4p configurations should not use high capacity low discharge cells

[woke rider]

"The real take away is that 4p configurations should not use high capacity low discharge cells.  The battery sag is significant, especially at lower states of charge.  When running near top speed that the wheel can manage at a given state of charge, it is very easy to over torque the wheel and cutout.  With the Extreme, we are seeing it happen faster than the alarms can detect and report the condition." @Rollin-on-1

I don't completely understand this, as an important power dynamic. So, to use my wheel as an example, Ninebot Z10, my first question is: 1> How would high discharge cells improve my wheel's performance? 2>How do high discharge cells increase torque? 3>How do high discharge cells improve safety?

[Rollin-on-1]

1 hour ago, earthtwin said:

"The real take away is that 4p configurations should not use high capacity low discharge cells.  The battery sag is significant, especially at lower states of charge.  When running near top speed that the wheel can manage at a given state of charge, it is very easy to over torque the wheel and cutout.  With the Extreme, we are seeing it happen faster than the alarms can detect and report the condition." @Rollin-on-1

I don't completely understand this, as an important power dynamic. So, to use my wheel as an example, Ninebot Z10, my first question is: 1> How would high discharge cells improve my wheel's performance? 2>How do high discharge cells increase torque? 3>How do high discharge cells improve safety?

I think your Z10 is an 8p configuation IIRC, so let's leave your Z10 out of the discussion and speak in generalities.

1) High discharge cells do not suffer from sag as much as low discharge cells do.  This allows for higher speeds at lower states of charge, or makes riding at a given speed safer than it would be with lower discharge cells.

2) Torque is not affected...the wheel's torque is based on magnet size and the number of windings and size of copper wire used for the windings.  Tire diameter affects the accessibility to the wheel's torque.  Don't confuse the negative effects of battery sag with torque.

3) With 4p or less battery configurations battery sag is significant.  Delivered voltage is what yields speed.  As voltage decreases, the maximum speed the wheel can go and maintain its balance also decreases.  If you are riding near that maximum speed and hit a bump or lean too hard, the wheel asks for a lot of current, which causes voltage sag, which eventually drops the voltage that can be delivered to a level that is less than is needed to stay upright.  An over-lean occurs, and you get teleported to the ground. Higher discharge cells =less sag, thereby reducing the risks.

For 6P and above battery configurations, high discharge cells become less important because the battery packs can deliver sufficient current thereby reducing battery sag.  

As for your Z-10, it is a unique wheel.  What it is cabable of for its system voltage is pretty incredible.  But that speaks more to the fw and quality of the components.  It was truly a wheel ahead of its time.  Too bad Ninebot isn't in the EUC game anymore.  I'm pretty sure they would make the top wheels on the marjet look like toys in comparison.

 

[alcatraz]

Depends on your weight and riding style too.

Heavy riders or accelerating/braking quickly is going to move a lot of amps. 

A light rider accelerating quickly or a heavy rider accelerating gently might get away with high capacity cells without issue.

Ambient temperature is also very important.

If you ride in hot or freezing temperatures your amp budget is going to be slashed. That's where you need high amp cells for those more demanding situations.

Edited September 9, 2023 by alcatraz

[Rollin-on-1]

3 hours ago, alcatraz said:

Depends on your weight and riding style too.

Heavy riders or accelerating/braking quickly is going to move a lot of amps. 

A light rider accelerating quickly or a heavy rider accelerating gently might get away with high capacity cells without issue.

Ambient temperature is also very important.

If you ride in hot or freezing temperatures your amp budget is going to be slashed. That's where you need high amp cells for those more demanding situations.

All good points.  With the current cost of the 50S, there really isn't a valid reason for manufacturers not to use them if their wheels are designed around 21700 cells.

[mhpr262]

Why shouldnt they be used? Most of them are rated for around 10A continuous and 14-15A pulse discharge. In a 134V wheel with a 4p configuration that would be 134V x 40A = 5360 Watt continuous and 7.700 W maximum power, more than pretty much any motor in any wheel on the market can use right now.

[alcatraz]

4 hours ago, mhpr262 said:

Why shouldnt they be used? Most of them are rated for around 10A continuous and 14-15A pulse discharge. In a 134V wheel with a 4p configuration that would be 134V x 40A = 5360 Watt continuous and 7.700 W maximum power, more than pretty much any motor in any wheel on the market can use right now.

Yeah, but if you have about a third of those 10A below zero or over 40C, then what? The pack provides 1800w but the wheel pulls 7700w.

It depends on the rider weight, riding style and ambient temp. For most of us it's ok but everyone?

[Rollin-on-1]

5 hours ago, mhpr262 said:

Why shouldnt they be used? Most of them are rated for around 10A continuous and 14-15A pulse discharge. In a 134V wheel with a 4p configuration that would be 134V x 40A = 5360 Watt continuous and 7.700 W maximum power, more than pretty much any motor in any wheel on the market can use right now.

Because of the battery sag.  Particularly in cold weather.

[Eyss]

On 9/9/2023 at 8:12 PM, Rollin-on-1 said:

With the current cost of the 50S, there really isn't a valid reason for manufacturers not to use them if their wheels are designed around 21700 cells.

Except for the short cycle life. 

From the spec sheet:

"① Capacity ≥ 2,940mAh @ after 250cycles

(60% of the standard capacity @ RT)

- Charge : 6A, 4.20V, CCCV 100mA cut-off @ RT

- Discharge: 25A , 2.5V cut-off @ RT

② Capacity ≥ 2,940mAh @ after 100cycles

(60% of the standard capacity @ RT)

- Charge : 6A, 4.20V, CCCV 100mA cut-off @ RT

- Discharge: 45A, 2.5V cut-off

(80℃ cut-off, re-discharge release < 50℃) @ RT"

I read this as the cells have 60% battery life after 250 cycles. So the adventue claims 140km of range, after 35,000km you'll have 84km of range. 

Compared to the 50e cells:

"$Capacity ≥ 3,802mAh @ after 500cycles

(80% of the Rated Discharge Capacity @ RT)

-Charge : 0.5C(2,450mA), 4.2V,CCCV 0.05C(245mA) cut-off @ RT

- Discharge: 1C(4,900mA), 2.5V cut-off @ RT"

Based on the adventure scenario, after 500 cycles/70,000km you'll still have 112km of range. 

50s might make sense on a wheel that demands a lot like the adventure, but generally I'd prefer a 50e version for resale value / longer life. While 35,000km sounds like a lot, that's based on a impossible value of 140km per cycle and it'd depend on quickly you drain your battery. 

People forget these wheels have a lot more power than most people would ever use. Run euc world, try doing a spirited run and see how often you hit the 40amps limit.

Edit: apparently the adventure doesn't use 50S cells but rather 50GB according to their website 

Edited September 11, 2023 by Eyss

[alcatraz]

I don't know if that capacity test was done by actually pulling 25A continuously for the entire 250cycles. 

That's not realistic for euc use, nor do we discharge a full cycle when the wheel starts to low battery complain (well before 2.5v).

What most people need are cells that don't overheat should we actually pull 25A for a period of time.

I'm not saying they can't be disappointing in some way. I just wish that they're compared with the other cells at the same amp draw. 

5A, 10A, 15A continuously while monitoring temperature, voltage sag and total energy withdrawn. That's fair. 50E, 50G, 50S and 40T compared. 

[alcatraz]

This is interesting. They're closer to 20A cells IRL. The capacity is tested to actually be 5000mAh (at low currents of course, as are all reported capacities)

They can take bursts of high amps like 35A which is nice. 

Edited September 11, 2023 by alcatraz

[alcatraz]

Here are the 40T (first version)

They're tested 10.1Wh @ 20A compared to 50S's 11.6Wh @ 20A. They can take ~25A continuous vs 50S's ~20A.

 

[alcatraz]

There are newer versions of the 40T cell and they seem to be able to tolerate a few more amps, at the cost of capacity. Up to 30A continuous with a capacity of ~9Wh@20A.

[mhpr262]

I am fairly certain that low cycle life is because of the crazy temps the cells reach at those high, continuous discharge rates. This will  never happen in real life unless you go up a super steep hill at ridiculous speed. In real life those cells will just be used to allow you to accelerate safely very hard, for a few seconds. I bet their cycle life is just as good or better than that of the 50E cells in those use cases.