DIY battery pack XXXL

[vulubalulu]

I replaced a fair share of cells on used up or defective ebikes, so I am not unfamiliar with this field. I had an idea recently. Instead of carrying around 4 heavy batteries with 50 cells each, why not build a big battery with 200 cells, i.e. 20p10s. I am aware that one faulty cell can ruin the whole battery without fuses between each block an charging time will quadruple. I'd like to be able to go on very long trips.
Does this idea sound sane? Why would this be a bad idea?

 

[biknut]

Nothing wrong with big battery's as long as they're decent quality. My great 2013 Stealth Bomber came with cutting edge technology for the time, but the biggest battery that would fit in the frame was only 18 ah. At traffic speed it could suck the battery dry in 20 miles. That was then, now my current battery is made with 200 18650 LG cells that are 3500mah. It's 20s 10p for a total of 72v, 35 ah. Now I can easily ride 50 miles at traffic speed, which is way betta.

I'm now in the process of building a new battery with Samsung 50s 21700 5000mah cells. It's going to be the same 72v, 35ah, but now with only 140 cells.

 

[addertooth]

I am considering the 17S10P (63.75 volt 50 Amp Hour) battery from Northeast battery systems for my Motor Goat v3 at this time. It uses the desirable Samsung 21700 5 Amp hour cells. It comes with an 80 Amp battery blender, and works with the existing 63.75 Volt 25 Amp Hour battery. I like the idea of having a total of 75 Amp Hour of capacity.

The thought of being able to run flat out for an hour and a half seems appealing. However, the thought of going light on the throttle and running at 20 MPH for 9 and a half hours sounds "less fun".

 

[CrossRoads]

I've thought about the same, but what's the advantage of one big vs two small, really? With small batteries in parallel with a battery blender you have the advantage of 1) higher wattage output, 2) redundancy enginnering, i.e., one battery fails you can get home on the other, and 3) rapid charging with two chargers plugged in at the same time. The only advantage i see in one big one is mounting the thing might be easier, but maybe not, and i guess you save a few bucks on not needing an extra bms.

Having said that, both my current e-bike setups both have 40 amp-hour batteries. Just looking back i probably would rather have two 20's.

 

[vulubalulu]

I've thought about the same, but what's the advantage of one big vs two small, really? With small batteries in parallel with a battery blender you have the advantage of 1) higher wattage output, 2) redundancy enginnering, i.e., one battery fails you can get home on the other, and 3) rapid charging with two chargers plugged in at the same time. The only advantage i see in one big one is mounting the thing might be easier, but maybe not, and i guess you save a few bucks on not needing an extra bms.

Having said that, both my current e-bike setups both have 40 amp-hour batteries. Just looking back i probably would rather have two 20's.

In my case it it would be four batteries I'd have to carry around on the sides which I try to avoid, but I see where you are coming from. Separate units are faster to charge and it's more flexible, that's why I haven't committed to it, yet I guess.