How to prevent the UPS from charging the battery?

Question

Do it yourself

I want to try a LiPo battery in an uninterruptible power supply. I know that it would be correct to charge such a battery with a balancing charger. There is such a device, it works from 12-14 volts.
The task arose - an uninterruptible power supply should work from the battery terminals when the mains power fails, but it should not be charged through these terminals when the power is restored.
The Internet explains that using a diode is inefficient due to voltage drop and high power dissipation. Suggested here https://www.youtube.com/watch?v=IrB-FPcv1Dc using MOSFET may not be suitable. Or fit?
How can you arrange so that the battery is only discharged over the same wires, but in no case is it charged? Making changes to the UPS board is not considered, it's too complicated for me.

Answer 1

relay maybe? switching speed is not needed

Answer 2

The proposed scheme is quite suitable, you just need to pick up a powerful P-channel MOSFET. The charge level control built into the UPS will not work, because. LiPo has slightly different voltage levels than lead. The UPS can drain the battery up to 7-8 V. If you put a battery of three cans (12.6 V fully charged), then when discharged, the voltage can drop to 2.3-2.6 V per can - for LiPo this is death. Therefore, overdischarge protection is needed.

Answer 3

You can use an ideal diode
tqfp.org/circuit-design/idealnyy-diod-na-mosfet.html

Answer 4

For starters, you would publish the exact model of the UPS and the battery, since each UPS is designed for native batteries and it’s not possible to simply insert the first one into it - both the charge circuit and the discharge circuit will fail, and because of this, on most modern UPSs, the controller is simply will not assemble a working circuit, because receives conflicting data about the battery, and in this case it is easy to kill the battery by overcharging / overdischarging. It is necessary to look at the diagram of a specific UPS whether it is possible and how to convert it to another battery.

Answer 5

you can pick up a fairly powerful diode with a minimum voltage drop, BUT you still SHOULD NOT indulge in circuits not designed for LiPo. LiPos also do not like high discharge currents, at which they can fail. On the model, when a short circuit in the engine control circuit, the battery also warmed up quite a bit, melting the packaging and the seat to a light haze.