Looking for custom battery, bms, and controller build help

[veranth]

Hello,

I've been lurking around here for a while now and there's a lot of great information and talented people. I'm new in this space but I'm soaking up as much as I can. I'm interested in building a stand up electric scooter. It will require a custom battery and controller. I've seen a lot of different off the shelf stuff but my project requires low profile equipment.

I'd like everything except the charger to fit in a 32 mm thick space. This includes lipo battery (roughly 48V 15Ah, bms, and controller for hub motor (like BMC for instance). The batteries and controllers that I see are always big bricks that you tack onto a bike frame. It seems possible to build low profile stuff but I haven't seen it done. Certainly the parts will need to be wide and long but I'm fine with that. I'm hoping that someone here can point me in the right direction to a builder or hobbyist who can help me out.

I'll add more specs and drawings as soon as I get them ready.

Thank you,
Veranth

 

[veranth]

Here is what I had in mind for the battery to keep the profile flat. Use 18650's which are 18.6mm diameter and roughly 65 mm long and 3.6V 2.9Ah per cell. I would stack them staggered like this:

I thought of doing 4 or 5 3s6p packs like this wired together serially to make a 12s6p pack (or 15s6p depending on what fit). I thought it would be easier for me to charge and manage with smaller packs. If a 12s6p or 15s6p is not difficult to charge as a single pack then I would likely go with one big pack. I was hoping that this arrangement along with bms and controller could fit in a space 32mm x 210mm x 570 mm (give or take).

 

[dogman dan]

This, for example would be 26mm thick. http://www.hobbyking.com/hobbyking/store/__17253__Turnigy_nano_tech_5000mah_3S_35_70C_Lipo_Pack.html

RC lipo (lico) would be the smallest physical size of anything, but limn would also be as small in pouch type cells.

48v 15 ah of 18650's is a big package however you stack them.

These would be 4 cells and only 27mm thick.
http://www.hobbyking.com/hobbyking/store/__21361__ZIPPY_Compact_4000mAh_4S_25C_Lipo_Pack.html

And if you want tiny, then the RC motors and controllers could be your ticket too. But mostly a 25 amps bike controller is not that big, it just comes in a big box. So you might be able to remove the box and mount inside a slimmer container that still heatsinks heat away.

Brushed contollers tend to be smaller, if you choose a brushed motor.

 

[veranth]

This, for example would be 26mm thick. http://www.hobbyking.com/hobbyking/store/__17253__Turnigy_nano_tech_5000mah_3S_35_70C_Lipo_Pack.html

RC lipo (lico) would be the smallest physical size of anything, but limn would also be as small in pouch type cells.

48v 15 ah of 18650's is a big package however you stack them.

These would be 4 cells and only 27mm thick.
http://www.hobbyking.com/hobbyking/store/__21361__ZIPPY_Compact_4000mAh_4S_25C_Lipo_Pack.html

And if you want tiny, then the RC motors and controllers could be your ticket too. But mostly a 25 amps bike controller is not that big, it just comes in a big box. So you might be able to remove the box and mount inside a slimmer container that still heatsinks heat away.

Brushed contollers tend to be smaller, if you choose a brushed motor.

I like the idea of using pre-built cells with balancing leads built in and those cells are a good height. I had previously ruled those out because I thought I would need to use 12-16 of the cells that you mentioned in order to get the Volts and Ah's that I need. If the zippy cell is 4Ah/14.8V wouldn't I need 12 to get 16Ah/44.4V? If that's right, I think it would be a larger space and weight than 72 18650's. I didn't account for the weight of soldering and wiring the 18650's together, maybe that would make up the difference?

I also like the idea of taking a bike controller and taking it out of the package. Is there one you would recommend? I just need the basic features.

 

[dogman dan]

I just thought the air space in the stack or round cans was sure to be less dense than pouches. Reading back, nearly 3 ah per 18650? I was thinking more in terms of 1 ah per can, and hundreds of them.

Definitely easier to assemble some HK pouches into a larger pack though. Nothing wrong with a 3 packs for testing purposes in 5 ah size.

 

[dnmun]

how can you make the electrical connection on the cylindrical cells if you stack them end to end? there is no way to spot weld them and soldering kills them.

 

[amberwolf]

Spot weld the tabs on first while cells are parallel to each other, then fold the tab over as you put the cell end to end. It's a common method of making connections in laptop packs, flashlights, cordless screwdrivers, etc.

 

[dnmun]

yes, if you have tabs on them then spot weld the tabs but i thought you said 15Ah and that requires about 14 of the little cylindricals to all be welded together in parallel first and then you make the connection to the next cell in the series. you can look at how the Vpower packs do it. to me it is just a short away from burning up when you use these cells like this. jmho.