Cordless power-tool battery repair  - Page 1
Forum section: electronics / repair

author: Liteace
author_rank: Regular Contributor
timestamp: November 17, 2018, 09:17:14 pm
content: Could someone please help me find the problem with my 20 volt cordless impact gun battery. I went to use the gun, checked battery charge with green led/s on battery, it was low only one led lit out the 4 but Ive used it before like this no problem, it worked for split second then stopped, checked charge again, no leds lit, put battery in charger and got red error light lit on charger.I have pulled battery apart to check, can't see anything out the ordinary nothing burnt or loose.I have checked the power on b+ and B- and got 18.5 volts, I dont know what / where to check next

author: Gyro
author_rank: Super Contributor
timestamp: November 17, 2018, 09:29:04 pm
content: I suspect that you may have over-discharged one of the cells and the protection has kicked in. Before messing with anything I'd be tempted to leave it a day or so for the voltages to recover and try it in the charger again. Repeated insertions into the charger may 'pulse' it enough to start charging normally.

author: Liteace
author_rank: Regular Contributor
timestamp: November 17, 2018, 09:34:29 pm
content: Thanks for the rapid reply, Ive tried to charge it several times over the last week at various different temperatures and still the same problem, the charge % indicator on the battery does nothing and still get red led lit on charger

author: Gyro
author_rank: Super Contributor
timestamp: November 17, 2018, 09:41:51 pm
content: Oh well, it was worth a try.The first step in that case might be to measure the voltage of each individual cell (assuming that you can get to the ends) to see if there's any legitimate reason for the error signal. I know that some laptop batteries can go into permanent lockout if a problem is detected. Hopefully not the case with power tool packs.

author: drussell
author_rank: Super Contributor
timestamp: November 17, 2018, 09:43:20 pm
content: What is the actual voltage across each of the individual cells currently measuring?Can you actually draw any current out of the B+/B- terminals? Probably not.

author: commongrounder
author_rank: Frequent Contributor
timestamp: November 17, 2018, 09:59:09 pm
content: How long has this pack been in service? If it has been in steady use for a couple of years, it’s likely one or more of the cells in the pack have failed. They can do that suddenly. In that case, either have the pack rebuilt, or replace it.

author: Liteace
author_rank: Regular Contributor
timestamp: November 17, 2018, 10:28:36 pm
content: The gun and battery have been in very light service for a couple of years always kept in a cool place and well looked afterI can draw / power up a small PC cooling fan from the B- & B+, Ive got nothing to hand that will draw moreHere's what Ive got at each cell, I assume the 4.0ish volts is because the way the cells have been wired

author: Gyro
author_rank: Super Contributor
timestamp: November 17, 2018, 10:42:28 pm
content: 2.3V definitely isn't health for a Lithium cell (it's 2 in parallel), there's the source of your problem.Power tools do push them pretty hard - I noted the 60A fuse on the board! It looks as if the pack has voltage balancing and monitoring but the cutout obviously didn't work fast enough when trying to use a discharged pack.I'm just tentatively wondering whether I would risk very gently trickle charging those two cells back into normal voltage range so that the charger can take over (afterwards). There are possible serious consequences, such as balls of flame! On the other hand it might recover the pack, the voltage balancing probably improves the odds slightly.I'd wait for a few other opinions on this.P.S. Don't try to draw any more power from it!

author: Liteace
author_rank: Regular Contributor
timestamp: November 18, 2018, 12:18:10 pm
content: I thought I'd disconnected the fan, I had but not properly, went done something else, when back fan was just about moving round, checked all cells very low voltage, put it in charger and bingo it charged and the battery % leds are again working.With battery showing fully charged on charger, Ive checked the voltage of all the cells, the yesterdays 2 top 2.3v are now 3.50v, the rest, 3.9v are now 4.15v and Ive a battery voltage of 20.1v on B+ and B-Is there a poss chance that as this is a 5 amp battery there is 4, 4 and 2Like 2 packs of 4 x 4 = 16 then the 2 x 2 making it up to 20 volts

author: coromonadalix
author_rank: Super Contributor
timestamp: November 18, 2018, 05:09:45 pm
content: Had problems with Dewalt 20v/60v Flex packs, they are made with 3 packs of 5 cells, they did output 20v or 60v, but the battery cells where not equal in voltage, they have a bms, but it doesnt work very well, had cells with 1v and other at almost 4 voltsThe bms is not able to recover and equalize the cells ?

author: Liteace
author_rank: Regular Contributor
timestamp: November 18, 2018, 05:20:48 pm
content: Sorry for being thick, what is a BMS ?

author: Bratster
author_rank: Frequent Contributor
timestamp: November 18, 2018, 06:57:49 pm
content: Quote from: Liteace on November 18, 2018, 05:20:48 pmBattery management system.It's supposed to keep all the cells at the same voltage so none get too high or too low.Sent from my Fi Moto x4 using Tapatalk

author: james_s
author_rank: Super Contributor
timestamp: November 18, 2018, 08:10:03 pm
content: Do you have a bench supply? You might try using that to carefully charge each cell to around 3V, that should be enough to satisfy the management circuitry. You have to be careful with Li-ion cells but the cylindrical metal type are much less prone to caching fire than the LiPo pouch type.

author: Liteace
author_rank: Regular Contributor
timestamp: November 18, 2018, 09:23:18 pm
content: I can knock together a charger for charging individually, what voltage do I want to be pumping into them and for how longWhat I cant understand it, if this is a 20v battery and it has 10 cells why are the cells not 2 volts each ?

author: Bratster
author_rank: Frequent Contributor
timestamp: November 18, 2018, 09:39:23 pm
content: The cells are grouped with two in parallel so you have more current available,and then those groups of two are run in series to get the voltage up high enough.So it is basically only 5 cells in series.Sent from my Fi Moto x4 using Tapatalk

author: james_s
author_rank: Super Contributor
timestamp: November 18, 2018, 10:01:10 pm
content: Charge each cell pair to about 3V, they'll be 3.7 or 4.2V fully charged depending on the chemistry they use but you don't need to fully charge them this way. I would suggest something in the area of 500-1000 mA charge current, it's not too critical though.

author: Liteace
author_rank: Regular Contributor
timestamp: November 18, 2018, 10:06:56 pm
content: So is the problem here the cells are cheap rubbish or the BMS not managing its job properlyAre these just the 3.7 or 4.2 standard blue that most things are fitted with these days ?

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 18, 2018, 10:25:18 pm
content: Quote from: Liteace on November 18, 2018, 10:06:56 pmNot quite they are high discharge current models, a standard laptop or whatever model would be destroyed at the first screw driven.

author: Liteace
author_rank: Regular Contributor
timestamp: November 19, 2018, 12:38:05 am
content: Quote from: shakalnokturn on November 18, 2018, 10:25:18 pmThanks for the info, what would I look for if I wanted to rebuild with new cells ?

author: KL27x
author_rank: Super Contributor
timestamp: November 19, 2018, 05:55:07 am
content: In this case, it is possible that only 1 or 2 pairs of cells are really bad. The majority of the cells might be perfectly fine.I would charge each pair of cells all the way to 4.2V, first. Then run the drill down. Then chuck which pairs of cells are abnormally low. It looks like your top pair is the most likely culprit, and some or even all of the others might be serviceable.Also, during your individual charging of pairs, you might find some cells which will not reach 4.2V. And/or if they do, they immediately drop to say 4V or less after you disconnect them from the charger. I would replace these pairs, too.If you want to replace cells, you would need to know the discharge and charge rates to make sure you match (or exceed) this rating. It will also be nice to match or exceed the capacity in Amp Hours, so that the replacement pair doesn't end up being the weakest link and making the battery cut out when the other cells still have significant charge left in them.If you have two pairs bad, you'd end up with 6 good cells. If you happened to find a bargain on cells that match or exceed the output capability (calculated by C rating times capacity) but are significantly different in capacity, you could break up the remaining good pairs and use 5 new cells in parallel with 5/6 of the remaining good pairs. This would maximize the capacity of the battery at the cost of discarding one of those cells. After someone complains that this is unsafe and stupid, I'll explain why they're wrong.It should go without saying, but your cells must have the same float voltage before you connect them in series. And all pairs should be holding a float voltage of 4.2V before you wire them into the battery.*There are some slight differences in max voltage between different chemistries of li ion cells, but as far as I know most all hand tools are using essentially the same chemistry that is dominating the portable computing world and the electric car industry. I think it's the manganese variant. But anyone piping up about this... uh.. you should also mention that Beta Max is different than VHS.

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 19, 2018, 03:50:12 pm
content: Thanks for the info, what would I look for if I wanted to rebuild with new cells ?If you intend to replace the weak pair, better be looking for the same model. (They should have some marking on the side.)Otherwise something along these lines:https://www.powerstream.com/p/INR18650-25R-datasheet.pdf

author: Liteace
author_rank: Regular Contributor
timestamp: November 19, 2018, 10:32:48 pm
content: Quote from: shakalnokturn on November 19, 2018, 03:50:12 pmSorry for all the questions, You guys are the experts, Im not, so need to ask.I have also found this:https://www.batteryspace.com/prod-specs/NCR18650B.pdfI do have 2 x Panasonic toughbooks that Ive has for about 5 years, the batterys on those or sh1t hot and still holding out, in your option/s would the Panasonic cells be better than the Samsung cells ?

author: KL27x
author_rank: Super Contributor
timestamp: November 20, 2018, 02:05:57 am
content: In the reality of things, the simplest and most effective way for your cordless tool to automatically cutout when the draw is too high is by measuring the voltage. So, the way your cordless tool decides what is "too much current" is really, in all likelihood, an indirect judgement based on the series voltage under load (or under stall, as the case may be).So matching of the discharge and charge rates and capacity is important, but not that important. You might lose some torque if your replacement cells are weaker in C rating. OTOH, if you were to use cells with super high discharge capacility, you might end up with so much torque you could burn out a motor winding or other component by the time the cutout kicked in. But in reality, if you stall or grossly bog down the motor, you probably will let go of the trigger. (If not, you should).The most important thing to do is to make sure your new cells are not being charged too fast by the charger. If you have one of those superfast chargers, this is a source of danger you have to pay attention to. The other important thing is to make sure each pair of cells drops in voltage at relatively the same rate. Similar to the way the tool decideds what is too much amps, the way it decides that the battery is dead is in all likelihood based on the cumulative series voltage of the cell. Yeah, it would be way way better for the tool to measure each pair of cells and cutout when the weakest one dropped to a certain limit. But most of these tools won't do that. So if the capacity of your replacement cells is way off from the rest, the worst cells will be repeatedly damaged by the time your drill decides to turn itself off. This is why in many cases there is just one really bad pair of cells in a battery, and the rest might be great. It's that one pair that is repeatedly abused.That said, if your new cells are not greatly matched, you might just decide to stop using the drill when the battery indicator gets to 1 bar or something. Don't keep using it until it dies. Put the battery on the charger preemptively. As long as the charger is not crap, it is fine to charge a li ion battery frequently. You don't have to deep cycle it or other voodoo you might have learned with other battery types.So if you are careful and you pay attention to what you're doing, and you observe the results and make sure the cells are staying within their limits when on the charger, you can probably get some useful life out of it. If it's not worth your time to take some voltage and temperature measurements/obserations for the first few cycles until you're sure everything is fine, then either don't do this yourself, or maybe put your charger in the middle of your yard when you want to use it.The charging is the most dangerous part, because no one has the patience to watch the water boil. OTOH, if the tool blows up and catches fire while you're using it, you might get a few scars, but you won't die. And if you are observant of the battery temp, even just touching the case the first few times you use it under heavy load, it is unlikely to ever get to that point.But you do this yourself, you take your own chances. This applies whether or not some other "expert" endorses your battery choice with their stamp of approval. Better you use a completely inappropriate battery but do the proper experimentation and observation than to get the best cell and think you're fine.

author: Liteace
author_rank: Regular Contributor
timestamp: November 22, 2018, 08:32:15 pm
content: Quote from: KL27x on November 20, 2018, 02:05:57 amYes it does have a very fast charger that I dont really need, I would, if it was poss to build or buy a very slow charger / conditioner as this gun now only gets used a few times per month, if anyone know of a good slow charger for these type of batteries I'd be interestedThanks

author: Liteace
author_rank: Regular Contributor
timestamp: November 22, 2018, 09:04:16 pm
content: Quote from: Liteace on November 22, 2018, 08:32:15 pm

author: SMdude
author_rank: Frequent Contributor
timestamp: November 23, 2018, 12:43:49 am
content: 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.

author: KL27x
author_rank: Super Contributor
timestamp: November 24, 2018, 03:21:50 am
content: QuoteThis 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.

author: SMdude
author_rank: Frequent Contributor
timestamp: November 25, 2018, 07:14:08 am
content: Quote from: KL27x on November 24, 2018, 03:21:50 amYes 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

author: Liteace
author_rank: Regular Contributor
timestamp: November 25, 2018, 09:31:11 am
content: The tool is the Ingersoll rand 20V High-Torque Impact Wrench W7150, with BL2022 battery

author: SMdude
author_rank: Frequent Contributor
timestamp: November 25, 2018, 11:31:02 am
content: 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.

author: abyrvalg
author_rank: Frequent Contributor
timestamp: November 25, 2018, 11:36:23 am
content: 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).

author: Liteace
author_rank: Regular Contributor
timestamp: November 25, 2018, 09:11:44 pm
content: Quote from: abyrvalg on November 25, 2018, 11:36:23 amSo 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 bothHave Samsung beat Panasonic now in the rechargeable cell world on quality ?Thanks again for ALL your help guys

author: abyrvalg
author_rank: Frequent Contributor
timestamp: November 25, 2018, 11:53:56 pm
content: Not all BMSes do balancing. Your one can be "protection only" type.

author: Liteace
author_rank: Regular Contributor
timestamp: March 02, 2020, 10:09:14 pm
content: 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 timehttps://www.eevblog.com/forum/repair/cordless-power-tool-battery-repair/msg1972589/#msg19725892 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 themIve 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

author: najrao
author_rank: Regular Contributor
timestamp: March 05, 2020, 09:12:37 am
content: 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 aretwomore 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 seehigh resolutionpicturesofbothsides of thebatterypcb, 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

author: Liteace
author_rank: Regular Contributor
timestamp: March 05, 2020, 06:49:34 pm
content: 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

author: najrao
author_rank: Regular Contributor
timestamp: March 16, 2020, 11:44:15 am
content: Littleace, I was hoping to see a nice picture of the pcb!