Author Options:

Do I "Have to" use an expensive li-ion charger for li-ion battery packs? Answered

I am building a 7.4v Li-ion battery pack (7200 mAh) with a PCM of course and i usually use my li-ion / liPo charger but i was curoious if their was another way. 
this battery pack will be installed in a portable gaming device and i want it to have its own wall charger. But i dont want it to take 6 hours.
I want it to be reliable and I want it to charge fast.
Most li-ion wall charger units for 7.4v only charge at 1.2A max, and charge at up to 8.4V. (And are like $25+)
PCM can handle much higher, up to 8A rate
Batteries are Rated up to 3.5A rate
Ultimate question
If I purchased 3 regular everday wall chargers, rated at 7.5V @1A (for $5 ea) and ran them in parrallel in a nice  enclosure running one charging plug, (hypothetically it "should" rate; input: 120V, output: 7.5V @3A).  Could i use this to charge the for-mentioned Li-ion 7.4V 6400mAh battery pack in just over or around 2 hours???? Or is this not feesable for some other reaon???


ABSOLUTELY. There is a VERY serious chance of causing a fire or explosion without a proper charger. It really isn't worth it.


hey steve, do you know why that is. What makes it so dangerous. I have been trying to figure it out. I have heard not to, but no one can tell me why. I figure if its true then it has to due with some internal protection circuit. but isnt that why we use pcm's. I just dont want to have to waist money if their isnt a real reason, besides an industry standard. What more to the equation is their besides, volts and amps. Is their a hertz equation that I dont know about. thanks for responding.

Look it up. Technically, if the charging voltage gets too high, free metallic lithium plates out internally, and the cathode becomes an oxidiser. Heat is generated....

....and if they are over DIScharged, free fibres of copper can grow internally and ALSO generate a fire.

The internal protection circuit specifically stops over discharge.

I have looked that up, and i agree. Iknow that if you over charge it it becomes volatile. and then you have an impressive show of sparks and fire. I read about the discharging rates as well. Basically, im trying to find out the difference in the two chargers, to see why I cant use a different charger. could it be a balancing reason. I know with my rc batteries i have to use a balance... nevermind, thats because they dont have protection circuits. Im not trying to anger anyone. and by know means should anyone assume I havent tried to research this. I must be overlloking something very simple, because I dont see a reason why one is so different from the other, besides people just saying, "no, you cant do that" with no solid reason. not to mention a 7.4V battery pack actually has a voltage of 8.4V, and my scenario offers a 7.5V charger. So their wouldnt be a risk of overcharging. the pcm has a cutoff so thats out. So what am i missing besides the general concensus. Steve, you know that I am always willing to take advice and listen, but this has me baffled

You can't make clever combinations of chargers, because you'll defeat the charge detection circuits, if it works at all.


I never thought of that, because ive seen it done before basically.
Wall outlet------>(inside enclosure) power rail-----> 3 chargers (internal pcbs)----> outputs in parrallel to one single output plug.
I cant remember where I saw it, but it had worked fine. I believe he used it to put out 11.1v at 3.6A.
I geuss that would make sense for combining, but still not to why one 7.5V 1A charger wouldnt work

well, after much debate and research, I agree tat it is unsafe, and had no intention of trying this, nor should anyone else. it was mearly a question that had been bugging me. from what I can gather, it has to do with the RATE of charge and current.

=1 - but on the other hand they do make a very spectacular fire.

although amusing, not helpful.

Helpful in that you don't burn your house down.... just sayin...

Ok, valid point. but do you know why.

I can't really say that I do... at least not in a way that I could explain it well, but I'm just saying that you wouldn't want to try it to find out. You could theorize all you want, but I wouldn't suggest trying it.