Misleading used battery % on display for ebikes !!

Ebiker01

Well-Known Member
If your battery has gone through a few hundred cycles after charging , the display shows 100% .

So, bat is 80% , display shows 100% of the 80% is full...But why not show the real actual value instead of this ? Why this error in programming ??

The used battery has most likely an 80-85% capacity left after that many cycles , but the dumb "intelligent" controller/bms can't read that or calculate the new numbers.

Why are the companies out there misleading the customers ? If you fill up an analog car's fuel tank , the reading will say how much it is based on the actual value not 100% based on 80%....this analogy is not that great though...but something to think about.

I'd like my display to show battery level @79% after charging my used battery to 100% of it's current 79% cappacity.

Thankfully i do know how many WH there are at 100% , b/c i use a Grin satiator which shows the total amps/wh. But on the regular display it is not accurate.

A correction would help to see a lot better how our daily usage/charging affects the battery capacity drop. If someone always sees that it js charged @100% they may forget that is actually 79-80%.

And after some riding , say the level gets to 40% , the battery has actually a 20% capacity left. Remember we start with a used battery...

Confusing for many new ebikers ! Most likely they are not even aware of the confusion.
 
Last edited:

GenXrider

Active Member
It would be great if we could rely on those battery level indicators to be precise. I know in another thread they were referring to the battery level indicator appearing to be way off by the time it drops a bar, and that was on a "new" bike rather than one that had gone through hundreds of recharging cycles. After that many cycles, they're not really "new ebikers" anymore.
 

Ebiker01

Well-Known Member
I think that depending on how good the battery is , even after 70-80cycles a battery would loose some %. Maybe 2-3% , maybe 5-7% ?
 

AHicks

Well-Known Member
The voltage of my battery when it gets done charging is the same after several hundred charges. That value is determined by the BMS or charger, not sure which. ALWAYS the same though. It's designed to shut down/stop charging at that number.

IF there was a difference after all these charges, it would be in how many miles it will last on a charge. I've seen no noticeable difference myself, but that's where I expect I'll likely notice it first....

Expecting an accurate bar graph reading is going to be an excercise in futility. NONE of them are worth anything more than just an idea of where you are at in the charge cycle. Kinda like a gas gauge on a car.....
 

Mr. Coffee

Well-Known Member
This is a hard problem in general to solve (knowing how much power/charge is left in the battery based on the voltage). So if I had solved that problem I doubt I'd be applying the solution to ebikes when there are lots of more lucrative places to apply that solution.
 

Ebiker01

Well-Known Member
This is a hard problem in general to solve (knowing how much power/charge is left in the battery based on the voltage). So if I had solved that problem I doubt I'd be applying the solution to ebikes when there are lots of more lucrative places to apply that solution.

It doesn't seem hard to solve. I'm researching about this now.





Great read and it proves that it is solvable but what i think that the issue is , nobody (battery manufacturer, bms maker, etc) is motivated to invest to build the technology b/c for now what we have is good enough ??


Well it actually is not good enough at all, it is very bad. B/c you can have a device @20% battery SOC when in reality is seconds away from shutting off.
Medical field should take notes !
 
Last edited:

Ebiker01

Well-Known Member
From that long article all that is needed to know for most people is this :

It is found in :

"Chapter 5.Conclusions

Experimental evidence has been presented to prove, for the first time, that the OCV of Li-ion cells can be used to provide accurate estimates of LLI, LAMPE and LAMNE. The diagnostic algorithm was evaluated for six different scenarios of degradation modes. Once the OCV model has been parameterized, the diagnostic algorithm requires only pseudo-OCV measurements. Since the algorithm uses the pseudo-OCV measurements as a direct input, rather than the derivative of voltage or capacity, it is less sensitive to noise compared to other techniques proposed in the literature. These attributes, combined with the low computational complexity of the diagnostic algorithm, make it ideal for BMS applications in order to keep track of the cells' SoH and to maintain safe operation.

Theoretically, the presented diagnostic technique can be applied to any Li-ion cell chemistry. This possibility will be investigated in future work. Further work also includes the identification and quantification of degradation modes in commercial Li-ion cells aged in a variety of use cases and throughout their service life. This should enable projections of the end-of-life for commercial Li-ion cells.
 

AHicks

Well-Known Member
And that applies to your bar graph voltmeter (or bar graph volt meters in general) how?

If you want exact, you are going to need a digital volt meter, or something that will read with that degree of accuracy - WAY beyond any bar graph I've ever seen.
 

JRA

Well-Known Member
I find it more useful on my CA3 bikes to track Ah's used as that info is supplied and I find more accurate to figure how much more I can travel figuring my wh/mi use also availabe at the display to that point.
 

FlatSix911

Well-Known Member
This is a hard problem in general to solve (knowing how much power/charge is left in the battery based on the voltage).
So if I had solved that problem I doubt I'd be applying the solution to ebikes when there are lots of more lucrative places to apply that solution.
It doesn't seem hard to solve. I'm researching about this now.
Great read and it proves that it is solvable but what I think that the issue is, nobody (battery manufacturer, BMS maker, etc) is motivated to invest to build the technology b/c for now what we have is good enough ?? Well, it actually is not good enough at all, it is very bad. B/c you can have a device @20% battery SOC when in reality is seconds away from shutting off. Medical field should take notes!

Apple has already solved this problem. ;)

Their battery app shows the actual battery degradation when compared to new... 79% in this example.

1594424774086.png
 
Last edited:

Ebiker01

Well-Known Member
I find it more useful on my CA3 bikes to track Ah's used as that info is supplied and I find more accurate to figure how much more I can travel figuring my wh/mi use also availabe at the display to that point.

Is that using the Grin Cycle Analyst ?
 

AHicks

Well-Known Member
Similar, but different, on the KT based equipment (similar to what Bolton sells). That display shows the common bar graph, but in addition you can push the middle button twice and get an EXACT, real time voltage reading to hundreths of a volt.

Point being, it's possible for display mfgr's to do it right now. It's just not available on some of the cheap displays used on OEM bikes, due mostly to cut throat pricing.....
 

Alex M

Well-Known Member
nobody (battery manufacturer, bms maker, etc) is motivated to invest to build the technology b/c for now what we have is good enough ??
There is a technology but there is not much implementation in ebikes.
There are 3 different quantities - SOC, diminished capacity (compared to new), and number of cycles.

1) SOC:
Automotive and RV industry have been using what is called "battery monitor" for decades, to determine exact SOC by counting the charge flow in and out. It is more accurate (much more) than estimating SOC by voltage like a typical ebike does, but it requires measuring the flow during charging as well. When battery is removable for charging, it means that such a monitor has to be embedded into the battery.

2) Number of cycles:
Again, in "big boys toys" there exist 12V and 24V Li batteries with built-in cycle counter (probably similar to battery monitor). It counts the cycle after 80% of full charge/discharge cycle, and it also reads the SOC. Implemented through the smartphone app.

3) Diminished capacity: easy to plot when you have a "smart battery" like in #2, it's a matter of dividing the number of cycles into total cycles. But I don't see it particularly useful because your cycle life may vary depending on how you treat your battery - heat, high discharge current and deep cycles negatively affect your total cycle life.
 
Last edited:

Ebiker01

Well-Known Member
Q- If a 48v battery is @ 80%capacity left, to charge it , in order to preserve what's left of it, it would mean , charge up to 80% ON the charger or 53volts ? Or even less voltage since battery is used up ?

80%charge on a 80%full battery(the rest of the lithium ions are gone)

And if it's done only for up to 80% on the charger , that battery would now have a 60% total charge.
Could charge xtra just before riding it, but not too much. Maybe not even do it, in order to extend it's life.

In terms of WH:
80% of 600WH(one of my batteries) = 480WH LEFT

- Charge safely to 80%=384WH🙁.
Can only ride it up to 20% left= ONLY 308 WH AVAILABLE🧐 ??

So, basically a used battery is garbage...what can you do with 300wh ?? And this is starting with a 600WH battery.
A 500WH would leave about 200WH only....


Is that calculation correct ?
 

AHicks

Well-Known Member
So many questions.....

Somebody seems frozen into over thinking this 80% thing big time. So let me ask, when was the last time your battery was FULLY charged?

Have you spent any time researching the benefits of balance charging? Fully understand the problems associated when you do not balance charge frequently enough? To my way of thinking, it's only when you fully understand those facts that you can make intelligent, fully informed decisions regarding any 80% plan. I don't care whos says any differently, because without fully considering the need for, and frequency needed for balance charging, that you can come up with a plan to get max performance and lifetime from a battery. -Al
 

Alex M

Well-Known Member
Charging only to 80% will not (most likely) achieve the balancing. You could charge it to 70-80% right after the trip and then to 95-100% just before the trip - if this 2nd trip is next day. If there going to be a 7-8 days (or longer) gap between the trips, it's better to leave it not fully charged, 40-60% is optimal, until you're ready to ride again.

Not discharging below 20% is always good for a battery. But if you can't complete the trip without discharging to 0%, then you have no choice.

Charging up to 70-80% will extend the life of single-cell batteries like those in cell phones and laptops that don't need balancing. I'm trying to keep cell phone and laptop in 30-70% range. Takes self-discipline but saves money.
 

FlatSix911

Well-Known Member
Q- If a 48v battery is @ 80%capacity left, to charge it, in order to preserve what's left of it, it would mean, charge up to 80% ON the charger or 53 volts? Or even less voltage since battery is used up?
80% charge on an 80%full battery(the rest of the lithium ions are gone) And if it's done only for up to 80% on the charger, that battery would now have a 60% total charge.
Could charge xtra just before riding it, but not too much. Maybe not even do it, in order to extend its life.
In terms of WH:
80% of 600WH(one of my batteries) = 480WH LEFT
- Charge safely to 80%=384WH🙁.
Can only ride it up to 20% left= ONLY 308 WH AVAILABLE🧐 ??
So, basically a used battery is garbage...what can you do with 300wh ?? And this is starting with a 600WH battery.
A 500WH would leave about 200WH only.... Is that calculation correct?

You don't need to do all the calculations... just remember 2 things when charging.
  1. Charge your battery to 80% if you are going riding in the next day or 2.
  2. Charge your battery to 100% if you are going riding the same day.
It's really simple to maximize the lifespan and effective range of your battery. ;)
1594571321123.png