S5 lipo battery management circuit for18v impact wrench - Page 1
Forum section: electronics / projects

author: cd_will
author_rank: Newbie
timestamp: December 10, 2017, 10:59:56 pm
content: hi alli am trying to design a 5cell lipo batttery pack for a 18v impact wrench to replace the nicad packi want to make if stand-alone to charge from a 24v source or from the original charger that can supply around 22vi have seen some TI chips that say thay can do it but i cant figure out how they do the balancingi hope some one can helpthanks all

author: ovnr
author_rank: Frequent Contributor
timestamp: December 10, 2017, 11:07:18 pm
content: The TI chargers do not balance your pack. You will need to bring your own balancing circuit.If you didn't plan to stick it in a power tool, I'd suggest something likethis BMS module, but the 15A limit will not work for you. Try searching for 5S BMSes. Alternatively, you could just remove the protection components from the one I linked and keep the rest, but I'd really suggest a proper BMS anyway.

author: Freelander
author_rank: Regular Contributor
timestamp: December 10, 2017, 11:20:53 pm
content: Quote from: cd_will on December 10, 2017, 10:59:56 pmHi, are you definitely planning on using LiPo ? or do you mean Li-ion - most normally use 18650 packs.If you are using 18650's (or indeed the lipo - then you can use an imax external charger / balancer B6AC - or a clone of. You can pick one up for about 15 UK Sheckles. The 18650's need to be the high C versions - and of a known source and make - NOT ebay (although the charger will be fine from ebay)Even for a lipo the imax b6ac is perfect.The only difference for the charging is that you will need the main charging lead and the balance lead.The B6AC is limited to about 5A or about 70 - 100w (iirc) ... ?? - great balance charger . No worries at all.

author: Freelander
author_rank: Regular Contributor
timestamp: December 11, 2017, 12:02:04 am
content: Just to add - a point worth seriously considering if going the LiPo route is that you must charge it and use it - never leave it 'charged' fully as this can permanently damage the LiPo. LiPo cells are designed to be charged then discharged within a fairly short time period.My cordless devices have multiple spare battery packs. If I went LiPo I could not safely have charged packs stored for use. The cells will usually puff out and fail (or one or more of the cells will)You ideally would need to discharge to a 'storage' level. Li-Ion are far far far better here. Yes, keeping them fully charged (at around 4.2V, may shorten their life -- eventually -- , but you will not damage them.I have had my Bosch Pro units on Li-ion for more than 5 years - still on same packs and they seem as new. If they have lost any capacity it is not noticeable.Lipo are really not a good choice for anything that may be charged and then stored. They are really a charge and then hammer the discharge type of cell.There are also many many Li-Ion units around (laptop batteries etc) - they virtually ALL use 18650 cells (as do all the power tools - that I know of) In most of the laptop batteries there is often no balance charging at all. In fact, I have never seen a laptop battery with true balance charging. Just 18650s in series or series / parallel with temp sensors on 1 of every 3 cells in series. There is some logic on the input but this is really to enable or disable the output and monitor levels. That can all be done via an external charger. In other words, balance charging is the natural choice however most series connected batteries simply don't bother.

author: cd_will
author_rank: Newbie
timestamp: December 11, 2017, 12:18:29 am
content: that is a very good point i hadn't considered the current pack hples 15 SC cells so i dont think 18650 will fit very welland yes i want to keep it fully contained in the pack

author: Freelander
author_rank: Regular Contributor
timestamp: December 11, 2017, 12:30:49 am
content: Quote from: cd_will on December 11, 2017, 12:18:29 amHave a look at what space you have inside the pack - you might get away with it. have you got 3 x 3 SC cells together ?If your SC are 43 / 23 mmm (I have seen slightly shorter ones) then the ;length; of the 3 stack is the same as 2 18650s (18mm x 65mm)So you could get 6 18650s in - IF the pack is stacked that way.... effectively a 6s - or, 5s with a spacer as the 6S might cause the drill to take off into the sunset

author: cd_will
author_rank: Newbie
timestamp: December 11, 2017, 12:40:59 am
content: eBay auction: #https://www.ebay.co.uk/itm/Battery-Rebuild-For-SNAP-ON-18-V-volt-CTA3850-CTB3185-CTB3187-3-0Ah-Rattle-Gun/182754818725?hash=item2a8d093aa5:g:A1UAAOxylpNTPkGbthis is the alternative but its nimh

author: cd_will
author_rank: Newbie
timestamp: December 11, 2017, 12:58:10 am
content: https://www.ebay.com/itm/18V-21V-18-5V-5S-30A-Lithium-5x-3-6V-3-7V-Li-ion-LiPo-Polymer-Battery-BMS-PCB/322366720925?hash=item4b0e8dcb9d:g:D8cAAOSwTdJXRWRFor ther is this

author: Freelander
author_rank: Regular Contributor
timestamp: December 11, 2017, 01:04:29 am
content: Quote from: cd_will on December 11, 2017, 12:40:59 amNiMh are - imho - about as much use as a one legged man in an arse kicking contest. The self discharge is crazy. You can charge them up and find they have lost 35% in a month - even a few weeks. ! they can lose 15% in the first 48 hours.NiCd can also suffer a similar fate but I always found NiMh far far worse.Every time I think of NiMh I get an image of a bucket full of holes.If you can get GOOD nicads I would be tempted to rebuild with those and have done with it. When we all used Nicads in RC stuff they were cheap as chips and damn good quality. Now it is the ying tong yip lottery.Also, 18650 in High C guise aren't cheap. I can get damn good 2c units at 2400mAH from one place I know (dirt cheap too!) but 2 C wouldnt hack it for you in a electric version of a windy gun - (I hadn't heard the term 'rattle' gun before!). I still use a compressor and a small windy gun or the 'BFO' windy gun. Pipework is a bit of a pain but hey ho. Some damn good small 'rattle' guns about though. Just don't use an extension......................

author: Freelander
author_rank: Regular Contributor
timestamp: December 11, 2017, 01:14:12 am
content: Cant work out what that is meant for, quick read sort of says - for Lithium, then NOT FOR LITHIUMCould be a good unit but not cheap and depends if you can fit it in the case.I would be tempted to just string 18650's in series and forget the balance. - or, it is simple to add a balance lead and go for the external charger / balancer. A B6 unit would work ok, the B6AC is better though as you just plug it into the mains. And, you can charge ANYTHING with it. I use it for my SLA units, NiMh units and also the Quads Lipos and the 18650 sets. Fully adjustable and programmable.Either way, that unit your link to may be fine. Worth considering the 22V you have would almost certainly not be enough to fully charge the battery due to the voltage differential needed to the board. the batteries (a 5s) would top out at 21V. A 1v difference is probably not workable. Probably mean you would need another supply - unless you can tweak the supply you have to around 24v ?

author: cd_will
author_rank: Newbie
timestamp: December 13, 2017, 04:04:56 pm
content: well i have a new style battery pack and it is a s5p2and the pack is rated for 18v 3.0Ah 45Whall the cells are printed inr1 18650-15m msamsung sdiem 121and under the wrap a5dz mbk21 a1the cells are rated up to 20amp / 1.5ah and 4 amp rapid charging safe, so 40amp / 3ah and 8amp charging if im correct

author: cd_will
author_rank: Newbie
timestamp: December 13, 2017, 04:36:49 pm
content: eBay auction: #https://www.ebay.com/itm/18V-21V-18-5V-5S-60A-Lithium-5x-3-6V-3-7V-Li-ion-LiPo-Polymer-Battery-BMS-PCB/222353609188?epid=1440597425&hash=item33c54ed1e4:g:23IAAOSwdG9XRWjtthis bms is an option even tho it said not for power tools (but even the 150A said the same thing )if it is the one in the picture it should be modifyable to shrink it down abit and will be able to fit a bit of a heat sink in the battery housingso whats peoples opinions on theQuote

author: cd_will
author_rank: Newbie
timestamp: December 13, 2017, 11:28:40 pm
content: and what do u wrecon with wireing it up like this as this is how the cells are curently wired up in there curent pack