Overcharging the Battery

[Adamsavage79]

I have a question about Overcharging a E-bike Battery.

As you know I decided to get a brand new E-bike. The Vendor that sells the Bike has claimed , that I've managed to overcharge the pack, and that I should not leave on the charger longer than 2 hours after the cycle is complete. I figured I would ask you guys, as I was a customer before and you of all places/people would know if this is even possible ?

I've been told by others at the same time, that overnight charging can be good, as it gives the pack a chance to balance itself. My basic knowledge and understanding of Lithium is that once the charge is complete, that's it. You cannot force more voltage to the cells.

The reason they claim this is because the pack will read 54.8V fully charged, and I'm told it should be 54.6 with 16 cells. Also, I've seen packs go a high as 56 volts, fully charged, but have a higher LVC point. I believe this was my Golden Motor 15ah Pack I had ?

Thanks for your time!

EDIT: Topic re-posted due to problem displaying posts in original topic.

[Bikemad]

The only way you can overcharge the battery is if the charger maximum output voltage was incorrectly calibrated, or you were using a charger designed for a different battery chemistry.

The actual maximum charging voltage will depend upon the number of cells in series and the chemistry of the cells, and the regulated output voltage is usually stated on the charger itself:

A charger for a 48.1V 13S LiMn battery should have a maximum regulated voltage output of 54.6V (4.2V per cell).
A charger for a 51.8V 14s LiMn battery should have a maximum regulated voltage output of 58.8V (4.2V per cell).
A charger for a 51.2V 16S LiFePO4 LiMn battery should have a maximum regulated voltage output of 57.6~58.4V (3.6~3.65V per cell).

You should not be able to overcharge your battery if you're using the correct charger, even if it is left on charge continuously for weeks on end.
However, Maintaining a battery at its maximum charging voltage for several weeks is likely to be detrimental to its longevity.

If your battery is a 13S LiMn battery and its charged voltage reading is as high as 54.8V (when checked accurately with a properly calibrated voltmeter) it is probably due to an incorrect charger (or an incorrectly regulated charger) being used.

If an incorrect charger (or an incorrectly regulated charger) was supplied with the bike, this would be the sellers fault not yours.

When I charge my 10Ah 48.1V battery, I typically charge it for at least 10 hour overnight using a 2A charger. Theoretically it should be able to fully charge a fully discharged pack in just over 5 hours (5hrs@2Amp = 10Ah).
However, unless a battery is equipped with a much more expensive active balancing BMS, the cell balancing will only begin to take place near the very end of the charge when the maximum charging voltage is reached, and balancing can take several hours (or sometimes even days if any of the cells are way out of balance) to properly balance the cells.

Most Lithium chargers use a fixed current for the majority of the charging process until the maximum charge voltage it reached, at this point it changes to a constant voltage charge where the voltage remains the same and the current slowly decreases until it reaches a very low level where it is often disconnected by the BMS.
My 10Ah battery's charger is internally disconnected at the end of a charge by the BMS, and it is not possible to charge the battery again until its voltage has dropped sufficiently for the BMS to allow the charger to reconnect.

However, neither of my two 13Ah 48.1V batteries actually disconnect the charger completely at the end of a charge, so I tend to use a plug in power meter to monitor the power being drawn from the mains socket, which eventually drops down to ~1.1 Watt when the battery is fully charged and nicely balanced. If I then unplug the charging lead from the battery, the power meter drops to 0.8 Watt, so the BMS circuitry and/or the DC/DC converter for the unused USB power outlet must be drawing ~0.3 Watt from the charger while it is connected.
The maximum battery voltage that I've measured so far at the end of a charge is 54.57V, which is close enough to 54.6V for me. 

The instructions for both of my 13Ah batteries clearly state to turn on the battery power switch during charging to fully charge the battery, which means that they cannot be recharged while fitted on the bike without the controller (and my permanently wired LED headlamp) being powered up at the same time. The strange thing is that the battery output is automatically powered up when the charging via the charging port even with the battery's power switch turned Off. 

Alan
 

[Adamsavage79]

This was I've been told on regards to overcharging and I've also posted on Endless Sphere with mixed answers. Some say you should never leave a pack on the charger overnight as it is dangerous and others say its fine. I've been doing it for years personally, on and off and never had a problem. I did find my smaller pack had improved range when I did few extended charges. That being, letting it sit on charger for several hours, after they charge cycle is complete.

Also, I'm also considering getting a charger that will only charge the battery to 80%, to help extend the life of the pack.

Here is a copy and paste of email I got, in regards to overcharging.

Yes, the BMS keeps on measuring each battery's voltage, and if it starts to exceed the allowed limits, it will shut off the charging cycle. But see the problem in what I said? it shuts off when each cell starts exceeding the recommended limits. A 3.7 V 18650 Cell is supposed to only be charged to 4.2 V, the more voltage you put in a battery, the more electrolytes that will travel from your positive terminal (Cathode) to negative terminals (Anode), having electrolytes rest on the anode will cause oxidation and will lead to an effect called plating, plating creates a layer of resistance on the anode and will therefore reduce its ability to receive Lithium from the cathode, the more this happens, the faster your fully charged battery will last. Here is a reference link, followed by a simplified version of it:

https://www.nasa.gov/sites/default/files/atoms/files/1-lithium_plating_azimmerman.pdf

https://www.upsbatterycenter.com/blog/lithium-plating/#:~:text=Lithium%20plating%20is%20the%20formation%20of%20metallic%20lithium,cause%20these%20rechargeable%20batteries%20to%20malfunction%20over%20time.

Your BMS will stop you from reaching intense voltages, but it will still get slightly higher than desired Now, if you would like to do a test to see if the battery does indeed overcharge, you can leave the battery plugged in overnight and see if the charge just before you unplug it in the morning would be higher than 4.2V, you have 13 rows built in series, therefore the battery charge should not exceed 54.6 V (4.2 V * 13 cells = 54.6 V).

Note that plating starts at 4.1 V per cell, and happens in higher magnitudes at the higher voltages.

Remember that last time you can in I told you that you can make your battery last longer by not fully charging it? This is for the same reason, by not charging your cells above 4.10 V, (4.1 V cell charge *13 series of cells =  53.3 V battery charge) you will significantly reduce the amount of plating your battery.

 Here is a slide by NASA to admire, Battery B is charged to full potential while battery A is not to exceed 4.1 V. The x-axis is the number of charging cycles, and the y-axis is the resistance, note that more resistance = less range per cycle.

Here is the Image I can't seem to upload.

https://imgur.com/vxDdFBw