Bike dies driving downhill

[jai134]

When my motorcycle is fully charged it cuts out power when I fully release throttle going downhill. Problem disappears after a short while. I always go downhill when it is fully charged because I live on top of the hill I think the problem lies in the BMS settings because I have another BMS and I don't have any problems when i use that one, only problem is that I can't use it because its not CE certified. I haven't enabled regen in controller settings so it shouldn't be overcharge protect but I can't think of another explanation. Any good ideas?
I have a Daly 14S 48V 250A BMS and a Kelly kls 72501 controller.

 

[E-HP]

Can you monitor your voltage while going downhill? Does it rise above 54.6V?

 

[dominik h]

Does your BMS stop the charging or does the charger ends bevor the BMS cuts off?

I have my charger set to 87.5V and the BMS to 88.2V. If I set my charger to the point where the BMS shuts off, than with a very little amount off regeneration the BMS will cut off power again.

Try to turn your charger a little down and your problems might be gone.

Some controllers do a very small amount of regeneration even when it is not set in the parameters.

Can you see in the App from the BMS what is going on during your downhill ride?

 

[Chalo]

A direct drive motor charging the battery when its back EMF exceeds the battery's resting voltage isn't the same as regen braking. It's a passive phenomenon rather than an intentional feature like regen braking (which requires voltage conversion in the controller). I think that's what's happening.

I'd try charging to say 4.05V/cell instead of 4.2V and see if the problem goes away.

 

[jai134]

Ok. Thank you! I dont think I can change anything in my charger but I will ask the support if its possible

 

[offGridDownUnder]

Ok. Thank you! I dont think I can change anything in my charger but I will ask the support if its possible

Can you view the voltage while charging?

On my set up, I can have the power on with the voltage displayed while charging - and I can stop charging at 85%. You may be able to do this to under charge.

BTW, it is dangerous to leave the charger on overnight or unsupervised at all - not all chargers are smart enough not to over run the battery management.

 

[amberwolf]

BTW, it is dangerous to leave the charger on overnight or unsupervised at all - not all chargers are smart enough not to over run the battery management.

The charger doesn't require any "smarts" if the BM is designed and operating correctly. It simply shuts off when current drops below a preset limit (usually a few mA, sometimes a few dozen mA). As long as it's termination voltage and current limit is correctly set for the pack it's charging, it will just do it's job as long as the charger itself is operating correctly, and stop when the BMS disconnects it from the battery--that's all it has to do.

The BMS does all the "thinking" and monitors the charging process, shutting off the input if any limits are reached/exceeded.

If the BMS fails to do this, the charger isn't normally designed to make up for that--I can't think of any offhand that do. Even the Satiator (the smartest charger intended to be used with a common BMS I can think of)


When you get into less common BMS designs that have communication between BMS and charger, or other systems where the charger is directly involved with the pack at cell level, the charger becomes the BMS as well, and is more complex and has more jobs to do, so has to have more smarts. But that's not generally the case, and is probably not hte case for this thread's system either.


It can still be dangerous to leave a system charging unsupervised...but not necessarily because of the charger itself, rather becuase of the BMS not doing it's job (design flaw, defect, failure), or because of a cell having a problem that the BMS can't detect due to pack / BMS design, etc. Both of those have caused fires (well, suspected to, as there isn't usually enough left to actually diagnose). :/

 

[jai134]

Yes I can view what happens during charging, I use the "Smart BMS" app from Daly and it is working well. I can stop charging whenever I want but then I will need to stand by the side of my bike and watch the app to know when to stop the charging. It would be better to have it automated.
I dont charge overnight, I don't need to.

 

[jai134]

If I stop charging at 57.1 the problem is gone so now I need a new charger or get to know how to lower the cut off value.

 

[amberwolf]

There are "voltage protection relay" modules people have used for this; I couldn't find one of the specific ones in a quick search of threads, but I know they are there.

A quick google found similar items like this that does HVC *and* LVC, but you wouldn't need the LVC part.
https://www.aliexpress.us/item/2251832829100395.html
If their onboard relays aren't able to handle the cahrge current you have, you could use that relay to drive the coil of a bigger one.

Just put the relay contacts between your charger's output and the battery's charging input.

 

[TommyCat]

The BMS does all the "thinking" and monitors the charging process, shutting off the input if any limits are reached/exceeded.

I have a different view of this…

I believe it’s the chargers responsibility to stop the charge at the desired maximum voltage that the pack considers a full charge.
With the BMS to act as a safety to keep the battery pack from overcharging.
You never want to depend on a safety for control.
Mainly thinking of typical non-programmable BMS’ here…

I can't understand how a 14s pack @ 48 volt nominal can be in such a high voltage charge range...
These two don't seem to fit together. Battery chemistry?

 

[E-HP]

A direct drive motor charging the battery when its back EMF exceeds the battery's resting voltage isn't the same as regen braking. It's a passive phenomenon rather than an intentional feature like regen braking (which requires voltage conversion in the controller). I think that's what's happening.

I'd try charging to say 4.05V/cell instead of 4.2V and see if the problem goes away.

Off topic. I've wondered about this. Since the motor only see the forward EMF being provided via the controller, would this phenomenon of energy flowing in reverse happen any time the back EMF exceeds the forward EMF provided to the motor, and not necessarily the resting voltage of the battery? My old KT controller, that had brake lever regen, exhibited this phenomenon when throttle voltage was below the normal throttle range, but above 0V. I wired a switch and voltage divider that would keep the low throttle voltage above 0V and I could use the throttle to control the phenomenon and provide slide regen braking in the lower throttle range. Seeing your statement above makes me think that's what was happening. At 0V, the controller would disengage, and the motor would coast.

 

[amberwolf]

I believe it’s the chargers responsibility to stop the charge at the desired maximum voltage that the pack considers a full charge.

Well, yes, but the charger still doesn't require any smarts for this. All it needs is to be a normal charger that is set to the correct final charge voltage, and has the correct termination-current so that when current drops below that threshold, it shuts off when both conditions are met. Most common Lithium-battery chargers (for ebikes, etc) do this.****

But the charger itself can't tell if a cell is overcharged, etc.; the BMS has to do this. ******

If the charger and BMS are in communication of some form (even an enable/disable line) then the BMS can tell the charger to stop, and some systems do this...but only ones that are integrated together, and for those you have to use the specific charger / BMS pair designed to work together (or be ready for some potentialy serious DIY).

But otherwise the BMS has to break the connection between charger and pack when any limit is exceeded.

only problem is that I can't use it because its not CE certified.

I would bet you that the Daly is not, either. Do they list a traceable certification document you can go look up at a central CE authority?

Many parts and systems of many kinds these days are marked with certifications they do not have because it means someone will buy them that way when otherwise they would not have.

Marketing...

With the BMS to act as a safety to keep the battery pack from overcharging.
You never want to depend on a safety for control.
Mainly thinking of typical non-programmable BMS’ here…

True, but...in these minimalistic cheap systems, it's almost unavoidable without adding expense and complexity and more DIY for the end-user, many (most?) of whom are not willing, qualified or capable of safely doing the work and making sure it's doing the job it needs to do. :/

I can't understand how a 14s pack @ 48 volt nominal can be in such a high voltage charge range...
These two don't seem to fit together. Battery chemistry?

I don't see any excessive voltages listed in this thread for the OP's pack?

A 14s pack should be about 52v nominal, typically, assuming a non-LiFePO4 chemistry. (13s is typically around 48v nominal).

The 14s pack typically charges up to around 58v, depending on the final max charge voltage of the cells (some are 4.2, some 4.15, etc).

The 12s pack typically charges to around 54v.



**** There are some chargers that do not have a shutoff current but instead just a max voltage; they're not as "safe" to use if the BMS doesn't do it's job.

Some have a shutoff current too, but a latch that keeps it off afterward until disconnected/reconnected or even power cycled, and this used to be so common with LiFePO4 chargers that it was a common design to have a little board installed on the LFP chargers that latched the output off once max voltage was reached. But some packs wouldn't balance because of this, so you could break the little board off and remove the latching, so that it would operate just like the non-LFP chargers that allowed normal balancing where the pack cuts off input so charger shuts down, then pack reallows input and charger starts again, etc.



****** This excludes systems like RC chargers that actually connect to every cell and monitor them directly, but most systems using those don't use a BMS at all.

 

[jai134]

Yes, the charger cuts off and it does that at 58.8V. They asked before building it and I wanted it that way. Didn't know better..
I can lower the charging overcurrent param in the BMS settings but that only lowers the point where it cuts out power so problem persists.
I got a certificate, or a photo of a certificate to be correct so you're probably correct, Amberwolf.
The main problem is, I think, that the Daly BMS I have to use, because of the registration process, works like this and cuts off power, my JBD BMS works a lot smoother.
I opened my charger and there's no adjustable potentiometer so for now I will manually stop charging at a lower voltage until I fully understand what I need to do. I have to ask a friend about the relay so I buy the correct one. I'm not really sure what to look for..

 

[amberwolf]

I can lower the charging overcurrent param in the BMS settings but that only lowers the point where it cuts out power so problem persists.

It isn't overcurrent you want to change, it is the HVC by whatever name they use--the per-cell charging shutoff voltage.

If you adjust those, you probably also have to adjust the balance start and end points and the charge restart point as well, unless it automatically adjusts those to match.

The main problem is, I think, that the Daly BMS I have to use, because of the registration process, works like this and cuts off power, my JBD BMS works a lot smoother.

What does "smoother" mean, specifically?

As a note, all BMSes can do is to shut power off completely when a limit is exceeded. They cannot modulate power (that's what your controller is there for, and to do that job it requires the controller's complexity and hardware, or that of an SMPS / DC-DC converter capable of the full worst-case power level of the entire system)

If a system has integrated BMS and controller communications, so the BMS can tell the controller a limit has been exceeded, the controller can then do what it's been programmed to do for that situation, such as rolling back power, etc. I don't know of any of those outside of OEM EVs that can do this; it requires the two be developed together and integrated in software and hardware.

But a BMS, by itself, like those you have there and every standalone BMS out there, can only enable power output full on, or disable power output full off.

 

[jai134]

It's happened only once that my JBD BMS did cut off and that was when I pushed it a little too hard during accel. With Daly it has happened several times. (I've had a little too low max A setting.)The difference is that I don't have to stop and restart the system with JBD which I do need with Daly.
I'll have a look at the params and see if I can understand what you are saying about cell charging shut-off value.

 

[jai134]

It looks like this. Do you mean a higher "Cell volt high protect" value? Isn't that a bad idea?

 

[E-HP]

If I stop charging at 57.1 the problem is gone so now I need a new charger or get to know how to lower the cut off value.

Insert three diodes in series with the positive charging conductor to get to your desired voltage.

 

[amberwolf]

It looks like this. Do you mean a higher "Cell volt high protect" value? Isn't that a bad idea?

You would use a *lower* value, so that your charger is forced to stop sooner, because the BMS would turn off the charge port once cells reach that value.

If you have a common port BMS where charging and discharging run thru the same port, then it will also shut off sooner doing regen braking that's charging the battery.

If you have a separate-port BMS where regen goes thru the discharge port and is uncontrolled, then it will not shut off doing regen braking but it will shut off the charger during charging.

 

[jai134]

If you have a common port BMS where charging and discharging run thru the same port, then it will also shut off sooner doing regen braking that's charging the battery.

So, if I understand you correctly, my problem will stay?
I think I change BMS after the registration.