bulk charging 18650 cells

[silviasol]

I opened all these dead laptop batteries I had. Seems that on most packs there is just one or two cells that are dead and the rest are good. They are all lithium ion 2-2.6ah 18560 cells. I wanted to charge them all and match them as best as possible based on how long the charge will hold after letting them sit for a month. Is there any kind of 6s3p carrier or harness, not sure what they would be called, that I can hook up to my b6-ac? Something plastic that I can slide the batteries into similar to charger linked below only a 6s setup.

http://www.ebay.com/itm/2x-18650-2400mAh-3-7V-Li-ion-Rechargeable-Batterys-18650-Charger-/220934492263?pt=Battery_Chargers&hash=item3370b8d067

 

[knighty]

http://www.ebay.com/sch/i.html?_trksid=p2047675.m570.l1313.TR11.TRC1&_nkw=18650+holder&_sacat=0&_from=R40

I bought 10 x 4 parallel cell holders, so I can charge 40cells at a time with a 4.1v psu


cell holders are no good for on your bike, but great for bulk charging your new (used) cells

 

[silviasol]

That is what I was looking for! Didn't think of searching battery holder. How many can I charge at a time with a b6-ac?

 

[dogman dan]

No real limit to how many you can parallel together to charge. It will just take longer with a 50w charger to do a big number.

 

[silviasol]

Ok I figured that. Now I just need a way to balance each cell in a 6s6p configuration. I could do it with 6s1p but that would take forever since I will have probably 200 cells.

 

[dogman dan]

Once all a fully charged, just parallel them in 1p and they are going to be all the same voltage. Generally that's step two I believe, after weeding out the obvious runts.

 

[Holocene]

Ok I figured that. Now I just need a way to balance each cell in a 6s6p configuration. I could do it with 6s1p but that would take forever since I will have probably 200 cells.

Hi silviasol,

Not really that hard. Just check the voltage on each cell before you wire up each parallel group of 6. You don't want a big voltage difference between cells or you'll get too much current flowing and melt the wires. But then those 6 cells in parallel will balance themselves without a charger.

Then when you are ready to charge, connect the 6 parallel groups in series and connect to your charger. Since your pack has only about 300 Watt hours capacity, the maximum charge time even from near empty would be about 6 hours on your 50 watt charger. Probably less since they won't be fully discharged to start.

With the Ebay battery holders linked upthread, you won't have separate balance taps, but it will be easy to pop out cells individually and check voltage. You'll need to do that anyway to weed out the weak sisters.

Good luck building your pack. Sounds like it'll be good fun!

Cheers,
Holocene

 

[silviasol]

Ok I figured that. Now I just need a way to balance each cell in a 6s6p configuration. I could do it with 6s1p but that would take forever since I will have probably 200 cells.

Hi silviasol,

Not really that hard. Just check the voltage on each cell before you wire up each parallel group of 6. You don't want a big voltage difference between cells or you'll get too much current flowing and melt the wires. But then those 6 cells in parallel will balance themselves without a charger.

Then when you are ready to charge, connect the 6 parallel groups in series and connect to your charger. Since your pack has only about 300 Watt hours capacity, the maximum charge time even from near empty would be about 6 hours on your 50 watt charger. Probably less since they won't be fully discharged to start.

With the Ebay battery holders linked upthread, you won't have separate balance taps, but it will be easy to pop out cells individually and check voltage. You'll need to do that anyway to weed out the weak sisters.

Good luck building your pack. Sounds like it'll be good fun!

Cheers,
Holocene

Ok, that makes sense. After they are in parallel groups of 6 and I attach them all serial will that level out the voltage of each 6s1p as well?

I am excited, too bad the holders won't be here for a few weeks.

 

[fivari]

I balance charge a large number of cells with a Hobbyking RC charger by putting them all in parallel between two sheets of aluminum foil. It is slow but easy and cheap. I bind them together with a small elastic band. I connect to the aluminum foils using two aligator clips.

 

[silviasol]

I balance charge a large number of cells with a Hobbyking RC charger by putting them all in parallel between two sheets of aluminum foil. It is slow but easy and cheap. I bind them together with a small elastic band. I connect to the aluminum foils using two aligator clips.

Good idea. I will keep it simple with the holders though. I have a ton of them so the easier the better.

Are these worth holding on to? I figure they must keep the cells balanced when they are not being used.

 

[Holocene]

Ok, that makes sense. After they are in parallel groups of 6 and I attach them all serial will that level out the voltage of each 6s1p as well?

Hi silviasol,

No, the serial connection will not balance the individual parallel groups of cells. But that's easy enough to do as well. Just parallel more groups! As always, check that the voltages are close before making the parallel connection, as too much current will flow if there's a big difference in voltage.

If the wires are getting hot, you know you've done something wrong!

I advise you to remain focused on the real task, which is to identify and weed out the weak cells. This will be convenient with your new 18650 holders, and a real pain once you've soldered cells into permanently paralleled groups.

Cheers,
Holocene

 

[silviasol]

Ok, that makes sense. After they are in parallel groups of 6 and I attach them all serial will that level out the voltage of each 6s1p as well?

Hi silviasol,

No, the serial connection will not balance the individual parallel groups of cells. But that's easy enough to do as well. Just parallel more groups! As always, check that the voltages are close before making the parallel connection, as too much current will flow if there's a big difference in voltage.

If the wires are getting hot, you know you've done something wrong!

I advise you to remain focused on the real task, which is to identify and weed out the weak cells. This will be convenient with your new 18650 holders, and a real pain once you've soldered cells into permanently paralleled groups.

Cheers,
Holocene

Sounds good. I won't solder them in packs however will add solder to the contacts when I sell them to make an easy install for the buyer.

Looks like finding the weak ones may be a chore. I was thinking let them sit for a few weeks and see which discharge the quickest?

 

[silviasol]

Just thought I would update this thread. I got the holders in last week and have about a fourth of the cells ready to charge now after balancing them in parallel with others. So far out of about 30 cells I only have 3 that were dead! It has been very interesting for me. Definitely understanding more now.

 

[silviasol]

Well I have a new problem now. Most of these cells are 4.2v. Is there a charger that will do 4.2v?

 

[Holocene]

Well I have a new problem now. Most of these cells are 4.2v. Is there a charger that will do 4.2v?

Most cell-phones use lipo batteries. 1S is 4.2 volts. Check your cell-phone battery with a multi-meter. If it's 4.2 volts when fully charged, it's charger will work on these single cell 18650s too.

Most RC chargers are multi-cell capable as well, ie: 1-6 cells. You should probably read into the FAQs for some more background :wink:

Cheers,
Holocene

 

[silviasol]

These came from laptop batteries. Most are for a laptop that I own. When I charge a good battery each cell is at 4v. Maybe I am reading the pdf spec file wrong. Could the laptop be charging them to 4v just because it will never draw more then .2c?

http://www.houseofbatteries.com/documents/ICR18650-20.pdf

 

[knighty]

you *can* charge them to 4.2v... but it reduced the life of the cells

charge them to 4.1v and they'll last much longer


at 4v they'll last even longer.... (which I guess is why your laptop was only charging to 4v)... but for most of us it's worth the extra capacity of going to 4.1v

 

[silviasol]

I am getting 3.8 as a max charge with my b6ac charger. Should I maybe stick with that voltage? I will be running the pack at just about it's max 2c rating over half of the time riding.

 

[knighty]

googled a few graphs... and it looks like there's about half an amp hour between 3.8 and 4.1v

so you really need to push for 4.1v

I guess 3.8 is ok while you're testing cells tho

 

[spinningmagnets]

Do you have a link for that 10-cell holder?

 

[knighty]

Do you have a link for that 10-cell holder?

I think he has a few smaller holders linked together.... there's too many wires for one holder

 

[silviasol]

googled a few graphs... and it looks like there's about half an amp hour between 3.8 and 4.1v

so you really need to push for 4.1v

I guess 3.8 is ok while you're testing cells tho

Sounds good. Now to just wire a 7s pack up and hope my stock charger will charge them ok. Otherwise I am going to need a 7s charger.

Do you have a link for that 10-cell holder?

I made the pack by soldering the wires to the terminals. There are holes that I used small screws to attach it to the board.

 

[diggler]

Well I have a new problem now. Most of these cells are 4.2v. Is there a charger that will do 4.2v?

I found this out too using the Imax b6 ac.
You can make it charge 4.2v per cell if you go into the menu and select Lipo instead of Lion.
Get to main menu that sais user set program, hit enter
Then it will say LiFe SET V. Type 3.3V (this is for Lifepo4's, and it will charge to 3.8v max per cell)
Or LiIo SET V. Type 3.6V (this is supposedly for Lion's, these are the type you have, in this mode it will charge to 4.1V max per cell)
Or LiPo SET V Type 3.7V (this is for Lipo's, and it will charge to 4.2V max per cell)

(You can charge your cells to what ever you want. 4.2v is probably better for testing if your not going to leave them like that for a very long time.
I finally went to 4.15 for the self drain test because I got a meanwell S-150-5 and moded it for lithium cells.
I suggest you get a S-150-5 and mod it if you want to go pro. It's only like 30 bucks and it's really not that hard of a mod even for a beginner like me. And then you can just set the open circuit voltage to what ever you want and walk away. And charge as many as you want at a time.)

Hit enter.
Then it will let you toggle between the three.
Hit enter when you get the one you want.

Then hit the back/stop/batt. type button twice.
Then you will be at the lithium charging main menu of your selection.

Hit enter.
Hit enter again to toggle to the amps and series selection.
Put it to 5 amp 1s
hold enter.
it will check things for a second
hit enter to start charging.

I am getting 3.8 as a max charge with my b6ac charger. Should I maybe stick with that voltage? I will be running the pack at just about it's max 2c rating over half of the time riding.

There's three possible reasons why you only got them to charge to 3.8V.
A) You had it in Lifepo4 mode, so it will only charge to 3.8V per cell in this mode.
B) You have really hi resistance in your cells! (if it's this bad you don't want to use them anyway) The B6 wont push past the max volts and if no more amps are going into the cells then it will stop the charge. Even if the cells are not up to the voltage selected.
C) You didn't change the time limit. This is in the user set program also. The factory setting is only 120min. After 120min it will stop charging.
Max time is 720min or you can urn the timer off.

I charged a bunch of really crappy lappy cells with the b6.
In the Lion mod I never got the cells to read the full 4.10V after charging.
It was usually 4.09 or 08 or even 07.
I was pretty anal about getting them all to the exact same voltage before letting them sit for the self drain test.
So I would use Lipo mode for a bit to push them to the 4.10V I was looking for. So they were all the same.