72v 65ah + direct drive. Estimated range (better from practical experience)

[Fathorserider]

I do really want to build a heavy (140kg/300lbs, including a rider) full-suspension direct drive bike. As I see it now it will be 72v 65ah + ~3kW direct drive motor. The only thing that stops me - I have never tried direct drives and have no idea how they behave: power consumption on low speed (20kmh/12mph) in Watts, how power consumption changes from low to above average speed (40kmh/25mph), power consumption on top speed. And the most important question - range.

Let's say I am cruising 30kmh/18mph average, let's say the route is 1km/0.6mi elevation per 70km/44mi distance (which is what I would describe as "flat with small hills"). What range/distance (no pedaling) to expect?

My estimations show 80km/50mi as absolute maximum (no pedaling).
Any thoughts?

Would also appreciate just some data (for direct drive motors) like: battery voltage/cruising speed/power consumption/terrain/pedal assist.
Info from mid-drives will work as well (at least it's better than nothing).

 

[harrisonpatm]

Your build spec is similar to mine, except yours is a pedal bike and mine is a motorcycle. This will work out in your favor: slower and lighter is much better for battery range. So i have a 72v, 72ah LFP battery, 110 pounds by itself. Bike plus rider weighs like 500 pounds. 8000w rated hub motor. And i regularly go up to speeds around 40-60mph, which is a much bigger power drain. And yet, my range is still 45-55 miles/80-100km. So maybe that's a helpful comparison for you?

As a generalization, hub motors are more efficient than mid drive motors, mostly due to not having a chain or belt as a source of efficiency loss. So if your main goal is max range, then hub motors is the way to go.

Another generalization, electric motors and batteries use exponentially more energy the faster you go. So if you're worried about range, go slower or pedal more.

 

[Fathorserider]

So maybe that's a helpful comparison for you?

Yes! Would also appreciate power consumption on a certain speed (if you have it). Like A Watts on 12mph, B Watts on 25mph, etc. Would really help me to calculate what to expect.

 

[Fathorserider]

Btw I am planning to build on 65ah prismatic Li-Ions (or LiFePo4). Absolutely the best in terms of saving space + high Amps.

 

[harrisonpatm]

Yes! Would also appreciate power consumption on a certain speed (if you have it). Like A Watts on 12mph, B Watts on 25mph, etc. Would really help me to calculate what to expect.

I don't have that for you unfortunately, not just because I try not to stare at the meter when I'm riding, unsafe. But also there's a ton of variables in play, like, inclines require more wattage for the same speed, whether I'm accelerating or coasting, current state of charge, ect. I pay attention to overall range, in that I reset my odometer to 0 at a full charge, which is how I estimate my range, and I have a dial ammeter to show me a physical needle that tells me to ease off the throttle when I'm approaching 200 amp draws.

Btw I am planning to build on 65ah prismatic Li-Ions (or LiFePo4). Absolutely the best in terms of saving space + high Amps.

Li-Ion or LiFePO4? They're very different.

 

[Fathorserider]

Li-Ion or LiFePO4? They're very different.

Really depends on: 1) size of a separate cell (as I am very limited by the size of my frame); 2) shipment costs

Assuming I am not really worried about weight, max ampers, max voltage of a cell - are Li-Ion and LiFePo4 that much different?
I just need max battery capacity, the rest are additional bonuses. I thought I would just build whatever fits the size of my frame (ideally 23s and above) and feed it to a controller having no low voltage protection.

 

[harrisonpatm]

Yes, they're very different, in many ways: energy density, nominal voltage, temp range, discharge capability... For one, 23s Li-Ion is 71-96v, while 23s LFP is 69-82v, roughly. That difference alone will totally change your build requirements

 

[amberwolf]

You can use the ebikes.ca motor simulator and/or trip simulator to guesstimate your actual power usage under your riding conditions. This will also give you a guesstimate of wh/mile, which will help you size your battery for the range you need.

Typically you don't want to specify a battery voltage and capacity and motor wattage, and then figure out what hte bike can do.

Typically you want to figure out what it takes to do the job you need the bike to do for you, and then get parts that can reliably do that job with some extra margin to account for aging, detours, conditions worse than you expected, etc.


Is there a specific reason you require a direct drive motor (presumably a hubmotor), vs any other drive system?


FWIW, there are also a number of threads specifically about power usage for various systems and conditions. Some of them are about Watts at Speed, some are about Wh/mile or Wh/km efficiency, some are about general data collection of all these things, etc. If you poke around the forums (probalby mostly in the Ebike General and Ebike Technical sections) you can find them posted over the years.

 

[m3vuv]

no lvc,great way to kill an expenive battery on the first ride,been there done that,learned the hard way!.

 

[Chalo]

no lvc,great way to kill an expenive battery on the first ride,been there done that,learned the hard way!.

Well, you could avoid running the battery all the way down. That's what I do with my packs that have balancers but not BMS. My controllers are all 36V compatible, but I only use 44V or 48V packs, so I can't rely on the controller's LVC either.

 

[Eastwood]

Btw I am planning to build on 65ah prismatic Li-Ions (or LiFePo4). Absolutely the best in terms of saving space + high Amps.

Is this 65ah battery going on a custom frame or?