Energy Consumption & Pack size on E-Bikes

[hayden55]

I'm looking at maybe designing an e bike with suspension and two 48v 26" wheels. What are your bikes consuming power wise? How big are your packs? I'm looking at over volting these a smidge and running 40 ish. Hard task but its fun to look at.

[ProDigit]

For scooters, 33cc 2 stroke, or 50cc 4stroke (2BHP) gets you up to 35-37MPH.
65cc 3,5BHP gets you to 55MPH.

1BHP = 745.7Watt.

So for the speed you'll be needing you'll need to have around a 1500W motor.

The speed will depend on the wheel circumference. Mounting the wheel hub on small wheels will limit the top speed, but increase acceleration torque.

That being said, if you're planning on using a bicycle without suspension, I would recommend to not go faster than 15MPH, and mountainbikes with some form of suspension and disc brakes no more than 20MPH.
This because potholes can break the frame, and bicycle brakes on the rim, aren't strong enough to slow down from higher speeds.
Good disc brakes might be ok.
Also, the tires need to be meaty tires. You really can't use regular bicycle tires to go 40MPH. They do have a lot of stability issues.
Which is why most scooters have smaller rims, and wider donut tires.

Once you want to hit 35MPH, you'll also need good suspension of at least 3 inch when compressed (when you're on the bike). That means you'll probably need around 5" unloaded suspension travel.

As far as the battery, that will depend on the range you will want to go, and what you want in aesthetics.
If you constantly travel at max speed, the motor will be pulling 31 amps.
The cheapest battery that would work, would be this one:
https://bmsbattery.com/ebike-battery...k-battery.html

It's a 48V 30Amp battery, with a capacity of 10Ah, allowing you a range of about 20 minutes, or 13 miles at top speed.
Probably the cheapest, high density battery you can buy as an end consumer.

More than likely, you'll be driving slower, as most street legal mopeds are limited to 20-30MPH, at which your motor will be drawing about 10 amp, and can run you an entire hour, or 30 miles; effectively almost tripling your range.

Go at 20MPH, and your motor will draw about 6 amps, which is good for 1 hr and 40 minutes, or 33 miles.

I used to have an electric scooter,
It had a 1600W hub in the rear wheel, and a 48V 20Ah battery, with a range of 20 miles. On average, it would take about an hour and a half to empty the battery, however, the way I drove the thing, it often lasted me an entire afternoon.

Charging does take a lot of time.

[Hersbird]

The Cyclone 3000 mid drive will push a bike to over 40 with a 60 or 72 volt battery. You may also need a better controller. I bet an average bike weight with the 72v and the high voltage ASI BAC controller would maybe 60mph. That would be scary. I have a heavy fat tire bike, a 52v battery, and that kit and can go 36-37 mph. Just a 60v battery would put it over 40 mph. For me 36 is too fast, I'd rather have more power down low. There is no pedal assist at speeds over 25 mph and that's were you can really add range. At full tilt no pedaling my battery would last about 20-25 miles, drop that to 20 and add pedal and it will go double that. Less wind resistance, rolling resistance, and me adding a few watts with my legs.

I have about $1500 in my bike and if I had to do it over I might just buy one of the Rad bikes out of Seattle for the same price (actually I see they just jumped the price $200 on all their bikes so maybe not). My battery is a little better at 52v and 14 AH, but their frame and other parts are better, and they have a front suspension fork. Theirs are speed limited to 20 mph as well. So thinking about it, I'm pretty happy with mine.

[Stubby79]

My pedal assist ebike is around 11wh/mile. My all-electric moped/scooter is more like 25wh/mile.

From another forum:

30-32 Wh on Cyclone 6kW eTrike at 28 mph average speed.
46-48 Wh on Cyclone 3kW eBike at 30 mph average speed.

So it all comes down to air(speed) and rolling resistance. I'd calculate for ~50wh/mile, though it will probably be worse running at 40mph.

As to pack size, I'd recommend running at "1C" or better to minimize strain and maximize range and battery life. 40mph x 50wh/mile = 2000 watt-hours, divided by 48v = ~42 amp-hours. That will theoretically get you an hour's run time going full out. Not sure if 2000w will get you to 40mph though. That's probably what a 1500w motor will actually draw from the battery.

Yes, you can run more that 1C (1x the capacity of the battery), if you have decent cells. Brand name power tool cells(high drain) can theoretically sustain 10C or more. I wouldn't want to run a cell at it's limit until it was drained over and over, mind you. Most people want to ride for more than 6 minutes at a time, mind you.

Bla bla bla...should be enough info there to get you started.

[vskid3]

Do you really need dual motors? That's a lot of unsprung weight and you can easily get enough power out of one motor.

You might want to look into running motorcycle tires and rims if 40mph is your goal. Many guys on Endless Sphere do that on high speed bikes.

What kind of range do you want? That and the peak power draw of your motor will determine how much and what kind of battery you'll want. If you don't need much range and want a small battery, you'll need something that can handle a high C-rate like hobby Lipo. A bigger battery won't need to be able to as high of a C-rate and gives you more options.

[hayden55]

1. Nobody on here run 18650 cells? They are a lot cheaper for the Ah and weight that those prebuilt packs and you can make your pack any size you want. So my goal is high voltage and low weight for the pack. Each samsung 18650 cell is about 4.89 and 3500mAh and 3.6V nominal... 4.2V charged. (also 2.65V cut voltage for life cycle).

2. I'm going to be using dual motors because heat is more of a problem than weight (unfortunately). Splitting the required wattage between wheels reduces the required load to each motor and I will mount so heat sinks to each hub.

3. I had a 2009 Honda moped in 8th grade and it was 50cc and went 43 mph and it was street legal with no title and tags.

4. Yeah the suspension and tire/brakes is a big item besides the power handling. I rode a friends walmart bike that could go 28 mph with his e bike. Even with "suspension" it only had an inch of travel and was horrible. Hopefully one of my friends who works at a high end bike shop can help me out.

5. Lastly one of the more important one is a lot of these bike motor kits do not list their maximum rated rpms. Besides possibly burning a motor I don't want to also overspin it going down a hill.

6. I'm thinking an hour of maximum speed would be a good design to use for the pack. I'll have to look into power required to move a bike with speed bars to 40 mph. Also maybe want to look into efficiency of the speed control, friction of the wires, and efficiency of the motor. Also the packs have reserve capacity too so I'll have to factor over bc the bottom % is unusable.

I'm going to go back through these and tally it up I like that mid drive that was posted. That would fix the gearing and power issue. A 72v battery rated at 40A discharge would be fun.

[samwichse]

Two hub motors on a full suspension bike is going to ride like a freight train.

One nice mid drive motor on a full suspension bike would be a sweet ride.

[Grant-53]

Each state has its own motor vehicle laws. Generally 30 mph is the upper limit for no registration. Cooling the field coils helps efficiency. If you are worried about high rpms destroying the armature use a high temp epoxy to secure the windings, have the armature dynamically balanced, and get the best ball bearings available for the shaft. A good aero body shell will reduce power demand.

[hayden55]

Unsprung weight ain't no thang. jk
The rules about motorized bicycles aren't very thought out in AR (this isn't the NE where things are super regulated). They only apply to gasoline-powered bikes and it says to stay under 49cc and the law has been out since the beginning of time. (no hard speed limit)
Then for e-bikes, you have your own set of laws which just came out last year. You have 3 different types of e-bikes and says if you can go past 28 mph with the assist still on stay off the bike paths. But you don't have to register.
I'm guessing we haven't had an epidemic of 50 mph unregistered bikes yet for the laws to change.

I guess the agenda has moved to look for nice mid drive kits and buying closeout bike through my friend's factory discount.

It looks like we wil have around a 20 pound even pack at 72 volts and a 12-pound mid drive mounted to the bike.
I weigh 175. The power kit will weigh something like 32 plus install. So it looks like a full suspension bike built for a 200-pound man would work.

Definitely going to look into pricing on the pack, it may look a little prohibitive.
If anybody sees a better mAh/$ deal than the LG F1L 18650 3350mAh 4.8A Battery let me know

[Hersbird]

The battery is the most expensive part unless you buy a higher end bike to begin with. Imagine my discomfort when my first $850 battery came bad on arrival. It would trip the built in BMS with only about a 2 amp draw. Thankfully after a lot of back and forth Luna cycle did take it back and refund the money including all shipping. They just couldn't believe the battery was the problem and had me test every other part first including sending me a new controller to try. Add to that the shipping restrictions on big Li-on batteries and it was hard just to get fedex to take it, definitely a PITA. So buy from a company that will make things right, had I gotten that directly form China I would have been up a creek although I think I could have fixed it with a new $100 BMS.