I need to learn about batteries

[ppTRN]

Hi everyone,

It seems that lately many project I have to work on requires battery power. I never really dived into the topic except for a small lipo charger and protection circuit for a single LiPo cell.
I want to know more about all kinds of battery that are often used, expecially for LiPo and Lead acid. In particular I am asking you if you have any document to suggest me in order to have all this infos in one place.

Other important topic I am intrested in regarding batteries are:

1. ICs for charging regulation of 12V lead acid batteries;
2. ICs for discharge protection and fuel gauge of 12V lead acid batteries;
3. Ways to add protection and fuel gauge for multicell LiPo batteries, like the ones on drills;

Before anyone says anything: I know that a google search will answare most of the questions above, but still there is such an immense amount of information that maybe I will miss the most simple and most common solutions to my problems.

Feel free to post your suggestions while I keep studying.

Thanks!

[Peacefool]

Hi, check out https://batteryuniversity.com/articles.  I'd suggest to start with articles BU106a and BU107.

[xvr]

TI manufactures a LOT of battery management ICs - https://www.ti.com/power-management/battery-management/overview.html

[Phil1977]

TI manufactures a LOT of battery management ICs - https://www.ti.com/power-management/battery-management/overview.html

And reading (and understanding) of many of the TI-application notes gives you more knowledge about a lot of topics than spending half a year at university. They often really are a invaluable source of information.

[ppTRN]

Thank you all for the precious infos. I will dive into them

[MarkT]

Don't forget LiFePO4 chemistry - many charging cycles (thousands?) and much safer than LiPo.

[tooki]

Hi, check out https://batteryuniversity.com/articles.  I'd suggest to start with articles BU106a and BU107.

You may not know this, but batteryuniversity.com is considered a very unreliable source (to the point of being blacklisted on Wikipedia, so it cannot be used as a source there) because of its complete lack of sourcing — and the fact that the author integrates things people say in the comments into the articles as fact! The info on the site might be right, might be wrong, and no way to know whether a given statement is true or not.

[tooki]

3. Ways to add protection and fuel gauge for multicell LiPo batteries, like the ones on drills;

Look at the reference designs (for projects, not just evaluation boards) from semiconductor manufacturers— they almost all offer them. They show partial and complete device designs. These are excellent ways to see how to integrate individual components into a whole system.

https://www.ti.com/reference-designs/index.html
https://www.analog.com/en/resources/reference-designs.html
https://www.nxp.com/design/design-center/development-boards-and-designs:EVDEBRDSSYS
https://www.monolithicpower.com/en/design-tools/application-reference-designs.html

[aliarifat794]

Here is a pretty short video regarding battery types: https://youtu.be/DzTlyM-IA-I?si=KY-Qf42FCV83Jwpy

[ppTRN]

Thank you all for your replies.
While I am pleased to find a lot of resources I am having troubble keeping everything as simple as possible. Let me explain, in those toy cars that children can drive, powered by a 12V Lead Acid battery (see link 1) I highly doubt that tey use a BQ24450 for charging and a BQ34Z110 for fuel gauging. They are quite expensive but they seems to be the first results that pops out every time.

Or think about battery powered power tools. They mostly uses NiCd battery packs but I do not understand how they are simultaneously fuel gauged.

Same story for LiPo multicell 3S or 4S battery pack. In the application I see them used I see very simple circuits for both recharging and fuel gauging, while when I look for ICs that are supposed to do that, I find myself with very complex solution that I do not see matching the reality, that uses cell balancing and expensive ICs. For example look at the circuit on link 2. That's a rather simple and inexpensive charging solution, but what about fuel gauge? Should I gauge just one cell and assume that that the value I read is applicable to all cells?

Also look at other different circuit I found. Seems a bit odd that circuit on link 2 performs just like circuits at link3 and link4.

I apologise if this topic seems trivial to you guys.

link 1: https://ataacars.com/it/prodotti/mercedes-gtr-mini-12v.html?id_product_attribute=246&go_campaign=AS_IT_MAX_2022&gad_source=1&gclid=Cj0KCQjwiMmwBhDmARIsABeQ7xQV0J5XpC_pVne3EkFr4TClLdOihq9qj5gXKqpYju28UsKKjboxlCYaAmmJEALw_wcB

link2: https://it.aliexpress.com/item/1005006183081642.html?src=google&src=google&albch=shopping&acnt=494-037-6276&slnk=&plac=&mtctp=&albbt=Google_7_shopping&albagn=888888&isSmbAutoCall=false&needSmbHouyi=false&albcp=19207365798&albag=&trgt=&crea=it1005006183081642&netw=x&device=c&albpg=&albpd=it1005006183081642&gad_source=1&gclid=Cj0KCQjwq86wBhDiARIsAJhuphnetGl50Lit8mvgjy902BMCWvlztjzVi6-vhWCk0eD7blUYnzQjeFoaAtiMEALw_wcB&gclsrc=aw.ds&aff_fcid=c51903b233224ab8801804f7d4d059e7-1712559817747-04296-UneMJZVf&aff_fsk=UneMJZVf&aff_platform=aaf&sk=UneMJZVf&aff_trace_key=c51903b233224ab8801804f7d4d059e7-1712559817747-04296-UneMJZVf&terminal_id=f3a047b2b11548698d35a79384c94f86&afSmartRedirect=y

link 3: https://it.aliexpress.com/item/1005005501508390.html?spm=a2g0o.productlist.main.11.219f152c1SIPWn&algo_pvid=27b1e7ef-9fe9-4b1d-a2c3-87f02e7906fa&algo_exp_id=27b1e7ef-9fe9-4b1d-a2c3-87f02e7906fa-5&pdp_npi=4%40dis%21EUR%218.65%217.01%21%21%219.16%217.42%21%402103895417125604733232716e9b66%2112000033328867724%21sea%21IT%214752065608%21AB&curPageLogUid=PDtouRSSxYJG&utparam-url=scene%3Asearch%7Cquery_from%3A

Link 4: https://it.aliexpress.com/item/1005004698800638.html?spm=a2g0o.detail.pcDetailTopMoreOtherSeller.8.3c26FpNnFpNntV&gps-id=pcDetailTopMoreOtherSeller&scm=1007.40000.327270.0&scm_id=1007.40000.327270.0&scm-url=1007.40000.327270.0&pvid=c9abfcf6-0588-4f04-b40a-341c183e2b95&_t=gps-id:pcDetailTopMoreOtherSeller,scm-url:1007.40000.327270.0,pvid:c9abfcf6-0588-4f04-b40a-341c183e2b95,tpp_buckets:668%232846%238111%231996&pdp_npi=4%40dis%21EUR%218.87%214.36%21%21%219.39%214.61%21%40210384b217125598187752491e093d%2112000030142305800%21rec%21IT%214752065608%21AB&utparam-url=scene%3ApcDetailTopMoreOtherSeller%7Cquery_from%3A&search_p4p_id=202404080003389713982330004443902542_7

[xvr]

> While I am pleased to find a lot of resources I am having troubble keeping everything as simple as possible.

Most simple way for charger and fuel gauging is use constant voltage for charge (just simple PSU) and use battery voltage as fuel gauge. It is most simple way, with moderate efficiency and accuracy. You will not kill your battery but will not get maximum capacity and live span from them. Fuel gauge also will be a moderate accuracy.

For LiIon/LiPol/LiEtc... most simple solution is CC/CV charger (as in your link 2). Simple fuel gauge is not possible.

[ppTRN]

I actually managed to find an IC that manage the charging process for many type of batteries, even with multiple cells, BQ2461x.
I find it very convenient to use and I will try to implement it in one of my designs.

As of fuel gauging multi cell batteries, maybe I can just fuel gauge the last one, the one with one terminal connected to GND and assume that all other cells are at the same level.

But then it comes to my mind, what if I build a battery pack with batteries that have different levels of charge? Won't the CC charging process damage the batteries that reaches first the full charge? at least just the first time they are charged

[xvr]

> As of fuel gauging multi cell batteries, maybe I can just fuel gauge the last one, the one with one terminal connected to GND and assume that all other cells are at the same level.

You can do it by whole battery voltage (it is simpler, than sense only one cell, and more precise), but only for LeadAcid and NiCd. LiIon has very flat discharge curve, so you can't say how much of charge in it only by voltage of battery. Fuel gauge IC literally count Coulombs flown in/out of battery.

> But then it comes to my mind, what if I build a battery pack with batteries that have different levels of charge? Won't the CC charging process damage the batteries that reaches first the full charge?

Yes, it could. That balancing circuits in BMS is made for. They take care of avoiding of overcharging of separate cells.

[wasedadoc]

You can do it by whole battery voltage (it is simpler, than sense only one cell, and more precise), but only for LeadAcid and NiCd. LiIon has very flat discharge curve, so you can't say how much of charge in it only by voltage of battery.

That NiCd and LiIon is the wrong way round.  The former has a much flatter curve than the latter.

[ppTRN]

Update: I think I find quite the perfect trio in terms of ICs for charging, balancinc and protecting and fuel gauging multi cell battery packs:

1. BQ24610 - Charger controller;
2. BQ76920 - Protection with INTERNAL BALANCING;
3. BQ78350 - Fuel gauge made to be directly connected to the BQ76920;

It is my understanding that I should be able to design my circuit as drown in the attached picture. Please correct me if tou think there is something wrong. My doubt is specifically about the connection of the charger. What if I try to charge the batteries but the protection mosfet is off? I assume it may be off not due to protection reasons, that would be good.

Now that I think about it, the mere fact that I connect the charger to the protection circuit should allow the protector to enable the mosfets, if there is no problems of course.

Note that the charger IC may also be configured with a power path

[ppTRN]

I guess that's case closed about Lithium batteries. From what I have concluded lead acid batteries are much easier to handle. The  discharge voltage curve is much less flat than lithium batteries' and it can be easily gauged with a voltage divider and a microcontroller.

I found many charging circuit that basically provided a CV with limited current so that the discharged battery will initially draw that much current and then settle to a CV mode. So I designed my own circuit that you find attached. It is a very simple emitter follower with CC = 1A and CV = 13.5V circa.

I have already tested the circuit with a dummy load and it works perfectly. The 3055 dissipates quite a lot but it does so only during the CC charging phase. Any ideas on how to improve it? I was thinking about a better feedback for current regulation using an op amp and some kind of "wired or" structure in order to add an enable signal in addition to the transistor limiting the current.