vonny232 avatar image
vonny232 asked

Use MPPT load output to drive battery protection opto/mosfet device


I have an MPPT 100/20-48v charge controller charging 2x 120Ah lead acid batteries in series. I want to drive an inverter (around 1000W) from these batteries to run a conventional fridge/freezer for X hours a day (with an Automatic Transfer Switch (ATS) to fall back to mains when the battery voltage falls below a certain threshold).

As we know, you must connect the inverter directly to the battery as the MPPT controller cannot supply more than 20A.

Problem is I dont 100% trust the ATS and I am very impressed with the MPPT load output features so I wanted to use the Automatic Load Disconnect of the controller to act as a fail-safe.

I had wanted to use the Victron Battery Protect (with remote control connected to the load output) to connect/disconnect the battery in the event of it becoming too low but I read this is forbidden.

I would have the ATS voltage threshold set to switch off and on the inverter mains at a slightly higher voltage to the MPPT, so in practice the fall-back device should not really be used unless the ATS fails.

Its odd such a "turn key" solution is not easily available for solar, as surely its a common requirement.

Dad reckons such a thing is feasible to make using an OPTO + heavy Mosfets and using the load output as a "remote control" signal to keep the battery connected, if the load output turns off, the Mosfets would disconnect the power.

Any advice would be appreciated?



MPPT ControllersBattery Protect
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1 Answer
vonny232 avatar image
vonny232 answered ·

Update - Rather than trying to disconnect the battery / inverter at the 24v side (which is admittedly heavy on any kind of relay and potentially damaging for the inverter) an alternative idea would be to use a relay to disconnect the inverter output at the 240v side.

i.e. use the BlueSolar Load Output to drive this relay, which would engage/disengage the live 240v output from the inverter.

And of course, this would only be the fallback. The ATS would also be monitoring the battery in parallel and would hopefully switch back to mains before this happens anyway.


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