PWM dimming.

I have a question for the electronic experts and perhaps G3Xpert.

I have a DPST fuel pump switch which had an 240AC globe. I replaced it with an LED and an appropriate resistor and it works great.
One pole is the fuel pump (+) and the other pole is a discrete ground back to the GAD27 for the annunciation of “fuel pump”. That all works great too.
The LED illumination joins the poles in the on position.

I’d like to dim this LED if possible. If I had a 3PST switch that would probably be quite simple.

Is it possible to run the ground for the LED back to the PWM dim circuit and also have that PWM as a ground for the discrete? Or is that a hare brained crazy idea?
I figure that the discrete is going to “see” a ground still, just oscillating at whatever frequency/duty cycle the dim is commanding.

Thoughts?

I have PWM dimming for my LED switches - works great.

The fact that you have a GAD 27 means you already have PWM dimming available and designed for this exact purpose to power your LED's. All you need to do is provide a potentiometer to control that feature.

I think there are 3 different PWM circuits available on the GAD 27, but you can confirm that in the G3X installation manual.

If I understand correctly, it sounds like you are using the discrete input on the GAD 27 to sink current, which I wouldn't recommend. I also wouldn't recommend connecting any kind of PWM signal to a GAD 27 discrete input.

mburch said:

If I understand correctly, it sounds like you are using the discrete input on the GAD 27 to sink current, which I wouldn't recommend. I also wouldn't recommend connecting any kind of PWM signal to a GAD 27 discrete input.

Click to expand...

Thanks

Yes this is what I am proposing. The current would only be a few milliamps at most.
Im sure it’s not what it was designed for, just spitballing to see if I could improvise.

Cheers

You can simply install an isolation diode between your GAD discrete input for the fuel pump on the same pole as the fuel pump power; this will provide the ground signal you want, but isolate the voltage potential from the GAD. An example of this is described and diagrammed in the Vertical Power installation manual section 5.21b Wiring Lighted Switches. Just substitute "GAD" for "VP-X".

And then use the other pole for LED lighting using the PWM capacity of the GAD.

Thanks Ron, I’ll check it out

Have you confirmed that the LED you installed is dimmable as well? Not all of them are.

agent4573 said:

Have you confirmed that the LED you installed is dimmable as well? Not all of them are.

Click to expand...

As long it's just the LED element and a resistor, it will be dimmable. "non-dimming" LED bulbs are more a result of, or affect, of the voltage regulation circuit, not the element itself. In this case, he'll be using a pulse wave voltage regulating circuit which is designed for "dimming" LED elements.

rongawer said:

As long it's just the LED element and a resistor, it will be dimmable. "non-dimming" LED bulbs are more a result of, or affect, of the voltage regulation circuit, not the element itself. In this case, he'll be using a pulse wave voltage regulating circuit which is designed for "dimming" LED elements.

Click to expand...

Yup, my bad. I went back and saw the "LED plus appropriate resistor". I thought he may have just bought a "12V LED" bulb and was trying to dim that. Should be good to go.

Common ground on Switch and LED and VPX for PWM LED illuinaton from GAD

Hello,

I plan on using lit rockers with 2 LEDs in each rocker that are each independent from each other and from the SPDT switch circuit. Note 2 SPDT switches in the switch I desire to use are not available. That would make this easy.

One LED will be lit at all time lighting is needed and I will use 1 input of the GAD 27. Power will come from the VPx and the grounds for just the LED will run to the GAD-27.

I am thinking about having the second LED lit only when the switch is in the closed/On position. Vertical Power shows how to do this using an Isolation diode to prevent back-feed into the VPX: (Section 5.21B page 43 of the on-line manual). Will this work with PWM. The chassis ground the VPX wants to see when the switch is closed now needs to run back to the GAD-27. Will the VPX still still ground? I am told the GAD modulates the Pulse on the ground side of the circuit. Does the GAD-27 also modulate on the positive side so I can use a common chassis ground?

Another way is to use a separate PWM that controls the PWM on the power side and allows for the use of common / chassis ground. I am cautioned that this might be noisy unless I run that ground back to the battery in the reas of my RV-10

Hopefully I explained this well. Any advise is welcome.