Electronic Building Blocks
By Julian Edgar
Quick and easy construction
Great results on a low budget
Re-purposing an old camera battery
were not providing as
many camera shots as
they once did. I looked
up the price of new
Nikon batteries – incredibly high – and
then settled on two
non-genuine batteries from a reputable
supplier. That left me
with the two original
Nikon batteries.
O s t e n s i b l y, t h e
original Nikon batteries were ‘worn
out’ – but were they?
I did some testing and
it seemed to me that
they had plenty of life
left. Not enough to
Fig.1. An old Li-ion camera battery drives this powerful LED torch.
power a camera, but
Batteries of this type may not have enough capacity to run a
camera, but they still have plenty of life left for other purposes. enough for other applications. However,
electrically connectere’s a project that will be ing to the batteries is difficult as they
ideal for some people – and not use flat terminals that engage with
at all ideal for others! It depends
spring strips when placed in either
on what you have already sitting on the camera or on the charger. So the
the shelf. But first, a bit of background. first step was to figure out some effecFor many years I’ve used a Nikon tive battery connections.
D200 SLR camera. It uses a separateIncredibly, a replacement charger
ly rechargeable Li-ion battery. That is, was available on eBay for only about
when the battery needs to be charged, £3, including post. Remove the chargyou remove the battery from the camera
ing circuitry, and you have an elegant
and clip it to a mains-powered charger way of connecting to the battery – and
– a small box.
as a bonus, you also end up with a
small enclosure.
One in camera, one ready for use
The voltage of the Nikon battery is
I’ve always used two batteries (one be- nominally 7.4V – an odd voltage in
ing charged and one being used) and these days of USB-standard 5V for so
they’ve lasted extraordinarily well.
many devices. However, buck convertHowever, all good things come to an er modules are available at very low
end, and I noticed that the batteries prices, and these can easily be set to
give a constant 5V output. (And they’re
also much more efficient than using a
5V linear regulator.) I had a buck converter in my parts drawers, so that was
good! I also happened to have on the
shelf a very powerful 5V miniature LED
spotlight that the battery could power.
When the charger arrived, it was only
a matter of minutes to open it up, remove the charging electronics and wire
the battery leads to the buck converter
(set for a 5V output) and then to the LED
spotlight. At this stage I’d spent only
£3 – I was just curious as to how effective the project would be. If it turned
out that the original camera batteries
were in fact no good, I could reinstall
the charger electronics and have a spare
charger for my camera.
The LED spotlight has three in-built
power levels ( 1W, 3W and 6W). I set
the light to its lowest level (still very
bright), ensured the battery was fully
charged and then clipped it into place.
On came the light, and I set a timer
running. An hour later, the light was
as bright as ever, and the battery voltage was still around 6.8V. That showed
that the approach was viable, so I built
the final unit.
I added an on/off switch (that nicely
fills the rectangular opening where the
original mains power cord plugged in)
and installed a small battery voltage indicator board. This has a dual colour
LED that changes from green to red
when battery voltage falls below an adjustable level. In my application, where
I was working right on the edge of the
lowest voltage at which this module
will work, the LED actually switches
off at the critical voltage. That means
it is still fine as an indicator – green
76
Practical Electronics | February | 2020
H
Fig.2. The body of the torch is made from a gutted charger that
suits the battery pack. Taking this approach makes it easy to
electrically connect to the battery. The on/off switch fills the opening
that previously housed the mains power connection.
Fig.3. Inside the charger body are the new electronics. The main
board is a buck converter to reduce battery voltage to 5V, and
the upper board indicates via a LED when the battery needs to
be unclipped and charged.
is good, white (off) means that the battery needs to be unclipped and charged.
n An output device: an LED light, or USB socket if you want
Requirements
So what do you need to make this a worthwhile project?
n A high quality Li-ion camera battery that still has plenty
of life left but isn’t quite good enough for the camera
n A charger for the battery
n A way of easily connecting to the battery – eg, through the
purchase of a second charger that is then gutted with just
the battery connections and enclosure used
n A buck (or boost) converter to provide the voltage output
you want (eg, 5V)
Obviously, you can buy USB powerbanks very cheaply, but
in my experience, good ones are still much more expensive
than this project. (Cheap ones that last only a few weeks of
use cost nearly nothing, but they fail just when you really
need them!)
to provide a general-purpose 5V supply.
Years of extra use!
Whenever I use my LED spotlight it’s a real pleasure to see
a battery that would otherwise have been discarded still
doing good and useful work.
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