as all of us have a big flash lights that runs with 3 or more cells and all of us suffer slow charging time i wanted to make a very fast DIY charger
so i got this idea and i want you to share you thoughts about it
well as we know the laptop battery have a 18650 cells inside it my laptop have a 9x cells in it and when charging it from 0 to full it takes about 1.5 hours well that is very fast to charge a 9x 18650 cells
so if we opened a laptop battery we will find the cells are attached to a smart charging circuit, i have tried to understand how it works and what voltage do this circuit takes to charge the cells well i failed
so my project here is to use this smart charging circuit in the laptop battery to make a very fast DIY charger, so as a beginning how about this idea ?
There is no magic bullet here. The only way to make a cell charge faster is to give it more current, and I've never seen a laptop battery that fully charges anywhere near that fast, not even close. I suppose some laptops indicate they're fully charged when in reality it's only at something like 85%, but keeps charging if you leave it plugged in. Just to head off the users who don't understand how it works and complain that the laptop sucks because it takes too long to charge.
Not sure how fast some laptops charge, but to even think about doing 9 cells in 1.5hr (with the laptop off) you’d need about an 80W power brick. With it on? Maybe 100-120W.
My Dell laptops have 65W & 95W power supplies. The last laptop I set up at work was a Dell Precision M6700 and it had a huge 200W+ power supply, for a “laptop”!
Nice. Note that having a big power brick doesn’t guarantee that you can charge quickly, I was simply commenting that not having a big power brick guarantees that you can’t charge quickly.
Taking a glance around on the internet for (purported) datasheets, here’s what I see. I see a Panasonic NCR18650B datasheet which does not spec a max charge current, but shows a graph for 0.5C. I also see an LG datasheet for the D1 which shows standard charge at 0.5C but Max charge as 1.0C. A UR18650ZT datasheet shows STD as 0.5C and does not show a max. Samsung’s ICR18650-30A “specification of product” shows 0.5C standard and 1.0C as “Rapid charge”… and they specify “Rapid charge” as a 2.5hr process.
It’s also worth noting that as you increase the charging current you get diminishing returns. HKJ’s mini-review of the v2 Opus BT-C3100 shows us the results of charging a single cell at 1A vs 2A. Termination is at 220minutes vs 122minutes.
If someone wanted to guestimate the maximum charge current their laptop provided the process would be simple.
Set your laptop to Hibernate when it hits 5%. Sleep is not acceptable.
Run your laptop all the way down until it hibernates on it’s own.
Attach the laptop’s AC adapter to a “Watts Up Pro” or “Kill A Watt” meter.
Attach the AC adapter to the laptop.
Attach the meter to the wall.
Read the wattage the meter shows.
Multiply that figure by 0.8 (this is a generous figure assuming ~90% efficiency at both the power brick and the charge circuit).
Divide the resulting figure by the number of cells.
Divide that figure by the estimated voltage of each cell (call it 3.5v - 3.7v).
That should give you a ballpark charge current. For a more accurate number, modify steps #6 & 9 in this way:
Set your laptop to Hibernate when it hits 5%. Sleep is not acceptable.
Run your laptop all the way down until it hibernates on it’s own.
Attach the laptop’s AC adapter to a “Watts Up Pro” or “Kill A Watt” meter.
Attach the AC adapter to the laptop.
Attach the meter to the wall.
Read the initial wattage number, then keep an eye on it. The wattage should increase slowly for a long time. About 1/2 to 2/3 of the way through the charge you’ll see the wattage start to drop. Note the maximum wattage value from right before it starts to decline.
Multiply that figure by 0.8 (this is a generous figure assuming ~90% efficiency at both the power brick and the charge circuit).
Divide the resulting figure by the number of cells.
Divide that figure by 4.2
We know the power (wattage) draw on a CC/CV charge will taper off as we hit 4.2v. The accuracy of the result here is controlled primarily by how bad the “0.8” figure in step #7 is. I expect the resulting current from these calculations to be higher than reality.
Don’t overlook that most cells used in laptop packs (and about all packs) are going to be around 2200mAh or less, the largest I’ve ever seen are 2600’s (and I take a lot of packs apart, I make weekly rounds to the battery bins at Home Depot and lowes) so even at a generous 1A charge rate your NCRB’s are going to take an hour or so longer.
Why not just get a hobby charger or even a LUC / dream charger?
New packs? The capacity of what’s inside the pack doesn’t matter that much anyway - it’s what C-rate they are charged at that’s key.
LUC / dream charger still take >2hr to charge only 2 cells! Hobby charger can do whatever you tell it to of course… and maybe if you obey the datasheet you can put a decent charge into a cell in 1.5hr at 1.0C. I haven’t tried (I charge LiPo cells at >1C, but I haven’t done it to my Li-Ion cylindrical cells).
Li Ion batteries are designed to be slow charged and have the ability to dump that charge quickly
You stress batteries by quick charging them highly reducing the recharge cycles when you do…sure those hobby Li Poly batteries fast charge but have you really seen them last more than 50 or so charges?
A little light reading that should help
Yes long charge times suck…but for the longevity of the batteries that is what they are designed for
C-rate is a a ratio of charge current vs capacity. Battery charger - Wikipedia
a 3000mAh battery charged at 1500mA is receiving a 0.5C charge
a 1500mAh battery charged at 1500mA is receiving a 1.0C charge
I do not know how to make a laptop battery charging circuit work.
If the max safe charge rate for a particular cell is 1 amp it doesn't matter what kind of circuit or how fancy or how simple, if it puts out 1 amp it will take a certain amount of time to fully charge the cell.
There are some chargers that will indicate a full charge too early, when the cell is actually only at 4.12-4.15v, and will only do a proper full charge if you let it run for another hour after the light turns green. A charger like that will be 'faster' than one that does it properly if all you're going by is when the light changes color.
I know this sounds a little extreme and I’m not trying be cynical here but for what your trying to accomplish you could always buy 3 additional batteries and have them charged and ready to go while using the other set.
Hi-Beam, you bring up a really good point. That’s how I generally handle all my batteries.
One caveat is that it’s often recommended that you be present for the entire charging process. It’s hard to do that when the process takes a long time.
Yeah, the slower you charge your cells the better. Charging at 1A is what’s recommended by most manufacturers.
Charging at 2A is ok but you’ll get less cycles. Anything above that and your cell may become hot during charge, which is bad for its longevity and might cause a thermal runaway.
You shouldn’t try to build your own charger from scratch because if your design fail, the cells might go kaboom.
I recommend buying a 4 slots charger that can charge at 1A in each slot and get more batteries…
I can’t tell you exactly how the PCB inside a laptop battery works, but I know that it communicates with the PC so it might be complicated to charge that way…
lets not just talk about fast charging OK forget fast charging, what i want is to make a DIY charger with this circuit found in the laptop battery, why i want to do that ? 1st it is a nice idea and i have too much of those circuits and it will save much money and buying a hobby charger will cost me a big number in shipping from USA to Egypt
, every post here gives me a lot of experience