What is the Maximum charge current from grid inverter to battery with a MultiPlus II 5Kva.

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gavin asked Aug 20, '22

What is the Maximum charge current from grid inverter to battery with a MultiPlus II 5Kva.

We have 10Kw of lithium, 6.6Kwp solar connected to a fronius 5Kw grid inverter on AC out of a MultiPlus IIGX for offgrid use. We often see the fronius being ramped down and don't know why.

The maximum charge current is about 50A, which is about 3200W. SOC is under 80% and battery temperature is not the problem(CCL 89.6A). The frequency ramps up and down with load as expected, but charge current is around 50A. Communications with the BMU is working and DVCC is on. I tried setting Limit charge current to 89A, know effect.

Multiplus-II

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Answer 1 · 2022-08-20T06:29:09Z

David answered · Aug 20, 2022 at 06:29 AM

70 amps is the limit.

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Answer 2 · 2022-08-20T06:48:21Z

gavin answered · Aug 20, 2022 at 06:48 AM

At 54 volts X 70 Amps should be about 3700W. Why is it being throttled.

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Answer 3 · 2022-08-20T07:33:36Z

nickdb answered · Aug 20, 2022 at 07:33 AM

Have you factored in the losses for AC/DC conversion from your PV inverter?

Also consider that at full conversion the multi may well derate a bit with temperature 70A is rated at 25C.

It's a warmer climate here, I've never seen 70A sustained.

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Answer 4 · 2022-08-20T07:48:26Z

gavin answered · Aug 20, 2022 at 07:48 AM

I have seen 70Amps with the generator on AC in, but not on the grid inverter which is on AC out. If the frequency is above 50Hz, there is more power that can be produced, so why is it throttling the grid inverter? Its winter here with day time around 15degC.

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Answer 5 · 2022-08-20T08:02:21Z

jeanmarie answered · Aug 20, 2022 at 08:02 AM

One possibility could also be the BMS that is sending a Charge Current Limit (look at the parameters of your battery in GX interface)

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gavin commented · Aug 20, 2022 at 11:10 AM

CCL at that temp and SOC is 89.6Amps.

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Answer 6 · 2022-08-20T12:49:29Z

johanndo answered · Aug 20, 2022 at 12:49 PM

220A for a 12V Quattro 5000.

Don't you read your data sheets / user manuals?

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Answer 7 · 2022-08-20T13:45:08Z

Alexandra answered · Aug 20, 2022 at 01:45 PM

@Gavin

Charging batteries from AC PV is less efficient than DC PV; so heat becomes a major factor here. So probably derating from that.

Also weak AC? If that is enabled it has an effect.

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