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Topic: any hvac gods out there? (Read 3935 times) previous topic - next topic

any hvac gods out there?

Reply #15 –
If all you want to know is if the 24v is on, and the contactor is closed, why not just tap the output of the contactor? Is it 110v or 220v? Just stick a little 110v ice cube relay on there and add one of its N/O contacts to your continuity loop.
CoogarXR : 1985 Cougar XR-7

any hvac gods out there?

Reply #16 –
no,,
because the dry contact monitoring circuit is not allowed to toggle when everything is ok.  it can only toggle when things are broke.

if I do it the way you describe, the monitoring relay would toggle every time the contactor came on

any hvac gods out there?

Reply #17 –
X

Maybe I wrote it out wrong. But this is what I was thinking. The only problem I see, is the brief milliseconds of time between the Tstat kicking on and the contactor closing might cause a 'blip' on the alarm. You could add a 555 IC in there after K3's contacts if you wanted to make sure the alarm condition exists for so-many-seconds before breaking the alarm loop.
CoogarXR : 1985 Cougar XR-7

any hvac gods out there?

Reply #18 –
actually I can control a delay within the programming of the local alarm system... from milliseconds up to 18000 seconds

by the way,,, my shown K2 ,, when there is continuity from 87 to 30,, that EQUALS NO ALARM.  when the loop is broken, this is an alarm.  This is what we call "supervised dry contacts".
it helps cover the idea or concept that if the wire is cut *or* the alarm condition occurs, the circuit is open.

any hvac gods out there?

Reply #19 –
I understand the continuity from 87 to 30 being a no-alarm condition. The only way the alarm condition would exist in my revision is when the Tstat is on, and the contactor is not closed. That's what you wanted, right?

In a no-alarm condition, you would have 24v present, but the new K3's N/C contact (now in the open state because it's energized) would be preventing it from passing to K2 to break the loop. Does that make sense?
CoogarXR : 1985 Cougar XR-7

any hvac gods out there?

Reply #20 –
yep, it does.......

any hvac gods out there?

Reply #21 –
ok,, this should work,, using the 120v feeder to one relay helped a lot.

any hvac gods out there?

Reply #22 –
Yeah, that should work. It's cleaner using only the 2 relays instead of 3. I only suggested a 3rd because I thought this was some existing circuit that you were trying to add to. The vibration switch is also an interesting addition. I don't have any experience with those, so I'll be interested to know how that pans out.
CoogarXR : 1985 Cougar XR-7

any hvac gods out there?

Reply #23 –
That vibration switch is a new one on me too. I hope it works for you.

Looking at the Emerson schematic you posted a link to, I don't see a neutral conductor.
Your diagram shows the relay coils referenced to ground.
As I recall, the ground (green wire) connected to the metal boxes etc. is required to be a non-current carrying conductor for bonding purposes only.
You may have to use a 240vac(208vac) relay for K2 and hook to two of the phase legs to the compressor motor.
K1 coil will have be connected to terminal block Y (T-stat signal) and terminal block 1 (the other side of the 24vac transformer)

The field I worked in always had Delta transformers supplying the 3 phase power. 208vac between legs and no neutral.
Y (Wye) transformers have 240vac between legs and have a neutral conductor.

Be sure to use AC relays for K1 and K2. DC relays can vibrate and the contacts flutter if used in AC.

any hvac gods out there?

Reply #24 –
The pn of the switch is on it,, there is an online video of it in use as well here...........  http://www.adafruit.com/products/1766
I wont deploy the "very sensitive" shake switch till I test the sample I have coming tomorrow... then I speculate a starter order of 100.  I have a quality relay in mind as well, and will start with 200.  I will make up the mounting bkt and harness all by my lonesome because the installers may end up doing it wrong or just rush and things go wrong when that happens.  I have to "series" up all existing HVAC units on each site so I speculate a min of 4 per site and that is very skinny IMHO.

did you happen to notice how I am telling the installer to install it?  its attached right at the end of the zip tie, installer can  use a sleeve of heat shrink or whatever to attach.
If a good vibration point cant be gathered, I have another idea.... those door strike sensors which are a reed switch and magnet kit... well toss the magnet.  Mount the reed switch on the part of the AC motor that causes the reed switch to change state due to the magnetic field. I tested this in my garage on a few ac motors and it worked.... I tested on the back of my car alternator and it worked, the switch changed stated.  only problem is it doesn't tell you if the motor is spinning.  A shake switch helps with that.

The voltages at each site will vary and over time the delta element has been migrated away from greatly , mostly Wye service entrances for the most part.
When I see a small and big xfrmr on a near by pole though with aerial drops to the facility, it sure does make me want to verify a N leg "is" actually present.  Ive seen a few ways someone attempts to build a N leg but you'll know right away when you find the wild leg,, sticks out like a green fly in a sugar bowl.  I did not show a N/G conductor either to simplify the drawing.. but there should be N and G terminal strips within each unit if not each N / G conductor should at the least be on the same strip,, although that is becoming more and more of a No- No ,,, in order to isolate current carrying conductors from actual ground.  People don't understand N legs do carry current especially in an imbalanced panel board.

The Emerson drawing is very generic in nature to embody list options that "can be had".
You have noticed there are optional dry contact relay options "if" ordered.  Most of the time it is not so I have to at least be prepared. 
I see about 20$ per hvac unit in materials for this small chunk of my scope, and I'll give 2hr labor at 75$ billable per unit to integrate this "kit".

there are other options out there to "add on" made by other monitoring companies but they involve tstat probes, ct's, ect and could cost me in about 700$ mat per unit to monitor and that is out of my budget.  To beat it all , my design is actually gathering a better "fail" alarm condition than those other devices I just pointed to.  The CT's will detect current flow but nothing about if the motor is running. 

In replacement of the "shake switch" I actually want something else..... something like a "thermo-disc" like in your dryer.
It would be an open circuit for a while putting the hvac in alarm when K1 energizes but as soon as the thermo-disc cools off, the alarm would go away.
I have my alarm system programmed for a 15min delay prior to delivery of the actual alarm out to the network operations center.  This would give me the ability to .......say.....
Tstat triggers K1, K2 detects contactor coil moved Hi-Line voltage, thermo disc went from open to closed thus the hvac **IS REALLY COOLING**.

I just cant find a "non - buttstuffog" switch like that.  it need to be open or closed only,, nothing fancy.


gonna take your advice on the N & G legs, all the hvac's are typically bonded already and if they are not we will toss in a #6 Rhh/RHW chassis gnd back to the main ground bar.

any hvac gods out there?

Reply #25 –
Revised,
I found my "simple" switch to detect ductwork temp.
if anyone "knows" of a thermal couple sensor that goes "open" and "closed" which is cheaper per unit price of 10$, please!!!!!!! let me know.