Please Help - Specs for E-Bike Kit

[vacious]

Hi, i'm planning to buy an E-bike kit but i'm unsure of the specs i'd need - Any ideas/help would be really appreciated!

- I want the e-bike to speed up my daily commute, I currently cycle at an average 30km/h and im looking for a kit that would increase that speed (with the same pedaling effort) to around 45 km/h
- My total commute is 25km and completely flat, i'd like a battery that could provide approx 25 minutes of work before needing to be recharged.
- I'm considering this kit : http://em3ev.com/store/index.php?route=product/product&path=36&product_id=138 , using an 8T motor, my wheel type is 700c
- For teh battery, ive been looking at this 48v/8.4A : http://em3ev.com/store/index.php?route=product/product&path=35&product_id=161

Would this motor/battery combination likely provide the power and battery life that i'm looking for?
Are there any other kits that could suit my requirements better?

Any help would be really appreciated!!

Cheers

Ben

 

[cal3thousand]

Hi, i'm planning to buy an E-bike kit but i'm unsure of the specs i'd need - Any ideas/help would be really appreciated!

- I want the e-bike to speed up my daily commute, I currently cycle at an average 30km/h and im looking for a kit that would increase that speed (with the same pedaling effort) to around 45 km/h
- My total commute is 25km and completely flat, i'd like a battery that could provide approx 25 minutes of work before needing to be recharged.
- I'm considering this kit : http://em3ev.com/store/index.php?route=product/product&path=36&product_id=138 , using an 8T motor, my wheel type is 700c
- For teh battery, ive been looking at this 48v/8.4A : http://em3ev.com/store/index.php?route=product/product&path=35&product_id=161

Would this motor/battery combination likely provide the power and battery life that i'm looking for?
Are there any other kits that could suit my requirements better?

Any help would be really appreciated!!

Cheers

Ben

That combo will meet your needs. It's a good fun kit and you should be able to complete that commute at nearly full speed. You'll be able to go even further if you keep the speeds down below 45 kph or have less stop and go.

 

[arkmundi]

Motor is fine, but you'll want to double the battery capacity. There is nothing more damaging than to consistently discharge a battery to lower than 20% capacity and the length of your commute will put you down in that range.

 

[Drunkskunk]

Good motor choice, unfortunately the battery is a bit small for your needs. It would function at 30kph, but at 45 you're going to need about double that battery's capacity. Roughly ~48v @15AH to give you a 25km range at 45kph. you will use less most of the time, but the battery needs the capacity to handle unexpected headwinds, hills, detours, the normal loss of capacity over time, and still maintain a 20% reserve, as running a Lithium battery down will seriously shorten it's life.
EM3ev.com makes a triangle battery in the 16.5ah range that may meet your needs.

based on your speed, I'm assuming you want to put this on your roadbike. You will want to rethink that. a good roadbike is designed to be strong enough for 1 human power. Not only will a hub motor take the frame far beyond the power it was designed for, but it puts stress on the frame in ways it wasn't designed for.
With a 500 watt motor you're better off converting a mountain bike frame. A 29er MTB can be set up like a good touring bike with drop bars and road wheels. With the weight you're adding from the kit, you won't notice the weight of the sturdier frame while riding, but you'll be glad of the extra rigidity and strength of a frame that can take the abuse of something that can produce more power than you.

 

[DAND214]

I take the bike is a hybred with 700c wheels.
I have 3 8t all on 26" wheels. On 51v and it is great. Top speed is around 35mph.
In your case i would get the 10t and a triangle pack. http://em3ev.com/store/index.php?route=product/product&path=35&product_id=123
You'll love the Mac 10t it will be fast with the larger wheel. The 8t would work but harder.

Dan

 

[vacious]

Thanks for all the responses - Really useful!

Unfortunately the larger capacity batteries are beyond my budget so i'm trying to workout whether the 48v/8.4A setup (seems the only option within my budget) is worth buying.

I normally cycle 30km/h and i want the e-bike to add another 10-15km/h to this speed (with me putting in my normal pedalling effort). The route is completely flat and on dedicated cycle lanes in rural areas (so only a couple of junctions/start-stops for the entire route). I just measured the distance and i'd need to go 23km before a recharge. I guess its really hard to estimate, but any educated guesses on approx how many minutes of battery assistance i might get before reaching 20% charge (assuming no wind)?

@ Drunkskunk - Thanks for the tip on frame strength, i'll check this out carefully!
@ DAND214 - Indeed, its a hybrid with 700C wheels

 

[dogman dan]

This is where the new guy can never quite picture in his mind, how much power it will take to add 15 kph. 0-15 kph takes nothing, but 30 kph to 45kph takes almost one horsepower. It's the increasing wind drag.

Lets' do some math, I'll assume you are pretty strong, and put your effort at 200w continuous. 45 kph will take close to 1000w, so you need 800w for 30 min. 400 watthours is the minimum you will use.

That's about the amount you get in 48v 10ah. So 8.4 ah is a tad short. If you went to a 10t motor, and slowed down, you might just make it.

The catch 22 is that your ride will take double that amount of wh on a really bad day, say, 50 kph headwinds. If you can swing it to buy a bigger battery, do so. If not, buy the slower rpm motor, and try to just make your ride easier, but at 35 kph. Also, choose the lowest amps controller offered. The small battery will not like big amps on the starts.

It's really bad for your battery to use 100% of it every trip. Anything above 12 ah in 48v will be fine.

 

[arkmundi]

The catch 22 is that your ride will take double that amount of wh on a really bad day, say, 50 kph headwinds. If you can swing it to buy a bigger battery, do so. If not, buy the slower rpm motor, and try to just make your ride easier, but at 35 kph. Also, choose the lowest amps controller offered. The small battery will not like big amps on the starts. It's really bad for your battery to use 100% of it every trip. Anything above 12 ah in 48v will be fine.

Ditto that. The batteries are the more expensive, and consumable, piece of equipment. Being budget conscious, the last thing you want to do is use it up quickly. Its going to fail eventually anyway, but you want to push that date out as far as possible. Another noobish thing that happens frequently is to be thinking your car lead-acid battery, or those long-lived lithium cells in a low draw device, which seem to last a long time, and make the analogy.

You'll be replacing your battery on a lithium-ion charge/discharge cycle basis and it seems you'll be having two cycles every day. So the best of the lithium are going to get 2000-3000 cycles. Mid-range 1000-2000, and low-end less than a 1000. So you should budget forward. Another noobish thing is to calculate cost on the basis of amp-hour capacity and not total life-time amp-hours including how well they cycle up and down. You'd be most budget conscious by buying the very best battery suited to your particular riding habits. That can't really be appreciated until you're doing it, tires on the road.

Since you've picked a good motor & component set (except for the battery), I'd stick with that, not downsize because you can not now afford more - its an investment - they'll last a lifetime (except for the battery). So go ahead, cheap it out on the battery (like a <500 cycle lipo), so it doesn't hurt much when it turns to dust. And in that interim, save up for the right battery. Another thing people do to save on costs is make their own batteries from the raw cells. Its what I do. The cost to performance of batteries is improving all the time. Hence a battery that might have been out of reach becomes reachable. Best.

 

[vacious]

Thanks for all the info guys, really useful! I didn't realize the power requirements as speed increases would be quite this exponential!

I've seen that this shop also offers an 11Ah battery pack made from Samsung cells (which isn't a hugely more expensive) - I'll try and stretch to this paired with the lowest amp controller that matches the motor/battery combo.

Cheers

Ben