18L Range and Battery indicator

[Circuitmage]

So, after almost a year of use, over two different control boards and about 2K miles total, I am starting to suspect my battery life is a tad bit lower than it used to be. Charging seems to be a bit more frequent and I've started charging when my wheel hits 40%.

I found the thread on faulty battery issues, but nothing specific to what I am seeing. Good info on that thread, so I will be checking my battery V in app after this charge today.

One thing I have noticed lately is my wheel is VERY unhappy with anything under what looks like 40% according to the side LED's. The low battery warnings start going off at 2 or 3 LED's (yellow) , which still makes sense. It just seems like this started happening a bit earlier than it used to. New, I used to go on long rides and realize very long range.

So, checking my app and gauging my last ride, I found I hit 27% battery after 27 miles. That works out to a 37 mile range (60km) for something that is supposed to have 105km range. This is using wheel log BTW, so I don't know if that could have something to do with it.

Looking at the wheel, it shows 4 LED's (40%?) , so my LED's are not precisely matching my V of 27% that the app shows.(WheelLog)

I never looked at this closely before, so it could just be all in my head...but I assume after 2k miles my batteries will have a bit of life squeezed out of them. Just not sure if I should be concerned or not. 

[svenomous]

Many factors affect how quickly and how badly battery packs "age," including how frequently they are charged/discharged, whether they tend to be deep-discharged, whether they're stored fully charged, the temperatures they're exposed to, etc.  Assuming "normal" usage patterns and an otherwise non-abusive environment, the change should be barely noticeable at this point. If you routinely charge to less than 100% you should occasionally (maybe once a month) do a full charge to ensure the cells get balanced (which the BMS only does when they cells are near their maximum voltages).

Was the 27-mile range test you performed done on challenging terrain (lots of climbs), or with hard accelerations and high speeds?  This has a lot of impact.  Did you do an equivalent range test early in the wheel's life, that you can compare to?

As for battery LEDs and battery level vs. warnings while riding, I don't know what account for the discrepancy between LED count and battery percentage reported by the app, but in general if you're down to 30-40% while standing still (when you get to see the LEDs) the voltage will sag during riding, especially hard riding or hills, and can easily get down to 10% or even 0% (meaning 60V in this case), and as soon as you stop the voltage recovers and the percentage is back up to 30% within a minute.  As the pack ages, the sag under load will be more pronounced.  A bad cell, of course, would make this much worse, as you would effectively lose one of the parallel strings in the pack altogether and have a lower overall capacity (and faster sags/recoveries on voltages).

 

[Circuitmage]

@svenomous thanks for the response.

No, I never checked the range early on,  I just knew early on this had much better range compared to my 16S. I recall only charging it once every 9 or 10 days. Now it seems I'm charging it every 4 or 5 days.

I just completed a charge to 100% and it reads 84.3V in app when I turn the wheel on , so I suppose my cells are good.

I typically use this for commuting, about 6 miles a day on flat, even sidewalks/pavement (not many hillls), plus often 10-15 miles on the weekend. My commute did get longer lately, by about 1 mile, but I didn't think it would make much impact. I have not had a cut-out, but I have had several low voltage warnings and gotten home to 2 LED's on (after leaving work with 4 or 5) . I did not check the V then, but I will start paying a bit more attention.

I'm keeping my tires just above where I can tell they get soft, so at ~40psi with my ~200# weight. As soon as it drops to about 25-30psi I can tell. But I've always kept the tire at that pressure, so doesn't make sense. 37 mile range seems low to me. Maybe I need to weigh myself again!  

[Mike Sacristan]

A 1600wh wheel like an MSX gets around 90km with my weight of 64kg.
18XL would get maybe 100km.
The range on your 18L sounds about right.
I went for a ride on a V10F the other day (960wh battery) and after 35km it was down to 38%.
After 2k miles @ 20-30 miles per charge you have probably charged it 100 times at most.
Are you sure you haven't started riding faster? 

[svenomous]

I agree that battery age and cycle count should not be enough (yet) to account for a major drop in capacity.  It may be noticeable, but shouldn't be much at this point.  Even if you've charged it 100 times, that's not 100 cycles unless the pack was basically empty each time.  Probably closer to 50-60 in terms of cycle count, and these cells are rated for several hundred full cycles before their capacity decays too much.  I don't have the specs for the cells used in the 18L at hand, but the Samsung 35e used in the 18XL specifies that after 500 cycles it should retain >=60% capacity.  Time also ages a cell, even if not used, but unless you're storing at high temperatures, after a year you shouldn't have lost much capacity yet.  So, under normal storage and usage conditions 50 cycles (and less than a year) is very little.  Give it another year and you'll definitely be seeing significant decay, as you would with any lithium ion battery pack that's 2 years old.

As for a bad cell, you can't tell whether there's a bad cell based on overall battery voltage.  I believe 18L is a 20s4p pack, so a single bad cell could (at worst, if the cell was just about dead) cause you to lose one of the four parallel strings of 20 cells, losing you 25% capacity, but the remaining three strings would still charge up to the right voltage (making the battery look "normal" from that perspective), and the wheel would still work.  You would just see sharply reduced range, more rapid voltage sag, etc.  Given the more subtle signs you've reported, and the assertion by Mike that the range "sounds about right" for an 18L, maybe other factors are to blame, such as a combination of more aggressive riding style developed over time (as Mike also suggested) and the increased commute distance you've mentioned.  This may be adding up to a "sense" that things aren't like they used to be.

The only way to be sure is to gather some data.  Do you use Android or iPhone?  On Android you could use WheelLog to gather and download some data about voltage during your commutes, and could compare the curves for a fully charged wheel on a normal commute, over time, to see if there's a measurable change happening.  DarknessBot on iPhone can also do some graphing, but I don't remember if it can export the data like WheelLog can.

[Seba]

On 7/16/2019 at 4:23 PM, Circuitmage said:

So, checking my app and gauging my last ride, I found I hit 27% battery after 27 miles. That works out to a 37 mile range (60km) for something that is supposed to have 105km range. This is using wheel log BTW, so I don't know if that could have something to do with it.

Looking at the wheel, it shows 4 LED's (40%?) , so my LED's are not precisely matching my V of 27% that the app shows.(WheelLog)

I never looked at this closely before, so it could just be all in my head...but I assume after 2k miles my batteries will have a bit of life squeezed out of them. Just not sure if I should be concerned or not. 

WheelLog is using optimized, more realistic battery level gauge, so if WL displays that you have 27 %, it means you have almost one third of battery to go. With WheelLog you can safely go down to 0 % and there will still be a small amount of battery charge to allow for a ride, of course with very slow speed and constant tiltbacks. Real 60 km (or 70 km as displayed in wheel data) with 27 % battery is normal for KS-18L and 80 kg rider @ 25 km/h.

Wind and riding speed are a major factors influencing effective range. With time and experience, riders tend to ride faster and more agressively, what in turn results with smaller range. Of course, battery wear is another factor, but it's much smaller and is usually hidden by effects of wind and speed.

[Meserias]

For the "Wheel distance correction" I set -19% for my KingSong 18XL

But what it's recommended value for "Wheel distance correction" in WheelLog ...
thank you

Edited July 18, 2019 by Meserias

[Seba]

1 hour ago, Meserias said:

For the "Wheel distance correction" I set -19% for my KingSong 18XL

Correctly. A value of about -18 % is a typical correction for this wheel with factory Chao Yang 18x2.5 tyre inflated to about 2,5 bar (35 PSI).

1 hour ago, Meserias said:

But what it's recommended value for "Wheel distance correction" in WheelLog ...

I suggest to leave this setting at 0 %.

[Circuitmage]

On 7/16/2019 at 4:49 PM, Mike Sacristan said:

A 1600wh wheel like an MSX gets around 90km with my weight of 64kg.
18XL would get maybe 100km.
The range on your 18L sounds about right.
I went for a ride on a V10F the other day (960wh battery) and after 35km it was down to 38%.
After 2k miles @ 20-30 miles per charge you have probably charged it 100 times at most.
Are you sure you haven't started riding faster? 

Of course I have been riding faster!  I've put about 40% more miles on this less than a year than I did on my 16S in 1 year.

But I was riding pretty fast from the start. Also, I realized my previous charge was not 100%. Evidently that last hour counts for a lot of extra charge. Right now I am at 24miles with 69% charge, so that works out to a range of ~77  miles in math. In reality I expect to hit that 30% mark where I need to recharge again at around 40 miles, which is a bit more than I first suspected, and still good.

Also, the discharge rate must not be linear...there's probably a chart around here somewhere.