Rebuild SLA battery into a Li-ion battery? - Page 1
Forum section: electronics / general

author: XOIIO
author_rank: Super Contributor
timestamp: July 28, 2014, 09:47:29 am
content: Hey all, neither of the batteries I have for my CMA4000 are good, both don't even charge at all, so I checked on ebay, I can get an official one for around $100 not including shipping, a knockoff one that looks like a good match is $40 without shipping or so, but I happen to have a generic laptop battery, lithium-ion, 11.1 volts, (6 cell) 4400mah, so I'd say almost double the life, though I've never had it run on battery to see how long it lasts.Anyways I was thinking, maybe it is possible to hacksaw or whatever the cap of the SLA off, empty out the contents, gut the LI-ION and put it's cells inside, close it up and have a nice replacement battery.Of course there is the issue of charging and protection, this is made for a laptop, but I am sure all that circuitry is inside, no clue what the charge input voltage is but I imaging 12v dc would work for it to charge up?I think the biggest issue would be opening the SLA and cleaning it out without ruining it.

author: XOIIO
author_rank: Super Contributor
timestamp: July 28, 2014, 10:02:59 am
content: Yup, seems to be just input and output on the connector, no communication with the computer or anything. Battery has a temperature sensor and what is likely a thermal fuse. I can easily hook wires onto the back of the board to connect in and see if it will charge fine on 12v or so. I think this might work fairly well though it's a bit long, I'll have to re-wire a couple batteries so it fits in the SLA.

author: Artlav
author_rank: Frequent Contributor
timestamp: July 28, 2014, 10:05:36 am
content: Bad idea!The lead acid charges at over 13V, while 11.1V li-ion have a maximum (as in, it explodes if over it) of 4.2V per cell, or 12.6V per pack.Without redesigning the charge controller in the CMA (or making a glue controller in-between) this would quickly end in a fireball.

author: Jon86
author_rank: Frequent Contributor
timestamp: July 28, 2014, 10:16:45 am
content: Yeah you might get away with it if you design your own PCB to go along with it, but I'm not sure how the charging controller would respond to being powered straight from a SLA charger... Probably wouldn't go too well.

author: XOIIO
author_rank: Super Contributor
timestamp: July 28, 2014, 10:17:50 am
content: Quote from: Artlav on July 28, 2014, 10:05:36 amHmm, you think? Wish I remembered which type of laptop it was for, then I could check what the input voltage is from the power jack, I imagine they pipe that straight through. I also imagine the controller would allow for 1 volt over voltage to charge it, it would just regulate it a bit.I have a fan hooked up to it to discharge the battery, going to leave it on while I sleep since it will probably take a long time to discharge (though I might not just so that I can do a partial discharge. The battery output was reading at 11.4 volts, I imagine the device would be happy with that or down to 12v, and I think with the PTC, thermal fuse and all the circuitry on this (it's actually decently complex for a Chinese battery) it could handle 13v input no issues. (basically I would wire the connections from the LI-ION's built in controller to the battery tabs after cramming the innards inside with liberal use of hot glue)Quote from: Jon86 on July 28, 2014, 10:16:45 amWhat is the behavior of SLA chargers? I kind of figured it is primitive enough it just gives it the charge voltage at all times.

author: amyk
author_rank: Super Contributor
timestamp: July 28, 2014, 01:20:19 pm
content: Quote from: XOIIO on July 28, 2014, 10:17:50 amNo they don't, there is a lion charger IC (usually based on a buck converter). It says on the battery what it's for... Quanta ZA3/Acer 751H. And indeed, a quick check of the schematic shows that it uses anISL88731charger, and the battery has a thermistor and I2C bus for the monitoring IC in it. You should definitely figure out the protection circuits on the battery first.QuoteAll you'll do is trip the overvoltage and maybe overcurrent protection if you try that... so I'dstronglyrecommend you stop and do a bit more reading about how these things work!...and don't even think about bypassing the protection, it won't end well.

author: XOIIO
author_rank: Super Contributor
timestamp: July 28, 2014, 06:15:21 pm
content: Yes, I know what LI-IONs are like, no plan on bypassing the protection.Anyways, totally failed to notice this before but there are other connections it seems, at least silkscreened on. Don't have much time right now to experiment, but the connector is set up like so.P+ P+ NC T C D P- P-I imagine T is for the thermocouple, C is to allow it to charge, maybe connecting it to ground? D might be for battery charge% data.The main chip on the right side is marked as followsbq306025KG4 (the G4 is in smaller letters that are underlined)C3EZhttp://www.ti.com/product/bq3060the other two small chips are as followsTPC8125strange dot markings238 (with the 38 underlined)http://www.toshiba.com/taec/components2/Datasheet_Sync/200912/DST_TPC8125-TDE_EN_11738.pdfSo, I'm going to look through the datasheet for the 3060 and hopefully that will let me understand what sort of voltages this can charge at. I will also desolder the connector as I do not need it, and it will let me see if those other pins even are connected.I am curious what the "gas gauging" feature is.

author: XOIIO
author_rank: Super Contributor
timestamp: July 28, 2014, 06:21:42 pm
content: Looks like it ahs a recommended max of 25v, and it looks more than capable enough to regulate the charging properly. There were to I2C connections or anything that jumped out at me, it seems like this is a self contained solution for charging and protecting the batteries.There is an SMBUS though, they could be using that. I'll have to take the connector out to see if there are any traces going to those pins.

author: XOIIO
author_rank: Super Contributor
timestamp: July 28, 2014, 06:59:58 pm
content: Alright, those other pins do have traces going to them.

author: Kevman
author_rank: Regular Contributor
timestamp: July 28, 2014, 07:54:59 pm
content: Quote from: XOIIO on July 28, 2014, 06:21:42 pmEither I'm confused, or you are. The bq3060 is a gas gauge (for telling how much power is left) and battery protector. It does NOT appear to be a regulator or charger of any sort.And the TPC8125 is just the FET that the bq3060 uses to disconnect the battery in the event of a fault... I don't think you've found any sort of charge regulator. You'll need your own.

author: XOIIO
author_rank: Super Contributor
timestamp: July 28, 2014, 08:06:25 pm
content: Quote from: Kevman on July 28, 2014, 07:54:59 pmlooking at the layout it has a built in regulator and battery over voltage, under voltage, etc features, it looks like it could be the brains for managing the charging. I could be wrong but looking at the block diagram in the pdf it seems that it could.

author: amyk
author_rank: Super Contributor
timestamp: July 29, 2014, 12:12:06 pm
content: The BQ3060is not a battery charger! All it does is monitor the current and voltage to determine how much charge is in the battery (integration) and ensure that it's within limits. If they're not, it willpermanently disconnect the pack. Look at thereference design, your pack won't be much different from it.I suggest you also get the schematic for the laptop it came from (Google "Quanta ZA3") and inspect it carefully... especially the power circuits.T is the thermistor,C is I2C clock,D is I2C data.

author: Kevman
author_rank: Regular Contributor
timestamp: July 29, 2014, 12:18:41 pm
content: Indeed. The regulator mentioned in the BQ3060 is just to drive chip's CPU and a few external logic parts. It can only source 10ma... Charging with that would take a while.

author: XOIIO
author_rank: Super Contributor
timestamp: July 29, 2014, 08:38:05 pm
content: Well then, any chips specifically good that I could use to make my own charging circuitry?

author: lowimpedance
author_rank: Super Contributor
timestamp: July 30, 2014, 03:13:30 am
content: And how much is your time/effort and cost of extra parts worth, the cost of an 'official' or otherwise drop in replacement battery ?.

author: SirNick
author_rank: Frequent Contributor
timestamp: July 30, 2014, 03:32:08 am
content: Brother, no one likes to hear this, but you are not ready for this kind of project yet. If we were talking about LEDs, I would say "go for it -- you'll burn out a few while you learn, but you'll get there." But with Li-Ion batteries? Well... learning that way might take life and/or limbs.No one's born with this knowledge, but you do need enough experience to know when you don't know enough to keep going. Your ambition is currently out-pacing your skill, and this kind of project is unforgiving of hubris.BTW, SMBus == i2c. Well, not exactly, but close enough.

author: TheBorg
author_rank: Frequent Contributor
timestamp: July 30, 2014, 04:40:49 am
content: At this point I have to agree with impedance and ask you to consider if it is worth buying a $100 or $40 knock off battery, versus messing around for a few weeks with charge circuitry and other parts.

author: amyk
author_rank: Super Contributor
timestamp: July 30, 2014, 09:44:41 am
content: Quote from: XOIIO on July 29, 2014, 08:38:05 pmYes, plenty of them.I also agree with the recommendation of others here that you should do a lot less experimenting and far more studying before you try something like this. Lithium-ion batteries are very safe if used with care, but the amount of energy they store is extremely high, and they are not at all forgiving of abuse.Incidentally this is also why I like to call them "lion batteries" - if you're not careful, theywillbite!

author: microbug
author_rank: Frequent Contributor
timestamp: July 30, 2014, 10:05:28 am
content: QuoteYou wouldn't take a hacksaw to a Li-Ion and neither should you to a SLA.Apart from the Li-Ion dangers that everyone else has picked up on, has have you thought about the contents of a SealedLead Acidbattery? Even if you can safely get them out (difficult), what would you do with them?It would be far safer just to find some smaller case that kind of fits and use that, or to make the (lithium) battery pack built in (i.e., non removable). Don't forget that with new(ish) cells the capacity should be as better than a new SLA battery.Side note: the cells in a 'generic' battery are probably going to be lower quality. If you want genuine new cells at a good price, buy a new name-brand laptop battery.

author: XOIIO
author_rank: Super Contributor
timestamp: July 30, 2014, 10:47:22 am
content: Quote from: microbug on July 30, 2014, 10:05:28 amThe design of the SLA battery makes it pretty much impossible to find something that would fit and contact the tabs inside.