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I raised my max current from 30A to 70A.

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    I raised my max current from 30A to 70A.

    I have been riding for the last year with my max current set to 30A (at 72V). This was fine, but sometimes the bike was a little slow to accelerate in traffic situations which called for higher acceleration.

    I recently experimented with raising the max current to 70A, and I have decided to keep it that way. My battery will not make it to work and back like this if I go WOT the whole time, so I still have to economize my 20Ah battery capacity by using the throttle to limit power.

    While I have a 100A BMS, the cells in my battery can only supply 35A continuous so I can only use about 70% throttle while cruising which still allows me to cruise at 30-35mph depending on how much my battery is charged.

    I hope I don't damage my cells by doing this. If I draw more current than the battery can supply, the BMS shuts off. This never happened when I had the current set to 30A, and it hasn't happened yet with the new 70A limit because I am judicious with the throttle.

    I can tell when the battery is straining to deliver high amounts of current because I can feel the power start to intermittently cut out. This phenomenon feels exactly the same as when I have a maximum speed setting in place; the rider can feel the power being trimmed (intermittent moments with no power).

    Does anybody think that I could damage my cells with this higher current limit? I would hate to cause the cells to get imbalanced or damaged. Would the BMS prevent such damage?

    #2
    Is this the BBSHD you`re talking about or something else??

    Comment


      #3
      Most certainly you can damage cells by exceeding their discharge c rating!!

      Comment


        #4
        20Ah only 35A max continuous output? That's not even 2C. What type and configuration cells are you dealing with here?

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          #5
          The motor is a Cromotor & the controller is a Lyen Mark 2. These two 36V batteries are in series & each have their own 100A BMS.

          The cells are 2200 mA LiMn 18650s. The C rating was advertised as 3, so I consider 3C to be a maximum.

          Comment


          • ykick
            ykick commented
            Editing a comment
            3C per cell? If so, you must have 8-10 paralleled to reach 20Ah? If so, that's within C rate spec for legit cells.

            How much voltage sag and thus IR can you determine when freshly charged? DC IR testing is where I'd be going with this. Simple to do and good info to better understand the health of ANY battery pack. I now do it for all chemistries, Li-ion/poly, Deep cycle lead, NiMh, etc.

            Here's where I got started with IR testing - https://www.youtube.com/watch?v=wP0MhOcPmQY&t=14s

          • JPLabs
            JPLabs commented
            Editing a comment
            Building on Ykick's comment:

            Even if 10P, or 22 Ah per group with the stated 2200 mAh per cell, that would be only 66A max at 3C, right? I don't see how they can justify a 100A BMS with that cell arrangement. If only 8- or 9S, it would be even lower. Right?

            I'd think 50A would be a proper BMS size for such a pack if 8S, or 60A if 10S.

            Commuter, can you figure out how many cells are in parallel?

            I think 70A is a bit much. Unless we don't understand your pack configuration.
            Last edited by JPLabs; 10-31-2017, 12:29 PM.

          #6
          Will the circuit breaker in the BMS prevent damage to the cells, I hope? I am drawing bursts of 70A on every ride. If I damage the batteries, I will have no way to get to work.

          The bike sure is a lot more fun like this.
          Last edited by commuter ebikes; 10-29-2017, 09:31 PM.

          Comment


          • JPLabs
            JPLabs commented
            Editing a comment
            Not necessarily, no.

          • commuter ebikes
            commuter ebikes commented
            Editing a comment
            Well then I won't risk it. My electronics tech said that my battery can definitely supply 30A continuous so I will just limit it to 30A.

          #7
          Looking ahead, what should I plan for my next battery? I plan on reusing the two 100A BMS units for two 36V batteries in series & I like 18650s.

          Maybe by the time I need a new battery there will be 4000 mA cells available. My electronics tech says that he will teach me how to build a battery. I will buy a proper spot welder. I am willing to build a higher capacity battery.

          I am now able to charge at work now so, as far as commuting goes, I only need to ride 5.5 miles between charge cycles. I will try this with the 2200 mAh cells in the 19.8Ah battery & post any problems in this thread.

          The motor can only handle so much heat. My rider, bike & cargo weight is 350 pounds with ridiculously heavy tires. Even with the current limited to 30A, the motor temp reaches 90 degrees C after 5.5 miles on a hot day.
          Last edited by commuter ebikes; 10-30-2017, 07:02 AM.

          Comment


            #8
            Build a trike and add another motor?
            Maybe you are over taxing the limits of a single Cromotor. It might be more efficient and effective to use two motors with single battery for each.

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