fredo gauvino
100 mW
- Joined
- Oct 11, 2009
- Messages
- 39
Hello all,
This winter I built a Magie Pie hybrid bike for my girlfriend. 8)
It went well, but the 48V 15A battery is ridiculously too heavy (10 kg) and way too fast (44 kph) for my girlfriend.
She does not feel safe, therefore she is not using it.
So this spring, I started gathering used laptop battery packs and experimenting with them.
Why not ! I got them for free...
My goal was to build a slower, lighter and "free" battery pack that she could use to do her 32 km commute, instead of her gaz-guzzling subaru.
I carefully opened each laptop battery, testing meticulously each cell pairs without removing the tabs...
- I discarded the cells that were < 3.0 Volts.
- Some of those batteries were really old ( < 2007) and would heat up while beeing charged. I discarded them.
- Others would charge well, but would sag like crazy when asked to give more current. I discarded them.
- I then started a long process of checking the actual capacity of each pairs.
- The cells that gave less than 3000 mAh per pair were also discarded.
Garbage/Keep ratio is about 50%... :|
Most of the remaining ones were > 3500 mAh =>/2 = 1750 mAh per cell
So about 80% of their original 2200 mAh capacities.
Not bad for used cells !!!
So I was left with 60 pairs of 'good' cells. For a total count of 120 x 18650 cells.
I chose to organize the batteries in 10S-12P configuration. This would become a 21 Ah / 37 Volts nominal battery (42V full) The battery weigth about 6kg.
I don't need 'that' much Amps/Hour, but since the cells are old and are not really capable of giving lots of amps, the more in parallel the better.
I then started thinking about where and how I would assemble them...
The cool thing with 120 batteries is that they can be placed in a equilateral triangle, like this :
The other cool thing is that the bike I plan to put the battery on has a very close to 60 degs angle between the downtube and the seat tube.
So it would be a near perfect place for them.
Putting a 6kg battery on the rear rack would probably be more stealthy, but with a Magic Pie, you are already not very stealthy.
the handling would also suffer.
So I hot-glued a large pyramid of 18650 cells in a triangle like this.
I ordered a 10S BMS and Li-ion 42Volts 2Amps charger from China, but it takes decades to arrive.
Meanwhile, I soldered everything so that I could use my Hobby charger in 2 x 5s configuration, just like my other bike's LiPos(2 x 6s)
Soldering went nice and easy, on tabs.
I just ducktaped the battery on my bike and did a quick test run, and...
It works !
I forgot to check the max speed and if the voltage was getting low during acceleration from a stop. I was too excited.
It fell not as quick on acceleration as the large 48V battery, but the bikes definitely handle much better.
I need to do more tests, but it looks ok for now.
Normally, at 50.4 Volts, the cycle analyst reports 24-25 amps on startup, then it lows down to 12-15 amps once up to speed.
This should ask 2 amps momentarely then 1 amp from each cell, I hope that they can survive this !
Also at 42 Volts, it should be slower, so it should require less current, no ? Not sure about this...
Now I am currently building a V shaped box to hold the battery in place using bottle mount screws.
I already started experimenting with aluminium and U shapes, it's promising. The side cover will be made from black coroplast.
Hopefully the battery will survive it's first 32km commute very soon.
Sorry for the long post and Stay tuned !
This winter I built a Magie Pie hybrid bike for my girlfriend. 8)
It went well, but the 48V 15A battery is ridiculously too heavy (10 kg) and way too fast (44 kph) for my girlfriend.
She does not feel safe, therefore she is not using it.
So this spring, I started gathering used laptop battery packs and experimenting with them.
Why not ! I got them for free...
My goal was to build a slower, lighter and "free" battery pack that she could use to do her 32 km commute, instead of her gaz-guzzling subaru.
I carefully opened each laptop battery, testing meticulously each cell pairs without removing the tabs...
- I discarded the cells that were < 3.0 Volts.
- Some of those batteries were really old ( < 2007) and would heat up while beeing charged. I discarded them.
- Others would charge well, but would sag like crazy when asked to give more current. I discarded them.
- I then started a long process of checking the actual capacity of each pairs.
- The cells that gave less than 3000 mAh per pair were also discarded.
Garbage/Keep ratio is about 50%... :|
Most of the remaining ones were > 3500 mAh =>/2 = 1750 mAh per cell
So about 80% of their original 2200 mAh capacities.
Not bad for used cells !!!
So I was left with 60 pairs of 'good' cells. For a total count of 120 x 18650 cells.
I chose to organize the batteries in 10S-12P configuration. This would become a 21 Ah / 37 Volts nominal battery (42V full) The battery weigth about 6kg.
I don't need 'that' much Amps/Hour, but since the cells are old and are not really capable of giving lots of amps, the more in parallel the better.
I then started thinking about where and how I would assemble them...
The cool thing with 120 batteries is that they can be placed in a equilateral triangle, like this :
The other cool thing is that the bike I plan to put the battery on has a very close to 60 degs angle between the downtube and the seat tube.
So it would be a near perfect place for them.
Putting a 6kg battery on the rear rack would probably be more stealthy, but with a Magic Pie, you are already not very stealthy.
the handling would also suffer.
So I hot-glued a large pyramid of 18650 cells in a triangle like this.
I ordered a 10S BMS and Li-ion 42Volts 2Amps charger from China, but it takes decades to arrive.
Meanwhile, I soldered everything so that I could use my Hobby charger in 2 x 5s configuration, just like my other bike's LiPos(2 x 6s)
Soldering went nice and easy, on tabs.
I just ducktaped the battery on my bike and did a quick test run, and...
It works !
I forgot to check the max speed and if the voltage was getting low during acceleration from a stop. I was too excited.
It fell not as quick on acceleration as the large 48V battery, but the bikes definitely handle much better.
I need to do more tests, but it looks ok for now.
Normally, at 50.4 Volts, the cycle analyst reports 24-25 amps on startup, then it lows down to 12-15 amps once up to speed.
This should ask 2 amps momentarely then 1 amp from each cell, I hope that they can survive this !
Also at 42 Volts, it should be slower, so it should require less current, no ? Not sure about this...
Now I am currently building a V shaped box to hold the battery in place using bottle mount screws.
I already started experimenting with aluminium and U shapes, it's promising. The side cover will be made from black coroplast.
Hopefully the battery will survive it's first 32km commute very soon.
Sorry for the long post and Stay tuned !
