Low Parts-Count, Low Heat, 4A, SMD Current Regulation?

[theboom]

My application is a single-cell lithium battery charger. I assume constant-voltage with current-limiting would work (but i may be mistaken).

There will be a group of disconnected cells (not a battery pack). All the cells in the group will be the same chemistry as each other. Need to support both Li-ion and LiFePO.

A single SMPS will supply regulated constant voltage for all the cells. So i think all that's needed is a current limiter on each cell.

The LM338 seems to have low-parts limiter, but apparently not available in SMD package, and (i'm told) not low-heat.

I found this current limiter for the TL431, but i'm told it will disconnect when limit is reached, rather than simply limit current to desired level.

If possible, I like the idea of shunting the excess current to other cells in the group, rather than wasting it as heat.

I'd be fine with a low-parts single-cell charger IC. Analog offers several, such as the LTM8026, but much too expensive for my application.

 

[danadakk]

It's sounds like you're saying "All designs and IC's with a given function will cost the same, and have the same number of parts." It seems to me that different IC's or circuits vary widely in COG and/or number of parts.

Not at all first sentence. Agree second sentence.



Regards, Dana.

 

[BradtheRad]

am i correct that we'll reduce dissipation if we lower the supply V going to the current regulator?

Should there still be an additional Rbias?

When I've made homebrew battery chargers for nicad/nimh cells, I felt relaxed doing so. They're low power, designed to tolerate careless charging and discharging.
Since then Li-ion type became wildly popular in the consumer market. However I'm nervous at the idea of making a charger for those. One mistake can be dangerous. For example airlines had to set rules about what size of Lithium batteries could be allowed on a plane. This was necessary after numerous reports of fires and explosions.

You need to gain experience with rechargeables that are easy to work with, such as nicad and nimh.
Watch an ammeter as you vary the charge rate. Watch voltage across the cell rise or fall.
Hold the cell and feel it get warm after a while. Does 100mA make it warm? 1 Amp?
Try different values of safety resistor inline with the cell. 20, 50, 100 ohms.
Learn to notice signs of a deteriorating cell, as compared to a healthy cell.
Try different biasing arrangements in your quest for a charge schedule that works for you.

Rechargeable batteries have become a consumer item so widespread and so lucrative, yet so difficult to evaluate a cell's quality. It gives an incentive for manufacturers to take short cuts making them. What about a battery management system? Is it required? Is it present? Is it effective? What mistake can we make when charging them that ruins them?

 

[theboom]

This project will be developed with care by professional electrical engineers. Our volunteer team includes engineers from Bourns, Apple, Samsung, and Keysight.

At this time, i'm only conducting preliminary research. Later, our engineering team will investigate these methods under safe laboratory conditions.

The goal of this project is to develop a simple, easy charging methodology (and components) to prevent common hazards among inexperienced battery hobbyists. We will produce a set of tested, validated modules which implement this charging method.

Our system will be certified for safety by UL or other recognized safety examiners.

It would be great if you can answer my questions!

theboom.org

 

[d123]

Hi,

I still think hoping to make a li-ion charger with 5 discrete components is grossly unrealistic, besides other things. A common error for beginners (self included) is having an idea and subsequently wanting something to do what it cannot, but electronics is cold reality of maths + true/false: if the numbers don't add up, it can't work, and being wrong is something to accept with humility, electronics and egos don't combine well, the laws of physics couldn't care less about what I feel, they just are a constant.

I'm not going to look for a 4A charger IC, that's your or the battery guy in your organization's task. I guess you might already have seen these pages:

4 Simple Li-Ion Battery Charger Circuits – Using LM317, NE555, LM324 – Homemade Circuit Projects

www.homemade-circuits.com

3 Smart Li-Ion Battery Chargers using TP4056, IC LP2951, IC LM3622

Oh, I can't add the link to his second page of homebrew charger circuits.

I have no idea how safe they are to use but the guy seems to usually do sensible homebrew circuits and seems to have some idea of what he's doing.

Only posted links for possible ideas, but myself - I'd acknowledge magnitude of task, be humbled and honest, laudable end-goal or not, and focus on >5-part solutions, even modules, and do a bit of backtracking and admitting the premise was overly-optimistic as I gather you are a mentor and in this way set a positive example to the kids your organization helps. It's okay to be wrong sometimes, it's not positive nor okay to be 'shouty' to try to maintain a public image of authority instead of admitting we are wrong.

Also, helps to remember li-ion might mean the battery only or some charge control stuff included in the battery package, so it is not necessarily possible to just slap 25 assorted batteries onto one charger circuit, charger circuits are not 'one size fits all'.

From the streets 'n' stuff well-meant and humble sincerity.

Best of luck with the project.

 

[theboom]

hoping to make a li-ion charger with 5 discrete components is grossly unrealistic,

1. Your comment appears to indicate a gross misunderstanding. That isn't the hope. The charger is an entire system, including the SMPS stage which precedes the <=5 part limiter stage. The preceding SMPS stage doesn't have that part-limitation.

2. This off-the-shelf charger IC, which provides a complete charging system, requires only 3 external parts (5 including the non-essential status LED).

if the numbers don't add up

Which numbers are you referring to? I'm not aware that anyone has posted any specific numbers which "don't add up". Please link to the comment.

I guess you might already have seen these pages:

4 Simple Li-Ion Battery Charger Circuits – Using LM317, NE555, LM324 – Homemade Circuit Projects

www.homemade-circuits.com

Thx for that! I have visited that site, and corresponded with the engineer who runs it. He generously donated some free private consultation for the project. His solutions are certainly included in my list of possible solutions to bench-test.

admitting the premise was overly-optimistic

Have you looked at the homemade-circuits page you linked? Or this thread? There are more than one possible <5 part potential solutions. Your statement appears incorrect.

it is not necessarily possible to just slap 25 assorted batteries onto one charger circuit,

i clearly and explicitly stated that's not the intention. You're criticizing without, apparently, having read the thing you're criticizing.

This has been a very fruitful and useful thread, which has produced some very useful circuit ideas! I'm very grateful for the on-topic, specific, electronics posts!

 

[d123]

Numbers in a general sense, electronics is unfortunately maths more than components or street cred.

Yeah, whatever..., you're always misunderstood by almost everyone else and always right about everything, and I'm just another incredibly stupid person.

From your reply now (exactly what I was expecting) and comparing the premise at the start of this thread to here, I can only repeat: ego, dude, ego - less is more...

Might be worthwhile pondering why this thread has received 'off-topic personal comments'. Here's one more: what can be perceived to be a consistently predominantly hostile, bullying tone doesn't 'butter parsnips'.

To get dragged into social-media-style spats certainly isn't why I engage with members of this forum. Time is valuable, negative argumentative stances are a waste of time.

Finally, great, I'm genuinely glad you've found a solution, glad the thread has been fruitful for you, especially since the goal of helping the disenfranchised is positive. Best of luck with it.

 

[theboom]

Numbers in a general sense

I welcome math which indicates the impossibility of my objective. "Numbers in a general sense" isn't saying anything. Claiming the "numbers don't add up", while not producing the numbers which supposedly don't add up, is what i would call a "negative argumentative stance", and "a waste of time".

@d123 You claimed my objective is impossible. I refuted your claim with a schematic. You're calling my schematic "ego".

How about let's stop talking about me? Let's talk about circuits.