DALI communications setup not working

Hello,
Please help us with our lamp which sometimes fails to correctly interpret DALI signals that are sent to it.

We have an offline, non isolated 150W LED lamp which is DALI dimmable.
In fact, whilst in the factory, before we ship the product, we send it a DALI signal which tells it what power level to start at, when its installed by the customer.
However, in the factory, when the mains cable running to the lamp was long, the lamp would not correctly interpret the DALI signal. When we shortened the mains cable, the lamp would correctly interpret the DALI signals.

The attached pictures show the setup which does not work, and the setup which does work.

It is inconvenient for us to use the short mains cable. What can we best add to the “long mains cable” setup to make it work?
I was thinking of passing the mains cable through a high permeability ferrite torroid several times just before it enters the lamp. Would this be best?

(incidentally, the lamp has a small 1W Buck converter bias supply, but the LED drivers operate in linear mode. The Buck converter has a differential mode CLC filter before it. There is no common mode filtration. That is, no Y capacitors and no common mode choke in the lamp. In fact, on the lamp PCB, upstream of the mains rectifier bridge, there is no filtration components at all, either diff mode or common mode.)

Using two extension reels is a perfectly acceptable and practical way of testing over longer distances. For telecoms tests I often used several 500m reels of cable in series to emulate typical run lengths.

The only thing that should matter is the length of the DALI comms line but even that should be capable of considerable distances. The most likely reason for failure is your laptop power supply is creating interference against the extra inductance of the power cable but the only way to be sure is to see for yourself what the DALI receiver is actually picking up. Either the desired DALI signal is corrupted or it is obscured by interference. The cure depends on which it is.

I don't think the inductor idea will simulate real life installations, in fact it may create a whole range of new problems.

Brian.

the only way to be sure is to see for yourself what the DALI receiver is actually picking up. Either the desired DALI signal is corrupted or it is obscured by interference. The cure depends on which it is.

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Thanks, we scoped the DALI signal as it goes into the microcontroller on the lamp PCB....it looks fine.

I don't think the inductor idea will simulate real life installations, in fact it may create a whole range of new problems.

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Thanks, though just to clarify, (you probably understood this anyway), we are not trying to simulate the real life installations, we are just trying to set the dimming level of the lamp via the DALI signal , before the lamp is shipped.

Using two extension reels is a perfectly acceptable and practical way of testing over longer distances.

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Thanks, please may i clarify, the extension reels are not for "testing over long distances"...the extension reels are there because our actual production facility is currently closed for redevelopment, and in the temporary facility, we at first needed the long mains cable extensions in order to get the mains to the product.

The most likely reason for failure is your laptop power supply is creating interference against the extra inductance of the power cable

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Thanks,..this does sound like a very good explanation indeed. I wonder then, would we be able to mitigate it by putting an x capacitor at the mains input to the lamp?. You see, its more convenient to do this work with the long mains cable. We do have a 220n, 630V ceramic capacitor downstream of the mains rectifier bridge on the lamp PCB, but no capacitors upstream of the rectifier bridge.
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Incidentally, when we tried to send the DALI signal to the lamp at a different location, (in the engineering office) where the mains cable was indeed short ( about 1 metre), the DALI signal was not received correctly if the lamp’s heatsink was not earthed. (the lamp driver PCB sits on an insulation pad on top of the heatsink)….but it was received properly when the heatsink was earthed.

You have some strange signal paths in your products!

I wouldn't add a capacitor to filter the interference, get a filtered plug or an in-line filter and connect the laptop through it. Something like this should work:
https://www.rapidonline.com/yunpen-...ilter-2-x-3-7-mh-250-v-ac-50-60hz-1-a-50-3968

Brian.

If this ideal setup causes trouble, have you ever tested your device in real DALI conditions, where the DALI signal runs side by side with the 230V supply in a 5 wire cable, with length up to 300m? 8-O

I wouldn't add a capacitor to filter the interference, get a filtered plug or an in-line filter and connect the laptop through it. Something like this should work:
https://www.rapidonline.com/yunpen-y...hz-1-a-50-3968

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Thanks, we will do that.
Also, we wish to be sure that in the installation, the DALI signal doesnt get wrongly interpreted, so i suspect we need some common mode filtering at the mains input to our product. Do you confirm that we seem to have a common mode noise susceptibility problem in our lamp? Though i appreciate that at the installation, there will not be a laptop installed alongside the lamp , so its maybe not as bad...but i suppose we never know which major electrical noise sources are going to be near to the installation.

If this ideal setup causes trouble, have you ever tested your device in real DALI conditions, where the DALI signal runs side by side with the 230V supply in a 5 wire cable, with length up to 300m?

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Thanks, but I don’t believe that that would be a particular problem. The problem is, we believe, the fact that in our production test facility, we have a laptop with a noisy power supply, which is fed from the same long mains cable that the lamp is fed from….and the laptop PSU, is drawing significant noise currents from the input terminals of the lamp, due to the high impedance “seen” going back to the mains. Do you agree?

In the installation, we believe that the long mains cable running to the product will serve as a nice little bit of filtration to any noise which may otherwise pervade around/in the lamp.

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Post #12 of this the following thread
https://www.edaboard.com/showthread.php?t=367927&p=1576544#post1576544
..appears to imply that we cannot solve our DALI problem by adding a mains filter to our product. Is this definitely the case?
(By “mains filter”, I mean a diff mode and common mode filter at the AC input to the lamp)

treez said:

Thanks, but I don’t believe that that would be a particular problem. The problem is, we believe, the fact that in our production test facility, we have a laptop with a noisy power supply, which is fed from the same long mains cable that the lamp is fed from….and the laptop PSU, is drawing significant noise currents from the input terminals of the lamp, due to the high impedance “seen” going back to the mains. Do you agree?

Click to expand...

My concern is that there's a lot more noise out there in the field, and DALI bus is designed to run in parallel with mains, in the same 5-wire cable, over long distances. So capacitive coupling of mains noise to your DALI wires could be much worse than your present testcase.

I suspect your DALI input is too sensitive to noise, and would get another DALI device to see if that operates properly in the same setup. A simple LED driver like the TCI Mini Jolly DALI should be sufficient for this test.