The pitfalls of using cheap chinese power supplies

[fasteddy]

I spent all weekend chasing a flickering issue with my lights on my display this weekend, many many hours of frustration. I have now somwhat overcome this issue by keeping the dmx cables as short as possible by placing the DR4s close to the controllers which meant a total reconfigure of my display
After going through a tedious process of elimination the issue has come down to the cheap chinese power supplies generating EMI (electro magnetic interferance)
This issue is seen when the power supplies get loaded somewhat by using colours like aqua, yellow, purple and white and is seen especially when dimming or cross fading these colours. What appears to be happening is the data signal is being effected and this seems to be radiating through the gutters where i have strip mounted and the longer runs of DMX cables (cat5) are acting like big antennas and absorbing this generated EMI. Some EMI issues could be easily sorted by moving a cable a certain way even though it was no where near any mains cabling.
So now with the changes i have done I have been able to eliminate 90% of the flickering which is now to a somewhat acceptable level.

So the question I have is would placing a capacitor on the output of the 350 watt PSUs help with reducing this and if so what size capacitor would best suit.

But in the end ive learnt a lesson here and that is spend the extra cash and buy some quality power supplies like the meanwell brand or else you could be in for a very frustrating time but i dont have the budget for that this year so ill have to deal with what I have

 

[David_AVD]

Not sure if you recall, but we went through a bunch of filtering options with Ryan's 24V "knock off" power supply last year. His PSU caused interference to his CCTV cameras and modem.

The only thing that seemed to fix the situation for him was replacing his PSU with a genuine Mean Well unit. Sorry, probably not what you wanted to hear.

 

[fasteddy]

Not sure if you recall, but we went through a bunch of filtering options with Ryan's 24V "knock off" power supply last year. His PSU caused interference to his CCTV cameras and modem.

The only thing that seemed to fix the situation for him was replacing his PSU with a genuine Mean Well unit. Sorry, probably not what you wanted to hear.

I accept thats what i will have to do next year but im just looking at some things to try to see if it can be further reduced, nothing tried nothing gained

 

[Mike]

Eddy is it just one of the PSU's or all of them doing this?

 

[fasteddy]

Just so everyone knows the power supplies i have are the 12vdc 350 watt power supplies purchased from Ray Wu. In the end you pay for what you get.
I reakon others are having this issue as ive heard reports of flickering in other post/forums

As far as if its only one PSU or all or a few i have not been able to get to this level until i have some decent power supplies to test with. Im sure its more than just the one as i had two sections that were doing this and both did this without the other connected.

 

[fasteddy]

Now to confirm 100% this issue is created by the cheap power supplies, David_AVD has been kind enough to send me a few 320watt meanwell power supplies to replace the existing cheap chines ones . If all the reamining flickering goes then that will confirm that its the power supplies causing this issue.
I hope to change these over next weekend, and im feeling confident that this will fix the issue, but it will be nice to actually confirm this once and for all so all can be wiser from my hardship
So stay tuned for the results.

 

[Mike]

would one of these help?
http://www.jaycar.com.au/productView.asp?ID=MS4001&keywords=emi+filter&form=KEYWORD


Hope you sort this out eddy

 

[fasteddy]

I did try an industrial 240v power conditioner on the supply and this didnt seem to help, so im not sure if the EMI is generated in the 240vac side or the 12vdc side. In testing in the garage i never saw these issues it was only when it all went up that this became a major issue. either way the meanwell PSUs that are coming should confirm if its the power supplies.

 

[David_AVD]

This is what some of the fake Mean Well power supplies look like:



It has the M W in red to imply it is Mean Well, but is not the same as the real Mean Well power supplies.

 

[Beacy]

In comparison to??

 

[David_AVD]

I'm glad you asked Beacy. Here's a genuine Mean Well power supply. Notice the lack of bent ends!

 

[Beacy]

In order to help identify the bodgy PSU's what brand markings do yours have Eddy as mine are marked as "ZWD" not Meanwell. As Ray gets his stock from a variety of factories, if it relates to one brand it may be worth notifying him of the issue with one particular brand as I did notice the "real" Meanwell is made in China.

 

[David_AVD]

Good point. Just because it's made in China doesn't make it bad. It think Eddy was trying to emphasise the cheap part, not necessarily the Chinese part. It's just that China seems to make more than their fair share of copies and dodgy stuff.

 

[fasteddy]

Most things are made in China, whats important is the design. Ill get details of the Power supplies im using, but the cheap $17 powers supplies are $17 for a reason and thats the reduced design specs which can then make it a hit and miss issue and when it misses it can cause a great deal of extra work and effort to find the issue.
As far as any more testing, all im going to do is replace the power supplies to see if the issue goes completely, this issue has already sucked up a whole weekend and has now put me behind so i now need to focus on more important things like finishing sequencing and putting in the final elements. but then once i have everything in place i can focus on further testing

 

[AAH]

I'm a little dubious myself that changing to the meanwell supplies will fix the problem. The rs485 cabling and standard should make it fairly immune to noise. My first thought without being able to diagnose the problem myself would be the possibly of ground loops cause by the fact that most of the supplies out there have the 0V rail connected to Earth. This provides the possibility of earth loops all over the place depending on how stuff is connected back to the mains. I'm kinda hoping that the meanwells don't fix the problem and that it's a wiring issue as i have a bunch of Rays power supplies that I will be using. Fortunately I have the tools (oscilloscope etc) to trace potential faults down.
With Eddys displays and so many dimmed channels going on and off at relatively high frequency with lovely sharp on/off transitions there will be massive amounts of RF noise floating around. i certainly hope that no-one listens to AM around your way Eddy.
I'll be waiting with baited breath to hear the results of the changeover from Ray to Meanwell