120v Normal Closed Relay Testing

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dw85745

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HVAC Tech
I think I have this worked out, but wanted to pass it by someone more knowledgeable to make sure I'm NOT doing anything DUMB!
I have a normally closed 120v relay I need to test live.
It appears to Ohm OK (don't have data sheet) but something is not right.
Pin1 to Pin2 (common) = Contacts and supplied by L1
Pin2 (common) to Pin5 = Coil is supplied by L2
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To test the contacts (light bulbs should light, using two in series for safety):
L1 > Light Bulb > Light Bulb > Pin2 (common) > Relay Contacts NC > Pin1 > L1

To test Coil is Working (light bulbs should go out) as Coils should open contacts
CONCERN LIES HERE BECAUSE OF L1 and L2
L2 > Pin5 > Relay Coil > Switch (contacts should Open) > Pin2(common) >Light Bulb > Light Bulb > L1

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Questions General
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1. My concern is will the activation of the coil by L2 occur fast enough so that only 120 volts
will appear at Pin2 (common), --OR- because L1 and L2 are out of phase it is Not a concern?

2) Does the above look reasonable?

Thanks
 
Perhaps a sketch is in order. testing in circuit is not easy because you may or may not have power on the contacts.

in circuit, if there is voltage on the contacts it will read zero volts across the contacts when it is closed and (usually) full voltage when it is open. no need for light bulbs or other hack work.

putting two light bulbs in series does nothing to make what you are attempting any safer.
 
dw85745 said:
...

============
Questions General
============
1. My concern is will the activation of the coil by L2 occur fast enough so that only 120 volts
will appear at Pin2 (common), --OR- because L1 and L2 are out of phase it is Not a concern?
Click to expand...
First of all, try rephrasing, because '120V will appear at Pin2' is meaningless. Voltage is always measured between two points.
It appears to me that you are worried that somehow 240V could be applied to the coil if both L2 and L1 are energized. I think the answer must either be that the relay is rated for such a configuration and it's okay, or it is not supposed to be wired this way at all, perhaps because L1 and L2 will short to each other. Without seeing a diagram or specs of the relay and knowing the intended purpose it's hard to respond to the rest.
 
Thanks both for replies.
petersonra:
I've been hesitant to take a voltage across the contacts as IMHO, that would be like trying to take the voltage on a wire. Am I wrong on this?
I have a sketch, will try and see if I can scan in and post. Late here so tomorrow.
 
dw85745 said:
Thanks both for replies.
petersonra:
I've been hesitant to take a voltage across the contacts as IMHO, that would be like trying to take the voltage on a wire. Am I wrong on this?
I have a sketch, will try and see if I can scan in and post. Late here so tomorrow.
Click to expand...
Are you trying to connect a 240v load with your relay, and jump one leg to open and close the coil?
 
As promised here is a schematic. Where the problem lies is that the NO relay only stays in circuit for less than a second and then the back EMF takes it out. One can ohm the contacts (my case (.)14 Ohms. Shaking the relay gently seems to indicate the contracts are NOT fused together.
In regard to the Coil. I have NOT got a good reading with my digital meter (UTI-61E). For those familiar with it I upgraded the meter some time ago using a Bourne POT, and ever since then stable and right on the money. For other than this COIL, readings are correct. HOWEVER, for this Coil,
It initially registers 14.556 KOhms then drops one Ohm at a time. Can't ever seem to get a stable reading. What is odd, is if I remove the leads from the Coil for 4 or 5 seconds, and put the leads back on, the meter starts counting down from where I left. I've tried this several times and each time the meter starts approximately when I left off in value.
 

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I think I've resolved the Meter Read Issue. The inductance from the coil and the meter combined are causing the readings to vary.
If anyone has any ideas on how to test this -- IN Circuit -- for example adding in a light bulb for testing to indicate open/closed -- would be great.
 
221106-1248 EST

dw85745:

Truly I have idea what you are describing, or what your circuit sketch shows.

You do have an L1 and L2.

You show some device consisting of a longer and shorter pair pair of lines connected to L1. I have to assume this is a switch contact ( not the way to draw a switch contact, with some labeling it might be a battery cell or battery }. Assuming contacts then. no indication of what controls the contacts, or if the other similar symbol in the L2 line is mechanically correlated.

We have two coils with a common connection to L2 thru another apparent switch contact.

Assume both these symbols are synchronized contacts that something controls, might be called a main toggle switch, and only serve the purpose to turn on or off the whole circuit. Thus, for further analysis we can ignore them.

We appear to have two coils. I don't know what they belong to or their purpose. One coil is always powered. The other coil is either not powered, or has power from some circuit that I cannot read or identify. Between pin 2 and 5 there appears to be something, possibly a resistor.

You clearly have no understanding on how to analyze a circuit, or how to clearly draw the circuit. If you understood circuits you could provide a more clear schematic, and could probably analyze your own problem.

.

.
 
Looks to be a potential relay (or at least wired as one) that puts a starting capacitor (SC (which he drew to look like a NO contact)) from the start winding (S) to L1 then drops out.

There is a coil and an NC contact.

Remove power. To check the contact, disconnect one side of the start capacitor and measure with your ohmmeter from 1&2. Should read zero ohms.

The coil is in parallel with the start winding meaning that you are going to have to disconnect either the compressor (does it have a connector) or the wire from pin 5 on the relay to L2. Measure from pin 5 to pin 2 which is the coil. And I have no idea what it should be other than open or shorted which means it's bad.

Check the capacitor to see that it is within what it says on the label. (Mfd)

Your meter creeps up because the capacitor is charging.

Have you looked in the SUPCO catalog for a replacement?

-Hal
 
gar: I'll let you have that debate with the electrical engineer(s) who designed the circuit. I'm just presenting it. See hbiss following post.
hbiss: You got it right. It is a potential relay and the Back EMF is what takes it out of circuit.
 
Ran out of time.
Thanks all for responding
gar: I'll let you have that debate with the electrical engineer(s) who designed the circuit. I'm just presenting it. See hbiss following post.

hbiss: You got it right. It is a potential relay and the Back EMF is what takes it out of circuit. The SC is the start CAP and if I recall correctly
--| |-- so identifies. I did NOT put the --| |-- for the RC which is the run CAP (my apologizes). Regarding the NO switch between Pin2 and Pin that is the symbol they use on the schematic I copied from. The symbols under L1 and L2 were designed to represent a momentary switch (contactor).
From Pin1 to Pin2 I get point .14 Ohms which is the same as my meter leads touching so accepted. The Coil (Pin 5 to Pin 2) was measured out of circuit.
Reseaching, I found that the meter reacting with the coil causes an induction. I also measured the start CAP -- had to unsolder the bleed resistor AND meets in spec. So from an Ohms basis it checks out. Re: SUPCO, I can get a new Relay. I'm, just Not a parts changer unless I know something is BAD.

FWIW:: trying to find why the compressor won't run has got me stumped. Electrically everything checks out. L1 and L2 give 240 and pass through the contractor. Both the Run and Start CAPS in spec. All wires between are OK. The compressor windings appear to Ohm OK BOTH at the compressor and through the wires (which should account for the overload NOT being triggered). (C2S) = 1.58, (C2R) = .68, (S2R) = 2.17 (off sightly but IMHO not material -- but what do I know! AND no breaker is ever thrown. Yet I can never get an AMP reading on ANY of the compressor leads. Hence my desire to check the potental relay in circuit to confirm the BACK EMF is actually pulling it out.
 
221106-1531 EST

dw85745:

Your first post states ---

" I have a normally closed 120v relay I need to test live.
It appears to Ohm OK (don't have data sheet) but something is not right.
Pin1 to Pin2 (common) = Contacts and supplied by L1
Pin2 (common) to Pin5 = Coil is supplied by L2 "

Note: your emphasis is on having a normally closed 120 V relay. In your posts where did you ever correlate parts of the diagram that were that relay?

This, your other comments that followed, and circuit diagram are incomprehensive to me.

Let me start with the following description. A true single phase motor is not self starting. You can start such a motor with a rope and pulley, or you can at least momentarily start it by making it at least a two phase motor. There are a number of ways to do this.

For one to easily analysis your problem one needs to know what are the different parts on the diagram, and their interrelationship.

.
 
ptonsparky:
If you never get amp reading on any lead you have an open circuit.
Click to expand...
I agree. BUT as stated in post #12
L1 and L2 give 240 and pass through the contractor.
Click to expand...
I know this for sure since I've AMP both lines and get 240V between them at the contactor Line Input.
There is another independent circuit on the Output of the contactor which also check out LIVE.
So the QUESTION BECOMES, why does everything OHM out in the circuit of interest BUT NOT AMPS ?
P.S. Forgot to mention above the compressor is NOT shorted to ground.

While I know the compressor leads are OK, one thing I haven't done is evaluate every wire in the circuit.
Never thought of it, but possiblly a break, but nothing chewed or appears burnt, so why the break.
Will give that a shot first thing tomorrow, though I'm still learning toward the replay UNLESS the overload is causing an open and then resetting itself quickly. Like the potential relay HOW one determines if that is a case is ???
 
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My guess is the relay is not wired correctly. The sketch shows the relay coil between 5 and 2. It also shows NC contacts between 2 and 1. Can't remember ever seeing a relay with a contact wired directly to the coil. Is this an octal, "ice cube" relay?
 
ptosparky:
Thanks for the wiring diagram to help confirm. This is a Trane Not Lennox, but wiring diagrams the same other than Pin5 is going to Supply Side of Contactor instead of load side. Most have a TOP. This one is NOT marked. There is a raised plastic bubble one side that I thought might indicate top, but relay won't fit if so oriented. Whether means anything? In attempting to cross, was able to find two on net with enough info to ID tops and pins. But each manufacturer is different, What's internal unknown and key because of contacts and gravity. One thought I had last night, before putting in new is to cut open old -- hopefully without destruct -- and see where things are actually located and also see if the contacts are actually opening. As I'm sure you are aware, they need to be matched to the compressor because of the back EMF.
 
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OK. Since there was nothing to ID the top on this relay (my understanding because of Back EMF gravity must work with the relay, hence contacts must be oriented certain way). I cut it open. I then reinstalled with cover OFF an the electromagneticfacing up. Fired the unit up and relay kicked in. (opened contacts). So that tells me the START CAP dropped out of circuit. Most interesting is the relay would close for a fraction of a second periodically. Say every couple minutes then seemed to settle being Open. I did an AMP check and now get AMPS both on Common and Run but they seem to vary widely. High about .14 and then back to 0 with most fluctation between .08 and .02 AMPS. The highest was around .89 (still less then 1 AMP). RLA is 17.0 and LRA = 91.0 I shut the compressor off and felt slightly warm. The discharge line was cold. So can one have a locked rotor, get low AMPS, and no breaker trip?
 
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