This BMS is good up to 50 amps. The mosfets are garbage 10 amp parts with very high Rds. The copper busses are typically not soldered down. The copper is too short and as is don't do a very good job. The mosfets are generally NOT soldered down very well either.
This is the BMS as I received it.
I took the covers off one of them and found this immediately. The 3 solder pads for B-, P- and C- have no copper anywhere near them. This is useless. You WANT the copper reinforcement to overlap the solder pads so that you can solder directly to the copper. You want the copper to span the entire length of the power buss, not just cover a portion of it.
Copper doesn't over lap the B- solder pad at all. This is critical for good current handling.
Copper is short by 1/2" and doesn't over lap the P- solder pad. This is critical for good current handling since the EV is powered from this solder pad.
Looking further, I found that on none of the 6 BMS of this version I have has the copper soldered down properly. On all of them the copper would have voids and gaps or lifted off sections. Once I pulled off the copper, I found entire sections of the solder traces with no solder on them connecting to copper and bare copper with no solder on it. I wish I had taken more pictures of this!
This first picture might be hard to see. Both ends and the middle of the copper are bulged upwards and NOT soldered down. There are 2 low places that actually make solder contact with the solder trace underneath. This is virtually useless!
These images show the copper at the B- solder pad completely floating and doing zero good at all.
As soon as the copper was pulled off, I tinned every surface of the copper and tinned all the solder traces. Since the copper was too short to even cover the entire solder trace they are supposed to reinforce, I used the copper strip from C- to extend the P- and B- traces. C- is for charging only and that will probably be at like 10 amps instead of 50-80 amps like P- and B- will see. IE: Copper on C- is much less important.
These pictures show the copper extends the length of the B- buss and over laps the B- solder pad. Later I removed that little piece of overlapping copper so that I could solder down larger shunts.
In this picture , you can see the P- copper buss extends over all the mosfets and overlaps the P- solder pad. The 5.5mm bullet is soldered direct to copper. I later over lapped those last 2 mosfets with copper.
The factory mosfets are HY3410's. They are rated for 17 amps and 105 mOhms. Pathetic in every way! I had quite a few IRFP4110's which are 120 amps and 3.7 mOhms. Not the best mosfet there is, but far superior to the HY3410 garbage. I don't replace the C- mosfets. At most they will see maybe 30 amps so who cares. The P- mosfets however can now handle easily 100 amps. The factory mosfets...most of them were barely soldered down and several were not soldered down at all.
Once the factory mosfets were pulled up, I retinned all the solder pads that they mounted to. I tinned the backs of all the IRFP4110's so that good solder flow between the solder pads and mosfet backs would happen. I pre-tinned the 2 remaining legs. I didn't bother with SMD 4110's since I already had 40 of them in TO-220. I made my own from the TO-220 version. Bending the legs, shortening them and clipping off the center leg is quick and easy.
Soldering them down starts with the 2 legs which I had pre-tinned. The solder pads were pre-tinned as well. Get the mosfets straight, heat the solder on the pad and the leg and it all flows together. Repeat for all the mosfets. Now go back to the first mosfet and with lots more heat, put solder on the tab and solder trace. After a little bit the solder on both items will start flowing together. Press down the mosfet so it lays flat. Notice the right most mosfet, the top of the tab is tinned and the hole is filled with solder. You will use this later when you add the P- copper.
The factory shunts could have been doubled up or replaced with larger ones. I doubled them on my first BMS mod, but later replaced the .5 watt shunts with 2 watt shunts of the same resistance. If I had doubled up the smaller shunts, I would also need to change the value of resistance in the PC app to account for half as much shunt resistance. It is probable the BMS could not successfully measure current with such a low shunt resistance of .1 mOhms. It was better to use larger shunts and keep the total resistance at .2 mOhms like it comes from the factory.
.5 watt vs 2 watt shunts.
.5 watt shunts doubled up on a BMS. Later I pulled them off for the reasons explained above.
Since 2 watt shunts are huge by comparison, I can't put 10 of them in the same space. I still needed 10 shunts in parallel to get the same resistance, but only 8 fit across the space so 2 go on the bottom of the board across the same 2 solder traces.
The final step is to span the mosfet tabs with copper and to overlap onto the P- solder pad. Later I fixed this short missing section. Notice how the copper is thoroughly coated and embedded in solder. As I heated up the copper, I'd push it down so it was pressed onto the mosfet tabs.