First Battery Use: Drain It Entirely?

[Ravi Kempaiah]

Hopefully at some point technical (and not too complicated) write-ups will be published that explain this.

At high charge voltages, a thick layer of gunk called "Solid electrolyte interface - SEI" covers the anode. This is what @MetroDuck meant when he wrote some kind of plating happens. But, at low voltages, this doesn't happen. This layer over a period of hundreds of cycles, block the passage of Li-ions and the battery loses capacity at that point. Here is a neat animation.

If you keep a cell at 20% State of charge and in very cold conditions, you can preserve them for 20+ years. Here is Prof. Dahn explaining this and I am linking the exact point where he is explaining that. @Acey , it is not just depth of discharge that matters ( from 90--> 80 or 90--> 70 or 60--> 50%, the starting point matters as well. Battery university is a good place to start with.

 

[tomjasz]

At high charge voltages, a thick layer of gunk called "Solid electrolyte interface - SEI" covers the anode. This is what @MetroDuck meant when he wrote some kind of plating happens. But, at low voltages, this doesn't happen. This layer over a period of hundreds of cycles, block the passage of Li-ions and the battery loses capacity at that point. Here


If you keep a cell at 20% State of charge and in very cold conditions, you can preserve them for 20+ years. Here is Prof. Dahn explaining this and I am linking the exact point where he is explaining that. @Acey ,

Thanks, I’d lost my link to Dahn. Nice to have data instead of forum anecdotes.

 

[tomjasz]

Most ebikes use instant current to "guesstimate" the remaining charge. They don't keep a track of watt-hours of spent energy. You slow down and the gauge goes up. Don't know whether calibrating it at the beginning by charging 100% and discharging to 5% (or whenever BMS will shut down) - don't know if this will have any effect on guesstimation work of an average ebike display.

Yes, you must guard it against deep discharges - like 10% remaining charge - when in use.
But, when in storage, the word is that keeping it 100% full is worse than keeping it near empty. Justin the Grin says so . Hopefully at some point technical (and not too complicated) write-ups will be published that explain this.

An underused relatively inexpensive “watt meter” can be plugged in occasionally to see how a battery is performing. Not as good as a battery test station like Grin’s but better info than displays or the 15cent battery level led.

Watt Meter Display Screen
Startup Screen
Each time power is applied to the watt meter (or the auxiliary power connector), the startup screen is briefly displayed. Then the Amp-hours, Watt-hours, Peak Amps, Minimum Volts, and Peak Watts parameters are all reset to zero.
Display Parameters
The display screen will continuously measure and display Amps, Volts and Watts. All other values are presented sequentially every second. In the lower left position of the display, data values are identified by their units (Ah, Wh, Ap, Vm, Wp).
Amps (Current) & Peak Amps (A, Ap)
Only current from source to load can be measured. Drawing current in reverse will cause damage to the meter. The Amps (A) value displayed shows the average current over the last screen refresh. The Peak Amps value (Ap) displays the maximum current drawn since the meter’s last startup. Spikes or peak amperage readings lasting a fraction of a second may also be captured.
Voltage & Minimum Volts (V, Vm)
The displayed Volts (V) value is the average voltage from the last screen refresh. The displayed Minimum Volts (Vm) value is the minimum voltage or “sag” measured on the source side, since the meter’s last startup.
Watt-hours (Energy) (Wh)
The displayed value is the total energy delivered in Watt-hours since the meter’s last startup. It is measured from the load side for the most accurate results.
Amp-hours (Charge) (Ah)
The displayed value is the total charge delivered in Amp-hours since the meter’s last startup. It is measured from the load side for the most accurate results.
Watts (Power) & Peak Watts (W, Wp)
The displayed Watts (W) value is the average Watts (Amps * Volts) from the last screen refresh. The displayed Peak Watts (Wp) value is the maximum watts measured since the meter’s last startup.


Cheapest and most expensive/reliable...there are some better Powerwerx clones. Be sure to read capabilities and review.

 

[Alex M]

Requirements that I consider necessary for WH meter:
1) must measure energy flow in both directions, with easy switch for when it's either charging or running motor,
2) must have a button to reset to zero.

It would be nice if it were user-friendly enough to be bike-mounted and transferred easily for when you're charging off the bike.

Probably most of them don't fit the criteria. This is something that ebike manufacturers need to address, but they seem to be focused more on either frame styling or cost-cutting as this is what an average consumer can relate to.

 

[Acey]

Here's an interesting study I started reading before I got so busy - the intro is in German, the research in English. The Technische Universität München (TUM) - "Using the material research diffractometer STRESS-SPEC at FRM II, the researchers installed a battery, in both charging and discharging states, into the neutron beam. The incident neutron beam is diffracted according to Bragg's law and collected in a detector. Using these signals, the researchers were able to indirectly deduce how much metallic lithium had formed." - from first link below.

They then tested various charging/discharging methods in an attempt to definitively understand what's happening inside the battery in real time. Previously you had to run the test, then open the battery to see the results and not what was actually happening during the test. Initial findings were reported in 2014, their final results published in 2017 (links below).

Preliminary findings:

• The faster the charging process, the more metallic lithium is formed. Up to 19 % of the lithium ions normally involved in the charging and discharging process take on the metallic form. (The measurements were made at -20 degrees Celsius).
• During a 20-hour resting phase following a fast recharge some of the metallic lithium reacts with the graphite, intercalating between the graphite layers as lithium ions. It is effectively a delayed, slow charging process. Albeit, only a part of the lithium plating is reversible.
• Low temperatures encourage the formation of metallic lithium.

Findings and general overview from 2014 . PDF of the research (April, 2017) - tests, procedures, findings.

I openly admit I have not read the PDF in it's entirety (but I'm getting there) so I'm not qualified to have an opinion on it at this time. Love the passion and level of knowledge on this forum. Hope this info helps the conversation!

 

[tomjasz]

What

Requirements that I consider necessary for WH meter:
1) must measure energy flow in both directions, with easy switch for when it's either charging or running motor,
2) must have a button to reset to zero.

It would be nice if it were user-friendly enough to be bike-mounted and transferred easily for when you're charging off the bike.

Probably most of them don't fit the criteria. This is something that ebike manufacturers need to address, but they seem to be focused more on either frame styling or cost-cutting as this is what an average consumer can relate to.

help me understand why you want current values in reverse, not just source to load? Thanks Alex!

 

[JRA]

Those are some expensive Anderson's.

 

[Alex M]

Thomas, - for WH meter to measure the battery state of charge correctly, it should measure the flow during both discharging and charging.
Either by transferring it back and forth from bike cockpit to battery, or by mounting the measuring chip on the battery.

The measuring chip should be able to measure in both directions. Ideally, measuring chip on the battery should have wireless connection to the bike display (and to the second display mounted on the charger, if needed). Such "smart" Li batteries exist in other formats but I haven't seen them on ebikes. With the cost of Chinese electronics these days this shouldn't be expensive.

 

[tomjasz]

Thomas, - for WH meter to measure the battery state of charge correctly, it should measure the flow during both discharging and charging.
Either by transferring it back and forth from bike cockpit to battery, or by mounting the measuring chip on the battery.

The measuring chip should be able to measure in both directions. Ideally, measuring chip on the battery should have wireless connection to the bike display (and to the second display mounted on the charger, if needed). Such "smart" Li batteries exist in other formats but I haven't seen them on ebikes. With the cost of Chinese electronics these days this shouldn't be expensive.

In other words the Grin battery tester is the more accurate method. Thanks for the clear response!

 

[Bruce Arnold]

Those are some expensive Anderson's.

Agreed. I bought a cheaper unit and put my own PowerPoles on.

 

[tomjasz]

Agreed. I bought a cheaper unit and put my own PowerPoles on.

Um, the Powerwerx version was cloned by China makers. It’s the only one with a one year warranty. I went through two before getting the Powerwerx. There were a rash of clones that fried under 60v.