Strange behaviour on a DMX chain

[sunray]

On 11/2/2023 at 11:27 PM, sunray said:

A completely different situation but I worked on an all LED system consisting of fairly cheap 8"  (par64) 150 LED fittings. The thing about them being all DMX was buffered in each fitting and they could work master/slave but still controlled by DMX.

However (I hope I remember this right) the master fitting sent data to the slaves on DMX 1-4 then forwarded incoming data on addresses 5 and above.

Hopefully this may make some sense, starting at the desk on the left any fitting on the DMX line before the master would follow the channels on the desk. After the master (Column 'F') all of the addressess are increased by 4 with the slave taking the 1-4 position.

Adding another master fitting added its slave at DMX 1-4 and moves everthing beyond it up 4, it doesn't take too much to realise that with multiple masters in the system there could be fittings dotted around the system addressed 5, 9, 13, 17 all controlled by desk channels 5-8.

 

Giving that some comparison with this thread, I realise the DMX line is continuous (not buffered in each fitting) but if the PI line were somehow able to change addresses in the system (corrupted)...

My apoligies, my comparison is really badly flawed. I was trying to work on the theory the units may be able to regenerate the DMX data at a different address but of course the ins and outs arecontinuous and such operation would be impossible. Sadly I can't delete old posts.

[sunray]

7 hours ago, Stuart91 said:

Just checked the one photo I have of the innards of the enclosure. 

Brown is connected to DMX positive on the CasDMX (lining up with A on the drivers)

Blue is connected to DMX negative on the CasDMX (lining up with B on the drivers)

Black is connected to "Return" on the CasDMX (lining up with GND on the drivers)

 

The internal wiring inside the enclosure uses different colours (I'm guessing whatever fell to hand as they finished off the wiring...) so it's not as straightforward to trace as it should be.

Thank you, that makes much more sense than your orignal description.

I know only too well the problems of random wire colours and have to confess to doing the same thing myself when pushed.

7 hours ago, Stuart91 said:

Meanwhile I've had a further play with the unit I have in my workshop at the moment. I hooked it up in a DMX chain with four other fixtures (just random LED battens from our hire stock, which are the same 4-channel RGB+White for control). No matter the order of fixtures in the chain, I can't get the same misbehaviour as I saw on site. 

However, I was able to connect the green wires (PO and PI on the driver) to my mains earth temporarily. The fixture started flickering immediately, although there wasn't any effect on the others in the chain. 

 

I've had radio silence from the fixture supplier regarding their opinion on what PI and PO are meant to be used for, so I'm inclined to agree with Tim and David's suggestions above. 

I'm guessing the PO  should not be connected to earth as it seems to be an output. Have you tried connecting it to the return black position instead?

 

1 hour ago, timsabre said:

David is right about the auto addressing thing. Ignore my comment about power.

I suspect you are closer to the mark than you think.

There is potentially a lot of (very high impedance) volts between ground black and mains earth and data flying around in the miswired PI/PO's.

I'm guessing the installer had no idea what the green/yellows are used for and assumed they are simply 'earth' as so many electricians do.

[Stuart91]

2 minutes ago, sunray said:

I'm guessing the installer had no idea what the green/yellows are used for and assumed they are simply 'earth' as so many electricians do.

That's exactly my suspicion too. I've since met the guy, he's a perfectly competent (if grumpy) spark, but has zero experience of DMX or these units. 

[sunray]

9 hours ago, Stuart91 said:

That's exactly my suspicion too. I've since met the guy, he's a perfectly competent (if grumpy) spark, but has zero experience of DMX or these units. 

And how many times have we encountered work done by electricians that is well beyond their abilities and rather than find out what the wires are for, just randomly tack them onto a random terminal and if it doesn't go bang just walk away?

[pmiller056]

In an installation with a mains electrical supply present, I would reasonably expect to find green/yellow coloured cable cores to be used as the safety earth/ground connection and never for any other purpose. If a green/yellow core in a cable is used for another purpose (even in a SELV application), it should have another colour sleeve fitted over it to show that it is not being used for an earth/ground function.

[sunray]

13 hours ago, pmiller056 said:

In an installation with a mains electrical supply present, I would reasonably expect to find green/yellow coloured cable cores to be used as the safety earth/ground connection and never for any other purpose.

I totally understand where that comes from. Your view is extremely common and some will even go so far as saying it's the only way it complies with BS7671.

Do you feel the same way about brown only being used for phase and blue for neutral?

 

13 hours ago, pmiller056 said:

 If a green/yellow core in a cable is used for another purpose (even in a SELV application), it should have another colour sleeve fitted over it to show that it is not being used for an earth/ground function.

For all we know it may have done prior to the cables being shortened but if I was presented with an appliance with 3 'earth', 3 phase, 3 neutral and 2 more phase wires I'd PDQ be looking at the MI's.

The mere fact that

On 11/6/2023 at 10:34 AM, Stuart91 said:

...I've since met the guy ... has zero experience of DMX or these units. 

as this was originally wired as a DMX product tells me that he MUST HAVE read the MI's otherwise it would have been impossible for him to install it.

 

I personally have encountered too many products which use the green/yellow for another purpose to be complacent. Even our good old british RS used to sell proximity switches for a while with standard harmonised colours for a changeover device.

Edited November 7, 2023 by sunray

[Stuart91]

13 hours ago, pmiller056 said:

In an installation with a mains electrical supply present, I would reasonably expect to find green/yellow coloured cable cores to be used as the safety earth/ground connection and never for any other purpose. 

Hi Peter. 

As others have said, that's a fair point. We also wouldn't expect DMX to be run in H07 rubber flex either.

There may well have been some other instructions / labelling on the cables but they have definitely been cut to suit and there's nothing obvious now. Whilst there is a CE mark on the LED driver, I think we all know what they're worth...

Manuals or instructions have been thin on the ground, and there's been quite a bit of uncertainty about what the PI and PO terminals actually do. 
 

31 minutes ago, sunray said:

as this was originally wired as a DMX product tells me that he MUST HAVE read the MI's otherwise it would have been impossible for him to install it.

Good point, my suspicion is that there have been an incomplete manual, or some verbal instructions issued at the time that were misremembered. 

[sunray]

1 hour ago, Stuart91 said:

Manuals or instructions have been thin on the ground, and there's been quite a bit of uncertainty about what the PI and PO terminals actually do. 

 

Good point, my suspicion is that there have been an incomplete manual, or some verbal instructions issued at the time that were misremembered. 

Or the DMX side of the instruction made some semse and the PI/PO part was beyond comprehension.

At this time I still have no idea what to do with PI,  however my searches have found  here: 

The driver looks fairly similar, albeit the markings show RED, blue, black and green despite the cable being brown.

[Stuart91]

This job has bounced back into my court today. 

The contractors removed all of the PI and PO connections. No change to the behaviour of the fixtures. 

I still wonder if we've got a wiring issue on the remaining DMX signal, but the problems when they occur seem to be consistent and repeatable - it doesn't feel to me like a dodgy connection that's coming and going. 

But meanwhile, other fixtures in the installation have started misbehaving (spontaneously) despite their "clusters" having not been touched. 

I think the only thing that will get us a permanent resolution is adding a DMX split to each cluster. Which gives me my next challenge, finding a small DMX splitter with a minimum of four outputs which can ideally be hardwired and as small as possible to fit into the enclosure...

[Bryson]

For a tiny splitter: Pathway DIN-mount PWREP4:

 

 

4"x4.5"x1.85".  Doubt you'll find much smaller.

 

 

[Stuart91]

1 minute ago, Bryson said:

For a tiny splitter: Pathway DIN-mount PWREP4

Looks excellent. 

I don't suppose you know if the screw terminals are likely to accept the 1sqMM H07 flex that's been foolishly used in this installation?

[Bryson]

Ah, that might be an issue, for sure.  I don't know the exact size but they're normal "euroblock" size terminals.

 

The UK contact might be able to tell you, though:  
Simon Aldred
+44 75 4072 6384
Simon.Aldred@eldoLED.com

 

 

[sunray]

3 hours ago, Stuart91 said:

Looks excellent. 

I don't suppose you know if the screw terminals are likely to accept the 1sqMM H07 flex that's been foolishly used in this installation?

I'm not able to open that link but if anything like these devices take 2x 1mm in a double ferrule with ease

Edited November 29, 2023 by sunray

[sunray]

5 hours ago, Stuart91 said:

This job has bounced back into my court today. 

The contractors removed all of the PI and PO connections. No change to the behaviour of the fixtures. 

I still wonder if we've got a wiring issue on the remaining DMX signal, but the problems when they occur seem to be consistent and repeatable - it doesn't feel to me like a dodgy connection that's coming and going. 

But meanwhile, other fixtures in the installation have started misbehaving (spontaneously) despite their "clusters" having not been touched. 

I think the only thing that will get us a permanent resolution is adding a DMX split to each cluster. Which gives me my next challenge, finding a small DMX splitter with a minimum of four outputs which can ideally be hardwired and as small as possible to fit into the enclosure...

Without going back over posts am I right that these are radio linked? I wonder if that might be getting corrupted.

[timsabre]

It's using Casambi which is a wifi protocol a bit like what Google Alexa does. The DMX is coming from a Casambi to DMX gateway unit. But wifi issues would not cause a loss of DMX to individual fixtures as is being described.