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You thought the last one was dazzling?
SERIOUSLY BRIGHT
10W 20W LED
FLOODLIGHT
Last February, we published a DIY 10W LED Floodlight, which has
been enormously popular. We said that one was almost blinding – but
to paraphrase Croc Dundee, that’s not bright. THIS one is BRIGHT!
S
Design by Branko Justic* Words and music by Ross Tester
CHIP has just returned
from two days at the Sydney
Electronex exhibition, where
we met a large number of existing
readers and also (hopefully!) new
readers. On our stand, we displayed
several recent – and even a couple of
future – projects.
Believe it or not, one project which
attracted perhaps the most attention
was the 10W LED Floodlight, featured
in our February 2012 issue.
This floodlight compared more than
favourably with PAR38 incandescent
and quartz-halogen floods we all know
so well. In fact, few could believe
just how bright this was and quite a
number wanted the Oatley Electronics phone number so they could order
their own kits.
ILICON
What’s this? A 20W?
As luck would have it, waiting for
us back in the office was another kit
from Oatley Electronics – this time a
20W version of the LED Floodlight.
We quickly assembled this kit and,
despite a few wrinkles (which we’ll get
to shortly) were very impressed with
the light output.
To the naked eye (no mean feat be66 Silicon Chip
cause it was far too bright to look at!)
it looked much brighter than the 10W
LED version, indeed, much brighter
than a 150W QI portable floodlight.
We ran some tests using a Jaycar
Lux meter on the original 10W LED
floodlight, this 20W LED floodlight,
the 150W QI floodlight we originally
compared the 10W LED to and finally
a 500W QI floodlight.
The results appear on the photograph opposite but you’d have to
agree that they are pretty impressive
for the LEDs.
Of course, the 500W QI does look a
lot brighter in the photos – and it is.
But remember, we are comparing this
to the 20W LED alongside. That’s 500
compared to 20 – 25 times the power.
It sure ain’t 25 times the brightness –
both are far too bright to stare into for
more than a brief instant.
Just a note of caution, though: we
don’t know what wavelength that
meter is calibrated to. So there could
be a “skew” in the figures if it is more
sensitive to the bottom (red) end of the
spectrum than the top (blue).
The QIs look very yellow indeed
compared to the LEDs – and we all
know that QIs have a very much
“whiter” light than do standard in-
The heart of the project is this
20W LED array. It contains
20 individual LEDs. Like all
LEDs, it requires a constant
current supply, as described
in this article. The light has
hit this module “just right”
to highlight the “–” and “+”
symbols moulded into the
plastic – these tell you the
polarity of the two metal
tabs (as it happens, the top
tab, under the finger, is the
positive).
siliconchip.com.au
candescents.
But as a relative A:B:C:D test, the
results are quite telling. And of course,
the LED lamps run MUCH cooler than
the QIs.
The LED array
As you can see from the photo below, the LED array (or module, if you
like) is rather large. The whole thing
measures 46 x 53mm (including connection tabs) while the “good bit”
(the section which actually produces
light) is a rather large 22 x 22mm.
Inside this rectangle are 20 individual SMD LEDs, potted in two
rows of ten. Together, they produce
a 6000-6500K light at between
1500 and 2500 lumens.
Given that your average 20W
fluoro tube produces about 1100
lumens, that’s a lot of light from
a small area.
Driving the LED array
In common with all LEDs, it’s not
possible to simply connect power and
away you go! The LEDs do not limit
current so will quickly burn out.
And driving a high-power LED is a
little different from the garden variety
LEDs we have been using for several
decades. These basically only require
a resistor to keep the LED current
within bounds.
The value of this current-limiting
resistor can be easily worked out from
Ohm’s Law – and even then, it’s not
very critical as long as you don’t overdrive the LED.
While you can drive a high power
LED using a resistor, it’s better to
arrange a constant-current supply,
which is exactly what we’ve done
here.
One advantage of a constant-current
supply is that (within reason) it can
handle a wide range of input voltages.
The claimed operational range of
this 20W LED Flood is from
6V to 30V.
Too much power!
One slight problem with the constant current supply included with
this kit is that it can supply a bit too
much power to the LED – 25W instead
of the rated 20W. This will cause the
LED to run too hot, thus reducing its
life, so there is a slight modification
required to reduce power, which we
will get to shortly.
The kit includes a 24V, 1A switchmode power supply – which we will
also get to shortly.
The Oatley kit
Everything you need is supplied
in the kit, right down to the heatsink
compound required to transfer heat
from the LED to the case.
Speaking of cases, a glass-fronted
floodlamp case is included which has
provision on the back for the power
supply. It is shown assembled above.
When we say “kit”, the controller
board is already pre-assembled. This
is fortunate, because there are a couple
of SMD components on the board – the
regulator IC plus a Mosfet used for
reverse polarity protection.
Incidentally, if you’d like an explanation as to the how, when, where
and why of using a Mosfet for reverse
Measurements using Digitech (Jaycar) QM1587 Light Meter
50 lux <at>1m
7.5 lux <at> 10m
25 lux <at>1m
4.5 lux <at> 10m
51 lux <at>1m
9.5 lux<at> 10m
250 lux <at>1m
40 lux <at> 10m
Comparison shot between (left to right) a 150W QI, 10W LED, 20W LED and 500W QI. This pic really doesn’t do justice
to the LED floods – they are rather brighter than would appear here. In fact, they’re dazzlingly bright!
siliconchip.com.au
November 2012 67
Some readers may remember the night-time shots of my fishpond comparing the 10W LED to a 150W QI flood. Here’s a
similar comparison, this time between the 10W LED floodlamp (left) and the 20W LED floodlamp (right). Both were taken
from the same place, with the floodlights in the same place, using identical exposures (1/4s <at> f/4).
polarity protection, see the “Circuit
Notebook” entry in the April 2012 issue (p70). It’s much better than using
a diode for the same thing.
Construction
The first thing we need to do is make
the modification alluded to earlier.
This involves removing the 0.33Ω
SMD resistor on the right side of the
PCB and replacing it with three 1.2Ω
resistors in parallel (ie, 0.4Ω).
Removing the SMD resistor is a bit
tricky – we used a thin blade to lift
one end while we heated the solder
join. Having got one end off the board,
complete removal is easy.
Obviously, three 1.2Ω resistors (even
1/4W types) in parallel are going to
take a bit more space than one SMD
resistor. But there is room to place
them – twist their leads together first
and bend the leads back under to make
a “C” shape and tack them to the pads
(on the top of the board) vacated by the
SMD resistor.
What’s the zener for?
There is a second modification required to the PCB if you plan to run
the flood from a 24V supply – either
the included supply or any other.
The problem here is that the Mosfet
used for reverse polarity protection
(STM4410A) has a gate-source absolute maximum of 20V so is in dire
danger of being popped at 24V.
The way around this dilemma is to
fit an 18V zener diode between the
aforementioned gate and source.
Fitting this zener is also a bit fiddly
– fortunately, three of the pins (1,2 and
3) are connected together as the source
on the STM4410A and these make a
handy point to solder the anode of
the Zener to. The cathode (stripe end)
can be soldered to the inner pad of the
10kΩ SMD resistor (again, it is tacked
to the top of the PCB).
Note again this mod is ONLY required if you intend to operate the
LED Floodlight from a supply greater
than 18V (it is quite happy to run at
12V, by the way, with full brilliance).
DC power supplies
Here’s where we struck a snag – and
we thought we’d better mention it before final assembly as it might make a
difference to what you do.
We mentioned earlier that Oatley Electronics include a Chinesemade 24V, 1A switchmode power
supply with the kit, which should
be more than adequate to drive
the power supply and LED array.
(20W/24V=830mA; add a bit for
losses and it should still be well under 1A).
But the power supply couldn’t cope
– it was as if it was continually starting
and shutting down under overload.
The effect was that it “strobed” the
LED array – fine if you’re looking for
a party light but not very practical for
a floodlight! Oatley Electronics told us
they had received occasional reports
of this happening but equally, large
numbers where it didn’t.
So we tried our prototype with three
other (identical) power supplies and
the same thing happened.
Switching over to a 12V, 3A supply solved the problem completely
– obviously the floodlight drew more
current (20W/12V=1.7A) but that was
no drama for a 3A supply.
So if your floodlight strobes like ours
did, you’re going to need a different
power supply. The circuit diagram
says a DC input from 6 to 30V; bear in
mind that the lower the supply voltage,
the higher the power supply current.
At 6V, you’re going to need a supply
capable of nearly 4A; at 30V, the supply can be less than 1A.
Assembly
Now that we have the fiddly bits
At left is the
PCB as supplied
by Oatley, while
the one at right
has our two
modifications
(circled). The
zener is only
needed for
operation on
supplies >18V.
68 Silicon Chip
siliconchip.com.au
At left you can clearly
see the four tapped
mounting holes for the
LED array. The two
outer holes are for
power wire entry. At
right, the LED array has
been mounted (with
heatsink compound
underneath) and the
two power wires (red
and white) soldered to
their respective tabs.
Note the red and black
marks we put on to
show which was which!
+
V+
L1
out of the way, it’s time to put it all
together.
First, you need to identify the “+”
and “-” terminals of the LED. It’s not
easy!
Unless your eyesight is in the macroscopic class, you’ll probably need a
magnifying glass. You’re looking for
a + and – symbol moulded into the
white plastic “case” which surrounds
the LED array itself.
Once you’ve found them you can
then identify which of the two metal
tabs is positive and which is negative.
(Our photo shows which is which).
We kept losing the symbols (especially under normal office light) so in
the end put a spot of red marker pen
against the + symbol. It helped!
On the inside of the main (large)
case, you’ll find six holes. The four
smaller holes form a square and these
are used to mount the LED module.
First, though, apply a good coat of
heatsink compound (supplied in the
kit) to the rear of the LED array and
smooth it out.
Mount the LED array with four of the
small countersunk-head metal screws
– the holes are already tapped. Any
heatsink compound that oozes out the
edges should be removed with a cloth.
The other two holes will be used to
10k
10k
+
K
G
D
V–
(5-8)
SC
2012
Q1
STM4410A
(4)
A
ZD1
18V
#
–
220F
20W
LED
ARRAY
3
SW
4
VIN
2
630V
DC
#
5536
(60V, 3A)
–
5
IC1
FB
EN
XL6005E1
GND
1
+
220F
0.4
–
3x
1.2
IN
PARALLEL
S
(1-3)
IC1
Q1
# SEE TEXT
20W LED Floodlight driver
8
4
1
5
1
Here’s the circuit of the 20W LED driver, published more for interest’s sake
than anything else because it comes pre-assembled on a small PCB. All you
need do is change a resistor value and, if needed, add a zener diode.
pass the power cables through shortly.
Wiring
You need to connect the wiring to
the PCB before mounting it in its case.
The case containing the power supply PCB is actually separate from the
main case and is attached to it via four
screws. In fact, it is the lid which is
attached to the case and the case body
screws down onto the lid.
There are four wires required to connect it – two “DC in” and two “LED
out”. The two LED out wires are simple – just solder some relatively heavy
duty pickup wire to the two terminals
marked LED OUT + and –.
These wires pass through the two
holes into the main case and are soldered direct to the metal tabs on the
end of the LED array – after once again
checking you have identified the +
and – tabs.
The DC in wires are simple enough,
a positive and a negative, but depend
on whether you are going to use the
power supply in the kit or some other
supply.
Either way, a cable gland is supplied in the kit which suits the round
cable from the DC supply. Pass the
cable through the gland and the hole
in the case, leaving the gland loose for
the moment. Around 100mm of wire
inside the case is needed to make connection simple.
The power supply PCB has a
heatsink attached to the back
which needs to be in intimate
contact with the case. Rather
than drill and tap holes, we used
a pair of TO-3P mounting pads
which are self-adhesive both
sides and therefore keep the
board in place, while transferring
any heat to the case.
siliconchip.com.au
November 2012 69
There’s a pre-drilled hole
in the case to accept the
cable gland (supplied).
It ensures that the box
is watertight and won’t
provide a warm, happy
home to ants and insects.
At right is the PCB
mounted in the case lid
attached to the main lamp
body. There’s no screws on
the PCB: it’s held in place
by a couple of self-adhesive
thermal transfer pads.
It’s probably easiest to cut any plug
off the DC supply and wire direct to
the PCB but you may need to identify
the + and – wires from the supply; in
our case there were four wires, red,
black, green and white.
The positive lead was red, as expected, but the negative lead was the
white, not the black. If you solder direct, make sure you insulate the ends
of the other two wires, as well as the
red and white, to prevent shorts.
The alternative is to leave the plug
on the power supply and drill a hole
in the side of the case and fix a panelmounting socket to the case, wired to
the PCB. This will make the floodlight
a lot more portable, if that’s your want!
Mounting the power supply
The power supply PCB has two
mounting holes but we cheated a bit
and glued it in place with self-adhesive
thermal pads intended for TO-3P transistors. These are more than capable of
sticking to the heatsink fins and also to
the case itself. (These are not supplied
in the Oatley kit).
70 Silicon Chip
For convenience, we mounted the
PCB on the case lid, with the wires
going directly from there through to
the LED.
Solder the power leads to the tabs
on the LED array, again making absolutely sure which way around they go.
With the + and – symbols towards the
bottom, the + tab is at the top and the
– tab is on the bottom. Pull any excess
wire back into the power supply case.
Putting it together
From here, it’s simply a matter of
screwing together the various bits –
screws are supplied.
The reflector mounts inside the
lamp assembly so that it sits on the
outside of the LED array; the glass front
slots into its frame and, via a gasket
(supplied) screws to the outer rim of
the floodlamp.
On the back, the PCB case back
screws onto its lid which should
have come already connected to the
floodlamp.
The U-bracket, used for mounting,
should also be already connected to
the floodlamp but you may need to
tighten its screws once in position. In
fact, you’ll probably have to remove it
to facilitate mounting.
Choose a mounting position (say)
under an eave or overhang. There’s
not much heat given out so that’s not
normally a worry.
SC
Where From, How Much?
The 20W LED Floodlight kit was
designed by Oatley Electronics, who
retain the copyright.
It is available as a kit (K329), for
$40.00 inc. GST from Oatley Electronics, PO Box 89, Oatley NSW 2223.
This kit includes all components
(PCB is pre-assmbled) and the case
as shown in this article. A 24V 1A
switch-mode supply is also included.
If operating from a supply higher
than 18V, you will also need an 18V
zener diode, as described in the text.
*Branko Justic is the owner of
Oatley Electronics.
siliconchip.com.au
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