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    Bike cut off

    I have a bit of a problem. When I'm riding my bike and I give it throttle suddenly the battery indicator comes on and the whole thing shuts. However if I have the bike lifted and I put it to the max speed 60+mph there's no problem.... The bike has been sitting over night so it's definitely cool and the battery is about 90% charged. How come it does that? This is the motor and display and controller I have.



    #2
    What are the specifications of your battery? What is the max current on your BMS (if you have one?)

    That kit has the potential to draw a lot of power. It could be causing enough voltage sag to hit the low voltage cutoff threshold on the controller. It could also be that your BMS can only put out so much power and is protecting itself and/or your battery.

    Definitely need more info to see the full picture.

    Pulling you and a bike up to speed presents a load to the motor and requires a lot more power than spinning a hub motor off of the ground. That is why I suspect it may be that your BMS or battery are not up to the task.

    Comment


    • Electricbiker100
      Electricbiker100 commented
      Editing a comment
      The battery I have is a 72v 26a battery. I'm not sure what the bms is..... However I just finished building this bike about two weeks ago, and the first day I went flooring it all over hitting 50+mph and then just suddenly today when I went out to try it that happened.....

    #3
    I'm not sure if I figured out the problem if so it's a bit embarrassing. Take a look at the picture below, that's a picture of my display. To the left you see the battery indicator which is yellow, and below it the voltage... Now what I noticed is that when giving it throttle the battery indicator fluctuates with the throttle rather than giving me a idea of how much percent is remaining like what you see on your phone. And below that is the voltage as I mentioned. So I happened to watch a video of someone else building ae bike and he said when it's full charge (hoc) it will say it's about 84v and when it's low charge it will say it's 60 something volts... So do you mean to tell me that 69v on the indicator means that it's dead? If so it's obviously very misinformative. I mean I did floor it quiet a bit and do a few burnouts but I didn't think it was dead just yet.... I'm charging now to figure out for sure.



    Comment


      #4
      Try giving a full charge and then seeing if it gives you these problems hot off the charger. Do you know what they set the LVC (Low Voltage Cutoff) to in the controller? You can email the seller and ask this figure; you should make a note of this default controller LVC. I imagine that there is also an LVC setting in the display--what is it?

      After it dies, try power cycling the battery by unplugging it, waiting a few seconds, and then plugging it back in. When you trip the circuit breaker in the BMS, power cycling the battery resets it. After that, try drawing less current and see if it rides okay at those lower power levels. When a battery is in need of charging, it is unable to deliver the same amount of current as when it is fully charged.

      These systems are designed to stop you if the LVC is reached or if the circuit breaker is tripped (which occurs when you try to draw more current than the battery can safely deliver). The idea is to recharge your battery before riding again. This is all in order to protect your battery from discharging too much which could ruin the cells.
      Last edited by commuter ebikes; 06-11-2017, 05:26 PM.

      Comment


        #5
        I have the same problem having just completed the same build with this 5000w rear hub motor coupled with 72v 29ah battery. The controller is 60V-96v . 80A-120A .24 mosfets. If I throttle quickly the power cuts off and will only restart if I disconnect the battery cable and plug back in again. If I go easy on the throttle the bike will power up to full speed. Although I had electric bikes before this is a new build project for me and I have to say I'm a bit green when it comes to troubleshooting this type of problem. I don't know what the LVC has been set in the controller but will find out. My display is different so I will check if it has an LVC as well.

        Electricbiker100 - have you figured out how to stop the cutoff happening? I could sure use some advice also.

        Comment


          #6
          Originally posted by Easy Bike View Post
          I have the same problem having just completed the same build with this 5000w rear hub motor coupled with 72v 29ah battery. The controller is 60V-96v . 80A-120A .24 mosfets. If I throttle quickly the power cuts off and will only restart if I disconnect the battery cable and plug back in again. If I go easy on the throttle the bike will power up to full speed. Although I had electric bikes before this is a new build project for me and I have to say I'm a bit green when it comes to troubleshooting this type of problem. I don't know what the LVC has been set in the controller but will find out. My display is different so I will check if it has an LVC as well.

          Electricbiker100 - have you figured out how to stop the cutoff happening? I could sure use some advice also.
          An easy fix for this problem is to incrementally decrease the value for max current until the problem stops. I would guess that your BMS is not allowing the large amount of current to be drawn from your battery; the BMS is doing this to save your cells from damage due to overdischarge.

          Hopefully your display has a way to set max current.

          Comment


            #7
            thanks - I've found some more data on my battery and motor. The battery is 72v 29ah with built in BMS 50A, discharge cutoff voltage 56V, max continuous discharge is 50A. The hub motor is a 48v-96v 5000w brushless with double hall sensor. Controller is 60v-96v 80A-120A with 24 mosfets. I have a 72v SW900 LCD display. I think the display is faulty based on both the manual I have on it and videos on youtube - none of the programming sets match up (ie P01 through to PO9 on mind display are not the same in either manual or on the videos) , it doesn't show battery watts (line is simply blank) - and I cannot decrease value for max current as I can't get that programming set to appear like it should. My concern is that with this set up the motor is going to pull too many volts from the battery, which can't handle it, and will always cut out. Am I correct? What's the best fix suggested? Appreciate any advice as I'm a hobby e-bike builder and still learning.

            Comment


              #8
              The controller can pull too much current (amps) and the battery BMS is preventing that. You say the controller can pull up to 120A, which I suspect is more than the max on the BMS (you only list the continuous current on the BMS as 50A).

              You should limit the current at the controller to less than what the BMS is willing to deal with. I think it is exceeding the current, not reaching LVC due to voltage sag.

              Maybe your controller can be programmed with a USB cable? Ask the seller. If they are sellIng this as a kit it should be programmed accordingly out of the box or they should help you program it as it is not right now.

              Comment


                #9
                Originally posted by Easy Bike View Post
                thanks - I've found some more data on my battery and motor. The battery is 72v 29ah with built in BMS 50A, discharge cutoff voltage 56V, max continuous discharge is 50A. The hub motor is a 48v-96v 5000w brushless with double hall sensor. Controller is 60v-96v 80A-120A with 24 mosfets. I have a 72v SW900 LCD display. I think the display is faulty based on both the manual I have on it and videos on youtube - none of the programming sets match up (ie P01 through to PO9 on mind display are not the same in either manual or on the videos) , it doesn't show battery watts (line is simply blank) - and I cannot decrease value for max current as I can't get that programming set to appear like it should. My concern is that with this set up the motor is going to pull too many volts from the battery, which can't handle it, and will always cut out. Am I correct? What's the best fix suggested? Appreciate any advice as I'm a hobby e-bike builder and still learning.
                I imagine that the BMS will prevent the system from drawing too much current from the battery pack. How would you feel about getting a direct replacement display or using a Cycle Analyst V3 http://www.ebikes.ca/product-info/cycle-analyst-3.html?

                With the Cycle Analyst, the DP http://www.ebikes.ca/shop/electric-b...ts/ca3-dp.html calculates speed by sensing the RPM of your motor (you have to input the number of poles on your motor--the motor manufacturer can tell you this value). The DPS http://www.ebikes.ca/shop/electric-b...s/ca3-dps.html uses a spoke magnet to calculate speed. I like the DP because it has less wires. With the DPS, you have to mount the spoke magnet pickup sensor to your fork.

                A CA V3 has a motor temperature sensor whereas the CA V2 does not. I definitely like to see my motor temp.

                While I cannot guarantee that a CA will work for your motor, I do feel that it is a near certainty. I love my CA3-DP, but I can understand if you just wanted to go with a direct replacement display which appears to be this: https://www.amazon.com/Display-Elect.../dp/B072LCZT5Y. If you bought another 72V SW900 display, you could compare your two SW900 displays side by side to see if they behave identically. I did not see a reference to setting a maximum current in the description of the SW900.
                Last edited by commuter ebikes; 06-22-2017, 07:47 AM.

                Comment


                  #10
                  thanks for the advice. I'm going to get the CA V3 - it looks like a very good programmable display.

                  Comment


                    #11
                    Originally posted by Easy Bike View Post
                    thanks for the advice. I'm going to get the CA V3 - it looks like a very good programmable display.
                    I give it an A+.

                    Comment

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