When to charge Lithium battery.

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Mark42

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May 9, 2015
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HI everyone!

I have spent an hour searching and reading posts about charging. Lots of stuff about BMS and such, but not what I was looking for.

At what point should a 48V Lithium battery go on the charger?

Right off charger the battery showed 54 or so volts. After driving a while, the voltage dropped to 47. What is the cut off voltage to ensure the battery is not damaged by over discharge?

Thanks,

Mark.
 
If your 48V battery is a 13s lithium-ion cells battery, 39V is the minimun that is safe (measuring it at resting), under loads you could reach lower values as 38V or 37V.

41V - 42V is super safe and caring rest voltage.

Depending on the chemistry you could reach lower safe voltages. with NCA cells like panasonic NCR18650PF you can reach 33V at rest with no harming issues in cell health, but is not recommended.

if you care about discharge, you must know that charging until the 100% (4.2V each cell - 54.6V the battery) is also as bad than a very low voltage. So you should charge the battery and use as soon as possible.

The long term storage recommended voltage is 48V, taking into account it will get lower voltages during the storing time, you should recharge if you reach 46V - 45V during long period storaging
 
Thanks for that info! Yes, my battery is a 13s lithium-ion cells battery. Exactly the info what I was looking for. Unfortunately these batteries from China come with no documentation. A managed to put a few more miles on the bike. Currently over 22 miles and battery voltage at rest is 47.5v. The LCD display shows the last quarter of the battery charge display.

Put the battery on the charger and will do some more distance vs mph tests tomorrow. This bike is exceeding my initial expectations the more I ride it. Torque is good all around, and battery has apparently been holding up its own.

Thanks for your response!
 
Nobuo said:
If your 48V battery is a 13s lithium-ion cells battery, 39V is the minimun that is safe (measuring it at resting), under loads you could reach lower values as 38V or 37V.

41V - 42V is super safe and caring rest voltage.

Depending on the chemistry you could reach lower safe voltages. with NCA cells like panasonic NCR18650PF you can reach 33V at rest with no harming issues in cell health, but is not recommended.

if you care about discharge, you must know that charging until the 100% (4.2V each cell - 54.6V the battery) is also as bad than a very low voltage. So you should charge the battery and use as soon as possible.

The long term storage recommended voltage is 48V, taking into account it will get lower voltages during the storing time, you should recharge if you reach 46V - 45V during long period storaging
Click to expand...

2.5V per cell at rest would be well over-discharged for NCA. Depends on rest time, but anything below 3.0V after 30 min rest I would consider over-discharged.

I drew a Model S cell down to 0V, and then held it at 0V for another hour, and it still recovered to 1.8V disconnected after a few hours.
The cell was ok, but it did take a small hit on capacity.
 
okashira said:
2.5V per cell at rest would be well over-discharged for NCA. Depends on rest time, but anything below 3.0V after 30 min rest I would consider over-discharged.

I drew a Model S cell down to 0V, and then held it at 0V for another hour, and it still recovered to 1.8V disconnected after a few hours.
The cell was ok, but it did take a small hit on capacity.
Click to expand...

I'm agree that anything below 3.0V after 30 min rest is over-discharged, but exclusively for NCA panasonic NCR18650PF 2.5V is possible according to Panasonic and several user tests and reports. They are suppose to be Zero technology and tolerance to 0V during short to medium-term periods of time.

You can also find on the official spread sheet that they can be discharged safety until 2.5V. http://industrial.panasonic.com/lecs/www-data/pdf2/ACA4000/ACA4000CE240.pdf

I don't know if all the NCA cells are able to go to 2.5V, I just put the example of panasonic PF, and marked that is possible but not recommended.

39V is safe for a single use on every lithium-ion chemistries, followed with a charge as soon as possible is highly recommended.

Mark42 said:
Can you check out this link to the battery and tell me what you think it is? Thanks!
http://www.aliexpress.com/item/free...-Battery-48V-20AH-with-charger/701895087.html
Click to expand...

that is a battery made with 18650 lithium-ion cells.

It can be controversial because you can read "Our LifePO4 battery is mainly made of prismatic cell", but according to the rest of the specs, and BMS, I'm sure they use chinese 18650 cells, nothing on the description fits with LiFePo4 chemistry.

You can follow the instructions I said on the first answer. However that cells are not NCA, they are probably NCM so the safe minimum voltage is 39V, not lower. (as soon as posible followed with a charge to 48V is always highly recommended)
 
Charge your battery EVERY TIME, before you use it.

Definitely, it can be best to wait till just before you use it, to fully charge it. So if you don't ride for days, leave it discharged till you are going to use it. But not too discharged, if you used it all up, charge it approximately half way before you store it.

Max charge 54.6v. So that battery at Ali express is a 13 cell pack, using one or another type of lithium cell that charges to 4.2v per cell.

The bms will (should) prevent overdischarge, or overcharge. 39v sounds about right for the low voltage cutoff, but it could stop at a higher voltage if one group of cells has lower capacity than the others. (out of balance)
 
Thanks for all the battery charge responses. Will keep testing the voltage so I have a good idea what the 4 bars on the LCD display represent. Have not gone below 3 of the 4 bars yet and the lowest voltage recorded is 47.5V after about 22.5 miles of riding (only one bar is still lit at this voltage). Its fully charged now so I have a full day of testing and "break-in" ahead of me! LOL!

I did run into one mechanical problem. The derailleur (Shimano Exage) will not reach the low sprocket. So it will only do gears 2-7. First gear is lost. Tried readjusting but the derailleur just is not capable to reaching that far inboard to engage 1st gear. Don't want to try bending anything especially because the Exage is all aluminum and there are no steel parts to bend. Oh well, guess I lost 1st gear.

I did notice its not hard to pedal, even with the weight of the battery and motor. Whatever parasitic drag there is from the motor, I just can't notice it.

Another cool thing was that the second bar on the battery charge display started to blink, then went out as the voltage dropped while climbing a long hill. Right at that time I reached the top of the hill and started a long down hill coast, about 1 full mile. During the coast, the second bar started to blink on and off again, then stayed on for a while even after reaching the bottom of the hill. I guess the regenerative charge is working?? Or did the battery just get a rest and voltage rose up?

One last thing. I mentioned somewhere that this was a Murray bike. Its not. I found pics of the bike when it was new and it is a Huffy 21 speed mountain bike. Good old fashioned heavy steel frame department store bike from the '90s. LOL!
 
your battery turned off because the BMS detected voltage on one channel that was below the LVC so it turned off the output mosfets. when the current demand stopped at the top of the hill then the cell recovered enuff for it to climb in voltage above the LVC.
 
Hills are hard on batteries. Long hills are very hard on batteries. Pedal.
Do you have a link for your motor kit ?
Where do you live ? Hills ?
Better to have a charged battery than a dead battery. Most battery problems are from not charging.
 
The battery link just confirms 13s, 9 p of 2.4Ahr 18650's
No brand or part number.
5.5 kg pack weight with 117 cells in total.
Max continuous discharge 30 A for the pack, ..60A peak.
BMS settings quoted at 54 v max cut off, 20v min cut off. (???)
It's a reasonable spec....IF they are quality cells !.
 
When you rest the battery, you get a bounce back of voltage, compared to just after a heavy load was applied.

I have no idea if your kit includes regen or not. If it does, you would know when it kicked in, when you pull the brakes. So I think you just saw the voltage rebound that is normal when you let a battery rest a bit.

If you really want to know what your voltage is, get a real voltmeter on your bike. Though my current bikes have a decent display with bars of voltage, and bars showing heavy or light amps drawn, I still put a Cycleanalyst on them. I like to know exactly how many ah, how many watts, at all times. Also gives me an odometer/ speedometer that is more accurate.
 
Have been paying close attention to regeneration. Going down hill, I only pull the brake lever until the throttle (mine is a twist grip) does nothing, but the brake is not actually applied to the wheel. Once I learned this 'setting' I noticed a distinct drag caused by regeneration. Until this time I assumed the drag was just the brakes. Now I know how to tell the difference.
 
This is an interesting topic which I asked Justin about when I met him at last year's EV Show. Justin told me there is nothing wrong with completely discharging a battery; the damage is caused by charging it too much. Justin recommends charging the battery to 80% and using it up completely until the BMS shuts it off.
 
To maximize the life of your lithium ion battery, you should use it between approximately 80% SOC and 30% SOC. The actual voltage for 80% and 30% varies depending on the battery chemistry. You can use the Grin Tech Charge Simulator to see exactly what the overall voltage should be at any percentage: Cycle Satiator Lithium Battery Charge Simulator

When Justin said run it until the BMS cuts it off, that is not 0%! The BMW that EM3ev uses will cut the battery off around 2.75V per cell group. That works out in a perfect world at 38.5V for 14S battery. Just FYI, the BMW will cut off the battery when any one of the cell groups reaches 2.75v so it may cut the battery off prior to the pack reaching 38.5v.

Deeply discharging as well as highly charging a lithium ion cell will decrease its life. 80%-30% is a reasonable compromise between getting the most energy/miles out of your battery per charge as well as getting a long life out of your battery.
 
Mark42 said:
HI everyone!
At what point should a 48V Lithium battery go on the charger?
Click to expand...

There is only one or more rules worldwide for optimizing lithium battery chargin & life!
Put at charge whenever possible!

The battery preferes small packets of charge instead of a full duty charge!
Allways carry charger with U, put battery at charge whenever possible, don't stole energy anyplace, energy is not free! :unsure:

and if possible don't go under 20% state of charge, and no more than 80%-90%
those seems to be some healthy rules to lithium batteries

PS: put at charge your smartphone whenever possible!
 
Comrade said:
To really maximize it it should be between 50.001% SOC and 49.999% SOC. :cool:
Click to expand...

There is only one way to keep any battery constant soc charged @ 50% +/-0.01%

The way is to connect a 50% SOC battery to veicule & to some high drain charge source simultaneous ( voltage equals number of S elements times 3.7V ), while Ur usin battery at veicule ride (charging same rate of discharge rate), is this possible?

exmple trotinete battery 10S soo u should use a portable source of 37V max10A current, to keep chargin trotinete ,while in ride (this way, veicule only sees a constant 50% soc 37V +/-0.01% tolerance (36,63V to 37,37V) battery..:unsure:

carry a mini gasoline generator at trotinete chargin battery while ridiin :bigthumb:

nothing more to say!
have a nice week
 
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