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Old 02-23-2017, 02:39 PM   #1 (permalink)
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TexasElectric - eBike build

Hi, my name is Adam.

I am in the early stages of building my first electric bike. I have been playing with electronic motors and batteries for many years, only in the past year or two I've gotten into circuitry and making my own batteries and super capacitors.

For my ebike I have chosen to use 32650 LiFePO4 cells. The reason for this is because of LiFePO's inherent safety over the more popular 18650 Lithium Ion cells. I purchased 80 32650 LiFePO4 cells. I plan to use 75 of the cells. Each cell weighs approx 145 grams. (75 cells x 145 grams = approx 24lbs)

Each cell is 3.2v 5500mah. 75 cells in a 5p x 15s or 15s x 5p configuration to give me 48v with 27.5mah.

Question 1:
If I connect the cells in a 5 parallel x 15 series configuration, is that the same as a 15 series x 5 parallel configuration? Is there a benefit of one configuration over the other?

Question 2:
What type of BMS (Battery management system) or PCB (Protection circuit board) do you recommend I use?

For the motor I plan to purchase a 48v 1500w direct drive rear hub motor. I plan to buy the motor and all associated accessories as a kit on eBay.

For the bicycle, I will be purchasing a used 26" mountain bike from my local bike shop. My budget for purchasing the bike is $400-$500. -just a side note, i've owned big box store bikes and currently own a high end name brand bike. There is a HUGE difference between the two, at the end of the day you get what you pay for.

I will store the battery and motor controller in a rear rack mounted bag that will sit on top of the rack.

I am an avid cyclist, I ride weekly by myself and with a club. On my bicycle I have what's called a power meter. Bicycle power meters are very accurate and very expensive ($xxx to $xxxx). For those that don't know, a bicycle power meter is a strain gauge that measures the torsion (or flex) of the surface it's mounted on. In the case of my power meter, it's mounted on the crank arm. The power meter calculates the RPM of my pedaling cadence and the strain (or flex) of the amount of force I apply to the pedals to give me a number represented in "watts".

My bike weighs approx 14lbs, I weigh approx 150lbs. When fully loaded with water, spare tubes, pump, etc... I estimate the total weight to be approx 170lbs.

When I am riding at a steady pace of 18mph with a 5-8mph head wind, I can hold 18mph by putting out 175-225 watts.

If I estimate this eBike i'm building 'with me included' to weigh: (approx 225lbs)
- Bike 17lbs
- motor 15lbs
- motor controller 1lb
- batteries 25lbs
- me 150lbs

Using the data I have from my power meter and the estimated weight/power of my proposed eBike. I estimate I would need 250-300 watts to maintain 18mph on a relativity flat surface with a small head wind. With an estimated range of 80 miles to 95 miles? (48v x 27.5ah = 1320 watt hours / estimated watts needed to maintain 18mph 'ie. 250-300 watts')

I'll post pictures and videos as things progress.

I'm sure i'm missing a few things, but that's what i've got figured out for now... i've got to go to work.

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