Aprilaire 8800...

itismyworld · August 2013

Hello all, hopefully someone has an answer for this....don't want to be blowing stuff up.

First, I have acquired a brand new Aprilaire 8800 TStat.

Can an 8800 (since my house only has one stat) be wired directly to a processor via RS-485? If so, what would that connection be?

If I do need a protocol adapter, will the older style red 8811 style work with the 8800? I can get a deal on one of those if needed.

Thanks to anyone that can help!!!!!!

John Nagy · August 2013

Yes, we do it direct all the time.

itismyworld · August 2013

Thanks John!

Last question...
When directly connecting the processor to the TStat, does ground of the 485 get connected to the "C" terminal of the TStat?

DHawthorne · August 2013

I'm pretty sure that C connection is for a power common and not a signal common. I've never had to hook it up, but then again I have never hooked up just one stat, and have been running through a disty panel.

itismyworld · August 2013

Thanks Dave. Yes, the C is for power common which is what is confusing me...

As far as I can tell, I connect A+,A-,B+, and B- of the termostat to TX+,TX-,RX+, and RX- on the serial port of the processor. But what about ground? Is ground not needed because of RX- and TX-?

Thanks!!!!

John Nagy · August 2013

DB-9 Pins On NI for Aprilaire 8870/8800 (RS-422, not 485)

1 B-
2
3
4 A+
5 REF
6 B+
7
8
9 A-

itismyworld · August 2013

Thanks John. That's what I have too but my only question is where does "REF" get connected on the TStat?

Thanks for helping me get this figured out!

DHawthorne · August 2013

itismyworld wrote: »

Thanks John. That's what I have too but my only question is where does "REF" get connected on the TStat?

Thanks for helping me get this figured out!

As I mentioned, you don't need to. The TX/RX +/- are balanced signals, and shouldn't need a signal ground. The only time I have ever used the REF terminal was for a drain on the cable's shield, and then I only connected it on one end.

itismyworld · August 2013

Thanks all! Everything is working just fine. Still have some fine tuning but besides that I'm good!

Aprilaire 8800...

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