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cres asked

MultiPlus II 12/3000/120-32 on small battery

1. Can MultiPlus II 12/3000/120-32 work with 12V 200Ah LiFePO4 battery if I limit AC charging current and max. battery discharging current to 100-200A.

2. What does 32A transfer switch means?

I want to boost generator output of 2.8kW to 4kW for occasional welding cause generator alone struggles with task.


3. Also I would like to know can Multiplus work without battery just connected to 12V MPPT controlled solar panels.

4. Can 48V Multiplus or Phoenix invert current directly from 41V solar panel (max. power voltage) without MPPT controller?

5. If I connect solar panels with 2nd inverter to MultiPlus II 12/3000/120-32, max. power of solar panel output would be 2400W at 25C or 32Ax230V (7.4kW).

Everything above is for off grid use, interested in Multiplus II cause of 13W power consumption and 12V cause in case of lifepo4 failure I can use temporary 12V acid battery.

Multiplus-II
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1 Answer
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Mike Dorsett answered ·

1) Yes, if you limit the loads and the battery current.

2) 32A transfer switch rating: This is the maximum current that can flow in the AC in circuit to the AC loads. The Peak load caused by a welder is very high, doing this boost is likely to exceed your battery current rating.

3) No, the inverter won't work with just the MPPT - there is not enough reserve capacity for current spikes, and the MPPT needs the battery to stabilise it's output. Whilst it might power up, the system would not be stable. The MPPT would also take too long to react to changes in demand, particularly when switching from Float to Bulk.

4) Again, no reserve capacity for the inverter. If the inverter load exceeds the power from the panels, then the system will collapse, also the inverter will see a variation in input voltage from Voc to below V max power.

5) The 2nd inverter would need to be a grid parallel type inverter...., again you would need to make sure the max charge rate from this does not exceed the battery's capacity.

Personally, I would go for a minimum of 24V battery voltage for this power level it makes the system so much more efficient - 1/2 current, 1/4 I^2R losses. It also gives the inverter more headroom. If you need an emergency battery, 2 smaller car batteries in series would also work. This would also allow you to use the full potential of the inverter, and run the welder without problems.

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