Having watched the forum for a while and learning a few things from the more advanced users of the ebike world I've finally built my old Carrera Kraken into an ebike..and I must say its only 250w yes street Legal but it's not bad at all..the Bafang bbs01b seems to pull ok and does certainly help with the odd Hill with the PAS on level 4.. I would recommend buying the USB lead and learning how to configure your settings as this has made this a completely different ride.i purchased this kit complete with the 15ah battery direct from China. It took about 30 days to get here. probably on the rethink I would purchase the battery over here. Some people say the Chinese batteries are crap but I'm not sure as I haven't used it enough to comment. Time will tell. A big thanks to all the me mbers that took the time to answer my questions and help me on the way with the bike build. 25miles today and going strong plenty of battery left as well. The bike apart from poss a gear ratio change is great + maybe a Break upgrade. The power has taken a bit of getting used to as its a bit weird matching peddling speed to the power if you pedal too hard it does not help you if you slow a little the power picks up. But if in doubt you the throttle..lol.Time now to enjoy and tweak this one up while I plan te next build

Jim Ebyke.

Hi

Nice job

Strange you have to peddle slightly less for more power

Is that something playing with the settings can sort out .

The Bafang motor produces maximum torque from low cadence up to around 70 rpm. It then ramps down to zero power at around 90 rpm because of the back emf. The Bosch motor ramps down to zero power at 120 rpm, but because the motor will have bad efficiency below 60 rpm, there must be an algorithm built into the controller software that increasingly reduces the power as the rpm reduces below 60 rpm, otherwise the motor would overheat. It must be this algorithm that's adjusted for eMTB mode to give more climbing power at low rpm.

 

Here's a power graph of the Bafang. Unfit people normally have a cadence around 60 rpm, for which it's well suited, but if you're fit and have a cadence of say 90, it would be less suitable. Basically, it'll give more support than the Bosch at a low cadence, but less at high cadence. It will also be more efficient with a lower cadence than the Bosch:

The Bafang motor produces maximum torque from low cadence up to around 70 rpm. It then ramps down to zero power at around 90 rpm because of the back emf. The Bosch motor ramps down to zero power at 120 rpm, but because the motor will have bad efficiency below 60 rpm, there must be an algorithm built into the controller software that increasingly reduces the power as the rpm reduces below 60 rpm, otherwise the motor would overheat. It must be this algorithm that's adjusted for eMTB mode to give more climbing power at low rpm.

 

Here's a power graph of the Bafang. Unfit people normally have a cadence around 60 rpm, for which it's well suited, but if you're fit and have a cadence of say 90, it would be less suitable. Basically, it'll give more support than the Bosch at a low cadence, but less at high cadence. It will also be more efficient with a lower cadence than the Bosch:

I think your right. It does seem like I'm out pedalling the motor so I spend a lot of time taking the load off the pedals. Simply looking for that sweet spot..if that makes any sense.lol. I'm not to sure if I can programm it a bit better so that sweet spot can be lengthened..

The Bafang motor produces maximum torque from low cadence up to around 70 rpm. It then ramps down to zero power at around 90 rpm because of the back emf. The Bosch motor ramps down to zero power at 120 rpm, but because the motor will have bad efficiency below 60 rpm, there must be an algorithm built into the controller software that increasingly reduces the power as the rpm reduces below 60 rpm, otherwise the motor would overheat. It must be this algorithm that's adjusted for eMTB mode to give more climbing power at low rpm.

 

Here's a power graph of the Bafang. Unfit people normally have a cadence around 60 rpm, for which it's well suited, but if you're fit and have a cadence of say 90, it would be less suitable. Basically, it'll give more support than the Bosch at a low cadence, but less at high cadence. It will also be more efficient with a lower cadence than the Bosch:

So can it be sorted with a user software tweek as obviously the OPs cadence is high as he is easing off which is really counter productive from an overall efficiency point ie rider and bike combined .

So can it be sorted with a user software tweek as obviously the OPs cadence is high as he is easing off which is really counter productive from an overall efficiency point ie rider and bike combined .

No, you can't change the basic characteristics of the motor. You can only turn the current up below 70 rpm. There's nothing you can do to increase the max rpm, nor the power above 70 rpm other than increase the battery and controller voltage to 48v or anything higher than 36v, except there is no 48v controller for a BBS01. Once the motor exceeds 70 rpm, the back emf is limiting the current, not the controller.

No, you can't change the basic characteristics of the motor. You can only turn the current up below 70 rpm. There's nothing you can do to increase the max rpm, nor the power above 70 rpm other than increase the battery and controller voltage to 48v or anything higher than 36v, except there is no 48v controller for a BBS01. Once the motor exceeds 70 rpm, the back emf is limiting the current, not the controller.

Thanks for the info

Im glad its not mine thou as it would really get me that i had to ease back to get power as obviously rider and system are not compatible in this instance .

I have tried running the GSM at 44.4v and it is quasi perfect for my cadence which is around 100. The higher power was not appreciated by the external 36v controller so next test is to turn the controller max down to 12 Amps.

So to to overcome the problem I would have to go to the non legal bbs02 say 500w 48v. And I take it this system is not affected because it's 48v..

It seems to me that these things are set up for that 'easy/lazy' cadence that you see on videos from Holland. To have the power reducing in the high 60's and have the bike dictate what my cadence should be would drive me nuts.

I have contemplated a BB motor for a second bike but this (along with the many other niggles they suffer) takes it too far away from the simple 'jump on it and ride', low maintenance machine I look for.

To the OP - maybe you need more gears to find that sweet spot? Although, thinking about it, that doesn't alter the fact that it sounds like the motor cadence is lower than what your legs want. NEW LEGS that's it!

You need to check because it's difficult to get precise information, but as far as I can figure out, the 48v BBS02 is 120 rpm. That would make sense since 48:36 = 120:90 and rpm is proportional to voltage. Another thing you can do is use an external controller, but that would go into the realm of experimentation. In principal, it should be a simple matter of connecting the battery and motor wires if you only want a throttle, but you'd have to be a bit more creative to fit a PAS.

You need to check because it's difficult to get precise information, but as far as I can figure out, the 48v BBS02 is 120 rpm. That would make sense since 48:36 = 120:90 and rpm is proportional to voltage. Another thing you can do is use an external controller, but that would go into the realm of experimentation. In principal, it should be a simple matter of connecting the battery and motor wires if you only want a throttle, but you'd have to be a bit more creative to fit a PAS.

Looks like I'm going to have to go illegal route next time around to get what I want..anyway if there are any members out there with a dead controller they want to part with I'm your man..I would like to get in there and check it out..or even a dead motor..maybe we need to rewrite the firmware and as you say maybe go the external controller route..it is possible..

If you are interested in learning more about your Bafang drive and it's capabilities, have a look over on Endless Sphere.

If you are interested in learning more about your Bafang drive and it's capabilities, have a look over on Endless Sphere.

Thanks Pete I'm more interested in the firmware in the controller. Also the type of components they are using.

Jim

Ok, I guess that is a completely different subject, although isn't what d8veh was saying about back emf a physical limitation of the motor and nothing to do with firmware or controller? Please educate me:)

Without complete investigation into things we will never know..believe me I've had great experience with Chinese controllers and there motors and generally they don't use the best of components or motors I would say they use what they have to hand.. They are great at copying and making things work but when it comes to the perfection.. well it can generally be improved..

I think these kits are aimed at the average cyclist.and to that point they do exactly what there meant to do.and if they can get people back in the saddle without killing them that's great I'm all for people getting fit. But what about the odd few that want more..the inventors amongst us lol..

hi jim

have had the laptop out on the 350watt the amps are set to 18 but try as I like the 250 watt will not go over 15 amps without an error code, but have seen 630 watts on the 250 in short bursts up hill, I have found on the 250w you always have to be one gear lower than feels natural to keep it happy. managed 27 miles the large battery still showed 39.9 volts and full bars appears to have very little sag but it makes the thing impossible to lift over a 5 bar gate have to meet for a ride soon

Hi Pete

I've been out testing the 250w it's ok and on a fresh battery it's got plenty of get up and go. Done 25 yesterday evening batt still reads 75% and voltage is still good. I'm might go to 100% on the Keep current and see how it performs. Yes I've heard of the error code thing when people up the amps but as mine is a late version I might give it a try..I've not found much in that display worth altering so might have to borrow that one of yours some time..not to sure if it will make a big difference or not as I don't know how the controller and displays distribute there power settings..

Jim

hi jim

have had the laptop out on the 350watt the amps are set to 18 but try as I like the 250 watt will not go over 15 amps without an error code, but have seen 630 watts on the 250 in short bursts up hill, I have found on the 250w you always have to be one gear lower than feels natural to keep it happy. managed 27 miles the large battery still showed 39.9 volts and full bars appears to have very little sag but it makes the thing impossible to lift over a 5 bar gate have to meet for a ride soon

It's what I was saying before. You have to understand how back emf works. On the 36v motor, the current is limited by the back emf when you exceed 70 rpm. You could have a 100A controller, but it would make no difference. The controller's maximum current regulation only comes into effect below 70 rpm and the closer you are to 70 rpm, the less you can change it.

 

If you look at the graph I linked above, you can see the horizontal part, which is where the controller is limiting the max current, then it ramps down from there because the back emf is generating current that opposes it.

 

What all that means is that with any DC motor, you can only get maximum current at the low end of the RPM range. Torque is proportional to current, so you only get maximum torque at low RPM too. The problem is that efficiency drops off at low rpm too, so you run the risk of over-heating if you go too slow, which is a shame.

I was trying to understand the back emf thing d8veh, so when you increase the voltage the motor will have a higher max. rpm and more torque, but will still reach the point where the back emf will reduce the current, just at a higher rpm.

I was trying to understand the back emf thing d8veh, so when you increase the voltage the motor will have a higher max. rpm and more torque, but will still reach the point where the back emf will reduce the current, just at a higher rpm.

 

Back EMF kicks in once you pass the maximum rpm just like on a hub motor. The thing is depending on gearing you can spin a mid drive motor faster than max rpm before the cut off speed. Back EMF is at about 90 rpm on the GSM so when I am climbing in a lower gear than necessary I have to remember not to spin at my natural rhythm.

 

The rpm for all the Bafang drives is on the spec sheets for both unloaded and loaded speed: http://www.bafang-e.com/en/components/motor.html

Put another way, any DC motor is also a dynamo - they are one and the same thing. So, when you apply a voltage to the motor a current flows through the stator windings creating a magnetic field which intereacts with the permanant magnets in the rotor - so causing the rotor to spin. As soon as it spins the magnetic field of the rotor magnets intereacts with the windings (copper coil) in the stator, so generating a voltage in the windings BUT this has a reversed polarity to the applied voltage. Hence back EMF (electro motive force). As the rate of spin increases so does the back emf, when the back emf equates to the supply voltage there can be no further increase in rpm. So rpm limit of any electric motor is a function of the way that motors work and, ultimately, not the controller or firmware.

So it seems to me that the relationship between cadence and motor rpm is one of the internal gearbox between motor and final drive.

Sorry if I'm stating the bleedin' obvious, but writing it out helps me understand it.

Thanks people

Nice bit of homework there..lol as the old saying goes you can't polish a turd.But you can cover it in glitter..yes I do understand where your coming from with the back Emf. So maybe we should put together a good list of what works the best for the bbs01 250w uk legal system.ie programm settings. The best chain ring size for what type of riding. And what type of rear gearing works well for the type of bike being used there's plenty of us on here. I don't know how many ride uk legal bbs systems. But there must be a few. There seems to be a shortage of info for this motor. Plenty for non uk legal specs out there. But when your new to it it's all a bit confusing.

Jim

Put another way, any DC motor is also a dynamo - they are one and the same thing. So, when you apply a voltage to the motor a current flows through the stator windings creating a magnetic field which intereacts with the permanant magnets in the rotor - so causing the rotor to spin. As soon as it spins the magnetic field of the rotor magnets intereacts with the windings (copper coil) in the stator, so generating a voltage in the windings BUT this has a reversed polarity to the applied voltage. Hence back EMF (electro motive force). As the rate of spin increases so does the back emf, when the back emf equates to the supply voltage there can be no further increase in rpm. So rpm limit of any electric motor is a function of the way that motors work and, ultimately, not the controller or firmware.

So it seems to me that the relationship between cadence and motor rpm is one of the internal gearbox between motor and final drive.

Sorry if I'm stating the bleedin' obvious, but writing it out helps me understand it.

Nice one, makes more sense now. I knew that a motor could be used as a dynamo, but hadn't considered it would be producing voltage when used as a motor. As you say this is down to the physical characteristics of any given motor and can only really be changed by external gearing, hence why I asked earlier how this could be improved by firmware or controller improvements.