Charging 25 Li-ions in Parallel
Charging 25 Li-ions in Parallel
(OP)
Hi All!
I have a custom battery pack that has 25 18650 li-ion batteries in parallel, supplying 3.7-4.2 volts.
I am having trouble finding a charger to charge them!
The charger I have, a typical intelligent charger, can supply up to 5 amps, which should be enough to give them a charge over a day.
http://www.ebay.com.au/itm/iMAX-B6-Digital-LCD-RC-...
But it tends to cut off at 3.8 volts, charging from 3.7.
I am expecting I will have to build my own charger, but I am unsure where to find information on how that many batteries in parallel will behave.
For those interested, it is powering 470 LED in a vest, that draws 3.5 amps.
https://www.youtube.com/watch?v=J8TyGCo32pY
I have a custom battery pack that has 25 18650 li-ion batteries in parallel, supplying 3.7-4.2 volts.
I am having trouble finding a charger to charge them!
The charger I have, a typical intelligent charger, can supply up to 5 amps, which should be enough to give them a charge over a day.
http://www.ebay.com.au/itm/iMAX-B6-Digital-LCD-RC-...
But it tends to cut off at 3.8 volts, charging from 3.7.
I am expecting I will have to build my own charger, but I am unsure where to find information on how that many batteries in parallel will behave.
For those interested, it is powering 470 LED in a vest, that draws 3.5 amps.
https://www.youtube.com/watch?v=J8TyGCo32pY





RE: Charging 25 Li-ions in Parallel
So buy 24 more.
Mike Halloran
Pembroke Pines, FL, USA
RE: Charging 25 Li-ions in Parallel
I need to charge them all at once.
RE: Charging 25 Li-ions in Parallel
Don't expect good results.
Also put a quick release buckle on the belt.
Mike Halloran
Pembroke Pines, FL, USA
RE: Charging 25 Li-ions in Parallel
That said, the problem is certainly that the voltage drop in the cables adds to the "perceived voltage" which makes the charger think that cell voltage is higher than it actually is.
Measure from charger plus to battery plus to find out the voltage drop. Then do same thing for the minus. Add those two voltage drops together and you will see why the charger turns off prematurely.
What to do about it? Make the cables a lot heavier.
There's also a possibility that the charger simply overloads and switches off because of that instead of doing it on voltage level.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Charging 25 Li-ions in Parallel
I have 12AWG wires, and it is fused at 10A. And yep, quick release clips. :)
I know its dangerous, but it beats a 12AH 6V Lead Acid bettery which gives me about 4 hours runtime. I want this vest to run from sunset to sunrise.
Will upload a pick of the battery belt when I get home.
From 3.6volts,The charger starts off at 1.8amsp (even though I specify 5) and trickles down to 200ma.
It reported 1200mah uploaded, and I measured the final voltage at 3.8v off the charger.
RE: Charging 25 Li-ions in Parallel
Also, if the resistance between near battary and far battery differs, you will never get the more distant batteries fully charged.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Charging 25 Li-ions in Parallel
Based on your numbers, only two or three of these would be needed to supply 12 hr of operation
TTFN

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RE: Charging 25 Li-ions in Parallel
Li-ion charger ICs are likely to contain a myriad of safety features, such as timers, based on their assumptions of the battery under charge. Find the data sheet for the IC in your charger and see what's what.
RE: Charging 25 Li-ions in Parallel
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Charging 25 Li-ions in Parallel
Z
RE: Charging 25 Li-ions in Parallel
It looks like I just might have to based on the consensus here. An overspec'd 10-15 amp regulator should not get too hot at 3.5 amps.
I have short circuited two series wired fully charged of these 18650's on another project and it melted the 22awg wires!
Apologies for not posting the picture yet.