Battery Charger Kit
Akizuki Denshi K-0074
Sealed Lead Battery Charger Kit
Simple but deep world
Charging a battery seems to be a
simple act, but development for a best charging method still continues
even after more than 100 years. It is indeed a deep world.
The battery charger for the bicycle headlamp
I purchased was so miserable, it broke after only 2 times of operation.
After that I charged the battery with my regulated power supply. I
wanted to build a battery charger so that I could use it in my van,
without bringing the battery each time to the workbench.
Charging circuit for a lead battery should be simple,
possibly I could build it from parts already in stock. However recent
situation did not allow me to do that.
Building and Test Run
Akizuki Electonics is so popupar among Japanese electronics hobbyst,
with their hundreds of kits for intermediate to advanced kit builders.
They have a kit of Sealed Lead Battery Charger, priced 1000 Yen. I
could finally have a time to visit Akihabara and purchased one.
The kit consists of parts, circuit board and manual
including technical document of sealed lead battery. Power transformer
is not included, but I did not need it because I intended to run it
The circuit is a standard one using 723 Voltage Regulator IC.
It has 2 trimmer potentiometers; one is to set the voltage when the
circuit works in contant voltage mode, the other is to set the current
when the curcuit runs in a constant current mode. 2 resisters are
provided for a current detection; suitable one is to be choosen
depending on the battery size.
When the charge
starts, the circuit is in a constant current mode. As the charge
proceeds, it switches to the constant voltage mode. This operation
provides trickle charge operation, eliminating the possibility of
Maximum rating of the charginig current is 2A. It can
be expanded more if desired, by adding a bigger power transistor and appropriate heat
The circuit board uses the universal
prototyping board, but the dedicated pattern with resist is formed. Silk printing
is provided. Seemingly this board is common with other models; there
are several parts which are not used in this model. Jumper wires are
necessary for them. This is quite amateur way, positively
speaking. Akizuki products always give possibility and
expandability for creative builders. Heat sink for a power transistor
comes with the kit, bit it is not mounted on the board. How to mount it is
completely up to the builders.
Real creative part, Packaging
Building the circuit board quickly completed, as the number of the
parts is less. I tentatively mounted the power transistor and heat sink
by using additional universal board found in my junk box.
Supplying DC12V from my regulated power supply,
adjusted the trimmer VR2 so that the output voltage becomes 6.84V, the
rated voltage for my bicylce headlight battery.
Next is to adjust the trimmer VR1 for the
appropriate charging current. Capacity of my battery is 4.2Ah, so I
assumed 0.42A for the charging current. The current sensing resistor I
choose was 5 ohms, so the voltage across the sensing resistor should be
2.1V. Adjustment went quite smoothly without trouble. The kit became
operational without problem.
circuit of this charger is series dropping, so approx. 2W of heat
should be dissipated by the power transistor (charging current 0.4A,
voltage drop by the power transistor 5V). The heat sink becomes warm
but not so hot under the passive air cooling. This should be
Now I've got a battery charger board. The bike's
battery can be charged while it is stowed in my van without worrying
about the overcharging. Next, and the real creative part is to give it
a good enclosure. Where and how to mount to my van should be
considered. Charging current meter or charge complete indicator is also
desired. Okay, let's think........
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Copyright(C) NoobowSystems Lab. Tomioka, Japan 2003
May. 31, 2003 Purchased at Akizuki in Akihabara.
Jun. 01, 2003 Kits assembled, Page created.