Motor cut off under load and speed

seba240698

100 mW
Joined
May 10, 2019
Messages
42
Hi all, I have a new issue with my ebike. The motor power cuts off when it :
1) hits a speed of 36 kmh or
2) it goes up a slight slope, even with speed lower than 36 kmh.
From the forums here and without during any test, it seems that it is the battery or rather, the BMS of the battery, cutting off. The battery is 36 V.
However, I would rather not conclude it so hastily as the battery was only out in use in May last year and I only use my ebike during weekends, each weekend only travel 40 km. So till now is about 2600 km and I charged it fewer than 40 times. The battery was bought online in Apr 2019, but I charged it every 2 months when not using it. I only used it since May 2020.
The battery is also the most expensive item in the electrical drivetrain.
Is there anything I can do to verify whether it is the battery or other components faulty?
The photos of the display, battery and controller are attached.
Thank you in advance.
 

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The battery is probably badly out of balance from inactivity, and one cell group is tripping the low voltage cutoff under the conditions you describe.

The easiest thing to do is leave it on the charger for a few days to balance, and see if it doesn't improve.
 
Thanks for the advice.
Just wondering, the BMS of the battery will stop the charger from charging once the battery is fully charged so what is the use for leaving the charger on for a few days?
 
seba240698 said:
Thanks for the advice.
Just wondering, the BMS of the battery will stop the charger from charging once the battery is fully charged so what is the use for leaving the charger on for a few days?

The only case in which it will do that is if the charger's voltage rises beyond the upper voltage limit of the BMS.

Most BMSes will begin to balance as the highest voltage cells reach their fully charged voltage. At that point, the BMS bleeds a small current (usually 20-50 mA) from the cells that are full, allowing the remaining cells to catch up. This can take quite a while. If you don't give the balancing cycle time to level out the cells, then they can fall father and farther out of balance the more times you cycle them.
 
OIC, thanks for the explanation.
I'll do it right away and get back to you the outcome.
 
I've tried and connected the battery to the charger for 3 days 2 nights but the outcome is the same.

Is there any other things I can do?
 
You can open the battery and check the voltage of each cell group, to see how well balanced they are. If you find one or more weak cell groups, that's probably the issue. You can try balancing them manually with a power supply that can deliver 4.0-4.2 volts. If they won't balance, there's little you can do but replace the problem cells, or start over with a new battery.
 
I am not confident to open up the battery with the warning sign on the battery.
I guess I'll just bear with it until I get the most mileage out of the life of the battery and then replace the whole battery.
Thanks again for the advice.
 
Chalo said:
You can open the battery and check the voltage of each cell group, to see how well balanced they are. If you find one or more weak cell groups, that's probably the issue. You can try balancing them manually with a power supply that can deliver 4.0-4.2 volts. If they won't balance, there's little you can do but replace the problem cells, or start over with a new battery.

Hi, finally I bought a brand new battery, 36V, 13Ah, Panasonic cells.

However, the same problem exists.

The motor will cut off after 5 to 10 sec after cut in, without any apparent reasons. I suspect it is due to too much current being drawn from the battery but I'm not really sure, it cuts off even when the speed is not high (about 20 kmh only), so I don't think it is due to the speed limiter.

This problem exists even when I use a brand new battery, so can I suspect it is the controller problem? My controller is brain power with a maximum discharge current of 13A. The maximum discharge current of my battery is 30 A.

Can anyone shed some light in this?

Thanks in advance.
 

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It's still not clear in your original poet and latest on what you mean by "cutout", so even though Chalo's advice is solid, it may ntr fix the problem you described. When a BMS cuts power, you usually need to cycle the battery off and on to reset it. Is that the case, or is it cutting out, the coming back without cycling the battery, the latter indicating the controller current limit being hit.
 
Hi E-HP, thank you for your reply.

I don't quite get what you mean by "cycling the battery".

What I encountered is this.

When I start pedalling, the battery will cut in, but after about 5 sec (sometime longer, sometime shorter but it never go beyond 10 sec), the motor will cut off. Then after about 2 to 4 sec, the power comes back, then after about 5 to 8 sec again, it cuts off again and the cycle repeats itself.
 
seba240698 said:
Hi E-HP, thank you for your reply.

I don't quite get what you mean by "cycling the battery".

What I encountered is this.

When I start pedalling, the battery will cut in, but after about 5 sec (sometime longer, sometime shorter but it never go beyond 10 sec), the motor will cut off. Then after about 2 to 4 sec, the power comes back, then after about 5 to 8 sec again, it cuts off again and the cycle repeats itself.
If the battery is "cutting in", that means there is no power at all before that (controller and display are off)? You are pointing people in the direction of a battery issue, but I've never heard of a situation where the battery cuts in when you start pedaling.

If it's a controller limit, the controller and display will stay on, and the assist comes back once below the limit.
 
Alright, let me rephrase it.

Before I ride, I switch on the battery, and the display turn on (with lights on the display, power indicator etc).

As a starts to pedal, the power assist comes in (I only have PAS, no throttle), but after between 5 to 8 secs, the power cut off (it loses power, the pedalling gets hard) but the display is still on, with background light and it indicates zero power bar, but display is always on).

After about 2 to 4 sec, the power comes back, but not for long. The power will stay for about 5 to 8 secs, then it goes off again. The cycle repeats itself continuously. The ride is not smooth as a result.
 
seba240698 said:
Alright, let me rephrase it.

Before I ride, I switch on the battery, and the display turn on (with lights on the display, power indicator etc).

As a starts to pedal, the power assist comes in (I only have PAS, no throttle), but after between 5 to 8 secs, the power cut off (it loses power, the pedalling gets hard) but the display is still on, with background light and it indicates zero power bar, but display is always on).

After about 2 to 4 sec, the power comes back, but not for long. The power will stay for about 5 to 8 secs, then it goes off again. The cycle repeats itself continuously. The ride is not smooth as a result.

You didn't need a new battery, but at least you got a good one :thumb:

What you are describing is normal behavior for a controller that's undersized for what you are demanding from it. It's protecting itself. What are the specs for your controller, your bike weight including rider, and your riding conditions??
 
My controller is brainpower, 36V, 250/350W, maximum current is 13A.

The combined mass of bicycle and rider is 117 kg.

Terrain wise is mainly flat, city riding, with slopes less than 5 degree gradient.

Undersized it may seem, but I have been using this controller for over 3 years, it didn't give me this problem until the last 1 year. Do controllers generally "degrade" over usage? :p

As for my 2 batteries, I will sell the "old" one on the online market and keep the fresh new one. :wink:
 
seba240698 said:
My controller is brainpower, 36V, 250/350W, maximum current is 13A.

The combined mass of bicycle and rider is 117 kg.

Terrain wise is mainly flat, city riding, with slopes less than 5 degree gradient.

Undersized it may seem, but I have been using this controller for over 3 years, it didn't give me this problem until the last 1 year. Do controllers generally "degrade" over usage? :p

As for my 2 batteries, I will sell the "old" one on the online market and keep the fresh new one. :wink:
Useful background. Controllers don't degrade. Can you monitor your current draw from the battery? There may be something regarding the motor that's making it draw more current, like a faulty hall sensor or something else messing up the timing.
 
If the display stays on when it cuts off, it means the battery BMS is not tripping.
When you try to pull more than a controller is set for, it should just start slowing down but not cut off. Cutting off is usually something like an over temp thermostat or some other issue with the controller.

Does the controller get warm? 13A isn't much, so it should stay cold.
 
E-HP said:
seba240698 said:
My controller is brainpower, 36V, 250/350W, maximum current is 13A.

The combined mass of bicycle and rider is 117 kg.

Terrain wise is mainly flat, city riding, with slopes less than 5 degree gradient.

Undersized it may seem, but I have been using this controller for over 3 years, it didn't give me this problem until the last 1 year. Do controllers generally "degrade" over usage? :p

As for my 2 batteries, I will sell the "old" one on the online market and keep the fresh new one. :wink:
Useful background. Controllers don't degrade. Can you monitor your current draw from the battery? There may be something regarding the motor that's making it draw more current, like a faulty hall sensor or something else messing up the timing.

Now you ask me about the motor, I realise, yes, the motor does give out whizzing sound when it is under load, not particularly loud but noticeable if the road traffic is light, I can hear it. This sound came only in the past 1 year, or thereabout.

Could it be motor going to fail?

In any case, I'll check the Hall sensor connection over this weekend. In which wire should I measure the current? There are 3 wires from the controller to the motor, green, yellow and blue.
 
fechter said:
If the display stays on when it cuts off, it means the battery BMS is not tripping.
When you try to pull more than a controller is set for, it should just start slowing down but not cut off. Cutting off is usually something like an over temp thermostat or some other issue with the controller.

Does the controller get warm? 13A isn't much, so it should stay cold.

No, the controller doesn't get warm in almost all riding conditions.

The power cut is a sudden one, no slowing down or whatsoever, in any case the power will gradually reduce to zero during when the bicycle reaches about 35 kmh, this is due to the speed limiter, I have no issue with that.
 
seba240698 said:
In any case, I'll check the Hall sensor connection over this weekend. In which wire should I measure the current? There are 3 wires from the controller to the motor, green, yellow and blue.

Actually wanted to know if your display shows that info (current or power consumption), which would be the battery current going into the controller. The phase current wouldn't be as useful, since it will fluctuate based on conditions. Also, are you saying there are only three wires total going to the motor? I'm assuming there's also the bundle of hall sensor wires going to the motor as well. Was it silent prior to a year ago?\

If your display does show current or power, try lifting the back wheel and twist the throttle to allow the wheel to spin up to max speed. The current/power consumption should be minimal (far less than 100W), so if it's high, then that would indicate something wrong with the halls or hall wiring.
 
There are typically several fault conditions that can cause a controller to shut down. One would be if a brake switch was activated. You can usually just unplug the brake connector to check this. Another one would be a fault in the motor hall signals. You can check the hall signals with a voltmeter by measuring each hall signal line while slowly turning the motor by hand (power on, no throttle). Each hall signal should toggle between around 5v and around 0v as each motor magnet passes by the hall sensor. Put the negative meter probe on the B- line when measuring. Another possible fault is throttle signal out of range, if you have a throttle. You can do the same test with a meter. The throttle signal should range from around 0.7v to around 4.3v as you advance the throttle.

It's strange that yours cuts of and then back on again at a somewhat regular interval. Some controllers have a LED on the board that will blink an error code. You have to open the controller to see it. Others may display a code on the display. If all else fails, I would suggest a new controller.
 
E-HP said:
seba240698 said:
In any case, I'll check the Hall sensor connection over this weekend. In which wire should I measure the current? There are 3 wires from the controller to the motor, green, yellow and blue.
Also, are you saying there are only three wires total going to the motor? I'm assuming there's also the bundle of hall sensor wires going to the motor as well.
Besides the 3 phase wires connected from the controller to the motor, there is a bundle of 5 wires, the Hall sensor wires, yes, they are connected.

[/quote]
Was it silent prior to a year ago?
[/quote]
Not so noticeable prior to 1 year ago.

[/quote]
If your display does show current or power, try lifting the back wheel and twist the throttle to allow the wheel to spin up to max speed. The current/power consumption should be minimal (far less than 100W), so if it's high, then that would indicate something wrong with the halls or hall wiring.
[/quote]
Yes, will check if there is current/power consumption in the display.
 
The hall sensors are the main thing that fails in a motor. If those check OK, the motor is likely good.
 
I checked the Hell wires, they are good, no loose connections.

Even when I disconnect the hall wires from the motor to the controller, the motor still works but the problem of motor cutting off and then cutting in still exists.

Should I change the controller and see how?

PS : I saw on the online website, some controllers do not have PAS connection, only throttle connection, can I buy those and connect my PAS To the throttle wires from the controller?

Some of her online forumers say yes, some say no.
 
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