# Charging Sealed Lead Acid Battery ?????

Discussion in 'Electronic Basics' started by bigdaddy, Jun 6, 2006.

I have this small 10V 1000mA (5 hr)sealed lead acid battery.

Is it all right to charge it with a 12V Car battery charger ?

The other thing is that is has three leads - RED; BLACK and BLUE.
I wonder what blue is for. By the way, It is from my grandsons toy
car.

If it can not be charged with the battery charger, then what charger
should be used. I like to build my own charger, if I lay my hand on a

2. ### ehsjrGuest

Yes. Either limit the current to the equivalent of a trickle
charge for the battery, or charge it through a resistance at
higher current and terminate the charge when the battery is
full. See below.
An LM317 is excellent for this, and will probably work
well with your 12v car battery charger. However,
suitable wall warts are cheap, so I'd use one of them.

Constant current charger:
15 - 18V
Wall
Wart -----
+ ---+--Vin|LM317|Vout---+
| ----- |
[.1uF] | |
| +----------+----> 100 mA To batt +
|
- ---+------------------------> To batt -

I'm assuming 100 mA is a proper trickle current for your
battery - you need to determine the right figure and then
compute the resistor needed as follow: R = 1.25/I where
I is the trickle current.

For a constant voltage charger:
15-18V
Wall
Wart -----
+ ---+---Vin|LM317|Vout---+-----+-----> To batt +
| ----- | |
| | | | +
[.1uF] +----------+ [1uF]
| | |
| [1.8K] |
| | |
- ---+---------+----------------+-----> To batt -

That will give you 11.47 volts, which is
about right for a 10 volt SLA battery.
Mount the LM317 on a heatsink. You can use
the above circuit as a power supply in place
of the battery, or to charge the battery.

Ed

3. ### RogerGuest

Sealed batteries are best charged slowly using a a current and voltage
limiting circuit. Easy way to do this is with the circuit below for
voltage mode (11.4V) using an LM317L regulator, the L suffix means the
current is limited to 100mA. Convinient!

***BUT*** this blue wire bothers me. Usually the "third connection" on
rechargable batteries is for a temperature sensor used to detect a rise
in temperature during high current fast charge which indictes that the
charge is complete.....BUT NOT FOR LEAD ACID. This technique applies to
be charged with a 12V car battery charger. If there is any doubt as to
the type of battery then use low current limited source **and** slowly
raise the voltage such that there is just enougth to get the desired
charging current. It is possible to establish the type of battery by
observing the characteristics, but difficult to explain simple and
reliable rules for doing this ;-)

4. ### ehsjrGuest

Not quite. The L suffix means that the device is
guaranteed to be able to provide at *least* 100 mA, not
that it will limit the current to 100 mA. Typically, it
will provide up to 200 mA, and at maximum, up to 300 mA.
To use it as a limiting device is wrong - it's the other
way around. You need to limit the current through it to
100 mA or less to be in its guaranteed range of operation.
(All the above for the voltages involved with the charger -
the device is less capable at higher Vin-Vout voltage
differential.)

Ed