Hi, new here and need some help to diagnose a fault/identify a fix. I have strange behavior from my Bafang hub drive controller which means it wont give me any more power that level 1 assist.

 

I can select different power settings (1-5) from the display, however regardless of power setting I get a maximum of about 10A (c.400w) output from the controller, which is equivalent to setting 1, but the speed setting at which power drops off increases at each level as it did before so the display is talking to the controller. It was working OK three days ago. Previously I would get a max of c.750W output from the controller in level 5 (rarely used).

 

Any inspired ideas would help, or if my controller is done some suggestions for where I can get a like for like replacement.

 

Set up is:-

Motor

BF RMG06 36V250W(9) 26 1712220024-6

Controller

CR S10Z.1000.SN.U 2.0 F20E1 RC040019

Display

DP C171

Give the motor full power on level 5. Keep the power on full while you apply the brake to slow it down to about 5 mph. Read the power while in that condition and let us know what it is.

Speed controllers have the same current in all PAS levels , one assumes being a Bafang controller it is speed control and not current control.

Give the motor full power on level 5. Keep the power on full while you apply the brake to slow it down to about 5 mph. Read the power while in that condition and let us know what it is.

Thanks, will give it a try tomorrow, although hill climbing today I wasn't getting more power out of the higher assist levels.

Speed controllers have the same current in all PAS levels , one assumes being a Bafang controller it is speed control and not current control.

That's not how this has behaved until today, which is what's confused me. Normally increasing assist level increased both power and the cut off speed. I think it's actually a 20A controller so should be getting >700W at full power (which I was till today).

Edited October 5, 20241 yr by Slartibartfarst

Give the motor full power on level 5. Keep the power on full while you apply the brake to slow it down to about 5 mph. Read the power while in that condition and let us know what it is.

Just realised I could lift the wheel off the ground and run it on the throttle with the brake on to limit speed. So didn't have to wait till tomorrow. I was getting 370w max (c10A) in any power level, so same power in all levels.

Just realised I could lift the wheel off the ground and run it on the throttle with the brake on to limit speed. So didn't have to wait till tomorrow. I was getting 370w max (c10A) in any power level, so same power in all levels.

That would happen if there are two shunts in the controller and one of them is no longer conducting because it's blown or has a bad solder joint. The shunt's normally only blow if you connect the controller the wrong way round, so probably a bad solder joint. Open it up and look inside. The shunt is a piece of thick wire bent into the shape of a staple. Sometimes, they use solid state ones which are flat black things with silver ends and a number like 005,002,001 written on them.

That would happen if there are two shunts in the controller and one of them is no longer conducting because it's blown or has a bad solder joint. The shunt's normally only blow if you connect the controller the wrong way round, so probably a bad solder joint. Open it up and look inside. The shunt is a piece of thick wire bent into the shape of a staple. Sometimes, they use solid state ones which are flat black things with silver ends and a number like 005,002,001 written on them.

Thanks, would it be a DIY fix with a bit of soldering?

 

Also just realised the 370w is way higher than level 1 was, I think it was about 230w before and 2 was 300 ish. So it seems to have defaulted to 10A regardless of setting.

Thanks, would it be a DIY fix with a bit of soldering?

 

Also just realised the 370w is way higher than level 1 was, I think it was about 230w before and 2 was 300 ish. So it seems to have defaulted to 10A regardless of setting.

You have a speed control controller, so power would be the same on all levels. Stop panicking. If my diagnosis is correct, you can fix it with a soldering iron and a screwdriver. Pray that your controller isn't potted.

Personally I would change out the control system and ditch the bafang speed controller, replace with a KT current control system and gain control of how much power one want's to put thru the hub .

With current control one can use minmal current/power to improve rider fitness , typically before my major recent surgery I was pretty much cycle fit ofr a 61 yr old with asthma and only needed to draw 60 - 80w of power to comfortably ride about at 14 - 19mph dependant on air resistance and weather conditions.

 

It will be many weeks if not months before I can cycle again , so will be intersting to see how my fitness and much lower body weight manages .

You have a speed control controller, so power would be the same on all levels. Stop panicking. If my diagnosis is correct, you can fix it with a soldering iron and a screwdriver. Pray that your controller isn't potted.

Thanks, opened the controller up and it looks pretty water damaged so I think it's time for a new controller. Note that the controller changed both power and speed with different levels so wasn't pure speed control.

 

So the question is, what controller do i replace a 36v 24a bafang controller with?

There are two types of speed controller .

Basic 3 spd crappy ones that have no change in current in any level and just have 3 levels of max speed assist .

The bafang and lishui are slightly better and have varying current levels from 40 - 100% in the assist/PAS levels.

If you want better control of power with wider varying current levels then KT are the way to go .

As I have often posted in the past these 5PAS assist levels are 13%, 20%, 33%,50% & 100% respectively, so the user can opt for which ever level is most comfortable for the terrain . Speed doesn't change one gets the max all the time and more if one pedals a little harder to rider above the max cut off speed of 15 - 17 mph.

If one opt's for a hub with higher internal gearing of up to 15.1 ratio then one can ride without assist and not feel very much in powered or non powered riding.

Edited October 6, 20241 yr by Nealh

It appears that water ingress may have shorted some tracks on you PCB oir damaged some of the components hence now why one is only seeing approx 10a of current at all levels.

There are two types of speed controller .

Basic 3 spd crappy ones that have no change in current in any level and just have 3 levels of max speed assist .

The bafang and lishui are slightly better and have varying current levels from 40 - 100% in the assist/PAS levels.

If you want bwttwer control of power with a wider varying current levels then KT are the way to go .

As I have often posted in the past these 5PAS assist levels are 13%, 20%, 33%,50% & 100% respectively, so the user can opt for which ever level is most comfortable for the terrain . Speed doesn't change one gets the max all the time and more if one pedals a little harder to rider above the max cut off speed of 15 - 17 mph.

If one opt's for a hub with higher internal gearing of up to 15.1 ratio then one can ride without assist and not feel very much in powered or non powered riding.

Thanks, I didn't appreciate the variants of speed control. Any KT controllers/suppliers you would recommend?

Typically the go to shop is topbikekit or their store on AliExpress and of course there are many other sellers on AliExp.