Richard P-W Posted December 18, 2013 Share Posted December 18, 2013 Looking at the PCB, is that a MOV (near the small transformer) that links the signal ground to the -ve output of the bridge rectifier? Most likely the source of the leakage you are measuring. Link to comment Share on other sites More sharing options...
Nicktaylor Posted December 18, 2013 Share Posted December 18, 2013 This is an interesting discussion. My question is not so much technical but liability. Client bought the bits. Op is trying to modify to make it safe. What happens if an accident happens and someone is hurt? Link to comment Share on other sites More sharing options...
Brian Posted December 18, 2013 Share Posted December 18, 2013 Looking at the PCB, is that a MOV (near the small transformer) that links the signal ground to the -ve output of the bridge rectifier? Most likely the source of the leakage you are measuring.It'll be a capacitor, put there to give the unit some sort of chance of meeting EMC requirements. It means that as originally designed the unit didn't have an incoming earth connection so you bypass any RF on the LV side back to a low impedance point on the HT side. And yes, they are a frequent source of stray voltages. Link to comment Share on other sites More sharing options...
bigclive Posted December 18, 2013 Share Posted December 18, 2013 It's the standard issue of switchmode power supplies where capacitive coupling occurs between primary and secondary windings and also through the blue capacitor between the high and low voltage side of the transformer. As the others have said, earthing the low voltage ground will generally solve that issue. The current would have been very low, but enough to be felt when the case was touched (literally millionths of an amp) and enough to cause weird meter readings on a typical 10-Megohm input impedance meter. By the way, the earth core of a cable is not suited for use as one of your output channels. Causing someones electrocution if they believe it to actually be an earth wire could see you being charged with manslaughter. Link to comment Share on other sites More sharing options...
LightOfCy Posted December 19, 2013 Author Share Posted December 19, 2013 It's the standard issue of switchmode power supplies where capacitive coupling occurs between primary and secondary windings and also through the blue capacitor between the high and low voltage side of the transformer. As the others have said, earthing the low voltage ground will generally solve that issue. The current would have been very low, but enough to be felt when the case was touched (literally millionths of an amp) and enough to cause weird meter readings on a typical 10-Megohm input impedance meter. By the way, the earth core of a cable is not suited for use as one of your output channels. Causing someones electrocution if they believe it to actually be an earth wire could see you being charged with manslaughter. Thats a very good point, the output wire are coloured RED, BLACK, BLUE and GREEN/YELLOW (earth cable) these do terminate into a sealed four pin socket which the plug side has the wires RED, BLACK,BLUE and GREEN or YELLOW. Unless the user cuts and strips the cable leaving the controller they would be non the wiser.I am always very aware about items from the far east Thank you all for the responses, I have earthed the DMX 0v pin internally and all seems to working fine with no stray voltages at all now. I shall leave the set up on test just to make sure nothing un-toward appears. Link to comment Share on other sites More sharing options...
timsabre Posted December 19, 2013 Share Posted December 19, 2013 As Brian hints, the modification will probably invalidate the EMC testing of the unit and may make it radiate interference over the limit (supposing it was ever tested in the first place which it probably wasn't). Link to comment Share on other sites More sharing options...
LightOfCy Posted December 20, 2013 Author Share Posted December 20, 2013 As Brian hints, the modification will probably invalidate the EMC testing of the unit and may make it radiate interference over the limit (supposing it was ever tested in the first place which it probably wasn't). My first issue with the installation was an interference as it is being used along side a motor controlled system. I managed to suppress the mains supply using an RS filter and this eliminated the interference. When I managed to ask the supplier of the DMX controller what suppression/filters has the product got, I got the incline that it was very minimal if any so what you say fits the bill.Cheers everyone and have a Merry XmasCy Link to comment Share on other sites More sharing options...
Brian Posted December 20, 2013 Share Posted December 20, 2013 I'm sure you know this and I'm sure it won't be a problem but, as the systems integrator, you are responsible for ensuring the installation does not cause any interference and that it meets CE marking requirement. Remember... CE + CE ≠ CE Link to comment Share on other sites More sharing options...
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