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[DPRG] Lithium Ion Batteries from BGMicro

Subject: [DPRG] Lithium Ion Batteries from BGMicro
From: Ed Paradis legomaniac at gmail.com
Date: Mon Mar 29 10:10:57 CDT 2010

Thanks guys.

I did a little experiment:

I connected the li-Ion cell to a 5V bench supply through a 10 ohm resistor.

The supply is current limited by its own crappy nature to around 300mA.

I monitored the voltage across the resistor to determine how much
current was going into the cell.  My hope was that the "protection
circuit" of the cell would somehow cut off current into the cell when
the cell was 'done'.

At first, the cell drew about 150mA, then settled down to about 80mA.

I didn't want to leave it sitting there forever, so I kept
disconnecting it when I left the house.

The "about 80mA" would slowly decrease over time, but I have no numbers.

I'll try to build some sort of monitoring circuit / data logger to get
more info.  These are pretty small little cells.. I might end up
building a little load balancer or series-battery-charging-monitoring
circuit to charge and use more than one cell at a time.

Many li-ion packs from laptops have all the charge monitoring and
limiting circuitry built in, and you really can use them in the same
way you use Lead Acid cells:  1) don't drain them past some magic
voltage   2) hook them up to a charger and just forget about them,
they will trickle charge themselves.

I was hoping these cells were something like that.  It sounds like
from John's experience that I can probably do that if I limit the
current.

That being said, this battery would be great for little handheld
devices.  I imagine that is where it came from.

Ed

On Mon, Mar 29, 2010 at 6:45 AM, Quinones, Jose <jquinones at ti.com> wrote:
> Hi Ed,
>
> Not certain about this battery pack in particular, but what I have often seen on lithium-ion battery packs is what the industry refers to as a gas gauge. Although, not filled with gasoline, the energy on the battery module is monitored in the same fashion your car gas tank is monitored.
>
> Except it is pretty easy to know how much gas there is on your tank. With a battery, however, how much charge is left is not that a trivial effort. So these devices are made aware of how much charge the battery can take, and then are at all times monitoring whatever comes in and whatever comes out.
>
> This allows the chip to know when the battery is reaching its full potential (either up or down), which is when you should not charge/use the battery anymore. Also, if the battery is above certain charge level (90% or 95% I think), the chip determines there is no need for charging, which is kind of dangerous.
>
> Hence, the protection chip is much more than just controlling the current flowing into (or out of) the battery.
>
> I think you could just allow a small current into the battery and monitor the temperature. If the pack starts to warm up, disconnect the charging current. I am not certain how super duper safe this open loop method would be, but I don't see why it would be unsafe. Run the experiment by your local firehouse, just in case ;-)
>
> Best regards,
>
> JIQ
>

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