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Mixing 18650s..........

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  • Defjr333
    replied
    As always things to think about. Thanks for the insight and links Pax!!

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  • paxtana
    replied
    I would bet batterybro has better price than vruzend on 25r.

    For the bms you would be hard pressed to find a better company than this one. http://m.en.szsmartec.com/

    But Bluetooth is overrated IMO. What is the point of having something that can wirelessly check cells if that feature can kill a long-term stored battery due to power consumption during standby?

    Think about it, on your phone do you keep Bluetooth constantly enabled? Probably not, because it sucks down power. On an ebike battery it's even worse, it can damage cells by draining it to LVC, and unlike a phone you might be storing it all winter before checking it. It would suck seeing that the cells are way outside the acceptable voltage for preventing cell damage during storage. And it would also suck finding out that happened purely because of the BMS in the pack. That is the entire reason we do not build with BT BMS at Luna.

    Some say low power BT is the solution to all that but it's still some percentage of a constant drain. Maybe one day they'll figure it out. A good idea would be something like only activating Bluetooth after pushing power through discharge, or some other way of turning on/off BT so it is not a liability. If a BMS like that exists I have not seen it.

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  • Defjr333
    replied
    Tad high, but a respectable source. And they get hard to find. I have a source for genuine cells already, but he does not sell BMS units, only cells.The BMS is they part i am hoping most for recommendations on and sources for. Appreciate the link tho, others may find it useful.

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  • zmarkjam
    replied
    Micah Toll has 25r's in stock on his VRUZEND site. 4 bucks a piece (don't know if that's a good price or not) https://vruzend.com/product-category/18650-cells/
    Last edited by zmarkjam; 09-13-2019, 01:46 PM. Reason: posted wrong link

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  • Defjr333
    replied
    After days of research and reading, I have decided to order more 25r's and NOT mix the different types. Just too many headaches to consider. I will find a use or sell the others. So, I am now looking for good BMS units to use for two(2) 20S8P packs. I would like them to have bluetooth connectivity, and 60A continuous/ 80A+ burst. I dont trust Ali or Ebay for these purchases, I want to go through a trusted company/ distributor. If anyone here has knowledge of good companies to consider, please feel free to list them here. Thanks for the input/ and concerns by all. These buggers CAN be dangerous.

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  • JPLabs
    replied
    If you choose to mix cells, making sure every parallel group matches is a strong need. If I WERE to do so, I'd use the same mix in each group, 5 of x and 5 of y cells, etc. Similarly, if the capacity or internal resistance varies between cells, you would be wise to match them up so every parallel group has the same performance. A few strong cells, a few weak ones, if you have both, for instance. The strong will help offset the weak, if they are in parallel.

    If the cells are parallelled, and not matched, at least the voltages are forced to stay balanced among all the cells in a group.

    That's a LOT better than making parallel groups differently, which is a recipe for an eternally imbalanced pack which is always trying to kill the cells in the weakest group.
    Last edited by JPLabs; 09-12-2019, 11:36 AM.

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  • valueseek
    replied
    The problem with using two bms in parallel is if(when) one turns off, the other half of the battery will be discharging the full current by itself which is obviously not good.(unless both packs can handle the current and someone is using an extra battery only for range).

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  • Defjr333
    replied
    Appreciate it pax

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  • paxtana
    replied
    Personally I would not do so but there's plenty of reports of folks on endless sphere using random assortments of old laptop batteries to cobble together a battery. Might want to look at a few of those threads for some insight ;)

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  • Defjr333
    replied
    I think I am going to grab a few more cells and build 2 20s8p and run them in parallel with 50amp continuous BMS units. While I don't plan to use 100amp continuous EVER, it will keep the max draw on any single cell well below it's thresholds. Same with the voltage. 20s fully charged is over 80volts, but I can charge it to a lower state similar to charging 80 or 90% to keep voltage where I want it. Any "pack" builders care to throw in some input would be appreciated. This will be on my BBSHD via a Grin Phaserunner. Absolutely love the BBSHD for it's ease of install and use, but I am starting on upgrades to the drive system and am willing and waiting for the motor to give out. At that point I will be moving on to either a QS motor, or something of that power level. This $h1t gets addictive. Lol

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  • Defjr333
    started a topic Mixing 18650s..........

    Mixing 18650s..........

    I have:
    200 Samsung 25r
    70 PanasonicMH12210
    19 Samsung 20q
    All fairly new and gingerly used. Only 1 failed testing. I would like to build 2 packs for a Phaserunner controlled BBSHD. Highest safe voltage and currents. Would any of you with better knowledge of 18650 pack building care to guide me along as to what my best configuration of the 2 packs should be? I need to order 2 BMS units(one for each pack) as they will be wired in parallel to keep current draws on each cell lower, while still allowing for up to 120amps continuous. I know the BBSHD cant take THAT much current, but it will only pull what it needs, no harm in over building for possible future motor changes. It is the voltage that has me concerned. What is the highest i should go on a Phaserunner/BBSHD? I have heard 80v/80a works on phaserunner forums. That would be good, but is it the highest safely? Also, what cells can go with which? Any concerns on mixing Samsung 25rs with the 20qs or Panasonic 12210? I am hoping they are acceptable due to running packs in parallel and that should prevent either pack from going over 40 amps continuous, 80 combined. Give me some pointers, problems, any insight will help. Thanks in advance guys.
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