EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Refrigerator on July 23, 2016, 01:22:06 pm
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For a while there's been one question in my head to which i could not find a solid, definitive answer no matter where i searched for so I decided to find the answer myself and also post it here in case anyone wants to use the circuitry from laptop battery packs.
The question i'm talking about is basically "how are they charged and what does the circuit do ?".
The quick answer is that the circuitry does over/under voltage protection, over heat protection, charge management, battery pack anayzing, cell balancing and over/under current protection, which are alot of great features that you can get basically for free.
I decided to rig a couple of wires to a pack and pop it into my laptop to see what it does.
Basically the laptop does the CV/CC charging while the battery pack circuitry balances and protects, simple anough.
So to charge the battery, depending on what battery you have, you plug a CV/CC power supply to the + and - terminals.
For example a 11.1V laptop battery has 3 cells ( 11.1V / 3.7V = 3S ) so the charge voltage will be 12.6V ( 4.2V * 3S = 12.6 V ).
The current will be the battery capacity multiplied by 0.5C . For example 4400mAh * 0.5C = 2200mA maximum charge current.
CV/CC ( constant voltage/current ) PSU is absolutely necessary because that's how Li-XX cells are charged, luckily they can be found on eBay for cheap.
http://www.ebay.com/itm/7-35V-to-1-25-30V-Step-down-CC-CV-Power-Supply-Module-Converter-LED-driver-New-/351328646847?hash=item51ccd1b6bf:g:nZAAAOSwBLlU8V0r (http://www.ebay.com/itm/7-35V-to-1-25-30V-Step-down-CC-CV-Power-Supply-Module-Converter-LED-driver-New-/351328646847?hash=item51ccd1b6bf:g:nZAAAOSwBLlU8V0r)
The converter linked above can be used to charge the laptop battery from a laptop PSU, or any PSU that has a voltage at least 2V higher than the required charge voltage.
Laptop PSU can not be used to charge the laptop battery directly !!! Or else it will damage the battery.
I hope this helps and thanks for reading.
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https://www.eevblog.com/forum/reviews/lm2596-dc-dc-step-down-modules-load-testing/ (https://www.eevblog.com/forum/reviews/lm2596-dc-dc-step-down-modules-load-testing/)
Thanks for the info.
I haven't tested the modules myself, but their reputation is infamous as not-as-titled.
The module in your attached eBay link has pictures that make the module look like it was produced by the loosers of a Chinese blindfolded soldering competition.
There are many circuit examples that can be found by searching LM2596. Many manufacturers such as ON Semi have extensive circuit design guides incorporated into their datasheet.... If your not into the popular trend of burning your house down... :)
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https://www.eevblog.com/forum/reviews/lm2596-dc-dc-step-down-modules-load-testing/ (https://www.eevblog.com/forum/reviews/lm2596-dc-dc-step-down-modules-load-testing/)
Thanks for the info.
I haven't tested the modules myself, but their reputation is infamous as not-as-titled.
The module in your attached eBay link has pictures that make the module look like it was produced by the loosers of a Chinese blindfolded soldering competition.
There are many circuit examples that can be found by searching LM2596. Many manufacturers such as ON Semi have extensive circuit design guides incorporated into their datasheet.... If your not into the popular trend of burning your house down... :)
That's because most of the LM2596s on eBay are fakes, but good enough to work as a CV/CC converter for the li-ion pack.
Also i forgot to mention that the chipset that is in some laptop batteries also has a function for a 4 or 5 LED battery charge meter. Once you get to know about those internal circuits they turn out to be great for projects an have anything you would ever want from them, even data logging, so much functionality that you would otherwise be throwing away.
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FYI, the management board on laptop batteries communicates using Smart Battery System protocols over SMBus. I have some documentation and example code for reading SBS data (http://powercartel.com/projects/packprobe/) on my website.