Battery Charging Pattern

[peterh_nz]

After having observed the in-bike charging pattern of my dual 500WH battery bike I decided to do some measurements to quantify the process.

Some of you may be interested in the result.

It seems that up to about 85% charge each battery is alternately charged in large steps. Above 85% both batteries are either charged together or in small alternating steps.

The power supply (230V AC) current to the charger was about 1.6A until the batteries reached 100% charge. After the fully charged point the current to the charger decreased, reaching near to zero after about 45 minutes. Presumably the post fully charged phase was to do with battery cell equalisation.

The recorded pattern is illustrated here:

(ideally I should have started recording the charging process earlier)

 

[Sparky731]

Yours is an excellent graph and description of the charging pattern. Thank you for your science.

I am a true believer in having a fresh, full charge on my 2 batteries every morning. As you can surmise, that last 15% when current is dropping, the batteries are being balance-loaded. It takes longer to top-off each cell with a full load of electrons, I like the idea of balance use and balanced charging.fully

Just as an FYI, my batteries do not match — one 625w & one 500w -- but they both load fully with each charge cycle. Smart power systems!

 

[fooferdoggie]

thats interesting since Bosch hides so much if the info. or just does not make it available.

 

[peterh_nz]

Yours is an excellent graph and description of the charging pattern. Thank you for your science.

I am a true believer in having a fresh, full charge on my 2 batteries every morning. As you can surmise, that last 15% when current is dropping, the batteries are being balance-loaded. It takes longer to top-off each cell with a full load of electrons, I like the idea of balance use and balanced charging.fully

Just as an FYI, my batteries do not match — one 625w & one 500w -- but they both load fully with each charge cycle. Smart power systems!

Thanks.

Sometime soon I'll extend the graph to the left by recording the charging pattern starting with lower battery levels.

 

[fooferdoggie]

do the lights on the battery go off on that last part?

 

[Solarcabin]

It is actually the battery BMS that controls charging and discharging.

"By calculating the state-of-charge, a BMS takes charging and discharging under control and thus protects the battery from premature capacity loss and prolongs its lifetime. Estimating the state-of-health is another important BMS function that helps users enhance the performance of their batteries."

Battery management system: SoC and SoH Estimation Solutions

Measuring battery SOC and SOH is an essential BMS function. Learn about reliable SOC and SOH estimation methods that we tried out in real-world projects

www.integrasources.com

Your chart shows how the BMS reads the cells and if your battery is not close to full it will allow the charger to run at full watts.

As it reaches peak it reduce the watts and as it its full it will shut off the charger.

Now the problem exists when you use short charge cycles and don't completely charge you can get a cell stuck at below full capacity and the BMS will read that battery as full when it is not.

That is why you should do a full charge and leave the battery on the charger for an extended period about once a month so it rebalances the cells. Opinions vary but recommend 10-15 hours. Do not do that if battery is damaged or is overheating.

The BMS will read each cell and over an extended charge will allow a trickle charge to bring all cells up to full capacity.

The old 20-80 rule is not applicable to ebike batteries and is left over from LIFEPo4 technology used for battery bank storage for solar power like used at my off grid cabin.

Yes, if you only discharge to 20 and recharge to 80 you will get longer life but you are greatly reducing the range and some high torque ebikes need a full battery to employ that torque. You are also not really extending the life that much because you will likely have to charge more often and you are maybe gaining 1 cycle for every 5 recharges.

I would rather have a full healthy battery and full range and torque and sacrifice some cycles at the end of life.

How Do You Rebalance An EBike Battery? (Explained)

How Do You Rebalance An EBike Battery? this question relates to the performance of the electric bike battery, so it is very important for us as electric bike riders, but

electricbiketricks.com

 

[peterh_nz]

do the lights on the battery go off on that last part?

Haven't monitored the on-battery lights.

I know the bike's tail light comes on when charging reaches 100%. A good visual indicator of charging completion.

 

[fooferdoggie]

Haven't monitored the on-battery lights.

I know the bike's tail light comes on when charging reaches 100%. A good visual indicator of charging completion.

I have never charged the batteries on the bike but that makes sense on the lights on the internal batteries. . I usually turn off the charger a bit after its done

 

[peterh_nz]

Just to clarify: the 100% charge level is reached at 00:00 on the time line. The current of the AC supply (yellow line ) is more or less constant until then.

 

[m@Robertson]

@Solarcabin is recycling advice from other threads where he made identical and equally wrong posts about battery chemistry. This was pointed out to him by multiple people who actually read the links he was posting (which he knows not to this time) and noticed his claims did not apply to ebike batteries.

The 20/80 'rule' is very much applicable to ebike batteries and has nothing to do with LiFePo4 batteries. Interestingly, since LiFePo4 is so much more tolerant of being left in a high state of charge, and is also much more tolerant of taking a full charge in the first place, thats the one li-ion chemistry coming into common use (in solar generators) that does NOT need the 80/20 rule. So his pattern continues of wrong answers that are wrong in multiple ways.

Back on topic: That charge curve sure looks like CC+CV mode (CC=Constant Current, CV=Constant Voltage), which is commonly used in li ion chargers and is often referred to as 'smart charging'. This mode resides in the charger itself. It delivers the requested current (amps) so long as the battery with the load added by the charger current is below the target voltage on the pack. Lets say its a 48v pack so that means a 54.6v result is a 100% charge. As the voltage reaches the final target, the charger slowly decreases the current (amps), which deceases the voltage level on the line to less than 54.6v. It will keep slowly ramping the amps down a tenth of an amp at a time until you see it wiggle between 0.1a and 0.0a a few times and at a certain point the charger will consider that a complete charge and you finally see a charge completion indicator.

When you see it hovering from a full charge back to 0.1a or 0.2a and then reading complete again... then back to 0.1 etc. that is the BMS kicking in and bleeding off some power/voltage from the cells with a higher charge state. Thats what the BMS does. It apportions power to low cells once the pack nears the 100% charge state. It also shuts off the pack's acceptance of power if the charger malfunctions and doesn't ramp down to the proper target voltage. But before that happens, the BMS is not involved (although it will also kick in if max charge current is exceeded).

If you have a charger that has detailed voltage and amperage readouts on it, this is a lot easier to visualize and make sense of. The Cycle Satiator has graphs and the whole bit built in to a little gui screen. A lab power supply will show the same thing out to three digits. Or just a simple watt meter.

 

[m@Robertson]

CC+CV is explained far better here (link below). Its easy to see why chargers do this.

Here's a graph of the charge curve from the article. You can see why I thought of the similarity to your curve. Note the 'CC' and 'CV' portions on the time axis.

https://www.researchgate.net/figure/Charging-curve-of-the-CC-CV-method_fig1_330030193