Cargo bike with Grin All-Axle : fast winding 52V or standard winding 72V ?

[Jil]

Hi !
I plan to build a cargo bike (long john), with Grin All Axle on the front wheel (20“) and 2 kWh battery.
My goal is to have a bike able to climb properly up to 12-13%, and to ride to ~30 mph (45 kph) max, even when the battery is nearly empty.
Should I build a 14S (52V) battery paired with a fast windings motor, or a 20S (72V) with a standard winding ?
What are the advantages of 72V ? Only higher power ?
Thanks !

 

[amberwolf]

Higher voltage doesn't provide higher power by itself; the controller would need to be able to provide the motor with more power and the motor would need to be able to use it under the specific conditions it's running under.

Assuming no wind and flat paved roads, speed is primarily controlled by the voltage of the system vs the motor winding vs the size of the wheel and any gearing in between (if it's not a hubmotor in the wheel).

When going faster speeds than 20-25mph, air resistance becomes a more significant factor requiring power to overcome it, and so available power starts making a difference to speed, too.

When climbing hills, available power will make a significant difference to speed as well.

Higher voltage vs lower for the same system otherwise means the motor will spin faster for the same throttle amount. With a different winding you'd have to calculate if that's the case based on motor kV (RPM/volt) and wheel size.

It also means the current draw from the battery to the controller will be lower for the same power output. (the controller will translate voltage and current as needed to power the motor based on load and throttle amount). That can mean that the cells see a lower load at the same power levels than with a lower voltage...but if you have the same number of cells either way, then you'd have more parallel cells for a lower voltage pack and thus the same load on them either way.

I plan to build a cargo bike (long john), with Grin All Axle on the front wheel (20“) and 2 kWh battery.
My goal is to have a bike able to climb properly up to 12-13%, and to ride to ~30 mph (45 kph) max, even when the battery is nearly empty.
Should I build a 14S (52V) battery paired with a fast windings motor, or a 20S (72V) with a standard winding ?
What are the advantages of 72V ? Only higher power ?

 

[Jil]

Higher voltage doesn't provide higher power by itself; the controller would need to be able to provide the motor with more power and the motor would need to be able to use it under the specific conditions it's running under.

Thanks for your reply Amberwolf. On the Grin simulator, with the same wheel, motor and controller (20“ + Grin V2 STD + Phaserunner), I get 2200 watts max power at the wheel with a 72V battery, vs 1400 watts with a 52V battery :

https://ebikes.ca/tools/simulator.html?motor=MGRIN_STD_SA&batt=B5220_GA&cont=PR&wheel=20i&mass=170&grade=8&cont_b=PR&motor_b=MGRIN_STD_SA&batt_b=B7223_AC&wheel_b=20i&mass_b=170&grade_b=8&bopen=true

 

[999zip999]

You have a link or pic of the bike.
Good info.

 

[999zip999]

The downside is 72v is more money with chargers but at 40amps with is 3,000 watts or 30amps is 2,100watts so as A.W. said less stress per cell.

 

[Bigwheel]

I have had a AnyAxle mounted on a 700c rim for 4yrs and as much as I like it I am not sure it is going to be right for your needs regardless of what the calculator says. My bike is fairly light at 43lbs with a 52v battery and averaging 30mph it will use 30wh/mi easily so factor that into your battery ah equation? Also I burned up a controller on a hot day climbing a similar grade with active pedaling.

For the target speed you wish to attain and a 20" wheel you will need a huge gear to be able to aid pedaling at speed also.

 

[amberwolf]

My bike is fairly light at 43lbs with a 52v battery and averaging 30mph it will use 30wh/mi easily so factor that into your battery ah equation?

It's likely to take twice that or more to climb hills, especially at speed; but with a 2kwh pack that's still potentially 30 miles of range.

For the target speed you wish to attain and a 20" wheel you will need a huge gear to be able to aid pedaling at speed also.

I suspect it has a larger rear wheel (not uncommon for longjohns to have 24" - 26" rear and 20" front).

 

[Jil]

I don’t have a picture of the bike as it doesn’t exist yet (it will probably be a bespoke frame).

It will look more of less like a Bullitt : 20“ front wheel, 26 or 27.5“ rear wheel.
https://www.larryvsharry.com/da/the-original-bullitt-build

 

[999zip999]

I saw one 11 years ago one full of lipo going 40mph so maybe 72v a friend of fafarelle. On a go-kart track.Hilarious it had good controll.
I think because the frame was solid.

 

[Jil]

I have used the trip simulator to compare both setups, the 72V is better.

18 km trip, starting with a short steep hill up to 17%.
Speed limit set at 45 km/h.
170 kg total weight (i.e. 40 kg bike, 80 kg rider, 50 kg freight), pedaling power 100 watts.

With standard windings and 72V battery : 24mn50", 21 Wh/km, min speed 21 km/h, core max temp 90°C.
With fast windings and 52V battery : 27mn01", 22 Wh/km, min speed 11 km/h, core max temp 122°C.

 

[999zip999]

Heat is your enemy batteries don't like it Motors don't like it controllers don't like. As 15% is pretty steep and how long or how many times. I have 3-72v batteries and 2-52v It just haven't hooked up the 52v I made.