Bafang CST Motors and elifebike.com

[jhendrickson]

I am so close to pulling the trigger on an ebike kit based on a Bafang rear CST motor... but I am baffled by the choices at hand. Ultimately the bike will be 48v, 700c wheels, 15Ah battery, 9-12 FET controller. I would like to be able to ride 25-30mph on flat without pedaling.

So elifebike has the following four motors. The 48V 500W would be the simple choice... but maybe an over-volted 36V 500W would be better for my situation? Can anyone interpret these models into the standard terms I see around here (like a code and rpm number at 36v)?

36V-CST 36V350W26-205
48V-CST 48V350W26-205
36V-CST 36V500W26-205
48V-CST 48V500W26-205

Thanks!
joe

 

[d8veh]

None of them will give you what you want. That 205 must be the RPM. If you run a 36v one at 48v, it will go 33% faster, which is 273 rpm or 22mph in a 700c wheel.

The 36v 500w one from BMSbattery is 260 RPM, which can do about 22 mph on the road. At that speed, you get a nice balance of speed and torque. You could run it at 48v for more speed, but efficiency at lowspeed would be compromised, so only do that if you don't have steep hills and/or your weight is 85kg or less.

The 350w versions won't have enough torque for those speeds. To do those speeds without pedalling, you really need at least a 1000w DD motor or one of the Em3ev modified MACs. 30mph requires about 1000w of output power, so say 1500w from your battery, which is 30 amps at 48v. 25 amps might just about be enough.

 

[jhendrickson]

I wanted to report back on how my build has turned out. I ended up getting the Bafang 36V, 500W CST motor on a 700c wheel. I've paired that with an S12S controller and a 48V 15Ah Li-Ion battery. Let me tell you, it moves! Full throttle on the flats is about 31mph (me=180lbs). Plenty of power from a stop. Goes right up a couple medium hills that we've got. I'm very happy with this setup.

So I went with the 36V500W motor thinking it would give me faster RPMs at 48V than the 48V500W with enough power to satisfy me and I believe I was right. I still have no idea how this translates to windings or codes but I assumed that BMSBattery was trying to make it simple for folks to choose... which only frustrates those of us who want the details to figure it out ourselves!

I have the grip throttle on the left and a grip shift on the right, attached to a 11-28T 7-speed cassette. Having any gears on a bike with this kind of power and top speed is pretty useless though, but at least the 11-tooth gives a little resistance as my legs go round and round for show.

I also put on the "dual hall sensor 12 signal PAS" for pedal assist but I really don't like it. It seems to be either full throttle or no throttle regardless of how fast I pedal. I can control the top speed through the "gears" on the S-LCD3 display but it gets dangerous when I need finer control moving about. Am I missing something about how a PAS should work?

I also have the hidden wire brake sensor which works great. No special brake lever with an extra wire required.

The LCD only shows a speed when under throttle. I understand that this is related to having a geared motor where the internals can rotate (or stop rotating) at different speeds than the wheel. I tried putting on an external (magnetic) wheel speed sensor but couldn't ever get it to work. But it's no big deal. I don't really care about the speed except when I'm under throttle anyway.

One problem I did have was a failure in the S12S controller unit. A solder joint on a resistor failed after a few rides and the bike wouldn't go anymore. I had to open it up and re-solder it back to the board. Quality control issue I'd say. Works fine now.

Another issue was that some of the wiring from the controller didn't match exactly the S-LCD3 display or the motor wires (connectors and/or colors). It took a little sleuthing to get the motor running with some help from a hall wire troubleshooting guide out there on the interweb.

That's about it. BTW, the bike is a new Schwinn Admiral from Walmart. Nothing like $1100 worth of electric gear on a $130 bike. It's my daily commuter and takes a little tweaking here and there. The whole project is not for the technically impaired, that's for sure.

Ride on!

 

[d8veh]

The S12S uses current control by default, where the 5 levels are different currents. In level one, the assist is quite soft, but it's indpendent of speed. The setting is P3=1. If you want, you can change it to speed contol, where the levels relate to different fixed top speeds in each level. In this case P3=0.

There's a setting in the LCD to select the correct speed sensor, so that the speed is properly displayed when freewheeling. IIRC P2 =1

You can download all the settings fom The BMSB page where the S-LCD is listed.

 

[poeli]

How reliable is elifebike in regards with the quality? I read some bad things about them, but that was 3 years ago. How're they now?

 

[d8veh]

They're selling items from a catalogue. They take stuff out of lots of boxes and put it in one box. Don't expect them to inspect the stuff nor do a system check. I'm shure they do some checks based on their knowledge of problems; however, I expect that they rely mainly on the manufacturers to check the stuff. A Bafang motor is the same quality whoever you buy it from!

Like with BMSBattery, many of the complaints come from the buyers' lack of understanding about the stuff they order and the ordering system. The stuff itself is relatively cheap. Though DOA stuff is very rare, dealing with it will be a problem for all concerned. You'd probably have to take it on the chin.