how to combine LI Batteries for more Voltage

M

MagicCat

Well-known member
Hi

Im wondering if someone can help here. I have a whole ton of good Lithium Ion batteries from various extinct devices laying around.

My basic question is this, I want to know if I can take two Identical LI Battery packs and run them in series to increase my voltage like you would with a bunch of AA batteries. IE: 4x1.5 AA batteries in series =6v. I know the LI type battery has some issues, and did not know if you could take the Idiots approach to them by hooking them up in series without causing a fire, or killing whatever chips exsist inside them.

I have allot of older Sony and Panasonic Camera batteries, as well as a bunch of small Motorola Cell phone batteries I bought for backups on my MotoQ. I want to re-purpose these batteries, especially the MotoQ's. They are so light weight and small, I could run some of my LED lights off of them for hours. I could combine 2 of them to make 7.4 volts, and maybe even add another set of two in parallel to increase current/runtime.

Can this be done?

David
 
I would say you can do it but let's wait some more expert :) I am actually planning some DYI battery package and thought about having 2 in series as well :) But probably I could avoid it.
 
I guess I could just take a couple Cell phone Batteries, hook em up, put a good load on them and run for cover. LIons only last for three years anyway so I might as well put them through some research.

I will say this, I had a couple cannon GL1 batteries with broken Case's. So I decided to combine the two packs into one giant one, gleeful visions of being able to run my camera for days danced in my head. NO GO. It did not last any longer than it did originally, and the charger did not take any longer to charge it. For whatever reason, it did not see the additional cells. I took a volt meter to it and found no increase in current either. I think the little circuit board in them pretty much decided the fate of the battery despite any alterations I did to it.


"If we knew what we were doing, it wouldn't be called research" ....Einstein

"A company, organization, or even an entire society that seems to operate without engineers, is just a monument to the Engineers that built it".... High School Teacher

CEO: Chief Engineering Obstructionist


"If at first you succeed, try and try again until you fail, or youll never understand what the hell you did to make it work the first time"
 
MagicCat, hate to disappoint you, but no, it will not work. Charging Li-Ion batteries is tricky, it needs to be done exactly right, or bad things would happen. The charger needs to be matched to the pack it is charging. If you try to hotwire a new battery contraption, you need to have a new charger made for that. But what is even more important, the cells inside a Li-Ion battery have to be exactly the same - same brand, size, age, lot number. Otherwise they will not charge at the same rate.
 
adolgin said:
MagicCat, hate to disappoint you, but no, it will not work. Charging Li-Ion batteries is tricky, it needs to be done exactly right, or bad things would happen. The charger needs to be matched to the pack it is charging. If you try to hotwire a new battery contraption, you need to have a new charger made for that. But what is even more important, the cells inside a Li-Ion battery have to be exactly the same - same brand, size, age, lot number. Otherwise they will not charge at the same rate.
Click to expand...


I guess this is why I ask. I know these things are dangerous and are also IC controlled.

I should probably make myself a little more clear here. I did not mean to muddy up my question when I referred to a previous experiment in where I added cells internally to a manufactured pack.

My question is: Assuming I have 2 Identical LI battery packs, that were charged independently of each other on chargers made specifically for them, prior to installing them in my device. Can or Will, the voltage be multiplied by running these two packs in series with each other, without any repercussions?

IE: Two Panasonic HVX batteries that put out 7.2 volts, could actually put out 14.4 volts if run in series. Or, 4 3.6 volt Cell phone batteries could produce 14.4 volts if run in series. These would all be pre-manufactured packs, I just want to wire them together in series.

Hope that defines this a little better.
 
Yes, this can be done, and being done. The only caveat is both packs have to be about the same capacity and charged up prior to using. The point here is while discharging the smallest one could reach the end of discharge point before the other one. Overdischarging a Li-Ion battery is bad for it.
 
Thanks!! that is what I was looking for. Now, I dont mean to be stupid here, but if running in series, will that not keep the pack at the end of the series chain charged until the first in the chain expires? In other words, I could rotate packs in the series hookup, to keep one from always being discharged first.

It also sounds like I do not need Identical packs from your statement here. Just relatively identical in voltage size as well as current. I understand that if they were not Identical in amperage, the lower current pack would probably get permanently wiped out quick.


Man, someone needs to start building battery enclosures that could take advantage of all the batteries out there. Starting with Cell Phone batteries. I understand the implication of that statement with the millions of different cells out there, but the advantages to the technologically adept persons, would be enormous. Let alone the Green Value.


Thanks for your input.
 
No, it is not how it works. Once wired in series, they all discharge together. We make a product vDoubler that is using the principle.
 
MagicCat said:
My basic question is this, I want to know if I can take two Identical LI Battery packs and run them in series to increase my voltage like you would with a bunch of AA batteries. IE: 4x1.5 AA batteries in series =6v.
Click to expand...
Yes.

In fact, if you open up a typical 7.2V camera battery, you'll find at least two Lithium cells in series already. The natural voltage of a Li-ion cell is about 3.6V.

They are trickier to use, of course. One caveat is that, if you discharge a Li-ion cell too much, it can die permanently. What happens is that, based on the design of the cell, a parasitic battery forms in one of the contacts, reverse polarity from the full cell, and starts to demolish that contact. This is one reason you always find multiple terminals on a Li-ion cell... there's usually some kind of independent monitoring terminal.

Charging is also an issue. A proper Li-ion charger follows a constant voltage charge cycle for part of the charge, then switches to a constant current charge. Fast Li-ion chargers also monitor temperature... fast charging can cause cell damage. Or explosions. Same thing when discharging... too fact, and the cell can overheat, and potentially explode.


MagicCat said:
I have allot of older Sony and Panasonic Camera batteries, as well as a bunch of small Motorola Cell phone batteries I bought for backups on my MotoQ. I want to re-purpose these batteries, especially the MotoQ's. They are so light weight and small, I could run some of my LED lights off of them for hours. I could combine 2 of them to make 7.4 volts, and maybe even add another set of two in parallel to increase current/runtime.

Can this be done?
Click to expand...

The series cell wiring is fairly safe... as mentioned, your 7.2V+ cells are already a wired pair. Smaller 3.6V cells, as used in cellphone batteries, may be a single cell (sometimes an odd-shaped Li-Poly cell), or a pair of smaller 3.6V cells wired in parallel.

Parallel cells really need good matching. The problem is that, if they're not matched, one cell will tend to the charge the other, and not in a good way. If they're the same brand, age, and use-hours, it's probably pretty safe to wire in parallel.

Charging these built-up batteries can also be an issue, since your original charger was designed for charging something of lower capacity and/or voltage. There are very intelligent chargers made for the R/C car market, where people regularly hack up their own battery solutions. These can handle just about anything, but they're not cheap.
 
MagicCat said:
My basic question is this, I want to know if I can take two Identical LI Battery packs and run them in series to increase my voltage like you would with a bunch of AA batteries. IE: 4x1.5 AA batteries in series =6v. I know the LI type battery has some issues, and did not know if you could take the Idiots approach to them by hooking them up in series without causing a fire, or killing whatever chips exsist inside them.
Click to expand...

This is so risky I would NEVER do anything DIY with LI batteries. They don't just catch fire, they can literally explode if shorted. There's a limit on how many grams you are allowed to take on an aircraft because LI fires can't be put out by conventional fire extinguishers, mainly because they can create their own oxygen once burning. They burn hot enough to go through the fuselage of the aircraft. Just search youtube.

You'd be mad to risk it.

jb
 
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