12V LED Strip not lighting up

[svpandion]

I'm going to start with the fact that I'm the most knowledgeable when it comes to electricity, although I'm sure that will become obvious soon enough.

I'm replacing some old burned out LED strip lighting in the cabin, with some new 5050 LED strips. They take a standard round connector (same as my laptop) that plugs into a small control box. I've cut the wire, so that I can wire it directly to the 12V the old LED's were plugged into.

Seems to me like that should be the end of it, but like all things boat, it has to be difficult.

When I check the voltage coming off the old wire with my trusty voltmeter it shows 12.xx volts. Why don't they work??

[BlackHeron]

Try reversing the polarity. LED lights only work one way. Sometimes cheaper stuff is built wrong so the red and black wires are actually reversed. I've encountered this a few times.

[svpandion]

Just tried that and no good.

Also, I check the voltage when the LED is hook up and on, and the voltage drops to 3.something. Maybe that's a clue?

[newhaul]

Check connections all the way back to source. Also check voltage at source for the run could be as simple as a dirty fuse . Or a loose connection

[four winds]

I think you are saying you cut the plug off the new 5050 strip. And that plug connected the new strip to its control box.

And then you connected the wires (sans plug) to 12v.

Could be that control box does something important.

5050 smd LED operate at 2.8 - 3.4 volts.

[rwidman]

Originally Posted by svpandion

I'm going to start with the fact that I'm the most knowledgeable when it comes to electricity, although I'm sure that will become obvious soon enough.

I'm replacing some old burned out LED strip lighting in the cabin, with some new 5050 LED strips. They take a standard round connector (same as my laptop) that plugs into a small control box. I've cut the wire, so that I can wire it directly to the 12V the old LED's were plugged into.

Seems to me like that should be the end of it, but like all things boat, it has to be difficult.

When I check the voltage coming off the old wire with my trusty voltmeter it shows 12.xx volts. Why don't they work??

You need to be more specific. You cut off the "control box"?

[Privilege]

Most LED's run on 12v or thereabouts so it's common practice to simply remove the AC transformer and wire the LED's straight to your 12v system as you have done, but check the transformer to make sure that it supposed to supply 12v DC. As others have pointed out, LED's are polarity sensitive and will only work if wired properly.
If your voltage drops to 3v when you connect the strip, that is your problem. You may have a short somewhere which is diverting the current but even if this is the case, your battery shouldn't be dropping that low unless it is completely dead. Even a dead battery can show 12v but cannot output a load without dropping voltage. Are your other loads working O.K when running straight off the battery?

[svpandion]

I thought as much. It feels like it maybe a short. My battery bank is definitely due for replacement, but other systems/lights etc are functioning fine off of them. The light switch panel was obviously a DIY and is cluster of wire and terminal blocks. They were nice enough to tuck it into a nearly impossible to see and hard to reach shelf that can not be disassembled without a saw. Adding to the fun is the wiring then goes into cabinetry and into the headliner, where even more terminal blocks are hiding. /rant

I'm going to try and hook this line into a known working circuit. At least I can narrow down which part of the circuit is failing.

Seriously though, thanks everyone for all the information. I'm happy to know there is a problem with the system and not my understanding. =)

[senormechanico]

I'd like to see a pic of the "control box".

[Brewgyver]

Before modifying, did you connect the intact LED + "control box" as designed? In other words, do you know that it worked before you started cutting wires?

If so, the problem likely is a poor connection somewhere, or even using the wrong wire.

[Cadence]

LEDs draw so little current to have that type of voltage drop I would bet on an awful connection someplace if the polarity has been switched, or you just bought a bad set of lights. Did you try them out of the box with the " box ". Have you check the box that it said 12V. A no. of those plugs look the same.i

[rwidman]

Originally Posted by Privilege

Most LED's run on 12v or thereabouts so it's common practice to simply remove the AC transformer and wire the LED's straight to your 12v system as you have done, but check the transformer to make sure that it supposed to supply 12v DC. As others have pointed out, LED's are polarity sensitive and will only work if wired properly.
If your voltage drops to 3v when you connect the strip, that is your problem. You may have a short somewhere which is diverting the current but even if this is the case, your battery shouldn't be dropping that low unless it is completely dead. Even a dead battery can show 12v but cannot output a load without dropping voltage. Are your other loads working O.K when running straight off the battery?

LEDs do not run on 12 volts, they "run" on about 1.5 volts. Actually the voltage depends on the internal resistance and it's the current that's important. Too little and they don't provide much light, too much and their life is shortened, sometimes dramatically.

When LEDs are installed in a "bulb" or fixture to be used on 12 volts, there are various ways to provide the optimal current to the individual LEDs. One of the best ways is with a constant current driver which controls the current through the LEDs and can be supplied with a wide range of voltages.

Without clarification from the OP, my guess is that he cut off the driver. It won't work like that and he may have permanently damaged the LEDs.

[svpandion]

Thanks to all of you I've tracked the problem down. It's the wire that runs behind everything and will be a nightmare to extract and replace. Hopefully it will at least help me in pulling a new pair through.

Here are some pics of my current hell. :P
The network admin in me dies inside looking at this.

[Peregrine1983]

Originally Posted by svpandion

Hopefully it will at least help me in pulling a new pair through.

Definitely. Consider duplex wire - it will be easier to pull through than two separate wires.

[hamburking]

I had the exact same problem with my tiller autopilot. There was 12 volts to the cockpit jack...I plug it in...nothing...unplug it, check with voltmeter...12 volts. So I figured the ap was dead and started messing around with it.

Turned out that the positive power wire had a weak connection at the battery end. There were volts, but not a good enough connection for any current. I tightened the connection, and problem solved. Then all I had to do was put the ap back together and hope that I hadn't ruined it looking for a problem that was not there.

Now I keep an old style 12 volt tester in my toolbox...its the kind that looks light a pointy screwdriver with a lightbulb inside. Instead of digital volts, you just see how bright the bulb gets when you touch the power. This ancient, analog device actually gives an incredible amount of information, and would have detected my power problem right away. BTW, they still sell these things...and they don't need batteries like digital voltmeters do. I highly recommend one as a valuable addition to any boat toolbox.