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Need Help With an Electrical Issue I Can't Solve

Nihon_Ni

Well Known Member
I've been working on installing my electrical system for a couple months now, and I'm starting to feel pretty confident with what I'm doing. However, I ran into an issue this weekend that I can't figure out, and I need some help from the collective to figure this one out.

I have two pairs of red LED lights that I'm installing in the cockpit on a dimmer switch.

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Gooseneck lights: https://www.aircraftspruce.com/catalog/elpages/britt-mgn-minigoose.php

Flood lights: https://www.aircraftspruce.com/catalog/elpages/intmaplight.php

Dimmer switch: https://www.aircraftspruce.com/catalog/elpages/singlechannelpwm.php

Before I installed these lights, I tested the circuit design using alligator clip jumpers I bought at the Fly Market this year at AirVenture, and they all worked in series. I soldered wires to the leads on each of the lights, according to the diagram I constructed, and crimped knife disconnects in the two locations on the drawing. But when I applied power and twisted the dimmer, nothing happened.

All my wires are labeled, and there isn't anything out of position. I removed the dimmer switch and added a jumper from the ground point to the ground lead wire (blue box #1) and another jumper from the power bus to the power lead (#2). This didn't turn the lights on.

With the power jumper still on #2, I disconnected the knife splices and moved the ground jumper to #3 and the right light came on.

I then replaced the ground jumper back to #1, and added a jumper from #3 to #6, (power still attached at #2) and both gooseneck lights came on. (I've also connected the knife disconnects at #3 and #6 and the goose neck lights work in that configuration.)

I then moved the power jumper to #4 and ground to #5 and the two flood lights came on.

The problem is, I can't seem to get the whole circuit to work at once. With ground at #1 and power at #2 I've added jumpers from #3 to #4 and #5 to #6, but none of the lights come on in that case. I can get either the two flood lights on or the two goose neck lights on, but I can't get either three or all four of them to light up.

I increased the fuse to 5 amps and that didn't solve the problem either.

I've removed the switch, so that isn't the issue. I'm stumped at what the problem might be. The lights all worked with jumpers before I soldered wires in place while drawing power from a 1A fuse, and I have triple checked to be sure I have the polarity right on each light.

Why do they work in pairs, but not all four together?

Stumped in Virginia
 
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Didn't have time to follow the whole post, but the LED lights need to be wired in parallel, not series, with the dimmer on the positive side before the lights.

Larry
 
Rob,

I'm having trouble understanding the way you have drawn your schematic. But, I think you are trying to run the lights in series and I think they need to be hooked up in parallel.

When LEDS are run off of 12 volts there are generally one or more in series with a current limiting resistor of some type. These lights expect the full 12 volts across them. When you put them in series they don't end up with enough voltage across them to turn them on. LEDS have a threshold voltage and they won't turn on unless they have enough voltage. I think this is the problem.

Instead of the way you have them connected try connecting GND to one side of all the lights and connect 12 volts to the other side of all the lights. This way they will all have 12 volts across them.
 
Do you actually have your + connected to - on the middle two? If so your middle two lights are not wired correctly. Red to red, black to black, (+ to +, - to -) everywhere.

And your diagram shows L13.1 with two grounds, which is also incorrect.
 
What Larry said. If you look at the specs for those lights, they are 12V devices, meaning that each light has its own current limiting device built in. Treat them like regular old 12V lights, and wire them in parallel; not series.
 
Good morning guys and thanks for all the input!

I know it's confusing, but the color of wires I've used isn't reflective of a light's true ground. On the flood lights, the positive wire is black and white and the ground is black as I have drawn it. I confused myself as I was wiring it, but at some point I had to pick a color of wire to make the connections, and this is what I came up with.

I wondered about the series vs parallel issue, but if it's true that I can't hook up more than two lights in series, why does it work with jumpers? I first tested this arrangement with a series of jumpers that replicated the schematic for everything except the switch. No that I have those jumpers replaced with soldered wires it doesn't work. That's the part I can't figure out.

The dimmer I have has four terminals: DC+, DC-, Out+, Out-. I could run power and ground to the switch, and then from there to a terminal block where all four lights would have power and ground circuits. Will that solve the problem?

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Since the two goose necks work in series, and the two flood lights work in series, could I have two series run by the same dimmer switch, or would it be better to run them all in parallel?

Thanks again,
Rob
 
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They ALL need to run in parallel. As mentioned, each of them needs a full +12v supply.

Vic
 
They ALL need to run in parallel. As mentioned, each of them needs a full +12v supply.

Vic

Vic, I just tested running two series (floods on one circuit, and goose necks on the other) and all the lights power up and both dim appropriately. Is this arrangement asking for trouble in the future? It would save me some rewiring if I can run two series, but I'd rather have it right.

Thanks,
Rob
 
Vic, I just tested running two series (floods on one circuit, and goose necks on the other) and all the lights power up and both dim appropriately. Is this arrangement asking for trouble in the future? It would save me some rewiring if I can run two series, but I'd rather have it right.

Thanks,
Rob

I really can't speak to the future (or I'd buy all of the winning numbers for that lottery right now!), but the fact that they work now is no gurantee that they will continue to work in the future. Honestly, they do need to be wired in parallel. Perhaps to visualize it better, just imagine that you only had ONE of them to wire---it would be connected straight to 12v. The fact that you have multiple ones doesn't really make any difference. Whether it's one or 10, they all need to be connected directly to the 12v source, even if it is a dimmer.

Vic
 
Vic, I just tested running two series (floods on one circuit, and goose necks on the other) and all the lights power up and both dim appropriately. Is this arrangement asking for trouble in the future? It would save me some rewiring if I can run two series, but I'd rather have it right.

Thanks,
Rob

Save yourself future headaches and rewire them in parallel. As has been pointed out they're designed to work with the full 12v across them. The dimming function will most likely work better this way too.

Wiring in series exposes you to all lights in the chain going off if one light fails. Not only will it go unexpectedly dark, but you'll also have to figure out which light in the series is bad.
 
Forward voltage

LEDs work on the principle of forward voltage. What that means is that it takes a certain amount of voltage before the LED will conduct and light. Each LED in series will drop the line voltage by the forward voltage.

So lets say you have LED lights designed with a 5 volt minimum forward voltage required. Two in series equal ten volts forward and would light with 12 volts supplied having an extra 2 volts left over (2 X 5 = 10). Three in series would require a minimum of 15 volts to light (3 X 5 = 15) and will not light on 12 volts.

The key to LED lights is that once they start to conduct (i.e. line voltage equals forward voltage) they will pull all of the current available. If there is not a current limiting device in the circuit, the LED will burn it's self up with a flash and smoke. In order to control current an appropriate resistor or a high frequency switching power supply is added to the circuit. Resistors are cheap, control current flow and properly sized work well, but waste some amount of energy as heat. So resistors are typically not used where energy availability is limited such as battery operated devices such as flashlights. In flashlights, switching power supplies are used because they limit current without wasting a lot of energy as heat.


To dim a series of LEDs all at once, wire them in parallel and add a resistor to control current (of appropriate wattage), then add an additional switching resister (commonly called a pot) to effect the switching and dimming on either the ground or power wire. The dimming will generally not be linier since LED light output is not typically linier with voltage/current variation.

It is the high frequency switching power supply that can cause the radio interference LEDs are so famous for. LEDs, current limited with resistors are never a source of audio interference.
 
Forward voltage

LEDs work on the principle of forward voltage. What that means is that it takes a certain amount of voltage before the LED will conduct and light. Each LED in series will drop the line voltage by the forward voltage.

So lets say you have LED lights designed with a 5 volt minimum forward voltage required. Two in series equal ten volts forward and would light with 12 volts supplied having an extra 2 volts left over (2 X 5 = 10). Three in series would require a minimum of 15 volts to light (3 X 5 = 15) and will not light on 12 volts.

The key to LED lights is that once they start to conduct (i.e. line voltage equals forward voltage) they will pull all of the current available. If there is not a current limiting device in the circuit, the LED will burn it's self up with a flash and smoke. In order to control current an appropriate resistor or a high frequency switching power supply is added to the circuit. Resistors are cheap, control current flow and properly sized work well, but waste some amount of energy as heat. So resistors are typically not used where energy availability is limited such as battery operated devices such as flashlights. In flashlights, switching power supplies are used because they limit current without wasting a lot of energy as heat.


To dim a series of LEDs all at once, wire them in parallel and add a resistor to control current (of appropriate wattage), then add an additional switching resister (commonly called a pot) to effect the switching and dimming on either the ground or power wire. The dimming will generally not be linier since LED light output is not typically linier with voltage/current variation.

It is the high frequency switching power supply that can cause the radio interference LEDs are so famous for. LEDs, current limited with resistors are never a source of audio interference.
 
Forward voltage

LEDs work on the principle of forward voltage. What that means is that it takes a certain amount of voltage before the LED will conduct electricity and light. Each LED in series will drop the line voltage by the amount of the forward voltage.

So lets say you have LED lights designed with a 5 volt minimum forward voltage required. Two in series equal ten volts forward and would light with 12 volts supplied having an extra 2 volts left over (2 X 5 = 10). Three in series would require a minimum of 15 volts to light (3 X 5 = 15) and will not light on 12 volts.

The key to LED lights is that once they start to conduct (i.e. line voltage equals forward voltage) they will pull all of the current available. If there is not a current limiting device in the circuit, the LED will burn it's self up with a flash and smoke. Pre-packaged LEDs have that current limiting device already built into them.

In order to control current an appropriate resistor or a high frequency switching power supply is added to the circuit. Resistors are cheap, control current flow and properly sized work well, but waste some amount of energy as heat. So resistors are typically not used where energy availability is limited such as battery operated devices such as flashlights. In flashlights, switching power supplies are used because they limit current without wasting a lot of energy as heat. Just be aware that it is the high frequency switching power supply that can cause the radio interference LEDs are so famous for. LEDs, current limited with resistors are never a source of audio interference.


To dim a series of LEDs all at once, that are pre-packaged with current limiting resistors, wire them in parallel , then add an additional switching resister (commonly called a pot) to effect the switching and dimming on either the ground or power wire. The dimming will generally not be linier since LED light output is not typically linier with voltage/current variation. A 1000 ohm pot works well for 12 volt LEDs.
 
Gents, thanks for all the help. Leok, your discussion of forward voltage makes sense and I appreciate the detailed answer. I'll rewire the four lights in parallel per the updated drawing.

Now, for educational purposes riddle me this: Why did all four lights work when I hooked them up in series with jumpers (bus to light to light to light to light to ground), but they don't work when I replaced the jumpers with soldered wires in the exact same configuration? I get that they shouldn't work in series due to forward voltage, but they did work when I had jumpers installed. The jumpers are probably 22 AWG wires of about 10" in length with alligator clips at each end, and I had to string together multiple jumpers to get from the bus to the lights in series and to a ground. If I recall, that took 8 jumpers to make that whole connection as a couple were placed end to end to span the distance between lights. In theory, the soldered connections should be better than an alligator clip, right? I can't figure out how jumpers carry more voltage than soldered wires, but apparently they do. That's the part that has me baffled.

Thanks,
Rob
 
Now, for educational purposes riddle me this: Why did all four lights work when I hooked them up in series with jumpers (bus to light to light to light to light to ground), but they don't work when I replaced the jumpers with soldered wires in the exact same configuration?

Might have less to do with the physical wires and more to do with the power supply. Any chance your battery was on a charger for the previous test and had a couple more volts to give, vs your test with the soldered wires?

Depending on the forward voltage drop of the LEDs (different for every diode, and who knows how the lamp manufacturers wired the individual diodes in each gooseneck and flood assembly), 4 assemblies in series could be very near the closed-circuit battery voltage (~12V). A battery on a charger at 13-14V (or a freshly charged battery) might be enough to exceed the Vf of the LEDs and light them up, yet that same battery by itself or slightly more drained may not.

Certainly could be other phenomena at work here but this is one possibility.
 
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good question

Kurt has a good theory, and in my view most likely.

LEDs function like a dam, blocking the current flow until the flow 'goes over the top'. So very small changes in voltage at the critical point can make all of the difference. A series of LEDs is like dams stacked on top of each other. Each drops the voltage by the forward voltage. If the residual voltage is insufficient to overcome the last LED in series, no current flows and none of them light up.

There can even be some temperature affects though small.
 
I'm not using a battery to power my system for checks during the build, I'm using a power converter that puts out 13.8 V. So there was less than +/- 0.1V difference between the multiple tests I ran with jumpers and soldered wires. The only variable I changed is jumpers for soldered wires. Power source and strength was the same, circuit design was the same. When I unwire everything I may hook up the jumpers again just to make sure my memory isn't mistaken.

There's a possibility (looking more like a probability) that I hooked up the circuit differently than I remember when I tested it. If I hooked them up in two series, that certainly would light them all up, as I proved to myself this morning.

inspirational-star-trek-quotes-discover-and-share-logic-quotes-explore-our-collection-of-motivational-and-famous-quotes-by-authors-you-know-and-love-most-inspirational-star-trek-quotes.jpg
 
Just a side note, LED's can be hooked up in series or parallel, or an array that combines both, depending on the product and/or how you are using them.
Most of the time for application of a finished product, they will have an integral driver designed for one specific requirement and be parallel wired.
Some products can not be dimmed outside of the input voltage tolerance they where designed for.
 
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That muddies the water for this discussion. Both linked devices have current control built in designed for a 12v supply, so they should be treated like any other 12v device.
 
That muddies the water for this discussion. Both linked devices have current control built in designed for a 12v supply, so they should be treated like any other 12v device.

Agreed. Let's try this.....

Make sure the product is dimmable and what technology they need for proper dimming. Constant Current products behave differently than Constant Voltage.
One of the products may allow a voltage reduction for dimming, the other a current limiter. This could explain why they work separately but won't work together when parallel wired to the same dimming source.

The LED product in my panel requires a PWM dimmer. Power is reduced but not peak voltage.

Does that make sense now?
 
Normal old fashioned bulbs would work no matter how wired, however led are
Very sensative to being wired correctly, + to + and - to - ...Tom
 
Agreed. Let's try this.....

Make sure the product is dimmable and what technology they need for proper dimming. Constant Current products behave differently than Constant Voltage.
One of the products may allow a voltage reduction for dimming, the other a current limiter. This could explain why they work separately but won't work together when parallel wired to the same dimming source.

The LED product in my panel requires a PWM dimmer. Power is reduced but not peak voltage.

Does that make sense now?

Yes, that makes a lot of sense. Thanks for helping me understand this. I was wondering if there was something about the fact that two similar lights worked together, but dissimilar brand of lights didn't.
 
Let there be light!

Gents,

Thanks for everyone who helped me understand the issues going on here. I rewired the circuit this morning according to my updated drawing and I was very satisfied with the results!

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I also discovered why the lights seemed to work with jumpers but not with soldered wires. I went back to the picture I took of the lights on with jumpers, and I noticed a clue in the corner of the picture -- I could see one of the daisy chained jumpers going from goose neck to goose neck. Thus, I had in fact hooked them up as two separate series, and not according to my first schematic. That's why I was able to get all four lights lit with jumpers but not once I wired them. I did disconnect the knife splices at one point during the troubleshooting and created two circuits in series, and they all lit in that setup (which shouldn't have been a surprise since this is how I constructed the initial test with jumpers, but I had forgotten that detail). I decided not to use this shortcut and build on based on everyone's advice, so I unwired everything and rewired it to common power and ground output from the dimmer switch. It's been a frustrating couple of days, but it made the victory even sweeter.

One more day closer to flying!

Thanks again for everyone's help,
Rob
 
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