RCS TR-40 Thermostats and ElkM1 Gold Help Please.

Well time to install the thermostats into the elk system. Here are my questions:

Thermostats are installed, and controllers are in the walls, all hooked up and working correctly.

I also have a Cat5 cable form each controller to the Elk cabinet. I have the serial expander all setup, per the instructions, for RCS thermostats.

The question I have is this.

Can I stick both sets of three wires (from the thermostat control units) into the same input ports on the serial expander?

I am confused. Do I need two serial expanders? (one for each thermostat)

Any help would be great.


You need to either get a RCS rs-485, rs-232 hub, or you can get an elk expander for each t-stat.

I am using the RCS TR-40 and the TR-16 t-stats. I am using a RS-232 hub. My hub was damaged by lighting (I think) several weeks ago. I called RSC for some techinal advice on how to trouble shoot it. They were really helpful. Since I am only using 3 t-stats, I was told to remove one of the extra chips from the unused channel and install it where the rs-232 chip was. I then moved a jumper and presto chango-------My rs-232 hub is now a rs-485 hub.

The moral of the story is to buy the cheapest hub, because you can change it to whichever you actually need.

You can buy the needed chip from Dallas, and the shipping costs more that the replacement chip.

Let me know if I can confuse you any more

Ok, I don't think I can be more confused... ;)

The elk serial expander docs said that up to 16 thermostats can be hooked up to one serial expander (gold edition elk system)

Also I have never heard of a RS-232 or RS-485 hub....
RCS uses a controller box that comes with the thermostat(s) and it is generally located at the HVAC air handler. There is a RS-485 data bus connection from the control box to the thermostat(s) and a separate connection to the M1XSP serial port expander. Reference the M1XSP instructions for a diagram of how this hooks up.
You CAN run up to 16 RS-485 TR-40's off of one XSP serial expander.

If all of your control units (not the wall displays) are together you only need 1 cat5 from the XSP expander to your controllers. Connect a cat 5 from the XSP to your first control unit. Then run a short cat5 from your first control unit to the second one, then from second to third, etc. Each control unit has to be set for a unique address.

This assumes that you have the RS-485 version of the TR-40. If you have the RS-232 version then you need a separate XSP expander for each control unit.
Well this creates a small dilemma for me. I opted for going to the thermostat locations (2 of them) and putting the controllers behind the wall where the thermostats are located. The reason for this is that the HVAC units are in my attic and during the day it is 115 degrees outside, so therefore in the attic is 1000 times worse.

Plus when I had the house wired, I had the extra cat 5's ran to the thermostat locations back to the elk system versus the actual hvac units, I didn't do the appropriate prep on these thermostats like I should have. It seems I read the manual on everything else...but these.

So I guess I will have to get an extra serial expander for each thermostat. Just one more...cheap mistake considering they only cost $55.

Well live and learn I guess....
Well if the Cat5 cables go from each thermostat (control unit mounted close to wall display unit) back to a common location like where the Elk is installed, then there is no problem with creating a virtual daisy chain. Assuming you ran 4 pair (8 wire) Cat 5, you could have 2 pairs running the RS-485 bus from the serial expander to the first stat, and then two other pairs bringing the bus back to where you could then connect them to your second Cat 5 cable going to the 2nd stat. You might also try connecting the serial expander the both Cat 5 cables directly, but if you do that you would need to make sure that the serial expander is not terminating the RS-485 bus. This might be a bit trickier. Yet another alternative would be to use a purpose made RS-485 hub.

Guy's alternatives are good and at least one of them should work.

The first scenario I would try is simply connect both of your home runs from the control units to the XSP's RS485 out terminals. I know the main RS485 bus (from M1 to expansion modules, keypads, etc.) can have up to two separate home run lines connected. The only unknown here is that when you configure the XSP for connecting to a RS485 TR-40 it's RS485 out bus is configured to match the characteristics of the RCS RS485 bus and I don't know if it has the same 2 home run capabilities (my knowledge of RS485 is minimal).

Second thing I would try is the virtual daisy-chain suggested by Guy. This should have the best chance of working as it electrically would be the same as the XSP's instructions say to hook up multiple control units.

Finally the hub configuration should work if all else fails.

Just make sure you set your 2 control units to separate addresses, i.e. 1 and 2.

I love my TR-40's and M1 combo.

Good luck...
Well I spoke to Brad this morning over at Elk. He said that having to RS-485 devices on one input on the serial expander should not be a problem.

So that should work fine.

BUT now I am reading the RCS manual and cannot find how to change the address of the thermostats so that one is number 1 and the other is number 2.

Anyone know how to do this?



DUMBASS Alert!! I figured it out...page 21 of the RCS TR-40 manual.....

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