BatteryProtect needed with smart LifePO4 battery?

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trougnouf asked Jun 20, '21

BatteryProtect needed with smart LifePO4 battery?

Is the BatteryProtect needed/useful with the smart LifePO4 battery?

Does the battery itself stop sending current when its voltage is too low?

The battery itself has an "Allowed-To-Discharge cell voltage" setting, the manual says "As soon as one of the cells reaches this voltage, the BMS will disable all loads by sending a signal to the load or to the load disconnection device.".

I don't understand if the battery is smart enough to stop sending power to devices once that voltage is reached, or it (and the VE.Bus BMS) needs a "load disconnection device" that acts like a switch between the battery and the load.

A standard load wouldn't care about a stop signal, unless that signal was a complete lack of current.

I often see the BatteryProtect in schematics but it seems the battery with the (VE.BUS BMS which is directly recommended) may already be equipped to protect against under/over voltage.

Lithium Battery Battery Protect ve.bus bms

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Matthias Lange - DE answered · Jun 21, 2021 at 03:53 AM

I guess you mean the Victron Smart lithium batteries. For those you need ab external BMS.

https://www.victronenergy.com/battery-management-systems

The BMS will give you a "charge disconnect" and "load disconnect" signal. The battery itself will not cut-off.

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trougnouf commented · Jun 21, 2021 at 08:47 AM

Yes, but I then also need something between the battery and the load which takes the "load disconnect" signal from the BMS, like the "BatteryProtect", right?

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Answer 1 · 2021-06-20T23:30:46Z

trougnouf answered · Jun 20, 2021 at 11:30 PM

From reading the VE.BUS BMS manual it seems that the feature is indeed only meant for devices that obey the disconnect signal, so I do need to put a BatteryProtect between the battery and the "dumb" loads.

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Answer 2 · 2021-07-01T10:13:56Z

drlbradley answered · Jul 01, 2021 at 10:13 AM

Still building mine, but I have a VE.Bus BMS, and then a Battery Protect on the load side, and a Cyrix Li-charge (CYR0101240430)on the charge side of my system, both of those taking their disconnect signal from the VE.Bus BMS.

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