Lithium ion charging?

[BatteryCharger]

I want to put some lithium ion batteries in a Mag. The batteries I want to use have over voltage protection. (4.4v on a 3.7v pack) Given that, for charging can I just give them a constant current (via LM317) until the over voltage protection kicks in?

 

[Doug S]

[ QUOTE ]
BatteryCharger said:
I want to put some lithium ion batteries in a Mag. The batteries I want to use have over voltage protection. (4.4v on a 3.7v pack) Given that, for charging can I just give them a constant current (via LM317) until the over voltage protection kicks in?

[/ QUOTE ]

Can you?? Yes. Should you?? No. If the overvoltage cutoff is truly set to 4.4V, that value suggests that it is there as a last ditch safety provision should the proper intended charger fail to terminate at a more appropriate voltage. Doing as you suggest has two shortcomings. 1) Charging to 4.4V is too high and will result in short cycle life, probably <25 cycles. 2) Using your constant current drive, should the 4.4V OV cutoff fail, the is no backup termination or limit to prevent possible disaster.

 

[MrAl]

Hello,

You can give them constant current, but you have to cut
off at 4.20 volts, not 4.40 volts.

Take care,
Al

 

[BatteryCharger]

Ok then - I think I'm going to try and modify my cell phone's charger to charge these batteries. My cell phone battery is also rated at 3.7v, 1400mah, so I should be fine. Just in case something does go wrong, will the over voltage protection circuit keep it from blowing up? /ubbthreads/images/graemlins/grin.gif

 

[moraino]

Has anyone built this circuit?
http://shdesigns.org/lionchg.html

If it works well then I have to look for the low voltage protection circuit next.

 

[Doug Owen]

[ QUOTE ]
moraino said:
Has anyone built this circuit?
http://shdesigns.org/lionchg.html

If it works well then I have to look for the low voltage protection circuit next.

[/ QUOTE ]

Yes, several times over the years. It's National's circuit for charging 6 Volt *lead/acid* batteries (although no doubt could be made to charge 12 Volters with a resistor change). Not Li ion cells.

Part of the clue might be in the complete lack of this simple circuit being used in commercial chargers. Real companies don't waste money like that, they wouldn't be going the big bucks route if something quick and dirty (like a current limited, fixed voltage supply with only fair voltage stability like this one) would do the job.

Li cell makers specifically tell us not to use a charger like this, right? I, for one, tend to listen to advice from makers rather than no doubt well intentioned amateurs when they don't agree.

Doug Owen

 

[moraino]

Alright, i give up on building that home made Li-ion charger.

There are a few Triton around $75. Wonder if they are on good condition. Has anyone bid for one?

 

[wptski]

[ QUOTE ]
moraino said:
Alright, i give up on building that home made Li-ion charger.

There are a few Triton around $75. Wonder if they are on good condition. Has anyone bid for one?

[/ QUOTE ]
One thing that you have to watch is that there was a revision made and the only way to tell is a colored paper sticker on the bottom. The upgrade is free but you'd have to send it back. I forget what all the changes are but one is the ability to change the charging current while charging but that only works on certain types of batteries!