BMS Switch

[Ljbezuidenhout]

Hi. I have just built a 120Ah LifePo4 battery using 4 cells with a BMS, which is all fitted into a battery box to be used for camping. I don't want to have to open up the battery box each time I want to disconnect the BMS when putting it into storage or unplug and plug in the balance leads too often. Is it possible to put a switch onto one of the balance leads and mount this switch on the outside of the battery box, to be able to "disconnect" the BMS via the switch? If it can be done, which balance lead cable would the switch need to be installed on? Thanks

 

[AussieSim]

I'm a newbie, but this might work

 

[Ljbezuidenhout]

Thanks AussieSim. I get the idea of this, but it isn't going to achieve what I'm wanting to do. The BMS I have has bluetooth and hence draws current from the batteries whenever the BMS is connected via the balance leads. Having a circuit breaker on the positive charge/discharge cable (as in the video you linked) will mean no current flows to or from the battery, but does not "disconnect" the BMS from the cells. I am trying to achieve a disconnect of the BMS from the cells, in order to stop any current draw whilst the battery is in storage.
I would think that putting a switch on the final cell positive or oven first cell negative balance lead, would achieve my objective, but not 100% sure.
Any further ideas would be appreciated.

 

[HRTKD]

This was posted in OverKillSolar's reddit area:

FYI I measured the current going to the Bluetooth dongle and found. .003A when connected and LED on and .0003A when disconnected.

That's a rather small draw. Not enough for me to worry about, but I'm going to have my solar connected all the time.

 

[Pierre]

One should be able to install an externally mounted switch that will interrupt the black (-ve) wire of the balance wire loom.
I have never done it but try. This should switch the BMS off.

 

[Ampster]

One should be able to install an externally mounted switch that will interrupt the black (-ve)

That is a good suggestion but each BMS is different and some may draw from more than one cell.

 

[MrNatural22]

Ok now th

That is a good suggestion but each BMS is different and some may draw from more than one cell.

Don't know if it makes a difference or not but on the Overkill 8s BMS BT programming you can turn the balance function off.
But you would still have .0003a draw from the idle BT module.

 

[Fred S]

Something to verify: If you disconnect the bms from the battery, upon reconnecting you many have to "activate" it again to power it up. My cheap ANT bms is activated on a separate set of 2 wires.

 

[Pierre]

Something to verify: If you disconnect the bms from the battery, upon reconnecting you many have to "activate" it again to power it up. My cheap ANT bms is activated on a separate set of 2 wires.

Not required for the DGJBD.

 

[Ljbezuidenhout]

One should be able to install an externally mounted switch that will interrupt the black (-ve) wire of the balance wire loom.
I have never done it but try. This should switch the BMS off.

Thanks Pierre, this is what I was thinking of doing. But too scared to try it Based on other comments, it appears that the bluetooth current draw is so small, it shouldn't cause any issues to just leave it connected, even for many months, so I will probably just do that.
PS.. Nice to see another member from ZA