Written by Ron/Spinningmagnets, November 2013
Bafang is now selling a compact 750W mid-drive system that we think will become very popular, due to the large percentage of the population in US/Canada that wants a street-legal electric bike system.
A few years ago, the Bafang company could not help but to notice that mid-drives were becoming very popular in the European and Asian markets, and that Bosch and Panasonic had made long-term investments in compact and well-designed mid-drives that were integrated into the bottom-bracket (BB) of the bicycles frame. Many European and Asian markets are in power-limited countries, such as the 250W limit in the EU and Australia.
It is easy to de-rate a larger motor by limiting the max amps (also allowing it to run cooler than normal), but it can be problematic to up-rate a smaller motor. Also, the Bosch and Panasonic units require a frame that is specifically made to fit the drive, so these Bosch and Panasonic drives cannot be retro-fitted onto common bicycle frames. For both of these reasons, I am very excited about the potential of the new Bafang BBS02.
I could not help but to take notice when the 350W Bafang BBS01 was introduced. The thing that really caught my attention was that the Bafang unit could be fitted to almost any bicycle frame. I do feel that the 350W unit is too weak for an off-road bike of any type (in my humble opinion), but there are no power restrictions for off-road electric bikes.
Because of the 750W power limit in the USA (along with the 500W power limit in the Canada)…the 350W BB-S01 seemed to be a good idea that was also a “missed opportunity“. Its true that it was first marketed in Europe and Asia where that power level was appropriate, but with just a little extra effort, they could have the best possible product for the growing interest in street-legal E-bikes in North America.
As it turns out, my concerns were for no reason. The BBS01 was so popular in their initial marketing push, that the factories were maxed out just keeping up with the 350W unit demand. Their production capability was ramped up recently to meet demand, and Bafang revealed at the Interbike September 2013 meet in Las Vegas that they have a 750W version which is just now beginning to arrive in North America (the first 750W prototypes were shown in the Shanghai show in May 2013 to gauge industry interest).
The 750W unit appeared to be the same physical size as the 350W unit, and my experience with exaggerated China-made performance claims made me skeptical of the 750W spec. However, I have recently been informed by a North American distributor that the motor is wound to a different Kv, so when it is run at 48V, it will spin at the same output RPMs as the 36V / 350W version. This allows the mechanical-gear RPM-reduction to remain the same for both units, and they can also share many of the same housing and interface parts. More volts can add more power without significantly adding more heat, and it is the heat that has frequently proven to be the limiting factor on these smaller motors.
However, we do not live by volts alone. The North American distributor has verified that the stator on the 750W unit is 5mm wider, which allows for a slightly greater copper mass (it is roughly one pound heavier due to the wider steel stator and extra copper wire in the coils). This means that the 750W motor can handle more amps than the 350W motor before reaching saturation. As you can imagine, I was very pleased to learn this. Both units have built-in over-temperature protection circuits that will cut power before the unit would be damaged.
In the picture shown, the “1307090018″ number on the motor housing means:
130709 = 13 (2013), 07 (July, 7th month), 09 (9th day)
0018= Serial number, this is the 18th unit produced that is a BBS02-48V-500W
The “JSCF0034.0″ and “13070012″ refers to the controller.
I do not yet understand the JSCF designation, but the 13070012 seems to mean that this controller was manufactured in 2013, 7th month, serial number 12. So far, there are seven stock controller/stator combination options:
250W = 24V X 18A
250W = 36V X 15A (greenbikekit.com)
350W = 36V X 18A
500W = 36V X 25A (Ali Express)
350W = 48V X 15A (BMS-Battery)
500W = 48V X 20A
All versions can be bought direct from China through Alibaba or Aliexpress, but if you want to try that…let the buyer beware!
ES member mwkeefer adjusted the shunt on a stock 15A controller, and was able to raise the amps to 17A without eddy-current losses or stator-saturation (on the narrower BBS01 stator), but then he also bypassed the stock controller and used a 6-FET for a quick test at 24A, which showed that significant heat was immediately being produced . The torque at 17A was a very healthy 68-NM / 50-ft lbs.
To be clear, if you put 25A into the BBS01 motor, it will provide more power than if you were limiting it to 17A, but some of the amps will be converted into heat instead of work, so you can only do this for short bursts (and to be fair, it does shed any accumulated heat very well). A long uphill with an unlimited controller allowing 25A will cause the over-heat protection to cut the power at some point, which will protect the motor and controller from being damaged.
Maximum efficiency (best battery range) was attained near 11A (roughly 520W @ 48V). The stock controllers capacitors were rated for a max 63V, so there’s no room for voltage upgrades unless you want to swap-in different capacitors, and also add a stand-alone Low-Voltage-Cutoff (LVC). The possibility exists that the stock controllers FETs would also have to be upgraded for higher voltage, but that has yet to be determined. If you want an external controller so the motor could take more heat (in stock form, the motor and controller are both producing heat inside the same case), then a Lyen 6-FET controller could run more amps than the motor, so a larger 9-FET or a 12-FET would be un-neccesary.
All this technical jargon just means that no extra performance was “left on the table” for hot-rodders to access. The performance was good, but if you need more than a continuous 816W (48V X 17A) at the BB to be happy, you’ll need a completely different motor. However, this also means that…if you are happy with 750W, then the BBS01/BBS02 is probably the smallest possible package in which to reliably get that level of performance.
Edit: a friend installed a BBS02 on his bike with 16-inch wheeled Moulton, and reported that the hill-climbing torque was so great, it was actually too much because the bike would wheelie way too easily, due to the short wheelbase and smaller diameter wheels. I recommended that he install the 48V drive on one of his larger bikes. I still recommended that he use the larger stator in the BBS02, but perhaps purchase the 36V X 25A = 500W version, and then use a lower assist setting, to limit the amps (there are 9 levels of assist). For a small-diameter wheeled bike, a 36V battery is more than enough and would be more affordable than 48V.
The primary reduction (shown above) reveals the secret to the BBS01 and BBS02′s quiet operation: the high-RPM half of the reductions gear-set uses wide helical gears with a synthetic-polymer driven gear. The drive gear is metal for longevity, but the less-loaded driven gear uses a strong plastic to absorb resonance, and the helical shape of the teeth softens the contact between each tooth as it spins. The surprising length of the primary reduction gears means that two helical teeth are engaged at all times at any given moment, which enhances the strength of the connection and further softens the power transmission. This is a brilliant design.
The secondary reduction (pictured below) is a conventional steel gear-set with straight-cut teeth.
You can also see in the pic above that the motor is a radial-flux, permanent-magnet brushless DC inrunner. Bosch, Panasonic, and GNG have all shown how this style can shed heat well if designed properly, since the stator (the hot part) has a wide area of contact that is bonded to the aluminum motor shell. A BB-drive gives the motor some gears, so it can keep the motors’ RPMs up regardless of the bicycles speed. This helps the power system to avoid creating excessive heat in the first place.
The primary reduction (high-RPM 32T:12T = 2.7:1) uses a helical gear (shown at the 2:22 mark in the video listed below), which dramatically helps the noise level. The lower-RPM secondary reduction also uses helical-cut teeth (62T:11T = 5.6:1), and the total reduction from the motor to the chainring is 15.1:1.
We were recently able to contact ES member lcrewse, who is a North American dealer for these drives.
Are you able to provide a warranty?
I provide a 90-Day warranty on all our Bafang Mid Drives (unmodified, and used with correct voltage).
What batteries do you carry?
36V / 11-Ah, Samsung Cells
36V / 14.5-Ah, Panasonic Cells
48V / 9-Ah, Samsung Cells
48V / 11.6-Ah, Panasonic Cells
The cells are cylindrical 18650, the same type that are found in laptop computers and cordless power tools. Both the Panasonic and Samsung cells are the safe LiMn chemistry.
Tell me about Lectric Cycles.
Lectric Cycles is based in metropolitan Phoenix, Arizona. I’ve been involved with electric bikes since purchasing a poorly designed kit and heavily modifying it almost 4 years ago. I began building E-bikes for other people and eventually decided to start a company to build and carry better designed kits, and also E-bikes more suited to the North American market. Our company was started in Oct 2012, and we partnered with Fat Sand Bike to develop the first Production Fat Tire Electric Bike to market.
We signed up to be a Distributor of Bafang mid-drives in the USA, and as a result of my early testing with the BBS01, encouraged them and gave them feedback on developing a North American specific Version (which was not originally planned), the BBS02.
We currently still market and sell the Fat E-Monster in conjunction with Fat Sand Bike. Soon, we’re going to release a Fat Tire Bike with the 350W or 750W mid-drive Bafang motors (we have the prototypes already, which were shown at Interbike in Las Vegas a month ago). Several other more conventional bicycle models will follow based on these drive systems.
Could you tell me more about the origins of the 750W Bafang BBS02?
After receiving one of the first pre-production samples in early 2013 (due to my existing relationship with Bafang), I began to heavily lobby my contacts to make a more powerful North American product. Bafang inquired as to what power levels and different features would be important to the NA market and developed the BBS02 variation based on that. I’ve been testing Samples of the 750W since July 2013 and received production units in Sep 2013.
Can you share any more details about the features on the kit?
The BBS02 has a user-configurable speed limiter up to a maximum of 25-MPH for the throttle, and unlimited for the PAS. There are 3 levels of PAS but they do not give the same amount of power as using the throttle. This is so that the PAS system isn’t as hard on the bikes conventional drivetrain. At a max PAS level of 3, the motor is drawing about 50% of it’s max power. This is still enough to reach the 25-MPH mark, but for more power, you can always use the throttle.
In addition, the units that I carry are also configured so that the throttle gives max power in all PAS modes as well as when PAS is Turned off. The kits I sell come with a choice of thumb or half twist throttle. The entire kit is plug and play, and uses waterproof plugs throughout. All BBS motors will mount onto a standard 68mm wide bottom bracket shell. I also provide (on request) hardware as well, to be able to adapt these to use on a 73mm wide bottom bracket shell.
In addition to this I can also disable the speed limiter (on request, and this reduces the warranty to 30 days). When unlimited, 30-MPH is easily achievable with appropriate gearing. Check local laws, because street-legal E-bikes may be limited to 20-MPH in your jurisdiction.
Price of the 750W kit from lectriccyles.com is $750, not including the battery and charger.
Here are some quotes from well-known and respected electric bike enthusiast “Kepler” on a 350W BBS01 unit he recently test-rode (He lives in Australia and they have a 200W power limit for street-legal bicycles):
“…Visually it is quite small and makes for a reasonably stealthy installation…Firstly: yes, it is quiet. As quiet as any electric setup I have ridden except perhaps for my 5405 Stealth Bomber motor…this bike had the speed limiter tricked for a max speed of 35-kph. Realistically, this is all you are going to get from a 350W system, so certainly the speed limit isn’t an issue on this bike. It is a bit of shame that that when you trick the speed limit by changing the wheel diameter settings, your speed and distance data is rendered useless…”
“…Nothing like actually seeing a product in the flesh and being able to test ride it. Conclusion for me is that; its full speed ahead with getting one of these kits for my next build. For me however, the 750W kit with speed limiter removed and 48T chainring will be what I will be ordering…”
BBS02 on a stand, shifting gears
BBS02 riding uphill on 30% grade
BBS01 being dis-assembled by the German distributor for the European market, www.bike-emotion.org
A few warnings:
If you have a bike with a step-through frame, the position of the “S”-shaped downtube may require that the motor position be rotated downwards, and this may reduce the ground-clearance to an unacceptable level. The drive fits best when mounted to a common diamond-frame.
Also, the kits PAS mode uses a common speed-sensor, so when you stop pedaling, it takes a moment for the power to sense the change in the wheel speed and change the power that’s being applied. This is something you need to be aware of when shifting. Torque-sensors perform better, but are typically more expensive. Bafang has stated that they are developing a torque-sensing option for this drive that should be available soon.
The proprietary single one-piece drive-sprocket is either a 46T or a 48T (a 38T and 52T option might be available soon), and when it wears out you may need to order a new one from the dealer you bought the kit from. Since it is not a chainring attached to a central spider, it would require a custom adaptation to drill precise holes in the sprocket arms to allow you to swap-in a larger or smaller chainring. This is the one thing I would have changed about this kit, it should be using a 110-BCD or 130-BCD spider that has a chainring mounted to it.
The crank spindle is 159mm-wide to allow for the wider 750W stator. Several owners have contacted me and verified that they have taken serious jumps with this drive, and the spindle is quite strong. I would recommend that if you are taking jumps, to use a full-suspension frame, but even on a hardtail E-bike, this drive seems to be holding up well.
Our friend Kepler sent us more ride reports:
“…I have had the opportunity to give the [750W BBS02] drive a good workout on a variety of single track over the past 2 days. Clocked up 60km of purely single tack with with plenty of tight twisty uphill together with lots of bone jarring tree roots, logs and ruts. Have had an absolute ball and now really understand what a mid drive is all about. The way the bike handles and skips over the rough stuff is such a nice change from [the weight of] hub motors…Most of the ride was on setting 5 (out of 9)…No problems with motor temp with the motor housing only reaching luke warm on even the hardest part of the ride…”
A friend of his also had a BBS02, and one wire shorted due to a manufacturing defect (found here), and fortunately for us, he decided to take pictures when he did the surgery!
European BBS01 250W owners manual in PDF form:
Dimensional blueprint of Bafang 350W BBSo1:
The endless-sphere discussion thread on the 350W/750W Bafang BB-drives:
Here is an article on mid drive kits to compare the BBS02
Here is a pic of the BBS02 mounted to a recumbent tadpole trike. The pic is courtesy of Declic Eco, a French company specializing in custom electric bikes since 2008.
ES member eride lives in Denmark, and he is producing and selling 130-BCD spiders and extra-large chainrings with 70T, 75T, and 80T, for small-tire recumbents using the BBS02.