AC300: dual MPPT vs max Voc

I have an AC300, the manual mentions dual MPPT and parallel use of DC1 and DC2. I can’t properly understand the implication, please help me figure this out.

AC300 has:

  • Max 2400W PV input.
  • Max 150V OC.
  • Max 12Amps.

I have 6 loose Trina Vertex S 405W available for this project, in brief:

  • 405Watts peak
  • <42V (open circuit voltage)
  • < 12Amps
  • full spec available here

The AC300 user guide indicates max OC voltage of 150V. This means I can only plug 3 panels in series (126V OC).

Now, AC300 has this dual MPPT thing and a mention of “parallel” is made in the userguide.
The unit has two pairs of MC4 leads named DC1 and DC2.

Does it mean that:

Option A
I can connect 3 panels on DC1 and 3 panels on DC2?
In this case, there are two separate 126V inputs with about 1200Watts each, reaching the 2400Watts maximum PV input in a safe manner (voltage and current wise).

Option B
I can connect a total of 3 panels, like DC1 has 1 panel and DC2 has 2 panels.
In this case, I need an additional device like the D300S to handle the input and properly send a 120V/12Amps on each DC input.

Thanks in advance for the help!

Go for option A. I have the same AC300 setup and I ordered six 400 W panels (48 Voc each) to be installed as two sets of three in series. This gets 144 VDC at 10 A per MPPT input (1440 watts), although the AC300 will only take in 8 A for just 1152 watts, close to the maximum per input, or a total of 2304 watts at maximun solar power.

Hello Raymond,
Thanks. So I understand you confirm it’s safe to apply max 150V/1200Watts per DC input.
Well, time to try this out!

You mention the 8Amps instead of 10. What happens to the “unused” current - is the “surplus” generated by the panel “re absorbed”? Pardon the layman terms here, I just want to make sure the panels don’t “push” the extra current into a device that can’t accept this much.

The best analogy is water flow. Voltage is equal to pressure while current is flow. When you apply pressure to a hose, the diameter of the hose limits the flow. In an electrical circuit, the conductors (wires) and the semiconductors ( the name is a true meaning of what the electronics do) limit the electric flow or amperage.

In this equipment, the photovoltaic panels generate the pressure defined as voltage to move electrons across the circuit. The panels have their maximun flow defines in amps, for example 10 A, but the equipment does not need to have the same flow capacity. If the equipment only allows 8 A, the panels are held back and cannot push more through the conductors. The excess is never lost, just unused.

In an ideal condition we wish the panels to supply the maximum amperage that the equipment allows, but the panels must never reach the maximum voltage that the equipment can handle. The other point is that solar conditions are never ideal or even uniform or constant. So we recommend more panels to supply excess amperage but less voltage when the Sun is not at maximum. The AC300 dual MPPT ( Maximum Power Point Transfer) circuits are what limits the excess amperage yet get the maximun power possible transfered to the batteries.

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Hey thanks for making it easy to understand :slight_smile:

This now makes sense to me. Thanks again!