What's the catch?

[Lunar Cappuccino]

I've got another thread going where I'm thinking of building a bike myself but I've also considered just buying an off the shelf e-bike. When it comes to those, though, I must admit to being incredibly confused. One is the whole price/power/battery capacity point. You see some bikes that come ready made with maybe 250W or a "really powerful" 400W. OK, my interests involve adding a zero to both of those numbers. As I said in the other thread, this is not for hot-rodding but climbing a particular notorius hill in Portland, OR every day and not having to pedal at all if I don't want to smell like a goat at the top. Anyway, those low powered bikes are still coming in at $1500-$2000. Then you see things like this: http://www.aliexpress.com/wholesale/wholesale-4000w-electric-bike.html. I understand physics well, BTW. I studied it at the college level for 3 years so, yes, I know that P=IA and that a 20Ah battery is better than 10Ah. What can possible be so different between the stuff you get if you type "electric bike" into google vs. the search I just ran on "bike hub motor 4000w". How, exactly do I get 10x the power for 1/2 the money??? Who is lying, in other words? Edit: forgot to mention - yes, I get heat dissipation too. Blasting 4000W through a motor that's really only rated for 400W might work right up until it melts. I want CONSTANT power in that range for the 10 minutes or so and 200m elevation gain this involves without seeing smoke.

 

[Lunar Cappuccino]

I think I see it. I was looking at 15,000 - 30,000kg orders. Bulk prices from China. As Church Lady used to say "Nevermiiiiiiind"

 

[dogman dan]

Or Rosanne Rosanna Danna, who said "that's different"

Chances are 3000w will get you up that hill, and quite possibly you will actually only use 2000w.

What you need starts with a strong battery. Nothing with a 2 or 3c discharge rate will do, unless it's huge.

72v 40 or 72v 30 amps controller. One moderately priced direct drive hubmotor. Generally rated at about 800w, but often sold as up to 2000w. But here is the catch, get the slow winding. EM3ev is one source, E-Bike Kit another.

The slow motor will make a bit less heat going up hills at slower rpms. You will slow some going up the steep ones. By running it at 72v, you get some of the speed back. You will get a bike with 30 mph top speed, but be able to climb hills as slow as 10 mph, for 10 min. 200 feet of climb won't faze this kind of setup.

Here is some vid of my similar setup going up a hill till it gets so steep It stalls out. I fail to climb the hill, but only bulldozers make it to the end of the road, which doesn't go all the way.
http://www.youtube.com/watch?v=6RpXuIyAnkY

 

[Lunar Cappuccino]

What you need starts with a strong battery. Nothing with a 2 or 3c discharge rate will do, unless it's huge.

Sorry, still getting used to the jargon - what is 2 or 3c discharge rate?

BTW, the hill is about 200 meters vertical rise. Thanks for the video. My hill is nice smooth pavement fortunately.

 

[Architectonic]

Then you see things like this: http://www.aliexpress.com/wholesale/wholesale-4000w-electric-bike.html.

HPC (HiPowerCycles) is a North American shop that sells hot-rodded bikes similar to ones that people on this forum build. The overall reliability is going to be similar to a hot-rodded kit.

They do not come from China like that and they cost a lot more than that. In a word, those adverts are clearly scams.

 

[torker]

It is a 10 ah size battery you "should" be able discharge it at 2c =20 amps 3c=30 amps

 

[sk8norcal]

I think I see it. I was looking at 15,000 - 30,000kg orders. Bulk prices from China.(

where are u reading that?


http://www.hi-powercycles.com/

 

[sk8norcal]

Then you see things like this: http://www.aliexpress.com/wholesale/wholesale-4000w-electric-bike.html.

HPC (HiPowerCycles) is a North American shop that sells hot-rodded bikes similar to ones that people on this forum build. The overall reliability is going to be similar to a hot-rodded kit.

They do not come from China like that and they cost a lot more than that. In a word, those adverts are clearly scams.

that's what i dont understand about aliexpress,
its supposed to be a legitimate site (people on here buy stuff off aliexpress all the time)
but then you see ads like these....

http://andrewminalto.com/alibaba-scam-exposed/

 

[dogman dan]

Oops, 200 meters, or more like 1000 feet of climb. As a dumb Yank, I still think in feet a lot, even when I read meters.

If the grade is less than 10% then 1000w will still get you up it. I did a 1000' vertical climb home every day from work for years. My climbs grade maxed out at about 6% though. The same 1000w setup, with a nothing special motor has done 3000' climbs, with 8- 10% grades. You don't really need more till you get into very steep grades.

You should be fine with just 2000w So something able to discharge 40 amps continuously is needed. Not a typical small bottle style battery.

 

[Harold in CR]

UHhhhhh Dogman, 200 meters is more like 660 feet. Yeah, I'm not real good at metrics, either but, I'm gettin there. :wink: :lol:

 

[torker]

UHhhhhh Dogman, 200 meters is more like 660 feet. Yeah, I'm not real good at metrics, either but, I'm gettin there. :wink: :lol:

Ah.. Google to the rescue for me.. :lol:

 

[dogman dan]

I thought meters were longer than yards, so more than 600 feet.

Always check dogmans math. :lol: I was an ag student, I couldn't come close to hacking engineering.

 

[Lunar Cappuccino]

I'm in the US but I always use metric units when talking about this stuff because we're dealing in watts so we're already using metric units. Also the English system confusingly weighs things in pounds which is actually a unit of force, not mass. The English mass unit is the "slug", which almost nobody even knows about. Using the English system in the conventional way thus leads to "conformability errors" while keeping things in kg, meters, watts, etc.. works out of the box. Yeah, I studied physics