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MattD

MCM5 Battery Fluctuating

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Hi guys, hope i can get an opinion on what i believe to be an issue with my relatively new MCM5.

I charged it to 100% the other day and took it for a ride. I seemed to get a momentary over charge tilt back nearly immediately on a small hill outside my house (hasnt occurred before and i ride the hill nearly daily). 

I started watching wheel log and my battery is going from 100% to 50% and back up extremely quickly. Meaning i am getting low battery tilt back within a few 100 meters (albeit at 30kph). 

I havent had any issues at all and was loving the wheel until this happened. 

Any ideas? I could post / send my wheel log if that helps identify any theories. 

Thanks for any help you can give.

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6 minutes ago, MattD said:

I charged it to 100% the other day and took it for a ride. I seemed to get a momentary over charge tilt back nearly immediately on a small hill outside my house (hasnt occurred before and i ride the hill nearly daily). 

If the fully charged wheel gets additional charge by regenerative braking (going down a hill) that's quite "normal".

What voltage is reported after fully charged?

6 minutes ago, MattD said:

I started watching wheel log and my battery is going from 100% to 50% and back up extremely quickly. Meaning i am getting low battery tilt back within a few 100 meters (albeit at 30kph). 

100m after having it fully charged?

Which capacity (Wh) has your battery?

6 minutes ago, MattD said:

I havent had any issues at all and was loving the wheel until this happened. 

How long do you have it already? About how much km ridden?

6 minutes ago, MattD said:

Any ideas? I could post / send my wheel log if that helps identify any theories. 

Maybe. 

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Wheellog is showing charge is 84 volt as expected at 100%. It is the 800wh version.

I have done around 80km on the wheel in the last 3 weeks without experiencing this until yesterday. It was very strange.

Charge is disappearing and reappearing depending on down hill or flat in moments. I will try and attach a log of a quick ride today. 

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6 minutes ago, MattD said:

Charge is disappearing and reappearing depending on down hill or flat in moments. I will try and attach a log of a quick ride today. 

Charge is calculated from the voltage measurement - so fluctuations between different burden situations are normal. Down from 100% to 50% sounds a bit much with an 800Wh battery.

Maybe it was around 75%, went shortly down to 50% going uphill then up to 100% by regenerative breaking going downhill again?

9 minutes ago, MattD said:

I will try and attach a log of a quick ride today. 

Great!

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The battery % is just the voltage. It fluctuates (drops) under load, that is normal.

But what you describe does not sound normal! Low battery/voltage tiltback with a fully charged wheel after 100m?!

Are both batteries connected (maybe the connection of the bigger one got loose and you only run on 20 cells instead of 60?). Maybe something's wrong with the battery. I'd be very careful with riding the wheel until you figure out what is going on.

Where did you buy from, maybe the seller can help.

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attached is the log of the short ride i took. It goes down hill for roughly halfway, then flat, then a small down hill at the end. it is only about 1km long total. You can see in the middle section my battery hits 50% at one point, despite starting at 90. As it is down hill to start and i used to get bad cut outs on an old ninebot, i religiously watched the app when i first got the wheel. And this is definitely not normal. The tilt back at 30off kph is not severe, but subtle. Also seem to be getting a more often high amp alarm, such as when just hoping up a driveway. 

The one odd thing that occurred before this is i did get a crackle when either installing or removing the charger immediately before i noted the problem. The wall socket was off at the time, so i didn't think it would have been possible to damage anything. 

in regards to seller, not sure how i will go. There is no dealers in Australia, so was purchased off Ebay... (buyer beware??)

2019_08_07_16_49_41 - Log.xlsx

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7 hours ago, MattD said:

attached is the log of the short ride i took. It goes down hill for roughly halfway, then flat, then a small down hill at the end. it is only about 1km long total. You can see in the middle section my battery hits 50% at one point, despite starting at 90. As it is down hill to start and i used to get bad cut outs on an old ninebot, i religiously watched the app when i first got the wheel. And this is definitely not normal. The tilt back at 30off kph is not severe, but subtle. Also seem to be getting a more often high amp alarm, such as when just hoping up a driveway. 

The one odd thing that occurred before this is i did get a crackle when either installing or removing the charger immediately before i noted the problem. The wall socket was off at the time, so i didn't think it would have been possible to damage anything. 

in regards to seller, not sure how i will go. There is no dealers in Australia, so was purchased off Ebay... (buyer beware??

Your starting voltage is 80.1V, the final voltage at around 79,5V - so not really much battery charge used by that part of the ride - although this are voltage values with battery under burden, so not really accurate for battery charge calculations.

The max voltage during your ride was 82.9V, minimum voltage 73.5V.

The 800 Wh battery pack is some 20s4p configuration with ~2700mAh cells? This would lead to an internal resistance of about 225 mOhm for the battery pack. For this to show an voltage sag of 80V-73,5V=6,5V while burdened a battery current of 6,5V/0.225Ohm=30A would be needed. This highest voltage sag you had at driving about 25 km/h with around 60A motor current reported.

This numbers fit and there is nothing abnormal to be seen.

FYI - Battery percentage is shown by the different apps, but calculated from the battery voltage. This is a common way, but shows no usable/meaningful values while the battery cells are under burden. To get a "real" capacity value one need to let the battery rest and settle. After 10-15 min it starts to show usefull values, after 30 min to 1 hour they should be quite exact. Also the battery level (percentage) shown by the EUCs does not correspond to real Li Ion state of charge - they are just some percentage between maximum and minimum voltage the wheel uses...

 

Edited by Chriull

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Chriull, thankyou for ypur reply. 

What concerns me is this is up and down hill so it is regenitive. If i only rode flat or up hill i think i may run out battery, which i hadnt noted before. Maybe i will ride down and log riding just flat and up hill from full battery and see what happens. 

Maybe i am over reacting....

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7 hours ago, Chriull said:

The 800 Wh battery pack is some 20s4p configuration with ~2700mAh cells?

20s3p 3500mAh

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