I can't switch R wires, since I only have a C wire from the a/c unit, and that is needed to power the stat.
Yes, it was double the voltage. When I disconnected everything, I got 0 VAC from (what I think were) both sides of the secondary windings at the boiler. So I assume that that means that neither of those are grounded? I did get 4 VAC to ground from both terminals when I had the stat connected, except for the R from the A/c unit (28v from a/c - 24v from furnace? Not sure what's going on there).If one side of the secondary is not connected to ground on either system, you might be able to swap the leads which would reverse the phase...that should get the two into phase and reduce the voltage (it should have been double the 24-28vac, or the sum of the outputs of both 24vac transformer's secondary windings).
Heh heh. Ok, but at this point it's purely academic. I can just use the stat that I was going to use at the other house here--it has separate Rh/Rc, but then I still wouldn't have control over my aux heat using the motison. My wife of course insists that none of this is worth my timeIts totally doable with one xfmr and that new tstat don't give up yet!
Yes"So you have hot water heat with one 24v transformer (xfmr) in or near the boiler correct?"
No zone valves. Only electrics used by the boiler is the circulator pump and the pilot, AFAIK."Do you also have controls on or near the boiler like zone valves that use this same 24v to power them?
Or do you have switching relays that use the 24v to trigger the circulator pump or pumps?
Yes, there's an air handler. It's not that easily accessible, so I haven't looked too closely at it. Not sure where the xfmr is. Condenser is on the roof.On the a/c side, do you have an air handler and is that where the 24v xfmr is located, or is the xfmr outside in the condensing unit?
So can I switch the phase either by moving the breaker to the other side of the service panel, or reversing my secondary leads, or is it more involved than that?
I'm going to try to upload a pic of my boiler controls--lmk if this is what you need to see.
Last edited by DonL; 02-21-2014 at 10:45 AM.
OK, so looking back there a bit more, it would appear that I'm measuring from the wrong terminals. Not sure what the box is posted above, but took another pic of what I think is relevant. So on the below picture, I get 24v to ground from the blue and black wires, and 24v from blue to yellow. Nothing from yellow to ground. The blue and yellow connect to the red and white tstat wires, respectively. On the upper left of the pic, the terminals are listed as "burner" (B1/B2) connected to blue and white wires. Beneath that is "circulator" (C1/C2, red/yellow). To the left of that is my 120v line input. Not sure what that is above the relay, or where the blue/red wires lead--looks like a timer switch or something?
I'm guessing that the blue wire is one terminal of the secondary. The yellow wire (connected to W) is the back side of the relay (which is bottom middle of the pic). Unless in use, that wire should be isolated. Correct so far? The black wire on the right is connected to a terminal marked "W" under the tag.
Further guessing that the first pic I posted is a power distribution box. Red wire on the left is coming from what appear to be some temperature limit fuses/switches. White goes to the B(urner)2 terminal in the transformer box.
Ok, so that first pic is fed by 24v and feeds the gas valves and ignitor. It should get power directly from the transformer, right? That would be the red wire? And the white goes to the second secondary terminal? One of them must be connected to the W wire from the stat?
In the transformer box, one side of the relay should be fed by the transformer (which wire?). The other side should be the W wire from the stat (yellow in the box). The stat connects the red (blue in the box) wire to the white wire, trips the relay, and supplies 120vac to the circulator.
So putting it all together, my understanding is:
Line voltage to transformer primary and relay. Transformer secondary (blue wire) goes to R in stat, which connects to W, which powers relay. The other side of the relay is connected to the other side of the transformer secondary (which wire, the black one on the right?). Somehow the red and white wires on the box in the first pic are energized when there's a call for heat, and then each is connected to one of the secondary terminals (?).
Sorry for the long post, just trying to learn something here
What is that jumper with the warning tag ?
What does it say ? And what does it say behind it ?
Does that transformer have a center tap ?
Hard to tell by that one picture.
Last edited by DonL; 02-21-2014 at 11:56 AM.
That may be a jumper that needs to be changed, So that It should be set to run the zone valves only. Maybe you could power the T-stat from the other unit. Or Run the T-stat on a small wall wart.
It may be saying you need a bigger transformer to run more stuff. That AT72D may be for running a T-Stat and more zones, and it is externally mounted.
Maybe Jim or another Pro has the correct answer.
Last edited by DonL; 02-21-2014 at 01:03 PM.
Found it! Here's the setup for my boiler. I think I've figured out all the components in my boiler system. My initial pic was of the ignition control module. Second pic is the transformer--that switch above the relay is the aquastat. Fig. 11 is my setup, except that my ignition module doesn't have a TH-W terminal. Per another honeywell manual, the wire that goes to TH-W in that schematic should connect to 24v(2) on my module. And I don't see the relay there anywhere. And with that wiring, it seems that the ignition module is powered regardless of the tstat? I need to look at this some more to digest it...
There are at least a few interlocks in the system...running 24vac to it does not mean it will run...it needs a complete circuit - IOW, a return path back to the 24vac transformer that powers it. That could include a path through the thermostat to make the complete circuit, or safety interlocks, over-temp sensor switch(es), and maybe vacuum switches or pressure switches if it is a closed combustion device to verify that the pipes are intact and not plugged or just open.
Often, somewhere in there, there will be a unit schematic. Or, if you have the documentation or can find it on-line, you can find it as well.
A 240vac device will probably not change anything by moving the CB, but you could swap the L1 and L2 leads on the CB, which should change the phase of the input, and thus the output of the 24vac transformer.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013
Done. The voltage between the R wires is now 3vac. I get 24v between the TV and Z/T terminals. However, I get 24v between Z/T and ground--Doesn't this mean that the system isn't isolated and I have a problem?It looks like you can just swap the the L1 and L2 input to change the transformer phase, If needed.
Everything appears to be Isolated by the transformer.
Lastly, could someone explain to me exactly how changing the phase resulted in a decrease in voltage? Were/are my transformers essentially wired in series, so that when the 2 ac currents are out of phase, the max amplitude of the sine wave (and therefore voltage) is equal to only one xformer's output, and when they're in phase, the waves stack on top of each other and become additive? And would switching the breakers to different legs on the main electrical panel have the same effect?
It is all about the angle of the dangle. And the phase will make the voltage add or subtract.
And Yes switching the breakers to different legs on the main electrical panel would have the same effect. But the other way was easier, switching at the transformer.
Let's assume your original system was wired as shown on page 8. This is slightly modified version of the page 8 schematic.
The thermostat's job is to connect either the Rc or Rh, as appropriate, to whatever is being controlled, or to provide an open circuit to turn the thing off. The thing being controlled , such as a relay, would be connected between the controlled terminal and C. Thus power provided = on. Open provided = off.
The two transformers in the page 8 2-transformer situation don't have either terminal of either transformer connected together.
In your thermostat, there is only an R terminal. Now the thermostat cannot provide power from the just the appropriate supply. Instead it can only provide power from the one terminal, if I understood the discussions here. I think that Rh and Rc could be connected to R since the non R legs of the transformer are not connected together.
Transformers should not normally have secondary windings in parallel. So connecting two transformers to a single R terminal and also connecting the other side of each transformer to a C terminal would be bad.
Suppose Rh and RC are connected together in your situation. Let's call the other secondary lead of the transformer that connects to Rh to be Ch. Let's call the other transformer's C line Cc.
Anyway, are transformer secondaries that have one wire in common in series? You could think of them that way. But since there is no real load AFAIK that is between Ch and Cc, there doesn't seem to be a reason to consider them to be in series or not.
That is until you put your voltmeter where you put it. Now you see the effects of the transformers, for this purpose, being in series. Depending on the phase, you will see more or less voltage between the terminals that you are measuring between. Yet that voltage is only academic.
If you reverse the primary lines on one transformer, you should get the same effect as reversing the secondary lines on that transformer. The phase changes. So yes, if you wire one of the transformers to a different side of the AC line, the phase changes.
To see a description of how you can get less voltage from two transformers in series, look up "bucking transformer". In an example of a typical case, a 120 vac transformer is put in series with a 12 vac transformer. Depending on how the wires are phased, you get 132 (boost) or 108 vac (buck).
So yes the voltages add, but they add as vectors or complex numbers. When we say 120 vac, that is only the magnitude, and magnitude is sufficient for most purposes. For computing the effects of combining voltage sources in AC, we need to include the phase in the math.
In the kind of thing you are doing here, considering only 0 degrees and 180 degrees is enough for most simple calculations. You can make a simple model by thinking of a 120 volt DC battery in series with a 12 volt battery. In 3-phase, it gets harder. The supply voltages are 120 degrees apart; the battery analogies don't work in that case.
Last edited by Reach4; 02-22-2014 at 11:53 AM. Reason: Tried to clarify two different subjects. annotated pix
That was nice Reach4. What is the name of your book ?
Are we having fun yet ?
Another way to look at it is, between L1 and L2, when one is going positive, the other is going negative. Depending on how each system is installed, if both units have L1 on the same terminal, they'd be in phase, but if they were swapped, both L1's on different units, would be going in opposite directions, and when measuring the difference between the two, when they're in phase, you'd have zero volts, but when they're opposite, you have the sum of the two. Works the same when it goes through a step-down transformer. Note, it really doesn't matter between two systems what phase they call the 'R' lead relative to the incoming or supply voltage.
The fact that you have 3vac between the two could be related to the output of each transformer may not be exactly the same or they were not careful about the phase angle when designing and winding the coils (not particularly critical on this type of device). It also means that there's a constant current running between the two - now, whether in the long term, that might create problems, I do not know. It would be much better if it was zero.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013