Building a new 48v 30Ah pack. This all checks out yeah?

[neptronix]

50S' larger max output rating is due mostly to it's ability to handle more heat shedding, instead of having substantially lower IR.
High IR is our problem.


Notice the 3C line ( 15A ). It looks close to the 3.25v nominal we get from the 50E.
It would be less likely to become a fireball due to critical heat levels ( due to voltage sag ) building up in the battery case during aggressive summer riding.

I would still shoot for way better than that.

 

[Skoomd1]

50S' larger max output rating is due mostly to it's ability to handle more heat shedding, instead of having substantially lower IR.
High IR is our problem.
View attachment 370834

Notice the 3C line ( 15A ). It looks close to the 3.25v nominal we get from the 50E.
It would be less likely to become a fireball due to critical heat levels ( due to voltage sag ) building up in the battery case during aggressive summer riding.

I would still shoot for way better than that.

The stock cells that I've been using are Eve 18650 2550mah cells. According to mooch's testing, they have nearly twice the IR. I'm only going to be pulling up to 45a. It cannot be be that bad? 50S are not only more expensive, but have terrible cycle life 60% capacity after 200 cycles

 

[neptronix]

Lower capacity usually = lower IR, with the exception being recent molicel cells, which don't have that tradeoff.

If you are only pulling 45A max, then you don't have the power to accelerate or climb a hill anywhere near the top speed you're looking for ( 45mph, right? ).
45A x 48v = 2140w
40mph requires 2000w on absolutely flat ground with no wind.
Typically you'd want 2x of that power on tap to accelerate and climb hills.

~2000w peak would be more ideal for a vehicle that has a top speed of 30mph ( ~ 1000w sustained )
In that case, this battery would work, and the vehicle wouldn't be so wildly overpowered considering the chassis that isn't up to the task of high speed.

 

[Skoomd1]

Lower capacity usually = lower IR, with the exception being recent molicel cells, which don't have that tradeoff.

If you are only pulling 45A max, then you don't have the power to accelerate or climb a hill anywhere near the top speed you're looking for ( 45mph, right? ).
45A x 48v = 2140w
40mph requires 2000w on absolutely flat ground with no wind.
Typically you'd want 2x of that power on tap to accelerate and climb hills.

~2000w peak would be more ideal for a vehicle that has a top speed of 30mph ( ~ 1000w sustained )
In that case, this battery would work, and the vehicle wouldn't be so wildly overpowered considering the chassis that isn't up to the task of high speed.

I know I won't achieve those speeds normally. I will be using field weakening. But even if I can't, my main goal is simply achieving more than I am now. I get 35mph on a full charge now with the Eve 18650 cells (10s6p), but that's with field weakening

 

[neptronix]

Just remember that field weakening increases amp draw, and said pack doesn't have much extra power to utilize.

 

[Skoomd1]

I do have a question about the IR. The IR of the 21700 Samsung 50E cells are 16.9mΩ DC and my current 18650 eve cells are 31.7mΩ DC. They do tend to sag pretty bad, but wouldn't the 50e cells sag way less? Idk how the chemistry and cell size makes a difference in this regard. I often see 45-50c in the pack after an aggressive 10-12 mile ride, which is about as high as I like to go on lion cells.

 

[Chalo]

I do have a question about the IR. The IR of the 21700 Samsung 50E cells are 16.9mΩ DC and my current 18650 eve cells are 31.7mΩ DC. They do tend to sag pretty bad, but wouldn't the 50e cells sag way less?

IR for the pack is the resistance for each cell, times the number of cells in series , divided by the number of cells in parallel. (Plus whatever resistance you get from the hokey interconnections of lipstick cells.) So comparing one cell against one cell doesn't tell you anything unless they're both the same capacity and you're using the same number of cells in either case.

 

[Skoomd1]

IR for the pack is the resistance for each cell, times the number of cells in series , divided by the number of cells in parallel. (Plus whatever resistance you get from the hokey interconnections of lipstick cells.) So comparing one cell against one cell doesn't tell you anything unless they're both the same capacity and you're using the same number of cells in either case.

Ah okay, ty. Using that calculation, my original pack comes to 52.83mΩ, and this new one i am building should be 36.61mΩ. So yeah theoretically it should have less voltage sag?

 

[neptronix]

if you had a watt meter, you'd be able to tell.

The voltage sags i calculated should be correct but don't take in account resistance from the power bus, BMS, and wiring. it will be a tiny bit worse in reality.

Compare the lowest voltage you see at full throttle with the resting voltage and you have a number to compare to.

 

[Skoomd1]

if you had a watt meter, you'd be able to tell.

The voltage sags i calculated should be correct but don't take in account resistance from the power bus, BMS, and wiring. it will be a tiny bit worse in reality.

Compare the lowest voltage you see at full throttle with the resting voltage and you have a number to compare to.

I see. Guess I will have to take readings from the smart BMS to be sure.