So theoretically, If I left my board on until it ran out of juice every cell should be at 2.9v right?
Guess I just got a defective BMS, any way I can verify?
That’s not exactly how it works. The Bms should shut down if even just one cell drops to 2.9 V. For example, if you have one cell that falls out of balance and goes lower than the rest. You could have nine cells at 3.0v+ and one cell at 2.9v. At that point the BMS should shut down. You could possibly have a faulty BMS.
Hey @Namasaki, finally I order my 12s BMS form bestech and have a question about overcharge settings. Your BMS has 4.28V detection voltage and 4.08V release voltage. Would it be possible to set the release voltage to 4.2V or ist it only possible with 0.2V difference? Because if the BMS would shut off due to regenerative braking with full battery the BMS stays off until the battery reaches 4.08V, or am I wrong?
You can request a different overcharge detection at the time you order the bms. I just went with the default setting. I did a full battery down hill braking test. The results where: As I was braking downhill with a full battery, the battery voltage climbed steadily until it reached 42.8 volts. At that point the voltage stopped climbing and held at 42.8v Apparently the bms blocks the charge current at that point. When I reached the bottom of the hill and released the brakes, the bms trimmed the voltage back down to 42v The bms did not shut down even at 42.8v, it just blocked the charge current. It may be possible that if braking down a very long hill with a full battery so that 42.8v is maintained for a long duration that the bms may overheat and shut down. When I ran my test, I was only at 42.8 for a very short duration. Probably 1 min or less. I am running dual vescs with min bat current set at -10a so thats -20 total regen. At that setting, the voltage climb is still not too fast. I assumed that since 4.28v overcharge detection was the factory default setting, that if was an acceptable amount. After running my test, there was no noticeable damage to the battery. I mean we are only talking about less than 1/10 of a volt per cell.
That’s great info! Good 2 know, thank you!
Let me explain with a little more detail. when my battery reached 42.8v I continued braking but the voltage never went over 42.8v So My assumption was that the bms blocks the charge current at that point.
I am looking to do a build with the Carvon V4’s also, but I’m going to go 4WD. I had originally planned on building a 12s4p using the Samsung 30Q’s, but I think I want to use the graphene batteries to do a 12s battery. What would the stats be for that and what BMS would I need to use?
That makes sense, I like the fact that it didn’t shut off. But that would mean that even a overcharge setting of 4.2V would be better if the BMS just stops the charge and doesn’t power off. But I read threads about problem with BMS which shut off above overcharge limit. I think I go with 4.25V for safety 
Also would I want to go with the 2s6, 3s4, 4s3, or 6s2, and why?
The thing to remember is that if the bms stops the charge current, It most likely is going to cause heat. And if the heat goes too high, the bms will shut off. Although the Bestech bms is less likely to overheat than others. Most other bms’s do not have heatsinks on the FET’s. The Bestech does. The Bestech has a balancing discharge current of 126ma Most other bms’s balancing discharge current is only around 60ma. Including the Battery Supports brand.
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30Q’s are good batteries and a 12s4p pack with a good bms would probably do well especially in terms of range. The drawback to using Li-ion cells, besides the size and weight of a 12s4p is that building such a battery requires more equipment and expertise because a poorly built Li-ion battery will not only be problematic but can be down right dangerous. There have been at least 2 cases that I know of where boards using Li-ion packs have caught fire and burnt to the ground. Several builders are using more advanced construction techniques such as cell lever fusing to improve safety and dependability.
It just depends on how thick you want the battery to be. I used 2s to have the thinnest battery
So in terms of performance there is no difference? I also want the thinnest setup, so I guess that means the 2s’s then.
The performance will only depend on the total number of cells, the capacity and the C rating. It is always recommended to get batteries with the highest C rating possible regardless of capacity however a combination of high C rating and high capacity is best. Be aware that C ratings are a not a reliable measure of actual discharge current capability. That is to say that a 5ah battery with 60C rating cannot really handle 300a The Idea of multiplying capacity and C rating to determine actual discharge current is simply false. As far as I know, there is only one distributor of Lipo batteries that states real discharge current capability for their packs. http://www.smc-racing.net/index.php?route=product/category&path=67_97
How would that compare to the graphene one that was discussed earlier?
That’s what I’m leaning towards making a 12s setup from now.
I have heard that the Graphene’s are good batteries. My Turnigy 5ah 60C batteries do well and sag very little so the Graphene 90C should do really well.
I think these are a better deal though and they are in stock. http://www.smc-racing.net/index.php?route=product/product&path=67_152&product_id=412
True, though I was just looking at their inventory, and I think getting four of these would be a better idea than the 2s, and they’re in stock, and they would be just $60 roughly more than the ones you linked.
The 3s would be a good option just thicker than 2s