Battery Size Affects on Acceleration, Power, and Weight

[Jesse Wilson]

My question is for riders who have tested the same model while fully charged with different sized batteries. Did the bigger battery increase acceleration, power, and/or weight?

[Steven D Wheeler]

I went from 1600WH Monster to 2400WH.

It added 7.5lbs

After installing it the Monster seemed more balanced than before.

I had to re calibrate after adding the battery.

There was no additional acceleration that I noticed, nor a decrease.

It remained the same, dang fast!

[meepmeepmayer]

Just for info, the wheel does not "see" the battery capacity, just the voltage. Which drops faster on a smaller battery, and may be less able to compensate sudden, high demands (only applies to small packs). That's all.

Any felt acceleration difference etc. would have to be purely due to the physical weight and placement  of the different batteries themselves.

(Some wheels have different voltages coming with the different battery sizes, like the Tesla or ACM/msuper V3, that's something else. Higher voltage = more power/acceleration felt)

[Bambino]

I have the KS 18s 1500/1650wh...

I feel some diferences when the batery is full charge.. 

It seems easier to maneuver and slides better ...

 

 

[mrelwood]

After upgrading a 340Wh Lhotz battery to a ~520Wh one (= +50%), I did feel it getting up inclines with slightly more authority. On my KS-16S going from 840Wh to ~1020Wh (= +20%) I didn't notice a change. Other than added distance ofcourse.

I believe meepmeepmayer is correct in that modern high powered wheels are indistinguishable regarding the relevant battery sizes, but it makes sense that the voltage sag is proportionally larger on a device with a small battery.

[Chriull]

On 30.10.2017 at 9:53 PM, meepmeepmayer said:

Just for info, the wheel does not "see" the battery capacity, 

Yes, but more cells in parallel can deliver more current, and the torque (acceleration/balancing) is direct proportional to the current. So higher capacity can deliver more current and by this more acceleration (and safety margin, meaning higher speeds were a specific acceleration is still possible) - someting about three to four actual 18650 cells should be about enough (depending on the personal usage profile and safety margin excpectations)- everything more is „just“ for extended range.

Quote

just the voltage. Which drops faster on a smaller battery, and may be less able to compensate sudden, high demands (only applies to small packs). That's all.

Any felt acceleration difference etc. would have to be purely due to the physical weight and placement  of the different batteries themselves.

(Some wheels have different voltages coming with the different battery sizes, like the Tesla or ACM/msuper V3, that's something else. Higher voltage = more power/acceleration felt)

That‘s just almost „hitting the point“. Available power/acceleration depends on the voltage motor combination and can be „just“ limited by insufficient current supply of the battery pack. It can also be linited by the firmware, as it was with earlier firmware versions of the ks16b which partially lead to problems „starting“ the wheel.

In more detail - the „normal“ voltage drop of the battery by its internal resistance is part of the maximum torque over speed limit graph of a wheel - this beforementioned „designed“ voltage motor combination which defines the abilities of wheel. But by higher loads and by this higher currents the liion cells temporarily raise their internal resistance (still within their nominal maximum current specifications) and by this lower the maximum torque over speed limit graph. By this actual acceleration is not influenced as long as one stays within this now more restricted limits, if not one overleans == less possible acceleration.

so more cells in parallel can keep up higher accelerations by raising the nominal internal resistance less because there is less „load“ per cell. And more cells in parallel means more capacity. At some point more capacity does not increase possible acceleration anymore because there is a firmware limit and a physical power dissipation limit limit(wires/mosfets).

so this has primarily nothing to do with higher voltage, just enough cells in parallel to keep the load dependend internal resistance in a range so the maximum torque over speed limit graph does not „deplete“ too much.

In regard to melting wires/connectors higher powers/accelerations can be achieved a bit easier with higher voltages.

....pffff... i hope this is understandable in „my personal english“... would be much easier for me to describe in formulas and german

 

[meepmeepmayer]

Ok, thanks for the refinement

I stand by my words, though (mostly to avoid confusion about the principles!): as long as the wheel is not limited by the battery being too weak and not being able to push enough current (= very small battery, or battery close to empty, or very high demand fringe loads), there should be (in principle) absolutely no discernible difference in behavior if the rest of the hardware stays the same. So starting with a more than 2P (3P or more) battery pack, let's say anything above 500Wh, a bigger or smaller battery should "make no difference". For such "modern" wheels, the battery is not the weakest part and therefore won't impact performance.

Of course, at low voltage the firmware might do something (like soften the pedals), but that's just because a smaller battery will be empty faster. Just like the wheel will stop when the battery is empty, but that's because it's empty, not because it's smaller.

--

Good info on the voltage. But that applies only to very high loads when the battery actually starts being the weakest part, right? Related: do you think you could realistically produce different behavior from e.g. 6P 1300Wh (2900mAh cells) vs 6P 1600Wh (3500mAh cells) battery packs, or would they be the same (other than, that, again, the smaller cells naturally  just empty faster)?

Anyways, in practice (at least for Gotways) the 84V ones are more or less proportionally stronger/torquier/better accelerating ones, that's why I said "higher voltage = more power/acceleration felt" (power not being literally the physical quantity, just how powerful it feels). Mostly so newbies would avoid buying the 67V Tesla variants (which I suspect exist only because Gotway needs to get rid of way too many ordered old 67V ACM/msuperV3 parts clogging their warehouse).

[Keith]

On 30/10/2017 at 4:38 PM, Jesse Wilson said:

My question is for riders who have tested the same model while fully charged with different sized batteries. Did the bigger battery increase acceleration, power, and/or weight?

Jesse, as ever in this forum, there is a danger of quickly diving into the exotic. Of course you will see very little difference jumping from (say) a 1200Wh battery to a 2000Wh one, the limitation is very likely to be in the electronics, not the battery.

However, you were looking at a lightweight, short distance commuting wheel and several of us warned about the very small battery wheels. Here the difference in battery can be huge. 

Most wheels use 18650 Lithium Ion batteries these weigh around 50 grams each so a set of 16 (in the typical 67V wheel) will weigh around 800g or 1.75lb. Typically these have capacities around 3 Ah with maximum around 3.5Ah so any wheel with a capacity of less than 200Wh is a single set of 16 cells. two sets of 16 cells in parallel will be 340-400Wh and so on.

Lithium Ion batteries do have significant internal resistance so drawing high current out of them will reduce the voltage, reducing the maximum power. Most 18650 cells can handle up to around 10 Amps which for a single set of 16 cells means max power is going to be 16 cells x 3.5 volts (under high load) x 10 Amps = 560W, probably a lot less as the voltage drop is likely to be even higher. So regardless of motor, electronics or anything else a battery under 200Wh will not be able to handle more than 500W for short periods.

Add a second set of 16 parallel cells and you add 1.75lb to the weight and a max of 1000W. Double that again so you get around a 680Wh wheel and you have another 3.5lb of weight for a max of 2000W power out of the battery - this is the point where electronics and motor are likely to limit instead of the battery.

Finally, voltage drops with discharge, a small capacity battery (even 340-400Wh) will have lost a significant power, to the point of being unpleasant to ride, by the time the battery is down to 50%, so true range (which is ridiculously exaggerated by most manufacturers) will really be no more than 50% of stated before you are in a sort of crawl home mode.

Obviously the 20 cell 84 volt wheels will have somewhat better power but even those need a minimum of two sets of parallel 20 cells to have reasonable power and ideally need at least 4 sets so something like 850Wh before the electronics rather than the battery become the limiting factor.

[Chriull]

1 hour ago, meepmeepmayer said:

...

Good info on the voltage. But that applies only to very high loads when the battery actually starts being the weakest part, right? Related: do you think you could realistically produce different behavior from e.g. 6P 1300Wh (2900mAh cells) vs 6P 1600Wh (3500mAh cells) battery packs, or would they be the same (other than, that, again, the smaller cells naturally  just empty faster)?

Should be about the same - just as sou said the lower capacity cells empty faster...

1 hour ago, meepmeepmayer said:

Anyways, in practice (at least for Gotways) the 84V ones are more or less proportionally stronger/torquier/better accelerating ones, that's why I said "higher voltage = more power/acceleration felt" (power not being literally the physical quantity, just how powerful it feels). Mostly so newbies would avoid buying the 67V Tesla variants (which I suspect exist only because Gotway needs to get rid of way too many ordered old 67V ACM/msuperV3 parts clogging their warehouse).

Having the same motor driven with a higher voltage increases the possible power output. As in 

seen the msuper v3s+ with empty batteries (68V) has the same „possibilities“ as a full charged 67,2V msuper v3?s?.  Just the „cell chemistry“ (internal resistance, load behaviour) and the firmware limitation will be different (limp home mode).

up to something around 30 km/h(for the fully charged 67,2V version) both versions should also behave quite similar (at least they could) - just the firmware and different cell configurations (number of parallel cells to support the high current cases) could make a difference. Also a maybe for less power designed motherboard of the 67,2V version could lead to limitations.

... and the active safety margin to handle bumps/holes is much bigger with the 84V version.So this could enable the firmware to balance more „aggresively“ leading to more „powerfull driving“/higher accelerations.

ps.: the lines for incline acceleration are to be ignored in the above linked post - still did not find the reason for the discrepancy between my calculations and real world data...

[Keith]

51 minutes ago, Chriull said:

seen the msuper v3s+ with empty batteries (68V) has the same „possibilities“ as a full charged 67,2V msuper v3?s?.  Just the „cell chemistry“ (internal resistance, load behaviour) and the firmware limitation will be different (limp home mode).

OK, we are insisting on taking this, what should be simple discussion, back to the esoteric again - so be it!

You are completely ignoring the fact that an 84v system will absolutely not have the same motor as a 67V system. The 84V motor might look like it is physically the same but it will have to be wound for a lower kV - I.e. more turns of thinner wire, so it will handle a lower maximum current. However torque is inversely proportional to kV so you will get the same torque at that lower maximum current.

In other words the physically same size motor wound for two different voltages will actually have, as near as damn it, the same maximum torque output and also same maximum power output as the higher voltage will be countered by the lower current of the high voltage motor.

The only real advantage of the higher voltage motor is reduced I squared R losses as heat due to the same power being generated at lower current, so the improvements you see are due to improved efficiency.

You absolutely will not have anything like the same power or torque on a motor wound for 84V running on 68 volts as you will the same motor wound for 67 Volt running on 67 volts.

[meepmeepmayer]

To the best of my knowlegde, they all use 60V ebike motors - both for the 67.2V and 84V wheels (at least ACM/msuper V3/Monster which is the same motor).

You're assigning way too much competence and financial clout to out beloved manufacturers  From the existence of the 67V Teslas, I guess GW has a shitload of old ordered parts that they must use somehow. We have seen one year old motors on current wheels here (wheel and motor production dates/code). Them using custom, differently wound motors for the different wheels would be the world's biggest surprise.

[Chriull]

On 1.11.2017 at 1:04 PM, Keith said:

OK, we are insisting on taking this, what should be simple discussion, back to the esoteric again - so be it!

You are completely ignoring the fact that an 84v system will absolutely not have the same motor as a 67V system. The 84V motor might look like it is physically the same but it will have to be wound for a lower kV - I.e. more turns of thinner wire, so it will handle a lower maximum current. However torque is inversely proportional to kV so you will get the same torque at that lower maximum current.

In other words the physically same size motor wound for two different voltages will actually have, as near as damn it, the same maximum torque output and also same maximum power output as the higher voltage will be countered by the lower current of the high voltage motor.

The only real advantage of the higher voltage motor is reduced I squared R losses as heat due to the same power being generated at lower current, so the improvements you see are due to improved efficiency.

You absolutely will not have anything like the same power or torque on a motor wound for 84V running on 68 volts as you will the same motor wound for 67 Volt running on 67 volts.

The Msuper V3 and the V3s+ motors have the same kv and extremely high chance to have just the exact same motor (http://forum.electricunicycle.org/topic/7549-current-demand-versus-battery-voltage/?do=findComment&comment=106135)