How do I add LEDs to an existing installation?

posted in: Drivers Products Constant Current


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First thing to do is use a Volt (VDC) Meter to measure total load on the driver's output.

If there is a dimmer, set to full bright.  Measure when first energized.  Forward Voltage (Fv) drops slightly when the system warms up).  Fv also drops when the LEDs are dimmed (if this Model is dimmable).

The driver Model will give you the maximum Fv on the driver.  model RPK-120-40D has a maximum load of 40 VDC (Fv), includes all LEDs and wiring.

If measuring 30 VDC at the driver, there is 10 Volts of capacity remaining, which will accommodate 2-3 LEDs on average.  We use a nominal  4VDC per LED when budgeting capacity (at 350ma), but the LED fixtures being powered by a constant current remote driver should give you the Fv of that specific fixture for sizing purposes.

If they do not, then you can divide the Wattage/Drive current to arrive at its Fv.
For Example 1.0Watts/0.350Amps = 2.9VDC for the LED (not including any wiring losses).  

The advantage of using a Constant Current Driver is that driving an LED at 350ma, if using 14 AWG wire from driver to LED, a 100 foot wire run = 0.2V drop. using 18AWG would be approximately 0.5V drop.

The new LEDs can be wired from the existing LEDs (in series) or all wiring can be brought back to the driver and wired in series there. Measure Fv and Drive current to verify the driver is wired correctly.  Wiring of 18AWG minimum is OK to use in most cases.

If the driver is overloaded, it may blink or not turn on at all.