Bafang 393RPM Hill Capability

johnamon

johnamon

10 W
Joined
Jun 20, 2011
Messages
68
Location
Aberdeen, Scotland
Hi all,

I am a complete noob - and in following this great tradition have ordered my first DIY e-bike kit after a week of reading the forums! I have ordered a Bafang 36V 350W Code 8 motor that provides approximately 393 no load rpm..

On my commute to my new workplace next month I expect to encounter 10° hills - max 690km per hill circa 10m elevation rise. When the map shows up, clicking on the blue line brings up distance / elevation details.

Could someone with a little experience please let me know whether or not I will make it up the hill shown with my high-speed motor?! I intend to assist the motor but I am certainly no ulrta-fit cyclist!

Thank you all!
 
Welcome to ES johnamon,

I can't give you any viable info in regards to your "hill climbing" question (I only use my Bafang style 400w gearded hub motor on mild and relatively level paths and trails).

However, I'm wondering what kind of ambient tempuratures you'll be using your Bafang kit in? I ask this because hub motor "heat buildup" will, imo, be one of your most important concerns.
 
Here are the two bicycle power calculators I like to use:
http://www.kreuzotter.de/english/espeed.htm
http://www.mne.psu.edu/lamancusa/ProdDiss/Bicycle/bikecalc1.htm

I wouldn't expect the Bafang to contribute more than 500W at 75% of its no-load speed. You should expect diminishing (maximum) power from the motor as speeds decline below 50% of its no-load speed.

How fast can you pedal up these hills unassited?
 
Thank you for the welcome.

The BPM's no load speed is 393rpm therefore:

26"(.660m) * 3.14* 393 = 814m/m
(814 * 60) / 1000 = 48km/hr

No Load Speed = 48km/hr

I would expect to just about pedal up the hill I linked to above at 12km/hr on my mountain bike; with a good run-up and the wind behind me!! I'm not a pro cyclist yet....

I would however have power assist to get me up to speed (20km/hr - pedal assisting all the way) at the base of the hill so the power applied early would help maintain speed within the motor's torque range.

Ambient temperatures probably aren't a problem extreme Summer = 25°C (77°F) Extreme Winter = -5°C (-41°F).

Lots of people are happy with their Code 10 motors, and they are supposed to only have 20% more torque. It's a shame that there aren't detailed specs on the motor's power curves for all the different versions that are built. It's very difficult to imagine the effects of the winding and torque variations.

Thanks!

John
 
johnamon said:
Ambient temperatures probably aren't a problem extreme Summer = 25°C (77°F) Extreme Winter = -5°C (-41°F).
Click to expand...


Ok, I'm thinking that you probably won't have too much trouble with overheating your hub motor. However, you may have some battery performance issues at lower temps if, you ride in weather that cold (I sure don't). Having said this, can you tell us about what type of battery that you're thinking about using? Various battery chemistry types (i.e. lead acid, NiCad, NiMh, Lipo, and LifePo4, etc) can have very different "reactions" to the cold weather temps you mention.



Note: Just "take it easy" on the internal hub motor gears (like ES member "pchen" wisely suggests). These gears are somewhat know for "stripping out" during heavy acceleration, hill climbing, "bumps", extreme heat, etc.
 
I have bought the 36V 10Ah Little Frog battery .

I'm not quite sure what the battery chemistry is although it's stated as Li Ion, but the discharge rates look fine for my use. I plan to charge the battery in the office (my favourite price per charge - Free!) during the day, which will keep the pack warm until I set off again when it should start generating it's own heat.

I will certainly be happy if the code 8 turns out to have a good torque! It appears to be the highest speed least torque wind that they manufacture! :? At least at 75kg I'm not toooo heavy for it... :mrgreen:

Thanks again,

John
 
Yep, "Li-Ion" indicates the battery "chemistry" type.

From what little I know, this general type of battery chem has a recommended ambient operating (discharge) temperature rating in the neighborhood of -20-55C. This, of course, is well within your expected ambient operating temp range. Note: the manufacturer may be able to provide a more accurate discharge temp range rating.

BTW,the battery link you provided shows a maximum discharge rate of 10 amps, which would give it a "1C" battery rating (1 "C" = 1 x the amp hour rating of the battery and 2 "C" = 2 x ...). This is, imo, a bit "on the edge" as far as how many amps you might draw (this could also be a "conservative" or "under stated" rating tho). The good news is that geared hub motors are well know for being "conservative" with how much amperage they draw (i.e. they're generally a pretty "efficient" motor design).
 
My newest Bafang held up to 54 volts for about a year on a heavy trike. That said, it is in a 20" wheel and was less stressful on the gears than a 26" wheel would be. It actually has less torque off the line than the 9C that replaced it. I have also used steel gears (1) in an older Bafang after the nylon ones stripped out. Also worked fine but was noisy! The 9C is much quieter.
otherDoc
 
Max discharge capability on the frog battery is 20 amps.
That's going to be really weak on a geared motor; they need a good supply of amps on hills. However, they can only handle so many. That's why for extreme duty like this, a very high power DD motor is more ideal.

On a 7% grade, i am using about 40 amps to hold ~75% of the motor's speed carrying a 230lb rider.
If you're tackling a 10% grade, you may need about 50 amps to hold that speed.

I don't think the BPM will handle it well. I doubt that even the larger MAC/BMC motors would handle that well either.
 
By the way, for extreme hill duty like that, if you're going to go geared, you need a low speed, high torque motor. Not a high speed, low torque motor such as the ~400rpm Bafang BPM.
 
Thank you for the advice neptronix (and everyone else!)

I'm hoping that my BPM Code 8 behaves well. Otherwise it's a quick email to cell-man about the MAC 500 10T!!

This evening on my first training cycle (no motors yet) I managed to maintain a minimum 13 kph - so here's hoping that baseline fitness which I'm aiming to improve on will allow the BPM to keep me nearer 20kph and in it's torque zone....
 
The cell man MAC 10T would behave just as poorly on extreme hills.
You need a low speed wind of whichever motor you're throwing on the bike.

Keeping a high speed motor at low speed is going to generate a ton of waste heat. This would keep it at it's least efficient range.

I hope you didn't order the BPM already too.
 
neptronix said:
The cell man MAC 10T would behave just as poorly on extreme hills.
You need a low speed wind of whichever motor you're throwing on the bike.

Keeping a high speed motor at low speed is going to generate a ton of waste heat. This would keep it at it's least efficient range.

I hope you didn't order the BPM already too.
Click to expand...
johnamon:

neptronix is correct. The BPM code(8) is one of fastest motor within BPM familiar. At 36v, this motor will run at 40 - 43km/h on 26" wheel. The code(8) motor is meant to be running at 20" wheel. Although the BPM is gear motor, and great for hill climbing, but with code(8), you find with these motor on 26", it will be sluggish at the start of hill (wasting energy), and pick up the speed later in the mid hill. Then you will ask where is the power when you needed the most, which is the beginning of the hill.

Ken
 
You need to add a temp probe before you tackle any hills with that fast of a winding. At least that way, if its getting too hot halfway up the hill, you can stop power and pedal the rest of the way...and you will still have something that is sellable, so that you can buy something that will do the job better.

Hill steepness capability of a given hubmotor is a vague science. How steep? how long is the steep part of the hill? If the motor doesnt overheat on the hill you commute over every day, no reason to get something else. But if its going to melt, you would be lucky to get $20 for a damaged hubmotor.

I am sure you are anxious to give it a go, but...if it really is a 10% grade for any significant length, you should use 48V on a very slow winding, even if it means having to settle for a slower top speed on the flats. Adding cooling holes may help too, but a $12 temp probe will answer all your questions.
 
The motor was ordered last Friday - I'm an overly excitable noob after all!

Anyway as spinningmagnets says, I'll give it a go and see if it gets me to work without melting; even if I am by the time I get there. Seeing as I have already purchased the 36v battery too - the backup option may well be to get a torqey 24v motor and run it at 36v to get some speed back.

I don't see the motors as being horribly expensive. I'd rather the motor blew than the batteries :lol:
 
johnamon said:
Could someone with a little experience please let me know whether or not I will make it up the hill shown with my high-speed motor?!
Click to expand...

If you can pedal 13 KPH up the hill in question I'd guess the Bafang will roughly match your pedaling power to help you achieve 25 KPH. That's (48/25) 52% of your no-load speed. Ebike setups are balance of compromises and here you have a nominal top speed of 40 KPH and an assisted hill climbing ability of about 25 KPH. I think this should work ok. The temp guage would be the ultimate arbiter.
 
neptronix said:
Max discharge capability on the frog battery is 20 amps.
That's going to be really weak on a geared motor; they need a good supply of amps on hills. However, they can only handle so many. That's why for extreme duty like this, a very high power DD motor is more ideal.
Click to expand...
How do you come you with all this crap!?
 
full-throttle said:
neptronix said:
Max discharge capability on the frog battery is 20 amps.
That's going to be really weak on a geared motor; they need a good supply of amps on hills. However, they can only handle so many. That's why for extreme duty like this, a very high power DD motor is more ideal.
Click to expand...
How do you come you with all this crap!?
Click to expand...

1. Specs from the battery's website.
2. Real life experience climbing very steep hills that are 5+ miles in length.
3. Real life experience finding out how many amps multiple geared motors can take before melting.

That's how i come up with crap like that.
 
full-throttle said:
Compare DD with geared on a climb (same Kv, same controller settings) and you'll find that geared will climb better. Just go to http://www.ebikes.ca/simulator/ and look at the blue line diff between say eZee 26" and 408

How "very high power DD motor is more ideal" with a 20Amax battery?
Click to expand...

Do you really think that a MAC/BMC/Bafang would climb hills better than a Crystalyte HT/HS/5xxx?
Because that's what i'm referring to here. Not Crystalyte's tiny little entry level 408 motor.
The difference is that the geared motors are more efficient, but they can't handle the same amount of juice.

What i was trying to get at is that the larger DDs can handle much more power for extended periods of time and have reliability be less of an issue, since we're talking about climbing 10% grades, which can even put a strain on cars. Heat generation will be high and melting gears and hall sensors is a reality at power levels like that.

I also stated from the start that the 20A max battery was a bad idea. Not sure if you caught that, or just felt like jumping on me.
 
neptronix said:
Do you really think that a MAC/BMC/Bafang would climb hills better than a Crystalyte HT/HS/5xxx?
Click to expand...
@ 20Apeak (what he's got): BPM (what he ordered) - def better, BMC/MAC - slightly better

Code-8 and 36V/20Apeak is not the best combo - agree

neptronix said:
What i was trying to get at is that the larger DDs can handle much more power for extended periods of time and have reliability be less of an issue, since we're talking about climbing 10% grades
Click to expand...
johnamon said:
I expect to encounter 10° hills - max 690km per hill circa 10m elevation rise.
Click to expand...
17.6% grades (10°), the rest is confusing. I'd assume he meant: 69m long with 10m elevation
 
Some real world experience. I've got a packaged bike that uses the sensorless BPM 36v350w 26"(11) motor, with 36v-10AHr of Phylion LiMnO2 battery and an LSDSZ controller marked as 9A continuous, 18A peak. Noload speed is 24mph. Real world flat speed is 20mph. The worst off road hill I could throw at it dropped the speed to 8mph, but it still wound itself up the hill. There's significant voltage sag under heavy load so I think that battery is marginal for the current being asked of it. Sensorless works fine. The only time you notice the briefest judder is when starting from a dead stop.

Using a code 8 in a 26" rim is going to give a lot more noload speed but a lot less hill climbing ability. Exactly how that pans out in the real world is going to take trying it. My guess is that it won't climb hills the way you want it to. I'm all for going one step for a bit of extra speed (eg code 10 in a code 11 rim) but I think you may have gone too far in the compromise of top speed vs torque.

By all accounts the BPM is pretty strong and will tolerate 1000w or so continuous. People have had big success with things like a Code 9 36v in a 26" rim with a modded controller 30A max and a 16s4p (48v) A123 pack (that's nearly 1500w peak Pin). I wouldn't worry too much about the horror stories of stripped gears. I suspect you have to get silly with the power (like 75v40A) and/or ride off road a lot on full power before this becomes an issue.
 
Sorry for the delay in getting back guys, my email notifications seem to have stopped! :oops:

I appreciate your message of experience jbond! The one thing that I hope will get my code 8 up the hill will be the fact that I plan to pedal assist (gently where I can!) the whole way during my commute. So long as the motor is supplying enough power to haul it's own + the battery's weight up the short but steep hill I'll be reasonably happy!

The horizontal distance in my initial post was incorrect btw, it's a 10m vertical increase over 69m - about 10°!
 
Hmm, rise/run(100) = % grade. So, 10/69(100) = 14.5% grade?

If you are pedaling this hill now, the Bafang with a 15A controller will provide some assistance (up to half?), but won't haul you up by itself. Your best bet will be to start the hill at 25 KPH minimum. And, as itselectric posted, it probably wouldn't be helping much at all from a stop at the bottom of that hill.
 
You must log in or register to reply here.

Similar threads

I
Greenbike Fat tire 500watt Hub drive Underpowered
Replies
3
Views
165
imgonnawreckthisthing
I
R
    • Like
Really good article comparing Bafang vs. Tongsheng vs. CYC
Replies
12
Views
10,621
999zip999
999zip999
B
2022 M2S Ultra HT (hardtail fat-bike) review
Replies
6
Views
2,341
2old
2
Jaded
Surly E•D•LHT - Touring eBike Build with BBSHD!
2
Replies
36
Views
9,421
jonsully
jonsully
B
Gearing a Bafang BBSHD Top Speed and Off Road
Replies
0
Views
2,115
Bullfrog
B
Back
Top