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  1. MAXIMUM_AMPS

    Can we parallel BMSs to handle high current ?

    #2 is not possible, unless the modules were unified into one big one. The BMS has to connect to each series cell connection in order to actually do its job. So if you have 3 modules and want to use 1 BMS, all the modules would have to be connected at the cell level. Effectively making them 1...
  2. MAXIMUM_AMPS

    36 V pack not charging

    Sadly you'll have to replace that whole group of cells from B1 to B-, and likely the BMS board. If you know someone with a battery spot-welder, this can be done cheaply, but if not, it's very difficult.
  3. MAXIMUM_AMPS

    Parallel "Groups" or Parallel Strings or Neither ?

    Alright, I'll keep it simple, omitting protection/balancing circuits, just cells and wires. While it is true that cells do automatically balance their parallel'd neighbors, if they are significantly out of balance, a huge dangerous current can flow between them. Which is why there are no...
  4. MAXIMUM_AMPS

    No Solder, No welding 48v 20Ah. Cheap battery Pack

    Looks like a clever design! I take it those "pillars" provide the necessary clamping force to get a solid connection?
  5. MAXIMUM_AMPS

    Parallel "Groups" or Parallel Strings or Neither ?

    I thought I did, sorry if I was unclear. Yes the concept of modular mini-batteries is sound at a small level, and has already been done with power tools. But in no way is it possible without a BMS for each module, that would be extremely dangerous. Sorry if I bored you with the small details of...
  6. MAXIMUM_AMPS

    Parallel "Groups" or Parallel Strings or Neither ?

    Ahhhh, now I understand what you meant in that other thread! I've seen this done in a smaller extent with power tool batteries. I forget which brand, but you'd see their large tools used multiple of the "standard" batteries in series. I thought it was fairly neat. This concept is interesting...
  7. MAXIMUM_AMPS

    Regen

    Fast-wind motors don't put out a lot of regen power. Consider swapping the motor with a lower Kv like a Crystalyte H3525. I'm gonna work you through the math here: Say your motor has a Kv of 10RPM/V. You can use the reciprocal of that to calculate 1/10th of a volt across the windings per RPM...
  8. MAXIMUM_AMPS

    No Solder, No welding 48v 20Ah. Cheap battery Pack

    Wow, very substantial bus-bars. How is the voltage drop under load? Judging only by the pics, I would think that the interface between the cell and the bars would impede the performance a bit.
  9. MAXIMUM_AMPS

    Circuit analysis of a cheap BMS, and why you shouldn't use one

    Interesting, why use series modules though? Is the load a passive component like a brushed DC motor? A SMPS with a wide range of input voltage? In 1S protection circuits there's often (not always) a shunt on each cell, and with coulomb counting multi-cell systems the large shunt at the bottom...
  10. MAXIMUM_AMPS

    Looking for a 60V controller

    You should be good to go: 63V is a common rating for the capacitors used in controllers. Generally you find passive components in the E-series of numbers, 10, 22, 47, 63, etc. If it's a "48V" controller it's likely also using IRFB3077 or similar FETs which are rated for 75V maximum.
  11. MAXIMUM_AMPS

    Reputable/reliable 48v batt sellers for BBSHD build

    Solid advice in this thread, an oversized, understressed battery is a reliable one.
  12. MAXIMUM_AMPS

    Circuit analysis of a cheap BMS, and why you shouldn't use one

    Sorry, forgot a word, I meant come close as in IR. Voltage drop of a protected 18650 for example will always be higher than a similar unprotected cell due to added resistance of the protection FETs and shunt resistor. I wouldn't recommend series modular batteries, as older cells in the string...
  13. MAXIMUM_AMPS

    Circuit analysis of a cheap BMS, and why you shouldn't use one

    I agree, not much point in going modular on an ebike BMS. A single 10-14S BMS is ideal for most ebikes. The advantages of using a >1S system I see: 1. Less voltage drop than a protection circuit with separate shunt resistors + 2 FETs in series on each cell. For example, you'll never see a...
  14. MAXIMUM_AMPS

    Why doesn't a li-ion battery take load?

    Interestingly enough, the cells with "fire" in the name carry the greatest risk of fire.
  15. MAXIMUM_AMPS

    Circuit analysis of a cheap BMS, and why you shouldn't use one

    Of course, there's 2 ways to go about it. The best way to build a modular system like that, is to use a chip that was designed to be "stackable". The chips will directly communicate to its above and below neighbors, so if one chip is dead/faulty, the entire output is shut off. Daisy-chainable...
  16. MAXIMUM_AMPS

    Circuit analysis of a cheap BMS, and why you shouldn't use one

    Ah, I understand now. Agreed, ultimately you can buy a $16 board, $100 board, a $500 board, not even connect it to anything yet, but cause irreparable damage to it due to ESD. Fortunately with the proper design, the circuit will not appear to be protecting when it's only partially...
  17. MAXIMUM_AMPS

    Circuit analysis of a cheap BMS, and why you shouldn't use one

    BMS being universally stupid and horrible? Not at all. There's definitely good designs and bad ones... Of course, the BMS is by no means the only possible cause of a battery fire, there's tons of RC LiPos going up in flames, and all those all rely on balance chargers. Balance chargers are nice...
  18. MAXIMUM_AMPS

    48v to 72v controller overvoltage at 82v

    82v is very close to 84v, could be that the voltage divider circuit in the controller is slightly off... In any event, it's better in the long run to only charge the cells up to 80v or so. You get about 2x as many cycles while only losing ~10% of the capacity. (but first make sure your BMS is...
  19. MAXIMUM_AMPS

    72 volt battery only chargers to 81 volts not 83volts

    That is ideal, but the vast majority of BMS boards are not like that. The nicer ones with bluetooth programmability and monitoring like what EM3EV offers on their batteries is not the standard, that's an exception that puts them above the competition. All BMS units need to cut off the charger...
  20. MAXIMUM_AMPS

    Stackable power wall kit with 18650 on ebike

    I've seen those, they're primarily made for powerwalls, and other low-current stuff. Performance is similar to the Vruzend V1.5 kits. They could work on an ebike for sure, but when you start asking for >5A per cell, you need spot welded connections.
  21. MAXIMUM_AMPS

    Circuit analysis of a cheap BMS, and why you shouldn't use one

    Removed BBCode tags, should be visible now.
  22. MAXIMUM_AMPS

    Circuit analysis of a cheap BMS, and why you shouldn't use one

    Is your BBCode disabled? the lists are showing for me, but I will edit the post. By OVP, I mean the BMS OVP for each cell group... The most critical protection feature of a BMS, besides balancing of course. For example, in a 2-wire BMS, if any one cell group is above 4.2v, or 3.7v for LiFePo4...
  23. MAXIMUM_AMPS

    Should I fuse my battery?

    I would use a fuse, BMS or not. Under a dead short circuit, it is possible that the BMS's FETs can go into an avalanche condition, where they are stuck ON and the BMS chip's FET driver cannot turn them off...
  24. MAXIMUM_AMPS

    Circuit analysis of a cheap BMS, and why you shouldn't use one

    Very sorry to hear that. I hope your insurance did you right. That's very common for a BMS to fail and become unable to trigger OVP. Overvoltage when charging is by far the most dangerous thing possible with a Li-Ion cell! Unfortunately human bodies are good capacitors, very effective at...
  25. MAXIMUM_AMPS

    Circuit analysis of a cheap BMS, and why you shouldn't use one

    Nice find! From the pic, I believe it's a clone of this (much clearer photos): https://imgur.com/a/DZ9X4tx I found this pic on reddit, a user blew his BMS. :( https://www.reddit.com/r/ebikes/comments/e4oxr8/i_just_bricked_a_130_bms_venting/ As usual, practice ESD safety at all times when...
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