Author Topic: Lithium battery PCM?  (Read 1961 times)

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Offline dteck

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Lithium battery PCM?
« on: April 23, 2015, 11:19:02 am »
Hi everyone,
I recently bought some cheap mp3 players off ebay. Naturally I pulled it apart to see the insides and I found some lithium batteries that don't seem to have any protection modules on them. In fact they seem to charge by simply taking the USB power line and dropping it over a diode to bring the voltage down. Now these things were dirt cheap and so I'm not too surprised by this. But I plan on powering them by other means so I'm going to be left with these batteries.
I've never worked with Lithium's before other than in finished products. But I know they are a risk if mistreated in charging/discharging. So I was hoping i could pick up some protection modules and just slap them on there. I was looking at eBay auction: #221359867467 but maybe someone with a bit more experience working wit Lithium's could tell me if this would be a good way to use them.
Past that could you recommend a good ic for charging them? I don't know what I'm going to use them for but I would like to keep them charged. There is no info printed on them so I don't know anything about the capacity or ratings. All I can tell you is that they read 3.87v.

« Last Edit: April 23, 2015, 12:38:44 pm by dteck »
 

Offline blueskull

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Re: Lithium battery PCM?
« Reply #1 on: April 23, 2015, 11:24:15 am »
If it is a soft pouch battery, then keep it and install a protection board. If it is a steel shell battery, wrap it with heavy vinyl tape, and dump it, they are BOMBS that can take your hand off.

Everyone knows not to overcharge it, but also never over discharge them. Over discharged Li+ batteries can explode upon next charging, so keep the voltage above 2.5V, preferably 2.8V.
 

Offline abit

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Re: Lithium battery PCM?
« Reply #2 on: April 23, 2015, 12:22:24 pm »
Could you think of a way reading them first? I think this should be your first priority, find a way to read the cells for their current charge level. If you make these cells into a learning experience might as well go all the way and start at the beginning? Good luck to you. I prefer LiFePo, and once or twice you get burned or blown to pieces by LiIon you are going to see it my way.
 

Offline dteck

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Re: Lithium battery PCM?
« Reply #3 on: April 23, 2015, 12:37:52 pm »
sorry I forgot to attach a pic. I added it to the first post

If it is a soft pouch battery, then keep it and install a protection board.
also never over discharge them
It is a soft pouch. And if the PCM boards will work they list a cutout voltage at 2.5v. I had heard that down past that about 2 volts they wont come back.

Could you think of a way reading them first? I think this should be your first priority, find a way to read the cells for their current charge level.
I'm not sure what you mean by read their charge level? I can read their output voltage with my multimeter. I don't really have a constant current source to try and gauge capacity. And without a protection board isn't that dangerous since I might over discharge the cell like Blueskull was talking about?
 

Offline amyk

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Re: Lithium battery PCM?
« Reply #4 on: April 23, 2015, 01:26:36 pm »
Yes, that would be the classic "ghetto lion charger" that tends to make people go :o in disbelief the first time they see it (that was my initial reaction too) but then you realise how many products with this circuit are in daily use, are not causing any noticeable increase in fires/explosions/etc., and wonder if they know something about lion charging that we don't... it's certainly not a tightly-regulated charge, but I guess it works well enough for a single low-capacity cell. However it's usually used with a protection circuit on the cell, like the ones you linked to.

If you just want to store the cells then keeping them in the 3.7-3.8v range is ideal. Self-discharge shouldn't be that high so just measure them periodically to get an idea of their self-discharge rate, and if they drop to less than 3.6v then give them a brief charge to 3.8v with any suitably well-regulated power supply. Judging by the size I wouldn't charge at more than 100mA.
 

Offline abit

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Re: Lithium battery PCM?
« Reply #5 on: April 23, 2015, 01:42:51 pm »
That is correct... you might over-discharge by a multimeter, or over-charge by a circuit you lifted from the internet. WHAT do you need me to say or do?
Please do forget what you posted: It is by your own design this is happening
 


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