Hub Motor Kit

General Discussion about electric bicycles.
Post Reply
tajanator   1 mW

1 mW
Posts: 12
Joined: Aug 08 2018 1:01am

Hub Motor Kit

Post by tajanator » Aug 18 2018 12:44am

Hey guys,
I wanted to buy a kit for a build I'm working on, and I was going to buy one of these.
https://www.ebay.com.au/itm/122870595676?
https://www.ebay.com.au/itm/223085595375?

As you can see, they're supposedly both 1500w, however the price difference is dramatic. I emailed the people selling the cheaper one, they said that the peak voltage is 1500w, and they said this regarding nominal voltage:

"Thank you for your message. Our supplier said it doesn't have nominal voltage. The voltage depends on how fast you drive."

Obviously that's not how voltage works though right? Should I just steer clear and go with the mid drive?

Cheers.

donn   1 kW

1 kW
Posts: 431
Joined: Aug 13 2018 10:30am
Location: Seattle

Re: Hub Motor Kit

Post by donn » Aug 18 2018 1:50am

I don't know, and I probably should keep quiet since I know hardly anything, but ... looks like a pretty good deal to me. You're really asking about Watts, and indeed there is no relevant number other than the max - 1500 (or 250.) Volts is 48V. It's cheap, so you can't expect premium quality anything, and you might miss the display/computer.

The other item is rather different. You'll probably be deciding what kind of configuration you want to build, one that uses this kind of motor or one that uses a hub motor like the first auction.

User avatar
Chalo   100 GW

100 GW
Posts: 7961
Joined: Apr 29 2009 11:29pm
Location: Austin, Texas

Re: Hub Motor Kit

Post by Chalo » Aug 18 2018 2:08am

Voltage dictates the motor's running speed. The controller determines what range of voltage you can use with your kit; the motor itself has no voltage requirement. The controllers in those 48V kits will certainly run on 48V or 52V. I wouldn't expect them to work with higher or lower voltages than that, but it's not out of the question.

Current (amps) determines how much torque your motor can make. If you don't make enough torque to run at X road speed, it doesn't matter whether the motor will run faster than that without a load.

Volts times amps equal watts of electrical power. RPM times torque equals mechanical power to the wheel. If you do a good job matching the motor speed with the power required to maintain that speed, your mechanical power at cruise could be as much as 80% of your electrical power, perhaps even more. If you mismatch these values, you could waste more power as heat than you deliver to the wheel.

A 1500W mid drive will almost always be much more capable than a 1500W hub motor, because you can match the road speed to the motor's power with the bike's gears. The hub motor is limited to a single ratio that gives you a single optimum speed to extract the best power from the motor. At any other speed, it will behave like a less powerful motor.

On the other hand, at that power level, a mid drive will be much more maintenance intensive and less reliable than a properly installed hub motor. It will put much more power through the bike's chain drive than it was ever designed to transmit. You'll be able to climb steeper hills, accelerate faster, and reach a higher top speed than with the hub motor-- but you'll have to replace chains and cassettes more often and you'll be much more likely to experience bike-disabling breakages out on the road.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

donn   1 kW

1 kW
Posts: 431
Joined: Aug 13 2018 10:30am
Location: Seattle

Re: Hub Motor Kit

Post by donn » Aug 18 2018 9:46am

Yes, indeed current is where they got a little turned around with the specs. Where the auction text says "1.The system requires a 48 Volt electrokinetic cell battery with a nominal capacity not less than 14.5Ah", I guess they might rather have said something like, the system requires a battery that can sustain a 30A output current. 30A X 48V ~ 1500W. The storage capacity (14Ah) will determine whether you can go 100km on it, or 80 or whatever.

I assume you don't want to use it in their 250W configuration. For that, you could use a much lighter hub.

User avatar
wineboyrider   100 MW

100 MW
Posts: 2672
Joined: Sep 30 2009 9:08am
Location: Tularosa, New Mexico
Contact:

Re: Hub Motor Kit

Post by wineboyrider » Aug 18 2018 9:54am

Chalo wrote:
Aug 18 2018 2:08am
Voltage dictates the motor's running speed. The controller determines what range of voltage you can use with your kit; the motor itself has no voltage requirement. The controllers in those 48V kits will certainly run on 48V or 52V. I wouldn't expect them to work with higher or lower voltages than that, but it's not out of the question.

Current (amps) determines how much torque your motor can make. If you don't make enough torque to run at X road speed, it doesn't matter whether the motor will run faster than that without a load.

Volts times amps equal watts of electrical power. RPM times torque equals mechanical power to the wheel. If you do a good job matching the motor speed with the power required to maintain that speed, your mechanical power at cruise could be as much as 80% of your electrical power, perhaps even more. If you mismatch these values, you could waste more power as heat than you deliver to the wheel.

A 1500W mid drive will almost always be much more capable than a 1500W hub motor, because you can match the road speed to the motor's power with the bike's gears. The hub motor is limited to a single ratio that gives you a single optimum speed to extract the best power from the motor. At any other speed, it will behave like a less powerful motor.

On the other hand, at that power level, a mid drive will be much more maintenance intensive and less reliable than a properly installed hub motor. It will put much more power through the bike's chain drive than it was ever designed to transmit. You'll be able to climb steeper hills, accelerate faster, and reach a higher top speed than with the hub motor-- but you'll have to replace chains and cassettes more often and you'll be much more likely to experience bike-disabling breakages out on the road.
+1 if you want low maintenance go with a hub motor.
ES IS SAVED! THANK YOU JUSTIN.

Philaphlous   1 kW

1 kW
Posts: 431
Joined: Mar 28 2017 7:17am

Re: Hub Motor Kit

Post by Philaphlous » Aug 18 2018 1:58pm

hub motor will be more flexible. You can run 36v or 72v if you want. Plus, depending on the stator diameter, if its 35mm then it can easily handle 2000w+... I ordered a 1000W kit that looks identical to that and its a 30mm stator from the looks of it. I easily get 1500w no problem when riding...and just so you know, its only around 650-700w at top speed...it only goes to 1500w when your accelerating. Plus you can enable regen with that controller probably which will save your brakes. You'll lose the stealthiness that you'll get with a mid-drive.

I'd go with the hub. It seems to be the best bet...

docw009   100 kW

100 kW
Posts: 1230
Joined: Aug 02 2015 7:43am
Location: Chicago area suburbs.

Re: Hub Motor Kit

Post by docw009 » Aug 18 2018 9:37pm

The Bafang Ultra in the second link is designed for frame builders. Unless you are a frame builder, compare the hub motor to a Bafang BBS02 or BBSHD. Still more expensive.

https://www.ebay.com.au/itm/BBS02B-48v7 ... SwKOJYKZ~u

Here in the USA, I can get a BBS02 for $450 USD, while the 1000W-1500W hub motor is about $170-240 USD depending on display. The direct drive hubmotor will be faster than my BBS02, but my BBS02 is a lighter bike and can use my bike's gears to climb faster.

Your choice depends on what kind of riding you will be doing. The DD is better suited for higher speed commuting. It moves you toward an electric motorcycle. Inexpensive way to go fast. The middrive keeps your bike feeling more like a bike,if that's what you want.

Post Reply