Inmotion V5F BMS charging behavior

[OzMek]

I checked their website, and found that the quiescent current is about 10mA. This is huge compared to the 10µA of the ETA3000. I did a test by exhausting the battery completely (I mean as much as you can, when the wheel switches off the battery and you have to plug in the charger to re-enable output.

Interestingly, after strong current inrush, this triggered balancing on several lines, for a few minutes. Let me call this "Low level balancing".
After that, once all leds were off again, I charged the battery as usual and achieved this : 83,5v full charge, much better than the previous 78-79v this battery was able to reach. I monitored the balancer during the full charge, no balancing has been triggered on any couple of cells.

And then I had a full tour, and ran more than 20 km (20,5 precisely) on my usual route. It almost doubled the mileage I can run, this is really good to me (my weight 77kg). I'm definitely convinced by this balancer approach. 0,5 v is approx 0,025v par cell. Sure that I would prefer a good 84v, but I'm not sure it's a big loss compared to 84v, and this is definitely economical to "refresh" the battery :-) (20€ for balancer+shrink tube, not including the workmanship).

Thank you for reading and happy rides
Emmanuel

 

Edited September 13, 2023 by OzMek

[OzMek]

Woohoo, the last charge reached 84v !

I thought the benefit of this balancer would requires several cycles, my experience tends to prove this.
Situation is much better with than without, but I can see the battery is quite worn as the voltage sag is important when climbing a steep slope.
I would like to have a measurement of the internal resistance, but I don't have the tool.

[v8nice]

Hi Ozmek, these results are excellent. I will eventually consider a system like yours, apart from the mounting support and the sealing it would be within my skills. Concerning the voltage drop during high demand I have the same problem on  mine which is 4400km and 7 years old, it's really the internal resistance which is bad. Have you compared the value announced in the application and the real value on the battery with the multimeter? Because at inmotion, the voltage measurement is often  poorly calibrated, sometimes it is more than displayed, sometimes it is less than displayed.

[zaqimon]

My V5F was unable to ride a week ago after charging. When it's turned on, it tilts backward and alarms "low battery" repeatedly. Currently my V5F can only be charged to 88%, voltage is 80.7V, mileage is over 5000km in the Inmotion App. My V5F has been used for more than 4 years without any major problem and I never disassembled it beside changing the tire. I rarely discharged my V5F battery lower than 30%.

I have removed the battery pack and check voltage with my multimeter. Total voltage is 78.6V, which is lower than the voltage displayed in the App. 19 pairs of cells are 3.92V~3.93V, only one pair is 3.85V~3.86V. Is this single pair of cells the problem of "low battery" alarm? What's the easiest way to fix it. I was thinking just charging up that single pair of cells a little bit might fix the problem!?

I also found some tiny rust stain on the BMS board. I guess some water might have been leaked into the battery pack!? But I don't think this is the root cause of "low battery" alarm. I don't know electronics, but I think my BMS board looks just fine.

[zaqimon]

I measured the output voltage of my V5F charger, it's 81.2V. It seems the voltage is too low. Maybe this is the cause of "low battery" alarm!? Because the battery voltage seems to be fine, only one pair of cells has slightly lower voltage than the others. Maybe the BMS of V5F has some sort of balancing capability!? I don't know. I'll try to adjust the output voltage of my V5F charger.

I also have a V8S charger, which seems to be the same one as the V5F charger, the only visible difference is the connector. I also measured the output voltage of my V8S charger, it's 83V, still lower than 84V.

I also measured some random power adapters to check if my multimeter is functioning correctly. I measured a 5V adapter, the measured voltage is 5.04V. I measured a 19V adapter, the measured voltage is 19.16V. I measured AC socket voltage is 112V. I guess my multimeter is fine.

[Chriull]

14 minutes ago, zaqimon said:

I measured the output voltage of my V5F charger, it's 81.2V. It seems the voltage is too low.

Yes! Without the charger providing more voltage the battery can't charge higher.

14 minutes ago, zaqimon said:

Maybe the BMS of V5F has some sort of balancing capability!?

Seems it has not

14 minutes ago, zaqimon said:

I don't know. I'll try to adjust the output voltage of my V5F charger.

+1.

As the difference from your Voltmeter and the mainboard measurement seems to be 2,1V try first to adjust it to 2,1V below 84V and look what the motherboard reports after a full charge. If on goes over 84V motherboard reported voltage one could risk overvoltage alarms. 

14 minutes ago, zaqimon said:

I also have a V8S charger, which seems to be the same one as the V5F charger, the only visible difference is the connector. I also measured the output voltage of my V8S charger, it's 83V, still lower than 84V.

So easiest to try a charge with this charger! 

 

[alcatraz]

You are way way way past most riders by measuring your cell groups. Well done.

Fix your charger and charge that single cell group to match the rest. Wheel fixed!

If the bms has snail pace bleed resistors for balancing it will take an eternity to sort out that imbalance. If you don't want to wait hook up a 4.2v single cell charge/power supply to that one group and set a timer. When it's at 3.93v like the others you're done.

It's better to balance like this below 80% charge level because any single cell charger slows down to snail pace if you're aiming to balance at 4.2v.

[alcatraz]

(Not every time, of course. Just like now when you have a near 0.1v imbalance which will take a long time, possibly forever, for the bms to sort out.)

[alcatraz]

A 4.2v single cell charger is often  what you get with every dirt cheap Li-Ion device. You can hook that up to the cell group.

They come with like portable lights, razors... Anything with a 4.2v battery in it that doesn't take regular usb but a proprietary adapter. 

Check that they're 4.2v before hooking up.

If you want to order one they're like 50cents off ebay and you get high current 3A and the input is usb-c. It's a tiny naked board. It needs a custom cable.

[zaqimon]

I've manually balanced all pairs of cells. I also increase the output voltage of the power adapter. But still no luck. I guess there're some bad components on the BMS, which is beyond my capability.

I can somehow trigger the BMS to charge for about 1 minute and then it stops charging on its own. The LED on the power adapter turns green. I have to connect the battery pack to the main board, press the reset button for more than 3 seconds to reset the BMS, which also turns off the battery output from the BMS. Then I disconnect the battery pack from the main board. Then I can plug in the power adapter to charge the battery pack for 1 more minutes.

While charging, everything looks fine. The power adapter draws around 135W from the socket, the LED on the power adapter turns red, and the voltages of battery cells also increase after charging. But the charging will stop on its own after about 1 minute.

I also found the middle part of the BMS always a little bit warm. The voltage of the battery pack also dropped 0.4V each day(0.02V for each cell). I don't know if this is normal?

[Chriull]

1 hour ago, zaqimon said:

I've manually balanced all pairs of cells. I also increase the output voltage of the power adapter. But still no luck. I guess there're some bad components on the BMS, which is beyond my capability.

I can somehow trigger the BMS to charge for about 1 minute and then it stops charging on its own.

Increasing the output voltage of the charger a bit too much could cause the bms to cut off because some single cell group voltages exceed the threshold of something around 4.25-4.3V.

1 hour ago, zaqimon said:

The voltage of the battery pack also dropped 0.4V each day(0.02V for each cell). I don't know if this is normal?

Each single cell group with a voltage above 4.2V gets discharged downto 4.2V again after charging. That's a main part of passive balancing. Afair it's reported here that if this happens at all by the V5f Bms the cells could only be discharged by way the high resistors...

Otherwise li ion cells settle to some "equilibrium" voltage over time. The higher their voltage, the faster.

Could also be some normal/higher self discharge? 0.02V drop er cell imho does not sound unrealistic for the first day after a full charge? Especially if this was not a saturation charge but prematurely cut off by the bms.

Or some drain by bms/ motherboard?

Is this drop  drop constant for the following days?

Edited April 10 by Chriull

[zaqimon]

Currently my battery is only 65%, 77.4V in the inmotion APP. I also measured with my multimeter, the battery pack voltage is 77.5V, each cell is the same at 3.87V. I already manually balanced my battery pack.

[zaqimon]

I measured the power adapter output voltage is 83.2V.

[zaqimon]

10 minutes ago, Chriull said:

Is this drop  drop constant for the following days?

Yes, the battery pack voltage drops around 0.4V day by day with nothing connected.

[Chriull]

19 hours ago, zaqimon said:

I measured the power adapter output voltage is 83.2V.

Sounds good.

19 hours ago, zaqimon said:

Currently my battery is only 65%, 77.4V in the inmotion APP. I also measured with my multimeter, the battery pack voltage is 77.5V, each cell is the same at 3.87V. I already manually balanced my battery pack.

Are the cells still balanced after charging?

20 hours ago, zaqimon said:

I can somehow trigger the BMS to charge for about 1 minute and then it stops charging on its own.

So no charging possible at all but this 1 min intervalls?

19 hours ago, zaqimon said:

Yes, the battery pack voltage drops around 0.4V day by day with nothing connected.

That's quite much! Should drain the battery from full to empty in about 1 1/2 month...

Seems something is really very wrong with your battery.

[alcatraz]

21 hours ago, zaqimon said:

I've manually balanced all pairs of cells. I also increase the output voltage of the power adapter. But still no luck. I guess there're some bad components on the BMS, which is beyond my capability.

I can somehow trigger the BMS to charge for about 1 minute and then it stops charging on its own. The LED on the power adapter turns green. I have to connect the battery pack to the main board, press the reset button for more than 3 seconds to reset the BMS, which also turns off the battery output from the BMS. Then I disconnect the battery pack from the main board. Then I can plug in the power adapter to charge the battery pack for 1 more minutes.

While charging, everything looks fine. The power adapter draws around 135W from the socket, the LED on the power adapter turns red, and the voltages of battery cells also increase after charging. But the charging will stop on its own after about 1 minute.

I also found the middle part of the BMS always a little bit warm. The voltage of the battery pack also dropped 0.4V each day(0.02V for each cell). I don't know if this is normal?

Whatever gets warm is part of the circuit that drains your battery. In an attempt to reascue the bms you can try to manipulate that circuit or try to disable it. See what happens. How about some pictures?

[zaqimon]

I think my V5F BMS is faulty. I may need some luck if I could find someone willing to repair my BMS.

Yes, my battery cells are still well balanced after several intermittent charging.

I asked someone familiar with EUC, he said, the battery module should be able to charge alone when a power adapter plugs in, aka the LED indicator turns red on the power adapter, without needing to connect to the main board. But I have to push the reset button on V5F for more than 3 seconds and wait for some time, then the battery module is able to be charged again for another tens of seconds to a minute. I guess there're some bad components on my BMS, which take some time to dissipate energy even after I reset the BMS, and which also trigger the BMS to stop charging after a short period of time.

He also said Inmotion is reluctant to sell the V5F BMS board alone. They sell only the whole battery module now. So it's hard to find a new V5F BMS.

I also found why my BMS keeps warm at the middle section. Because after I measured the BMS with my multimeter, it somehow triggers the BMS to leave "reset state", and starts the voltage output on P-/P+ pins. I also don't know how to turn off the BMS without connecting to the main board. If I leave the battery module in the "reset state", aka no voltage output on P-/P+ pins, then the whole BMS stays cool. So if you're not going to ride your V5F for a long time, it's better to press the reset button for more than 3 seconds to truly turn off the BMS, your battery will last longer in the "reset state".

I also found a youtube video fixing V5F BMS. Doesn't seem like an easy job, but he finally fixed it.

 

Edited April 12 by zaqimon
typo

[Chriull]

16 minutes ago, zaqimon said:

So if you're not going to ride your V5F for a long time, it's better to press the reset button for more than 3 seconds to truly turn off the BMS, your battery will last longer in the "reset state".

"Normal" wheels do not drain batteries. Just some ill designed like the Z10, adair some begode with power distribution boards and some ks with firmwares that do turn on the mainboard after charging...

[zaqimon]

Does anyone know this thermistor model on the V5F BMS? There seems to be something wrong with this thermistor. The resistance values vary greatly every time I measured. My room temperature is about the same, the resistance values are sometimes around 60 ohm, sometimes greater than 600 ohm, sometimes around 100 ohm. I also measured different parts of the same trace to rule out bad contact situation, and the resistance value was sometimes stable and sometimes widely fluctuating.

I guess maybe the bad thermistor is the reason for "low battery" warning and the inability to charge. Maybe the bad thermistor's low resistance value triggered overheating protection on the BMS.

After experiment, this is a 100K ohm NTC thermistor. If resistance below 25K ohm(aka. temperature too high), BMS stops charging.

Edited May 2 by zaqimon
answer to myself

[Chriull]

8 hours ago, zaqimon said:

I also measured different parts of the same trace to rule out bad contact situation, and the resistance value was sometimes stable and sometimes widely fluctuating.

If you did not remove the li ion cells from the bms you did try to measure resistance in a live circuitry which will not work out. The changing values could be the ohmmeter trying different ranges? 

8 hours ago, zaqimon said:

the reason for "low battery" warning and the inability to charge

Low battery warning should normal be single cell (groups) beeing below some 2V. Did you measure the li ion cell voltages? 

[zaqimon]

My V5F is back and riding normally. The 100K ohm NTC thermistor on the BMS is bad, just replace it.

My V5F has more than 5000 kilometers mileage. The battery is still in good shape.

This is the battery used in my V5F - EVE ICR18650/26V 2.55Ah
https://secondlifestorage.com/index.php?threads/eve-icr18650-26v-cell-specifications.8390/

 

Edited May 7 by zaqimon