Got circuit made by questionable freelancer

Thread Starter

ejnarwj

Joined Jan 20, 2023
31
Have you decided on a solution?
Well actually, I was going to go with the MAX1736, but it seems that they are rather expensive, which is not going to work well, as this is products i will be selling. Therefore as far as my research stands, i will be going with LM3622 which also offers high input voltage and seems rather simple. Which is good, since i am a complete noob, when it comes to circutry.
 

Audioguru again

Joined Oct 21, 2019
6,759
The voltage regulator IC would cause the Li-Ion cell to explode and catch on fire.
A Lithium charger IC makes many important tests and limits to avoid explosion and fire because a Lithium battery cell is not a simple resistor.
 

Audioguru again

Joined Oct 21, 2019
6,759
The limit is 8V because a Lithium cell is charged at only 4.2V and more than the extra 3.8V times the charging current makes too much heat in the charger.
 

Audioguru again

Joined Oct 21, 2019
6,759
Buck converter charging chips minimize waste heat by efficiently stepping the voltage down using an inductor.
A Switching Buck voltage converter reduces its output voltage using an inductor that reduces its heating. But it is NOT a Lithium battery charger circuit.
The Chinese TP4056 Lithium battery charger IC has a maximum allowed input of 8V because IT GETS HOT and needs a "radiator" that is connected somehow Under It.
 

Thread Starter

ejnarwj

Joined Jan 20, 2023
31
Got room for a regulator before the charger chip? What is your max voltage input and charging current required?
Okay, so I think I have been leaving to much information out of my project. I have 2 different products one which contains 2 batteries and the other one containing 3. I was thinking of leaving them in parallel, therefore I thought I could just go with a single cell charger, but thinking about it, that is going to take forever.

as i stand now i think the SY6912 multi cell charger is a good bet, since it is very accesable, not too expensive and it can both do 2-cell and 3-cell and also has that high input voltage which is good, since I will be using 12 v 1A dc input:)
 
Last edited:

bassbindevil

Joined Jan 23, 2014
836
A Switching Buck voltage converter reduces its output voltage using an inductor that reduces its heating. But it is NOT a Lithium battery charger circuit.
The Maxim MAX745 and Silergy SY6912 are all high efficiency switching chargers, not just regulators.
MAX745 "Switch-Mode Lithium-Ion Battery-Charger" "±0.75% Precision Li+ Charger Delivers 4A Without Heating"
https://www.analog.com/en/products/max745.html
SY6912A "2A Multi-Cell High Efficiency Switching Charger"
https://datasheet.lcsc.com/lcsc/1810081413_Silergy-Corp-SY6912AFCC_C129777.pdf
Consonance makes both switching and linear chargers. Some work in boost mode to charge multiple cells from a 5V source.
http://www.consonance-elec.com/en/products_28/
Used in boards like these (got one to try as a back-up or travel charger for a 3S4P power bank):
https://www.aliexpress.com/item/1005004760217921.html
 
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Thread Starter

ejnarwj

Joined Jan 20, 2023
31
Hello again. I am currently looking at the datasheet of the SY6912A , to find out how to put the circuit together. Does anyone have the ability to decode what excatly Rut and Rot is ment to replace in the section of calculating the values for the NTC resistors at application information at page 9?

I know that Kut and Kot is the threshold for under temperature and overtemperature and i am going for the default values of Kut=75% and Kot=30%

The only explaination is " Assume the resistance of the battery NTC thermistor is RUT at UTP threshold and ROT at OTP threshold ", but i do not have the farerest idea, what that is supposed to mean?
Any help is appreciated:)

https://datasheet.lcsc.com/lcsc/1810081413_Silergy-Corp-SY6912AFCC_C129777.pdf
 
I worked with Li-Polimer battery chemist in the past. There is some advanced science with 'smart' Li batteries charging.
All to do to extend lifespan, or accelerate charge rate and so on, target depended.
For example if client specify maximum lifespan and reliability, then charger will control:
- max/min voltage changed
- charge rate / current reduced
- cell temperature measured or predicted and controlled during cycle
- cell and be put to stand-by for some minutes before charging. Not allowed to charge immediately after discharge cycle
I think there are more elements to it, but above is just shows that battery charge circuit when done properly is highly specific to application and tech requirements.
 
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