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Old 18-10-2010, 11:38   #1
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LED Lighting Adding Line Noise ?

Hey folks,

I have installed a bunch of 12v LED strip lights in my liveaboard sailboat. Unfortunately I couldn't afford the $$$ marine-grade stuff they sell at the boat store, and now I get interference on my onboard stereo and VHF when they're on.

I suspect the interference is electrical rather than RFI, because I notice that the LEDs flicker a bit in time with the music when the stereo is playing.

All the lighting for each cabin is on its own circuitbreaker - is there something I can add into that circuit, a line filter or capacitor or something, that will soak up the interference? I'm very handy with a soldering iron and can follow instructions, I just don't have any formal electronics training.
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Old 18-10-2010, 12:12   #2
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I know my way around basic RF and DC, so here's what I can add:

LED lights "flicker" at a really fast rate, far too fast to be seen with the human eye. If you're seeing a flicker there's something else entirely going on. My guess is current draw from the stereo (really the magnets in the speakers) is drawing enough power that you're seeing it in the lights. You can check this by cranking the volume on the stereo and/or playing something with a lot of deep bass. The higher the volume the more the magnets have to move, the more current you're using.

The fact that it's "timed" with the music means the beat (which causes the magnets to use juice) is likely the culprit.

If it happens regardless of the volume (curren through the speakers) than I'd look towards RF interference.

As an example of how intermixed all this is, I had a hum in my VHF transmissions when my battery bank was being charged by shore power. The 60Hz wavelength from the charger was ending up getting sent out along with the waves generated by the VHF for transmission.

You have have both going on (RF and insufficient current), but I'd check the current draw first as it's a lot easier to troubleshoot. RF interference can end up being fairly black magic to diagnose unless you can identify the frequency of the interference.
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Old 18-10-2010, 23:09   #3
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thanks for the reply.

I'm pretty sure you're right, that it is just current draw... that's kind of the conclusion I'd already drawn. what I'm asking is more what to do about it... is there something I can add to the circuit to smooth things out, like a capacitor or something?
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Old 18-10-2010, 23:21   #4
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You could try a capacitor across the power terminals of each LED strip. Maybe a 1uF 25v ceramic. I'm guessing. It's a tiny little thing. More in more places along the strip the merrier.

How cool, a noisemaker, ideal radiating antenna, and light source all in one
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Old 18-10-2010, 23:32   #5
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Hey Drew. Hi from down the dock!

LED lights are more sensitive to voltage drop than incandescent, so any current draw that is enough to cause line loss could do it. I have a similar setup using inexpensive led light strips and they do dim briefly when the fridge starts running as the inflow current causes a brief voltage drop across the entire panel. I only have 10ga wire feeding the lower-current panel. My stereo draws 3-5a if I really have it up loud (without dimming), if you were running something less that 10ga to the panel, that might do it.

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Old 19-10-2010, 00:06   #6
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LED lighting

Lots of misinformation in this thread.

LEDs running on direct current do NOT flicker at all, they generate continuous output. They also do not generate RF interference, they are nothing more than diodes that emit light.

Are you driving the LED strips from 120V shore power? In that case you probably have a low-voltage power supply to run the strips. If the power unit is a switching type, it may be a source of RFI that you hear in the stereo an VHF radio (switching supplies incorporate a high-frequency oscillator).

When the LEDs flicker with the beat of the music, it means you're getting a voltage drop due to resistance in your power wires. Try heavier gauge lines from the house or shore power to the stereo unit.
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Old 19-10-2010, 00:13   #7
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Can you provide more detail about the interference in the stereo and VHF? I agree with socal... the leds are pretty simple, assuming you're driving them directly off 12v.
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Old 19-10-2010, 00:23   #8
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Quote:
Originally Posted by sail_socal View Post
Lots of misinformation in this thread...Try heavier gauge lines from the house or shore power to the stereo unit.
Nope. Heavier wires to the stereo is not what is needed. To avoid dimming lights with loud sounds one perhaps needs heavier wire from the power source to the panel supplying the stereo AND lights.

But the internal resistance of the batteries is probably more than the existing wires, so there is no good solution.
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Old 19-10-2010, 10:07   #9
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The easiest solution to the stereo induced flicker is an electrolytic capacitor across the 12 volt input to the LED string.

No need to add extras in the middle of the string(s).

Voltage rating of the electrolytic should be higher than the highest expected voltage in the circuit.

I'd start with a 1,000 ufd/25 volt. Positive to positive, negative to negative.

The actual capacitance isn't at all critical, more needed with more load, i.e. more LED's.

You might get by with considerably less.

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Old 19-10-2010, 10:51   #10
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Originally Posted by sail_socal View Post
Lots of misinformation in this thread.

LEDs running on direct current do NOT flicker at all, they generate continuous output.
Last I checked light travels at a frequency, as I said, far too fast to be detected by the human eye.
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Old 19-10-2010, 11:13   #11
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Some LED drivers utilize a switching power supply (DC/DC converter). It could be producing the noise.
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Old 19-10-2010, 11:36   #12
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Last I checked light travels at a frequency, as I said, far too fast to be detected by the human eye.
*groan*!

as far as I can tell, the LED strips do not have any form of pulsewidth modulation circuit to provide dimming or DC/DC conversion, and they're running directly off of the 12v supply.

I *am* currently on shore power (a rarity for me), but the shore power is going through an Ample Power PSC30-12 DC power supply to give me 12v onboard.

The stereo is a tiiiiiny little 20w amplifier with no bells and whistles, just a little box with RCA inputs, speaker outputs and a volume knob... perfect for the iPod. It barely drives the speakers, but they're an old set of Bose bookshelf speakers with decent efficiency so it sounds ok. I am currently powering it directly from the 12v system, but it came with a 12v 400mA wall adapter, so imho it shouldn't be drawing enough to flicker the lights!

Senormechanico - since I have all of my lighting for each cabin tapped off a junction box (with 14ga going to that box), would it be ok to add a larger capacitor further up the chain, ie covering all of the lighting?

...further to that, each light has an independant switch. if the lights are switched off, will the capacitor across the still-active lines mean a small-but-steady drain on my batteries?
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Old 19-10-2010, 13:07   #13
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Drew,
The capacitor needs to be at the head of the light string, closest to the power source.
The junction box sounds like an obvious spot.
You could also put one at the power leads to the stereo.
It would serve the same purpose.
No discernable drain from the capacitor, maybe measurable, but not enough to consider.

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