Converting from line voltage to 24v. (840T)


  #1  
Old 12-08-16, 04:33 PM
S
Member
Thread Starter
Join Date: Dec 2016
Posts: 12
Received 0 Votes on 0 Posts
Converting from line voltage to 24v. (840T)

Just moved into a new house and wanted to install programmable thermostats, specifically ecobee3 thermostats. As of right now there is no central air just a 2 zone boiler with a thermostat on the first and second floors. Both of these are currently lux 110v thermostats so I would need to convert both to 24v. I thought I could just get two Honeywell RA89A' but after looking at it don't think there is a spot for a C wire. Is there an all in one solution similar to the ra89 that will accomplish what I want to do? If it matters I do plan on adding central air after the winter.
 
  #2  
Old 12-08-16, 05:25 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,872
Received 1,480 Votes on 1,368 Posts
Welcome to the forums.

Are you sure they're 120v stats ?
Rarely are two 120v stats used together.

This relay module is exactly what's needed to convert to low voltage..... even electronic.... thermostats.

RC840T-120 - Honeywell Aube RC840T-120 - 120v Relay w/ Built In 24V Transformer
 
  #3  
Old 12-08-16, 07:11 PM
S
Member
Thread Starter
Join Date: Dec 2016
Posts: 12
Received 0 Votes on 0 Posts
Thanks for the quick reply Pjmax. I will double check the voltage on the upstairs. I had checked the first floor and just assumed the 2nd floor was the same since it was the same thermostat. So no need for the RA89A at all then correct? I was looking at the RC840T on amazon and see most people are using them with electric baseboards. Theres no issue using this with a boiler?
 

Last edited by Steve Morgan; 12-08-16 at 07:37 PM.
  #4  
Old 12-17-16, 07:42 PM
S
Member
Thread Starter
Join Date: Dec 2016
Posts: 12
Received 0 Votes on 0 Posts
Honeywell RC840T Hookup

Posted a week or 2 ago about converting 2 thermostats from line voltage to 24V to hook up 2 ecobee thermostat. I picked up RC840T-120 tranformer/relay but just wanted to make sure before I wire it up that I have it correct. This is for a peerless wbv-03 boiler with a riello 40F5 burner & there are 2 zones. In the first picture 2 of the 3 electrical wires on the right of the box are going to the thermostats below. the two wires coming out the top are going to the 2 taco 007-f5 circulators. The line coming out of the bottom feeds an old oil fired water heater and the line coming out of the left feeds the riello burner. On the RC840T I have black, white and red wires. I think I am only connecting the black and white and capping the red correct?

Name:  ts1.jpg
Views: 4937
Size:  36.0 KB

Name:  ts2.jpg
Views: 6272
Size:  33.9 KB

Name:  ts3.jpg
Views: 4917
Size:  25.6 KB
 

Last edited by PJmax; 12-17-16 at 09:40 PM. Reason: reoriented pictures
  #5  
Old 12-17-16, 10:29 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,872
Received 1,480 Votes on 1,368 Posts
I combined your two threads.

Now.... this is important.
Follow my directions carefully and be careful.
You're going to need a meter or voltage tester to measure AC voltage.

The first thing you need to do is to located the 120VAC into that box. It may be the bottom cable. You need to follow the white wire from that cable to its splice. It is probably the splice with many white wires. This is where the relay BLUE or WHITE wire will connect.

Locate the cable going into that box that corresponds to the stat you are replacing.
Disconnect that cable from the two splices and remove it from the box. Now the cable going to the stat will be dead.
You will have two open wires in the junction box. Measure from each one to ground (box).
The wire that shows 120vac goes to the BLACK of the relay. The wire that doesn't show any voltage goes to the RED of the relay.

You need three wires between the 840 and the new thermostat. Since you have an NM cable in place and it has three conductors.... you could use that. You would make the white wire W. The black wire would be R and the bare would be C. You would have to add small jumpers to the ends of the wires if they didn't fit into the 840 or stat terminals.

I would run a new thermostat cable. That may not be an easy job for you.

Name:  rc840.jpg
Views: 7308
Size:  20.8 KB


I would add a 4" square extension ring to that box to make it easier to install the relay and add some extra wiring room.

Name:  1900ext.jpg
Views: 4742
Size:  3.3 KB
 
  #6  
Old 12-18-16, 06:50 PM
S
Member
Thread Starter
Join Date: Dec 2016
Posts: 12
Received 0 Votes on 0 Posts
thanks for the detailed instruction. It took awhile to get the new thermostat wire fished up the wall but it's all in place. Now the bad news is that I got the ecobee wired and installed and it runs but it keeps randomly rebooting when the heat comes on so I had to switch back to the lux. I see other people are having the same issue so I will probably return this and get the nest. At least the wiring is in place now though.
 
  #7  
Old 12-18-16, 07:59 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,872
Received 1,480 Votes on 1,368 Posts
That should not be. I've never seen that problem with that adapter.
Have you verified your wiring ?

Hmmmmm.... I'm wondering if the Ecobee is pushing the 24v limit of the adapter.
I'm looking into it. Unfortunately I don't have an 840 spare here.

The stat requires 3.5va
The transformer delivers 1.2va
The Ecobee requires a healthy supply current.

Another choice is to replace the 840 with a fan center. That's a transformer and relay on a 4" square plate.

90-113 - White Rodgers 90-113 - Fan Control Center, 120 VAC Primary 24 VAC Secondary, SPDT Relay
 

Last edited by PJmax; 12-18-16 at 08:25 PM.
  #8  
Old 12-20-16, 12:38 AM
S
Member
Thread Starter
Join Date: Dec 2016
Posts: 12
Received 0 Votes on 0 Posts
I ordered the fan centers and they should be coming today. Would you be able to tell me how to wire that up? Thanks for all of the help.
 
  #9  
Old 12-20-16, 06:08 AM
Geochurchi's Avatar
Member
Join Date: Nov 2012
Location: United States
Posts: 5,026
Received 91 Votes on 86 Posts
If you are using 2 fan centers you will need to do some rework there,add a second 4"sq with a nipple under the existing box,you will be removing the old Stat wires from the existing box and connecting the fan relay wires to the remaining wires left to control the boiler.blacks from the fan center will be tied to the supply wires in the box,white from the fan center will be connected to the supply whites in the box,red from the fan center will be connected to the remaining wire which was left from where the old stat wire was removed.
 

Last edited by Geochurchi; 12-20-16 at 06:26 AM.
  #10  
Old 12-22-16, 08:58 PM
S
Member
Thread Starter
Join Date: Dec 2016
Posts: 12
Received 0 Votes on 0 Posts
Thanks Geochurchi. Haven't had a chance to install the fan center yet but just want to make sure I have my wiring correct before I do . SO there are black and white wires coming off of the transformer and black, red and brown wires coming off of the relay. White will connect with the other whites, black off of the transformer will connect to the 110 that was feeding the old thermostat and red from the relay will connect to the black wire that feeds the water circulator leaving the black and brown from the relay connected to nothing and capped or is the black on the relay connected to the same wire connector as the black on the transformer? The R/W/C from the thermostat will connect to the R/W/C on the relay.
 
  #11  
Old 12-23-16, 08:22 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,872
Received 1,480 Votes on 1,368 Posts
If you haven't got this resolved.... I'll be back tonight. Let me know which fan centers you have.
 
  #12  
Old 12-23-16, 10:01 AM
A
Member
Join Date: Jun 2012
Location: USA
Posts: 1,679
Received 50 Votes on 45 Posts
Yes, the black going to the relay should be combined with black going to the transformer as an always hot wire. Brown does need to be capped off.

Since the 90-113 is a "fan" control center you use the R, C, and G terminals. G will then go to W on the thermostat.
Name:  90-113 relay.png
Views: 5329
Size:  25.0 KB
 
  #13  
Old 12-24-16, 09:15 AM
S
Member
Thread Starter
Join Date: Dec 2016
Posts: 12
Received 0 Votes on 0 Posts
Thanks for all of the help everyone. The thermostat seems to be working and no reboots so far.
 
  #14  
Old 12-24-16, 10:03 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,872
Received 1,480 Votes on 1,368 Posts
That's good news. Thanks for your help astuff.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: