6S BMS question

[SentinelAeon]

Hey, i am using the BMS 6S from the attachment (model of BMS if it helps is hx-6S-a06). I like this BMS. But there is 1 problem. The scheme how ur supposed to connect it is in the attachment. Till now i built several packs like this but today it got me thinking. Do you see that + and - are connected to their respective pins on board ? Well today i didnt connect any wires to B+ and B- and P+ and P- still gave me 25.2V. So i am thinking, is it possible that if u connect + of the pack to B+ and - of the pack to B-, that ur actualy ignoring the whole BMS and u do not get the protection ur supposed to ?

 

[audioguru]

You have extra wires to what I found in Google:

 

[SentinelAeon]

Thank you for finding this. But i am still not sure. It says B+ on the board and also B+ on the red wire coming out from the connector. If i understand the left picture, then the right picture simply connects to B+ 2 times, which is just fine ? My friend also said, it might be so that it can handle more current (2 connections).

Anyway, this is the downside of buying cheap chinese stuff. Even though i really really like this BMS. But anyway i decided to do a test. I would like to see if the low voltage protection kicks in in both of this cases:

1) when i connect exactly like it is connected on the right image that you attached

2) when i only connect the wires but do not connect to B+ and B- pin on board a second time.

 

[rjenkinsgb]

Check if the two B+ and two B- are internally connected on the board, with a multimeter.

If they are, you probably do not need the extra two. If they are not, the balance circuit is probably disconnected without those wires.

 

[SentinelAeon]

Hmm, good call, cudos. I just measured and using multimeter between both B- will give me 0.1 Ohm. Same happens when connecting both B+.

So now it got me wondering even more, why add 2 connectors that are connected together. The only thing i can come up with is ... this board allows 8A current through it. Maybe they added this so there would be less resistance since ur spliting ur current through 2 wires instead of just 1. Though even if thats true, this will only help the flow from batteries to BMS. Internal bms components will still have only 1 way for current to flow.

I am still unsure whether to use 2 wires or 1 wire. My max current will be in the area of 2A. I will test tomorrow if there is any difference between both ways as far as low voltage protection goes. If i find that it works either way, i will just use 2 wire connection.

 

[Nigel Goodwin]

By connecting the extra wires you're increasing the accuracy of the measurement:

Four-terminal sensing - Wikipedia

en.wikipedia.org

 

[rjenkinsgb]

By connecting the extra wires you're increasing the accuracy of the measurement:

That's why I asked for the resistance reading, to see if it was intended as a four wire setup.

That would make definitely sense if they were not also directly connected at the PCB - but they are, according to a previous answer.

 

[SentinelAeon]

So what do i do now, connect or not ?

 

[Nigel Goodwin]

That's why I asked for the resistance reading, to see if it was intended as a four wire setup.

That would make definitely sense if they were not also directly connected at the PCB - but they are, according to a previous answer.

It still makes perfect sense, as you're removing the cables from the measurement, which is what four wire is all about.

 

[SentinelAeon]

Connect or not to connect ?

 

[Nigel Goodwin]

Connect or not to connect ?

Your choice, connect is 'better' but I suspect the difference is only small, particularly for your light use.