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Ebike help
#1
Hi Guys,

So I've been harvesting cells for a few months now. I've got about 120 good cells (most have 2000+ aH) and my goal is to make a ebike. I got some question that hopefully you guys can help me out with. I'm trying to make a battery that can power my ebike so it can take me to work and back, and thats roughly 30 miles. I'm a big guy. I weigh 230 pounds (104.3 kg) and im 6 feet 3 inches (190.5 cm) tall. 

How many wH should i aim for?

I'm goign to buy a conversion kit that has a 48V1000W brushless gearless hub motor. I believe i can make a 4.94 kWh battery (103aH * 48v) with 52 cell (103aH/2000mAh **roughly). Is my thinking wrong on this? is this enough?

Guidence appriciated.

Thanks.

EDIT:
Turns out i did my math wrong... I am making a 13s4p battery. So its 4 * 2000mAh = 8Ah. Then it would be 48.1v * 8Ah = 388.8wh. Is this right?
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#2
Are you getting a bafang motor set up? I have that motor and run a 13.2ah battery and get roughly 70km out of a charge. I'm 80kg and 167cm, I am also a Fit person and still ride it as much like a normal bike as possible. If I don't put much effort into pedalling and use it more like a motor bike I can get around the 20 to 30km from a charge. This is me riding at an average of 30km per hour.
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#3
Hey mate,

I've made 2 ebikes and learned a lot.  Both have a 48V 1,000W hub motor on a 26in rear wheel.

1) 1st attempt used a 13S8P battery made from recycled laptop cells (av 1.95Ahr so ~ 750Whrs)  1,000W hub motors pull about 20+ Amps so using laptop cells in an 8P configuration was too few (2.5A discharge per cell)

Would go about 20km with a few mild hills (I'm 85kg) and battery would get hot, voltage would sag badly and BMS would cut out if pushed too hard.

2) 2nd attempt much better - 14S10P using Samsung INR18650-20R (and 25R) from recycled Ego 56V packs - each cells happy at 20A discharge so no more voltage sag.  Capacity is 20.58Ahrs or 1.07 kWhrs - easily gets me 26km to work including 3 very steep hills (Strava says 520m elevation gain).  

Volts drop from ~58.8 to ~50.9V - so roughly down to 3.64V per cell so somewhat under 50% capacity (very roughly).

26km trip takes around 42min averaging 38km/hr - takes 5hrs on a 2A lead acid charger to get the volts back up.

A lot of fun to ride.  Done ~ 1,000km on it so far.

Recommendations:

a) use high current cells to avoid voltage sag you get with laptop cells
b) bus bars between cells in series to be min 20A capable (~ 4.6mm2 DC cable)
c) replace plug in connectors from controller to hub motor with soldered joints (a couple had melted when I looked)
d) upgrade thin wires from controller to hub motor with at least 4.6mm2 cable ~ 20A capable
e) make sure your bike has disk brakes ;D
Bdaearth and BoomBoomShroom like this post
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#4
If you haven't sourced your motor yet put some thought into a mid drive so you can still have 10 gears on the rear wheel.

http://dillengerelectricbikes.com.au/ele...afang.html

This is the kit I put on my bike but this was well before I found anything about doing a complete build yourself. I have the 11.6ah battery not a 13.2 as said previously, it was the only option when I got it, but you are building your own so you don't need to worry about that.
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#5
Hello Emerca, first of all sorry for my english, im spanish. I wat to make a battery for my 48v 1000w ebike kit. My ideas was: 13s10p battery with old laptop cells (all 2000mA). The controler can maximun off 26A. So 26/10= 2,6A per cell? Apart of that i wwant to put 5A fuses each cell? That was safety?, to discharge each cell to 2,6A? Thank you for readingSmile
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#6
(11-04-2018, 01:50 PM)IkerTronic Wrote: Hello Emerca, first of all sorry for my english, im spanish. I wat to make a battery for my 48v 1000w ebike kit. My ideas was: 13s10p battery with old laptop cells (all 2000mA). The controler can maximun off 26A. So 26/10= 2,6A per cell? Apart of that i wwant  to put 5A fuses each cell? That was safety?, to discharge each cell to 2,6A? Thank you for readingSmile

Hi IkerTronic - ha your english is fine mate - far better than my spanish!

Sorry to say I can't recommend laptop cells for an ebike - unless you go 13S20P (or go a lower wattage motor).  

IMHO laptop cells are usually rated for max discharge at ~500mA - I have tested a few thousand at 1,000mA (on Opus testers) and they don't get too hot - that's why I say 20P min for laptop cells.  If it's your 1st pack and want to have some fun and don't mind damaging cells - your 13S10p will work for a few hundred km.

Another suggestion is to go 16S10P - the BMS is still cheap and the increased volts will lessen the amps.

The main problem is that an ebike battery using recycled cells must have a BMS and at say 20A on laptop cells they will heat up quite a bit, voltage will sag (amps increase) and will cause a low voltage disconnect - just when you don't want one.

Maybe do what I did and build a laptop pack, have some fun and see what happens while you get some high current cells from power drill packs??


And yes I fuse both +ve and -ve with .26mm copper wire to protect against shorts etc.

Good Luck!
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#7
(11-04-2018, 03:52 AM)emerca Wrote: Hey mate,

I've made 2 ebikes and learned a lot.  Both have a 48V 1,000W hub motor on a 26in rear wheel.

1) 1st attempt used a 13S8P battery made from recycled laptop cells (av 1.95Ahr so ~ 750Whrs)  1,000W hub motors pull about 20+ Amps so using laptop cells in an 8P configuration was too few (2.5A discharge per cell)

Would go about 20km with a few mild hills (I'm 85kg) and battery would get hot, voltage would sag badly and BMS would cut out if pushed too hard.

2) 2nd attempt much better - 14S10P using Samsung INR18650-20R (and 25R) from recycled Ego 56V packs - each cells happy at 20A discharge so no more voltage sag.  Capacity is 20.58Ahrs or 1.07 kWhrs - easily gets me 26km to work including 3 very steep hills (Strava says 520m elevation gain).  

Volts drop from ~58.8 to ~50.9V - so roughly down to 3.64V per cell so somewhat under 50% capacity (very roughly).

26km trip takes around 42min averaging 38km/hr - takes 5hrs on a 2A lead acid charger to get the volts back up.

A lot of fun to ride.  Done ~ 1,000km on it so far.

Recommendations:

a) use high current cells to avoid voltage sag you get with laptop cells
b) bus bars between cells in series to be min 20A capable (~ 4.6mm2 DC cable)
c) replace plug in connectors from controller to hub motor with soldered joints (a couple had melted when I looked)
d) upgrade thin wires from controller to hub motor with at least 4.6mm2 cable ~ 20A capable
e) make sure your bike has disk brakes ;D

I did some more research and was going to attempt a 13s10p setup. But from the info you guys seem to be giving me it seems like i need to avoid the voltage sag, so I'll attempt a 14s10p. I just need more cells. I sadly did a count recently and only have about 90 cells. Could have sworn i had close to 120 lol.

I plan to have a bus bar and fuses on my pack. What kid of bms do i need? Is it a 14s 52v 20A?
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