adding inverted power to the genset's. Enable Dynamic Current Limiter to soften the effect of any harsh load changes on the genset.

I'm still curious why there's a gap in the power anyway, might be in the way the genset trips. The questions @Alexandra asked are relevant, also are you running other things like ESS?

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Alexandra ♦ commented · Apr 17 2024 at 4:27 AM

I was wondering why it would need to be seamless if one inverter is not switching to and from the generator? If it is straight inverting then it suggests that when the other inverter drops the generator the battery voltage is sagging suddenly. Maybe that is the issue.

So obviously I am keen to know are they two separate systems or one on the ve bus. And yes what do you mean the generator stops working? Hopefully also the generator capable of running 4000w is not actually a 5kva?

@JDenergy

Definitely not enough of the information needed here to troubleshoot. More is needed.

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jdenergy commented · Apr 17 2024 at 7:08 AM

The input current limit is set to 17A, the Power assistant is enabled boost factor 2.0.
The dynamic current limiter is enabled.

The generator is tripping, it looks like too much power is requested by the inverter, and stops the power supply. When this happens the machine stops, it looks like a power dip.
I replied to an earlier comment as well for more information.

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JohnC ♦ jdenergy commented · Apr 17 2024 at 8:56 AM

@JDenergy

You'll really need to measure these things, guessing isn't enough. A GX device and VRM useful for this.

For what it's worth, my guess is that your genset can't handle the set A. Gensets aren't created equal, nor is W equivalent to the VA they're usually rated at. Some grossly disappoint at reaching spec values.

The Multi set at 17A Input has a safety margin, and I wouldn't expect to see more than 15-16A allowed. Try setting it much lower as a test, and work up.

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Multiplus II generator charging problems

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