Bafang Bpm, how many RPM?

[d8veh]

The most important thing is to match the motor to your normal speed that you expect to be going. It can make a significant difference to your range if you have a mismatch. When a 393rpm motor is laboring up a steep hill at 200 rpm, efficiency could be as low as 60% compared with the maximum of 78%, while as a 201rpm motor would be achieving the 78%, but you only get half the top speed.

You do get half speed with slow wind, but DO NOT get 60% efficiency with fast one while the slow is doing 78. The difference can be couple per cent, not more. I go as far as assuming you get even more losses in the controller/wiring than the difference in motor efficiency, if you decide to use same voltages on both systems. Simply because you need to half the voltage and double the current with the fast motor, while just passing all the voltage to the motor with the slow one.

Have a look at the Ebikes.ca simulator. Choose the Ezee motor as the nearest equivalent. Top speed at 36v is 30kph with efficiency of 78%. On a 10% incline, it slows to 15kph with an efficiency of 64%. That means that your wasting 18% more.

[miuan]

Have a look at the Ebikes.ca simulator. Choose the Ezee motor as the nearest equivalent. Top speed at 36v is 30kph with efficiency of 78%. On a 10% incline, it slows to 15kph with an efficiency of 64%. That means that your wasting 18% more.

You are wasting 18% more efficiency on the uphills because you require MORE power at LOWER rpm!
If you ask the same power of a slower motor at the SAME speed up the same hill, you will still bog it down in a similar way.
If you are more interested in this topic, check out my recent thread, especially what Alan B posted.
When using the simulator, choose BPM500W, it's a 10 turn wind afaik.
viewtopic.php?f=2&t=35359

[casainho]

I just bought from BMSBattery the Bafang 48V500W BPM Front Driving Hub Motor 393 RPM. While I live on a relative flat place and the 393 RPM should do 47km/h at maximum and maximum Efficiency is on that velocity, I guess. But I will not be able to run always at 47km/h!! There are places, even if flat, I will need to go at 20km/h or even less due to obstacles. My question is: if I put the throttle at 50%, the RPM should be 393/2, right? so the velocity will be 23.5km/h and the Efficiency of the motor will be the maximum at that velocity?

I am using right now a Cute-85 250W 24V motor for 16'' but installed on a 26'' wheel (see my post here). I will change for the Bafang 48V500W BPM 393 RPM soon as it arrives:


Example of my riding (pictures from my Android My Tracks software):

[miuan]

Yes that's right. Efficiency is always good if you don't load the motor too much. So on flat road, it should always be about 77-82% depending on speed. It only drops when you want more power (acceleration, ascents).

[d8veh]

Nice bike. I think you'll find that the BPM motor will make your journey a lot more enjoyable. Let us know how you get on.

[casainho]

I just got my motor and all other components (6 days delay on portuguese costums. I am blogging here, with more pictures.

Since the motor manual says it is IP54, do you guys think it can handle rain? is it safe to use it on rainy days?

IP54:
Dust protected: Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment; complete protection against contact
Splashing water: Water splashing against the enclosure from any direction shall have no harmful effect.

Battery Charger not working

The first time I connected the battery charger to my house power mains, all the power went black/off!! I tested again and I got the same result. I started to inspect the 230V fuse on the charger and it was perfectly. Then I did open the charger to see if I could visually see anything wrong. I did suspect of earth connection and I went to compare this charger with the other I have working. Turns out that the earth connection were soldered on wrong place - I just soldered it on correct place and now the charger is working and charging the battery

I must say I have electronics knowledge and I have a small company of electronics. I am sad to know that BMSBattery ship not tested components. But I must say I am happy with their products and they even resolved some issues (like refund money from costums because they did a mistake and sent me the package by DHL instead of EUEXP), they take no more than 24h to answer by e-mail. This is my 3rd electric system that I bought from them and I am an happy costumer.

[d8veh]

The BPM motor is not completely waterproof. Water can get in the hole where the wire comes out. Make sure that the wire goes downwards from the motor and then back up again. This stops the water running down the wire into the motor. Also, you can put some sealant there after installation. You might want to put some sealant on the disc brake screws as well.
Faulty wiring is common on this Chinese stuff - best to always check it. Also check that the sequence on each side of your, throttle and pedal sensor connectors is correct (colours).

[casainho]

The BPM motor is not completely waterproof. Water can get in the hole where the wire comes out. Make sure that the wire goes downwards from the motor and then back up again. This stops the water running down the wire into the motor.

Good idea Thanks.

Faulty wiring is common on this Chinese stuff - best to always check it. Also check that the sequence on each side of your, throttle and pedal sensor connectors is correct (colours).

I am sure it is a person who solder the wires. I understand why the mistakes, since the factories seems to do slavery "labor".

Bafang 48V500W BPM Front Driving Hub Motor spokes

My mechanic is having a lot of difficult to lace the spokes (on 26'' wheel) because he can't find spokes of 220mm length (he thinks that 220mm is the correct size). Also the motor touches on the brake (from the disk brake) and seems that the solution is to go from the 160mm to 180mm diameter disk brake and put the brake far 10mm from the center. Resuming: find first the correct size of spokes and buy them from BMSBattery or buy the full wheel. Also this motor is larger than the others I used so please verify in your bicycle using the mechanical drawing of this Bafang motors.

[d8veh]

I bought my spokes and rim from BMSBattery. The spokes are 210mm from the middle of the bend to the end . The rim is 530mm from the inside of the rim from one side to the other. I bought two sets and have already built one wheel with these parts so I no that they are exactly right. I used a cross 2 spoke pattern.

Some brake callipers are thinner than others. There was a thread about this about 2 months ago. You need at least 180mm disk. If your caliper mounts on a carrier, you can thin down the carrier a bit by filing or milling to bring the disk a bit closer to the frame.

When you have the disk in the right position and your wheel installed, the rim probably won't be central, so you need to give it back to your wheel-builder to dish the wheel: That means move the rim away from the centre of the hub but central to the frame. The hub-motor is not symmetrical.

[casainho]

I bought my spokes and rim from BMSBattery. The spokes are 210mm from the middle of the bend to the end . The rim is 530mm from the inside of the rim from one side to the other. I bought two sets and have already built one wheel with these parts so I no that they are exactly right. I used a cross 2 spoke pattern.

Thanks. Right now my mechanic found the spokes he needed (I guess 220mm) and laced the motor. He says he used 3.5mm diameter spokes while the originals from the bicycle were about 2mm diameter... so, it's now more a electric motorcycle than a bicycle

Some brake callipers are thinner than others. There was a thread about this about 2 months ago. You need at least 180mm disk. If your caliper mounts on a carrier, you can thin down the carrier a bit by filing or milling to bring the disk a bit closer to the frame.

Thank you, I will pass this information to the mechanic.

When you have the disk in the right position and your wheel installed, the rim probably won't be central, so you need to give it back to your wheel-builder to dish the wheel: That means move the rim away from the centre of the hub but central to the frame. The hub-motor is not symmetrical.

He told me that he did this already when laced. I didn't saw yet the result, will see tomorrow morning.

[casainho]

PUTA MADRE, I almost killed myself!!

I went to make a quick test drive after my mechanic got the motor laced and the brake disk ready. The first thing I verified was that the wheel skidded (and I weight near 100kg). I drove for 60 meters and my mechanic told me after that I went for more than 50km/h, that I were quicker than a motorbike!! He told me that he were afraid.

At the end of the 60 meters I braked and turned back, were I decided to pull the throttle to full and again the wheel skidded and I quick decided to make a small raise the wheel so it could run at full speed and than skid even more when touching in the road, BUT, when the wheel touch the road it instead broke the fork!!! I took a fall, and I am ok but I could be dead for now if this happened when I got high speeds.







So, I would like to know in what kind of bicycle are people using this motor...... can you please share some pictures? Are there some special forks to handle all this power??

My mechanic told me that he was afraid because the motor is heavy and large... we think that the wheel got movement and with all his weight and being large it can't be quick stopped... that is what happened when I did the small raise and when it touched on the road.

right now I am really afraid to use again this motor and bicycle. I don't even know if I trust on the 250W motor and this bicycle, since I got top speeds of 40km/h.

Any suggestions/help for a cyclist that is now afraid to use electric bicycle at higher speeds than 25km/h and with a motor more powerful than 250W? thank you.

[cwah]

You need 2 good torque arms on the bike fork. Otherwise the forkend may not be able to handle that power and just crack as it did.

[casainho]

You need 2 good torque arms on the bike fork. Otherwise the forkend may not be able to handle that power and just crack as it did.

Thank you!! Do you know if I can find it on some online shop? or will I need to do them for myself? -- I wish I can buy it on BMSBattery or something like.

[cwah]

The ones from doc seem quite strong (but not very pretty):
http://endless-sphere.com/forums/viewtopic.php?f=31&t=29129

[rojitor]

For front kits two torque arms is a must and c washers are very important as well.

[casainho]

For front kits two torque arms is a must and c washers are very important as well.

Now I remember to see some "special" washers that came with the Bafang motor, it they are the C washers.

I can't find a site/shop with clear information for arm torques to ALU front forks/fron hub motor......

[rojitor]

Try here meu amigo http://www.crystalyte-europe.com/home.php?cat=299 or maybe even here because they are partners http://www.greentarget.pt/

[cwah]

What's the difference between torque arm and C washer? They look very similar to me.

[rojitor]

I guess you see a similar shape with doc's torque arms cwah, they are nothing alike though, a c washer weighs like 2 grames and is smaller than your thumbnail,like 1/10 size of the axle nut, it is designed to make the perfect pressure on the dropouts.

[cwah]

Ok, it's like the standard washer I already have on my motor axle. Thanks.

[casainho]

Seems to me that C washer handle the motor torque and spreeds it on the axle. This C washer fits the motor to avoid it rotating and damage the axle, but sure, it may not be enought, I wil go also with the arm torque.

[rojitor]

c washer


torque arm


check this thread out : http://endless-sphere.com/forums/viewtopic.php?f=3&t=31521 it is a very good example.
If you use front kits you will break eventually the dropouts.... but they will last long if you use double torque arms and c washers.

[casainho]

rojitor, thank you for all that info!!

And I am sharing now a picture of the washers BMSBattery sent me. I must say that I didn't know about this and so I didn't told to my mechanic. He didn't used the washers in a correct way, I guess. Anyway, just the washers aren't enough, I guess.



Rear Driving more safe than Front Driving hub motor?

With the little time I had in my hands the Bafang BPM 500W front wheel hub motor, before it shot out and broke the fork drop outs, I verified the front wheel did skidded a lot!! I think that will be a problem when making a turn, if the front wheel loses traction. Also if the fork/drop outs brake and the wheel shot out, I think I will jump front the bicycle and probably be dead.
1. Isn't safer to put the motor/wheel with traction on rear wheel?? -- I am now thinking in use the Rear Driving Bafang BPM motor.

2. Does anyone knows if the 350W version is really 350W or if 350W is just the peak wattage and the normal wattage is 250W? -- I am afraid to use the 500W version, it seems to have much more power than what I need and so it is dangerous...

Thank you for all the help.

[Scottyf]

A front wheeled setup with a high powered gear motor is just asking for trouble as you've found out.
You need good solid torque arm's to avoid those problems.

The rear ones are usually stronger as standard on most bikes.

Sorry to see you broke it but you really needed torque arm's on this kind of setup.

The only time you don't need them is on little 250w front setups that don't kick out more than 400watt. An even then its best to have them just in case.

[rojitor]

. Isn't safer to put the motor/wheel with traction on rear wheel?? -- I am now thinking in use the Rear Driving
Bafang BPM motor.

Indeed, rear motor is safer, one or two torque arms recommended,and those washers of yours are a good idea
I use this on the rear motor and two torque arms.