by ENERC » 26/10/19, 19:33
If the batteries are 150AH as shown in the diagram, in fact it works normally.
I will try to explain why:
- a lead acid battery has a high electrical resistance. If you charge too much current, the voltage rises. The value is equal to the battery voltage plus the voltage due to the load.
- If you charge too fast, the voltage rises quickly to 57V, and the MPPT then believes that the battery has finished its absorption.
- the MPPT then puts the battery in float. And therefore zero current.
As a reminder, the load is like this:
Bulk (up to about 52V) -> Absorption (57V) -> Float (50 V)
The Bulk must be at C / 10 maximum, 15A for a battery of 150AH. 15A in 48V is 720W. Never again if you will destroy the batteries. It's because you send too much current that the batteries dry up.
So set the MPPT to send the maximum 20A in the batteries.
On the hybrid inverter side, the electrical resistance works in the other direction: the voltage at the battery terminals is the no-load voltage minus the loss due to discharge. So if you draw more than C / 5 (30A at 48V -> 1500W, the inverter considers that the battery is completely discharged since it sees its voltage well below 48V).
Conclusion: it works normally for 150AH batteries under 48V.
If you want more power, there are two solutions:
- either batteries much bigger (to feed a house it is necessary between 500AH and 1000AH - thus 4000 with 8000 € - ouch- 1000AH in 48V for plates of cooking and water heater)
- or use an inverter on which the panels are connected: in this case the current goes from the panels to the house without going through the batteries.
The advantage of hybrid inverters is that they take the juice off the grid when there is not enough sun or too much battery power.
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