DIY 18v drill battery problem

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Dragosh Shescu

New member
Joined
Oct 4, 2017
Messages
6
Hello,

I'm currently trying to build a battery to power a drill, the configuration that I use is 6s3p. The problem that I ran into is that when powering the drill to above 70% power the battery starts to sag and 1 specific cell, the one in the middle of the first series pack from the negative terminal (the battery heats at the positive end). And after the cell heats the motor cuts the power.

How do I fix that? The same problem existed when I had the configuration 5s3p and even after I replaced the cell.
The battery is charged to 25v and the cells are pretty balanced.

I know I may have not explained the problem properly due to limited experience, but please feel free to ask any other details.
 
We need more info, What brand and model are the cells? What is their Capacity (tested) is there any external BMS or other contributing factor
 
jdeadman said:
We need more info, What brand and model are the cells? What is their Capacity (tested) is there any external BMS or other contributing factor
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The brands are mostly samsung and LG 18650, the capacity is in between 1400 - 1800, and no BMS.
 
Generally when using Cells that are mismatched in capacity and Max draw there will be issues when using a low parallel count pack. I just did a Milwaukee Hammer drill battery that has 5 26700 series cells with 10 18650's All the Same capacity (within 50mah) and the exact same model. I can run this back down to the bottom with zero issues.
 
Dragosh: Why did you double post thread? Delete the other one, please.
 
Korishan said:
Dragosh: Why did you double post thread? Delete the other one, please.
Click to expand...

I posted it twice because I didn't know it takes a few minutes for it to be posted, and I would delete it if I knew how :D
 
Do a full edit on the post, then at the top of the page theres the option to delete the whole thread. ;)
 
And what models are the cells? Are you using reclaimed 18650s from laptop batteries for a powertool? That is never going to work properly.
 
DarkRaven said:
And what models are the cells? Are you using reclaimed 18650s from laptop batteries for a powertool? That is never going to work properly.
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I am using salvaged batteries from laptop batteries
 
Dragosh Shescu said:
DarkRaven said:
And what models are the cells? Are you using reclaimed 18650s from laptop batteries for a powertool? That is never going to work properly.
Click to expand...

I am using salvaged batteries from laptop batteries
Click to expand...

Laptop cells being used in tools is going to be problematic. The reason being that they are not designed for amp draw. Most are rated at or around 1C. A power tool needs something that's rated around 10C or more to be effective. For a pack that's for a lawnmower is a little different because usually that pack is built with 15p or more to handle the amp draw. Plus those motors don't normally pull a lot of amps except on start up, then drop fairly low afterwards.

For use in power tools, you need a different source. Like other power tool packs. If you can get a hold of damaged/non-working power tool packs and take out the cells, replace the bad ones, add another stack or 2 in parallel, you'd get a really good pack in the end.
 
Korishan said:
DragoshShescu said:
DarkRaven said:
And what models are the cells? Are you using reclaimed 18650s from laptop batteries for a powertool? That is never going to work properly.
Click to expand...

I am using salvaged batteries from laptop batteries
Click to expand...

Laptop cells being used in tools is going to be problematic. The reason being that they are not designed for amp draw. Most are rated at or around 1C. A power tool needs something that's rated around 10C or more to be effective. For a pack that's for a lawnmower is a little different because usually that pack is built with 15p or more to handle the amp draw. Plus those motors don't normally pull a lot of amps except on start up, then drop fairly low afterwards.

For use in power tools, you need a different source. Like other power tool packs. If you can get a hold of damaged/non-working power tool packs and take out the cells, replace the bad ones, add another stack or 2 in parallel, you'd get a really good pack in the end.
Click to expand...

Thank you very much for the advice! And btw, I still didn't manage to find the delete thread button for my other post.
 
DragoshShescu said:
Thank you very much for the advice! And btw, I still didn't manage to find the delete thread button for my other post.
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Doing a "Full Edit" on the thread, at the top of the page is the following:

image_tmyrce.jpg
 
image_pzrprz.jpg

Korishan said:
DragoshShescu said:
Thank you very much for the advice! And btw, I still didn't manage to find the delete thread button for my other post.
Click to expand...

Doing a "Full Edit" on the thread, at the top of the page is the following:

image_tmyrce.jpg
Click to expand...

This is what I see, no delete option.

image_oxeqcm.jpg
 
DragoshShescu said:
image_pzrprz.jpg

Korishan said:
DragoshShescu said:
Thank you very much for the advice! And btw, I still didn't manage to find the delete thread button for my other post.
Click to expand...

Doing a "Full Edit" on the thread, at the top of the page is the following:

image_tmyrce.jpg
Click to expand...

This is what I see, no delete option.

image_oxeqcm.jpg
Click to expand...
I can confirm that on a thread that I had started (Multi Purpose Custom Battery Packs) if I do a "Full Edit" on the first post in the thread, there is no delete thread option like your screenshot.
 
Ok, good point. That is odd. It used to be visible as I had pointed another user to do the same thing. Will be checking in with the site coder.

I'll delete your other thread. ;)
 
I agree with the comments about the use of laptop packs in high drain applications. You really need to source "power cells" or high drain cells which are designed to dish out the current.

Laptop cells unfortunately are designed for more of a sustained low amperage draw. They generally have a higher internal resistance as well, but as a trade off they generally are available in higher capacity/mAh.

Unfortunately high-drain are hard to come by unless you have a source for power tool packs... I had to re-do a drill pack and bough some new Samsung 25R cells and the performance was pretty amazing. I was very impressed what a 5s1p batter was able to deliver (40 amps peak / 700 watts). The only downside is I had to spend money on new cells, but it was worth it in the end.

Here is a link to my thread if you are interested.
https://secondlifestorage.com/t-Converted-tool-battery-pack-from-NiCad-to-Lithium
 
Crimp Daddy said:
The only downside is I had to spend money on new cells, but it was worth it in the end.
Click to expand...

Still cheaper than buying a new battery pack for the tools, though ;) Plus you probably got better quality cells in the end.
 
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