BBS02 500w versus BBS01 350w

[culy30]

It has a big effect on the motor's efficiency. Ideally you want the motor to be at about 2/3 its maximum speed at your natural cadence, so for me that would be a max motor (crank) speed of 90 rpm. If it can spin faster, it's efficiency will reduce while pedalling, or yours will.

I read somewhere that the BBS01 36v 250W (15A) max power is achieved at 78rpm. The BBS02 36v 500w is 120 rpm (ish)and the 48v 750w is around 140 rpm.(??) In each case a tolerance of +/- 6 (ish?) rpm was quoted. These were not "NO-LOAD" figures. I'll see if I can find the articles and come back to post them. My anecdotal experience is that BBS01 and BBS02 36v units keep delivering power at high cadence. I dont notice a drop off at all, but I do notice a steady increase (not necessarily linear) all the way through the range. It's more to do with the rider capability to pedal fast and how the controller is programmed. 90rpm is a fairly typical max comfortable cadence for many riders, its no surprise that the BBS units deliver close to max power at this cadence. Personally I find that 100rpm feels the most efficient combination of me and motor, but going up to 120rpm still feels like the motor is providing the majority of the power(BBS02 500w de-tuned to 15Amps) I do have a power meter (static cycle trainer with a power meter) I might rig it up in the winter and do some testing both with PAS and throttle only. Power at max throttle in each gear on a simulated 10% gradient at 10rpm steps from perhaps 60rpm to 140 rpm (or max rpm) maybe??? Then re-run PAS only................in each PAS setting......................sounds like I need to recruit Chris Froome.................................

 

[trex]

the no load RPM is proportional to the voltage. The 78RPM is where the motor produces maximum power for 36V BBS01 and BBS02, 96RPM for the 48V BBS02. The no load RPM is about 30% higher but is not useful to pedal over 78/96 RPM because the motor produces less and less torque at higher RPM. More torque equals better acceleration. BBS02 36V 25A has same RPM as BBS01 but has 60% more torque than the 15A version. The 36V has high enough RPM for most people. I can't see any situation where you would need 48V. I usually recommend BBS02 25A to those who weigh more than 15st-16st.

 

[tommie]

yes, well put culy, as long as you dont let the motor bog down on the hills you`ll be ok, keep dropping down the gears,
also on the level i see me backing down the PAS so i feel some input to the pedals again.

 

[manneokoko]

Thanks trex for your explanation, Ive been searching for this info everywhere until now.

Two questions:

1: With BBS02 36V 500W, since it has more torque at lower rpm than the 48V version - would it be possible to use bicycles gearing to get the same speeds out of both version, with the only difference in them being the pedaling rpm?


2: If I get a BBS02 36V and limit current to 18A (with reprogramming software), would it give exactly the same effect as having a BBS01 350W?

 

[trex]

1) you get about 24mph with the 36V BBS02, 30mph with the 48V BBS02.
2) No. The BBS02 will always make your bike feel a bit more powerful.

 

[manneokoko]

1) you get about 24mph with the 36V BBS02, 30mph with the 48V BBS02.

Why? Shouldnt it be possible to get the same speed when using bigger chainwheel and smaller back gears? I mean, they both ouput the same Watt - the same power, then it should be possible to convert torque to speed with gears. No?

2) No. The BBS02 will always make your bike feel a bit more powerful.

Again, why? when reprogramming the BBS02 36V 500W to 18A, it has exactly the same specs as BBS01 350W ?

 

[Deleted member 4366]

You need about 1000w of output power to reach 30 mph on a MTB type bike. That means about 1300 w from your battery or about 30 amps at 36v. No gearing can change that. You can gear your bike to do 100 mph, but the only way to get that speed is if you chuck it off a cliff.

 

[manneokoko]

hmm.. 500W is 500W, the same power. The 48V version run at 18A, and the 36V at 25A. Both output the same power amp*volt=900W. The 48V with more speed, less torque - and the 36V with less speed more torque. Correct?
Then gearing should be able to change the torque to speed, or the other way around. Is my thinking flawed?

 

[trex]

the maximum speed is just an anecdotal thing, depending on the clothes you wear. I am pretty lightweight and wear just a T-shirt when cycling in Southend, so the same result may not apply to you. The track along Southend beach is not very long and perfectly flat, easy to cycle fast especially if the wind is with you. I have always noticed that 48V systems give higher top speed.

 

[Deleted member 4366]

hmm.. 500W is 500W, the same power. The 48V version run at 18A, and the 36V at 25A. Both output the same power amp*volt=900W. The 48V with more speed, less torque - and the 36V with less speed more torque. Correct?
Then gearing should be able to change the torque to speed, or the other way around. Is my thinking flawed?

That's correct. Don't worry too much about speed. The 900w is input power. output power will be around 600 - 700 watts, which is enough for about 25 mph. I doubt that you'd want to go any faster than that because:

1. You'll get noticed. The risk of getting caught would go up a lot with speed. Any normal person can see the unrealistic speed and acceleration of a bike with more than a 250w system.
2. Faster than 25 mph on a bicycle requires a lot of concentration, which wears you down after a bit. Bicycles can't handle it like motorbikes can.
3. You get too many near-miss accidents. Cars and other road vehicles don't expect a bicycle to go so fast. They pull out on you, cut you up and everything else - as you'll find out.

IMHO 20 -22 mph is a good maximum speed to aim at for a bicycle. Don't get me wrong. I'm not scared of speed. I normally hit 43 mph on my bike every time I use it. It's one thing doing a short burst for fun, but it becomes tedious and wears you down doing it for much longer.

 

[manneokoko]

Yes, I agree about the top speed. I had an ebike with Q100 hub motor and I found that about 24 mph was a good maximum speed, but 20-22 mph was my normal speed.

My concern is that everybody seem to recommend the 48V version of BBS02 500W. Im trying to figure out if it really is better and why?
Seems like the 36V should be better for speeds below 30 mph, but everybody recommends the 48V - some shops don't even have the 36V version.

 

[trex]

I can't see much of a point recommending the 48V version because the 500W 36V version is fast enough and has the same torque as the 750W 48V. Another point to recommend the 36V 500W version over the 750W 48V is about battery. 36V batteries are cheaper and easier to find.

 

[manneokoko]

I can't see much of a point recommending the 48V version because the 500W 36V version is fast enough and has the same torque as the 750W 48V. Another point to recommend the 36V 500W version over the 750W 48V is about battery. 36V batteries are cheaper and easier to find.

Is not that more torque than necessary? Seems like a waste to have that much power for a rider of 70kg not intending to travel that fast.

Thats why Im asking the questions, if its possible to convert a bit of that torque to speed with gearing and to remove some torque to save battery by reprogramming lower max current. Sounds like a good plan?

 

[Deleted member 4366]

Is not that more torque than necessary? Seems like a waste to have that much power for a rider of 70kg not intending to travel that fast.

In that case, it's probably better to get the 250w version and reprogram the current a bit higher. At least it would be legal, and with your weight at only 70 kg, the power would easily be adequate. The 48v version is only necessary for heavyweights like me or those that want an electric moped.

 

[manneokoko]

In that case, it's probably better to get the 250w version and reprogram the current a bit higher. At least it would be legal, and with your weight at only 70 kg, the power would easily be adequate. The 48v version is only necessary for heavyweights like me or those that want an electric moped.

Hence my question if it would be the same to get a BBS02 36V and lower the current to match the BBS01. I would like to have a bit more power than the 250W, since I want to travel as fast as 25 mph from time to time.

The BBS02 is not much more expensive and it seems more robust. Is there any downside of getting BBS02 and limit current, instead of getting BBS01 and upping current?

 

[Nealh]

Get the 250w as the 250/350 uses the same controller with settings set a bit different the main one being the amp setting. My reprogrammed 250/350w controller @16a does 24mph on a mtb with 2.25 knobblies's, max gearing is 44 x 12 higher gearing and road tyres would see a speed increase. The 250/350 is a capable bit of kit if sensibly programmed.

 

[culy30]

The 36v 500w has a bigger casing and (I'm guessing) the stator/rotor is heavier duty to facilitate the higher current of 25A as programmed at the factory. I have both the BBS01 250w and the BBS02 500w. I've reprogrammed both. The 500w motor is slightly heavier than the 250/350w motor. I can say that the BBS01 is a very capable unit, but if you are looking for speed over any other criteria, then you need more watts. (or pedal harder) Gearing is a factor, but there is no point in overgearing a 250w unit to get more speed, the motor just wont overcome the wind resistance. I'd go for gearing that allows you to a) climb the steepest hill you are likely to come across.............for me that's a 42t chainring and 34t biggest cassette sprocket. I then have a top gear of 42t chainring x11t smallest cassette sprocket. If I pedal at a comfortable 90rpm with my 700c x 35c wheels/tyres in top gear I can maintain a speed on level ground in still air of about 27mph using PAS 6-7. BUT that will restrict how far I can go. You could use the 46t standard chainring to get a higher top speed, but a 250w motor wont overcome the wind resistance like a 500w motor. The 500w motor given an identical situation will always be faster.

I tend to ride both motors in PAS 3-5. I recently did a 55 mile road ride over hilly roads on the BBS02 equipped bike and averaged just over 20mph, including riding through the middle of Gloucester and up some very steep hills. The battery voltage had dropped to about 34v after the 55miles. If I took my super light 7kilo road bike (no motor) on the same journey, I'd have averaged about 17.5 mph and I'd have been hot, sweaty and exhausted.

The 500w unit will you more in reserve..................and used sensibly its carried me over 80 miles on a single charge. Mine is reprogrammed to 16A max with 100% restrict speed, I just restrict current (progressively) in each PAS level.

 

[Rohloffboy]

Slightly of topic, but I noticed that you can get the BBS02 (36v) badged/marked as 250w although within the settings it can be configured as 250w, 350w or 500w.

Does this mean that the motor is UK street legal if set to 250w, or is it the case as I understand it, that because it obviously must contain a 500w motor, it would still in actual fact be illegal for street use.

I only ask, as I am on the cusp of ordering a Bafang 8fun mid drive, to enhance my Rohloff IGH equipped bike.

 

[culy30]

I'd suggest you read the legislation available on the Forums home page. My understanding to be legal is that the motor MUST be stamped no more than 48v and no more than 250w. Speed should be limited to 25kph (just over 15 mph). There is something to do with throttles as well.

I cant answer your BBS02 query, but by reprogramming you can achieve just about anything you want.................until the controller melts!

 

[Rohloffboy]

Yep, it seems the motors are marked/badged or stamped as you put it as 250w it could be worth me asking the seller to send an image, as they also mentioned that some of the exact same model motor are marked/badged 500w and you are to state when ordering that you require the 250w marked/badged model.