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Cmoy power: Li-ion batteries in series? - Page 2

post #16 of 26
I actually use 4x 1600mah Sony li-ion batteries in series in my amp. I charge them with an automatic charger but without balancing. I admit that it isn't ideal to charge 4 li-ion batteries in series but in a low current application like this it should be OK. I wouldn't do this in higher current applications. And li-po / li-fe batteries should always be balanced. I always charge my lithium batteries on a nonflammable surface.
And never use the "foil bag" type of batteries inside any device / whatever!! I've watched one go off (on purpose) and a single cell produced a 2m high cloud of steam which ignited and...
The "metal can" contained ones are significantly safer IMO and a lot less spectacular when they go off.

To put it simply, Ni-xx batteries are a better, easier and safer choice for low current applications. Li-xx batteries offer higher performance at lighter weight, but do we really need that in a cmoy? smily_headphones1.gif
Edited by UnknownAX - 2/19/14 at 1:02pm
post #17 of 26
Thread Starter 

So I have done some more research and this is what I have come to understand: (please correct me if I am wrong)

 

1. Since all of my cells have their own protection circuit, arranging them to charge in series won't cause a dangerous situation. They will only charge until the weakest link is full, thus cutting the circuit.

 

2. Similarly, discharging them should be safe too, I would just lose max efficiency since my batteries will discharge until the weakest one reaches its cutoff voltage, thus cutting the circuit.

 

3. Wiring/charging in parallel seems to be ok, due to the same age/same battery set up I will use. I just need to make sure my batteries are fully charged before wiring them up to avoid any big current shifts (which the protection circuit should catch anyway though, right?) I also understand the C rating for charging, and all of my charging options will be at a 0.6C max, assuming my battery ratings are true.

 

I have an old laptop and the battery is 14.8v with a balancer circuit built in so I might rig that up for charging. The AC adapter has too high of current though, so I plan to run an 18v 0.8a adapter to the circuit. This should be ok right?

 

Thanks!

post #18 of 26

Well, now, you would think so, but I built an amp with CCCV charging using protected cells and I thought the protection circuits would look after the cells, but leaving them on constant charge caused them all to die, so I've had to add a timer.

 

Quote:

Originally Posted by nutt7 View Post

 

I have an old laptop and the battery is 14.8v with a balancer circuit built in so I might rig that up for charging. The AC adapter has too high of current though, so I plan to run an 18v 0.8a adapter to the circuit. This should be ok right?

 

...also your last statement betrays a fundamental misunderstanding of basic electrics, the current taken from the adapter is independent of it's maximum capability, so as time goes on I become less convinced that you are the right person to be messing with lithium cells.:(

 

w

post #19 of 26
Thread Starter 
I think you misunderstood my misunderstanding smily_headphones1.gif. I understand that circuits only draw the current they need, and that 800mA is the max available. I may be under a different misconception though. I thought li ion cells need to charge under a specific current value. It seems that if they had a 3 amp supply (my laptop adapter) they would use it, even though my batteries should charge with under an amp.

The laptop battery can put out 4.4 amps so I am unaware of the current that they charge at and I am afraid it would be higher than my batteries are supposed to charge at. Does the pcb limit the current? Or do the batteries take what's available? This is what I may be misunderstanding.
post #20 of 26
Quote:
Originally Posted by nutt7 View Post

I think you misunderstood my misunderstanding smily_headphones1.gif. I understand that circuits only draw the current they need, and that 800mA is the max available. I may be under a different misconception though. I thought li ion cells need to charge under a specific current value. It seems that if they had a 3 amp supply (my laptop adapter) they would use it, even though my batteries should charge with under an amp.

The laptop battery can put out 4.4 amps so I am unaware of the current that they charge at and I am afraid it would be higher than my batteries are supposed to charge at. Does the pcb limit the current? Or do the batteries take what's available? This is what I may be misunderstanding.

May I suggest that whatever you come up with, test it in an abandoned parking lot first, and stand well clear...:eek:

 

You cannot use a charging circuit designed for a laptop Li-ion battery to charge an iPod mini battery.  It will toast it.

 

Actually, if the circuit is any good it will fail to charge as it will interpret the iPod cell as a faulty one.  Don't rely on it though...


Edited by 2leftears - 2/23/14 at 10:06am
post #21 of 26
Thread Starter 
Quote:
Originally Posted by 2leftears View Post
 

May I suggest that whatever you come up with, test it in an abandoned parking lot first, and stand well clear...:eek:

 

Lol, will do! I still have more learning to do before I take action...thanks all of you, for the advice so far...

post #22 of 26
I think you should just forget the whole idea with the iPod batteries and the laptop battery balancing circuit. It won't work properly and it's far from safe. Always having to look for abandoned parking lots in order to charge your amp isn't too convenient either...

If you really want to use lithium batteries in your cmoy, buy normal, round, unprotected cells and charge them with a automatic lipo charger. And store your cmoy in a lipo safe bag/container while charging.
post #23 of 26
Quote:
Originally Posted by UnknownAX View Post

[..] Always having to look for abandoned parking lots in order to charge your amp isn't too convenient either...
 

 

You'll soon remember where they are.  Eventually attracting the attention of the CIA or MI6 is a bigger problem.  Try talk your way out of that one. "This guy was testing a lithium bomb, but he keeps calling it a cmoy..." :p

 

Quote:
Originally Posted by UnknownAX View Post

If you really want to use lithium batteries in your cmoy, buy normal, round, unprotected cells and charge them with a automatic lipo charger. And store your cmoy in a lipo safe bag/container while charging.

 

Looks like nutt7 View Post is hell-bent on not going that route though...

post #24 of 26
Thread Starter 
Quote:
Originally Posted by 2leftears View Post


Looks like nutt7 go_quote.gif is hell-bent on not going that route though...

Oh come on, now. I haven't DONE anything yet. Just trying to learn. I love DIY and I get satisfaction out of using things I already have, so I look for that route first. I will not use the laptop set-up due to the advice above. Thanks! I read and seek advice to figure out the limitations of my ideas. I'm not against safety, I'm just trying to learn before I do. I have taken NO action because I am not comfortable with the amount of my li-ion know how. Help me learn smily_headphones1.gif
post #25 of 26
We're trying to help you learn, but tread a fine line short of encouraging you to do anything dangerous.

Myself, I've done many dangerous things in the course of learning, but I've been lucky. I've had more shocks than I can remember, starting about age 3, I've come close to blowing my fingers off more than once and I thought I'd lost my hearing after making a particularly loud bang. I like to do chemistry too, that means explosives, strong acids and alkalies. I would probably be resentful if I felt people were taking an overprotective attitude toward me. I'm a grown man, if I want to take drugs, that's my business.

Anyway, you've been warned, lithium cells do catch fire on occasion if mishandled, and they are very difficult to extinguish. Be careful, and good luck.

w
post #26 of 26
Quote:
Originally Posted by nutt7 View Post


Oh come on, now. I haven't DONE anything yet. Just trying to learn. I love DIY and I get satisfaction out of using things I already have, so I look for that route first. I will not use the laptop set-up due to the advice above. Thanks! I read and seek advice to figure out the limitations of my ideas. I'm not against safety, I'm just trying to learn before I do. I have taken NO action because I am not comfortable with the amount of my li-ion know how. Help me learn smily_headphones1.gif

Well,

 

Then I would say UnknownAX View Post suggestion of using standard lipo batteries plus charger is not a bad option.  You would just have to make the batteries easy to change in your CMoy.

 

The likelihood is also that those would still be available in a few years time when you come to replace them, whereas new iPod mini batteries <may> be hard to find then.  Lipo batteries lose rechargeable capacity due to the chemistry aging, even when not being used.  Even 10 year old unused ones will have deteriorated significantly, unless correctly stored in a fridge (taking careful precautions to prevent condensation).

 

I share your satisfaction of using things you already have though.  Too much wastage around for my liking...

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