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cedarm asked

Multiplus not respecting current limit

I live on a boat with a 13.5KW LiFePo4 battery bank with REC BMS, 4 SmartSolar MPPT, and a Multiplus 12/3000, and a Cerbo GX. Charrge control is via DVCC, controlled by my BMS. I use the AC input current limit on my Multiplus, which I adjust from the Cerbo GX, so I don't over-tax sketchy power pedestals on docks. It usually seems to work. It was working this morning in fact. Today I was running on our generator for the first time in a long time (it's been broken), and I would like to use AC input current limit so as not to overload the generator. However it didn't seem to be respecting the limit at all. Generator and shore power both use the AC-IN L1 terminals, they don't use seperate terminals, so it seems these should behave exactly the same. Does anyone have trouble shoothing ideas for why current limiting would sometimes work, sometimes not?


Any advice would be apreciated.



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MultiPlus Quattro Inverter Chargercerbo gxDVCCcurrent limit
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2 Answers
Alexandra avatar image
Alexandra answered ·

@cedarm

Is the generator overloading?

Sine wave and rms readings is usually part of the explanation.

Dirty sine wave usually comes from a generator. Plus all the other 'noise' and interference.

If you measure with a clamp meter to verify it will help. Then you have to tune specifically for that

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cedarm avatar image
cedarm answered ·

Thanks for the suggestion. I do have a clamp on RMS meter (Klein CL800), but not sure if that meter is suitable for measuring power quality.

The generator is a "Pure Sine Wave" inverter generator. It is not overloaded. It happily outputs much more than the 2100w and 12.6 amps pictured. (I guess the mismatch between amps and watts is because of the power factor of the load???). The issue is that it far exceeds the 8amp limit. It seems like the problem is shore power vs generator, but I"m not so sure. I think that might be red herring. I think it might have something to do with the fact that we only run our watermaker (very large inductive load) when we are away from the dock, on the generator.

I've been noticing some wonky behavior that perhaps I will post separately about. If the system load is below the current limit, the Multiplus works in "Ext Control" mode as expected (I think this shows up because of DVCC?). If the system load is well above the current limit the Multiplus works "Assist" mode as expected.

All that is fine. The trouble starts when the system load is very close to the current limit. The Multiplus seems to rapidly switch between "Assist" and "Ext Control" modes, and the AC system voltage is very unstable, and I can hear clicking from the Multiplus.

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JohnC avatar image JohnC ♦ commented ·
@cedarm

That last paragraph is a clue. Bear in mind that Assist mode has a minimum A that it can apply. I looked up yours and it's 1.5A. So that 1.5A switching might explain the instability. The genset might be struggling to keep up with such, then the Multi rejects the power, hence the clicking.

If you haven't already, enable Dynamic Current Limiter in the Multi, this should soften it down. Most gensets need this.

Could be something else too. I've even seen a dicky gen power cord cause similar.

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cedarm avatar image cedarm JohnC ♦ commented ·

Thanks you for the reply. I'm desperate to enable Dynamic Current Limiter, I feel like it might solve some of my issues, but the Fischer Panda manual specifically warns against enabling this setting. I must say their explanation of why not to use it makes no sense to me. Here is what the manual says.

Dynamic current limiter must be deactivated.
With inductive load the dynamic current limiter will raise up the Voltage in the DC circuit. These over voltage can damage or destroy the PMGi.

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