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Microcontroller project for my pool pumps

ShawnJ

Aug 20, 2016
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My ohmmeter reading is 0.4Ω when I leads are together once I hold them steady and settles. Reads 0.L when they aren't touching.
 

BobK

Jan 5, 2010
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And you get 0.6Ω for the coil? Then I would submit that the coil is shorted out. It looks to me like you have one working contactor and a second one with a shorted coil.

Bob
 

Sunnysky

Jul 15, 2016
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A zoom image of the recommended transformer on your original link indeed shows 40VA 24Vac
f0bdd7b9-6514-40fc-992d-6acd8f24cde7_1000.jpg

If you are sensing remote contacts with low current and these contacts are not rated for <2A (i.e. gold plated) then they will oxidize and fail sooner than you expect.

My solution which works well is low ESR or tantalum cap across the remote sense contact closure to "wet" the oxide insulation on the contact closure on each use. 10uF or so. with R pullup to Vcc . Then use twisted pair. and ferrite bead around pair if Murphy's Law creates an IRQ. :)
 

ShawnJ

Aug 20, 2016
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That's a bummer if it's a bad transformer...

Sunnysky, I will look into that transformer instead of what I have. Gosh, it sure seems weird that a damn relay would need that much current to engage the contacts. I'm really scratching my head on that one. Waste of energy it seems.

Oh, and btw, I'm a technical guy in my field and now I know what I sound like to the noobs.
"My solution which works well is low ESR or tantalum cap across the remote sense contact closure to "wet" the oxide insulation on the contact closure on each use. 10uF or so. with R pullup to Vcc . Then use twisted pair. and ferrite bead around pair if Murphy's Law creates an IRQ"

...this statement will take me a bit of time to decipher. I'll be back in a week! haha ;)
 

eKretz

Apr 8, 2013
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The transformer isn't bad (just underpowered) but as Bob mentioned, it sounds like your relay (contactor) coil may have a short.

As for the techno-speak, SunnySky is just giving you an easy way to prevent oxidation on the contacts from causing problems.
 
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ShawnJ

Aug 20, 2016
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Thank you, eKretz.

All, your time and information sharing is very appreciated.
 

Bluejets

Oct 5, 2014
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Back in #13 you said your tranny was 20va ...???
Anyhow, why muck around , you have 110v (or 240 for that matter) with an isolation relay on the micro, so why not use that on a similarly powered pair of contactors.
Just a noter that contactor coils are like motors, large inrush currents at startup so if not enough juice, the 24vac will drop like a rock.
 

ShawnJ

Aug 20, 2016
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Well, my trans is 20VA, but that is because I was using what I had...and I'm showing my lack of attention to detail on that portion. Frankly, it blows me away that it would need that much current to make the electromagnet work. I erroneously read that relay coils require very little.

I got these two contactor relays from researching what I could find. I am seeing a lot more now that time has gone further. I really liked your suggestion. I was able to find this. Would you recommend me swapping these for my current units?

As I've said, I'm learning a ton from this project, so I can absolutely see where major efficiencies in my design can be made.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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Just wondering if I've missed you actually confirming your transformer can power the second contactor on its own?

I'd hate to think you were accidentally using the wrong terminals.

Contactors and relays are different in many respects. The power required to switch a contactor, while large compared to a small relay is still small compared to the power the contactor itself can switch.
 

ShawnJ

Aug 20, 2016
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I've been thinking a lot about your response, Bluejets. "Why in the heck didn't I purchase a 11V relay coil relay to begin with?" Well, honestly, I had such a hard time finding a 220V, 2-pole relay that I basically got whatever I could find. Now, I'm seeing sources for more of them.

I'd like to avoid the extra step of the 24VAC transformer altogether. Do all of you agree that I should swap it out w/ the one I mentioned in my previous post? (link was embedded) That way, I can use the 110V I already have in that NEMA enclosure and just switch in the 110V to the relay coil w/ the existing design I already have.

One last question. Do I need a current limiting component to this design? Right now, there's nothing. I read somewhere I can use an inline cap and resistor between the hot and neutral, but I don't quite understand why and how that works. That's the last part I'm concerned about...

Thanks.
 

ShawnJ

Aug 20, 2016
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Steve, I just saw your post after sending my last one. I was thinking the same thing. Originally when I installed it I did test it and it work by itself. Lately I've only tested it when the other is working, so I'm going to do that test tonight. I'll provide an update ASAP.
 

ShawnJ

Aug 20, 2016
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Dead short in the other relay... Darn. The other transformer will not kick it on.

Looking forward to all of you thoughts on the relay option I was pointing out above.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Contactors are designed to switch higher power at higher voltages than relays. If your load is inductive and a reasonably high power then the contactor is a safe option.

Measure the resistance of the coil of the working contactor and then measure around the various connections on the other one (looking for some similar resistance) to make sure you haven't accidentally wired up the wrong connections.
 

Bluejets

Oct 5, 2014
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That way, I can use the 110V I already have in that NEMA enclosure and just switch in the 110V to the relay coil w/ the existing design I already have.

One last question. Do I need a current limiting component to this design? Right now, there's nothing. I read somewhere I can use an inline cap and resistor between the hot and neutral, but I don't quite understand why and how that works. That's the last part I'm concerned about...

Thanks.

None needed.
 

ShawnJ

Aug 20, 2016
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Thank you. I'll order the relay I mentioned and post the results.
 

BobK

Jan 5, 2010
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Dead short in the other relay... Darn. The other transformer will not kick it on.

Looking forward to all of you thoughts on the relay option I was pointing out above.
I told you so, several posts back. That was the only thing that made sense, given your readings and the description of the behavior.

Bob
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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I've been out of town vacationing in the surf. Didn't bring my laptop and don't do smart phones. I have enough addictions already.

Anyway, I told you way back in this thread to monitor the 24VAC output of the transformer with your DMM while connecting the contactor coils to it. This test would have shown you that either the transformer is underrated or that one of the contactor coils is shorted.

Chris
 
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