Motor cutouts at high load on new battery with *less* voltage sag than previous battery

tauru

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Mar 4, 2021
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Hy everyone,
This is my first post here and i hope its in the right place (please excuse my bad english). I read this topic and i have the following problem :
I have an electric scooter with 2 sensorless bldc motors. They are rated at 52V. In the atachement you have some pictures of the controllers (JP 52V 25A).
Now I have the following problem :
- the original battery was a 52V 26Ah chinese brand battery (14S10P)
- now i have a custom 52V 52Ah LG MJ1 3500mAh batteries
When i was running the original battery the voltage drop at full charge was around 3.5v (from 58.8v to 55.3v) at full acceleration and everything was fine. Now when i am running the bigger battery, the voltage drop is max 2v (from 58.8v to 56.8 - 57v), and this causes a problem : when the battery is fully charged (until it reaches 55v discharge) at every start (when i leave a stop light) the whole scooter is budging (it starts, the it stops very very briefly, and the its at full acceleration again) - this is when i press the acceleration all the way. I want to mention that you have to kick push it to engage the acceleration. After it warms up, it does the same thing, but not that bad (50%).
This does not happen if you push the acceleration lighter and after it moves a few meters you push it all the way.
The battery has a daly 14s 60A BMS with separate charge and discharge ports.

Can you give me some ideas at what the problem is, or what can i look into?

thanks in advance
 

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tauru said:
Now when i am running the bigger battery, the voltage drop is max 2v (from 58.8v to 56.8 - 57v), and this causes a problem : when the battery is fully charged (until it reaches 55v discharge) at every start (when i leave a stop light) the whole scooter is budging (it starts, the it stops very very briefly, and the its at full acceleration again) - this is when i press the acceleration all the way. I want to mention that you have to kick push it to engage the acceleration. After it warms up, it does the same thing, but not that bad (50%).
This does not happen if you push the acceleration lighter and after it moves a few meters you push it all the way.

This almost always indicates that there is too much voltage sag (drop) at the controller itself, and that it is cutting off power to protect the battery (the controllers have an internal LVC different from and higher than that in the batteries' BMS). This, in turn, is almost always caused by a poor connection between battery and controller.

Where is the sag being measured to get your numbers? If this is measured by the controller and displayed on the controller's LCD, then this is not likely the problem. If this is measured on a wattmeter or similar device right out of the battery, or on a phone displayed from BT info the BMS is sending out, then it doesn't tell you what voltage the controller sees.

Also, when it cuts out, does the controller's display (if any) stay active, or does it blank?

If you had previously had a lot of voltage sag and now had virtually none, I would suspect the controllers were cutting out from too high a power level (thermal cutout perhaps from monitoring sensors in the motor windings, for example), but since your old sag was very similar to the new sag, this is not that likley an issue--you would have had these kinds of cutouts on the highest loads like going up slopes and whatnot, as well.

But...since it stops happening when the pack voltage drops below a certain point, this could still be the problem.

Since it is *less* of a problem after warm up, it still points more towards a connection issue than anything else, as most connections issues happen less often or affect things less the warmer it is, and are worse the colder things are.

So my first recommendation is still to check the battery-to-controller connection.

My second recommendation is to see if the controller has any programmability, or settings that can be at least viewed if not changed within it's own display if it has one, to see if any of those settings relate to maximum allowed power or current. (I wouldn't change them yet, just check for them).

My third recommendation is to verify the voltage sag on the new pack at the controller itself, with a multimeter, and then do the same test at the battery itself, to see if the sag is greater near the controller, to verify that it is not cutting out because of a connection issue.


BTW, your English seems perfectly fine to me. :) I also moved your post and this reply out of the original thread into it's own, as taht one is really for a different thing, so you will get better visibility and help. :)
 
tauru said:
When i was running the original battery the voltage drop at full charge was around 3.5v (from 58.8v to 55.3v) at full acceleration and everything was fine. Now when i am running the bigger battery, the voltage drop is max 2v (from 58.8v to 56.8 - 57v), and this causes a problem : when the battery is fully charged (until it reaches 55v discharge) at every start (when i leave a stop light) the whole scooter is budging (it starts, the it stops very very briefly, and the its at full acceleration again) - this is when i press the acceleration all the way. I want to mention that you have to kick push it to engage the acceleration. After it warms up, it does the same thing, but not that bad (50%).
This does not happen if you push the acceleration lighter and after it moves a few meters you push it all the way.
The battery has a daly 14s 60A BMS with separate charge and discharge ports.

Can you give me some ideas at what the problem is, or what can i look into?

thanks in advance

Seems like some kind of current limit. The motors will pull the most amps from a standing start and/or when you peg the throttle when going slow. The new battery is able to provide more current than the old, so more current in those situations than with the old battery.
 
5.jpgThank you very much for your help.
Bellow i will try to answer your questions the best i can.

"Now when i am running the bigger battery, the voltage drop is max 2v (from 58.8v to 56.8 - 57v), and this causes a problem : when the battery is fully charged (until it reaches 55v discharge) at every start (when i leave a stop light) the whole scooter is budging (it starts, the it stops very very briefly, and the its at full acceleration again) - this is when i press the acceleration all the way. I want to mention that you have to kick push it to engage the acceleration. After it warms up, it does the same thing, but not that bad (50%).
This does not happen if you push the acceleration lighter and after it moves a few meters you push it all the way."

Here i want to mention that the scooter is in the kick push mode, this is what i meant. It also has a non kick push mode, but i consider that this is a risk factor, cause one can push on the acceleration accidentaly.

"This almost always indicates that there is too much voltage sag (drop) at the controller itself, and that it is cutting off power to protect the battery (the controllers have an internal LVC different from and higher than that in the batteries' BMS). This, in turn, is almost always caused by a poor connection between battery and controller.
Where is the sag being measured to get your numbers? If this is measured by the controller and displayed on the controller's LCD, then this is not likely the problem. If this is measured on a wattmeter or similar device right out of the battery, or on a phone displayed from BT info the BMS is sending out, then it doesn't tell you what voltage the controller sees."

The battery was made by a friend of mine. Bellow i will put some pictures with the battery. He gave me the battery without putting jacks on it. I used XT60 connectors for the battery to controller and MT60 connector for controller to motors.
The voltage drop i measure it by reading the voltmeter (attached picture) that is connected directly to the controller (through the wires that go to the main display( attached picture) that also has the trigger acceleration.

"Also, when it cuts out, does the controller's display (if any) stay active, or does it blank? "
Its improper to say it cuts out, but i cannot find another word for it. Its kind of a small jerk that i can feel. The display stays on when this is happening.

"If you had previously had a lot of voltage sag and now had virtually none, I would suspect the controllers were cutting out from too high a power level (thermal cutout perhaps from monitoring sensors in the motor windings, for example), but since your old sag was very similar to the new sag, this is not that likley an issue--you would have had these kinds of cutouts on the highest loads like going up slopes and whatnot, as well."
The problem is that my old sag (with the old battery) was double than the new sag (with the bigger battery). Can the difference of only 2 volts cause such an increase in temperature...? I think the motors can handle more, and i belive the motors do not have any monitoring sensors (attached you can find pictures of the open motor)

"But...since it stops happening when the pack voltage drops below a certain point, this could still be the problem.
Since it is *less* of a problem after warm up, it still points more towards a connection issue than anything else, as most connections issues happen less often or affect things less the warmer it is, and are worse the colder things are.
So my first recommendation is still to check the battery-to-controller connection."

All the soldering of the XT and MT connectors was done by me and they are super solid, no cold seams.

"My second recommendation is to see if the controller has any programmability, or settings that can be at least viewed if not changed within it's own display if it has one, to see if any of those settings relate to maximum allowed power or current. (I wouldn't change them yet, just check for them)."
Bellow are the settings that i can change on the controller and what i have now :
P0=10 (wheel diameter)
P1=43 (voltage cut off)
P2=17 (magnetic poles in hub motor) - by changing these you see different speeds on the speedometer - it was 16 but it was off by 5 km/h and now at 17 its off only by 1 km/h (the problems is at 16 and 17, the jerking)
P3=1 (speed sensor function)
P4=0 (its for km/h) if i put 1 its for m/h
P5=1 (for kick start) if i put 0 its for non kick start
P6=0 (cruise mode off) if i put 1 its on for the cruise mode
P7=1 (power start) and 0 for normal start (its too sluggish at normal start)
P8=100 (motor power) i can change it from 0 to 100
P9=0 (electronic brake off, at 1 is medium and at 2 is high)

The scooter is dual motor. From the test i made, this problem is only if i use 2 motors, if i ride on single motor, this jerk is not present.I did not test yet with dual motor connected and to go down on P8 and play also with P7 (i will try this later and will come back with the results)

"My third recommendation is to verify the voltage sag on the new pack at the controller itself, with a multimeter, and then do the same test at the battery itself, to see if the sag is greater near the controller, to verify that it is not cutting out because of a connection issue."
This is kind of impossible :)) i have to connect he voltmeter and the same time to ride the scooter :))

Also attached are some pictures of the bms.
Now i ask you this : is there any possibility that the controllers demands more than 60A from the bms (2x30A) even if the controllers are rated at 2x25A, and the bms cuts the power? But in this case the display should go black right? and the scooter should stop.....?

LATER EDIT :
I just came back from some tests. We have the following :
1. DUAL MOTOR, P7=1 (power start), P8=100 (motor power) > PROBLEM
2. DUAL MOTOR, P7=0 (normal start), P8=100 (motor power) > NO PROBLEM
3. SINGLE MOTOR, P7=1 (power start), P8=100 (motor power) > NO PROBLEM
4. DUAL MOTOR, P7=1 (power start), P8=90 (motor power) > PROBLEM
5. DUAL MOTOR, P7=1 (power start), P8=80 (motor power) > PROBLEM (with a 90 kg rider no problem, with me at 120 kg is a problem)
Also, the problem (the jerk) comes after you travel 3-4 meters, a fraction of a second is the jerk, then its all back to normal.

So, in my oppinion the problem lies in the controllers....what can i do with the controllers to resolve the problem? :confused:
 

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tauru said:
The voltage drop i measure it by reading the voltmeter (attached picture) that is connected directly to the controller (through the wires that go to the main display( attached picture) that also has the trigger acceleration.
OK, so the one on the trigger (throttle?) isn't what the controller itself is reading internally, just a separate meter that is reading the voltage passed thru one of the controllers.

If the display on the round blue LCD is what the controller actually reads and sends as data to the LCD, then it is what the controller itself is actually reading (at the MCU where decisions are made); if it is read and displayed by the LCD itself, then it is still just a voltmeter and doesn't tell us what the controller thinks is happening.

This means (though not that likely) that it could still be the controller stopping operations due to a momentary voltage sag issue. It is very unlikely, but without being able to know exactly what the *controller* (well, both of them at the same time) sees, then it's difficult to know for sure, until some other problem is found to cause it and is fixed. :)


Its improper to say it cuts out, but i cannot find another word for it. Its kind of a small jerk that i can feel. The display stays on when this is happening.
Then it isn't the battery itself disabling it's output, even momentarily. But the controller shutting down for whatever protection mode wouldn't shut off the display, just cease motor operation.


The problem is that my old sag (with the old battery) was double than the new sag (with the bigger battery). Can the difference of only 2 volts cause such an increase in temperature...? I think the motors can handle more, and i belive the motors do not have any monitoring sensors (attached you can find pictures of the open motor)
It's very unlikely to be this problem. But because it only happens within a certain voltage range....it could be something related to it.

All the soldering of the XT and MT connectors was done by me and they are super solid, no cold seams.
It doesn't have to be solder issues to cause connection issues. It can literally be anything between one point and another, even inside the wire.



P2=17 (magnetic poles in hub motor) - by changing these you see different speeds on the speedometer - it was 16 but it was off by 5 km/h and now at 17 its off only by 1 km/h (the problems is at 16 and 17, the jerking)
I don't know for this specific controller, but for most of them the number of poles is typically the number of magnets, divided by two (for DD hubmotors like yours, vs geared hubmotors). I count 30 magnets in the hubmotor internals picture, which means you should be using 15 to be "correct". Whether that makes it accurate or not, I don't know.

If it makes the jerking go away, it means that this setting is not *only* used for the speedometer, and is actually being used to correctly commutate the hubmotor for whatever reason, and most likely you'll need to use this as the value for that setting.


The scooter is dual motor. From the test i made, this problem is only if i use 2 motors, if i ride on single motor, this jerk is not present.
Do both controllers have the same settings, and are the motors identical?

Also, typically a problem that happens with more of a load on the system but not with less, which so far your tests all seem to indicate, is usually a problem with voltage sag somewhere. But depending on the interaction between controllers (do they actually communicate with each other?) maybe with both motors at higher power they interfere with each other.


"My third recommendation is to verify the voltage sag on the new pack at the controller itself, with a multimeter, and then do the same test at the battery itself, to see if the sag is greater near the controller, to verify that it is not cutting out because of a connection issue."
This is kind of impossible :)) i have to connect he voltmeter and the same time to ride the scooter :))

Not really, if you use something (clips, tape, zipties, etc) to secure the meter leads, and then ziptie or tape the meter to the handlebars. :) I've sometimes had to get rather creative to make measurements for troubleshooting aggravating problems. :/ But I don't think it's necessary in this case, and I don't think it would matter given the way you describe the handlebar mounted meters are already hooked up.


Now i ask you this : is there any possibility that the controllers demands more than 60A from the bms (2x30A) even if the controllers are rated at 2x25A, and the bms cuts the power? But in this case the display should go black right? and the scooter should stop.....?
If the BMS cut the power, the displays would shut off. So while it's possible (and normally this is the problem this kind of thing indicates) the controllers are drawing more current than expected, and voltage sag is greater (perhaps only for an instant, and isn't visible on the displays you have, perhaps because their refresh rate is slow?)...it's almost certainly not the battery actually shutting off.
 
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