Building a TSA travel friendly 13s1p battery using 18500 cells.

[scm007]

I am building travel friendly < 100wh battery packs for a 48V Bafang M820. Originally I was going to target the Panasonic NCR18500A cell : NCR18500A - Lithium-ion Batteries - Secondary Batteries (Rechargeable Batteries) - Panasonic

This cell has a capacity of 2.040 ah @ 3.6V. 13 of these in series yields 46.8V x 2.040 AH = 95.5 WH.

However the voltage is 3.6V. My understanding is that I need 3.7V cells (13*3.7 = 48.1) (13*3.6 = 46.8)?

I will have 5 of these that I will wire together with a parallel switching circuit that drains the subpacks properly (off the shelf item). Charging I haven't figured out yet but will likely just charge them in parallel once I know they are all approx the same voltage.

I am an experienced engineer but I have never built ebike batteries before. I would prefer to order from a supplier who can build the packs for me. I don't mind ordering from China.

Can someone recommend:
1.) High quality 18500 cell that 13s1p will be 48V and < 100WH
2.) BMS to manage the cells
3.) Manufacturer who can create ~10 of these prototypes.

Thanks!

 

[mike_kelly]

I don't build my own battery packs because it can be dangerous. That said yes you need the full voltage required by the specified motor voltage. But you can get there any combination the ends up with 48v.
I can't answer any of your other questions.
Another approach, although it might not be sized to the requirement, might be to look into pre-made rc batteries. Just make as harness to plug them into.

 

[gido]

ebikes.ca makes high quality travel batteries but 36v, ask them for 48v

LiGo Batteries - Grin Products - Product Info

The LiGo battery is a modular 36V pack designed and manufactured at Grin that is just under the 100 Wh limit allowed for passenger air travel. This allows you to bring multiple small batteries with you in your carry-on baggage, and then hook the packs together to behave as a single large battery...

ebikes.ca

 

[Waynemarlow]

I am building travel friendly < 100wh battery packs for a 48V Bafang M820. Originally I was going to target the Panasonic NCR18500A cell : NCR18500A - Lithium-ion Batteries - Secondary Batteries (Rechargeable Batteries) - Panasonic

This cell has a capacity of 2.040 ah @ 3.6V. 13 of these in series yields 46.8V x 2.040 AH = 95.5 WH.

However the voltage is 3.6V. My understanding is that I need 3.7V cells (13*3.7 = 48.1) (13*3.6 = 46.8)?

I will have 5 of these that I will wire together with a parallel switching circuit that drains the subpacks properly (off the shelf item). Charging I haven't figured out yet but will likely just charge them in parallel once I know they are all approx the same voltage.

I am an experienced engineer but I have never built ebike batteries before. I would prefer to order from a supplier who can build the packs for me. I don't mind ordering from China.

Can someone recommend:
1.) High quality 18500 cell that 13s1p will be 48V and < 100WH
2.) BMS to manage the cells
3.) Manufacturer who can create ~10 of these prototypes.

Thanks!

Be careful with what appears a very limited knowledge of batteries. Can I suggest perhaps doing quite a bit of research into battery building before proceding down this route. Little things like parallel charging with approx. voltages can lead to some serious problems. Choosing the wrong cell, the wrong BMS, the way they are connected between packs, the heat dissipation of the wrong cell being asked to supply too much current could have dire consequences. My own view is that lots of small packs just complicates an already complicated situation.

As to travelling with 100Wh packs, airlines seem to add up the packs to a total rather than individual packs but that differs so much between airlines. Some of the EU riders now post the batteries to their destination such is the totally almost chaotic way we move batteries around the globe. I'm afraid there is no easy answer to this problem.

 

[mike_kelly]

If you do want to do this then Grin is close to you and they know what they are doing. But as noted, airlines are flakey in following their own rules and many gate agents don't know the rules.

 

[randycpu]

I am an experienced battery builder and a EE.
I suggest a book by Micah Toll titled "DIY Lithium Batteries: How to Build Your Own Battery Packs". You will need a quality spot welder and lots of pure nickel strip. And balls of steel.

BMS choice is the most important ingredient, and the balancing function is the most important BMS feature. There are 1000s of 13S BMSs.

Questions to consider:
1 - Why constrain yourself into the 18500 format? (TIL about 18500s.) There are only 2 18500 manufacturers on my Chinese cell supplier's current price sheets. Sanyo and Panny (and the Sanyos are not available).
2 - 3.6V cells connected 13S make 46.8 volts. 100WH/46.8V=2137mAH. So that is your target max (legal) cell capacity. There are several low capacity 18650 cells available that will be close to 2000mAH. Their market niche is high current capacity (up to 10C), so they an excellent choice for a 1P pack.
3 - The problem you are trying to solve is getting the packs accepted by a gate agent that does not understand what they are looking at. To them the label is all that matters, and you are the one printing the label. You can mentally fudge manipulate the numbers a bit to be able to in good conscience label the packs under 100WH. For example, set their max charge to 4.10 instead of 4.20 volts. Now you can use 2200mH cells, of which there are many good quality examples. And the cells will last a lot longer. But simple BMSs will not balance below 4.20.
4 - Don't worry about 3.6 vs 3.7V cells. I feel that there is some specsmanship here. Nominal voltage is the mean point over time of the voltage discharge curve between the minimum allowed voltage and max voltage. The max voltage on all NMC chemistry cells is 4.20V.
Five years ago, most NMC cells' nominal voltage was 3.6 or 3.65 volts. Now the trendy spec is 3.7 volts.

I am concerned about the functionality of the "parallel switching circuit". This is new to me, and it is critical to your idea.

Lastly, you are in the wrong forum. Have you heard of Endless Sphere DIY EV Forum ? That is the center of the universe

Good luck

 

[sethimus]

micah toll? the guy that only suggests cheap unsafe bikes over at electrek? who can’t ride a mountain bike? that guy?

 

[powerup]

Micha Toll is the guy who was overvolting using the high capacity golden cells. That guy!