Re: Use power supply to charge battery

On Sat, 23 Jun 2007 13:52:57 -0700, w_tom <w_tom1@xxxxxxx> wrote:

On Jun 22, 11:17 pm, budgie <m...@xxxxxxxxxxx> wrote:
No, I *don't* understand "why some do discharging before recharging"

It is a largely pointless exercise which only eats away at useful cell cycle
life.

We measure cell voltage. It is lower. Does that mean a cell is
fully charged or requires charging? Same number can mean either.

I don't know where you are getting your "information" or "knowledge" of Li-xx
cells, but I suggest you do a cold boot and reacquire.....

The off-load voltage is a *very* good indicator of SOC.

Connecting partly charged (aka partly discharged) Li-xx cell to a CLCV charger
is a VERY normal practice, carried out in my estimation many million times a day
by the owners of cellphones and other small portable appliances. Why do you
seek to complicate and/or obfuscate everything that is simple and ordinary?

As an engineer, budgie would have seen that chart - same voltage can
indicate two completely different battery states.

Nope, quite the opposite.

Discharging is a
first tests performed by some lithium battery controllers - one of
many algorithms used.

In the real world, there is ONE charging regime ("algorithm") that is employed,
as I have mentioned previously, and it doesn't include preparatory dicharging.

If discharging creates a battery voltage
reduction, then cell may be recharged.

If it didn't, I'd be *very* worried. The resting-voltage-vs-SOC curve for Li-xx
is monotonic. No inflections.

Apparently budgie is only familiar too few lithium recharge algorithms.

The real world simply doesn't do the things you describe.

A battery may measure same voltage when fully charged or when
significantly discharged.

You need a better voltmeter.

Do we charge a fully charged battery? Or
do we first learn whether the battery can accept a charge without
explosion.

A fully charged lithium cell can be safely connected to a CLCV charger. And as
long as the cell temp is within the charge SOA, and the cell OC voltage is above
the safe minimum, the same applies.

Some recharging algorithms do this by discharging.

I don't believe that.

How do we recharge a battery. Some first perform a discharge - in direct
contradiction to what budgie posted.

I don't believe that.

Meanwhile, that same chart for lead acid batteries only has one
(highest) voltage for fully charged and a completely different voltage
for discharged. Therefore lead acid (and NiCd) batteries can be
recharged with a regulated power supply.

Apart from having nothing to do with lithium cells, NiCd and NiMH cells require
a totally different approach. They are charged using a (constant-) current
regime, with end-of-charge detection by means of voltage inflection.

Lead acid batteries use voltage-driven charge regimes BUT these are rarely just
simple constant voltage except in certain float duty situations. Flooded cells
require periodic destratification charging. On VRLA/SLA types, more effective
efficient and appropriate charging requires an over-voltage during part of the
charge cycle - a good example of their proper care and feeding can be found in
the data *** for the TI/Unitrode UC3906 charge controller.

None of these lead or nickel chemistry cells in fact can be properly charged
with the CLCV simplicity of lithium, but thanks for trying to introduce another
red herring.

Of course lead acid batteries and discharing are irrelevant to the
OPs question.

At last, some common ground.

He cannot and must not try recharging lithium batteries
with a power supply.

He can.

Whether he "must" or "must not" is not for us to determine.

Consequences by others have demonstrated the
explosive threat. He would not be the first person to have created an
exploding battery by using a power supply.

No, and I bet that if you want to be thorough in your claims you'd find there
are far more explosions with automotive lead-acid batteries than lithium types.

Discharging is sometimes used to recharge a lithium battery,
obviously, from electrical charts for lithium batteries. Those charts
demonstrate why recharging microcontrollers have sophisticated
algorithms by discharging, monitoring temperature, or other
parameters.

Your whole line about discharging is a crock.

IOW the OP should buy a lithium battery charger and not
use a power supply - to avoid threats to human life.

I have already suggested he would be better off using a commercial Li-xx
charger, but his question was "can I ..." and the answer to that is "yes, he
can, with provisos already explained way back in this thread".
.

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