Li-Ion: Should I top off the battery cells to 4.2v?

[neptronix]

Battery 10ah x 20c = 200amp discharge capability

The 9FET can handle 40 amps constant, or more if ventilated.
Mine survived 43 amps constant for 15 minutes at a time with no ventilation.

Your motor is going to have 16 gauge wires so i'm going to guess that 30-40 amps at your voltage would be fine. Just an educated guess, i don't have real life experience.

Let's not derail this thread too much..

 

[DrkAngel]

Cycle life vs charging voltage:
The cell phone industry did a study looking at the effects of ending
charge voltage on cycle life.
Under laboratory conditions, and with an 80% depth of discharge,
terminating the charge

at 4.1 volts, you get over 2000 cycles.
at 4.2 volts, you get roughly 500 cycles.
at 4.3 volts, you get under 100 cycles.
at 4.4 volts, you get less than 5 cycles.


The RC people have seen similar results, and one test that is ongoing
is at roughly 800 cycles with a charge termination of 4.15 volts. This
seems to be the sweet spot for performance and cycle life.

In normal use, you can extend the life of your battery by limiting the
maximum charge to below 4.2 volts, and limiting the depth of
discharge.

Excellent test info!

Remember tho!
These tests were run on on 60mah cells, very small and designed for a very slow, steady output - hours!
Bike application cells, (lipo), are 2000-5000mah, very large and designed for a fast "surge" output - minutes!

I concur, that charging above 4.2v is damaging, and that reducing, top charge voltage can increase charge cycles.
However, given the 2, vastly different types of cells, the comparative percentages might be greatly skewed!

 

[Andje]

recumpence has posted at least once somewere about his lipo which he is very careful with and because of a regimented charge/discharge of i think 90%/20% (but i honestly cant remember or find the post) he said it held full capacity years into it's life. So it would seem that the max delta that you charge/discharge does effect the overall lifecycle of the HK lipo, at least the stuff made a few years back. I think thats the forums current overall belief at least. seems like tuxman provided a good thread on that.
I also read a post from someone about the new nano tech which supposedly can be charged to 4.3 with no danger even though it isn't advertised as such.

 

[neptronix]

recumpence has posted at least once somewere about his lipo which he is very careful with and because of a regimented charge/discharge of i think 90%/20% (but i honestly cant remember or find the post) he said it held full capacity years into it's life. So it would seem that the max delta that you charge/discharge does effect the overall lifecycle of the HK lipo, at least the stuff made a few years back. I think thats the forums current overall belief at least. seems like tuxman provided a good thread on that.
I also read a post from someone about the new nano tech which supposedly can be charged to 4.3 with no danger even though it isn't advertised as such.

Yeah, it's pretty common knowledge that, as far as RC lipo goes, shallower cycles, more so at the top than the bottom, are the big life extender. Second to that would be keeping the C rate low ( easy enough to do on an eBike )

You can charge even ordinary lipo up to about 4.5v and maybe a little beyond that with no danger, but the lifespan will be reduced drastically. Like, it will be reduced to less than a dozen cycles that way.

At 4.3v, you may get 50-100 cycles or less, according to lore

 

[fechter]

There are a bunch of research papers and tests that show the total energy stored does not increase much by going from 4.1v to 4.3v. Charging time will be faster at the higher finishing voltage, but the charger better cut off the juice as soon as it reaches that level. Even with slightly slower charge time at 4.1v, I think you'd reach 90% capacity in about the same time, since the charger will be running CC up until about that point.

 

[DrkAngel]

BTW, I've tried to search for an answer before asking the forum.

My ten 3.7v cell li-ion 12ah battery pack is 41.7v full. But, I've read 4.2v per cell is the sweet spot. Should I adjust the charger to 42v? Should I bother with this slight indifference?

Up-charging from, 4.17v to 4.2v, will increase capacity, by a mere 3%, as reported by Tesla, (18650 Lithium-ion (Cobalt)).

Will 41.7v max help to pro-long the life of the battery?

Most all sources agree that, reducing max voltage, will increase the usable cycles. Percentage of max voltage reduction vs increase of cycles received is not specifically defined, but US military specs charge to 3.92v, presumably for maximum life span, (some purport 2x), downside is severe capacity loss.

3% capacity loss, at 4.17v, should increase "cycles" by, more than, 3%!

Also, when I get done with a short ride, down to 40.1v, should I top off the charge? At what voltage should I top off at?

Max life storage voltage is reputed to be 3.7-3.8v. Maintaining-recharging, while above these voltages, would logically, slightly, reduce lifespan.
You need to balance convenience, capacity, range, vs maximum lifespan.
Personally, if I'm sure I won't be needing the range, I don't recharge till down to the 3.7-3.8v area.

Update:
Discharge test showing mAh every 100th V, shows any battery capacity above 4.17 V to be insignificant.
As determined with recycled Li-ion, (LiCo - Lithium Cobalt based), cells.
Maximum usable charge 4.18V!
Minimum usable charge 3.6V!
Chart, listing mAh per 100th Volt, and graph - Homemade battery Pack!

 

[veloman]

Since I pretty much am within 13 feet of my bike/charger an average of 18 hours a day, I tend to try leaving my pack at about 50-70% charged overnight, then plug it in in the morning, so that come lunch time I can take it out, fully charged. I don't take it out without a full charge, unless I KNOW I'm only going a few miles. Most of my rides are 7-10 miles, or about 50-60% DOD.

I charge my lipo to 4.15v, and the lifepo4 charger stops at 41.5-41.8v or so, but then it settles to near 41v.

 

[Sunder]

My Hobby King Max B8 charges to a purported 4.2 but in reality is anywhere between 4.2 and 4.26.

The only way I can drop cut off voltage is by changing the charge type from Lipo to Lion.Is this safe? I know for example, different nickel chemistry use slightly different full detection methods and using the wrong one can shorten the life of the battery. is this true for lithium as well, or should I just change it?

 

[DrkAngel]

I don't believe there to be a "detection" difference between Lipo & Li-ion.
With the iMax B8 or B6's, I use the Lipo setting, and charge Lipo & Li-ion to 4.2V, plus or minus slightly.
I learned not to rely on the iMax voltage metering, I use an external digital meter to confirm voltages.

The iMax LiIn setting charges to a full 1/10th Volt less, 4.10V.
Since I intend on bottom balancing at 3.65V, and the comparative capacity is so low, above 4.10, I believe that I will charge at the LiIon setting.
With bottom balancing, I prefer to leave a larger safety margin at the top end.

 

[DrkAngel]

I've been recommending a cheap non-balancing Li-ion charger.
7S 25.9V - charges to 29.4V.
It charges to, an average, ~4.2V, no adjustment.
Rather than attempting any form of internal modification, I put a 3amp "blocking diode" inline, on the positive wire.
Worked nicely! Dropped the Voltage nicely .3V, supplying an average of ~3.16V per cell.
The added benefit of no danger of electrical "backwash", plugging the battery, into an unpowered charger.

Quality-voltage reduction of blocking\rectifier\bypass diode, varies widely, by manufacturer. ~.2V to 1V+.
I received a .3V drop, from a unknown brand diode, nice "fit" for my purpose.