Author Topic: How to DIY Charge-Balance 4 Li-ion 2000mAH  (Read 8860 times)

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Offline SuzyCTopic starter

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #25 on: October 18, 2021, 07:49:35 pm »
Amyk:  What do you consider extremely low?  I would say in 0 to 1 milli-ohms.

I have googled 18650 Li-On internal resistance and found results ranging from 25 milli-ohms(new, fully charged) to 400 milli-ohms(exhausted battery)

At >= C/2 CC charge rates, this resistance is significant in determining a precise battery EOCharge cutoff voltage that doesn't damage the cell.

Also, while a large number of charge cycles clearly shows a large loss of charge acceptance of a cell, the internal resistance remains nearly constant.

I have also learned how internal resistance can affect charge balancing.  A cell that has developed a high internal resistance will appear to be over charged in comparison to the other cells in a battery while  CC charging. Attempting to equalize voltage in a cell in this condition makes a weak cell end up with even less charge than the other cells in a multiple cell battery.
« Last Edit: October 18, 2021, 08:48:54 pm by SuzyC »
 

Offline SuzyCTopic starter

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #26 on: October 18, 2021, 08:22:04 pm »
i seem to be getting little help with my original posting subject on this forum.

Replies here seem even to be unable to realize that I am able to improve my ability to design circuits and seem obsessed with the profitable encouragement for viewers of this forum to buy buy buy (modules) and not try on their own to learn how to design things themselves( Don't get me wrong, hobby ways of doing things are fine for hobby-oriented people, I am tying to learn electronics and electronic design not just make some bulky, expensive, dodgy device work by throwing money at a problem.). 

Googling, I have found an obsolete (2004) research paper about this subject (attached). There are also a few postings of some interest on StackExchange.com This paper fails to realize many of the problems and offers no realized solution.

I would also say that I can circuit design as good as the best groups of engineers by learning their technology, their methods to solve this  problem using up to date battery-charging/balancing IC's.

 

Online beanflying

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #27 on: October 19, 2021, 12:33:21 am »
i seem to be getting little help with my original posting subject on this forum.


Partly because a lot of us will see little advantage in reinventing the wheel when you can buy a good one for around $30.

It is 'normal' for example for low number runs in commercial products to use commercial block or modules even the big boys do it a lot with Power Supplies in all sorts of gear instead of starting from scratch. My cludge with a dedicated PCB for 4 cells will 'look' anything but dodgy and most importantly will work be simple to make and not cost much. You should never dismiss this approach regardless of project in a lot of cases it just makes good common Engineering and $ sense. Any Engineer costing a company $1k+ to do a $20-30 job will have a short company life.

I seriously suggest you read this https://dlnmh9ip6v2uc.cloudfront.net/datasheets/Prototyping/TP4056.pdf buy some of the cheap boards (cheapest source for low volume TP4056 IC's and play with them. The staged charge diagram needs to be imprinted in your head. This playing is a great way to learn the basics.

Then as you are determined to go from scratch then you need to start with a basic block layout or topology to make it more sensible to approach the relevant parts. I have included some happy snaps of the Imax mentioned earlier under the display almost certainly is some sort of STM or clone Micro driving the output channels and monitoring/controlling the voltage and current via FETS and sense resistors. Lower Left is the DC-DC boost converter as this one is designed to run off 12V but can charge 6S so likely 30VDC output. Lower Right is a larger FET and associated bits for Non Balanced charging at high currents of NiMh/NiCad etc.
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Offline tooki

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #28 on: October 19, 2021, 09:06:19 am »
i seem to be getting little help with my original posting subject on this forum.

Replies here seem even to be unable to realize that I am able to improve my ability to design circuits and seem obsessed with the profitable encouragement for viewers of this forum to buy buy buy (modules) and not try on their own to learn how to design things themselves( Don't get me wrong, hobby ways of doing things are fine for hobby-oriented people, I am tying to learn electronics and electronic design not just make some bulky, expensive, dodgy device work by throwing money at a problem.). 
The problem is that you don’t seem to accept that making things yourself — which everyone here understands the joy and educational value of — is rarely compatible with “cheaper” and “smaller”.

If you said simply: “I want to make this myself from scratch to understand how it works. I know I could buy it cheaper, but I want the experience”, nobody would disagree, and you’d get plenty of help. We all do projects like that.

But your arrogance of thinking you can out-engineer teams of people who have spent years designing dedicated chips and/or products around them? Nah, not a snowball’s chance in hell you’ll manage that. Even if you design a circuit that does everything a dedicated chip does, and does it equally well, it will not be as small and cheap as the dedicated chip. And your flippant responses to people giving you reality checks aren’t doing anything to curry favor.


I would also say that I can circuit design as good as the best groups of engineers by learning their technology, their methods to solve this  problem using up to date battery-charging/balancing IC's.
So now suddenly you are willing to use dedicated ICs? That’s a very sensible approach. Later you can build your own truly from scratch.

P.S. I’m speaking from personal experience here — I learned a ton about charging systems by building one NiMH and one LiIon charger, each around a dedicated IC. And I actually would like to build my own from scratch at some point. But the learning from starting with the ICs was invaluable.
« Last Edit: October 19, 2021, 09:12:25 am by tooki »
 

Offline salihkanber

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #29 on: October 19, 2021, 09:09:38 am »
Chinese packs even dont have balancing circuits and they work well for some years :)
 

Offline SuzyCTopic starter

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #30 on: October 19, 2021, 10:36:10 am »
 beanflying "Partly because a lot of us will see little advantage in reinventing the wheel when you can buy a good one for around $30."
Again, beanflying, I am not interested in buying modules or even dedicated BM IC's if I can avoid it if I can design my own circuits.

I am interested in furthering my experience in designing circuits, to learn how to design circuits.

I am not a newbie. I have been designing and successfully building my own CPU-based power supplies and Li-Ion chargers for  projects for over 20-years.

I am therefore not trying to "start from scratch."

Buying a module is not engineering, it is a hobbyist's desperate attempt to achieve a dodgy result by buying clumsy modules that are bulky and not integrated into a design of their own.

My advantage is clear, to design my own circuits to not have to buy a module or IC that I can myself design to emulate and therefore then allow me to refine my design and then build something that best fits in the small spaces available in my project.

Tooki: So now suddenly you are willing to use dedicated ICs? That’s a very sensible approach. Later you can build your own truly from scratch. 

I never said I was willing to use dedicated ICs. I don't understand how you misread what I posted to think this is true.

My goal is to try to achieve the smallest footprint without resorting to buying a dedicated chip and certainly not a pre-built module. I may not be able to closely achieve that goal but I will make that effort.


My solution may not even be as cheap, but it will be my design. It will by my design and undergo testing, so I am sure to say it is able to very closely work as well as the pre-built module or dedicated IC. 

If I design a circuit to accomplish my goals, I will be able to completely control the circuit operation, integration into a PCB and size to fit my needs for performance, parts sourcing, cost and safety.

Finally, I can say (after quite a lot of Googling)  that charge-balancing is not really complicated or something "taboo" to play with. 

Charge balancing needn't be complicated nor unsafe to attempt.

I had hoped my topic posted would  have been about sharing experience with charge-balancing instead of spending post after post attempting to convince others that I am not interested in modules.
« Last Edit: October 21, 2021, 02:27:46 pm by SuzyC »
 

Online beanflying

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #31 on: October 19, 2021, 11:45:38 am »
Given your last post then we are clearly wasting or having our time wasted then  :palm: Everything you have typed so far just doesn't gel with the following.



I am not a newbie. I have been designing and successfully building my own CPU-based power supplies and Li-Ion chargers for  projects for over 20-years.

I am therefore not trying to "start from scratch."


Any Li-Ion charge experts out there?

I want to DIY a 4S li-ion charge balancer and I have some questions:
When to begin/continue charge balancing in charge cycle ( at 10% of charge or  50% of charge or at 100% of charge?
    (0r actively charge balance the entire charge cycle and also while the battery pack is in use?)
 
 
 Assume I'm charging 4 series-connected cells to 4.2 V charge cut-off voltage at CC 500mA

I am going to use a dedicated 10-bit A/D MCU to accomplish this job, using opto-isolators as sw's to a NPN BJT to load a 10-ohm resistor across the battery being reduced in voltage for balancing?
« Last Edit: October 19, 2021, 11:59:49 am by beanflying »
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Offline amyk

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #32 on: October 19, 2021, 01:39:53 pm »
At >= C/2 CC charge rates, this resistance is significant in determining a precise battery EOCharge cutoff voltage that doesn't damage the cell.
Note that still putting full charge current into the cell as it approaches the upper voltage limit will wear them out much faster than a more gentle tapering off.
 
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Offline SuzyCTopic starter

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #33 on: October 19, 2021, 03:45:19 pm »
Thanks Amyk for focusing on the actual topic of this post.

Always in charging LI-Ion, current must throtle down once the 4.2V (or 4.15 or 4.1V) desired cutoff voltage limit is reached.

Proper charging always allows the constant-current to decrease during the voltage float phase of charging, once the target cutoff  voltage is reached while charging.

The only way to force current into a Li-Ion battery over an established level in charging would be to increase the allowable charging voltage.  Exceeding the voltage cutoff limit is damaging and not permitted in any charging scheme I use.

This is why voltage balancing seems enticing, because some cells could reach the cutoff voltage before others and equalizing prevents these cells from being damaged by over-voltage while allowing any lower-voltage cells to continue charging.

What I've learned so far:

Charge-balancing is accomplished in two ways. The first is to switch on a shunt (resistor or constant-voltage shunt regulator) across a cell that is too high in voltage (relative to other cells in the battery) to slow its charging.

The second way (and I am not sure if it is used in modern charging circuits) is to momentarily shunt a capacitor across a higher-voltage cell and then transfer this charged capacitor to shunt a lower-voltage cell to discharge this charge-transfer capacitor.

The second idea seems enticing because it does not waste charging current, but could be less safe and very complicated to achieve in a charging circuit without a very large number of extra parts. It would also mean the charging circuit would have a larger footprint and be more expensive in part costs.

NASA has made available to the public a multi-cell charging scheme that uses pulse transformers to individually charge cells. This idea is not economically practical in most instances in non-space use, but could be very important on any space vehicle or other outer space device, where all power supplies need to not waste any energy.
« Last Edit: October 19, 2021, 04:13:18 pm by SuzyC »
 

Offline tooki

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #34 on: October 19, 2021, 04:11:39 pm »
beanflying "Partly because a lot of us will see little advantage in reinventing the wheel when you can buy a good one for around $30."
Again, beanflying, I am not interested in buying modules or even dedicated BM IC's if I can avoid it.

I am interested in furthering my experience in designing circuits, to learn how to design circuits.

I am not a newbie. I have been designing and successfully building my own CPU-based power supplies and Li-Ion chargers for  projects for over 20-years.

I am therefore not trying to "start from scratch."
Nobody said you'd be starting from scratch. I said you intend to build it from scratch, which means "not relying on premade things", i.e. in this case, avoiding modules and ICs. I used "build from scratch" to avoid using "DIY", which has connotations that might not be applicable here.

Like, haven't you ever heard anyone say "I'm going to bake a cake from scratch"? That means starting with flour, sugar, eggs, milk, baking powder, and vanilla, as opposed to starting with a cake mix that only needs eggs and milk. It doesn't mean that it's their first time baking!!



Tooki: So now suddenly you are willing to use dedicated ICs? That’s a very sensible approach. Later you can build your own truly from scratch. 

I never said I was willing to use dedicated ICs. I don't understand how you misread what I posted to think this is true.
Easy, because your lousy punctuation and run-on sentences make it easy to misunderstand what you mean.

You wrote:
I would also say that I can circuit design as good as the best groups of engineers by learning their technology, their methods to solve this  problem using up to date battery-charging/balancing IC's.
That sentence construction (Do X by doing Y) means that the Y is qualifying how you will do X. Using italics to mark X, and bold for Y, your sentence parses as either:

I would also say that I can circuit design … by … using up to date battery-charging/balancing IC's.
or
I would also say that I can … solve this problem using up to date battery-charging/balancing IC's.



Either way, you end with the qualifier of using modern ICs.




My goal is to try to achieve the smallest footprint without resorting to buying a dedicated chip and certainly not a pre-built module. I may not be able to closely achieve that goal but I will make that effort.


My solution may not even be as cheap, but it will be my design. It will by my design and undergo testing, so I am sure to say it is able to very closely work as well as the pre-built module or dedicated IC. 

If I design a circuit to accomplish my goals, I will be able to completely control the circuit operation and size to fit my needs for performance, parts sourcing, cost and safety.
You say that now. But above, you stated repeatedly how your goals were to:
a) match or undercut the price of a low-cost product from a supermarket
and
b) minimize space

Well the first one is practically impossible anyway, so let's ignore it. But if space savings matter, which they seem to be since you bring it up every time, then you'd want to go with a dedicated IC.

As I said in a prior reply: if your actual #1 goal is to avoid using anything premade, even ICs, then you should not have kept insisting on low cost and compact.


Finally, I can say (after quite a lot of Googling)  that charge-balancing is not really complicated of something "taboo" to play with. 

Charge balancing needn't be complicated nor unsafe to attempt.
Nobody said balancing was taboo. Without knowing your skill level (which you didn't share until your final tirade), the etiquette here is to err on the side of safety, which is why you will see people express warnings about lithium charging.



I had hoped my topic posted would  have been about sharing experience with charge-balancing instead of spending post after post attempting to convince others that I am not interested in modules.

The first person to mention a module to you, to which you immediately freaked out, said to look at a module to see how they do it. They did not say to buy the module!  |O


The reason you're getting so much pushback, SuzyC, is your awful attitude. You've been on the defensive since the first reply was posted, a reply you didn't even read properly. You attack everyone, and then oscillate between acting like a newbie and claiming you're super-experienced, ultimately spending more time whining than anything else. Your sloppy use of terminology also makes me very skeptical of your claimed expertise.


Always in charging LI-Ion, current must throtle down once the 4.2V (or 4.15 or 4.1V) desired cutoff voltage limit is reached.

Proper charging always allows the constant-current to decrease during the voltage float phase of charging, once the target cutoff  voltage is reached while charging.
You are always in either constant-voltage (CV) OR constant-current (CC) mode — you can't be in both at the same time. (Float charging is something else, btw.)

When the CC phase has finished by reaching the termination voltage, the charger switches to the CV phase, during which current (not "constant current") drops until reaching the termination current.

This is why voltage balancing seems enticing, because some cells could reach the cutoff voltage before others and equalizing prevents these cells from being damaged by over-voltage while allowing any lower-voltage cells to continue charging.
I think a better word than "enticing" is "necessary". But yes, that's exactly why you need balancing.


Charge-balancing is accomplished in two ways. The first is to switch on a shunt resistor across a cell that is too high in voltage (relative to other cells in the battery) to slow its charging.

The second way (and I am not sure if it is used in modern charging circuits) is to momentarily shunt a capacitor across th higher-voltage cell and then transfer this charged capacitor to shunt a lower-voltage cell to discharge the transfer-capacitor.

The second idea seems enticing because it does not waste charging current, but could be less safe and very complicated to achieve i a charging circuit without a very large number of extra parts.
Another way it's done is with inductors as energy store. See e.g. how the Analog Devices LT8584 does it. But it definitely adds lots of parts (even more so when rolling your own control circuit.)

There are also some systems that use an additional, dedicated cell as the energy store for balancing.
 

Offline SuzyCTopic starter

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #35 on: October 19, 2021, 04:24:12 pm »
Thanks Tooki for your help in and pointing out some of the confusing phrases and word choices I have used.
I don't always have time to both try to explain whats on my mind and then carefully edit my postings.

However, when I scan over the many topics posted on this forum, my main complaint is seeing too often almost unintelligable, very vague postings. I choose to make clear my ideas and spell correctly and pay attention to grammar, and that in itself, seems unusual.

If I was that perfectly careful, I would be writing a book! If I was writing a book, I wouldn't have time to work on my current  projects.

I do have a strong tendency towards run-on sentences.
Thanks for reminding me.
I will be more careful to try to parse my phrases into separate sentences.

As I am posting replies, I am also, in the process, getting a better understanding on my mindset and ways I present my understanding of a problem and the way to achieve my goal.
My postings are a process, an evolution of the ideas that I am playing with.

If I knew exactly what I was doing, I wouldn't bother to post a topic here.

I am actively trying to better understand  the problem I am dealing with and then hope I can even change my ideas when I can better understand how to accomplish my goals.

-------

While in constant current charging, the "constant current" remains constant at an ever-decreasing value once the farget float voltage is reached. (Both at the same time?) As I understand it, perhaps I should say that constant current mode evolves into a mode of decreasing current limiting to prevent overvoltage. In any case, it is simply a choice of words.
It is necessary to determine the  point that the constant-current decreases to reach the end of charge current level that terminate charging.
« Last Edit: October 19, 2021, 05:19:51 pm by SuzyC »
 

Offline David Hess

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #36 on: October 19, 2021, 04:37:03 pm »
I have always though the way to go for a simple circuit is a voltage follower with class-B output stage to drive each junction between cells.  The collectors of the output transistors are driven from adjacent cells and have a series resistor to limit current.  The reference voltages come from a string of precision resistors, which can be high value if the input bias current is low.
 
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Offline SuzyCTopic starter

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #37 on: October 19, 2021, 04:50:03 pm »
Thans David!  I am trying to conceptualize what you've posted and I am not quite disambiguating the circuitry required.

I know its probably too much to ask, but a simple schematic is worth a thousand words. 

With your idea, the cost of implementation, circuit complexity and footprint, as well as cost pop-up first in my mind.

I see a lotta difficulty determining how to control the charging real-time total voltage applied to the batteries.
« Last Edit: October 19, 2021, 04:53:38 pm by SuzyC »
 

Offline David Hess

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #38 on: October 19, 2021, 08:02:23 pm »
A voltage follower with a class-B output is shown below.  Essentially it just forces the output to the input voltage applied to the non-inverting input, with the transistors boosting the output current.  Only one transistor conducts at a time.

A further refinement would be to disconnect the output of the operational amplifier from the bases of the transistors to disable balancing, with an analog multiplexer or maybe a FET.  Without this the circuit would balance the cells during both charge and discharge, but this would not necessarily be a problem in all applications.  Some operational amplifiers include a shutdown function which disconnects the output which could be used for this and would be ideal.

The operational amplifier and output transistors are only running on the voltage supplied from adjacent cells, so a micropower type of operational amplifier should be used unless shutdown is used.  For the same reason the input resistor divider should use high value resistors, which also means that the operational amplifier should be a low input bias current type.

Place small power resistors in series with the collectors to limit the current.  Voltage across each transistor is about 2 volts depending on the voltage drop across the power resistors, so figuring 2 watts rating from power surface mount parts, a balancing of current of 1 amp is feasible, but of course it could be higher or lower depending on the application, and under normal conditions the battery state will limit the current lower except under high current charge or discharge.
« Last Edit: October 19, 2021, 08:07:40 pm by David Hess »
 
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Offline SuzyCTopic starter

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #39 on: October 19, 2021, 08:46:37 pm »
Thanks David for posting a reply and a simple schematic. I must say this idea is so very different from anything I would have imagined and I can certainly see how this approach would be avoided because:
The cost of the additional parts, esp. regarding the  use of bipolar power supplies and adding an opamp per battery.
This circuit might require these charge-equalizers to be located on the battery.
It needs a way to precise current and voltage in each balancing module and for the whole string of cells.


The complexity is excessive.  Because of the use of bipolar supplies, this design looks like in might be found in a mains/battery powered oscilloscope or other expensive instrument.
« Last Edit: October 19, 2021, 08:57:12 pm by SuzyC »
 

Offline SuzyCTopic starter

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #40 on: October 19, 2021, 09:09:37 pm »
As my study of charge-balancing continues I am wondering if charge balancing is a good idea to use at all.

Salihkamber posted that "Chinese packs even dont have balancing circuits and they work well for some years :)"


If any cell set has a failing battery, charge balancing can only exacerbate the problem.
A cell that has developed a high internal resistance will appear to be over charged in comparison to the other cells in a battery while  CC charging. Attempting to equalize voltage in a cell in this condition makes a weak cell end up with even less charge than the other cells in a multiple cell battery.

If any cell starts to be significantly different in charge voltage or charge acceptance or series resistance, this would indicate that cell is gone south and there is an impending  need to replace the whole battery pack. Balancing doesn't help.

Battery packs have very identical cells, they should remain that way during the service life of the battery when properly charged.

Is this guess correct?
« Last Edit: October 19, 2021, 09:48:47 pm by SuzyC »
 

Offline David Hess

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #41 on: October 19, 2021, 09:32:44 pm »
The cost of the additional parts, esp. regarding the  use of bipolar power supplies and adding an opamp per battery.

The operational amplifiers are supplied from adjacent batteries.  It could be built into a battery pack.

Quote
This circuit might require these charge-equalizers to be located on the battery.

Nothing prevents the balancing modules from being located remotely if all of the junctions between batteries are available.

Quote
It needs a way to precise current and voltage in each balancing module and for the whole string of cells.

Each balancing module uses a pair of precision resistors, which are relatively cheap, to establish a reference voltage between two cells based on the existing cell voltages.

Quote
The complexity is excessive.

It uses common inexpensive parts and requires no state control unless shutdown is desired and even that could be tied to a charge indicator.  It is more complex than a dedicated ASIC, and requires two power transistors in place of one.

Quote
Because of the use of bipolar supplies, this design looks like in might be found in a mains/battery powered oscilloscope or other expensive instrument.

I have seen it used in older dual cell battery packs for consumer stuff, but it would be a good candidate for balancing cells used in battery backup of continuously powered equipment.

 
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Offline David Hess

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #42 on: October 19, 2021, 09:38:15 pm »
Chinese packs even dont have balancing circuits and they work well for some years :)

How much longer would they work with active balancing?

I ended up taking apart a Milwaukee M12 battery and they do not use active balancing, although the do monitor the voltage of every cell.

LiFePO4 cells should require less active balancing because they can tolerate more overcharge.
 
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Offline SuzyCTopic starter

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #43 on: October 19, 2021, 09:51:51 pm »
Thanks again David.

You say you took apart a Milwaukee pack, but you didn't reveal if the matching of cells and their voltages remained the same after long use.
« Last Edit: October 19, 2021, 09:58:31 pm by SuzyC »
 

Offline Psi

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #44 on: October 19, 2021, 10:59:52 pm »
On the first page I suggested you look at that IMAX B6 HOBBYKING SCHEMATIC  because that is built from discrete components and a MCU for overall control, which is exactly what you are talking about building and will give you lots of ideas.
But for some reason I got pushback against the suggestion. Or maybe it just seemed that way from your post after.

However I suspect most of the issues in this thread are related to miscommunication and terminology issues.

I think you got a lot of hacky/module solutions recommended to you because you said...

There must be a more cheap'n'dirty way to do this without significantly sacrificing battery life or fire safety.
« Last Edit: October 19, 2021, 11:07:53 pm by Psi »
Greek letter 'Psi' (not Pounds per Square Inch)
 
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Offline SuzyCTopic starter

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #45 on: October 19, 2021, 11:42:24 pm »
Psi thanks and I have perused the schematic and have found it to be an unintelligible hobbyist creation. Almost all of the interconnect labeling is completely blurred, making the schematic totally useless.

BIAC, The circuit seems not to make any good design sense to me and my lasting impression is (if this circuit really works at all) it is still obsolete and extremely over-complicated using far too-many components because it is fabricated using cheap and dirty thirty to 40-yr-old technology.

Altogether quite crude in design. I don't see a MCU in the schematic attached, and if it was shown there or on another page, and yet without the commented source code, the whole use of the schematic remains working with a bag of worms.

I don't pretend to be a MSEE just matriculated from MIT, but the level of my expertise shows this schematic is far too  primitive to give me any help.
« Last Edit: October 20, 2021, 12:17:58 am by SuzyC »
 

Offline tooki

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #46 on: October 20, 2021, 12:31:43 am »
As my study of charge-balancing continues I am wondering if charge balancing is a good idea to use at all.
Proper technical forum etiquette is to do your basic homework before asking for help.

If any cell set has a failing battery, charge balancing can only exacerbate the problem.
A cell that has developed a high internal resistance will appear to be over charged in comparison to the other cells in a battery while  CC charging. Attempting to equalize voltage in a cell in this condition makes a weak cell end up with even less charge than the other cells in a multiple cell battery.

If any cell starts to be significantly different in charge voltage or charge acceptance or series resistance, this would indicate that cell is gone south and there is an impending  need to replace the whole battery pack. Balancing doesn't help.
The whole point of balancing is that you don't overcharge a weaker cell, because doing so causes a vicious cycle of accelerated aging. You use balancing to protect the weak cell from overcharging, so that it isn't overstressed.

The cells in a pack are never identical, so even if they start out with identical capacities, they won't stay identical forever. So you have to protect the weaker cells, lest you constantly overcharge them, causing damage to them, further reducing their capacity.

Battery packs have very identical cells, they should remain that way during the service life of the battery when properly charged.

Is this guess correct?
Nope. "Identical" cells, even from the same production lot, will not actually be identical, and will not age identically.

The fact that practically all properly-made commercial series battery packs use balancers should make it obvious that it needs to be there; they'd save the expense if it were useless (never mind harmful).


This entire reply of yours really makes me question your claims of supposed expertise with lithium charging. Either you don't actually have that experience, or you've been abusing your cells over the years.



Psi thanks and I have perused the schematic and have found it to be an unintelligible hobbyist creation.
Yeah, I mean, IMAX is merely one of the most respected names in battery charging, particularly in the RC (radio control) world, which pushes cells hard and thus needs to handle them carefully. But what would they know…  ::)

Almost all of the interconnect labeling is completely blurred, making the schematic totally useless.
Regarding schematic sharpness: You have to download the PDF of the schematic, not just a preview JPEG, silly goose! ;) So that's entirely, 100% on you.

(I googled "IMAX B6 HOBBYKING SCHEMATIC" and literally the first hit is on elektrotanya, which has a nice clear PDF for download.)

This page in Russian has a more detailed schematic, including MCU: https://ru-radio-electr.livejournal.com/1295897.html


BIAC, The circuit seems not to make any good design sense to me and my lasting impression is (if this circuit really works at all) it is still obsolete and extremely over-complicated using far too-many components because it is fabricated using cheap and dirty thirty to 40-yr-old technology.
…which is literally precisely what your design intent is for your charger, since you expressly want to eschew modern integrated technology.


Altogether quite crude in design. I don't see a MCU in the schematic attached, and if it was shown there or on another page, and yet without the commented source code, the whole use of the schematic remains working with a bag of worms.
The only part of that reply that has any merit: I couldn't find a schematic of the MCU section, either.


I don't pretend to be a MSEE just matriculated from MIT, but the level of my expertise shows this schematic is far too  primitive to give me any help.
  :-DD

You certainly pretend to be an expert, when clearly you're not! (I'm not an expert, either, but at least I know where I'm at!) You certainly aren't knowledgeable enough to be making proclamations about "good design sense" on circuits you don't even understand...
« Last Edit: October 20, 2021, 12:42:20 am by tooki »
 

Offline SuzyCTopic starter

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #47 on: October 20, 2021, 12:43:52 am »
Tooki, thanks for the valuable criticism of my criticism of the schematic.

Funny, before this day, I always thought IMAX was a kinda big screen place to watch moving pictures.
 

Offline Psi

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #48 on: October 20, 2021, 01:36:52 am »
Part of being an engineer is knowing how to pull useful info out of a sea of crap info.

One note, be aware that there's many companies making clones of the IMAX chargers due to their popularity.
That Russian link appears to be the official one, but always treat anything you find on the internet as potentially fake.
« Last Edit: October 20, 2021, 01:38:48 am by Psi »
Greek letter 'Psi' (not Pounds per Square Inch)
 
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Offline SuzyCTopic starter

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Re: How to DIY Charge-Balance 4 Li-ion 2000mAH
« Reply #49 on: October 20, 2021, 01:40:35 am »
Psi..should I wear gloves and a mask?
 


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