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justmurph avatar image
justmurph asked

Multiplus 5k ignores input current limit with power assist

I have a Multiplus 24/5000 that I am using to run the dive compressor on my boat (2.7kw) and a Honda 2kw generator connected to the AC1 input to provide the power when solar doesn’t keep up.

The Multiplus runs the dive compressor (3 phase motor driven by a single to three phase VFD) easily on its own.

When I’m not running the dive compressor, the multiplus honors the 8.5A input current limit I’ve set, however when I fire up the dive compressor it seems to ignore that limit and will try and pull all of the power from the generator, with little to no power assist.

Running the compressor at full speed the generator will overload and trip. If I lower the compressor speed with the VFD I can get it to a point where the genny can just keep up at around 10A, with the multiplus saying it’s assisting by maybe 200W on top of the 2000W from the gen. It's not ideal running the compressor this slow.

So it appears that power assist is doing a little bit, but no where near enough and the input current limit is being ignored. I can turn the input current limit right down to 4 and the behaviour doesn't change at all.


The minimum input current limit for my 5k is supposed to be 3.9A and I’m on firmware 430. Any ideas?

MultiPlus Quattro Inverter ChargerGeneratorpowerassist
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4 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

I don't think you can load you 2kW Honda with a 2kw inductive load.
Take a look in the manual/datasheet of the generator.

I guess you have to lower the input current more to 6-7A.

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justmurph avatar image justmurph commented ·

I've updated the original question to be a bit more clear.

That is exactly the point. The multiplus ignores the input current limit. I can lower the input current limit to 4A and it doesn't make any difference to the behaviour, the Multiplus just ignores it and puts almost all of the load to the generator. It does say it is assisting, but not by much (maybe 200W).

When just charging, will limit the load on the generator to whatever I set. It's only when you have a larger AC load that it ignores the input current limit.

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ justmurph commented ·

First you should try to update the firmware to the latest version. 430 is about 3 years old. The latest version is 481.

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psp-maxi avatar image
psp-maxi answered ·

Hi justmurph,

may i ask you what type of dive compressor do you have? and what type of VFD?

I have 2x Multiplus 3000 in parallel and the dive compressor companie BAUER say, it is not possible to start the BAUER compressor with 2KW in this setup.

Thank you for your help

Thomas

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justmurph avatar image justmurph commented ·

It's a Bauer Junior II, which I've swapped to a 3 phase motor and a single to three phase 3kW Siemens V20 VFD. Before this I tried to make it work with the single phase motor using an adaptive soft starter, but the startup current was still too high.

The setup with the VFD works brilliantly, but there is a bit of a loss of efficiency.

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justmurph avatar image
justmurph answered ·

I've updated to firmware 481, no change.

What I've worked out is that it seems to be an issue with how the multi measures the input current when the load is highly reactive, as it is here with the VFD. When I put a 2kW resistive load on, the multi will limit the input current to whatever I set.

Interestingly, with the input current set all the way down to 4A, and the compressor turned down the point where the generator juuuuust keeps up (about 11A input current), if I plug that 2k resistive load in as well as the compressor (now 4kW......but less reactive) the multi now pulls less current from the generator (8A).

So....where to from here?

- I'm guessing that there is no settings change that will make it work.

- Is this something that could be fixed in a future firmware, or is this a hard limitation of the hardware in the multi?

- Maybe with a front end harmonic filter on the VFD I can get the power factor up to point where the multi can control the input current. That's an expensive test.

Any help is appreciated. :)


A few figures:

AC IN

V = 232V

I = 9A

Real Power = 1550W

Apparent Power = 2088W

Power factor = 0.74


AC OUT (including ~200W of power assist)

V = 232V

I = 12A

Real Power = 1750W

Apparent Power = 2784W

Power factor = 0.62

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·

Hm... I think the bad power factor could cause that problem but I never done something like that.

I don't think this can be solved with a software update, I guess it is a hardware limitation.

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cjhwhite7 answered ·

I have had this same issue with Air Con, also a compressor basicly.

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