Bafang BPM Motor

[NRG]

OK that seems reasonable, I'll have to get one of these motors and try it on my Peugeot.

 

[Scottyf]

Sounds reasonable. Thats why I emailed Alien bikes to ask about the controller and battery as really there isn't much difference in the spec other than the 18amp controller and BPM motor.

Either way its a better motor with more potential so its worth the £150 notes for that. If it works as i've spec'd it, I'll either sell my old controller and motor for a super knocked down price at about £50 with controller or use it in the girlfriends bike...

Either way Win Win.

 

[jbond]

Of course there's some other trade offs. The BPM is heavier (1.5Kg), has more copper and a larger diameter. I think this is where the greater torque for a given current comes from.

Ironic that while you're thinking of swapping to a BPM, I'm thinking of using a QWSX motor for the next build, but over-driving it. Using a small rim wind in a big rim to get the speed of the BPM and 36v25A in the controller to get back some of the torque. For me it's all about the weight. I've rejected 48v20A because of the effect on battery weight. If I can work it out, I also want to implement an "Economy" mode of something like 36v5A to encourage more pedal effort while still having the full power available for the big hills.

 

[Deleted member 4366]

If I can work it out, I also want to implement an "Economy" mode of something like 36v5A to encourage more pedal effort while still having the full power available for the big hills.

I think of few of us have had this idea: However, none of the cheap (sorry, good value) controllers seem to have this function. Let us know if you can figure out a good value way of doing it

 

[jbond]

If you have a CA already (not cheap) then this capability is already baked in with a small external link to the throttle. Of course I want to take this a stage further which requires a bit more circuitry. My ideal is to combine the Pedelec PAS, throttle and CA into one input that goes into the controller throttle input. Throttle over-rides everything, PAS is 5A limited (switchable).

To avoid the CA expense there's a couple of circuits out there for duplicating the current limiting function on it's own. eg
The Recumbent Bicycle and Human Powered Vehicle Information Center

The trouble is, my electronics is good enough to turn a circuit into a veroboard build, but not good enough to design the circuit in the first place. And combining the voltages is going to take more than just a diode matrix due to the voltage drops across the diodes. It really needs a little op amp circuit to take all the inputs and produce the output to the controller.

 

[NRG]

The ecrazyman 6fet controllers can be set for a minimum of 7amp battery current that would work well as an economy controller. Downside is you can't change it on the fly.



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[jayuk]

I have the infineon controller with my kit & i may look into limiting the speed to 25mph, average speed over 150 miles hss been 18mph. To be honest once you try the bpm motor you wont go back to anything less, its great fun riding a bike again after 20 odd years

Jay

 

[jbond]

The ecrazyman 6fet controllers can be set for a minimum of 7amp battery current that would work well as an economy controller. Downside is you can't change it on the fly.

That's the catch. The trick here is to have economy mode as the default with no thought required. And then have an easy over-ride for when you need it. Hence using the pedelec as a low power cruise control that requires no thought at all. Pedal and get some assist, freewheel and the assist turns off. But then to always have the throttle as an over-ride for extra bursts of full power. So when you hit the big hill drop to a lower gear and slow down, if you decide it's too much effort or too slow, you can just wind in some throttle. When you reach the top of the hill just let go off the throttle and go back to cruising on the pedals.

Like this there's no need for mode controls or pedelec-throttle switches. And the low power assist from the PAS should reduce the jerkiness when the PAS cuts in. Since we're over-riding the PAS voltage with a current limiter circuit, it shouldn't be too hard to introduce a soft-start ramp into this as well.

 

[Scottyf]

I have the infineon controller with my kit & i may look into limiting the speed to 25mph,

Indeed but your also running the BPM at 48v - 500w with probably a top speed of 30mph..

I've opted for a 700c wheel with a load speed of around 22mph (26mph no load speed) so I would imagine I'll loose some effciency and torque while chewing up more amp's.

Even if it meant I cut my range down to half the current motor / controller battery easily copes with a 18 mile a day round trip to work.

But I can easily charge at work if need be.

The safest discharge of the panasonic cells in the my current battery are 2c I believe so the max watt I can ever get will be 648w. Still i'm hoping for more of a continous use of 400w mark instead of the average of 230w I am currently getting.

I take it if you draw more than the rated max discharge is gets rather hot, may set on fire and generally destroy the number of cycles you can achieve.

 

[Scottyf]

Oh and if you I did just want speed I could have opted to over volt the motor.
But since the battery is new its cheaper to have a spare Motor / wheel / controller than replace a battery or add a battery in series.

 

[NRG]

Decided not bother with the BPM, I'll stick to the standard 250W motor...it climbs well (especially with my tweaked controller and a few extra volts) plus is lighter as JB points out.

 

[Scottyf]

What Volt / Amp are you putting through it?

 

[NRG]

I've set 16.5amp for the battery current but it's pulling 20amp measured and the phase is set for 38amp. All this at 44.4v. I've upgraded the capacitors and FETs so its capable of running 48v or more if necessary.