2WD bike - regen engaging at high rpm

[Pwd]

Hi everyone,

I've got a 2WD e-bike with a Magic Pie 4 on the front. I recently switch from a Magic Pie 2 to another type of motor on the rear. Just as I'm reaching top speed (around 54kph), regen braking feels like it is enagaging and prevents me from going any faster. When release the throttle, the problem goes away until I reach top speed again.

I don't recall having this issue when I was running the Magic Pie 2 on the rear. The new rear motor is a faster wind than the Magic Pie 4. Could this cause the Magic Pie 4 to engage its regen when it exceeds its maximum rpm or is there something else happening?

Thanks

[Bikemad]

54kmp/h is ~434rpm for a 26" wheel, and at this speed, the motor will be trying to produce a higher voltage than the battery voltage, and this may cause it to automatically perform like a generator.

I once spun up a Magic Pie by spinning the pedals very fast by hand with the bike suspended from the ground and no battery connected.
The voltage on the Pie's battery connector went right up to ~77V, but it instantly pulled the voltage back down to ~60V the moment I applied the brake on the other wheel to activate the regen.

If the battery had been connected, I'm sure the voltage would not have risen this high, as the battery would have absorbed any current produced if the motor voltage tried to exceed the battery voltage.

I don't recall having this issue when I was running the Magic Pie 2 on the rear. The new rear motor is a faster wind than the Magic Pie 4.

I am confused as to whether your bike used to exceed 54km/h without slowing before, or whether it simply didn't reach that speed with the slower rear motor? 

If it used to regularly exceed that speed without slowing, it must be something to do with the new rear motor.

Are the two controllers wired in parallel on all of the wires (Battery, throttle, cruise, brakes etc.) or do they have independent controls and/or separate batteries? 

If they share the same brake signal wire, it is possible that the rear controller could be interfering with the Magic Pies regen function.

If this is the case, a diode wired into the rear controller's brake signal wire should solve your problem, as it would still allow the brake lever switches to ground out both motor's brake signal wires, but it should prevent the rear motor's brake signal wire from interfering with the Brake signal wire on the front controller.

Alan
 

[Pwd]

Thanks for the reply Alan

I am confused as to whether your bike used to exceed 54km/h without slowing before, or whether it simply didn't reach that speed with the slower rear motor? 

I'm pretty sure that I have reach that speed before with the previous rear motor. IE going down a hill etc... but not 100% sure. I agree that if that's the case then it must be something with the new motor however the same controller was used and the settings have remained the same.

The two controllers are wired on parallel for the battery but the throttle and brakes are separate. I've modified the throttle so it has two hall sensors, one goes to the front and the other goes to the rear. The left brake goes to the rear controller and the right goes to the front MP4.

After reading your response, I realize I still have some troubleshooting to do but you've given me some food for thought.

I will try disconnecting the front motor and see if I can replicate the problem.

[Tommycat]

Interesting dilemma, can a wide open throttled pie be pushed beyond it's unloaded speed without a negative effect?

In an effort to get some data points I ran my MP5 on a 26.5 wheel and a 52 volt battery with the following non-stock controller settings.


Set maximum wheel RPM to 100...as I will have to pedal it over speed, I choose something in my wheel house.     This turned out to equal 6.2 MPH.

So having my amp meter in reverse to be able to read regeneration amperage, my battery voltage at about 48.5 volt, I had the following results.

With throttle wide open and the controller limiting max speed to 6.2 MPH... I pedaled to increase speed. (rear motor)  Resistance to me was just the same as a typical ride with the motor disabled. And there is power being produced as indicated by an amperage reading of ~.5 amps at about 11.2 MPH, with the voltage going up to 50.5 volts.
Now immediately hitting the brakes to enable regen, produced an amperage of 4.5 amps, with voltage also going up and the corresponding hefty drag.

So my thoughts.  Is regeneration actually taking place, or is it just that the MP4 has run out of helpful push? Does the OP have an amperage meter to help show this?  Is it possible that the Maximum Wheel RPM setting getting in the way?
Is the front throttle putting out maximum voltage? (4.3 volts) BTW any pictures of this neat sounding mod? 


Regards,
T.C.

 

[Pwd]

Hello again,

I did a bit of troubleshooting and my results were as follows:

• No change/replicating the problem - I got the bike going up to approximately 54 kph (slight downhill) and the same problem occurred. The MP4 braking/regen kicked in when I reached 54 kph. I have to release the throttle and the braking effect goes away until I reach the same speed.
• Disconnected brake signal cable to front MP4 motor - the same result as before/as above.
• Disconnected the power harness + the brake signal cable to the MP4 motor - the bike accelerates past 54 kph and reaches a top speed of 58 kph without the braking or regen problem kicking in.
  

In an effort to get some data points I ran my MP5 on a 26.5 wheel and a 52 volt battery with the following non-stock controller settings.

Thank you for testing this, your effort is appreciated. It is definitely regen kicking in, my Cycle Analyst is showing a negative wattage reading of approximately 300W when the problem occurs. Similar to what I would see if I applied the brake handle.

Is the front throttle putting out maximum voltage? (4.3 volts)

The throttle is putting out maximum voltage.

I am beginning to wonder about the maximum wheel rpm setting, however my MP4 controller is unable to be programmed anymore for some reason (see this https://goldenmotor.com/SMF/index.php?topic=6331.msg35173 topic I created). When I last had it working with the programming software though, I don't recall changing the rpm setting.

[Bikemad]

• Disconnected the power harness + the brake signal cable to the MP4 motor - the bike accelerates past 54 kph and reaches a top speed of 58 kph without the braking or regen problem kicking in.
  

I would not recommend high speed use with no battery connected to the controller, as there would be nothing attached top the controller to absorb the excess voltage being produced at the higher motor rpm.
The voltage generated passes into the controller and will become far too high, which will could damage the capacitors in the controller, as they are only rated for up to 63V.

I don't think this has anything to do with the rpm setting in the controller (which I seem to recall only allows a maximum entry of 380 rpm anyway) it is simply down to the motor's velocity constant (K_v or rpm/volts ratio) and the speed the motor is being driven at.

A running motor generates a back-EMF proportional to its rpm. Once the motor's rotational velocity is such that the back-EMF is equal to the battery voltage, the motor reaches its limit speed.
If this speed is exceeded, then the current will automatically begin to flow in the opposite direction, which would result in charge flowing into the battery and reverse torque being applied to the motor, hence the electromagnetic dynamic braking effect (just like regen) that you have experienced.

By applying full throttle at high rpm, you are effectively providing a pathway for the reverse current to flow back through the controller and into the battery.

Releasing the throttle completely, removes the pathway for the current to flow through the controller in either direction.
So, no power can be delivered to the motor below its maximum rpm/battery voltage and also no power is taken from the motor (and no electromagnetic dynamic braking force is produced) above its maximum rpm/battery voltage.

If you tried the same experiment with a 24V battery on the front wheel you should experience a similar braking effect, but at ~27km/h instead of 54km/h.

If you insert a switch into the throttle signal wire going to the front motor, this would allow the front throttle to be disabled at high speed (without disabling the rear throttle) and this should enable those extra 4km/h to be extracted from the rear motor. 

Alan
 

[Pwd]

• Disconnected the power harness + the brake signal cable to the MP4 motor - the bike accelerates past 54 kph and reaches a top speed of 58 kph without the braking or regen problem kicking in.
  

I would not recommend high speed use with no battery connected to the controller, as there would be nothing attached top the controller to absorb the excess voltage being produced at the higher motor rpm.
The voltage generated passes into the controller and will become far too high, which will could damage the capacitors in the controller, as they are only rated for up to 63V.

I don't think this has anything to do with the rpm setting in the controller (which I seem to recall only allows a maximum entry of 380 rpm anyway) it is simply down to the motor's velocity constant (K_v or rpm/volts ratio) and the speed the motor is being driven at.

A running motor generates a back-EMF proportional to its rpm. Once the motor's rotational velocity is such that the back-EMF is equal to the battery voltage, the motor reaches its limit speed.
If this speed is exceeded, then the current will automatically begin to flow in the opposite direction, which would result in charge flowing into the battery and reverse torque being applied to the motor, hence the electromagnetic dynamic braking effect (just like regen) that you have experienced.

By applying full throttle at high rpm, you are effectively providing a pathway for the reverse current to flow back through the controller and into the battery.

Releasing the throttle completely, removes the pathway for the current to flow through the controller in either direction.
So, no power can be delivered to the motor below its maximum rpm/battery voltage and also no power is taken from the motor (and no electromagnetic dynamic braking force is produced) above its maximum rpm/battery voltage.

If you tried the same experiment with a 24V battery on the front wheel you should experience a similar braking effect, but at ~27km/h instead of 54km/h.

If you insert a switch into the throttle signal wire going to the front motor, this would allow the front throttle to be disabled at high speed (without disabling the rear throttle) and this should enable those extra 4km/h to be extracted from the rear motor. 

Alan

Very interesting Alan, I will try a throttle switch next. So if I had disconnected only the throttle to the MP4, the problem would have went away during my testing?

Thanks for your insight and help!

[Bikemad]

So if I had disconnected only the throttle to the MP4, the problem would have went away during my testing?

I am convinced that it would have, but if/when you try it out you'll quickly discover the answer. 

Alan
 

[Pwd]

So if I had disconnected only the throttle to the MP4, the problem would have went away during my testing?

I am convinced that it would have, but if/when you try it out you'll quickly discover the answer. 

Alan

It works as you suggested. I unplugged the throttle to the MP4 and the regen effect never happens.

Thanks 

[Tommycat]

Well done lads!

 I use the red button on the Luna full twist throttle to disable the power to the throttle... in an effort to keep from running over my feet while the bike is armed.

So lets get that controller talking!

After I connecting the USB lead to the computer, running the software and clicking connect I get the "No response because of timeout" message. At that point I turn on the power to the controller but nothing happens. If I understand correctly, this is when the controller should connect.

Using the latest (I think) software...V3.3.0 b150501 on a Vista laptop...the following procedure works for me.

Start P.C.
Connect communication cable.
Verify Com port in Device manager.
Open PI-800 software.
Set to correct com port.
Turn battery 'ON' (power to controller)
Press connect button just to the right of the com port selector box...I think upload works also.
Hopefully you get "Upload Parameters Successfully"

This differs just a bit from your sequence.

Oh, and it helps to always have the controller physically lower than the P.C. so the electrons know which way to go..well o.k..to help me remember what direction the uploads and downloads are going!


Regards,
T.C.

[Pwd]

...
So lets get that controller talking!
...

I gave that another try following your steps but I had no success. I am convinced that the programming chip on the controller is bad. I'm going to live with it for now. Thanks for your help.


For the record, I did install a switch as per BikeMad's recommendation to get around my original problem. Have a look at the attachment. It works fine as long as I don't forgot to flip the switch ahah 

Thanks for the input guys, my bike is that much more enjoyable now.

[Tommycat]

Please forgive my curiosity... But does your front pie work correctly from a standing stop with the rear motor throttle disconnected?

[Pwd]

Please forgive my curiosity... But does your front pie work correctly from a standing stop with the rear motor throttle disconnected?

Hi TC,

the Pie (front motor) works fine from a stop with the rear motor's throttle disconnected.

[Tommycat]

Hi pwd,
Roger that. Had the wheels spinning in my head but after your reply found research that has put this issue to rest. Great to hear your up and running!