# Is there a way to "convert" a Multiplus 12/1200/50 to 24/1200/25?

Hi there, we have an exisiting 12 V system with Multiplus 12/200/50, MPPT 75/15, BMV700, and two Lead-Carbon batteries (in parallel). We are currently investigating the options to raise the DC-Voltage level to 24 V. MPPT and BMV should accept that easily, batteries could be wired in series - but how about the MultiPlus? Is there any way to "convert" that to a 24/1200/25-configuration (by dip-switches, software configuration, or whatever)?

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Matthias Lange - DE answered ·

No this is not possible. It is a hardware limit. You have to buy a 24V Multi for that.

Also have in mind that the MPPT needs a PV voltage 5V higher than the battery voltage to start charging.

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Hi Matthias, many thanks for your quick answer and valuable information. Regarding the MPPT minimum PV voltage: We have one PV panel only, which has ~25..30 V when sun is shining (see VRM plot below). Would you consider that critical?

vrm.png (56.7 KiB)

Not critical.
But I think you will lose some yield.

With a 24V system you will have likely a idle voltage of around 25.0-25.5V.
So you will need a PV voltage of at least 30V before the MPPT will start charging.

The absorption voltage of that system will be around 28.8V so there is not much space to the 1V difference needed to continue charging.
If there comes a cloud or so the voltage will drop below that 1V difference and will stop charging.
But because the battery voltage is still high (it will drop slowly) you will need a higher PV voltage to start again.

If possible you should add another identical panel in series to double the PV voltage.