question

stefanh avatar image

Lithium Smart Batteries protected individually?

The Lithium Smart battery range require an external BMS and low/high voltage/temperature protection. We are looking at connecting 4 x 200Ah batteries in parallel. However if you use 1 x smallBMS and daisy chain the leads, then if 1 battery in the bank has a fault, the BMS will shut down the batteryProtect and no power will be available.

Is it possible to add a smallBMS and some BatteryProtect/Cyrix devices to each battery to create what is similar to a superpack. The pack would have a separate charging and load connector.


Note: Superpack batteries will not fit in our enclosure.


The following image is taken from the battery protect manual.

If we assume the following:

- "Battery Charger" is a RED keyed Anderson for charging input

- "DC Load" is a GREY Anderson connector for load outputs

Would it be possible to connect 4 of these in parallel. Or would the main 220A Battery protect have to be changed to a Cyrix module as there may be reverse current connecting the batteries in parallel.

The BatteryProtect manuals state: Caution: uncontrolled reverse current will flow through a Battery Protect if Vout > Vin. Therefore never use a Battery Protect for battery to battery charging.

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This way, if one of the packs fails and the BMS switches one off, then the other three would still be able to function.

Battery Protectbattery
1612751040211.png (174.8 KiB)
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4 Answers
offshore avatar image
offshore answered ·

Hello Stefan,


I asked some weeks ago the same question, because I really don't like, that when one single batterie fails, the complete bank fails. On a boat for example, it can never be installed this way.

I was told that there is no solution. Not even the Victron small BMS on every battery should work. I don't know why this shouldn't work.


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stefanh avatar image
stefanh answered ·

Thanks for your response offshore. Hopefully someone else can answer and guide us correctly.


I have created a diagram so that there is no confusion.


My concern is the Load Battery Protect might receive some reverse current when connected to the bus bar. So should these be replaced with Cyrix-Li-load?


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The Cyrix-Li-load will disengage when its control input becomes free floating. If the battery voltage recovers after disconnection (which will happen when no other loads are connected to the battery), the output of the BMS will become high and the Cyrix will reengage after 30 seconds. After 3 attempts to reengage, the Cyrix will remain disengaged until battery voltage has increased to more than 13 V (resp. 26 V or 52 V) during at least 30 seconds (which is a sign that the battery is being recharged). Alternatively, a BatteryProtect can be used (advantage: very low power consumption).




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offshore avatar image
offshore answered ·

Hi Stefan,

"my concern is the Load Battery Protect might receive some reverse current when connected to the bus bar. So should these be replaced with Cyrix-Li-load?"

I would say this is no problem, the load Battery protect is perfect for this case, because it is unidirectional and only allows current to pass in one direction. (so for Charge protect you only have to reverse the IN & OUT)


What kind of charging sources do you have? For example, if you have an inverter with a charging option (Victron Quattro), I don't know how to connect it, as it is both a load and a charger.


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stefanh avatar image
stefanh answered ·

The battery protect only likes current flowing from the IN terminal to the OUT terminal. When the batteries are connected to the bus bar, even when all fully charged there will be some differences in voltages and each pack attempt to balance. ie some current from Battery Pack 2 could flow into Battery Back 1, which is in the opposite direction preferred by the Battery Protect.


Datasheet states: * The BatteryProtect is not designed for reverse currents from charging sources

Manual states: Reverse currents from OUT to IN terminals are strictly forbidden, and will damage the device

Caution: uncontrolled reverse current will flow through a Battery Protect if Vout > Vin. Therefore never use a Battery Protect for battery to battery charging.


Charging will not be a problem as the battery packs will be swapped out as needed and charged elsewhere with a mains charger with no load connected, using the red charging connector through the second Battery Protect.

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Is in the big battery protect 220 not a big diode? I thought it can only let the current go in into one direction but maybe aim wrong.

When charging will not be a problem, why are u not using some other kind of relay and then this solution should be ok for you.