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I'm trying to controll 4 parallel 12V DC LED strips with an speedcontroller. I am able to dim the lights from 100% lit to about 5% lit, but it never turns them off completely. My multimeter can't detect the phases that the speed controller is generating, so it reads 2.0V at 0.0A when all the way dimmed. When fully turned up, its at 11.5V and 2.0A.

The speedcontroller has a 100k omh potentiometer on it and is specified for 12V DC up to 2A. The LED strips are 12V too, and should consume about 10W in total. What are my options to get it working as intented, so that it's turned off completely?

Help is much appreciated!

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  • \$\begingroup\$ A "Mickey Mouse" 1st try: Place one or more suitably current rated diodes in series with the strips. Using eg 3 x silicon diodes in series (1N400x will probably be OK) will drop around 2V before substantial current flows. If this "almost works" try either a 4th diode in series or a resistor in parallel with the strips to conduct some of the controller current. The LEDs need non zero voltage to light but the resistor will draw current at any voltage. The diodes will reduce the maximum current that the LED strips will 'see' and so MAY reduce max brightness slightly. \$\endgroup\$ Commented Dec 9, 2018 at 12:12

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An "inelegant" 1st try:
Place one or more suitably current rated diodes in series with the strips.
Two or three may be OK. Four MAY be needed.

Using eg 3 x silicon diodes in series (1N400x will probably be OK) will drop around 2V before substantial current flows. If this "almost works" try either a 4th diode in series and / or to N diodes add a resistor in parallel with the strips to conduct some of the controller current.

The LEDs need non zero voltage to light but the resistor will draw current at any voltage.

Note that the diodes will reduce the maximum current that the LED strips will 'see' and so MAY reduce max brightness slightly.
For 10W max ~= 1A load, try say 0.1A resistor current max.
Try say a R = V/I = 12/0.1 ~= 120 Ohm resistor to start.
Lower or higher may suit.
Resistor max dissipation = Vmax^2/R

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