Powering DALI gateway

[alertcom]

Hi,

  New to exchange - if I am repeating the question, please point me to the previous answer

  We recently completed the installation of KNX lighting automation with DALI gateway MTN6725-0001 at an apartment which uses a Diesel Generator (DG) and has no inverter or UPS. So whenever power fails, there is a small time of 45 sec (dead zone) for the DG power to start. We use a small desktop inverter for the KNX power and hence KNX electronics is always on. We then tried connecting the same power to the DALI Gateway Line (L) terminal. With this, we see that the DALI bus is always powered on even during the 45 sec gap. But the power is cut off to the ECGs (some are Meanwell, some others Helvar) during the 45 sec dead zone. What puzzles us is that when the power comes back after 45 sec, some ECGs that were previously OFF turn ON. As you can see this is a big nuisance for the family staying there, especially if the power fails in the night or when they are away.

 So my question to the forum are:

   1. what is the recommended way to connect the DALI gateway power in a house with just a DG and no full house UPS where there will be a 45sec to 1 min dead zone?

   2. Does the standard mandate the ECGs to retain current state information (ON, OFF or Dim level) when power fails and revert to the same state when power comes back on?

   3. Is it a good practice to not connect DALI gateway to UPS power thereby forcing it to reboot every time power fails even if for < 1 min  ?

Regards

[Thomas_Rohde]

Hello and welcome to the forum! 😉

   1. what is the recommended way to connect the DALI gateway power in a house with just a DG and no full house UPS where there will be a 45sec to 1 min dead zone?
I am not sure if there is a recommended way due to the fact that your usecase is pretty special and that your installation is just a part of the total building.

   2. Does the standard mandate the ECGs to retain current state information (ON, OFF or Dim level) when power fails and revert to the same state when power comes back on?
Depending on the ECG you can define the state of the ECG when power comes back (See picture attached). Please double check that within your ETS-Project to make sure that the lights are switched off at least in the bedrooms. 

   3. Is it a good practice to not connect DALI gateway to UPS power thereby forcing it to reboot every time power fails even if for < 1 min  ?
If possible I would keep it powered.

[alertcom]

Thanks Thomas,

 My ETS setting for the ECG is exactly what you gave; but looks like the ECG loses it when power turns OFF momentarily. The only way to get it back is to make the Gateway reprogram it over the DALI bus. To make the Gateway to reprogram, we need to forcibly reboot it whereby it sequentially reprograms all the ECG's - hence the need to keep the Gateway out of the UPS power. Even with this we see quirky behaviors - for instance an ECG may turn ON instantly when power comes back and then turns OFF after some time when the sequential Gateway reprogramming process gets to it. The whole system looks very complicated and unstable - would appreciate a solution that consistently works.

[Heribert_Dölger]

Some background information why you see this behaviour:

The DALI gateway permanently monitors the status of all ECGs. Depending on the number of connected ECGs this process can take up to 2 min.

During the 45sec power cut in your installation the DALI gateway will have detected some of the connected ECGs as no longer present but the others not yet. If an ECG is detected as present again the DALI gateway will sned its last value to the ECG. But this will only happen for the ECGs that before were detected as "missing". Not for the others. This is why you see "strange" behaviour that after power return some ECGs are on and others are off.

The indicated parameter "Value on ECG Power Recovery" is written into the ECG. The ECG will adopt this value when power returns after a power cut, independent from the gateway. Instead of configuring a fixed value (0% as you mentioned) you should rather set this parameter to "last value". ECG value after recovery and value from the gateway then should be the same (as it was before the power cut) in case there is no new command coming via KNX bus.

[alertcom]

Thank you Herbert. What you said makes lot of sense for the case where the Gateway is always powered ON - the "missing" ECGs eventually get back to the right programmed state. I guess, if I delay the Generator dead zone to about 3 mins, all the ECGs may be reported as missing and they may all get back to the right state when power comes back on. Something to try out. 

I am still confused as to the right powering option for the Gateway - keep it on UPS and hence always on or allow it to reboot every time power fails.

[Heribert_Dölger]

With a delay of 3min on the Diesel Generator for recovery it would allow the DALI gateway to detect all ECGs as missing. Once they will be found again the DALI gateway will set the last value. Disadvanteage might be that the power is missing for longer time. 

But you could as well use the option to not buffer the DALI gateway (230V and KNX bus power) and use the parameter "last value" inside the ECGs to let the them adopt the latest value after re-powering the ECGs.

[alertcom]

Yes. 3 min delay may not be acceptable to the client. I was only referring to testing with 3 min delay.

I guess, the only solution is what you have mentioned and what we have also arrived at by trial and error. That is to keep the DALI gateway on the mains without UPS. This works 99% of time - but occasionally, we have seen 1 or 2 ECG's being left out. But I guess this solution, though not perfect, is the best option now. As a future development, I would request Schneider to have a simple power detection circuit that can reliably reset the entire DALI bus when power fails momentarily and comes back on.

[Erwin-vd-Zwart]

What you could do is add a binary input 230V and when the power returns send a on telegram after a small delay to set the eventual missed evg’s again to it’s last value

[Heribert_Dölger]

Adding a power detection circuit inside the DALI gateway will not necessarily solve the problem. The power supply of the ECGs usually is separated into several circuits and is not necessarily the same circuit that provides 230V to the DALI gateway.

[alertcom]

That is right. The function needs to be architected for a generic case. But a signal that tells the gateway to (optionally) reset the bus to last value or a fixed value is required.

[alertcom]

Erwin, this is an interesting solution. But we don't know which ECG's need the reset. They keep changing. We can send a broadcast ON/OFF to the gateway, but I am not aware of a broadcast "set to Last Value" command. Is there one?

[Heribert_Dölger]

Don't understand why it doesn't work 100%. When the gateway isn't powered it should be the ECG that adopts the correct value. What in addition might have an impact is the parameter "value on DALI power fail". When the power of the DALI gateway fails somewht earlier than the power for the ECG then the ECG might detect failure of DALI power. If you have fixed value this will then be the last valeu and be adopted after power recovery. Due to that you should set this parameter as well to "last Value". this has to be done for each DALI group and single ECG.

Another point of influence might be the general setting of behaviour on KNX failure and KNX voltage recovery. If the gateway detects KNX bus failure but mains supply still is present it might send ON or OFF value when configured like that. You should set both parameters to "no action".

[Heribert_Dölger]

[alertcom]

Attaching a couple of screen shots.

I usually keep the "value on DALI power fail" and the "value on ECG power recovery" the same. I had kept them at OFF for some time and then switched to "Last Value" currently. The KNX power recovery setting is also set to "Last Value".

[Heribert_Dölger]

The setting of "last value" on KNX power recovery might have an impact in case there was a new command on the bus while the ECGs were unpowered. In such case there might be a mismatch between last value inside the ECG and last value of the gateway.

[alertcom]

I think most of the problems, I see are due to race conditions during power up or power down. Let me summarize the conclusions from our discussion so far:

1. In a situation with a DG having a short (< 3 mins) black out period, it is better to connect the DALI gateway to the raw power and allow it to reboot every time power fails.

2. In a situation with a DG having a long (> 3 mins)  black out period, it may be ok to keep the DALI gateway on UPS power.

3. In ETS, set "Behavior on KNX voltage recovery" to either "No Action" or "Switch to Last Value"

4. Set "Value on DALI power fail" to "Last Value"

5. Set "Value on ECG Power Recovery" to "Last Value"

6. Watch out for race conditions that will make the "Last Value" setting inconsistent

Please let me know if my understanding is correct.

Unfortunately, I am unable to do further experiments at the client site due to the pandemic restrictions. The small setup in our office do not have enough number of ECG's to re-create the problem.

[Heribert_Dölger · Accepted solution]

Well concluded.

[alertcom]

Thank you Herbert for your help.