improving charging time of 18650's

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Kreunt

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As my supply of 18650 cells starts to increase I am looking at chargers.

I have seen the reviews on YouTube that various people carry out but they are not answering my queries.

I do not know if what I am asking is too much or even a factor of the battery cell make up but here goes.

Starting with an Imax, I can set the amps for the charge within quite a wide range, some people suggest 0.5, some say 1 amp some say 2 amp, yet regardless of what I set the IMAX reduces current to 0.1 to 0.2, this happens quite quickly, the cell then takes many hours to charge (sometimes as long as 480m but does get to a half decent mAh.

1. Is this a function of the battery cell or the charger?

I did consider building my own charger based on the TP4056, although this would not display the mAh capacity by iteself. Again looking at YouTube people show that as the charge increases the current is dropped to cram in every last drop of energy. This is what I would expect but not as quickly as the IMAX does it.

2. We see the Opus and other chargers on YouTube, do these also drop the 1ampor do they remain constant during the charge.

3. Are they any quicker at charging?

Is there a profile somewhere to show what to expect on an 18650 during the charging cycle?
 
1A is the standard that people use, but as the battery gets full, the charger will lower the current. So you might have an empty cell and that'll start charging at 1A, but if you grab a cell that's already mostly full, even if you set it to charge at 1A, it'll read the battery's state and start charging at 500mA or whatever.
 
Every charger that has a properly designed CC/CV charging profile is going to do that that is the entire point of CC/CV charging is to switch from CC to CV when the voltage reaches 4.2 or whatever your chargers set point is (mine is 4.1), and then it ramps down the current to maintain that CV until it terminates the charge.

If you tried to push more, you will damage the cell as the voltage will rise.

This is also a dependent on the cell itself, its internal resistance, capacity, and whatnot and will vary from cell to cell.

To improve on volume, I would just do more in parallel. I have an iCharger with a 30-40 bay parallel charging cradle where I put in cells that have very similar voltages, within .2-.3 v differential and just blast it with 20-25 amps.

Alternately, I have separate chargers that are based on the TP4056 for individual cell charging, along with the Opus/Nitecore/liitokala style units.

Also I dont look at the mAh in, I only care about the discharge test for recorded capacity.
 
CC-CV is the keyword here, Constant Current - Constant Voltage. These are the two main phases of charging lithium cells. You start with a constant (limited) current of 0.5A, 1A or whatever is suitable for the cell you are charging. Could be less, could be more. For reclaimed cells 1A is fine. Once they hit the end of charge voltage, typically 4.2V, then the second phase starts and it's not the current that is constant anymore, but the voltage. The current then drops until it reaches the set termination current, typically 0.1A.

There is no way to do this quicker or slower, it always takes the same time. Well, more or less. The cell will have specifications on how long it should take to charge it using the standard charging rate for that cell but for used cells this might be off.

If you have a cell that drops to 0.2A or 0.1A very quickly and then stays there for hours you have either a bad cell or something is messed up with your settings. Or the charger has some issues. As a very rough guideline, you can expect an empty reclaimed cell to completely charge within three hours at 1A.
 
What I have observed is the Opus reduces current before the battery gets to 4.2V (or even close), especially on the 2A charge setting. I've seen it drop to <1.5A when it gets to around 3.7V. My MiBoxer on the other hand does 1.5A right up until CV stage, then drops appropriately to keep 4.2V on the cell. So the charger's design is definitely a factor, but the other factor is cell internal resistance. A high internal resistance cell will charge much slower, since the constant current stage will be shorter (imagine 1A flowing across a 0.3 ohm resistor, the cell will hit CV at only "3.9V" at 1A, vs. a 0.1 ohm resistor, it will make it to "4.1V" before changing to CV). This is the main reason why you can't charge a Li-Ion battery much faster than ~1 hour. Even if you pump 2-3A into a cell, the cell will hit 4.2V sooner, and still take ~45 minutes or however long to "soak" at 4.2V until it's full.
 
for lithium cobalt based cells, switching from CC to CV mode should occur around the 4.1V range. Full current to 100mA should happen from 4.1V to 4.2V. So around 4.15V, the current would be somewhere around 500mA (if 1A is the max charge setting).
But, each charger will do this scheme a little differently as they each have their own algorithms.
 
Moving behind CC/CV, from my very short experience in processing cells I went with opus , but I do precharge on tp4056 and postcharge on foxnovo F08
Most of processing I do is at 1000 mA and foxnovo charges to 4.20-4.22 consistently with 850 mA.
In any case; you have to count on 6 hours of minimum of processing each cell: 2 hours precharge, 2 hours discharge/capacity test and 2 hours postcharge. I'm sure many will disagree, since 1000 mAh capacity cell will only take 3 hours to complete the cycle and 3000 mAh cell will take 9 hours.
I found some things to speed-up my processing:
1; Do not postchrge cells that do not meet your minimum capacity requirement
2; Do not spend time on heaters or blown CID cells
3; Postchrge cells to storage voltage of 3.7V instate to full 4.2V
4; buy more charges :)

P.S.
I do not recommend IMREN K8 charger.
 
Are there any multi-bay chargers that support charging to storage voltage? Only my Turnigy Accucel 6 (same as Imax B6) supports it, other than using a bench supply.

Oh, I guess you could use an Opus (or other charger) set for LiFePo4, termination should be around 3.6-3.7V.
 
You may use LiFe mode on i-max charger to bring the cells to 3.6v.
2 4-cell holders at max of 6 A will do the job in about 1.5 hour.
 
Korishan said:
for lithium cobalt based cells, switching from CC to CV mode should occur around the 4.1V range. Full current to 100mA should happen from 4.1V to 4.2V. So around 4.15V, the current would be somewhere around 500mA (if 1A is the max charge setting).
But, each charger will do this scheme a little differently as they each have their own algorithms.
Click to expand...

Well, no, by definition this can't happen. It's not possible. Chargers switch to CV when the end of charge voltage is reached. If it's 4.2V then this shouldn't happen at 4.1V. If it does then 4.2V will never be reached. That's why it's called constant (!) voltage, it won't change anymore after that. When the charger switches to CV at 4.1V then the cell will be charged to 4.1V.
In CC phase the current will be limited to the set value while the voltage goes up. In CV phase the current will go down so the voltage doesn't exceed the set end of charge voltage.
You can't go to CV at 4.1V and then lower the current between 4.1V and 4.2V. As it's CV you will stay at 4.1V then.

rev0 said:
Are there any multi-bay chargers that support charging to storage voltage? Only my Turnigy Accucel 6 (same as Imax B6) supports it, other than using a bench supply.

Oh, I guess you could use an Opus (or other charger) set for LiFePo4, termination should be around 3.6-3.7V.
Click to expand...

The MC3000 supports it.
 
DarkRaven said:
Well, no, by definition this can't happen. It's not possible. Chargers switch to CV when the end of charge voltage is reached. If it's 4.2V then this shouldn't happen at 4.1V. If it does then 4.2V will never be reached. That's why it's called constant (!) voltage, it won't change anymore after that. When the charger switches to CV at 4.1V then the cell will be charged to 4.1V.
In CC phase the current will be limited to the set value while the voltage goes up. In CV phase the current will go down so the voltage doesn't exceed the set end of charge voltage.
You can't go to CV at 4.1V and then lower the current between 4.1V and 4.2V. As it's CV you will stay at 4.1V then.
Click to expand...

If the charger is applying a Constant Voltage of 4.2 to the cell when the cell is 4.1V, then the cell will charge to 4.2V. If you look at the charging curves for the lithium cells, they all shift around the 4.1V mark. It's not CV at 4.1V, it's CV at 4.2V, but starts the curve at 4.1V

With the TP4056, it starts closer to 4.0V in the change in the curves. Current slowly tapers off from 1A to about 280mA from 4.0V to 4.2V.


image_spzfsx.jpg


Addendum: Looking at few other controllers, and a few cells in the database, it looks like they are supposed to be charged at CC up till voltage reaches almost or at 4.2V, and start tapering off the current. Some are tested with tapering around 4.18V, others at 4.2V.
Ok, so readjustment in my thinking has sunk in. I misread the data before :p But depending on the charger, it can vary slightly when the CC mode ends.
 
Seems to be a specific behaviour of the TP4056 then. Maybe to prevent an overshoot and to make it easier to adjust the 4.2V. However it still isn't CV. What it does then is limiting the current prior to reaching the end of charge voltage and switching to CV. Most chargers won't do this and it isn't strictly necessary either. It's not part of the usual CCCV scheme.
 
Another oddity we must all watch out for. *sigh* This stuff is supposed to get easier as you learn more, not harder :p
 
marcin said:
You may use LiFe mode on i-max charger to bring the cells to 3.6v.
2 4-cell holders at max of 6 A will do the job in about 1.5 hour.
Click to expand...

Thanks for reply, I might try that on some cells I do not care about in case it damages them.

One thing I have learnt is not to buy cell holders with springs, I had just for for a proof of concept connected in series. I checked the voltage with voltmeter and the spring went red hot then melted plastic in holder. this is the problem with cheap Chinese tat on eBay.

I was thinking of connecting some holders with the batteries in parallel and using the IMAX capabilities of charging multiple batteries.

Korishan said:
for lithium cobalt based cells, switching from CC to CV mode should occur around the 4.1V range. Full current to 100mA should happen from 4.1V to 4.2V. So around 4.15V, the current would be somewhere around 500mA (if 1A is the max charge setting).
But, each charger will do this scheme a little differently as they each have their own algorithms.
Click to expand...

Thanks for reply

I think that there is something wrong, either with my Imax or the batteries

If I set it to 1amp it starts dropping immediately then hovers between 0.01 and 0.02, that is the current I would expect it to drop to at the end when the battery is full, but I hocked up a voltmeter and is not near 4v

I think I will try to calibrate the IMAX, saw a video on it on YouTube.
 
Why should it damage them? Charging methods for all lithium cells are the same and differ just in end of charge voltages. By charging LiIon cells on LiFePO setting you are effectively charging them to 3.6V instead of 4.2V. It's simple.

As for the springs, sounds like as if you have shorted something or generally put too much current through it. This has nothing to do with bad quality and can happen any time and with any cell holder.

You can put cell holders in parallel and charge many cells at once with the IMAX. However, make sure that all of them are at a healthy voltage (like 3V or more) and that there is no huge difference between the voltages, otherwise you will have huge current spikes going through the cells and holders. The IMAX B6 series is limited to 6A so 12 cells is a reasonable maximum. 500mA per cell, this takes twice as long as charging cells with the TP4056. Charge 6 cells if you want the same charging current of 1A and therefore the same speed.
 
Using an IMAX in parallel is no different than using a TP4056 in parallel or any other single cell charger. The benefit of parallel charging with a hobby charger is easily adjustable charge rates. Depending on how many cells you have in the cradle just select the appropriate charge rate. 10 cell, 10 amps, 20 cells use 20 amps...

What the IMAX and other balance hobby chargers can do that the single cell chargers cant do is have the ability to charge cells in series, along with being able to balance them while in series.

Just for visual example, this is what I use for my parallel charging... just some cell holders all wired in parallel with a copper bus bar. 20 I can charge at a full 20 amps, and using alligator clips, sometimes I expand it to more cells (up to 40 so far) where I can throw the full 20 amps at it and have 40 cells charge at 500mA each.

The only time consuming step with this process is making sure the cell voltages don't have too big of a differential before throwing them into the cell holders, I allow for a .30v differential


image_wunlaa.jpg
 
DarkRaven said:
Why should it damage them? Charging methods for all lithium cells are the same and differ just in end of charge voltages. By charging LiIon cells on LiFePO setting you are effectively charging them to 3.6V instead of 4.2V. It's simple.

As for the springs, sounds like as if you have shorted something or generally put too much current through it. This has nothing to do with bad quality and can happen any time and with any cell holder.

You can put cell holders in parallel and charge many cells at once with the IMAX. However, make sure that all of them are at a healthy voltage (like 3V or more) and that there is no huge difference between the voltages, otherwise you will have huge current spikes going through the cells and holders. The IMAX B6 series is limited to 6A so 12 cells is a reasonable maximum. 500mA per cell, this takes twice as long as charging cells with the TP4056. Charge 6 cells if you want the same charging current of 1A and therefore the same speed.
Click to expand...

Thanks for clarifying, I just figured they had a different setting for a reason, but as you say if voltage is lower should be better.

Imax tip makes sense.
 
Learjet said:
marcin said:
...
P.S.
I do not recommend IMREN K8 charger.
Click to expand...

I was thinking of buying the K8. What's wrong with it?
Click to expand...
Well, The price is OK, but
Cells are too close to each other and one will heat up from the other.
The plastic casing split up front and I am using a wood clamp to hold it together, if I don't the tabs will not touch the cell negative.
The tabs are to soft and after 2-3 weeks of using they bend backwards and to not touch the cell negative terminal.
If you let the tab loose too fast after removing cell the spring inside may dislodge and you have to open the charger to fix it.
It has happened to me twice.
If you do have to open the charger the screws are under each and every rubber pad, not only on the corners.
Other then the physical design issues the electronics are working fine and the charger is consistent with end voltage 4.2-4.24
easy to use and set the desired amperage, power supply plug is stable as well, no disconnects and it will start charging the cell if it is 4.1v or 0.7v.
I try to reach out to the only ebay seller after the ebay return time expired and seller declined the return/exchange.

This is my experience only.
 
Just wanted to add a couple graphs from my primary cell testers to illustrate the difference in charging method:


image_myivqx.jpg


image_ispkes.jpg


Basically, the MiBoxer allows you to do 1.5A charge and discharge, but on discharge it drops current at thresholds of 3.2 and 3.0V with a final discharge current of 0.4A. On charge, it's a "proper" CC-CV with the CV transition happening just over 4.2V. The Opus does only 1A discharge (0.9A real, according to the measurement), and is constant until the termination voltage. On charge, it allows up to 2A (1.9A real per the measurement) if using the outer 2 slots only, but drops current starting at 3.8V, and drops below 1.5A at 3.93V. Overall test time of the 2 chargers is therefore pretty close, with the MiBoxer being slightly faster, but of course only able to handle 2 cells at a time.
 
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