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Bafang 750W 135mm front for fatbike

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    #16
    Originally posted by MoneyPit View Post
    52v nominal (58.8 peak). 35a peak. About 2200w per motor on a full charge so on the once-per-month balance charge or long-distance trip days, I am running 4400 watts, and I do peg the throttles as we have bike lanes on 50 mph superarterials here where I have no issues cruising on PAS at about 54 kmh. With a smaller person and no loaded panniers I'd be faster. The front wheel will spin if you don't apply the throttle carefully. It will still lose a bit of traction at the highest PAS level.

    Since this pic was taken I have mounted that same rack on the front. 60T chainwheel lets me pedal up to that 54kmh speed.
    I had a question about choosing the right battery. What kind of battery do you use? Please tell us about its characteristics: what type of batteries, maximum and nominal currents, voltages, as well as capacity and total weight. And most importantly - how much distance on it you can travel on it in different modes (for example at 20 km / h, at maximum speed, with and without pedals).

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      #17
      You need to just research batteries in general and understand the capabilities of different 18650 cells. Understanding what makes up a battery - the cells and the BMS - tells you everything about the battery you are trying to buy and the battery you should buy for your needs.

      This is a good place to start: http://www.electricbike.com/category/technical/

      Quick notes:
      • You either get high capacity for lots of amp hours in your cells, or you get high amp output. Generally you can't get both at the same time.
        - Panasonic GA's are a common go-to for high capacity storage
        - Samsung 25R's are the king of high amp output and excel for motors like a Cyclone
        - Samsung 30Q's are a new-ish battery that gives you some of both capacity and high output. They are not ideal on either end of the scale.
      • When you pick a battery, pay attention to the BMS. What is its continuous capacity and peak capacity? Match that to your controller's continuous and peak capacities. It is good to have the BMS exceed the controller's maximums. It is bad to do it the other way around.
      I like Samsung 25R cells and battery management systems with high output limits. My 17.5ah Luna Storm that powers my rear Bafang 750 has a 50/70 BMS. My front motor is powered by two 30Q mini cubes parallel'd together to make a 12ah battery with a 60/100 BMS (do not try and use that many amps or you will kill the battery). My next bike will have a 20ah 25R with a custom 60/90 BMS and run both motors. I want to try and use just one battery for charging convenience. For long trips I can run the front motor with a 14ah triangle that has GA's and a 30/60 BMS which will run fine with my 35/17a controller.

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        #18
        Originally posted by MoneyPit View Post
        - Samsung 30Q's are a new-ish battery that gives you some of both capacity and high output. They are not ideal on either end of the scale.
        I like Samsung 25R cells and battery management systems with high output limits. My 17.5ah Luna Storm that powers my rear Bafang 750 has a 50/70 BMS. My front motor is powered by two 30Q mini cubes parallel'd together to make a 12ah battery with a 60/100 BMS (do not try and use that many amps or you will kill the battery). My next bike will have a 20ah 25R with a custom 60/90 BMS and run both motors. I want to try and use just one battery for charging convenience. For long trips I can run the front motor with a 14ah triangle that has GA's and a 30/60 BMS which will run fine with my 35/17a controller.
        I'm going to do a battery on the Samsung 30Q elements. Configuration 20s5p:
        - rating 72V 50A;
        - maximum 84V 75A;
        - capacity 15 Ah;
        - weight 4.9 kg.

        Controllers: two 6FET at 25A maximum.

        Motor wheels front and rear Bafang:
        - 750W;
        - measured 394-401 rpm without load on 53.9V;
        - that is, 7.43 turns per volt;
        - according to the marking of the motors, they have 7 poles, so this is not a traction motor but a high-speed motor. This is confirmed by measurements.

        With this configuration, the design speed will be as follows:
        - at 84V, the speed is 83.5 km / h;
        - at 72V, the speed is 71.6 km / h;
        - at 50V the speed is 49.7 km / h.
        The question arises: can a current of 25A per motor (50A for both motors) provide similar speeds? The target speed is in the range of 50 to 70 km / h.
        Last edited by prof.power; 02-03-2018, 11:18 AM.

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          #19
          I can confirm that a single 52v (58.8v peak) 25R battery with a BMS of 50a continuous, 70a peak, can power two of those same motors where each has their own controller that peaks at 35a with a 17a continuous rating. i.e. more powerful than yours.

          The above configuration yields a peak speed of roughly 50 km/h. A bit less than when I run two batteries to power the two motors.

          I only ran that bike with the single battery for a limited time. The battery was a good size of 17.5ah. Running two motors on it worked fine... but range was compromised of course. If you are planning on running only a 15ah battery you can expect to a) have short range and b) not expect that battery to last a long time since you will no doubt be charging to full capacity and have a deep depth of discharge every time. Pretty much beating the hell out of it.

          My new AWD bike with a BBSHD in the back and an economy tune on it is eating about one volt every 3.1 miles. I have a 52v, 25R 20ah battery that loses about 5 volts for each leg of my 2-leg commute. On an 80% charge I can make the round trip of 31 miles and be at around 45 volts... 18% left which is skating on thin ice. I charge at work though so I'm fine.

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            #20
            Originally posted by MoneyPit View Post
            I can confirm that a single 52v (58.8v peak) 25R battery with a BMS of 50a continuous, 70a peak, can power two of those same motors where each has their own controller that peaks at 35a with a 17a continuous rating. i.e. more powerful than yours.

            The above configuration yields a peak speed of roughly 50 km/h. A bit less than when I run two batteries to power the two motors.
            Now I use a battery on the LG MH1:
            - rating 48V;
            - maximum 54V 35A;
            - capacity 15,6 Ah;
            - weight 3.2 kg.

            I feed 16A to the motor. It feels very powerful. Very fast start and set speed up to 50 km / h.
            I think that the battery at 72V on the Samsung 30Q will be more than enough. And it will be enough to feed 25A per motor.
            But the mileage is not enough. I drove relatively little on the current configuration, but at the maximum speed you can drive at least 25 km. It suits me to ride to work and back.
            I'm afraid to imagine how powerful the 35A configuration is on the motor. But I can not find out yet. Controllers will not allow.

            Soon I will make the light: front light, front and rear indicators, brake light and beep. Cruise control and power button on the controllers are already there. Everything will be displayed on the steering wheel straight to the motorcycle buttons. Very convenient solution.
            A friend will make a wattmeter and then it will be an ideal electric bike for quick movement around the city.

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