Battery charging

Am I right on this:
When a battery being recharged is nearing full charge, it would accept
less and less current, say around 1A or less, as indicated by ammeter
on the charger (if there's one).
So that means you can hook a charger (say 6A) up to a battery and
leave it, since the battery won't overcharge. No matter how high the
charger capacity is, a near-fully charged battery will only take in
<1A.


Pete

On 23 Jan 2005 16:10:47 -0800, (Peter) wrote:

>Am I right on this:

No.

>When a battery being recharged is nearing full charge, it would accept
>less and less current

because the internal impendence of the battery increases as the
batteries voltage increases.
I=e/r

>, say around 1A or less, as indicated by ammeter
>on the charger (if there's one).
>So that means you can hook a charger (say 6A) up to a battery and
>leave it, since the battery won't overcharge. No matter how high the
>charger capacity is, a near-fully charged battery will only take in
><1A.

No.

It depends on the _charger_ not the battery.

What maximum voltage will the charger supply when the battery is fully
charged? If you don't know the answer to that question, you can't
answer the question, except by saying "no" to CYA.

If you want a trickle charger that can be left on indefinitely, then
BUY a trickle charger and be done with it.

Or, if the charger says "automatic" then you're probably OK.
Otherwise,

No.

Lg



>
>
>Pete

Peter wrote:
> Am I right on this:
> When a battery being recharged is nearing full
> charge, it would accept less and less current,
> say around 1A or less, as indicated by ammeter
> on the charger (if there's one).
> So that means you can hook a charger (say 6A) up
> to a battery and leave it, since the battery
> won't overcharge. No matter how high the
> charger capacity is, a near-fully charged battery
> will only take in <1A.

The final charging rate depends on both the condition of the battery
and the voltage applied to it by the charger. The battery's voltage
rises as it's charged, placing a lower load on the charger, which makes
a manual charger's voltage increase. This is no problem with a trickle
charger, but higher-amp chargers will never taper down below 1-3 amps,
which can damage the battery if not stopped, maybe in about 12 hours
with 2-3 amps, 1-2 days with 1A. Automatic chargers prevent
overcharging by regulating their voltage to limit it to about
13.6-14.5V even at full charge, usually resulting in a final charge
rate of .15-.5A., and .5A should be safe for several days, < .2A for a
month. These amp rates don't include the current draw by the car's
electronics, and any car equipped with an engine computer (almost all
since 1981), clock, or alarm system will draw .01-.70A, even while
parked. Also a battery with a bad cell or just generally worn out will
have a higher charge rate, whether attached to an automatic or manual
charger. The final charge rate with an automatic charger isn't a bad
indicator of battery condition.

It's just not a good idea to leave a charger hooked up to a battery and
go away, period.
In situations where emergency cells are maintained, like in the
hallways of hotels and such, they have fairly complex circuitry
onboard that prevents overcharging. Cell phones often have the same.
Car battery chargers generally do not.

Hi Pete,

Please take a look at Section 9 in the Car and Deep Cycle Battery FAQ
on www.batteryfaq.org. The whole Section is about lead-acid battery
charging and chargers.

Kindest regards,

BiLL.......

On 23 Jan 2005 16:10:47 -0800, (Peter) wrote:

>Am I right on this:
>When a battery being recharged is nearing full charge, it would accept
>less and less current, say around 1A or less, as indicated by ammeter
>on the charger (if there's one).
>So that means you can hook a charger (say 6A) up to a battery and
>leave it, since the battery won't overcharge. No matter how high the
>charger capacity is, a near-fully charged battery will only take in
><1A.
>
>
>Pete

Thanks LG.

The charger I have is manual. Still the charging current drops to 1A
or less when battery is nearly charged. Is that not the same as
trickle charging?

One problem I can see is that if the battery is faulty and always
takes in as much current as the charger can give, and overheated or
gas itself dry.


Pete

Lawrence Glickman > wrote in message >. ..
> No.
>
> It depends on the _charger_ not the battery.
>
> What maximum voltage will the charger supply when the battery is fully
> charged? If you don't know the answer to that question, you can't
> answer the question, except by saying "no" to CYA.
>
> If you want a trickle charger that can be left on indefinitely, then
> BUY a trickle charger and be done with it.
>
> Or, if the charger says "automatic" then you're probably OK.
> Otherwise,
>
> No.
>
> Lg

I use a rule of thumb from a book that a dead battery will take 50 amp-hours
to recharge. For a 5 amp charger that's 10 hours. For a 6 amp charger
that's 8 hours. And so forth. That's the maximum charging time. If the
battery is not dead it will take less charging time.


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The boxes containing cable transmission devices all
have a series of batteries continually being charged
to serve as cable system backup.

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q

On 24 Jan 2005 05:55:30 -0800, (Peter) wrote:

>Thanks LG.
>
> The charger I have is manual. Still the charging current drops to 1A
>or less when battery is nearly charged. Is that not the same as
>trickle charging?

Not really. You'll might see bubbling in your electrolyte even with
this current if the battery can't accept any more charge. That isn't
a good thing. In a Sealed Battery, I don't know what happens to this
extra hydrogen, but I wouldn't be surprised if the case bulged or
broke somewhere.

>One problem I can see is that if the battery is faulty and always
>takes in as much current as the charger can give, and overheated or
>gas itself dry.

It can do that even with 1 ampere if it can't accept any more charge.
What happens then is electrolysis occurs on the water in the
electrolyte. You'll "boil it away" and have to top it up again, but
this becomes problematic on a "sealed battery."

Lg

On 24 Jan 2005 14:43:19 GMT, (John W.
Bienko) wrote:

>
>The boxes containing cable transmission devices all
>have a series of batteries continually being charged
>to serve as cable system backup.

I ran a similar setup here for years as an uninterruptible power
supply, but I did it with _automatic_ chargers that knew when to stop
pumping current through the batteries. I am certain that there is
sophisticated electronic circuitry in the cable transmission devices
that cut back on the charge when the batteries are up to capacity.

You may not find this in the *manual* charger types.

The charger I own now is a
Schumacher
Fully Automatic
Microprocessor Controlled
Battery Charger with
Battery Tester and
Alternator Tester

Model SC-1200A

What happens is when the battery in question reaches full charge, the
charger turns itself OFF. IOW it doesn't go into *trickle mode* or
any mode but OFF Mode.

Lg