hi! i need some piece of advice. a have a big old flashlight which i'm gonna mod with several cree-r2 drop-in modules (it is huge, so space inside wouldn't be a problem). as a power source i'm gonna use some set-up from 6 18650 li-ion rechargables. the set-up is gonna be 2*3 (two groups of 3 batteries in parallel connected in serial). so the voltage would be 3.7*2 = 7.4V and a capacity (assuming that batteries are 2400mAh) would be 2400mAh*3 = 7.2Ah. the problem is charging such a battery set-up. the most easiest way that comes to my mind at first is to buy two channel 220AC charger for 2x18650, disassemble it and install it into flashlight's body that way so each channel could charge each group of cells. in other words, would it be ok if i try to charge li-ions connected in parallel? am i right if i think that charging current would be devided between cells in groups and all of them would be charged up-to the same voltage?
DIY flashlight built-in li-ion charger (220AC) need help
- Thread starter alex_g2k
- Start date
Help Support Candle Power Flashlight Forum
VidPro
Flashlight Enthusiast
so far that all seems kosher, and a good way to charge the 2 series , is indeed with either a balancing charger, or TWO chargers 
and parellel in the case of Li-IOn voltage max charging works good.
(simpler than with parellel ni-?? v-drop charging)
just one note that you dont need, if you ran both chargers off the SAME dc power source, like the wall wart or a car cord item, you would want to insure that the "grounds" of the two chargers are isolated.
as long as you have 2 chargers being converted from your mains to dc, it shouldnt be a problem, in fact its pretty good, vrses series charging. ways to check would be to insure your charger voltages when connected as they would be when connected to the battery, then check for any residual AC , ground loops or any unforseen things, by switching your meter to AC and checking it again.
and parellel in the case of Li-IOn voltage max charging works good. (simpler than with parellel ni-?? v-drop charging)
just one note that you dont need, if you ran both chargers off the SAME dc power source, like the wall wart or a car cord item, you would want to insure that the "grounds" of the two chargers are isolated.
as long as you have 2 chargers being converted from your mains to dc, it shouldnt be a problem, in fact its pretty good, vrses series charging. ways to check would be to insure your charger voltages when connected as they would be when connected to the battery, then check for any residual AC , ground loops or any unforseen things, by switching your meter to AC and checking it again.
Last edited:
two-channel charger i've bought provides about 800mA charging current through each channel. it means that charging two single 2400mAh batteries takes about 3 hours. and if i would try to charge a battery pack of two sets of 3 (or even 4) batteries it would make a charging time somewhat 9-12 hours which is not acceptable at all! what if i buy 4 of these chargers and use each two of them for charging each group of batteries? what i'm concerned about are two things: woudn't be a problem connecting two different chargers in parallel? and another thing i'm worried about is possible difference of internal resistance of batteries. allthough i would buy batteries of same manufacturer and same capacity i assume they could be slightly different in their parameters. so what if internal resistance difference would cause significantly different currents through each battery in parallel set and a higher charging current then is acceptable for a single cell as a result?
VidPro
Flashlight Enthusiast
some external resistance can make more differance then the internal resistance
if you use the same brand same batch, and same time cells, and they are good cells, and you CHeck them before assembly, everything will be fine on the parellel side, untill they are no longer good cells. and heck you got balancing and seperate charging to keep everything together. i really would use some good Name brand reliable cells like LG or sony or sanyo, or pana, and not that junk that gets sold if you are worried about the parellel and the time it would last, and i would not worry so much about excessive capacity, a good 2000-2400 cells are built well.
indeed when your parellel dont USE all 2X of what you have, meaning dont parelell it up 2X if you want to get 2X the specs out of one, if your going to shred one, so your using 2 , use 3 or 4 , and keep the whole thing doubled up over the max specs, that way if it leans a bit more into using one cell or another after well aged, it dont matter so much..
you know you can make a Li-Ion charger that ramps beutifully if you use a FAT voltage regulator like the big fat 8 amp one, so nothing goes wrong, and a fat linear transformer. then you can stuff fat amps in at the first of charge, and it slows down as the voltage differential is reduced.
then if you put a pulser in, you get the best of all worlds potentially you could run a 50-50% pulse to each battery , and charge BOTH with one linear voltage fixed charger, switching back and forthe with DPDT to both batteries.
you get a charge to 80% in a few hours, and with the max voltage LOCKED out to 4.2v it never goes above.
i mean if your gonna tie a bunch of crappy chargers together, might just as well make your own, its like 3parts to make it and 3-4 more parts to make it clean and steady. and its not that much harder to assemble than 4 crappy chargers it just wont fit insides the light then.
if you use the same brand same batch, and same time cells, and they are good cells, and you CHeck them before assembly, everything will be fine on the parellel side, untill they are no longer good cells. and heck you got balancing and seperate charging to keep everything together. i really would use some good Name brand reliable cells like LG or sony or sanyo, or pana, and not that junk that gets sold if you are worried about the parellel and the time it would last, and i would not worry so much about excessive capacity, a good 2000-2400 cells are built well.
indeed when your parellel dont USE all 2X of what you have, meaning dont parelell it up 2X if you want to get 2X the specs out of one, if your going to shred one, so your using 2 , use 3 or 4 , and keep the whole thing doubled up over the max specs, that way if it leans a bit more into using one cell or another after well aged, it dont matter so much..
you know you can make a Li-Ion charger that ramps beutifully if you use a FAT voltage regulator like the big fat 8 amp one, so nothing goes wrong, and a fat linear transformer. then you can stuff fat amps in at the first of charge, and it slows down as the voltage differential is reduced.
then if you put a pulser in, you get the best of all worlds potentially you could run a 50-50% pulse to each battery , and charge BOTH with one linear voltage fixed charger, switching back and forthe with DPDT to both batteries.
you get a charge to 80% in a few hours, and with the max voltage LOCKED out to 4.2v it never goes above.
i mean if your gonna tie a bunch of crappy chargers together, might just as well make your own, its like 3parts to make it and 3-4 more parts to make it clean and steady. and its not that much harder to assemble than 4 crappy chargers
it just wont fit insides the light then.
Last edited:
thank you for your answers, they helped me very much!
so if i use two simple chargers each of which gives ~1.8A current and stops when 4.2V is reached for charging two sets of 3 protected 18650 (2400mAh each cell) the charging current for each cell in a set would be ~600mA which is only 0.25C assuming the cells are in ballance. and even in worse case when two of three cells become dead (does it mean that their inner resistance raise? btw) the charging current for one cell would be 0.75C which is not a big problem as far as i can guess besides i'm gonna use protected cells anyway. so in case i don't try to get a fast charging by using more chargers i shouldn't expect any problems, should i?
another issue i'm concerned about is that in this configuration "-" of one charger would be connected to "+" of another one. the first time i was gonna use only one charger (which is two-channel) for charging two sets connected serially. but when i measured the voltage between "+" of one channel and "-" of another i saw somewhat ~3.6V or so. that means the chanels were not separated as i expected at first. i don't have a second charger yet so i can't check if there any voltage between their opposite contacts.
so if i use two simple chargers each of which gives ~1.8A current and stops when 4.2V is reached for charging two sets of 3 protected 18650 (2400mAh each cell) the charging current for each cell in a set would be ~600mA which is only 0.25C assuming the cells are in ballance. and even in worse case when two of three cells become dead (does it mean that their inner resistance raise? btw) the charging current for one cell would be 0.75C which is not a big problem as far as i can guess besides i'm gonna use protected cells anyway. so in case i don't try to get a fast charging by using more chargers i shouldn't expect any problems, should i?
another issue i'm concerned about is that in this configuration "-" of one charger would be connected to "+" of another one. the first time i was gonna use only one charger (which is two-channel) for charging two sets connected serially. but when i measured the voltage between "+" of one channel and "-" of another i saw somewhat ~3.6V or so. that means the chanels were not separated as i expected at first. i don't have a second charger yet so i can't check if there any voltage between their opposite contacts.
VidPro
Flashlight Enthusiast
thats right, you gotta check to make sure of that, no mater what charger it is, it could have some crasy cross connection via a ground looping type of things through the AC even.
if only one side of a cheep piece of junk was connected through stuff to the ac, no problem for ONE seperately connected item. but without checking it when you combine, it only then could become one. so you do the DC check, then check for any residual AC when the charger is not using a simple linear DC (wall wart) input, or even if its a non-isolated thing. it would have to be a pretty sad design to have that problem but then again there are a lot of sad designs out there
and the .75C when things have gone bad for a battery in the parellel set is ok, BUT remember the charge is ALSO supposed to slow down neer the end and finish up slowly. i assume there are 2 purposes behind the slow down.
1) if the cell is not accepting charge , it will have its biggest non-acceptance neer the end .
2) if a cell was going to gass out, it will do so neer the end of charge, so by being cool then, the li-ion which should NEVER gas, is kept best from doing so.
and as you know charge acceptance starts going slower when most of the rest of the chemicals/elements have switched up, and only few chemicals are left to change up, that is why neer the end they slow down, so the charge put in is all accepted.
so when you toss numbers about , as usual they dont mean a lot to me you can push a LOT at first (2C even), as long as you slow down neer the end.
if only one side of a cheep piece of junk was connected through stuff to the ac, no problem for ONE seperately connected item. but without checking it when you combine, it only then could become one. so you do the DC check, then check for any residual AC when the charger is not using a simple linear DC (wall wart) input, or even if its a non-isolated thing. it would have to be a pretty sad design to have that problem
but then again there are a lot of sad designs out there and the .75C when things have gone bad for a battery in the parellel set is ok, BUT remember the charge is ALSO supposed to slow down neer the end and finish up slowly. i assume there are 2 purposes behind the slow down.
1) if the cell is not accepting charge , it will have its biggest non-acceptance neer the end .
2) if a cell was going to gass out, it will do so neer the end of charge, so by being cool then, the li-ion which should NEVER gas, is kept best from doing so.
and as you know charge acceptance starts going slower when most of the rest of the chemicals/elements have switched up, and only few chemicals are left to change up, that is why neer the end they slow down, so the charge put in is all accepted.
so when you toss numbers about , as usual they dont mean a lot to me
you can push a LOT at first (2C even), as long as you slow down neer the end.
Last edited:
