On the old forum there was this guy (dont know if he migrated over here as well) that did some pretty cool posts about not using bms. He he had fund it was not that necessary when using quality cells and doing other measures.
BIG DISCLAIMER: I AM NOT ADVOCATING NOT USING BMS. USE ONE FOR GOODS SAKE.
Anyway… in September I made a 12s4p 40t battery for my short track board. The bms hadn’t shown up before I had to use the battery, so I decided to go ahead and add the bms later. Well the bms is still not added and today I checked p-groups to see how things were.
All 12 groups measured 4.21 exactly.
Battery have been used on a 4wd on short track = relatively hard acceleration and braking, though it looks like each motor doesn’t get more than 60amp when accelerating.
Battery have been charged with between 5-15 amps according to how fast I needed the battery to charge. Made this neat charging solution where I have three 5 amp chargers so I can charge 5, 10 or 15 amps.
I even shorted the battery once with one of the chargers while being stupid when charging.
Thank for your post!
Almost no one needs a BMS with a new pack. It’s what happens as the pack ages, or if the pack is stored for a long time, that leads to needing one. Discharging a pack down to lower voltages makes having a BMS good too (to prevent any imbalance from taking a cell below 2.5V).
I’m glad that your pack is still behaving well and that, hopefully, you are taking whatever precautions are needed to prevent any cells from dipping below 2.5V during use or storage. You might never need a BMS. Or perhaps eventually you may. I look forward to your updates!
(Edit) A good BMS can be handy though for other things besides balancing…
It can prevent overcharging of the pack if the wrong voltage power supply/charger is used.
It can prevent a charge port short circuit from destroying the pack and the board.
It can keep you from charging a pack if it is too hot or too cold.
Plan was to add bms with this one. But maybe I should leave it be and see what happens. I have the hood of this build constantly, as that’s the only way I can charge it, so I can easily keep an easy on it.
If I remember correctly Whitepony had an over two years old pack that still measured equal.
And again just for the record (these non BMS post had a tendency to turn in to a helmet like post back then ) I am all for BMS. They should be used. All my other builds have them plenty
Just a side note….
We all want to use the experience of others to help us make decisions regarding stuff like this but their experiences are irrelevant.
Our packs use different cells and are assembled, used, and stored differently. We can’t assume anything regarding a need for a BMS, or not, based on the experiences of others.
Just to be clear, repeating what I said earlier, many can go without a BMS. But we can’t make any decisions based on the fact that others haven’t needed one…yet.
My 13s4p 21700 pack without bms is almost 2 years old already @ around 60 cycles.
I (under)charge it only up to 52V and discharge it only down to 43.5V.
Bms is not quite relevant in such voltage range unless it’s a smart bms.
And since I’m undercharging and underdischarging it, the cells’ life span are extended which means it takes quite long time to get the pack out of balance unless something else goes bad.
I might add that the more cells in parallel the longer it takes to get out of balance. Correct me if I’m wrong.
