BMSBATTERY kit

jbond

Esteemed Pedelecer
Jul 29, 2010
411
2
Ware, Herts
www.voidstar.com
What would/does it take to make RC style Lipo or Lifepo batteries as user friendly as the typical e-bike specific battery? It feels like we need a source of an E-Bike BMS with suitable connectors and programming to "just work". Along with a moderately intelligent charger. It ought to be possible to put together either a 36v5AHr or 36v10AHr pack where you really don't need to know about over-under charge or cell balancing. That should be automatically safe and handled for you. Perhaps what I'm asking for here is for somebody like Ping to make up packs c/w BMS and charger but using whatever cells it is that Turnigy use instead of LiFePo pouches. Business opportunity?

It sounds to me like your setup is very similar to the Alien Aurora. Although it's a front motor and sensored, it's the same code and the Aurora controller is also marked as 9A rated, 18A peak. Your top speed and hill climbing ability matches the Aurora.

Given that your batteries have a much higher C rating. (20C vs 2C ish), it should be possible to use a controller with a much higher current rating. This won't get you more top speed but it might give you even more hill climbing ability. I get the feeling the BPM motor is capable of much more than it's rated 350W for short periods. But then perhaps allowing it to draw 1kW will just mean stripped gears. :(
 

NRG

Esteemed Pedelecer
Oct 6, 2009
2,592
10
My Peugeot SWXB pulls 1KW on a regular basis ;)

For Lipo BMS I think Gary @ Tppacks.com has a neat solution but its not a really a plug-in-and-go solution, some DIY expertise is still required:

Products
 

jbond

Esteemed Pedelecer
Jul 29, 2010
411
2
Ware, Herts
www.voidstar.com
FWIW, I just put the cycle computer on the rear wheel and ran it up to max no load speed. It showed 23.5mph. Which compares with a max speed on the flat of about 20-21 mph. The circumference is set to 2045mm which seems to be GPS accurate with a 26"-1.75" MP tour tyre.

23.5mph = 37.819584 kmph
= 0.6303264 kilometers per minute
= 630326.4 mm per minute
630326.4/2045 = 308 rpm

This page on ES Endless-sphere.com • View topic - Bafang BPM Pics and Specs - Large 3.9Kg Sensorless Geared has a reference for the BPM motor. Code 11 (which we've both got) shows a no load rpm of 285 rpm +-10% So 308 rpm is at the high end of that. It was driven by a freshly charged Alien 36v10AHr lipo battery showing 41.5v A real 36v should give 308*36/41.5 = 267rpm. So both 267 and 308 are within tolerance.

On various other threads we'd been talking about the drag on these and similar geared hub motors. I've got a hybrid with the same Shimano 7 speed megarange cluster. I ran them both up to 30mph. The BPM ground to a halt in about 20s. The hybrid wheel was still spinning well after 1 minute. I'm wondering exactly where this drag comes from and if there's anything that can be done about it. The free wheel cluster on both bikes has been oiled and is pretty silent The unpowered wheel has just a pair of correctly set ball bearings. By comparison, the BPM has got really quite a lot of sealed bearings as well as the planetary gear cluster and internal freewheel. Quite apart from the hassle of taking it apart, I don't imagine there's much that can be done to free up the bearings and seals or do much with the nylon gears.

It would be interesting to compare the drag from all the different geared hubs. And I do wish there was a way of using them where the remaining motor drag could be avoided when the motor is off. But that leads to mid mounting and another big can of worms. ;)

ps. on this page http://www.pedelecs.co.uk/forum/electric-bicycles/6775-supplier-8fun-bafang-bpm-hillclimber-kit-4.html?highlight=Cute-100SX Mechaniker quotes Bafang's rpm/sizes. "175rpm is for 28",195rpm is for 26", 220rpm is for 24",255rpm is for 20", 275rpm is for 18" and around 320 is for 16"." Presumably the 26(11) 36v350w BPM is the 195rpm version. So more confusion. We have 195rpm roughly corresponding to the 25kmph EU limit. but the motor actually has a no-load rpm of more like 300 with a nominally 36v battery. And none of Mechaniker's numbers match the no-load rpm on the ES page. Hey ho.
 
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NRG

Esteemed Pedelecer
Oct 6, 2009
2,592
10
Voltage can make quite a difference to the RPM, I'm using the 195rpm 26" motor in a 700c wheel, unloaded max. speed is about 24mph. Yes the drag is very real as I mentioned before, I find it very noticeable when compared to a normal wheel on the road. However, it seems to vary from same type motor to the next which is a bit weird, some motors OK others a real......drag :)
 
D

Deleted member 4366

Guest
NRG, I think you're right about voltage. Assuming that 285 rpm is for 36v, 41v from a freshly charged set of batteries should give 285x41/36 = 324.5rpm without load, which is approx. 25mph.
Woops! Sorry, Jbond. I didn't see that you had already done that calculation but the other way round.
 
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