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Topic ClosedInstallation of rear camera - Event Date: 24 Jun 2017
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DavMar View Drop Down
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Posts: 592 		Direct Link To This Post Calendar Event: Installation of rear camera
    Posted: 24 Mar 2019 at 7:11pm
Originally posted by offgrid

I
I'm getting more curious how the LED lights in our trailers are driven, going to go take a look when I get the chance.


I believe at least the interior LED lighting are integrated LED bulbs with their own driver built in to maintain constant current flow but don't quote me on it! Wink
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Posts: 5290 		Direct Link To This Post Posted: 24 Mar 2019 at 11:29am
If you look at the IV characteristics of the LED's in GlueGuy's reference link you can see why control circuits or at least current limting resistors are needed. The IV curves go nearly vertical, meaning a miniscule voltage change causes a huge change in current. You also can have a thermal runaway effect. The voltage drop through a diode goes down and the currents go up when it gets hot, so once you turn on the LED's and they get warm, the currents go up, making them hotter yet, and so on. 

I'm getting more curious how the LED lights in our trailers are driven, going to go take a look when I get the chance.
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Posts: 2630 		Direct Link To This Post Posted: 24 Mar 2019 at 11:01am
There are all sorts of control circuits for LEDs. The more complex are in a 120VAC circuit, where the AC voltage needs to be rectified and then dropped down to a voltage that the LED can handle. Lower frequency (longer wavelength) LEDs operate at (usually) lower forward bias voltages than higher frequency (shorter wavelength) LEDs. So you will usually see infrared LEDs operating in the ~~ 1.2V area, and blue and white LEDs operating at higher voltages (3-4 volts depending). 

LEDs are more current operated devices, with forward bias current (usually) in the 10-30 ma range.

So in an automotive application, where "12 volts" actually varies between about 12 volts up to 14.6 volts or so, there will usually be some sort of current limiting circuit. In the simple case, you can stack LEDs in series, or maybe just use a current limiting resister to keep the current from going too high. More sophisticated LED lights will have some kind of current limiting circuit to keep the current from burning up the LED.

Here is a simple explanation of some of the issues. It's somewhat dated, but covers the basics.
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Posts: 5290 		Direct Link To This Post Posted: 24 Mar 2019 at 5:40am
Obvioulsy you need some kind of driver circuit to run LED's from a 120Vac supply, but I was wondering why you can't just string 4 LEDs in series and connect to a 12V supply and call it good, because white LEDs look like they want to operate at around 3V. 

It appears that you can if you have a well regulated 12V supply, but we don't. The problem is that the current flow through the diodes is very sensitve to how much voltage is applied to them. So if you have basically an infinte source of current like your house battery you need some way to control the current flow as the battery voltage changes. Hence the need for some kind of active driver circuit. Or, you can just use a dropping resistor or trim pot in series with the LED's. The resistor/trim pot will keep the current from getting too high when the battery voltage is high. That kind of passive dc circuit shouldn't create any rf noise.

So if you're a ham operator or AM talk radio fan or using wifi for video transmission and having trouble with noise from your LED lights you could make up your own lighting circuits with LEDs and appropriately sized dropping resistors or trip pots, or see if you can find a commercial product that comes that way. 

Maybe some ot the LED lights in our rpods already do, I've never opened them up to look. Has anyone?
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Posts: 592 		Direct Link To This Post Posted: 23 Mar 2019 at 8:24pm
Originally posted by offgrid

LEDs themselves are just diodes and operate at around 3-4Vdc so when fed a dc supply should not emit any rf noise.  So, power supply drivers for the LED lights must be the culprit. These are bucking power supplies to reduce the voltage in order to maintain constant current to the LED's, so they contain switching devices which can produce RF noise. 


offgrid, I think you have come up with the reason why some LED light strings put out RF interference. The driver for some reason never entered my mind and all I thought about was the LED bulb itself which we both know is just a diode. Good call!
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Posts: 5290 		Direct Link To This Post Posted: 23 Mar 2019 at 7:34am
LEDs themselves are just diodes and operate at around 3-4Vdc so when fed a dc supply should not emit any rf noise.  So, power supply drivers for the LED lights must be the culprit. These are bucking power supplies to reduce the voltage in order to maintain constant current to the LED's, so they contain switching devices which can produce RF noise. 
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Posts: 39 		Direct Link To This Post Posted: 23 Mar 2019 at 7:11am
I bench tested the unit, utilizing our 12 volt system on our vessel, no issues. When tested on the Rpod, interference, when the LED was still hooked up and none, when the LED was removed. In all fairness thou, the LED that I tapped into was right next to the camera antenna, probably too close. I had read somewhere with some other units, that the LED must be located 2” to 3” away from the antenna. In my application that would not have worked

Thanks again for the input 
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Posts: 592 		Direct Link To This Post Posted: 22 Mar 2019 at 8:38pm
Originally posted by Kahonu37

Did the camera install today. Pulled the center LED out an tapped into it with posiconnectors, for power. Hooked up the wireless system and was getting interference. Disconnected the LED and the interference went away. Go figure. Maybe it’s the style of camera. Kind of worked to my advantage, no new holes.

We also are live aboard cruisers, as a matter of info, I received this notification from the USCG,  on LED navigation lights interfering with with some VHF & AIS signals. See attached PDF website.


Thanks for the input


You learn something new every day I suppose? I spent over 30 years working on VHF radios and never had an RF interference problem from LED lights. Which doesn't mean it can't happen I suppose?

Tell me when you hooked up your system and I will assume you got your power from the LED light power wire was your video tearing or freezing up? I'm curious, because when I tested my camera system from the bench supply I was using the video was tearing and freezing up which made it of course not usable. I suspected that maybe the low amperage my power supply was putting out was the problem and sure enough once I raised it no video problems. So I'm wondering if the amperage to the LED lighting if you tapped off of for your camera maybe the problem??? Stranger things have happened as your Coast Guard bulletin points out.
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Posts: 1215 		Direct Link To This Post Posted: 22 Mar 2019 at 7:07pm
  The Furrion I think has a filter to block interference. I just double checked the manual it does have a filter for the camera. We have our camera mounted just below a rear LED strip of marker lights, and there is no interference in the picture that I can detect. Maybe a filter can be purchased to add to a camera that does not have a filter.
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Posts: 39 		Direct Link To This Post Posted: 22 Mar 2019 at 6:33pm
Did the camera install today. Pulled the center LED out an tapped into it with posiconnectors, for power. Hooked up the wireless system and was getting interference. Disconnected the LED and the interference went away. Go figure. Maybe it’s the style of camera. Kind of worked to my advantage, no new holes.

We also are live aboard cruisers, as a matter of info, I received this notification from the USCG,  on LED navigation lights interfering with with some VHF & AIS signals. See attached PDF website.


Thanks for the input
2018 179
2012 NISSAN XTERRA (retired 12/19)
2019 RAM 1500 WARLOCK (new)
A.R.E. V Series Topper
WDH Equalizer 600/6000
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