Author Topic: Question about LI-ION battery pack  (Read 3369 times)

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Offline RTFM

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Question about LI-ION battery pack
« on: October 12, 2016, 12:17:19 pm »
Hello everyone recently I found 10.8v cordless drill with li-ion batterys I belive they are three 18650 batterys in the pack.But I don't have charger for the drill so I bought some really cheap ac to dc adaptor. Battery pack is 13000mah,so I get 600mah charger fo li-ion batterys. Here is where the problem comes the charger output 13.2 v instead of 12.6 volts. I charge the battery pack once knowing that the battery pack have protection circut build in and I checked the voltage constantly with my mulitimeter when it gets 12.6 volts I disconnect the battery pack,it wasn't warm or anything. My question is isn't it bad for the battery pack if voltage is 13.2v isn't that a bit high. I was thinking of puting some silicone diode in series with plus of the charger and by getting voltage drop from 0.6-0.7 to put the voltage to 12.5-12.6 volts but I don't wanna do it if it doesn't matter. SO is it dangerous for the battery pack if charger outputs 13.2V instead of 12.6? I'll appreciate your advices,thanks in advance!
« Last Edit: October 12, 2016, 12:22:33 pm by RTFM »
 

Offline tahp

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Re: Question about LI-ION battery pack
« Reply #1 on: October 12, 2016, 01:59:56 pm »
in my experiences with chargers, they would always output slightly higher voltage so I think you're safe.
 
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Offline Audioguru

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Re: Question about LI-ION battery pack
« Reply #2 on: October 12, 2016, 02:21:23 pm »
3 Li-ion cells should be charged to a maximum of 12.6V, not higher. Old Ni-Cad cells or newer Ni-MH cells are charged higher than their rating. One 18650 Li-ion cell has a capacity of only about 3000mAh and three in series also will be about 3000mAh, not 13000mAh.
When the battery charging voltage reaches 12.6V it is not fully charged, it is still charging until its charging current drops low, then the charger should detect it and shut off.

Your 13.2V voltage source might not be a Li-ion charger but instead it might be the power supply for a charger circuit. Its output voltage is probably not regulated and sometimes will be even higher than 13.2V. It is very dangerous to try charging Li-Ion without a proper charging circuit.

There are many cheap fake Li-ion 18650 battery cells. Some have a good photo of a protection circuit (not a real circuit) glued to one end.
 
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Offline RTFM

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Re: Question about LI-ION battery pack
« Reply #3 on: October 12, 2016, 02:40:45 pm »
Battery pack say 1300mah not 13 000 wich I charge with 600ma current and 13.2V my bad but still the pack originaly have some protectuon circut from the manifacture wich should stop overcharge and overdischager. Inside  the charger there is no electronic in charging unit contains only in adapter wich produce exactly 13.2v every time. I know it is dangerous that's why I wanna ask what do u think about my idea to limit the voltage with silicon diod to drop the voltage...and does it matter I don't belive in the charger it's very cheap that's why I constantly measure the battery pack and when it gets to 12.5v I disconnect it cause I'm not trusting manifacture protection circut ether. But strange thing is that I don't see any heat beeing produced. Maybe 13.2 is normal at 600ma as long as I never leave the pack to go more than 12.6 it doesn't matter that charger puts 13.2 dunno that's why I'm asking u guys...what should I do I really don't wanna spend 60$ for charger considering that drill is basiclly free. And yeah I know at 12.6 volts battery is not full cause current should start to go down I don't need to be full all the times I need only to charge them in some way no matter if they are 90 not 100%...my other choice is cheap chinese benchtop power supply circuit at 600ma and 12.6 volts cc then cv but...
« Last Edit: October 12, 2016, 02:54:04 pm by RTFM »
 

Offline buffoon

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Re: Question about LI-ION battery pack
« Reply #4 on: October 12, 2016, 03:15:36 pm »
The battery would pull the source down to its voltage. It should be fine as long as the current is at or under your desired rate AND you can really disconnect the battery every time before it gets above 12.6. it doesn't get warm because your charg rate is low at <0.5C.

 Not a great idea in my opinion.

« Last Edit: October 12, 2016, 03:17:28 pm by buffoon »
 
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Offline Gyro

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Re: Question about LI-ION battery pack
« Reply #5 on: October 12, 2016, 03:27:27 pm »
Battery protection circuits are there as 'emergency shutoffs' to prevent a cell meltdown in a fault situation, they are not there as charge voltage limiters as they cut off somewhat above 4.2V (per cell). Relying on this will seriously shorten the life of the battery pack.

An additional concern... if you use the emergency shutoff as part of the charger circuit, then where is your second level of protection if it fails? Li-ion need to be treated with caution and respect.
Chris

"Victor Meldrew, the Crimson Avenger!"
 
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Offline CraigHB

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Re: Question about LI-ION battery pack
« Reply #6 on: October 12, 2016, 03:30:15 pm »
I'll second that comment about charging, it ~is~ quite dangerous in terms of fire or even explosion charging a Li-Ion pack without a proper Li-Ion charger.  Though if you insist on doing it, there's two critical specs. 

Voltage can not exceed 4.2V per cell for a standard Li-Ion.  Though there are high voltage Li-Ions that terminate charge at 4.35V per cell, they are not typically used in power tool packs.  This can be problematic for a pack charger in lieu of a balance charger that does not have a mechanism to balance cells.  Pack chargers have no way of preventing an imbalance that can cause a cell to go over tolerance, specifically that's 4.25V per cell absolute maximum with less being preferable.

For a standard Li-Ion, charge current can not exceed 1C or one times the charge capacity.  Power tool packs use high drain cells which are typically good up to a 2C charge rate or two times the charge capacity.  In your case that would be 2.6 Amps.  Current limits are not something easily guaranteed by a simple power supply.

As long as you don't violate either of those two specifications, you'll be good.  However, it's not something easily ensured without a proper Li-Ion charger.  Without a tightly regulated supply, voltage tolerance can easily be exceeded.  When packs are depleted, charge current can and likely will exceed tolerance. 

« Last Edit: October 12, 2016, 03:51:29 pm by CraigHB »
 
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Offline jitter

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Re: Question about LI-ION battery pack
« Reply #7 on: October 12, 2016, 03:59:40 pm »
Yes, I was wondering about balance charging as my Makita 10.8 V 1300 mAh battery has all the contacts on the outside to do this (2 main + 2 balance therminals + Temp).
Using a multimeter, I can measure each individual cell without even cracking the pack open, and they are almost industinguishable from eachother, voltage wise, despite being over 5 years old.

@RTFM: could you tell us what make and type of battery you have there?
Does it have only the two terminals or more?
« Last Edit: October 12, 2016, 04:23:24 pm by jitter »
 

Offline RTFM

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Re: Question about LI-ION battery pack
« Reply #8 on: October 12, 2016, 04:12:14 pm »
I have Einhell 10.8V cordless drill,I have 3 terminals, + -  and T wich is to watch the temperature of the pack I guess. I don't have original charger but I think so that is what it does,but my battery pack can be opened and there is 3 cells inside and protection circuit. It was completly dead and now is working fine...duuno for how long I don't use it too often but still working and have good amount of power. I never measured balanced or not but I don't think original charger have way to balance cells too cause only 3 external terminals,of course the protection circuit have taps between each battery but does it balance it I don't know. Thanks to anyone who replay to my topic guys...I'll see what I'm gonna do...Now everything is working but I must find more efficient way to charge that pack and safer too.
« Last Edit: October 12, 2016, 04:18:17 pm by RTFM »
 

Offline jitter

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Re: Question about LI-ION battery pack
« Reply #9 on: October 12, 2016, 04:13:45 pm »
..my other choice is cheap chinese benchtop power supply circuit at 600ma and 12.6 volts cc then cv but...

I missed this bit.

Yes, the bench supply is the only way to go if you don't want to buy a proper Li Ion charger circuit. The max. voltage can be set and is probably a lot more stable than that cheap adapter. Keeping it below the maximum permissible voltage is by far the most critical thing to do with Li Ion batteries, followed by limiting the current to a specified max. current (depends on the type of cell, cordless power tools will most likely have reasonably high current capabilities).
But maybe you could look around AliExpress. Something like this for less than € 10 should do. This particular one is designed for use on a solar panel, but no doubt it could work off your bench supply as well.
« Last Edit: October 12, 2016, 04:21:56 pm by jitter »
 
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Offline jitter

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Re: Question about LI-ION battery pack
« Reply #10 on: October 12, 2016, 04:20:06 pm »
I have Einhell 10.8V cordless drill,I have 3 terminals, + -  and T wich is to watch the temperature of the pack I guess. I don't have original charger but I think so that is what it does,but my battery pack can be opened and there is 3 cells inside and protection circuit. It was completly dead and now is working fine...duuno for how long I don't use it too often but still working and have good amount of power. I never measured balanced or not but I don't think original charger have way to balance cells too cause only 3 external terminals,of course the protection circuit have taps between each battery but does it balance it I don't know.

Einhell is a budget brand, so the pack will most likely not be balance charged.
"T" will indeed be for temperature so that the drill and/or charger (most likely the latter) cut out when the pack gets too hot.

Einhell sells "1-hour" chargers for these batteries, so you most likely don't have to limit your bench supply to 600 mA, 1.3 A (or slightly more) should also be safe, and then you will notice the battery getting warm.
« Last Edit: October 12, 2016, 04:31:40 pm by jitter »
 

Offline CraigHB

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Re: Question about LI-ION battery pack
« Reply #11 on: October 12, 2016, 04:58:32 pm »
There are some consumer devices with Li-Ion packs that use a pack charger (just two wires) in lieu of a balance charger.  It's generally bad design to charge a Li-Ion pack that way, but you know how these products out of China can skimp on safety.  It can be done, but there is some risk of an imbalance driving the weakest cell over voltage tolerance.  It actually takes a good amount of voltage in excess to cause a healthy Li-Ion battery to go up in flames.  The main issue is pack charging can greatly accelerate wear.  In terms of safety, any propensity to fail is more likely with voltage over tolerance.
 
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Offline RTFM

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Re: Question about LI-ION battery pack
« Reply #12 on: October 12, 2016, 04:59:19 pm »
Yeah I get it,still I thought that if u charge it witch less current it will be more slow but u extend the battery life,not sure it's true.
 

Offline CraigHB

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Re: Question about LI-ION battery pack
« Reply #13 on: October 12, 2016, 10:30:33 pm »
Lower charge rates do reduce battery wear.  It depends though, the difference is greater with higher rates.  In other words there's a bigger difference between a 1C and 2C rate compared to a 1C and 1/2C rate.  Though once you get below 1/2C, the difference in wear is not worth much concern.  There's other things that can have a bigger impact.  Operating temperature is a significant one.  Another is how deeply the battery is discharged.  A battery running cooler taken to a shallower discharge will last longer than a battery running warmer taken to a deeper discharge.  The difference would be greater than that of a 1/2C and 1C charge rate.
« Last Edit: October 12, 2016, 10:44:50 pm by CraigHB »
 

Offline jitter

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Re: Question about LI-ION battery pack
« Reply #14 on: October 13, 2016, 04:33:18 am »
Added to that is that I once read that a Li Ion battery will slowly degrade over time anyway, i.e. lying there charged but unused.
How quickly will depend on the quality of the battery. I experienced this with the lower quality replacement battery for my Nikon camera. I had one original and three replacements. 5 years later, the original is fine, but the replacements had become mostly unusable as a result of increased internal resistance. I never let them run down completely, but they also never had many charge cycles as I don't use my camera that much. So this must have been self degradation.

Even just topping up the self discharged capacity once in a while doesn't mean the Li Ion will last forever. Actually, I also seem to remember that the self degrading is least prominent when the battery is stored at around 80% charge, not 100%. But this is only if I remember correctly.
« Last Edit: October 13, 2016, 05:20:20 am by jitter »
 

Offline CraigHB

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Re: Question about LI-ION battery pack
« Reply #15 on: October 13, 2016, 12:38:02 pm »
Shelf life is a another consideration with Li-Ions.  They're actually not the only secondary (rechargeable) battery type that suffers from degradation over time.  Lead-Acid batteries degrade similarly.  NiMH batteries typically have better shelf life, in some cases it can be much better than Li-Ion or Lead-Acid.  For example the Eneloop AAs have amazingly long Shelf life. 

Li-Ion shelf life can be extended by storing batteries with a charge around 50%.  Factories tend to store their stocks at 40% charge which is 3.8V per cell.  There's also the impact of storage temperature.  Storing in a cooler environment extends shelf life.  Though I've seen data sheets recommend against cold storage for more than a year, it's debatable.  I have some stocks of Li-Ion cells I use for various projects and I store them in a refrigerator indefinitely.  Don't want to put them in the freezer though, that's below recommended storage temperatures.

One caveat to Li-Ion shelf life is the LiFeP04 type of Li-Ion.  Though that type has a lower voltage (3.2V nominal) and thereby lower energy density it has the best shelf life of any Li-Ion, similar to a NiMH battery.  LiFeP04 also has the best safety being the least volatile of the Li-Ion types.  It's actually the best Li-Ion type to use if it's possible to afford the lower energy density (cells are larger and heavier).  There's a really good maker for those by the name of A123 Systems.  They offer an 18650 as well as other sizes.
 

Offline Audioguru

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Re: Question about LI-ION battery pack
« Reply #16 on: October 13, 2016, 03:49:01 pm »
Li-Ion batteries hold a charge for a long time. I have the Li-Ion battery from my daughter's first cell phone that is 19 years old and it still holds its charge.
Shelf life is not the duration of holding a charge. Shelf life is the storage duration when the battery does not work properly anymore. A Li-Ion battery cell must be stored at about half-charged (3.8V) for it to survive. At full charge it is doomed after about 3 months.
 

Offline jitter

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Re: Question about LI-ION battery pack
« Reply #17 on: October 13, 2016, 08:08:05 pm »
Li-Ion batteries hold a charge for a long time. I have the Li-Ion battery from my daughter's first cell phone that is 19 years old and it still holds its charge.
Shelf life is not the duration of holding a charge. Shelf life is the storage duration when the battery does not work properly anymore. A Li-Ion battery cell must be stored at about half-charged (3.8V) for it to survive. At full charge it is doomed after about 3 months.

Really?
Why is it then that the original battery that came with my Nikon camera and both battery packs with my Makita drill are still fine after 60 months (give or take a few)? I have always stored them fully charged.
 

Offline CraigHB

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Re: Question about LI-ION battery pack
« Reply #18 on: October 14, 2016, 02:02:15 am »
If the Makita uses a LiFeP04 type Li-Ion battery, storing with a full charge will not have a big impact on shelf life.  The high drain cells most commonly used in power tool packs employ a lithium-manganese chemistry which has longer shelf life than a standard lithium-cobalt chemistry.  Standard Li-Ions lose about 20% of their charge capacity per year stored at room temperature with a full charge.  Lithium manganese drops that almost in half and lithium-iron-phosphate drops that again more than half.
 

Offline jitter

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Re: Question about LI-ION battery pack
« Reply #19 on: October 14, 2016, 07:38:36 am »
That's not the case. The Makita pack is 10.8 V and looks to have three cells of 3.6 V, so no LiFePO4. The Nikon pack is a single celled 3.7 V Li Ion battery and after 5 years I still got a (slightly) better capacity from it than specified. The replacements had all gone high internal resistance based on their discharge curvces. I haven't made a curve of the Makita packs yet.
 


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