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Alternate LED Module Power

houston08

Apr 24, 2011
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Howdy all!
I'll begin by saying that obviously I'm new... and I have no idea what product i need in order to accomplish my needs. So I'm here. Here's my situation.

I have an LED Lightbar(I'm a Volly at a Fire Dept. here in Texas), and I'd like to use two of the White LED Modules as scene lighting, or "Takedowns". They use just a 12v source to power on.

Here's the problem.
If I just directly splice into the LED module, it will power the entire lightbar, and not just the individual LED Module. Here is a picture to hopefully help illustrate my needs, pardon the unprofessional look.

pub


So basically, where the switch is... I need SOMETHING, that will take power from EITHER power 12v power source, and send it to the LED module, but NOT send it back over the other wire. The Control Box isn't receiving power until I turn on a switch, so it's not an issue.

I need the switch to provide precedence to the External Power source, as there are times where I need to have the light flashing, but my scene lighting still available.

Thank you very much and I appreciate the help!
 

Resqueline

Jul 31, 2009
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I'd believe diodes will do the job.
1N4001-7 is good for up to 1A and 50-1000V. 1N5401-8 is good for up to 3A and 50-1000V.
Schottky types of the same size is good for double the current but only 25-80V (which is good enough).
Schottky diodes have a lower voltage drop and so dissipate less power for the same current.
 

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houston08

Apr 24, 2011
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Thanks! That did it, but only half way.
I picked up four 1N4001's, the radioshack didn't have the -7 or -8, so i'm not quite sure which i got. The individual LED Modules will now light up without lighting the rest of the bar.

I put one 1N4001 between the Control Box and LED Module, and then attacked the outside power source to the end of the 1N4001 going to the LED Module(i don't know the correct terminology, sorry).

I finished up by Splicing into the (-) cable and made the connection complete as well. Lights up just fine. So the Takedown/Scene Lighting function works just fine now. The Problem is when I want to use the entire bar in alternating mode, where it will flash every other module, and then the opposite. Now instead of of flashing the newly diode'd LED modules, they stay on solid, as I have the (-) wire spliced into the wiring. Apparently the Control Box makes the LED modules flash by completing and disconnecting the (-) wires. So obviously by me giving it an always available route that MUST be available for the Takedown/Scene lighting, the light always stays on.

Any ideas on how to fix this so that when I want them to alternate they will, UNLESS i have takedowns on as well? I will try to go grab a video so it's easier to understand, but it's about to rain.

Takedown Issue
There is the video, sorry for the quality, but it was on my phone and I wanted to grab it right quick. But you can still see how the White LED Modules are staying on when they should be flashing due to the Other available (-) wire spliced in.
 
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Resqueline

Jul 31, 2009
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Ok, if there are several modules with common positives and separate negatives going to the controller then this is how you have to do it.:
 

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houston08

Apr 24, 2011
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Wouldn't that still power on the Control Box and thus turn on all the lights again? Even if I added a diode like I have currently, it would still be able to use the always available (-) wire from the outside power source even when I don't want it to, right?
 

Resqueline

Jul 31, 2009
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No. That's the only way with switched negatives - as you indicate (and which sounds logical).
I don't know if you noticed the non-connection between the two dark-blue wires crossing?
Please draw the complete circuit like it really is - if I'm missing something here.
 

houston08

Apr 24, 2011
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The new solution did not work.
Turning on Strobes by itself would flash all the lights except the takedown lights, which would still be solid. Turning on takedown by itself would do the exact same thing. I've shown my exact wiring diagram that I have setup currently. minus the other lights, but this is enough to show what i'm doing. I'll also attach a thumbnail.

If anything is unclear, please let me know. Just so it's we're still clear, I want all the lights to strobe like normal unless Takedown is on, then I want the Two White LED modules I have wired for take down to stay solid. And Obviously just Takedowns on if I have only that switch flipped.

I appreciate all the help! Thanks!
 

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Resqueline

Jul 31, 2009
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Hmm, ok.
I think I'll need you to ohm what wires (if any) are connected together & straight through in the control box. Disconnect the extra grounds to the white modules first.
 

houston08

Apr 24, 2011
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Can you explain what you mean by ohm'ing the wires? Each module is tied in separately to the control box to the best of my knowledge. I've disconnect the extra ground wires now.
 

Resqueline

Jul 31, 2009
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You switch off power to the circuit and use a DVM/ Ohm-meter from point-to-point on the control box, noting which connections that give approx 0 Ohms to each other.
The point is to find out which wires are connected to each other and which are not (and so goes through electronics) in the control box. This helps to solve the problem.
 
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