Builiding of a complete 6kW PV inverter with MPPT chargers


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-dex-
Regular Member

Joined: 11/01/2024
Location: Poland
Posts: 86
Posted: 08:18am 02 May 2024      

I tested another MPPT again, with the same diodes as before (I had nothing to do, waiting for new ones   ) and with set of small batteries. Up to about 1.5 kW everything was fine, then my wife turned on the dishwasher and the total consumption was about 2.5 kW. Then MPPT went BANG BANG - it got damaged, but unlike before, it made it even worse - only the mosfet is shorted. This means full voltage from the  pv panels on the bus bars - ~100V. Good thing I was nearby and managed to disconnect the batteries, because they were already starting to bubble.

I see a pressing need for another layer of protection - against too high voltage from a shorted MPPT. Need to protect it when LifePo4 nominally ~51V receives 100V and is charged with an uncontrolled current and the voltage increases. There would have to be a circuit that measures the voltage on the bus bar and, for example, above 65V it disconnects additional the serial relay


The lifepo4 battery has a BMS from JK model 200A, but it will not survive when it sees 100V DC at the input, the inverter may also be damaged. It would be best to disconnect the PV inputs, but a good gas-sheathed DC relays (4 pcs for mine) are expensive. So perhaps a good solution would be to disconnect the entire MPPT group. I just don't know what in situation where one MPPT fails, and send high voltage to rest MPPTs outputs  Maybe we should also disconnect 12V from them, when one mppt fails.




Edited 2024-05-02 18:31 by -dex-