E-scooter for cross country

[Desertprep]

I have fought with my hip for more than 15 years and finally given up...bicycling will have to wait until I get a new hip I live in Beijing and will be moving to Chengdu this summer. The road trip is about 1,200 miles. I am entertaining the notion of riding a scooter there. There are 5 cities that I can stop at along the way - the largest gap would be about 220 miles. I am shopping for a new scooter - the old one is ready to be put out to pasture. Regulations in Chengdu limit motors to 48v, so that will be my limit. I would like to get a bike with fat tires because of the amount of cracks and holes that I find on roads. Finally, I would like the motor to be at least 700 watts to make headwinds and hills more tolerable. Wheels will likely be 14" or 16". I need to do a reality check here. How many amps of battery would I need to travel 250 miles on flat land with no headwind?

 

[Dauntless]

https://www.ebikes.ca/tools/simulator.html

The simulator is limited, maybe not able go as high as your scooter needs to be. I don't think 700w will cut it if you want to make your 220 mile leg before sundown. Are you going to have a way to FULLY charge the battery overnight? Are you planning a 1,200 mile battery so you don't have to charge?

Let's just say you have that 700w motor, you put a 700wh battery in, hey, you can go 1 hour. But are you at 20mph? How much does your scooter weigh? 700 divided y 48 is about 15a, if these numbers were good so far you'd get more than a dozen of these and you'd go your 250 miles. But you say you need to go faster? How big of a battery is too big to charge overnight?

Oh yeah, a lead acid battery pack will weigh over 500 pounds. Don't know enough about the finished bike, but I'd definitely say this would be more than half the weight on your ride. The lithium should be 100 pounds, but this is all theoretical.

I would suggest you find out if someone makes this ride on an electric, you could learn a lot from that person. I think the reality check will tell you this won't work out for you. I feel the need to predict a 2500w motor, probably 72v, maybe a 350a pack.

http://www.smartgauge.co.uk/peukert2.html

 

[amberwolf]

First, you wont' need any amps of battery to do a specific distance. You would need a certain number of amp-hours, however. It is a VERY important difference; if you mix them up when buying a battery you're not going to get what you need.


Second, I wouldn't assume completley flat with no headwind for your calculations--nothing is ever really flat, and there's never really no winds at all, almost certainly not for a trip that long. I don't think you'll want to have to camp out on the roadside waiting for every breeze to stop just so you can make it to the destination, and you absolutely don't want to run out of power before you get there.



But if you like you can assume that, and probably take around 25wh/mile for 20MPH (which means a miniumum of 11 nonstop hours of riding for that 220mile leg). So if you used 25wh/mile for 220 miles, that would be a minimum of a 5.5kwh battery. That's very large and heavy. My 2kwh hour EIG pack on the trike is about 35lbs, and the size of a stack of hardback books. Your battery will have to be almost three times that size, minimum, so call it a little under a hundred pounds of battery, the size of a small human torso.


I'm guessing that the 220 miles is not a door-to-door distance, but just the basic distance between cities. If so, then you should add at least several dozen miles to account for in-city routes and detours, between recharges, so you don't end up stuck somewhere. So you could just go with a 6kwh battery, minimum.


Keep in mind you can't necessarily go by the advertised battery specs, either--many of them cannot deliver the "rated" capacity because they've calculated that based on the individual cells' lab-tested specs that go from completely full to completley dead, and if the pack has a BMS it won't let you drain them that dead (it shouldn't, anyway). Then you have to allow for the cell quality (or lack thereof) in most battery packs, that wont' actually let you get the full capacity because of cell variation, imbalance, etc.

So you may have to add 20-25% to the expected capacity, to guarantee you will not run out of power somewhere between cities. That brings your pack up to about 7.5kwh, so it's now well over a hundred pounds and the size of a largish human torso. Not sure where you're going to carry that on the scooter, unless you've installed panniers or are going to pull a trailer.


Then, if you want to allow for wind and hills, and potential detours, you may have to add another 20-25%. The pack is just getting bigger and bigger and heavier and heavier. At this point it's added so much to the scooter that it's going to take some of the battery power just to move itself, and you may have to start making teh pack bigger to account for that.


If you need to go faster than 20MPH, the pack grows even larger even faster, because power usage due to air resistance goes up rapidly after that point.


I'm pretty sure you'll be better off pulling a trailer with a small *reliable* gasoline generator capable of putting out at least as much power as you'll need to keep the battery charged (or stopping for long enough to let it recharge the pack whenever it gets low), and using just a small battery that takes care of your in-city usage needs. It'll cost a lot less, be smaller, and weigh less, and you can sell it once you're at the destination if you're not going back..

 

[Desertprep]

Thank you both! That is why I asked here before I continued on.

 

[Dui ni shuo de dui]

I won't speak of theoretical values here but based on my actual experience and experience of my friends, it is possible to do 100km in one charge with a 72V 20Ah lead acid battery set up.
Note that this experience I'm talking about is valid for Shanghai, which is a flat city without any hills, and at really low speeds, like no more than 30-35km/h. Speed will exponentially waste energy.

You want to do 250miles, which is 400km, so almost four times that distance.
So, logically, you'll need at least a 72V 20Ah x 4 battery, so 72V and 80Ah. That's quite big, and it can only be lithium (lead acid would be way, way too heavy).
An other way of thinking could be to use a battery chemistry capable of fast charging, like the lithium titanate cells. This way you could make a few stops on the road (eating or whatever), and pay a small fee to the locals to charge your bike. LTO cells can charge really, really fast so I guess in 30-45 minutes it could be topped up.
I guess many scenarios are possible, you'll need to do the math and see whatever works best for you.

Anyway the original plan might be doable, but that means a lot of work and many modifications to your scooter/s chassis to fit all that. Also, a more powerful motor should be more efficient (it will waste less energy to heat), so going for a 700W unit wouldn't be wise. Go for a more powerful version, which will also be far more reliable, and get a controller capable of limiting current, if possible a programmable one.

You'll also need to make everything totally waterproof, cuz when it rains here it really rains... Range is important, but reliability should be your main concern too. So that means rebuilding entirely your wiring harness, using waterproof connectors, good quality wires, soldering everything you can... Also changing for reliable, thick tires, better brake pads, if possible better ball bearings all around to lower rolling resistance...

Anyway, what you're talking about doing will need a lot of work and preparation, I feel like you have not put as much thought into this project that it would actually need.

 

[amberwolf]

So, logically, you'll need at least a 72V 20Ah x 4 battery, so 72V and 80Ah.

Good to see realworld data; that's almost 6kwh, so about in line with my guesstimates above.

 

[Dui ni shuo de dui]

Good to see realworld data; that's almost 6kwh, so about in line with my guesstimates above.

Yeah, your estimate was pretty much spot on