Charge rate with Mutiplus and solar (MPPT)

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grizlyadams asked Sep 14, '23

Charge rate with Mutiplus and solar (MPPT)

Hi,

I have a Mulitplus 2 inverter charger 12/3000/120 which has a maximum charge rate of 120amps.

That's hooked up to a 560ah lifepo4 battery with rec-bms Victron integrated BMS. I also have a MPPT 150/100 with approx 1kw of solar panels. Connected via a cerbo GX

All fitted to my RV.

Question is, I have the BMS set to a charge rate of 250 amps (a little less than the 0.5C rating of the battery) and the input to the Multiplies is set to 16amps.

If I start the generator (5.5kva) and the solar is generating 20amps of power I only ever get 120 amps going into the battery (well, about 115 in reality)

I get that the Multiplus is a 120amp charger but surely I should get 140 amps going into the battery in the above scenario?

Why does the cerbo limit it to the multiplus rating and not what it set by the BMS?

When I look at the parameter for the rec-bms in Cerbo i see the CCL set as 120a but I don't understand where that is being set or how to change it..

Multiplus-II

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Modifications Space

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Answer 1 · 2023-09-15T04:55:32Z

kevgermany answered · Sep 15, 2023 at 04:55 AM

Usually a BMS connected to the Cerbo will supply it's own values which will control the system and override any other settings. If this BMS is not supported, results are unpredictable.

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Answer 2 · 2023-09-15T05:12:51Z

nickdb answered · Sep 15, 2023 at 05:12 AM

As stated, the CCL you see on the GX is sent from the BMS over CAN, the GX is just doing what it is told. This is what appears to be set in the BMS and Victron has no control over it.

It appears DCL was only set to 250A, not the CCL. The settings would have to be determined by the battery specs.

It is an unsupported combo so you would need to consult the manufacturers.

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Answer 3 · 2023-09-15T13:41:40Z

grizlyadams answered · Sep 15, 2023 at 01:41 PM

Thanks all for the response - I knew that the Cerbo got it's setting from the BMS (and the parameters show are from the BMS) but I didn't have a clue how to set it on the BMS - it's not intuitive at all. I can see in the REC-BMS documentation that there are (many) parameters but there's no reference how to set them, specifically the "MAXC" parameter (max charge rate)

Anyway, I had a reply from REC-BMS and they told me how to set the individual parameters - pasted below for anyone else with the same question.

"It's coming from the BMS, that is its default value when programmed. When you have the BMS connected to the Cerbo it follows the settings set by the BMS. In case the CAN communication between the two would be lost, Cerbo would then go by its internal settings.

To change this on the BMS, use the BMS Control software. Under the BMS tab there click Communicate (BMS software has to be unlocked for it to be available). Set the "Send to Address" to 2, Send Message should be "MAXC 250" and then press Query (see picture below). MAXC is the command for Maximum Charge Current and 250 is the value in Amps.

In case you would also like to change the discharging current, the command is MAXD."

As I said, not exactly intuitive, but easy once you know how.

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