Aprilaire 8800...

itismyworld

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

Yes, we do it direct all the time.

itismyworld

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

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

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

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

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

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

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