Bafang/BPM 350w motor for first build

[ammodave]

I'm still trying to zero in on a first build motor. I've seen lots of encouraging reviews here on this BPM motor http://www.bmsbattery.com/ebike-kits/345-bafang-350watts500watts-bpm-motor-e-bike-kit.html but I still have questions. I plan to run this on a 28" Jamis commuter using a 36v 10.4ah bottle battery. Total weight of bike+rider (without electrics) is 175lbs. The motor is available in a 201rpm or 328rpm version. The website suggests the 201rpm motor for 28" wheels. Is this rpm my best choice considering my low body weight and the nearly flat terrain in my neighborhood? The bike is for pure recreation and a 10mi range is acceptable.

 

[motomech]

You need to do more research. Start with the posts of D8veh, who has used that motor and has recently talked about it in various applications.
Or wait for him to respond.
One thing he will tell you is, that battery is too small for that motor.
And I will tell you, the BPM is too big for those spindly little forks.
Not a good combo of bike and motor/motor configuration.

 

[ammodave]

Care to recommend another motor? What's your advice on the rpm issue?

 

[d8veh]

Care to recommend another motor? What's your advice on the rpm issue?

It would be best if you explained why you thought about a 350w motor. Is it for increased speed or what?. It's always better to clearly state what you're trying to achieve rather than what bits your thinking of buying.

Those forks do look a bit spindly for a high torque motor. Getting the right speed is the hardest part as the 201 rpm motors for 26" wheels are normally too slow, and the high-speed versions for 20" wheels are too fast. The BPM motors come in a whole range of speeds, but it's not easy to find someone supplying the middle-speed versions. Your 28" wheels will give a top speed of about 19 to 20mph with a 201 rpm motor. The 328 rpm motor will try to do about 31 mph, but it doesn't have enough power for that,so it'll be very inefficient.

You can get more speed by using higher voltage. A36v 201 rpm motor will do about 24mph with 12S lipos at 48v, but lipos aren't plug-and-play, so you need to look-up how to use them. You can make your own bottle battery out of plastic drain-pipe and a pair if 5000maH lipos, which should easily do 10 miles if you don't have steep hills.

If you want light-weight, then the Q100 with 12S lipos will be a good solution, but if you want a motor with some grunt for hill-climbing then the Bafanf BPM or CST rear motor is a good solution. If you want to spend more money, there's loads of other motors, but I'm assuming you want an adequate low-cost solution.

Those ready-made bottle batteries can't supply enough power unless your happy with 15mph and a 250w motor at 15 amps or less.

Some of the Bafang 250w motors might also be good for you. Greenbike kit do the SWXH in 260rpm, but you have to build your own wheel. They'll do it for you, but it'll slow down your order.
http://www.greenbikekit.com/index.php/swxh.html

If you have a look on Alibaba.com, there's now loads of 250w motors with cassette splines now, but they don't seem to have found their way to suppliers that sell single items.

 

[ammodave]

I was looking for a stealthy, clean build that's why I was going for the bottle battery. A range of at least 10mi is adequate but I still want at least 20mph on the flats. I have an 8 spd internal rear hub so I need to use a front drive. I can change out the forks if necessary but I felt two sturdy custom torque arms could cure that problem. Cost is not really a problem but I'm reluctant to double the cost of my build unless I get a good return on my investment.

 

[johnamon]

Hi ammodave,

I have the 350W front wheel drive 328rpm motor installed on my commuter - I like it, but I'm running 26" wheels with lipo (treat with extreme care & understanding) batteries.

d8veh is absolutely correct that a bottle battery will not allow your motor to draw sufficient amps to use anything like all it's power, really the motor will be hampered. I replaced my 'Frog' style battery for lipo's this year for that very reason. I consider the original frog battery to be £150 wasted, because I did the classic 'start cheap and pay more later' approach that you are in danger of heading down :wink:

Also the BPM motors are large, I had to have the disc brake mount machined off mine to fit my non-disc forks....

 

[-dg]

If you can run 48 volts, consider the Bafang SWXK. It is smaller and lighter than the BPM but stronger than the Q100. I'd guess around 22mph in a 26" wheel (I get 23+ in 700c).

 

[zukster]

If you can run 48 volts, consi

• der the Bafang SWXK.

It is smaller and lighter than the BPM but stronger than the Q100.

I'm not sure if the SWXK is stronger. I had to replace the nylon gears with metal when operating at 48V after two years. The Cute 100's are going on one year on 48V. They are double geared and this I think helps spread the load on through the gears. On the cute 100's I limit the amps to 15A via bmsbattery's KU63 controller. I run my own cute 100 on 14S (52v nominal, 58v fresh of the charger) and I'm 150lbs and my bike is 30lbs. The cute 100's don't seem to heat up as much as the SWXK. However, with ebike.ca's 25A controller, 6xIRFB4110, a metal geared SWXK seems more torquey at 14S (of course) and seems okay so far with 16S and pulling a trailer. I make sure I don't push it hard enough to overheat it now after burning up one running it too hard at 15S. The metal gears were noisy at first but after a good douse of fluid film inside the motor at first, they settled in after about a week. Still more noise that the nylon gears, but just a bit.

Ya, and as mentioned, at 48V, the 201rpm wound motor will have a higher top speed. About as fast as I can pedal comfortably with a compact 44 big ring up front an a small 11 ring on the back.

 

[sacko]

I have posted this elsewhere, but it seems to be pretty much the same question.

http://www.endless-sphere.com/forums/viewtopic.php?f=3&t=42162

It will pull you up any hill, and top out at 28mph on the flat (44.4v lipo).

I used 44.4v 15ah, which would allow me to reach 30 miles range.

Giant XTC SE 21" frame
Hydraulic Disk Brakes
Schwalbe Big Apple 26x2.15"
EV Falcon Frame Bag

KU123 controller
Bafang 36v 500w Code 12
Twist throttle

 

[zukster]

I have posted this elsewhere, but it seems to be pretty much the same question.

Nice looking build for the bigger, faster motor. Clean. I tried to keep my KU63 Cute 100 clean too. A piece of stretchy velcro hides the controller. Even when I don't put it on, people never notice its an ebike, even on the seabus or skytrain. The KU63 is so small. This of course is a less powerfull setup. If I head out today I'll check the top speed with the help of my smart phone!

And a battery pack:

 

[d8veh]

I was looking for a stealthy, clean build that's why I was going for the bottle battery. A range of at least 10mi is adequate but I still want at least 20mph on the flats. I have an 8 spd internal rear hub so I need to use a front drive. I can change out the forks if necessary but I felt two sturdy custom torque arms could cure that problem. Cost is not really a problem but I'm reluctant to double the cost of my build unless I get a good return on my investment.

That's made it a bit clearer. You can choose between the Bafang and the Cute motors. They should both be OK. The cute is lighter, smoother and quieter, but the Bafang is bigger, so should be more torquey; however; the Cute does seem to have more power when pushed. I can't choose between them. Which ever one you go for, you want the 201 rpm and run it with a 36v controller set to 17 or 18 amps with 12S lipos, or a 48v 15 amp controller with a 48v battery. You can probably add one or two amps to the Bafang.
You can save a lot of time by getting the complete kit from BMSBattery or Greenbikekit because they have the motors ready-built into a wheel - not the best quality, but adequate. You might want to think about a Lyen programmable Minimonster controller if you're going up to 48v, but I don't know whether it works with the Q100, which needs a high speed controller. Check with Lyen.
http://www.lyen.com/

You can adjust the current of the 36v controllers by adding a bit of solder to the shunts.

 

[zukster]

There are two Bafangs. Power options from low to high are Cute 100(250W), SWXK,(350W), Bafang 36v 500w Code 12(500W).

Of course you can dump more power into an xyz rated motor, its just not recommended by the manufacture. The over volted setups I mentioned seem okay so far.