Unsure About Changing Cell mAh Rating On Battery Rebuild

Thread Starter

PGB1

Joined Jan 15, 2013
119
Hello To All!
I have a driver-drill by AEG that has served me faithfully for 27 years. It is the old, still German, AEG model ABSE 13.
The batteries are composed of (8) Sub-C NiCd at 1400 mAh each.

About a year ago, one battery failed to fully charge. Meter readings indicate 5 cells are bad. The other one failed today. Meter readings show 4 cells are bad. I wish to replace the cells, but have not been able to find 1400 mAh in sub-c. The closest I found were 1800 mAh.

The charger is labeled 11.6 vdc output and 1.5 amp DC. The battery packs have what I believe is a thermistor for protection. (Photo attached) It is labeled "6K8K", but I could not find a data sheet. It's connected across a terminal marked "R" and the negative battery terminal.

I've studied here & elsewhere about battery capacities and chargers, but so much information is in direct conflict with another article, so I got confused.

My primary question is whether using 1800 mAh cells will allow the battery packs to fully charge or will it damage either the charger or cells?
Is there any advantage to using the 1800 mAh cells (or larger) for longer run time, or will the charger simply stop at the 1400 rating?

And, to verify, changing to NiMh would be a very bad plan, as I understand chargers & charging. (Also, as I understand it, NiMh are not very good for motor loads.)

Thanks For Helping me with these questions. I appreciate the education & guidance!
Enjoy This Day,
Paul
A.JPG B.JPG
 

dl324

Joined Mar 30, 2015
12,917
My primary question is whether using 1800 mAh cells will allow the battery packs to fully charge or will it damage either the charger or cells?
Assuming you're not planning to mix and match cells with different Ah ratings, whether your charger will charge the larger cells is an unknown. In theory, larger capacity batteries would just take longer to charge. But a member recently tried to charge a larger SLA battery than his charger was designed for and it broke...
Is there any advantage to using the 1800 mAh cells (or larger) for longer run time, or will the charger simply stop at the 1400 rating?
It depends on the charger, but it's most likely that the charger will keep charging until it reaches whatever it determines to be complete.

If you're considering repairing your battery pack, keep in mind that manufacturers use matched cells when constructing packs. This gives them the best chance at providing a reasonable lifetime. What typically happens in a battery pack is that one cell will weaken before the rest. When it becomes exhausted, it's stronger neighbors will reverse charge it. It takes very little reverse charging current to destroy a battery.
 

Thread Starter

PGB1

Joined Jan 15, 2013
119
Thank You dl324 for taking time to reply & educate. Your help is appreciated!

I'll buy all eight cells at once so hopefully they will be matched. It seems that 1800 mA will be the closest I can get in the Sub C size, so time will tell if they charge fully or if they get damaged. If one rebuild is successful, I'll do the other pack. I'm not concerned if the 1800's only charge to 1400 mA. Since I work so s l o w l y, by the time I exhaust pack one, pack two will be well charged.

I thought about going to the local battery rebuilding shop, but it will be more fun as a DIY project (and much less expensive). Hooray for solder tabs!

Regarding charging termination, the best I can figure out by studying the charger's circuitry is that the component in the attached photo is a thermistor. It is wired to a comparator (LM339N), so I believe (possibly mistakenly) that when the resistance changes in the thermistor by heat, the comparator will switch from full charging mode to trickle mode.

Thank You Again for your help. I do appreciate it.
Enjoy This Day!
Paul
 

dl324

Joined Mar 30, 2015
12,917
I'll buy all eight cells at once so hopefully they will be matched.
If they're not in the same package, chances of matching are slim to none. Even within the same batch, there will be variances. You have to test each battery to get closely matched characteristics.

Hooray for solder tabs!
Make sure you use a high wattage soldering iron to minimize heat buildup in the batteries.
 

ebp

Joined Feb 8, 2018
2,332
How long did it take to charge the original battery when it was new? The output current of the charger is high relative to the cell capacity, which may mean that the original cells were specifically designed for very fast charging and "ordinary" cells, even though slightly higher capacity, may not cope with such a high charge rate. (just had a look at a cell from Panasonic - 1800 mAh rated for fast charging at 2.7 A! https://media.digikey.com/pdf/Data Sheets/Sanyo Energy/KR-1800SCE.pdf )

There is little concern with matching for nickel cadmium cells. They are "always" overcharged to some extent to assure that each cell in a battery gets fully charged (see datasheet linked above). Typically with fast chargers, a high current is applied to start with and eventually the charging current is dropped to so-called "trickle" level. NiCd cells can be kept continuously on low-current trickle charge without damage, which actually makes the the easiest of the common cell types to charge. The cells will become unbalanced over time as they age differently.
 

ian field

Joined Oct 27, 2012
6,539
Hello To All!
I have a driver-drill by AEG that has served me faithfully for 27 years. It is the old, still German, AEG model ABSE 13.
The batteries are composed of (8) Sub-C NiCd at 1400 mAh each.

About a year ago, one battery failed to fully charge. Meter readings indicate 5 cells are bad. The other one failed today. Meter readings show 4 cells are bad. I wish to replace the cells, but have not been able to find 1400 mAh in sub-c. The closest I found were 1800 mAh.

The charger is labeled 11.6 vdc output and 1.5 amp DC. The battery packs have what I believe is a thermistor for protection. (Photo attached) It is labeled "6K8K", but I could not find a data sheet. It's connected across a terminal marked "R" and the negative battery terminal.

I've studied here & elsewhere about battery capacities and chargers, but so much information is in direct conflict with another article, so I got confused.

My primary question is whether using 1800 mAh cells will allow the battery packs to fully charge or will it damage either the charger or cells?
Is there any advantage to using the 1800 mAh cells (or larger) for longer run time, or will the charger simply stop at the 1400 rating?

And, to verify, changing to NiMh would be a very bad plan, as I understand chargers & charging. (Also, as I understand it, NiMh are not very good for motor loads.)

Thanks For Helping me with these questions. I appreciate the education & guidance!
Enjoy This Day,
Paul
View attachment 164370 View attachment 164371
My solution isn't for everyone, but I just upgraded my old (2005) Parkside drill (lidl own brand) with a Dyson lithium pack from the recycling bin (same shop).

The pack is 21V/6 cells and my 18v drill only needs 5 of them, but the intact pack makes a good "foot" for the drill - so I didn't bother destroying it.

Still need to find a 5 cell balancer PCB, so for the time being I have to supervise charging and balance individual cells as required. But both of the old Ni-Cd packs were self discharging in a matter of days...………

battery weight is what makes the unwieldly drill (allegedly) stable on its "foot" - the old cells were left in place but isolated, and the new pack glued on the bottom.
 

Thread Starter

PGB1

Joined Jan 15, 2013
119
Thanks Dennis, Ebp & Ian for replying.

Regarding the charge rate that Ebp asked about- Originally it took about an hour to charge an exhausted battery. As the batteries aged, charge time was shorter. I suppose the bad cells caused the pack to heat faster, telling the charger to switch to trickle.

I looked into various cells rated for fast charging, like those linked to by Ebp. The cost was about 50 USD for (8) fast charge capable cells versus about 6 USD for (8) 2800 mAh no-brand. For this old drill tool, I may experiment with one battery pack & buy the highest capacity cells I can get in the low price range to see if the charging circuit damages them.

If the new cells soon fail, I'll choose between investing for the fast charge cells and changing the entire project over to Lithium, as Ian mentioned. Lithium would be a 'just to learn & see if I can do it' project and not cost justifiable for this drilling tool- but fun anyway.

I'm hoping that, since (I think) the fast charge cycle is terminated by temperature, I can 'behave' and be sure never to put the battery in & out of the charger before running it low- hoping for accurate temperature sensing. My theory is the temperature sensing will help protect the cells from the damage of fast charging. (Totally an uneducated theory.)

Once I read (somewhere & long ago) that new NiCd cells should be built into the pack and then charged as slowly as possible for, perhaps, a day. The idea behind this was to try to balance the new cells by slowly bringing them to the same charge level. I have a 150 mA DC power supply to use for this. I can adjust the voltage to suit. Hopefully an initial slow charge will be beneficial to the cells.

Thanks Again everyone. I sure appreciate your help and advice.
Paul
PS: Let us know how your lithium conversion goes, Ian. I'll be curious to hear!
 

ian field

Joined Oct 27, 2012
6,539
Thanks Dennis, Ebp & Ian for replying.

Regarding the charge rate that Ebp asked about- Originally it took about an hour to charge an exhausted battery. As the batteries aged, charge time was shorter. I suppose the bad cells caused the pack to heat faster, telling the charger to switch to trickle.

I looked into various cells rated for fast charging, like those linked to by Ebp. The cost was about 50 USD for (8) fast charge capable cells versus about 6 USD for (8) 2800 mAh no-brand. For this old drill tool, I may experiment with one battery pack & buy the highest capacity cells I can get in the low price range to see if the charging circuit damages them.

If the new cells soon fail, I'll choose between investing for the fast charge cells and changing the entire project over to Lithium, as Ian mentioned. Lithium would be a 'just to learn & see if I can do it' project and not cost justifiable for this drilling tool- but fun anyway.

I'm hoping that, since (I think) the fast charge cycle is terminated by temperature, I can 'behave' and be sure never to put the battery in & out of the charger before running it low- hoping for accurate temperature sensing. My theory is the temperature sensing will help protect the cells from the damage of fast charging. (Totally an uneducated theory.)

Once I read (somewhere & long ago) that new NiCd cells should be built into the pack and then charged as slowly as possible for, perhaps, a day. The idea behind this was to try to balance the new cells by slowly bringing them to the same charge level. I have a 150 mA DC power supply to use for this. I can adjust the voltage to suit. Hopefully an initial slow charge will be beneficial to the cells.

Thanks Again everyone. I sure appreciate your help and advice.
Paul
PS: Let us know how your lithium conversion goes, Ian. I'll be curious to hear!
DIY lithium packs are only for the brave and foolish - and probably not a great idea to do fast charging indoors.....

I was desperate enough to chance it till I get hold of a suitable balancer board. If you burn your house down - its not my problem.
 

toffee_pie

Joined Oct 31, 2009
215
27 year old drill, the sensible thing to do is leave it rest in peace and buy a new drill - its all well and good having a go at 'fixing' this up but having worked with lithium cells they are not for fooling around and like the poster said, if you burn your house down how much will it cost relative to a new drill?!
 

Thread Starter

PGB1

Joined Jan 15, 2013
119
27 year old drill, the sensible thing to do is leave it rest in peace and buy a new drill
You know, Toffee-pie, you've got a good point. Since it is my favorite drill tool, I will try some inexpensive cells on one battery and see how it goes. If successful- maybe battery number two will be next.

Why Even Try?
I am admittedly quite illogical about this drill-driver. To me the tool is, indeed, pretty spiffy. It's compact to fit in small places. It's geared so far down that it always had great torque. The removable flashlight is kinda-sorta handy, as is the removable bit holder base. But my favorite feature is that the chuck comes off easily & leaves a 1/4 hex socket behind for driver bits. Oh Yeah- It's the only one my wife likes to use.

As far as experimenting with lithium in concerned: As soon as I posted my reply I thought about it & voided the idea, remembering how dangerous lithium ion & lithium polymer can be. (Thinking back on what happened when one of our lap top batteries self-failed.)
I'd have to learn much more than I wish to learn before proceeding. I'd rather use up my learning power on more fun & useful electronics.
 

ian field

Joined Oct 27, 2012
6,539
27 year old drill, the sensible thing to do is leave it rest in peace and buy a new drill - its all well and good having a go at 'fixing' this up but having worked with lithium cells they are not for fooling around and like the poster said, if you burn your house down how much will it cost relative to a new drill?!
My mistake was rebuilding a weird shaped laptop pack while I had an evil dose of flu..

Pretty lucky none of the little "rocket motors" disappeared under any furniture...…………….
 
Top