Re-celling a dead Li-ion

[Screwdriver]

There's an old thread here: https://www.mig-welding.co.uk/forum/threads/bosch-10-8v-12v-upgrade.91244/ but looks like I didn't spin it out to the punchline. FWIW, I ended up with some seriously high spec battery units fro my 12v range of tools.

Recently I bought a dead circular saw off @angellonewolf which we both assumed had dead battery cells. We were both right. Half the cells are dead and I will go through the process of re-celling this pack just so you can see what that entails (and whether or not it works!)

I popped the case off and peeled back the protective layer of foam insulation. This thing is now very dangerous. Short it out and a lot of amps are going to escape, all at once.

A quick check reveals low voltage, a sure sign of a dead cell, about 16v iirc compared to the 19 or 20v you should expect with 10 cells, five in series, then parallel. The board has to come off and there's a temperature sensor tucked away in between the middle cells.

I am fairly gung-ho about ripping these things apart so I prise off the spot welds which is absolutely not recommended! Some of them came off easier than others...

That's about as far as I got. All the cells are free, five out of the ten are stone dead, not all in the same circuit and I might expect some to recover though they're all going in the recycle bin. popping the weld off means the case is already compromised and I have a ton of spare cells waiting to find a new home.

Some battery packs have a battery backed switching circuit which disables the unit permanently if all of the cells are removed. That's common in laptops and high value items, some tool manufactures are doing it too but I am hoping this one doesn't. Soon find out.

 

[eLuSiVeMiTe]

Lipo?
Look like lion to me

 

[Screwdriver]

Lipo?
Look like lion to me

oops. yep sorry, Li-ion 18650s.

 

[angellonewolf]

thanks for the tag @Screwdriver looks like you could not wait i watching in hope it all goes well

 

[Matchless]

I just replaced some cells in a Segway battery, well after stripping the battery I bottled it and sent it to a geek on the Segway forum, one of two on the X2se, 92 lifepo4 18650 cells in each battery from memory

replaced 16 with good used of the same capacity,

 

[mtt.tr]

Makita have a small board which drains 2 cells, battery is then unbalanced so wont charge 3 attempts it kills the battery

 

[eddie49]

with 10 cells, five in series, then parallel

The way the nickel strips are arranged, I think each cell in the 5-series string is also paralleled with a partner in the second 5-series string.. The battery would be described as 2p5s.

 

[Screwdriver]

Finally all apart, tidied up the ripped off connectors.

This is a big no-no. Received wisdom states never solder directly onto the cells or they may overheat. Yeah well, I don't care.

I like to live dangerously. Connectors are well tinned as are the caps, solder in place and hold down the connection as the solder cools.

All done. The solder joint isn't as bad as it looks here, this is the dirty side where all the gooey tape was.

Bit of insulating tape to protect the sides (from what I don't know).

Gratuitous picture of a battery not in pieces.

...and after just a few minutes with these secondhand, ex. vape shop battery cells, I get a green light. That's not to say it's definitely fixed but there was a definite problem with some cells and there's no problem with them now.

It lives! 180mm brushless circular saw with a 20v 5Ah 90Wh battery. Somebody tell @angellonewolf, he'll be delighted to hear it.

Very nice bit of kit. Can't wait to start cutting stuff up.

 

[Screwdriver]

Incidentally, I should say I lucked out with the batch of cells I rescued from a local vape shop. They were mostly Samsung 25R, 2500mAH 20A cells, the exact same version as I took out of the dead battery pack. For reference some of the good cells from the old pack were registering 4.3v, I found 10 off good secondhand ones which all had 4.1v life left. Internet says the cells need to be within 0.1v of each other to maintain a good balance in the battery pack.

 

[Screwdriver]

Well it works, went through some damp 25mm marine ply easily enough though I think that's a realistic limit for the blade at least.

I haven't flattened the battery pack yet but I think I should at least do that once just to make sure it's all good.

Super happy with it but I need to brush up my circular saw skils (see what I did there?). I think the blade seems a little flexible, certainly "it" wandered off track on me but it was a quick and dirty test and I haven't used a circular saw much. I did have this one briefly: https://www.mig-welding.co.uk/forum/threads/the-eagle-has-landed.83277/ but I decided to give it to the same chap I just made those shelves for. What goes around comes around.

 

[angellonewolf]

good to see you got it working

would have been to see a video of the fix next time the testing and soldering

what soldering iron/wattage did you use

 

[Screwdriver]

I would dearly like to get going on my YouTube production but so many hurdles to jump before I can commit to it. Soon though.

No idea what the wattage is, it's fairly chunky though. Here's my little soldering station.

And I'll also look this up and see if Google knows.

 

[Matchless]

you can easily make a battery spot welder from a capacitor or a 12v battery according to youtube so it must be true,

 

[Munkul]

Nice work

I've replaced the dead PCBs in a couple of Makita 18v batteries now, the PCBs seem to die before the cells! This is the newer 5ah ones with voltage feedback from every cell pair. You remove all the contacts from the PCB, and the new (chinese copy PCB) wires to the +ve and -ve ends of the cell string, and pulls voltage feedback from a single cell pair like the original makita batteries. It also doesn't have the charge level indicator either, unfortunately. But the batteries seem to work just as well as they did when new.

 

[AndySV1K]

We've done quite a lot of battery refreshing. Made a spot welder to do the job as soldering is risky to the batteries, you need a really powerful iron with a large tip. At least 100w so you can dive in and solder within a second or two without heating up the cell.

It's nice to get something working again that someone else thinks is scrap!

 

[Screwdriver]

you can easily make a battery spot welder from a capacitor or a 12v battery according to youtube so it must be true,

I think if I do many more of these cell replacements, spot welding is the way to go for sure. Soldering is fraught with problems but if a weak cell does go bang, I'd rather it did it at that stage than later.

 

[angellonewolf]

you can easily make a battery spot welder from a capacitor or a 12v battery according to youtube so it must be true,

yea and remove your hand as well when the battery goes bang

quite a few years ago a friend of a mate put a microsoft 360 in a freezer because youtube said it would work

sufice to say after he took it out the freezer (and also never waited for the console to even warm up and dry out it released a puff of smoke after a fair size bang

 

[mtt.tr]

Nice work

I've replaced the dead PCBs in a couple of Makita 18v batteries now, the PCBs seem to die before the cells! This is the newer 5ah ones with voltage feedback from every cell pair. You remove all the contacts from the PCB, and the new (chinese copy PCB) wires to the +ve and -ve ends of the cell string, and pulls voltage feedback from a single cell pair like the original makita batteries. It also doesn't have the charge level indicator either, unfortunately. But the batteries seem to work just as well as they did when new.

They have a 3 failed attempts strikes the battery off

 

[Munkul]

They have a 3 failed attempts strikes the battery off

Yes, but like I say, they pull voltage feedback from every cell pair now, not just one. So in theory unless a cell actually goes bad, they should never have a failed charge attempt.

The cells on the 3 batteries I've done - none of the cell pairs were anywhere near out of spec.

One of the batteries was a mate's, who had had it for 2 months and had done practically nothing with it... and the cell string measured about fully charged! around 20 volts anyways.

So... why do they have failed attempts to charge at all?

 

[mtt.tr]

Yes, but like I say, they pull voltage feedback from every cell pair now, not just one. So in theory unless a cell actually goes bad, they should never have a failed charge attempt.

The cells on the 3 batteries I've done - none of the cell pairs were anywhere near out of spec.

One of the batteries was a mate's, who had had it for 2 months and had done practically nothing with it... and the cell string measured about fully charged! around 20 volts anyways.

So... why do they have failed attempts to charge at all?

Frustrating isn't, i had a flexvolt batter die about 2 months old. Just pleased they did it under warranty.