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'[EE]: Li-ion battery "emulation"'
2005\04\01@102520 by Hector Martin

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Hi all,

I'm trying to use a PDA for a different purpose than its original one :-)

I'd like to run it from external power only. The problem is that,
since I'll be running it from a power supply that already powers other
equipment, and doesn't have much power to spare, I'd rather remove the
battery to avoid it using too much current during charging (during
normal use it shouldn't use much. It's supposed to be battery-powered,
isn't it?)

Of course just removing the battery won't work. I can get to the
diagnostics menu with an off-contrast screen only, no normal power-on
(blinking LEDs, presumably it knows there's no battery in there).
Since li-ion cells are supposed to drop in charging current when done
charging, I just stripped out the cell and left in only the battery
circuitry. Diag shows up fine, but no power-on (no blinking). I think
the problem is that it tries to stop charging and run from the battery
for a moment, and, of course, it just turns off.

Maybe I could add a resistor to the battery circuitry to make it
believe it never stops charging? Although it might still try to run
from it for a short while and still fail... Other ideas? Maybe power
it through the battery with a suitable supply instead of through the
charger plug? BTW, the battery is a single-cell 3.7V 950mAh.

Regards,
--
Hector Martin (spam_OUThectorTakeThisOuTspammarcansoft.com)
Public Key: http://www.marcansoft.com/hector.asc

2005\04\01@103803 by Bob Axtell

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That's pretty easy, really.

The LiIon pack normally puts out 3.6V - 3.9V. I would get a decent LDO
3.6V regulator
that can deliver 1A (sometimes heavy current is drawn instanteously) and
a good tantalum
cap, about 22uF @ 6.3V across the output. You'll not have any trouble.

You MIGHT have a battery indicator that indicates close to low, but it
won't hurt anything.

--Bob

Hector Martin wrote:

{Quote hidden}

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2005\04\01@104036 by Steve Halla

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Which PDA is it, as control methodology is slightly different for many PDA's?

Steve Halla - Specialty Department Chair
Technology & Engineering Teacher
LEAP Academy University Charter High School
549 Cooper Street
Camden, NJ 08102
856.614.0400


Quoting Hector Martin <hectorspamKILLspammarcansoft.com>:

{Quote hidden}

> -

2005\04\01@115029 by Hector Martin

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Steve Halla wrote:
> Which PDA is it, as control methodology is slightly different for many PDA's?
>

Sharp Zaurus SL-5500.

I've tested straight 3.6V through the battery connections, and through
the battery logic into the battery connections. Same as always, diag
OK, no normal turn-on. I think I noticed it needed the charger for a
second with the original battery after disconnecting it to be able to
turn on, which it has never needed before. I think the backup battery
has something to do with this, since it's disconnected right now. I'll
connect it and test. If it comes out to be the culprit (I thought all
that whould happen is that the RAM would be erased if it loses total
power, but it may also have something to do with the charging
circuitry) now I have to emulate *two* batteries. I need to do more
testing.

I might just as well leave the batteries connected normally and  hope
that the main power supply can cope with the charging.

Regards,
--
Hector Martin (EraseMEhectorspam_OUTspamTakeThisOuTmarcansoft.com)
Public Key: http://www.marcansoft.com/hector.asc

2005\04\01@115614 by Bob Axtell

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Hector Martin wrote:

{Quote hidden}

No, the problem , as I stated earlier, is that at turnon, the current
load is heavy. The
battery can deliver it, the regulator cannot. You have to design the
regulator to deliver
as much as 50X normal running current. And a low impedance output cap
isn't a bad
idea, either.

--Bob

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2005\04\01@144030 by Robert Rolf

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Could it be that this unit requires a 'smart' battery?
With the number of counterfeit batteries out there, manufactures
are adding ID chips to the batteries so that the unit will ONLY
work with a  'validated' battery in place. Many of the newer
Sony camcorders will not work with 3rd party NON Infolithium batteries,
for example (I am told by a sales droid).

R

Hector Martin wrote:
{Quote hidden}

2005\04\01@180131 by Hector Martin

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Yup, a power issue. The supply should be able to keep up with the
current, but the issue seemed to lie with the voltage. Incrementing it
up to 3.8-3.9V did the trick. Thanks! Right now it is running straight
to the battery terminals, no battery circuitry, no charger, no backup
battery.

Now that this is running with the bench supply, what do you suggest
for lowering the original 12V from the main supply to the 3.9V that
this requires? Wouldn't a regulator dissipate a lot as heat?

Bob Axtell wrote:
{Quote hidden}

Regards,
--
Hector Martin (@spam@hectorKILLspamspammarcansoft.com)
Public Key: http://www.marcansoft.com/hector.asc

2005\04\01@181008 by Bob Axtell

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Hector Martin wrote:

{Quote hidden}

No, because it will only draw a lot of current for just an instant.
After that, it will settle down to normal 25-30 mA...

--Bob

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2005\04\01@184747 by Hector Martin

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Actually, power consumption with full backlight etc is about
100-200mA. But I guess the regulator should be able to cope with it.

Bob Axtell wrote:
> No, because it will only draw a lot of current for just an instant.
> After that, it will settle down to normal 25-30 mA...
>
> --Bob
>


--
Hector Martin (RemoveMEhectorTakeThisOuTspammarcansoft.com)
Public Key: http://www.marcansoft.com/hector.asc

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