Should I go for the bafang 250W front hub?

[kaltsoplyn]

Hello all,

another newbie for electrocution. Gathered a bunch of questions to ask, so I'd better get down to it, or it's going to take forever. It's going to be a long post, but I want it to be detailed so that the answers will have more chances of, well, actually addressing the questions. Things tend to go astray easily in a forum...

I live in Iraklion (Crete, Greece, y'know, kinda like Europe), which although smallish as a city, it seems to introduce random numbers of hills to my A to B commute, regardless of which actual locations points A and B stand for. Regardless. There's always a hill in between. Fed up!

So I want to electrify my bike. I considered the mid-drive, rear hub and front hub options and I seem to be leaning towards the front hub for a number of reasons. I know that it is probably the worst of options as far as performance and handling of the bike is concerned, but it's simple, easily reversible, improves weight distribution of an upright bike, it's internal gear hub compatible and, in my opinion, the most elegant solution.

What I require of my electrified bike:
- To still be a bicycle. This means a total weight < 20kg. I 'll build on a ~13kg bike so the whole kit should be on the order of 5-6 kg with a max of, say, 7kg.
- the motor should help me climb up hills and nothing more. I 'll still pedal on the hill, but I want it to feel more or less like a flat. And I always pedal on the flats (and lazily coast downhill).
- For my daily needs I can do with just a 10km range. This should hopefully bring down the capacity of the battery.
- No billion euro battery.

So, up to this moment I have come up with the following setup:
- a bafang 250W front hub motor from electrorad.de (Frank Scheftlein)
- electrorad controllers seem too pricey so I opt for the e-crazyman controller and thumb throttle
- custom machined torque arms.

My questions follow...

 

[kaltsoplyn]

My questions:

a) is the motor+torque arm a safe combination on a vintage road fork or should I go for something beefier?

b) are the e-crazyman controllers and throttle compatible with the motor? The bafang is sensorless so I need the sensorless controller, right? Are these controllers of the type where you have to start pedaling for it to kick in? Can the 36V controller be reprogrammed for 48V?

c) The electrorad site states for the motor that it's 250W / 36V. Is there a 250W / 24V bafang motor or a 250W / 48V? Or is it the same motor outputing, say, 150 to 350W when powered with 24 to 48V?

d) will this motor fulfill my requirements? My rough calculations show that going up a 20% hill slowly (say ~3m/s), would take something like 600W. Which means that the 250W motor would make the hill feel like a 10% (for the same speed), which is still not quite flat. Is the motor too gutless? should I opt for more W? Which revives the previous question: can I run this motor at 48V and squeeze some tens of extra watts out of it? Or maybe just increase the amps to boost the torque? Is there some other - trustworthy - motor as light as this one?

e) and finally the batteries: I think I only need 5 - 10Ah. I can't spend 400 euros on high quality nor want to spend 100 euros on questionable LiFePO4. I will if necessary, but what do you think of NiMH battery packs (drill batteries or generic packs of C or D size cells)? How many amps can they normally provide safely?

Oh my God, that's bloody huge! I hope someone can endure the reading and help me out. Feel free to answer any portion of any question. I'll be doing the patchwork in the end.

Thanks.

 

[flecc]

The 250 watt rating is a legal nicety, not a measure of actual power. Typically 250 watt rated motors have maximum power of about 400 watts available from about half to maximum speed with maximum torque at about half maximum speed or a little over.

Therefore an EU legal hub motor bike with it's maximum assisted speed of 25 kph will typically have the coincidence of maximum power and torque for optimum hill climbing at about 13 to 16 kph. Therefore, adding pedalling to keep to around that speed area gives the best climb performance. Climbing at lower speeds still benefits from maximum torque but the available power reduces rapidly as speed declines.

The production of suitable high discharge NiMh D size cells suitable for e-bikes went into decline as lithium took over and satisfactory cells are difficult to obtain and expensive. It can be better to use C cells in parallel as well as series formations, since these are still available in the fairly high discharge ratings that our motors need.

I can't help on controllers since I'm not familiar with sensorless Suzhou Bafang motors. My one is their most powerful 250 watt rated sensor one with a maximum net power of 576 watts on 36 volts (720 watts gross). I still have to work fairly hard on a 20% hill and I weigh less than 70 kilos, my bike some 26 kilos, though I can climb 12% easily on motor only.
.

 

[john]

My questions:

a) is the motor+torque arm a safe combination on a vintage road fork or should I go for something beefier?

If the fork is steel then this should be ok. The important thing is that the nuts seat correctly and are tight.

b) are the e-crazyman controllers and throttle compatible with the motor? The bafang is sensorless so I need the sensorless controller, right? Are these controllers of the type where you have to start pedaling for it to kick in? Can the 36V controller be reprogrammed for 48V?

e-crazyman produces different controllers including sensorless ones. Make sure it is an immediate start type as you cannot spin the motor by pedalling.

c) The electrorad site states for the motor that it's 250W / 36V. Is there a 250W / 24V bafang motor or a 250W / 48V? Or is it the same motor outputing, say, 150 to 350W when powered with 24 to 48V?

Bafang make a number of motors, I'm not sure if any are rated for 48V though. At that voltage you need to take care not to strip the gears.

d) will this motor fulfill my requirements? My rough calculations show that going up a 20% hill slowly (say ~3m/s), would take something like 600W. Which means that the 250W motor would make the hill feel like a 10% (for the same speed), which is still not quite flat. Is the motor too gutless? should I opt for more W? Which revives the previous question: can I run this motor at 48V and squeeze some tens of extra watts out of it? Or maybe just increase the amps to boost the torque? Is there some other - trustworthy - motor as light as this one?

I think that Bafang is a good choice. The current to the motor is mostly down to the controller current limit. You probably want at least 15-20A continuous. To get more performance you would have to go for a motor with significantly more weight like a Puma.

e) and finally the batteries: I think I only need 5 - 10Ah. I can't spend 400 euros on high quality nor want to spend 100 euros on questionable LiFePO4. I will if necessary, but what do you think of NiMH battery packs (drill batteries or generic packs of C or D size cells)? How many amps can they normally provide safely?

Have you had a look at Ping batteries? Just about the best value in terms of cost per mile.

 

[kaltsoplyn]

wow!

Wow, great answers people. Thank you. Really.

It can be better to use C cells in parallel as well as series formations

The thing is: can I use a single series of C cells? Can they handle the amps? We 're talking about a >1C discharge rate for 9Ah C cells. And it's already 30 cells to get to 36V, so it would take another 30 for a parallel series which would, in turn, double the weight of the battery to more than 5kg!

I weigh less than 70 kilos.

I *SHOULD* weigh that much, but I weigh closer to 80kg. And now, with the power assist and all, well, I don't know man!

Have you had a look at Ping batteries?

Yeah sure, he's a kind of powerhero around pedelecs I think, huh? Anyway his nicest batteries are still at about 250 euros (is a charger included?), whereas I can build my own NiMH for less than half. Maybe. Also I like the simplicity of NiMH: you wire them up and, voila, they work. The LiFePO4 BMS scares me, the circuit quality usually seems dubious and I'm too bored to figure out how to DIM (Do It Myself) and I feel it's just another hi-tech electronic disaster waiting to happen. Well, maybe not quite so, but something like that. Besides, next year these batteries will be half the price... hopefully.

 

[daniel.weck]

Hello !

I'm using a Suzhou Bafang (8-Fun) SWXK front hub motor, 36V 250W 255RPM (model designed for 20" wheels). I bought it from Germany Das Elektrorad von Frank Scheftlein: Komplette Pedelec- / Elektrofahrrad Umbausätze und Ersatzteile von Bafang, Puma (eZee), Tongxin u.a. (Frank now lives in China but still operates his business). It came as a kit with controller (6-MOFSET e-Crazyman), throttle and Pedal Assist Sensor. I bought a 36V 10Ah LiFePo4 battery from Li Ping.

I really love this setup, it is delivering in terms of reliability (so far), flexibility (3-speed controller, throttle+low-cadence versus PAS+high-cadence), and raw hill-climbing torque. I like to pedal though, so let's be clear: it's not powerful enough for a throttle-only moped application. Otherwise as a cyclist you will be very happy with the 8-Fun.

Most of the time I use the battery just over 1C discharge rate, so my peak consumption is 10-12A (approximately 400W taking into account the voltage sag). I'm sure that the controller can easily get to 15-20A, but for anything higher I would need to swap for a controller with more MOSFETs. I'm sure that the battery would handle a higher peak current draw fine, maybe 2C or even 3C. However I have not tested this myself. The advantage of LiFePo4 is longevity / battery life, and I'm sure that with my typical low-power usage I will enjoy many charge cycles over the next few years. The motor is known to be strong when "over-clocked" to 48V, but then of course reliability issues may ensue due to the nylon gears (one of which can be swapped for a steel gear, if required). The controller would need to be upgraded to a 48V one though.

There is more information on these pages:

http://www.pedelecs.co.uk/forum/electric-bicycles/4682-diy-stage-1-received-bafang-tongxin-kits-photos.html#post59183

I invite you to use the search function of this forum, which is quite good.

All the best, and good luck with your e-bike project !
++
Dan

 

[flecc]

The thing is: can I use a single series of C cells? Can they handle the amps? We 're talking about a >1C discharge rate for 9Ah C cells. And it's already 30 cells to get to 36V, so it would take another 30 for a parallel series which would, in turn, double the weight of the battery to more than 5kg!

9 Ah C size NiMh cells? Afraid not, about 5 Ah is the limit and high discharge types are usually 4 to 4.5 Ah. It's D cells that are commonly 9 Ah, and the currently available ones of that capacity have such poor discharge rates that e-bike manufacturers like eZee and Powacycle refuse to use them any more.

Besides, next year these batteries will be half the price... hopefully.

........... ..............

There's two ways in which the prices will reduce. The smallest is by technical advances in manufacturing procedures and that's a slow process.

The largest is when we get out of our present UK economic mess and the world's currency traders let us have more favourable exchange rates again. With a trillion pounds national debt that's far off.
.

 

[fishingpaul]

I would ask ecrazyman the maximum continous amp output of the controller you are looking at,i have a 350 watt ecrazyman brushless 36v 25 amp controller,and it does not deliver enough continous amps about 15 i am told making it slow and gutless on hills,i replaced mine with an infineon 30 amp controller the difference is amazing.

 

[kaltsoplyn]

More coherent answers! never saw that coming!

Oh boy, oh boy! more great, COHERENT answers. This has to be the best forum I've ever been to. E-bikers rock!

@daniel.weck: That's my setup you got there mister! bring it back immediately.

flexibility (3-speed controller, throttle+low-cadence versus PAS+high-cadence)

So, what's your opinion: 3-speed controller or throttle? The PAS seems like more clutter than good. I think I'll pass.

I invite you to use the search function of this forum, which is quite good.

Hehe, thanks for the subtle tip. I will.

9 Ah C size NiMh cells? Afraid not, about 5 Ah is the limit and high discharge types are usually 4 to 4.5 Ah.

So this guy is probably lying.

The largest is when we get out of our present UK economic mess and the world's currency traders let us have more favourable exchange rates again. With a trillion pounds national debt that's far off.

Now that's interesting. It's been a couple of months now that all media in Greece is trying to persuade people we are going bankrupt and the exchange rates we are getting are out of this planet and that it's my personal obligation to work 24/7 to pay the debt. Me. Now. Forever. All other economies, including yours, are presented as in peachy condition. It's the same over there, eh? Makes me wonder (about things I already knew)...

 

[jerrysimon]

So this guy is probably lying.

That listing does not detail what the discharge rate is, but given the cost I doubt it is high.

These are the type of NiMh cells that I think Flec is talking about.

12v NiMH 4600mAh Rechargeable Battery Vapextech on eBay (end time 03-Jan-10 13:32:25 GMT)

Note 30amp discharge rate.

Regards

Jerry

 

[flecc]

So this guy is probably lying.

For your purposes, effectively yes, that size might only be rated as 9 Ah at a miniscule discharge rate. There's a direct connection between capacity and discharge rates. For example, that latest 10 Ah hour battery used on the more powerful eZee bikes produce under 7 Ah when used to to the full in hilly territory, the 10 Ah is only available in optimum flat conditions at low discharge rates. This is true of all batteries, but I choose this one because A to B magazine have tested this one in practice.

In the unlikely event that these C cells have a 9 Ah possibility at a very low discharge rate, they won't be able to deliver anywhere near the currents an e-bike needs due to the very high cell density.
.

 

[kaltsoplyn]

In the unlikely event that these C cells have a 9 Ah possibility at a very low discharge rate, they won't be able to deliver anywhere near the currents an e-bike needs due to the very high cell density.
.

Yes, I figured that much.
I was thinking that the 9Ah rating must have been measured at 0.01C or so
I'd still be ok with a 5Ah capacity @ 10A discharge, but the problem is that 10A coming out of these batteries is something that's probably never going to happen.

 

[jkirkebo]

For example, that latest 10 Ah hour battery used on the more powerful eZee bikes produce under 7 Ah when used to to the full in hilly territory, the 10 Ah is only available in optimum flat conditions at low discharge rates.

I don't quite agree with that, I usually get about 9Ah from my Ezee LiPo. Some hills, mostly full throttle. Typical discharge on the flat is ~400 watts, which is about 10A (I have a 12Ah 7.2v NiMh booster pack).

 

[flecc]

I don't quite agree with that, I usually get about 9Ah from my Ezee LiPo. Some hills, mostly full throttle. Typical discharge on the flat is ~400 watts, which is about 10A (I have a 12Ah 7.2v NiMh booster pack).

I think the difference is probably in the conditions. I'm in a very hilly area where there's only up or down and A to B's testing was in several different conditions to specifically give the full range of discharges. Neither of us use a booster pack and we are both using the same top power Bafang motor on full throttle continuously for the highest discharge rate tests.
.