Another power question / problem

S

shenandoah75

Active Member
Well i've been running with the following setup for weeks w/o issue
http://www.cocoontech.com/index.php?s=&amp...ost&p=78493

Came home tonight and the christmas lights (house side) were off (shop was on)...

Problem is that the power supply feeding the coils on the contactors appeared to have tripped. I'm using the ELK-TRG2440 (40VA). Now again, it's run for hours on end at night and for weeks w/o an issue. The transformer was real warm to touch. So i got out the multi-meter and sure enough with all 3 contactors fired up, it's pulling 1.22 amps when i wire the amp meter in line on one of the A/C feeds. I assume that the 24VAC is sort of like 2 phase 240V where each leg would put out 12V between ground. If so, that amerpage is on one leg and i would need to double the amperage draw to see total consumption, right?. If that's wrong, then i have no idea why it keeps tripping as it's well under the 40VA spec.

If so looks like i'm looking at .8amps per contactor with a possible draw of 3.2 amps if all 4 are on at once... Since i've only been running three, 2.4 would still be 57.6VA so why did it never trip in the weeks past? Also, shouldn't be common, but i also have the potential draw of sprinkler valves (.2-.3A holding vs inrush each) and eventually my pool valves (.75A each) too. since i would never run multiple sprinkler zones at one time. So i think i likely need a 24VAC supply with a 5A capacity or more... I could split the loads a bit and get something like the following for the lighting/120V/240V control and keep the elk for the sprinklers... i only have one outlet in the can where this is fed from, so getting tweo plug units in this location would be difficult. although i could put it another can and feed the power through the 18AWG sprinkler wire i've got connecting all locations.

http://cgi.ebay.com/CCTV-24-VAC-75VA-Power...ksid=p1638.m118

Any suggestions (including specific devices) welcome :)


For now i'm going to move my christmas light loads to 4 poles on only two contactors which should get me to just under 40VAC for the short term / through christma...

thx in advance
-brad
 
Something is not adding up here.

First 24 VAC should be measured "across" the contactor's coil. Check this first.

Also, are you measuring current with the proper leads in the proper slots in your multimeter (also in AC Amps)?

I'm confused with your measurements. You state:

If so looks like i'm looking at .8amps per contactor with a possible draw of 3.2 amps if all 4 are on at once... Since i've only been running three, 2.4 would still be 57.6VA so why did it never trip in the weeks past?
Click to expand...

Is this powered off of the 40 VA rated transformer?

Can you provide a schematic and coil resistance ratings of the contactor? Is this the type of contactor that is "latching" or does it require a "steady state" voltage to the coil to pull in the contacts?
 
BraveSirRobbin said:
Something is not adding up here.

First 24 VAC should be measured "across" the contactor's coil. Check this first.
Click to expand...


Ya that the case - well i'm measuring effectly between the leg headed to the elk relays and the other that goes to the contactor. But that has to be 24vac... I'll verify at the coild tomorrow when i have daylight and access to a ladder.


BraveSirRobbin said:
Also, are you measuring current with the proper leads in the proper slots in your multimeter (also in AC Amps)?
Click to expand...

Yep...


BraveSirRobbin said:
I'm confused with your measurements. You state:

If so looks like i'm looking at .8amps per contactor with a possible draw of 3.2 amps if all 4 are on at once... Since i've only been running three, 2.4 would still be 57.6VA so why did it never trip in the weeks past?
Click to expand...
Click to expand...

well at ~.4A for each coil * 4 = 1.6A (now my question is is that doubled since i'm dealing with two hots rather than hot and neutral/ground? Apologies for my ignorance on this... But the 3.2 is assuming the answer to that is Yes. If not, than i can' texplain why it's tripping.

Also note that i have 4 contactors, but right now only using 3 of them. so .4a * 3 = 1.2A.... * 24 = 28.8 VA * 2 or no?.



BraveSirRobbin said:
Is this powered off of the 40 VA rated transformer?

Can you provide a schematic and coil resistance ratings of the contactor? Is this the type of contactor that is "latching" or does it require a "steady state" voltage to the coil to pull in the contacts?
Click to expand...


Yes... sorry looks like even though extra spaces are stored in the post, the display drops them, if i paste i notepad, it looks good - let me know if you can't get it to display (should be a vertical line on rights side similar to left conacting other side of contactors in parallel.

----------------- TRANSFORMER ----------------
| |
--- ELK RELAY1 -> CONTACTOR1 <- |
| |
--- ELK RELAY2 -> CONTACTOR2 <- |
| |
--- ELK RELAY3 -> CONTACTOR3 <- |


my amperage measurment was taken by connectting one leg on the tranformer to the parallel loop going to the relays...

Regarding resistance will check tomorrow as well... That's just between the spade connectors for the coils right?

RE: latching servuse steady, they are "spring loaded" so voltage must remain on or they let go - so assuming that would meet your later definition?

thx
-brad
 
So the problem is between the 24vac and the contactor's coils then correct?

also, if measuring the resistance of the coils, remove all the power and wiring to them first.

What happens if you just wire the output of the 24vac of the transformer to the coils directly? I am guessing you can't play around with this a lot due to their physical locations.
 
The current is the same throughout a series circuit. Assuming a power factor of one (i.e. non-inductive loading of the coil) you should only be able to handle two contactors with that transformer (unless I'm not seeing something here correctly).
 
Yep... (technicaly, this doesn't matter because the circuits are the same, but the left hand side of your diagram is actually on an M1XOV + (2) M1RBs)

And also note that those parallel runs go to other circuits on the right hand side. I.e. ground (and ultimately "+" via other relays) is also wired in parallel to:

sprinkler1
..
sprinkler8

(but none of those will ever close at the same time as the 120V loads on the contactors)

I'll grab the coil resistance around lunch time...



BraveSirRobbin said:
The current is the same throughout a series circuit. Assuming a power factor of one (i.e. non-inductive loading of the coil) you should only be able to handle two contactors with that transformer (unless I'm not seeing something here correctly).
Click to expand...


Also, i think i'm missing something then. I think you're implying that putting a load between the two 24VAC legs of the transformer implies it is a series circuit (make sense). If you're saying current measuring through one leg of that series circuit is the same (i.e. .4 A per coil), and the supply is rated to handle 40VA, why can't it support 4? (40 / 24 = 1.66 A). (Again, i've only been running 3 so far)


thx again
-brad
 
Say you have just this simple circuit, the transformer connected to one coil (simple series circuit). The current is the same no matter where you would measure it (just correcting your "double" statement).

It sounds like you are on the verge of maxing out the transformer with two coils turned on. Plus your statement that other items are attached to the 24 VAC transformer, consider their draw also.

How many coils do you have on at one time?
 
Maybe someone can check my numbers, but your total resistance with three contactors running is under four ohms (again assuming pure resistance). What was the total current draw you measured with three contactors running (comming right off the transformer)?

The current for each contactor is "added" since they are wired in parallel to the transformer. Each "leg" (transformer to contactor) has the same current. You need to add the draw for each contactor for the total current.

You said you measured only 1.22 amps with three running though. I'm missing something here maybe someone else can point out. I am thinking you should have a lot more current draw with all three running.
 
BraveSirRobbin said:
Maybe someone can check my numbers, but your total resistance with three contactors running is under four ohms (again assuming pure resistance). What was the total current draw you measured with three contactors running (comming right off the transformer)? You said you measured only 1.22 amps with three running though. I'm missing something here maybe someone else can point out. I am thinking you should have a lot more current draw with all three running.
Click to expand...

Yep, 1.22A was whati got. I even double checked and had the mrs turn on one a time. It fluctuated a bit, but

first coil = .44A
adding second = .82
adding third = 1.22

The thing was pretty hot and green led was out. I unplugged, plugged back in, green led lit, but it tripped shortly after. I then rewired outside so i could rn everything off two circuits and dropped contactor #3 from the 24VAC load. This time it was on until the elk rules engine shut off the lights for the night.

Its possible my meter is not calibrated right too... but the fact i could run three at a time for weeks leads me to believe otherwise and maybe the PTC i the transformer is overreacting? Or for some reason it's just getting that hot?


thx
-brad
 
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