eee291 said:
So i just received my 40A BMS from Lithiumbatterypcb.com and this is what it looks like on the inside.
https://imgur.com/a/SYshbIc
Looks like the copper issue was fixed a long time ago. it's just that most Aliexpress sellers still sell the older versions.
I am planning on replacing the Mosfets on the B- side and discharge through the P- port, since the C- Mosfets should withstand up to 40A.
eee291...thank you for the link to your images! They gave me further ammunition for what I've been saying all along.
NOTE: When you read this, understand a few details. These BMS do a pretty good job of balancing your pack and they are a cheap, effective smart BMS. However they lack sorely in some key areas...which I focus on below. And have focused on previously. Fixing the below items makes these BMS pretty darn good!
I do like the 40A version becasue it has less garbage mosfets to remove and replace! Assuming the Chinese HY3215 is anything like the IRL3215, those specs are below. Commonly Chinese parts are NOT as good as the legit part they copy. If you look closely, one of the mosfets is an HY3712 (4th from the left in the below picture). Doh!
IRL3215 or HY3215 specs:
166 mOhms Rds, 12 amp, 80 watt, 150v (Can you say horrible mosfet?)
2SK3712 or HY3712 specs:
580 mOhms Rds, 9 amp, 40 watt, 250v (That won't be a problem at all mixed in with the 3215's! Can you say horrendous mosfet?)
Replace with AOT2500 mosfets. They are your best bet in 150 volt parts.
There's a total of ten 4 mOhm .5 watt shunts on this BMS. That's .4 mOhms total. I wonder what the PC app says the resistance is? In the 50 amp version which has 10 of these shunts, it says .2 mOhms.
I would have to emphatically disagree about the copper issues are "fixed". It looks like the copper is at least flat so maybe it's soldered down completely now. There is solder flow around the edges of the copper so that's good....on the top of the board at least.
Partial copper at P-. That's 1 of the 2 most important places for copper to be placed! No where does any existing copper cover the entire buss or extend onto the solder pad where you connect. At the B- terminals the copper needs to actually touch the screw terminals and have good solder connection to them. Look at the mosfet legs that goe to the copper. There is no solder at all that connects the leg to the copper. This is 100% depending on the thin circuit trace for all current. Same for around the shunts.
I know this is the 40A version, but the copper ought to cover the entire buss and no copper at all at P- is just bad.
No copper overlapping the P- solder pad...or even close to the solder pad. Solder is an average conductor...and that's for legit, good quality 60/40 solder NOT the low grade garbage Chinese solder these BMS have on them. Using solder to make a large current path is not advisable...that's why copper is used...it is a great conductor. Solder should bridge the gaps between the circuit trace and copper or part and circuit trace. It should NOT be the actual current path.
This is a close-up of the underside of the board and the angle isn't great. The copper has no solder flow around it and it looks lifted off to me on the right end. None of the copper on the bottom of the board shows any evidence of solder flow around it. I bet it's all barely attached.