LightOfCy Posted December 18, 2013 Share Posted December 18, 2013 Hi,I have a DMX RGB controller to control some High voltage (110V DC RGB ribbon tape)The problem I am having is I am getting 48V AC @ 100mA between Ground/Earth/ Casing and the 3 pin DMX pins!! When I add additional DMX/RGB controllers the voltage is added. I will need Three controllers in series for the installation I am using but this equate to around 120V AC on the pins.I am using a stainless wall plate where I am also testing this voltage and under EEC regulations this is obviously not acceptable. I need to know why I am getting this voltage? (is it common to see?) Would a 120 ohm resistor cure this ( I believe the resistor is just for signal clarity?) I will be stripping down a controller over the next few days to try and fault find this phantom voltage but any help will be appreciated. Link to comment Share on other sites More sharing options...
timsabre Posted December 18, 2013 Share Posted December 18, 2013 What controller/driver is powering the LED tape? Sounds a bit scary - it sounds like the ground of the LED driver is floating above mains ground (where the DMX common is). 100mA is a lot though. A DMX splitter with opto isolated outputs would get it working, but obviously there is a safety issue here that you need to resolve. Link to comment Share on other sites More sharing options...
LightOfCy Posted December 18, 2013 Author Share Posted December 18, 2013 What controller/driver is powering the LED tape? Sounds a bit scary - it sounds like the ground of the LED driver is floating above mains ground (where the DMX common is). 100mA is a lot though. A DMX splitter with opto isolated outputs would get it working, but obviously there is a safety issue here that you need to resolve. Its a controller from the far east.I have one in bits now, the earth cable just goes to the metal casing so at least that is safe but the voltage is being transmitted up the DMX cable to the stainless wall controller, like you say this is scary and by no means can I use is as is. On the circuit board the positive and neutral cables from the mains go through a rectifier / then uses mosfets to control the red, green & blue output. On the low voltage/DMX side the same kind of set up. Should the circuit board be earthed at some point as this voltage is just floating around at main kind of voltage. should the DMX 0v be grounded or should this be floating at a lower voltage level e.g. 5V?? Cheers Cy Link to comment Share on other sites More sharing options...
timsabre Posted December 18, 2013 Share Posted December 18, 2013 DMX 0V should be at the same potential as mains earth, because it will be connected to earth at the control desk. DMX interface chips (RS485 standard) will withstand a voltage of 12V before things start blowing up. This sounds horribly like there is no isolation between the mains and the DMX side. If this is the case you should place the item in the bin and walk away quickly. How is the "low voltage" side connected and/or powered? Link to comment Share on other sites More sharing options...
sleah Posted December 18, 2013 Share Posted December 18, 2013 This sounds rather like the old disco sound to light units (the one's with Bulgin outputs :) ) where the entire PCB floated at some lovely high voltage. most had no external connections except mains, and if they had a sound input it always went through an isolation transformer. I reckon this controller should *really* have an opto-isolated input! :o Link to comment Share on other sites More sharing options...
Brian Posted December 18, 2013 Share Posted December 18, 2013 Got a camera to hand? Post up a decent photo of the PCB, ideally both sides. Link to comment Share on other sites More sharing options...
musht Posted December 18, 2013 Share Posted December 18, 2013 110V tape sounds unusual as well, any reason for using this over a low voltage 12/24V tape? Link to comment Share on other sites More sharing options...
timsabre Posted December 18, 2013 Share Posted December 18, 2013 110V tape sounds unusual as well, any reason for using this over a low voltage 12/24V tape? Think of the length of tape you could drive ... 12V you can only go about 5m before volt drop kills the green and blue, but 110V would go just about forever (well, 50m probably) Link to comment Share on other sites More sharing options...
LightOfCy Posted December 18, 2013 Author Share Posted December 18, 2013 Got a camera to hand? Post up a decent photo of the PCB, ideally both sides.Thanks for all of your replies. Here are some photos. I am trying to see if I can modify the pcb the bring this voltage down as the controllers and LED tape etc have all been supplied by the person that I am doing the project for. If it comes down to it I will have to tell them the product is not suitable for the application but I like a challenge. The last photo is just to shown the device, the cheap meter wasn`t reading the voltage. I now have purchased a decent meter. http://i1114.photobucket.com/albums/k524/86cybus/IMG_20131218_130021.jpg http://i1114.photobucket.com/albums/k524/86cybus/IMG_20131218_125955-1.jpg http://i1114.photobucket.com/albums/k524/86cybus/IMG_20131218_125943-1.jpg http://i1114.photobucket.com/albums/k524/86cybus/IMG_20131210_162925.jpg http://i1114.photobucket.com/albums/k524/86cybus/IMG_20131210_161138.jpg Link to comment Share on other sites More sharing options...
timsabre Posted December 18, 2013 Share Posted December 18, 2013 OK so it does have isolation from the mains.I would try putting a link on between the 0V of the low voltage side and mains earth. Link to comment Share on other sites More sharing options...
LightOfCy Posted December 18, 2013 Author Share Posted December 18, 2013 OK so it does have isolation from the mains.I would try putting a link on between the 0V of the low voltage side and mains earth. ok just to clarify, from the 0v from the voltage reg link to earth/ case?I was considering this. cheers Link to comment Share on other sites More sharing options...
timsabre Posted December 18, 2013 Share Posted December 18, 2013 I would go from the pad where it says SGND on the board, near the DMX connectors. Or from the Pin1 pad of one of the DMX connectors. Link to comment Share on other sites More sharing options...
Shez Posted December 18, 2013 Share Posted December 18, 2013 The problem I am having is I am getting 48V AC @ 100mA between Ground/Earth/ Casing and the 3 pin DMX pins!! Your last photo shows 24mV DC? Link to comment Share on other sites More sharing options...
LightOfCy Posted December 18, 2013 Author Share Posted December 18, 2013 The problem I am having is I am getting 48V AC @ 100mA between Ground/Earth/ Casing and the 3 pin DMX pins!! <br style="color: rgb(28, 40, 55); font-size: 13px; line-height: 19px; background-color: rgb(250, 251, 252);">Your last photo shows 24mV DC? the last photo was just for identification. the meter I was using didn`t show the voltage, even though you could feel it when you touched the wall controller. A new meter ( better quality) has now been purchased. I have now grounded the Pin1 on the XLR DMX plug and the system still works ok. I can`t fathom why this is not designed like this from the factory and I shall be inquiring to find out. Link to comment Share on other sites More sharing options...
timsabre Posted December 18, 2013 Share Posted December 18, 2013 the last photo was just for identification. the meter I was using didn`t show the voltage, even though you could feel it when you touched the wall controller. A new meter ( better quality) has now been purchased. I think Shez was suggesting you should maybe have set it to AC mode rather than DC. "Designed" is a difficult concept when dealing with chinese electronics. They are very good at copying and modifying existing circuits and building things very cheaply, but (in my experience at least) not so good at actually understanding how it works. Link to comment Share on other sites More sharing options...
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