Range comparison - 24V, 20Ah versus 36V,16Ah battery

[liared]

Hi,
I live in Europe (Sweden) where max 250 Watt motor combined with pedal assist is required by law.
I have a 24 V 250 W motor system with a 24V 20Ah Ping Lifepo battery. The battery lasts about 35 kilometers which equals my daily commute distance to and from work in town. I have read here that it is not healtty for the battery to be "run it down" completely every time. Therefore I charge it both at home and at work (recharge avery 17 kilometers).
A friend of mine is now considering getting an DIY e bike system. He wants a system that makes the roundtrip to town without a need for recharge in town.
= wants to run 35 kilometers in one "run" thus recharging every 35 kilometer. His children will now and then use the bike for trips to town with no possibility to recharge there.
Will a 36 V 16Ah 250W system give longer range than a 24V 20Ah 250W system thereby not draining the battery too much after a full "roundtrip"?
Shall I advice him to get a 36 V 16Ah 250W system insted of a 24V, 20Ah system?
Bengt

 

[dogman dan]

Get a 36v 20 ah.

Assuming the cells are 4 ah, a 36v 16 ah will have 36 cells in it, 3 cells per group, x 12 cells (3p-12s)
A 24v 20 ah will have 40 cells in it 5 cells per group, x8 cells (5p-8s)

So the 36v 16 ah is even smaller than your battery.

 

[liared]

Thank you very much Dogman for for your info that a 36 V 15 Ah battery will require less space/volume than a 24V 20Ah one.
But my most important question is:
Will a 36V 15 Ah battery give a longer riding range than a 24V 20Ah on a 250 watt motor assuming all other factors are the same - same speed, same weight, same terráin et cetera?

 

[liared]

I just found the following text in another thread:

A 48V/10Ah battery stores more energy (480Wh) compared to a 36V/10Ah battery (360Wh). If you go the same speed with each pack you should consume roughly the same Wh/mi and go further on the 48V pack. However if for example you ride at 25 mph with the 48V pack just cuz you can instead of the 20 mph you rode with the 36V pack then you'd probably find you'd have less range with the 48V pack simply becasue it takes a LOT more energy per mile to go that few miles per hour faster.

-R

This implies that a simple calculation can be made:
24 Volt, 20 Ah battery = 24 x 20 = 480 Wh
36 Volt, 15 Ah battery = 36 x15 = 540 Wh

The 36 Volt battery thus holds more stored energy and will therefore give a longer riding distance than the 24 Volt battery (assuming other factors are constant).
OK!?

 

[nathan_jones]

A 48V/10Ah battery stores more energy (480Wh) compared to a 36V/10Ah battery (360Wh). If you go the same speed with each pack you should consume roughly the same Wh/mi and go further on the 48V pack.

can i ask what are peoples practical experience regarding the beformentioned quote

 

[dnmun]

if you are talking the same chemistry, then you could compare based entirely on weight and volume. the larger, heavier pack will go further. period.

the higher voltage will go faster, period.

buy a 48V20A pack and go as fast and as far as you want, don't let the guvment tell you how fast to go. refuse to let them inspect it without a court order. period.

 

[Joey]

Sorry I don't have empirical results, but I did see something on the ebikes.ca simulator regarding efficiency that might be of interest.

A Clyte 408 motor and controller using 36V battery pack is operating at peak efficiency (about 80%) at 20 mph in a 26" rim. The
same motor and controller using a 48V battery pack is about 70% efficient at 20 mph (the peak efficiency occurs above 25 mph).

A Clyte 406 motor and controller operating with 36V battery pack is about 70% at 20 mph in a 26" rim (the peak is above 25 mph).
The same motor and controller using a 48V battery pack is about 67% efficient at 20 mph (the peak efficiency occurs at a little
under 35 mph).

I may be wrong, but this suggests to me that if your pack voltage puts the motor at peak efficiency at your typical traveling speed
then if you increase pack voltage to get more Watt-hours, the increase will not be quite as much as expected since the motor may
not be operating at the same efficiency at the same given speed. In the case of the Clyte 408 in 26" wheel at 20 mph, comparing
battery packs of 36V and 48V, both 10Ah, instead of getting 1.333x range increase with the 48V pack compared to the 36V pack,
I think one would only get a 1.167x range increase.

Joey

Edit: Oops, I was wrong. The efficiency peak moves with the throttle setting. When I adjust the throttle to move the efficiency
peak to align with the desired mph, the efficiency is the same for the 36V and 48V cases. .. live and learn.

 

[dogman dan]

Woops! Dang, nobody busted me on a simple math error! I'm good at those, I can count to ten still since I never sawed off a finger on the job.

A 36v 16 ah pack will have a 4p-12s configuration. not 3p-12s ! So the 36v 16 ah pack has 48 cells in the pack, and the 24v 20 ah has 40.

8 more cells in the pack means the 36v is physically bigger, and will go farther if rode as slow as the 24v pack would go.

Joey has a good point, it does make sense to choose a motor and a voltage that will match each other as best as possible for best range. Out on the road though, that stuff will matter less than the weather, or tire pressure. Sometimes it may be nice to have the extra when you need it, like a big hill, or the occasional use of a trailer. The efficiency game is very fun, but just remember the end goal is to get somewhere. The middle of the road bikes, 36v, 20 amp controller, setups work well in most situations, but can still climb a hill if you have one. Reduce your power too much to gain a bit of efficiency, and some day you will find a certain place where you get to walk up, instead of ride up a hill. No big deal if you live in florida though. 8)

 

[dnmun]

my point is:

'JUST SAY NO'


don't let the guvment tell you that you can only go 20mph or 30kph, or that you have to pedal to get the assist.

consider civil disobedience. fight unjust laws and regulations imposed by the ruling car driving class.

i was stunned to know that they can fine you guys tons of money for riding as fast as the guys who are young and strong.

it is age discrimination, and a form of class structured domination by the young and the car ego addicts.

fight for the right to ride as you wish, change the laws to reflect reality.

the civil authorities can restrict speeds when needed for public safety, if they can justify it, but they should not be able to fine you for riding a bike at 50kph. jmho.

FIGHT age discrimination in the form of unjust euro regulations on speed and power.

 

[Joey]

Oops, I made a mistake with the ebikes.ca simulator. I did all the efficiency comparisons at 100% throttle. When I reduce the throttle on the Clyte 408 with 48V battery from 100 to 76, I get the same efficiency at 20 mph as I do at 36V and throttle at 100. I placed and edit at the bottom of my first post to acknowledge the mistake.

Joey