polarseal avatar image
polarseal asked

Battery protect with Lithium

Has anyone used a Battery protect with a non victron lithium battery? The batteries would have internal BMS with no external communication capabilities. Could a person set switch/relay from a BMV or Venus (once the virtual switch update comes out?) to control the battery protect?

Lithium BatteryBattery Protectsafety
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2 Answers
Anil Ghatikar avatar image
Anil Ghatikar answered ·

Yes I tried to do it a while back for a 10 KWh(5 Kwp) Lifepo4 witha 5 KVA quattro . The Battery protect does not allow the inverter power on showing a short circuit due to inrush charging current of the quattro.

However, I am using BP100/48 with a 800/48 Multi without any issues The BP gets switched(<20%) off on LOW SOC using BMV 702 . Mainly the reason is I already had BP and BMV 702 and did not want to spend to upgrade to BMV 712 ( recommended for Lithium due to low current)

But after playing around with the system with various combinations I realized that Most Lithium batteries need a BMS to properly balance and monitor the battery cells and most BMS have a LOW/High Voltage, SOC and short circuit protection making the investment in BP redundant.

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nebulight avatar image nebulight commented ·

Correct, you shouldn't connect an inverter to a contactor or Mosfet due to the inrush current. Also the for the battery protect, current should only flow in one direction so if the Quattro is setup to charge, you're probably going to damage the BP. If you have an external BMS with two signal (charge and discharge signals) you should wire them to the Quattro and program a two signal BMS assistant.

And the BP isn't redundant in my opinion. It can be used for disconnecting DC loads when a BMS triggers a low voltage alarm. It can also be used to disconnect dumb charge sources that don't have on/off abilities for a high voltage alarm.

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nebulight avatar image
nebulight answered ·

How would you want it to be controlled? What parameter would you want the BP to turn off or turn on at? Maybe you can use the BMVs internal relay to trigger the bmv to shut off the BP.

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polarseal avatar image polarseal commented ·

Exactly- If i set a high/low voltage and temperature alarms on the BMV could the BMV relay control the BP? I just want to ensure that everything i would need with regards to the BP is there and capable of doing this? Alternatively, if i could connect it to the Venus GX which would have the same information, it may be better as the Venus would also have information from the Charging side of the system.

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nebulight avatar image nebulight polarseal commented ·

The only problem with using the BMV is it only has one relay. And if you are going off the high or low voltage of the BMV, it doesn't take into account single cell voltage (which is what your BMS should handle). However since you have no external communication then you are kind of stuck. If your BMS internally will handle high and low voltage disconnects, then you could use the BMV for temp monitoring since I assume you are asking because the BMS doesn't handle temp? I'd just set the temp low and high settings on the BMV (Settings/Misc/Aux Input = Temp). Then go to Settings/Relay/ and set your high and low temp settings.

This is how I plan to setup temp monitoring to prevent charging below freezing. However I have an external BMS and I'm going to run my charger disconnect wire through the BMV, then to a Battery protect. Since the battery protect is a mosfet you should only have current going in one direction so it's going to turn off the battery protect (which my solar controller battery side is going through) and it will also turn off my DC to DC charger (from the alternator) and to the multiplus.

At least that's how I plan on doing it.

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