Boosting my Bafang MG310_Std

[gibrocksonne]

Hello,

Since 3 years, I'm using a MG310_Std on a MTB bike with semi-slick 26" tires to go to work : 11km/day, (7 miles) bike lane on urban area, absolutely flat. I have a 36V battery, biker+bike weight is 75kg (165lb). Depending on the wind and battery voltage, I'm cycling at 29-36km/h (18-22mph).

My battery is a 36V/11Ah with 5P-10S Samsung INR18650-29E, assembled by me, 5 years ago. It has something like 10000km now. Capacity have dropped a little bit, probably -20%.

My motor is a Bafang MG-310-std. Is is really light and I really love it.

I always take care about the motor and I've limited the power to 400W to avoid high torque and high battery current (and bad efficiency).

I'm using the pedals, I think I give something like 100-160W of power at all speeds (48-11 max bracket, 2x9 config).



In the next months, I may move further. I will have to do 30km/day (19 miles) : 10% urban and 90% on a dedicated lane for bikes, with almost nobody, outside the city. Still almost flat (0.4% avg / 1% max slope). I would like to boost my speed to 35-40km/h (22-25mph).

I'm looking for minimal change on the bike: ideally I would like to change only the motor (and eventually bracket). Next time I will re-build my battery, I may change from 5P-10S (voltage range 30-42V) to 4P-12S (36-49V, -20% capacity), if needed.

I looking for a good candidate to replace the motor :
- The same motor in fastest version (MG310-fast)
- Bafang SX2 Fast
- Q128C (328RPM version)
- Any other option you'll give me :wink:

Since I will spent 90% of my time at 38-40km/h (290-310RPM, 26"), I'm looking for a motor that will have its best efficiency at this speed. I'm also looking for a very good reliability and maybe bafang motors are better, but I may be wrong.

On the ebikes.ca site, they said the fast version of SX2 is intended for 20" wheel. It may imply that this motor don't have enough torque to keep its nominal speed with 26" wheel (or not at a good efficiency). The MG310-fast is ligher, I'm not sure it will have more torque.

Please fill free to give any advice or share your experience
Many thanks

 

[Mclewis1]

My take would be - if you keep the voltage and amperage to the motor the same (same 36v battery and controller) then changing to a faster wind motor will reduce the torque available.

I built a faster commuter type of bike a few years ago. I wanted year round capability (so good winter tire options) and good reliability with 40+kph top speed. I also didn't want a big heavy motor, I wanted to retain the bicycle riding experience as much as possible. The bike was going to have 27.5 or 700c wheels. I'm 220lbs and intended to carry 20-40lbs of additional "cargo" (work clothes, laptop, etc. or groceries or other shopping). My area is generally flat with a few longer hills. I would be riding on multi use paths (MUPs) and smaller city streets (no highways, no heavily congested arterial roads).

I choose a standard wind Shengyi SX motor (500w "class" in Grin's words), BaseRunner controller, and a 52v battery. I've been very pleasantly surprised with this combination. It's been very reliable over 2+ years and is surprisingly quick in top end speed (45kph). I configured the bike with both a PAS and throttle. With the throttle I have the ability to push over 1000w through the motor for short periods of time (few minutes) for hill climbing, or quickly accelerating and top speed runs in traffic.

I'm no expert but my suggestion to get more top end speed without making huge changes would be to keep that nice lightweight standard wind Bafang 310 motor and change over to a 48 or 52v setup (battery and controller). Yes it would be more money than just a new motor and wheel build but it's a proven capability to get the speeds you want from a bike with 26" wheels. One specific feature I would want is temperature monitoring on the controller/display as you are going to be pushing that little motor quite hard so overheating would be something to watch out for on hot days.

 

[hias9]

I would recommend going to a 48V battery.
That's a very good match for the G310 with 10T (=standard) winding and 26'' wheel and it will run efficiently in the speed range you mentioned.
For the G310 it is important not to go above 35Nm (which is about 35 phase amps for your motor) because the nylon gears are the weakest point.

 

[beemac]

I would recommend going to a 48V battery.

you could test out the effect of a voltage increase using a dc-booster - i've used them in the past to maintain a 'full battery' or higher voltage but the extra bulk isn't something I saw as a good cost/benefit ultimately. But it's a cheap way to see if the battery swap will be worthwhile.

https://www.aliexpress.com/item/32828748704.html

 

[glend]

Its good to know the bafang is capable of 10,000 km+. I have just done a tad over 900km on my G311 fitted to Yuba Mundo. Total weight including myself perhaps around 120kg. But my poor motor has to lug that weight over very hilly terrain. But its doing a great job so far. I also like the fact that I can exercise (without power) on the weekend with the same bike. Previously I used two bikes. One to travel to work, the other for exercise.

Have you checked the ebikes.ca motor simulator? They have Bafang G310_Vfast lasted (there is fast and very fast). With an 20 amp controller they have the max speed of Bafang G310_Vfast at 41.9kmh in a 26" wheel using 17.4 Wh/km. If you chose to go semi recumbent the same motor will only use 9.2 Wh/km at the same speed.

That's the thing, its really not motor efficiency that's the killer. Wind resistance at higher speeds isn't linear. At 35kmh a mountain bike requires 423W. At 40kmh that increases to 622W. That extra 5kmh requiring a massive 200 watts. So good efficiency is only achievable by overcoming wind resistance (recumbents, velomobiles etc). A more efficient motor in itself will only achieve a nominal benefit in comparison. If you do decide to try out a Bafang G310_Vfast its easy enough to swap over into the shell of your current wheel without requiring a rebuild.

Here is my beast ...

 

[motomech]

I agree w/ the other posters, spend the money on a new batt. 36 Volt packs are lame and if yours is down 20 % now, it will soon drop more.
"Standard" doesn't really tell me what exact speed range the motor is, but 18 to 20 MPH on 36 Volts would indicate a "mid-range" (a good thing).
The last two geared smallish Bafang systems I built spec.'ed like this:
Bafang FM G020.250/350.D (SWX02) motors (both).
Mountain bike w/ 26 inch whl.s., 2.0 tires
52 Volt pack w/ 17 Amp (max.) controller
On the flat, no peddaling.
11 turn, 23 to 25 MPH
13 turn, 25 to 27 MPH.
(variables, how big the pack is and state of charge)
I perfer the 11 turn.
Your gearing is good, you should be able to peddle up into low/middle 20's MPH before your legs get too busy.
A 4 MPH increase doesn't seem like much on paper, but on the road it is. as you probably know, under 20 MPH is boring, lower/mid 20's is fun and one actually feels like you are getting somewhere.
If you go w/ a higher speed range sm. motor w/ low voltage, the acelleration though the mid-range will be sluggish.
I think your speed target is good and doable with a battery change.
You might see a little better distance/energy used ratio with a 52 Volt system as it is more efficient to use higher Voltage/lower motor speed than low Voltage/higher motor speed.
Obviously, you will want as much capacity as will fit in your space to go 20 miles w/ any kind of reserve.
If you have any money left over, spend it on flat resistance tires w/ real tread. Murphy's law of e-bikeing; "The further you are from "home base", the greater probability of a flat tire".