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Old 04-06-2013, 12:10 PM
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Question on PWM of LED's in dash lighting

I have a question on wiring this PWM module for my dash LED's to control dimming. It is my understanding that the PWM takes place on the negative of the output.



Here is the unit and suggested wiring.

As you can see both input and output are isolated from each other.


My question is that I cannot easily seperate the two negatives, as I have a 1958 thunderbird, which utilizes the metal dash as the return (negative).

Can I tie both negatives to the metal, without harming this unit, and will it still function properly. There is no trouble keeping both positives seperate.

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Old 04-06-2013, 03:02 PM
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It will not function if wired that way.
The bulbs need to have the ground seperate from the vehicle.There are bulb sockets available that you can get that have 2 wires and do not conduct to ground through the bulb socket. That would make it easy to isolate the load side ground of the controller
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Old 04-06-2013, 03:05 PM
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Like this ..........


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Old 04-06-2013, 06:05 PM
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Have you tried a multimeter to see if the grounds are common on your module? If they aren't hook up a battery to the input as normal, using a single LED bulb hook the Anode (long leg) to the pos output and the cathode (short leg) to the battery ground, if it doesn't work, try hooking the short leg to the module and the long leg to the battery pos...... in theory it should work, but you might fry the LED, I don't think you'll fry the module.

BTW where did you purchase your module?
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Old 04-06-2013, 08:13 PM
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Pwm

X2 on the LED must be isolated from chassis ground when using a PWM dimmer.
BTDT..
Try to dim the dash lights using the standard resistance type dimmer. But I'm thinking the load is so small with LED that they won't dim at all.
A pot type (variable resistance) voltage reduction would work. When you know the load of the LED dash lights, using OHMS law the resistance range of the pot can be calculated.
Honestly, there are so many doers out there I would stick with the PWM dimmer and find a way isolate the LED from ground.
LED Lights, Bulbs & Accessories - SUPER BRIGHT LEDS sells the PWM dimmers.

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Old 04-15-2013, 03:40 AM
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Did you ever get a solution?
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Old 04-16-2013, 11:05 AM
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I picked up a series of resistors to add to the rheostat on the light switch.

I checked the unit I posted a picture of initially, and the two 12v terminals were already common, so I couldn't make the two negatives common.

That was on the thunderbird. On my fiberglass Avanti, all the grounds are seperately wired, so I am taking the ground to the instrument lamps and wiiring them to the unit itself. Should be fine.
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