Aprilaire 8870 to M1XSP to M1G

[arctec37]

I have just installed a M1GSYS4 in my house. It went pretty good so far. I am now ready to hook up the Thermostats.
I have 3 zones which I am going to use Aprilaire 8870 stats on each zone. My question is can I hook the stats up directly to the RS-485 connection on the M1XSP or do I need to use the Aprilaire Protocol Adapter 8811?

If I can hook them up directly do I wire them the same way I have the Keypads? I have home runs for the 3 stats back to the panel so I think I need to connect the data lines in series; is that correct?

SYSTEM DESCRIPTION
M1GSYS4
(2) M1KP - Keypads
M1XSP – Serial Port Expander
(3) Aprilaire Thermostats
M1XRF2G – Wireless Receiver and Input Expander
M1XEP – Ethernet Port

 

[sic0048]

Page 5 of the M1XSP manual tell you how to hook the thermostat up. It looks like the 8811 Protocol Adapter is required while the 8818 Distribution Panel is optional. That is how I read it at least.

 

[felixrosbergen]

I haven't done my install yet (my ELK is on the fritz) but this is my understanding as well. T-Stats connect to the protocal adapter which then connects to the M1XSP which sits on the Elk databus.

I believe the protocol adapter has ports for 2 T-stats, so with your 3 i don't know if you can just splice one in or if you have to use the distribution panel. My setup will only have 2 so i never researched the distro panel option much.

Good luck.

 

[arctec37]

Thanks, I was pretty sure I did need the protocol adapter and after speaking with tech support the RS 485 on the M1XSP is proprietary to ELK. I am now getting both the 8811 protocol adapter and the 8818 distribution panel.

 

[Sacedog]

I have done this type of install twice now, and have only used the protocol adapter. The distribution panel is not needed.

 

[dBeau]

I second the use of the distribution panel. True, it is not required but when you consider the price of the 8870's adding the distribution panel in doesnt change things much. The benefit is that it gives you a place to terminate the wires. It also has switches for isolating an individual 8870 from the network. This can help with debugging. Further, it gives you a nice way to power the stats independently of the HVAC system. For this you'll need a 24vac adapter. Aprilaire sells one but it has a built in fuse. Touch the wires together and you'll need a new one. For about the same money, Elk makes one with an auto-resetting fuse.... much better.

Strictly speaking, you dont need the Aprilaire protocol adapter. You do, however, need something to convert the RS485 of the stats to the RS232 of the M1XSP. Again, Aprilaire loses when it comes to the power adapter. They use 7vac! Of all the wall warts I've seen, this is the only 7vac device I know of. So, in theory, a different RS485 to RS232 adapter will work. If you are not familiar with configuring these devices and how they are spec'd, I'd have to suggest going with the Aprilaire. Follow along with their installation instructions and you'll be fine. If you leave the well marked trail, you could get lost in the wood for a while.

Personally, I dont use the Aprilaire protocol adapter. Instead, I go from the M1XSP to an rs232-tcp adapter, over the LAN and back out a tcp-rs485 adapter to the distribution panel. The point being, you can do almost anything if you put your mind to it

 

[felixrosbergen]

dbeau:

Can you confirm that if i only have 2 stats i can terminate both of them on the protocol adapter without the need for the distro panel. If you recall correctly it has 2 ports for stats and 1 for comm to ELK right?

 

[dBeau]

dbeau:

Can you confirm that if i only have 2 stats i can terminate both of them on the protocol adapter without the need for the distro panel. If you recall correctly it has 2 ports for stats and 1 for comm to ELK right?

The protocol adapter is simply an RS485 to RS232 converter (with an odd choice of wall wart for power). The RS232 side goes to the M1XSP. As you have noted, there are two sets of RS485 outputs. The way it all works makes that irrelevant. RS485 is a shared bus. You can (and the distribution panel does) run many 8870s from a single port. The statnet protocol is all based on timing. There is one master that transmits on one set of wires. All of the stats listen to the master. When it comes time to reply, each stat waits it's turn based on it's address and transmits back on the other set of wires. Again, this is all one full duplex (four wire) RS485 port.

The distribution panel is not needed regardless of the number of stats you connect. It just makes the install a lot easier. Sure, if all goes well, and with only two stats, it probably will so you might not care. With many stats, it would take just one to be wired wrong and it will affect the entire network. With the distribution panel, you can turn each stat off at the panel until things start working again, easily isolating the problem stat. Using the panel implies that you will be making a home run for each stat. Generally this is a good idea. If for some reason you plan not to make the home-runs, the panel wont help much anyways.

With just two stats (and no panel) I'd terminate the cat5 from each stat with an RJ45 and plug each into the protocol adapter. This gives you the ability to unplug one or the other if you suspect a problem. Note also that this assumes you'll be powering the stats via the HVAC control wires. You'll need to make sure that those wires carry a constant source of power (in a heat only system, this is unlikely). If you plan to power the stats over the cat5, you'll need to splice into it somewhere before the RJ45. Once you do that you'll have a mess of splices on your hands and probably wish you had a place to terminate everything. The distribution panel is just such a place.

 

[felixrosbergen]

THe funny thing is that the 8811 i received doesnt have the RJ45 ports and it's not red either. Has aprilaire changed their design?

The one i have has a simple serial port on each side with a breakout board to terminate the T-stats on. The red 8811 with the RJ45 connections was a much cleaner solution.