High Pitched Tone From LED Driver

Discussion in 'The Projects Forum' started by Cofpalos, Dec 7, 2013.

  1. Cofpalos

    Thread Starter New Member

    Dec 7, 2013
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    Hello!

    I'm working with a guy on converting a school bus into a party bus. We all the bells and whistles from TVs, speakers, and LED lighting. I've installed many AV systems into cars, boats, and houses over the years, but this was my first time working with LED lighting.

    So here's the break down...

    We purchased and installed 7.5 rolls (120') of RGB High Density LED light tape. Installed an LED driver/controller with keypad, which was made for limos. Also 6 speakers with 2 full range amplifies.
    On the original installation, I was unaware that HD LEDs were purchased instead of SD LEDs. This doubled the current draw and in turn cause a defeat in the LED driver, I believe. So we replaced the driver and added a relay to take the load off of the driver. Lights now dim and cycle perfectly.
    But...
    When you turn on the stereo with amps a very loud high pitched tone is heard through the speakers. With further research we found this tone was a product of the driver and it faintly travels through other switches(lighted) and lights. At the moment we have the amps bypassed and the lights "work" fine, but a faint tone is heard coming from the driver.

    Any input would be great. Below are the links for the product.

    Thank you in advance!

    LED Tape Lights
    http://www.hitlights.com/ls5050-rgb-extension.html
    LS5050_RGB300WPNA

    LED Driver
    http://www.mtgparts.com/lighting/litesync-rgb-driver/
    LED-RGB-MOD

    Basic hookup diagram
    [​IMG]
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Classic ground loop. The chopping frequency used in the LED driver is modulating the current that flows along the bus body/frame. Your audio system is connected to the bus body (ground?) in more than one place, violating the principle of "single point ground".

    Good luck. One suggestion, lose the damn switching power supply that drives the LEDs. ( I hate switchers!)
     
  3. GopherT

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    Nov 23, 2012
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    The LED driver uses pulse width modulation to drive the lights in different colors. The 'carrier' frequency is likely 10k to 20kHz square wave and the duration of each pulse changes to make each color. That frequence can ring back if current load is high for the LEDs.

    You can dampen this in the same way as motor noise can be dampened from a Microcontroller.

    Add a diode to the + out from the relay and then a big capacitor (3300 uF) across the + out to ground (between the diode and LED strips). The high frequency of switchers (10k Hz or better) allows a reasonably small capacitor for the high current.
     
    Last edited: Dec 7, 2013
  4. MikeML

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    And I predict that this will do absolutely nothing to solve the underlying problem...
     
  5. GopherT

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    Nov 23, 2012
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    Well, how about offering a WORKABLE solution for the OP. I don't view a 15 amp linear supply as a workable solution, even if you "hate switchers". I am really interested in your offering.

    Edit: it may not be a perfect solution but it will be a significant improvement. And way more than your laughable prediction of "absolutely nothing".
     
    Last edited: Dec 7, 2013
  6. MikeML

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    I have solved these issues with sensors in robots (low level analog sensors mixed with high power motors/actuators) professionally. I also work with audio systems in aircraft, where the problem is getting alternator whine out of the audio. More recently, the racket comes from PWM used with Nav lights, Strobes and Landing lights.

    Filtering helps occasionally. Shielding helps slightly. but the only way to get rid of the audio squeals and howls is to understand "Single Point Ground" and how it applies to the audio wiring...
     
  7. GopherT

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    Well, your opinion on filtering has changed from "absolutely nothing" up to "occasionally".
     
  8. Cofpalos

    Thread Starter New Member

    Dec 7, 2013
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    I don't think it's a grounding issue. That cause more of a low freq hum in most cases. Audio system is also wired with a single point ground cause I wired it that way.
    Switching power supply?
    Many tread have mentioned using a Cap. Any recommendations? Amazon link, maybe.
     
  9. Cofpalos

    Thread Starter New Member

    Dec 7, 2013
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    Please excuse my poor English skills this morning. lol
     
  10. MikeML

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    I will believe you understand single point ground principles after you answer these questions:

    Where does the audio amp get its power, especially the 0V return?
    Is the 0V in the amp Ohmicly isolated from the shield on the audio input?
    Is the 0V in the amp isolated from the enclosure it is mounted in?
    Does the amp enclosure touch the bus frame?

    Where is the head end for the audio system? Away from the amp?
    Where does the head-end get its power?
    Where is Ov from the head end connected?
    Does the head-end enclosure touch the bus frame?

    Are any speakers connected to bus frame?

    Where do the lights get their power?
    Where do the lights get their 0V connection?
     
  11. Cofpalos

    Thread Starter New Member

    Dec 7, 2013
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    Same bolt as above

    I'm not trying to get into a ******* match with anyone. I've been beating my head over this for a while now. I'm not some car hack, trunk slammer. I'm just looking for some help.

    Thanks
     
  12. Cofpalos

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    Dec 7, 2013
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    While that didn't come out as expected. Sorry I'm writing from my phone.
     
  13. MikeML

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    Good answers and technique.

    Does the HU incorporate a FM tuner with a whip antenna? If so, try disconnecting the antenna while listening.

    Try lifting the HU and Amp's +12V leads and 0V leads from the battery chassis bolt (leaving everything else that is connected there still connected) and then measure resistance between lifted wires and chassis. If you have a true single point ground, then there should be no continuity. If you find a low resistance, then there is a path you (and I) haven't thought of...
     
  14. THE_RB

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    Feb 11, 2008
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    A lot of those cheap Chinese PWM LED drivers are really under-capped, causing them to draw their DC power in high current pulses.

    I would first put a large cap 2200uF or 3300uF DIRECTLY on the +pwr and GND terminals on the driver (as close to the dreiver as possible). That should help a lot.

    I apologise to GopherT if that is the same as what you were saying in post #3, as I wasn't sure if you were saying to put the large cap directly at the LED driver module.
     
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  15. GopherT

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    Nov 23, 2012
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    RB,
    I was maybe making it too complicated by adding a diode too. In any case, there was extra noise on the circuit and this thread so I appreciate you stepping in.
     
  16. Cofpalos

    Thread Starter New Member

    Dec 7, 2013
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    I will look a little more into ground loop, as well as, adding a capacitor on to the drivers power input.

    Also adding a diode to the relay might not be a bad idea.

    Any other ideas? I really want to hit this problem head on with a full bag of tricks!

    Thank you
     
  17. Cofpalos

    Thread Starter New Member

    Dec 7, 2013
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    So I found 3 different valued capacitors.
    3300uf 35V
    2200uf 50V
    3300uf 25V

    I'm assuming each one would work fine. But I'm going to install the 3300uf 35V to be safe.

    I was looking for diodes also...
    I was able to find a 5 watt diode also (1N 5365B)

    Now the only thing I'm just a tad confused about is the placement.
    I think one post said to install diode/capacitor on the relay powering the lights and another post said to install them on the driver itself. Please clarify.

    I have not been back to look at the bus for any grounding issues, yet.
     
  18. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    You should take power and 0V for you lights directly from the battery terminals; you can then be sure that you do not have any lighting currents flowing through the vehicle chassis and any other equipment, assuming there are no accidental 0V returns to chassis. If the problem does not go away; do the same with the audio system.

    If the noise is still present; then it may be that the audio system is picking up RF radiating from the lighting wiring, in which case careful cable separation and routing may be the answer.
     
  19. Cofpalos

    Thread Starter New Member

    Dec 7, 2013
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    So I had some time to return to my bus project today. I tried to install a cap on the input 12+ and Gnd terminals of the driver. This didn't fix the problem. Although I was able to check a few things out before I had to run.

    First off, the tone is only present when high current flow is needed. ie. White or Yellow lights cycle.
    Second, I didn't find any signs of resistence between the Ground terminals.
    Third, around 5volts is present on the R, G, B inputs.

    I will be returning to work on this issue in the morning. I found a line isolator that I will try to install. Also, I am going to increase the wire gauge and placement of a few of my ground connections.

    Does anyone see an issue in connecting my ground wire directly to the negitive post of the battery?

    Thank you
     
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