Master caution & Warning dimming

bobmarkert · #1 12-12-2012, 07:12 AM

I need help with the design of my master warning and caution panel. I want to put 5 lights on a rheostat (pot) to make them dimable. is it possible to run all the grounds from the lights to a single ground wire and then through pot and dim the lights. Restated, can the pot be "downstream" of the lights and still dim the bulbs or does the pot have to be before the bulb? Does the answer change if I decide to use LED lights assuming I get a pot that can dim LEDs? Thanks in advance for helping.

DGlaeser · #2 12-12-2012, 07:28 AM

Yup, electrons don't care if you adjust them upstream or downstream

All of my lights are LEDs and dimmed that way. Any dimmer will do, resistance is resistance. Mixing filament bulbs and LEDs on the same circuit is not an issue electrically, but they probably will dim differently. One of the reasons I went all LED.

bobmarkert · #3 12-12-2012, 07:34 AM

Thanks Dennis. That is the ans I was hoping for!

Scott_F · #4 12-12-2012, 11:56 AM

Bob,
May I suggest that, instead of a rheostat, you might want to use some fixed level of reduced brightness for warning and caution lights - perhaps on a day/night mode switch. Unless you have a way to hold the pot to some minimum brightness level, you run the risk of accidentally running it all the way down so that you might miss a caution or warning light during daytime. Military airplanes (and I assume commercial also) will have a specified minimum fixed luminance level for alert signal for both day and night modes. Just a suggestion.

Regards,

rapid_ascent · #5 12-12-2012, 01:56 PM

Let me add on to Scott's comments. Be careful how you hook up your dimmer pot.

If you use a pot for a dimmer this is probably OK where you have a fixed load. For example gauge backlighting. If however you have a variable load because all of the lights are not always lit as is the case for warning lights then your indicators will change brightness as more of them turn on or off. This doesn't seem like what you would want.

Bill.Peyton · #6 12-12-2012, 02:11 PM

I would suggest that you put a relay which closes when you turn on your nav lights. The coil is connected to the nav light circuit.. Use a fixed resistor to dim the lights and have the relay short the resistor for full brightness. When the relay is pulled, it removes the short across the resistor and dims your lights. If you are using incandescent lights, calculate the current and size the fixed resistor accordingly. You could also use the relay to hook the lights to your dimmer circuit, just be cautious in that the dimmer may dim the lights too dim, or you may leave the nav lights on by accident and not see the warning. Or... you could use 24v bulbs and leave it alone like I did. Bright enough during the day and night