TROUBLESHOOTING LED’S
CURRENT RATED LED’S
GETTING STARTED
FIRST THINGS TO CHECK
Polarity.
Series connection at all connection points (even at driver).
Batch codes on LED’s.
Voltage drop reading.
Minimum voltage rating of driver.
Maximum voltage rating of driver.
LED’S IN A ROW ARE DIFFERENT COLOURS
LED BINNING
LED’s are tiny and as with any light source they are made to a specific tolerance. Due to the
size of the LED it is extremely hard to manufacture LED’s to a consistent tolerance. This tolerance directly affects the colour temperature of the LED which is why LED’s are ‘binned’ much
like wallpaper batches to achieve colour consistency. While technological improvements will
ensure a tighter tolerance and allow the binning of LED’s to improve they may still show some
variation in colour.
At John Cullen we only use very tightly binned LED’s to ensure colour consistency, however
we do not feel that this is where we should stop. All John Cullen LED products are not only
binned by the LED supplier but they are also binned in our warehouse store. Additionally,
John Cullen labels each product with a batch code so that we can identify incorrect colours in
our store and also ensure deliveries are from the same batch. This ‘on product batch control’
allows for quick identification of a colour difference on site simply by confirming whether the
batch codes on the queried LED’s are different or the same.
Remedy: Check binning of LED’s and only group similar batched LED’s in separately seen
LED locations. i.e. group the kitchen LED’s to the identical product batch code LED’s.
LED’S IN A GROUP VARY IN BRIGHTNESS
SERIES WIRING, (NOT PARALLEL)
A current rated LED i.e. 350mA etc requires a constant current at every point in the circuit
which is achieved by series wiring. When a circuit is connected in parallel the current will flow
between the parallel circuits delivering a smaller amount of the supplied current output to each
individual LED therefore producing dimmer light.
Remedy: rewire as a series circuit.
SALES: 020 7371 9000
1101240412©
DESIGN: 020 7371 5400
www.johncullenlighting.co.uk
TROUBLESHOOTING LED’S
AN LED IN A CIRCUIT DOESN’T ILLUMINATE
POLARITY
A current rated LED i.e. 350mA etc requires a constant current at every point in the circuit
which is achieved by series wiring. With this wiring method the circuit will also need to follow
a polarity wiring i.e. a positive feed connected to a negative feed etc. If the polarity is not observed and the circuit is energised the LED will fail beyond repair.
Remedy: Check polarity before wiring and ensure correct before powering the circuit. LED will
need replacing if incorrectly wired.
CONNECTING WHILST ENERGISED
An LED requires a soft start up which is achieved by connecting the LED to the LED driver
before the power is supplied. If power is supplied first and the LED IS then connected to an
energised driver the LED will over stress and result in a failure.
Remedy: Check the power is fullY off when connecting LED’s onto a circuit. LED will need
replacing if incorrectly wired.
A GROUP OF LED’S ARE DIM
SERIES WIRING, (NOT PARALLEL)
A current rated LED i.e. 350mA etc requires a constant current at every point in the circuit
which is achieved by series wiring. When a circuit is connected in parallel the current will flow
between the parallel circuits delivering a smaller amount of the supplied current output to each
individual LED therefore producing dimmer light.
Remedy: rewire as a series circuit. LED will need replacing if incorrectly wired.
SERIES WIRING CONNECTED IN PARALLEL
Sometimes on installations with groups of LED’s at either side of a room or in two separate
locations they often get fed back to the driver and connected together in parallel at the driver
location. This reduces the supplied current to each group and makes the LED’s appear dimmer
than specified.
Remedy: Turn off the power and connect the two or more groups together at the driver location
in a series circuit observing the polarity of all the connecting groups. LED will need replacing
if incorrectly wired.
SALES: 020 7371 9000
1101240412©
DESIGN: 020 7371 5400
www.johncullenlighting.co.uk
TROUBLESHOOTING LED’S
A GROUP OF LED’S ARE FLASHING ON AND OFF RAPIDLY
FORWARD VOLTAGE EXCEED THE DELIVERED VOLTAGE
A current rated LED circuit will also require not just a constant current, but a delivered forward voltage (this could range from 2v to 36v depending on the LED) i.e. if you have a circuit
of 2 x LED’s and each LED requires a forward voltage of 3v the total voltage of the circuit
would be 6v. A standard LED driver will normally have an output voltage of around 50v DC.
When the voltage loading of the circuit is exceeded i.e. 17 x 3v fittings (51v DC) on a 50v DC
driver.
Circuit voltage required: = 17 x 3v = 51v.
Delivered voltage:
= 50v
So
Circuit voltage = Delivered voltage – Circuit voltage required
Circuit voltage = 50v – 51v = –1v
This would result in the LED’s struggling to start up and force them to start to pulse on and
off. This will overstress the LED and cause it to fail beyond repair.
Remedy: Split the LED’s into two equally split groups and reconnect.
FORWARD VOLTAGE EXCEEDS THE DELIVERED VOLTAGE DUE TO VOLTAGE DROP
Whilst delivered voltage from the driver is important, it is also important that the cable used
does not cause voltage drop (voltage is normally lost whilst travelling through cable over
distances). If voltage drop occurs due to too thin a cable being used it will reduce the amount
of delivered voltage to the circuit. i.e. 16 x 3v fittings (48v DC) on a 50v DC driver with 5%
voltage drop (2.5v DC) would result in the LED’s struggling to start up and force them to start
to pulse on and off as the delivered voltage has reduced to 47.5v DC and the required voltage is 48v DC.
Circuit voltage required: Delivered voltage:
Voltage drop (5%)
= 16 x 3v = 48v
= 50v
= 50v - 5% = 2.5v
So
Circuit voltage = Delivered voltage – Voltage drop – Circuit voltage required
Circuit Voltage = 50v – 2.5v – 48v = –0.5v
This will overstress the LED and cause it to fail beyond repair.
Remedy: Split the LED’s into two equally split groups and reconnect, or step up the cable
thickness.
SALES: 020 7371 9000
1101240412©
DESIGN: 020 7371 5400
www.johncullenlighting.co.uk
TROUBLESHOOTING LED’S
A SINGLE LED IS FLASHING ON AND OFF RAPIDLY.
FORWARD VOLTAGE IS UNDER THE MINIMUM OUTPUT VOLTAGE.
A current rated LED circuit will also require not just a constant current, but a delivered forward
voltage (this could range from 2v to 36v depending on the LED) i.e. if you have a circuit of 2
x LED’s and each LED requires a forward voltage of 3v the total voltage of the circuit would
be 6v. A standard LED driver will normally have an output voltage of around 50v DC and a
minimum output voltage from 0v to 10v. When the voltage loading of the circuit is under the
minimum i.e. 1 x 3v DC fittings on a driver with a minimum voltage loading of 5v DC.
Circuit voltage required: = 3v
Minimum delivered voltage: = 5v
So
Minimum circuit voltage = Circuit voltage required – Minimum delivered voltage
Minimum circuit voltage = 3v – 5v = –2v
This would result in the LED struggling to start up and force it to start to pulse on and off. This
will overstress the LED and cause it to fail beyond repair.
Remedy: Use a driver with a higher minimum loading or add additional fittings onto the driver.
SALES: 020 7371 9000
1101240412©
DESIGN: 020 7371 5400
www.johncullenlighting.co.uk