KNX/EIB More than 64 devices, IP-router or line-repeater.

[McKajVah]

I'm going to hit more than 64 devices soon and need to expand my setup. I already have an older siemens IP-router that I use.

Would you just install a line-repeater or add another IP-router?

Line repeater:
-Cheaper
-More reliable?

IP-router:
-More flexible
-Risk of "backbone" failure (network failure)

What to do....?

[StefanSweden]

Tjena,

well it's not absolutely necessary to split a line if you have more than 64 devices. However, a few things should be considered:
- newer devices, for example from MDT, use TP-256 that allow up to 256 devices per line
- if older devices (TP1) share the same line, it can be assumed that the max. amount of devices ranges somewhere between 64-256 devices, however the exact amount for this setup is trial and error
- the power supply needs to be able to drive all devices on a line

Another IP Router is usually more expensive than a TP Line Coupler. The IP Router is faster on the backbone, since this is Ethernet. Thus, for lines with heavy traffic, an IP Router could be the better choice if many telegrams need to be send to the backbone. Keep in mind that an IP Router coupled system requires a functional Ethernet (Multicasting). Avoid running KNX Routing (Multicast) over WIFI, many home router can not handle this probably. Can your KNX installation tolerate a KNX IP backbone that went down?

So more reliable might be the TP Coupler, no Ethernet, less connector, etc. All KNX Routers and TP Line Coupler can use filter tables and will only forward telegrams that need to be transferred to the other line. This reduces bus load and increased reliability. You may run a TP Line Coupler also as TP Line Repeater, if necessary.


To sum up, if you have the setup at your own place, you can give it a try to extend even if you have older TP1 devices on the line. This usually works fine, especially if you do not utilize the max. cable length. If you go far beyond the specified limit, split the line, take a second independent power supply and run the Router/Coupler with active filtering.

For a setup at a customer you will take the risk for a setup with more than 64 devices (when non TP-256 devices are involved), since neither the KNX Association nor a manufacturer will give you a guarantee.

Hälsningar
/Stefan

[Beleuchtfix]

If you use a line repeater, you stay inside the same line number (1.1.x) If you use a TP line coupler, you will have to put new devices in 1.0.x , if you want 1.2.x you need two couplers! If you use a IP Router you still need two couplers-

Imho the easiest way is to use a line repeater and a second power-supply.

Regards Florian

[McKajVah]

Thanks for the answers. I'll first try to "stretch" my installation by going over 64 devices. I was not aware this was possible.

Some follow up questions:

If I keep my older (TP-1) devices in the 1-64 range and the known TP-256 devices (MDT?) from 64 ->, will everything work as normal and I don't have to worry about the TP-1 devices not working or is it still a "game of chance"?

Is there a way to find out if a device is TP-1 or TP-256?

Thanks.
Kaj

[eXec]

Sry, for my question, but why don't you use a power supply with more performance like MDT STC-1280.0 with 1280mA...?

[McKajVah]

Sry, for my question, but why don't you use a power supply with more performance like MDT STC-1280.0 with 1280mA...?

Problem is not power, but the amount of devices (addresses) on a single line.

[hjk]

Problem is not power, but the amount of devices (addresses) on a single line.

There is no problem. All devices which not older than 8-10 years are TP-256 devices. So its no game, it ill work.

[eXec]

Ok, I'm sorry. I think I understand your problem.

Maybe this will help you, but StefanSweden wrote it before in the 2nd post:
https://knx-user-forum.de/forum/%C3%...56-ger%C3%A4te

[McKajVah]

There is no problem. All devices which not older than 8-10 years are TP-256 devices. So its no game, it ill work.

Do you mean this as a "general" rule for all manufacturers or only for MDT devices?

Thanks.
Kaj

[StefanSweden]

I had a quick look at some datasheets. Even the old TPUART 1 can handle up to 256 devices per segment. This probably means that most newer devices should support more than 64 per segment. Well, there are also discrete build certified bus couplers, I have no idea if they also support TP-256.

I think it comes down to the capacitive load every node is adding to the bus. The first devices more than 25 years ago didn't use so sophisticated semiconductors than the once available nowadays. If a node is adding less capacitive load, more nodes can operate on the same segment. Thus, it shouldn't matter if you have a couple of older or unknown devices on the bus if you don't extend a segment to the top.

If I keep my older (TP-1) devices in the 1-64 range and the known TP-256 devices (MDT?) from 64 ->, will everything work as normal and I don't have to worry about the TP-1 devices not working or is it still a "game of chance"?

On the software side, neither the ETS nor a device, require to set the PA 64 blocks. Just make sure all devices on the same segment use the PA associated for the line, for example 1.1.x where x = 1-255. If you got lost now, please have a look at the documents for valid topologies. As hjk already mentioned, this isn't a game. KNX is damn robust, it even works over a dedicated 3G1.5 if it really needs to.

Is there a way to find out if a device is TP-1 or TP-256?
Kaj

I guess a screwdriver would do if nothing is mentioned in the device datasheet.

[hjk]

Do you mean this as a "general" rule for all manufacturers or only for MDT devices?

Thanks.
Kaj

Yes, its a general rule for all devices.

[McKajVah]

Thanks everyone for the great information.

I find it strange that in the official basic course documentation books only mentions 64 devices per line and not 256. I think this could have saved a lot of money for people if it was better known and mentioned in the course documentation books.

I also guess the max 640mA per line is also not that valid anymore and only really depends on the power supply and choke you use...?

-Kaj

[Beleuchtfix]

At the beginning there were only powersupplies with a maximum of 640mA, die average load per device was 10mA - so you had the restriction of 64 elements. Perhaps EIB (at that time) hat a restriction of device names with only 64, but once you are able to address 254 separate elements it should work with enough power.

Good Luck
Florian

[hjk]

The limitation is the power. Max allowed/specified power supply is 1280mA by KNX. So normally 128 devices is the maximum.

[StefanSweden]

Thanks everyone for the great information.

I find it strange that in the official basic course documentation books only mentions 64 devices per line and not 256. I think this could have saved a lot of money for people if it was better known and mentioned in the course documentation books.

Well, this is actually a good point. I noticed this even at the tutor course some months ago, nobody was aware what TP-256 actually means. Until now I haven't found any information in the basic, advanced or tutor course documents. Some hints in the course documents would be great.

I also guess the max 640mA per line is also not that valid anymore and only really depends on the power supply and choke you use...?

It was always allowed to use more than 1 power supply per line. This should be mentioned in the basic course documents ;-)