m620 reduced power issue

[mcfizzlestag]

Last weekend i assembled a new ebike with a seroxat frame and a UART m620 motor. After several rides i've been encountering the power output limiting once my battery reaches around 47V (~30%). Once i hit this wall, my max power output is about 350 Watts, no matter the assist or throttle input. If i turn off the power and wait for a bit, the voltage raises above the threshold and i get a brief period before it throttles the power again.

Some basics:
Max Current: 18A
Battery: 14S6P (20.4 AH) samsung 35E cells from em3ev
Display: Eggrider v2 (tried Release and Beta Firmwares)
Controller and Motor both marked as 52V.
Typical Trip: 27km each way, charged each side of the trip

This battery has been used on a BBS02, BBSHD and CYC stealth gen3 kit and this behaviour does not happen with any of them with a similar max current (16-18A). Voltage sag is typically 1-1.5V and the V(delta) fully loaded is about 35mV, so a battery that stays balanced. Just to further eliminate the battery as the problem, i've even tried using the battery after my commute on the Ultra and am able to sustain 800+ Watts below 47V on a different motor. So essentially the Bafang Ultra has prevented me from utilizing my last 6AH of my battery pack and forcing me to charge my pack to 100% more often which shortens its lifespan.

Temperature wise, the motor has been cool to the touch, not even the temp of a BBSHD. On the way to work, i normally run in on an 80% charge and i hit the 30% mark just when i start to climb a short low grade hill right after a long 2km descent. The commute to work also is mostly pulling 400-600 watts. On the way home from a full charge, the 30% mark is hit in the middle of a 4km mountain climb, so a horrible time to be limited to 350 watts.

Is there a variable that can be set that this low power mode is based on, or is there a different firmware that just eliminates this feature?

 

[mcfizzlestag]

After multiple days of testing i've found the Power Save mode is 43% of your programmed current limit. (verified in Road Mode at 30%, Offroad still enters powersave, haven't yet verified at what percent)

Default (and maximum) Current limit is 30A, so you will get maximum current you will get is 13A (611Watts) once you pass the 30% threshold. Unless there is a firmware that disables this feature, or allows for a higher current above 30A to be set, this is the best you can do.

So if you want to still limit your current, i will recommend leaving the Limited Current: 30 Amps. Instead change your Assist levels to compensate. Ive set my Assist 9: Limited Current 60% which equals 18 Amps.

 

[smorgasbord]

Can you discuss more about "Power Save mode?" I've not heard that term used with the Ultra motor/controller before. When I saw your first post I was thinking that your 18A Max Current was the issue and that I've not seen an Ultra configured from the factory with less than 30 as its Max Current, nor why one would ever set that lower.

So, what is "Power Save mode" and how/when does it engage and how is it different in Road vs Off-Road (Sport vs Eco)? Thanks.

 

[mcfizzlestag]

Can you discuss more about "Power Save mode?" I've not heard that term used with the Ultra motor/controller before. When I saw your first post I was thinking that your 18A Max Current was the issue and that I've not seen an Ultra configured from the factory with less than 30 as its Max Current, nor why one would ever set that lower.

So, what is "Power Save mode" and how/when does it engage and how is it different in Road vs Off-Road (Sport vs Eco)? Thanks.

First off, thank you for your guide, i reference it a lot when finetuning my torque profiles and appreciate the thoroughness! still not done my tuning, but getting there

As for this Power save mode, i just gave it a name since theres so little information out there about this characteristic of the m620, or atleast this firmware revision of it (from greenbike w/ latest rotor). Reading up on the issues i've experienced, some have mentioned phrases like aggressive power saving, or others have had their battery packs blamed. It was suprising how little information i could find dedicated to this motor, especially after spending so long using the bbshd. But this is likely due to the canbus uncertainty, third party controllers and vendor specific forums spreading out information.

No one mentioned how bad it was for them as it seemed to be for me though. So i figured i'd worsened it with my programming and worked to find out just what its based on. The first variable i tried was the Low Voltage cut off, 39 and 43 both gave me the same result maximum 250W output..... Got home, huffing and puffing, charged the battery then tackled the next variable the next day, low current limit. Which is what i explain above.

Testing Scenerio:
Ride home from work from a full charge, approx 27km, with the final stretch being a mountain, 2.9km of it is climbing at an average grade of 9.25%. Normally i get to the bottom with roughly 50V of the pack left to make the climb.
I use the 37T rear cog (I have 40T chain ring), set assist level to pull 16 amps with both my pedalling and throttle held down.
The current stays constant and I monitor the voltage slowly dropping as i climb up. When i dip below 47.0V, the current automatically cuts back to 13.0A and stays there all the way home. I have checked the BMS app several times after this point to see if theres any sagging cell group out of sync with the rest, but with me only running the battery pack at 0.75C normally, sag is pretty minimal and even..
Verified in both Sport and Eco modes.
(if you dont keep the current constant, like in PAS only, you sometimes will cut out a bit early or a bit later)
thankfully if i restart the display, set the Assist level a couple notches lower, i can avoid it hitting the 47V threshold again during the steepest sections where i'd want every bit of assist i can get.

The interesting thing is, this behaviour does happen to a BBSHD and BBS02, but its at a voltage level very close to the low voltage cut off and it battery doesn't last much longer after that before kicking out. I just assumed it was due to the voltage sag going below the cut off, but it should actually have required a display restart if this was the case. This leads me to believe there may be a variable related to this that may be programmable...

Now as to why I choose 18 Amps? because thats the maximum i tend to use, and normally dial it back to 16 amps once im happy with the set up. Im 300lb person who commutes on my bike about 1000km each month every season. I live in the Pacific north west, and i have big hills and a mountain to traverse during my commute. I also use urban trails and sometimes do easy trail riding with the kids. Wear and tear is massive, so i dial back the watts where i can, make sure the motor isn't bogged down, and assist the motor to the best i can (by my day 6 of the work week, knees dont have much in them). This also allows for my battery packs to last a long time, what good is green technology if we abuse it and am forced to replace it every year. My BBSHD got me through several years of commuting, it needed a complete rebuild and it had major chain line issues... So i got a cyc stealth to avoid a completely new bike, but that motor is not meant for the watts they say it can pull, or for someone who actually rides it daily, so i asked my wife when she was sleeping for permission to build a whole new bike and her grunt of acknowledgement sounded like a yes.

 

[smorgasbord]

Ride home from work from a full charge, approx 27km, with the final stretch being a mountain, 2.9km of it is climbing at an average grade of 9.25%. Normally i get to the bottom with roughly 50V of the pack left to make the climb.

On a 52V battery, full charge is 58.8volts and 50volts would be just under 50%. That's only 17miles of "normal"? riding to drain half the battery.

When i dip below 47.0V, the current automatically cuts back to 13.0A

It's likely the BMS has its own low voltage cut-off. That said, 47v is too low for a 52v pack.
EDIT: I meant high, sorry. Cut off should be around 41 volts.

set assist level to pull 16 amps with both my pedalling and throttle held down.

Just to be clear on this, for the throttle, you choose one of your existing levels from the Basic tab for "Designated Assist." If you've chosen a different level for your PAS levels, then it's unclear to me which "wins" when you are both pedaling hard and using the throttle at full. Note that if you're already pedaling and then add the throttle and you get more power, then your settings are such that you're not achieving the max you can get pedaling, so looking at your Torque settings may be worthwhile.

So if you want to still limit your current, i will recommend leaving the Limited Current: 30 Amps. Instead change your Assist levels to compensate.

Just to re-re-emphasize, this is the standard way to setup/tune a Bafang Ultra motor. I think Limited Current is designed to protect the controller, not to control how much power the motor produces from pedalling/throttling.

 

[mcfizzlestag]

47v is too low for a 52v pack

Here's a pic attatched of the bms after the ride, I don't approach the low voltage cut off of the battery even with voltage sag under load. As to why the range seems low for its capacity, the pack is down to 80% of it's rated capacity, still not degraded near enough to retire it.

Just to be clear on this, for the throttle, you choose one of your existing levels from the Basic tab for "Designated Assist."

My settings are
Designated assist: Display Command
Throttle mode: Current.

Eggrider group replied to my inquiry about this power save/conservation setting and said it used to be customizable but Bafang locked it down in newer firmwares. They also confirmed this is normal behaviour for the m620s, so I'll likely be looking for a third party controller.

 

[Gionnirocket]

I'm not sure I understand your need for a different controller.
If you've deduced it's tied to the Global Max Current setting... why not raise your 18a max to meet your your needs?
That said I have mine set to 25a as I'll never need more than that and choose to protect the system from unintentional spikes. So far I've seen no noticeable reduction in output as my battery drains.
Additionally this is the first I'm hearing of this issue/set point and if it was customizable in the past I've never seen where in the programming or heard anyone mention it before.
Most leave the Global Max at 30a.. so that may explain why.

 

[mcfizzlestag]

If you've deduced it's tied to the Global Max Current setting... why not raise your 18a max to meet your your needs?

i did set it to 30, and its been a huge improvement. I reduced the Current Assist % to max out at at 60% essentially doing the same thing i was after. With the BBSHD their power save threshold was much much lower, so never had issues using the current limit this way.

Additionally this is the first I'm hearing of this issue/set point and if it was customizable in the past I've never seen where in the programming or heard anyone mention it before.

Dont think it was programmable in the sense we program the settings, just customizable in the firmware, which if needed, could have been accessed with the software. But with it being a locked value now, a moot point.

I'm not sure I understand your need for a different controller.

while i've been fine making it up right now, i have a knee issues from years of heavy cable pulling (joys of being my size), sometimes i need to rely on throttle more when they act up. 14.5A is the minimum current for mostly throttle only up the 11% grade portions of the commute, so if the controller is blocking me from pulling the necessary current that both the battery and the motor can support, then it is the thing i need to change. I bought my battery intentially oversizing it for my commute so when it can even get me home at when its degraded to 60-70% max capacity. The original plan was to get the HV controller kit when its done development for this motor, not to run at 72V, but for better customization of at 52V and maybe a bump to 60V down the road.

 

[smorgasbord]

14.5A is the minimum current for mostly throttle only up the 11% grade portions of the commute, so if the controller is blocking me from pulling the necessary current that both the battery and the motor can support, then it is the thing i need to change.

Instead of using "Display Command" for "Designated Assist," why not use level 9, which is set to 100% current? You can always modulate the throttle to get less output if you don't need it all.

 

[gregor_sin]

so i asked my wife when she was sleeping for permission to build a whole new bike and her grunt of acknowledgement sounded like a yes

I have to try this method

My friends and I have exactly the same symptom. A 52V battery fully charged to 58.8V can squeeze the full 30A from the motor. If the voltage drops below 48V, the controller cuts the power to 600W, this also applies to the throttle. When the voltage is below 44V, the controller completely turns off the support (about 15% of the battery remains). Setting PAS1 to 1% of 10A still does not turn on the assist. The BMS in the battery itself gives the full 30A, allows me to go down to 40V. Any changes to the PAS modes, amperage and cut-off voltage do not change anything in this aspect. Even setting the battery type to 48V does not allow the controller to turn on support below 44V. This appears to be hard-coded into the controller. I received a file with software for the M620 52V from the seller, but unfortunately I do not have the BESST tool to upload it and check if it changes anything. I can share this file if someone has the opportunity to upload it to the controller and see if it changes anything.

 

[Gionnirocket]

@ak907 ...you might end up finding a solution in this thread as time goes on.

I did a little testing on my August 2022 manufacture date M620 and I don't have this issue. 48v system and riden down to 42v with no change in motor output. I thought perhaps which display used might circumvent the issue but I got the same results with the stock Bafang DPC18 and APT 860c so as all suspect, it's baked in the newer motor firmware.

 

[napatom]

I have a similar issue with a BBSHD that I just solved today. It is a 52V - 28amp unit with a 52V 17.5AH battery rated at 40amp continuous 120-amp max. This issue I am having is when I get to around 46-47v, I get capped at 500w max. The EggRider setup that I am using is set at Current Limit 100% and Speed Limit 100% when on setting 9. I have the Low Battery Protection set at 42 volts. I could not find anywhere in the EggRider setup to set this current limit point. I contacted the vender that sold me the motor and of course he blamed it on the battery I was using. I did not purchase the battery from him. He said the issue was when the battery got to 46 volts the BMS cut back the max amp output.
Issue Solved. After several hours of research and testing I found firmware on the internet that fixed the issue. Once I flashed the motor It allowed me to set the max amps to 30amps, a bonus, and on the first test ride I was able to take the motor all the way to the cut off voltage that I have the EggRider set to. I tried three different BBSHD firmware and only one of them would let me change the max amps to 30amps after flashing the unit. I am not sure if I am allowed to post links here so if you are interested search YouTube for “Tuning the Bafang Controller with UNLOCKED firmware” by “First Timers Cycling”. On their details section they have a link to the firmware. Need a laptop and you need to make sure you have the correct motor, or you might brick it. I am not worried about the warranty time has passed and it is no longer under warranty.

 

[ak907]

I have a similar issue with a BBSHD that I just solved today. It is a 52V - 28amp unit with a 52V 17.5AH battery rated at 40amp continuous 120-amp max. This issue I am having is when I get to around 46-47v, I get capped at 500w max. The EggRider setup that I am using is set at Current Limit 100% and Speed Limit 100% when on setting 9. I have the Low Battery Protection set at 42 volts. I could not find anywhere in the EggRider setup to set this current limit point. I contacted the vender that sold me the motor and of course he blamed it on the battery I was using. I did not purchase the battery from him. He said the issue was when the battery got to 46 volts the BMS cut back the max amp output.
Issue Solved. After several hours of research and testing I found firmware on the internet that fixed the issue. Once I flashed the motor It allowed me to set the max amps to 30amps, a bonus, and on the first test ride I was able to take the motor all the way to the cut off voltage that I have the EggRider set to. I tried three different BBSHD firmware and only one of them would let me change the max amps to 30amps after flashing the unit. I am not sure if I am allowed to post links here so if you are interested search YouTube for “Tuning the Bafang Controller with UNLOCKED firmware” by “First Timers Cycling”. On their details section they have a link to the firmware. Need a laptop and you need to make sure you have the correct motor, or you might brick it. I am not worried about the warranty time has passed and it is no longer under warranty.

Awesome, when I have time I definitely am going to try this, super useful, thank you!