question

pekkaj avatar image
pekkaj asked

Is external BMS needed for battery with internal BMS?

Is it safe to regularly (every night) drain a lifepo battery having internal BMS by running a 12V device? Or does external Victron BMS add something to the system? For AC output I have Multiplus II which can protect battery, but for 12V only a fuse block.

BMS
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4 Answers
kevgermany avatar image
kevgermany answered ·

External BMS adds nothing if the battery has an internal one. They may not work well together, either.

Make sure the battery is sized to handle the overnight loads, but it's safe to leave them on. Worst case is the battery's BMS cuts the supply.

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nickdb avatar image
nickdb answered ·

Victron BMS's are for Victron smart batteries, they aren't intended for any other purpose.

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klim8skeptic avatar image
klim8skeptic answered ·

@pekkaj For AC output I have Multiplus II which can protect battery, but for 12V only a fuse block.

For the multi, please ensure that you set its low voltage cutout to shut the multi down before the battery is discharged and the BMS disengages the battery.

Likewise for the other 12v loads, use a Battery Protect (or something similar) to cut power before the battery is empty.

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pekkaj avatar image
pekkaj answered ·

Oh, sorry I mixed up Battery Protect with BMS, so they are different thing. So I should use Battery Protect for 12V output even with battery build-in BMS?

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klim8skeptic avatar image klim8skeptic ♦ commented ·

@pekkaj you are better off for the loads to be disconnected from the battery, before the BMS cuts all loads and chargers due to low voltage.

Waking up a battery when the BMS has shut down requires extra effort.

What procedures does your battery require to re-enable charging?

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