Cordless power-tool battery repair

[SMdude]

STOP!

No, use the charger it came with, it is made for this battery and its protection circuit. Using other types of chargers is just asking for trouble. This is how those videos of battery fires eventuate!

What is the usual charging time for this battery from flat?

Get a full set of new batteries, make sure you ask that the ESR of the cells be matched, or as matched as possible. Do not go mixing and matching new and old cells(or old and old!). The capacity and cell esr will be different. Then the voltage drop across the cells will be different during discharge and charge(if it is not a balancing charger) and can cause the cells to drop below their critical low voltage before the protection circuit shuts off the battery, depending how it is all designed.

It is best if you can identify the cells used and replace with the same. You might have to use one of the good cells and put a load on it and measure the voltage every 10 minutes or so(depending on the load) until the battery is discharged to 3.2v and plot the curve to compare with the curve from other battery datasheets. Some chargers can plot the battery discharge curve and tell you the ESR. Some are considered discharged at a higher voltage than other cells and this is important as the protection circuit will be set for this. Also some devices will charge the battery over 4.2v/cell and if this one does this you need to select appropriate cells. They do this to get a bit extra capacity without the extra weight.

The Samsung INR18650 are used in many power tools as they are suited to the high discharge/charge currents. But I don't know if these will suit your battery, this is for you to figure out/risk!

How much is a replacement battery for your tool?

The thing you need to do is charge the battery occasionally in storage. If Li-ion cells discharge below their low voltage limit, they will be permanently damaged, especially if they are not charged straight away.

[KL27x]

How much is a replacement battery for your tool?

This is the same game in every country/market, isn't it? The manufacturer's batteries cost at least 1/3 as much as the tools, and sometimes more than the tool, itself!
Then the generic replacements might arrive, a year or two later, if your tool is popular.

I concur, though, that unless you have some experience under your belt, I wouldn't make a home-made charger. A noob making a one-off circuit with more than two components and 4 or 5 connections, and any number of things can break/fail.

Personally, I would calculate the charge rate of your charger, and get cells that meet that discharge/charge rate. If you know the charge time, you can sorta extrapolate that half the charge is finished in the first 1/3 of that time. So a 2 Ah battery that finishes charging in 30 minutes means the charger is pushing at least 6A of max current, or thereabouts. So you want a 2 Ah cell with at least 3C charge/discharge capability. Mind ye this is super rough, and you have to monitor temp and voltages to make sure things are working correctly. Super rough only works if you are competent and do some due diligence. This is what I would do... but I'm content with what I know, and I would be watching that water boil very closely for many cycles before I would turn my back on it.

Please, don't try this if it's a tool that you have to rely on and don't have time to mess around with. I only even suggest this is if you can afford to use this as a learning experience. You may quite likely have issues that could be dangerous. Burning down your house, death. The downside is pretty big. So if you are doing this to save money, once, so you can finish some other project, don't do it. If you do this, it should be the project, and expect to spend 12+ hours of your attention on it with DMM and what not, learning the reality, not just trusting the words on a computer screen. There are a hundred ways you can misinterpret and misapply what you have read. What this is is a chance to learn useful knowledge for pretty cheap, if you are careful and attentive, which you will be able to apply for the next 50 years.

[SMdude]

How much is a replacement battery for your tool?

This is the same game in every country/market, isn't it? The manufacturer's batteries cost at least 1/3 as much as the tools, and sometimes more than the tool, itself!
Then the generic replacements might arrive, a year or two later, if your tool is popular.

I concur, though, that unless you have some experience under your belt, I wouldn't make a home-made charger. A noob making a one-off circuit with more than two components and 4 or 5 connections, and any number of things can break/fail.

Personally, I would calculate the charge rate of your charger, and get cells that meet that discharge/charge rate. If you know the charge time, you can sorta extrapolate that half the charge is finished in the first 1/3 of that time. So a 2 Ah battery that finishes charging in 30 minutes means the charger is pushing at least 6A of max current, or thereabouts. So you want a 2 Ah cell with at least 3C charge/discharge capability. Mind ye this is super rough, and you have to monitor temp and voltages to make sure things are working correctly. Super rough only works if you are competent and do some due diligence. This is what I would do... but I'm content with what I know, and I would be watching that water boil very closely for many cycles before I would turn my back on it.

Please, don't try this if it's a tool that you have to rely on and don't have time to mess around with. I only even suggest this is if you can afford to use this as a learning experience. You may quite likely have issues that could be dangerous. Burning down your house, death. The downside is pretty big. So if you are doing this to save money, once, so you can finish some other project, don't do it. If you do this, it should be the project, and expect to spend 12+ hours of your attention on it with DMM and what not, learning the reality, not just trusting the words on a computer screen. There are a hundred ways you can misinterpret and misapply what you have read. What this is is a chance to learn useful knowledge for pretty cheap, if you are careful and attentive, which you will be able to apply for the next 50 years.

Yes the genuine batteries are never cheap.
The generic replacements that come about are never as good as the genuine batteries either.
There is such a variation in the price and performance of li-ion cells starting at junk for a few dollars each up to quite expensive!

It would be very handy if the brand and model number were printed somewhere on these cells.

What is the brand/model of power tool? This could provide some hints.

Cheers

[Liteace]

The tool is the Ingersoll rand 20V High-Torque Impact Wrench W7150, with BL2022 battery

[SMdude]

Ahhh, so this tool is the good stuff! They have probably used cells from the more expensive end of the scale.
I actually have one of these at work, however I won't be pulling the cells out to identify.

Looking at the colour of them, they remind me of the panasonic ncr18650a.
If you are settled on needing to remove and replace them, it might be worth your while removing at least the bad pair and seeing if there is any model number on them.

If and when you get replacement cells, if you don't have a battery tab spot welder, make sure you get replacement cells with solder tabs.

[abyrvalg]

The problem is in those 2 top cells, but it looks like it can be possible to get them back to life if they got charged to 3.5V in your test. They didn’t reach the full 4.15V (this is the setpoint of your charger) just because the other cells had higher initial voltage so they reached the full voltage faster and the charging process was stopped (it stops when ANY cell reaches the setpoint, it’s impossible to continue to charge the others without overcharging the already full cells).
You need to charge the top cells to the same voltage as on the other cells with a bench supply:
- measure the voltage of the "better" cells
- set the power supply’s voltage to that voltage
- set the power supply’s current to 1A (this is a no-stress for these high power cells for sure)
- connect to the top cells, observe the current and voltage (it will drop)
- leave it charging until the current drops to near zero (the voltage will raise back to the set value)
Check the cell voltages after that - they should be close to each other now. Try using the tool normally for some time, then check the cell voltages again - they should not run away.

If you decide to replace the cells - you need a 30A+ rated ones, like Sony VTC series (€3-4 per piece, https://eu.nkon.nl/rechargeable/18650-size/discharge-current/30-35.html). You need either two cells of the same model as the originals (they’ll run away otherwise since the charging speed will differ) or replacing all of them.

Edit: depending on the country there can be "vape shops" selling the high current cells (overpriced, but easier to buy).

[Liteace]

They didn’t reach the full 4.15V (this is the setpoint of your charger) just because the other cells had higher initial voltage so they reached the full voltage faster and the charging process was stopped (it stops when ANY cell reaches the setpoint, it’s impossible to continue to charge the others without overcharging the already full cells).

So the Battery management system is basically a load of shite, its sort of managing but not really,, problem is its got 2 batteries and Ive mixed them up now and dont know what one was the bad one, Im going to use the gun for a bit as see how it goes, use both batteries until just under half and test the voltage of all the cells in both

Have Samsung beat Panasonic now in the rechargeable cell world on quality ?

Thanks again for ALL your help guys

[abyrvalg]

Not all BMSes do balancing. Your one can be "protection only" type.

[Liteace]

Sorry Guys to dig this one up but need more help, I replaced the 2 under voltage cells with 2 brand new (not refurb'ed) Samsung INR18650-25R, these cells are identical to the 2 cells that I took out, I placed it on the charger unit and it charged, Ive got a high powered led worklight that also is uses this battery, I used the work lamp and left it on to discharge the battery pack so I could check it will charge again, it didnt.

I checked the all the cells again and same problem as last time
 
https://www.eevblog.com/forum/repair/cordless-power-tool-battery-repair/msg1972589/#msg1972589

2 end cells, low voltage, so the problem is not the cells may its the BMS?

 Ive managed to bring these new cells back up to voltage by trickle charging then with a 500ma charger, when they're up to voltage the main charger will charge them

Ive got 2 of these battery packs, the other 1 is OK, good job, I would like this one to be ok as well, whats the next step please, why is the BMS letting only these 2 end cells go under voltage?

Thanks

[najrao]

Liteace, with your permission I deviate from your problem - and ask about mine.

I have this exact same WR7150, but no battery at all, and no access to one even dead. When I got it, it had a motor connection detached (bad crimping), but I replaced the wire and soldered both ends. The switch trigger seems to be in good condition. It has a multilayer pcb with a microcontroller, and a Kapton ribbon cable to the innards, almost impossible to decipher.

Apart from the + and - power terminals, there are two more connections to the battery. From your photographs of the battery pcb, I identify them as "ID" and "OK", whatever that may mean.

Now, the motor will not power on wthout signals to these. I have tried all tricks I know, but to no avail. (I use an external high current dc source).

If I can get to see high resolution picturesof both sides of the battery pcb, there is some chance I can decode the ID required. (I think I already know what OK needs).

I hope it is not asking too much. Would you help, please?

NAJR

[Liteace]

Ill try take a good foto of the top side of the PCB, I cant take a foto of the bottom as its only held on by the metal power strips and I don really want to remove them

[najrao]

Littleace, I was hoping to see a nice picture of the pcb!