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Multiplus as ac charger

Hi, I have 3-phase off grid with 3x Multiplus 15k supported by 80kWh of BYD LVS and 40kW solar through multiple MPPTs. All works great. I want to extend to use the 3-phase as ACIN to 3 more MP15k with ac- coupled solar on the output and more BYD LVS as battery. I'm sure this is all good too. But, here's the twist, I want also charge the new batteries from an ac source. The plan is to add another MP15k just to charge the 2nd set. Problem is, the BYD BMS is connected to the 2nd Cerbo controlling the 2nd set of MP15k. So how to control the charging? I am thinking it's OK to use a BNV and shunt, just for the charger. And maybe take a switch off command from the Cerbo at 90% SOC. Bit is there a smarter way to do this? If the charger was a MPPT it would work easily enough, but because it's a MP2 I don't think the carbon can recognise it as a charger. Any good ideas?

Multiplus-II3 phasemultiple inverters
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Alexandra avatar image
Alexandra answered ·

@DavesOffGrid

Since BYD have two different settings for off grid and on grid, setting it correctly and leaving it to work on voltages will be fine.

BYD measure their own SOC and current in and out so measuring SOC with a shunt is not entirely necessary for that.

What you can do is remote switch off the MP2 used for AC charging from the Cerbo relay. If you really want to you can switch on has DC system and add a shunt as a DC meter to measure what it is contributing (and that way the system will know what is coming in as well).

With the two different voltage settings though overcharging won't be an issue.

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davesoffgrid avatar image davesoffgrid commented ·
Hmm, my interest is the control of the charging, rather than monitoring. The Cerbo on the 3-phase system is capable of controlling the charging because it has access to the BYD BMS. But the Cerbo cannot also control additional chargers (unless they are MPPTs). So how is it best to control the ac charging when the Cerbo already has 3x MP2 connected for discharge?
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