Need some help with Transformer/Contactor

Thread Starter

onesquin

Joined Nov 18, 2022
10
Hey I'm a NOOB trying to complete a DIY project of hooking up a thermostat to my garage heater. I am following this video...


I ordered the exact contactor and transformer linked in the comments.

I can't get the contactor to close. The highest voltage I have seen from the transformer is 5.5VAC. It should be outputting 24V. I am guessing that the transformer is bad. The only thing I am doing different than the video is I ran a dedicated 110 circuit for the transformer as I had a plug right next to the heater. In testing I hooked both sides of the transformer to the contactor bypassing the thermostat and it would not close. I have tested the input to the transformer and I am getting 120+ VAC. I also took everything apart and bench tested the transformer and can't get 24VAC out of it. This is not really applicable at this point but I am using a simple programable thermostat and not a WiFi thermostat.

NOOB Questions:
1. I am not sure how to test the output of the transformer with my meter. When wired in the heater with the red and green output wires connected on each side of the contactor I had my meter on VAC and the black meter lead grounded to the chassis and the red meter lead was getting 5.5V on each the red and green output. When on my bench I can't get a reading on the outputs when they are not connected to anything? What am I doing wrong or is the transformer just bad.

2. Does the contactor need to be wired a certain way? I just assumed since it is a relay the 240 VAC can be either input and the side 24VAC connections can be either side but maybe it needs to be wired correctly. The contactor is labeled L1/L2 and T1/T2. I had L1/L2 the input from the breaker panel. I figured the side 24V connections didn't matter either as they just closed the circuit?

Please see the pics as well of the components. Sorry I know this is whiffle ball for all of you but I thought this would be a pretty easy project as I have done tons of home wiring but I am quickly figuring out I am a little out of my element lol. I have done a bunch of searching on troubleshooting transformers and contactors but there are so many and it was just confusing me more...

Thanks
onesquin
 

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KeithWalker

Joined Jul 10, 2017
2,609
NOOB Questions:
1. I am not sure how to test the output of the transformer with my meter. When wired in the heater with the red and green output wires connected on each side of the contactor I had my meter on VAC and the black meter lead grounded to the chassis and the red meter lead was getting 5.5V on each the red and green output. When on my bench I can't get a reading on the outputs when they are not connected to anything? What am I doing wrong or is the transformer just bad.
Thanks
onesquin
You are measuring between the red secondary winding and ground, and the green secondary and ground. The only connection the secondary winding has to ground is through leakage and capacitive coupling so you are just reading some arbitrary low voltage. Disconnect the heater and contactor from the transformer and measure with your meter connected between the red and green secondary wires. You should get 24VAC.
Let us know what you get and we will take it from there.
 

MaxHeadRoom

Joined Jul 18, 2013
26,264
The green is most likely connected to a copper screen between primary and secondary, as Keith implied, the green is not a part of the functioning windings.
Normally in use, you would connect it to earth ground.
 

wraujr

Joined Jun 28, 2022
40
Based on label, the secondary (SEC) side of your transformer are the RED and GREEN wires.
These wires should be isolated from the metal case of the transformer.
This is AC so there is no "polarity".
As noted, your primary (PRI) is BLACK and WHITE for 120VAC (once again there is no polarity)
Set your meter to VAC and connect meter leads to RED and GREEN wires (and again polarity doesn't matter)
With 120VAC input you should get 24VAC (probably higher with no load) on the RED/GREEN pair.
Also you have a single output transformer (not multi), so ignore lower section of instruction page)
https://www.packardonline.com/products/pf42440/
 

MisterBill2

Joined Jan 23, 2018
13,712
The meter reading can not be seen in the video, all I see is black. You can tell us the numbers displayed on the meter. I do not demand proof! And like others have stated, ground has no part of the scheme. What I did not see in the video was the actual connection to the transformer. I did not see if the probe tips were actually contacting the wires inside the insulation. So it conveyed no useful information to me.
In the past I have seen wires connected to screw terminals without the insulation removed, and wire-nuts used without removing wire insulation, also.
 
Last edited:

LesJones

Joined Jan 8, 2017
3,897
Your test seems to indicate that the transformer is faulty. (Which is very unusual as transformers are normally very reliable.)
With nothing connected to the transformer measure the resistance between the white and black wires. (The 120 volt primary.) and then the red and green wires. (The 24 volt secondary.) Report the results.

Les.
 

Thread Starter

onesquin

Joined Nov 18, 2022
10
Your test seems to indicate that the transformer is faulty. (Which is very unusual as transformers are normally very reliable.)
With nothing connected to the transformer measure the resistance between the white and black wires. (The 120 volt primary.) and then the red and green wires. (The 24 volt secondary.) Report the results.

Les.
Thanks Les... So with everything disconnected I am getting 0.8 Ohms for the 24V Secondary(red/green) and 0.L MOhms on my meter for the 120V Primary(black/white)?? Not sure why it is registering that resistance. It seems like there is no or very little resistance across both connections?
 

Thread Starter

onesquin

Joined Nov 18, 2022
10
You are measuring between the red secondary winding and ground, and the green secondary and ground. The only connection the secondary winding has to ground is through leakage and capacitive coupling so you are just reading some arbitrary low voltage. Disconnect the heater and contactor from the transformer and measure with your meter connected between the red and green secondary wires. You should get 24VAC.
Let us know what you get and we will take it from there.
Thanks Keith... I posted a video below and some new findings in the resistance across the transformer.
 

Thread Starter

onesquin

Joined Nov 18, 2022
10
The meter reading can not be seen in the video, all I see is black. You can tell us the numbers displayed on the meter. I do not demand proof! And like others have stated, ground has no part of the scheme. What I did not see in the video was the actual connection to the transformer. I did not see if the probe tips were actually contacting the wires inside the insulation. So it conveyed no useful information to me.
In the past I have seen wires connected to screw terminals without the insulation removed, and wire-nuts used without removing wire insulation, also.
Thank you.
 

MaxHeadRoom

Joined Jul 18, 2013
26,264
Probably one of the common thermal fuses, I have had them buried so deep you cannot jumper or replace them. :oops:
Check to see if you see a couple ends sticking out.
 

Thread Starter

onesquin

Joined Nov 18, 2022
10
Probably one of the common thermal fuses, I have had them buried so deep you cannot jumper or replace them. :oops:
Well I just bought this on amazon so it is already in return status with a new one on the way... Will report back Sunday when the new one gets here and I get to REDO all the work I did and I will be sure to bench test the transformer before I go through all the hassle of wiring everything up...

THANKS TO ALL WHO HELPED ME TODAY!!!! I REALLY APPRECIATE IT...
 

wraujr

Joined Jun 28, 2022
40
So, a transformer is basically two coils of wire, a primary coil and a secondary coil. A coil of wire, depending on wire gauge, can be less than 1 ohm to less than 20 ohm (in other words, very low resistance) An infinite resistance (or open) indicates a break in the coil, a bad connection from wire to coil, or as Max suggested, a blown internal fuse.

For grins, measure the following resistances on the PRI side (not the RED/GREEN SEC side)
WHITE-BLACK (this we know is open)
WHITE-RED
WHITE-ORANGE
BLACK-RED
BLACK-ORANGE
RED-ORANGE
 

wraujr

Joined Jun 28, 2022
40
This is my guess as to what your transformer looks like.
Someone else needs to confirm (and we need your ohm readings), but you MIGHT get away with a BLACK/ORANGE connection.
Anyone else think this? My specialty is not transformers....
Transformer.jpg
 

LesJones

Joined Jan 8, 2017
3,897
I was just thinking of that possible solution and was looking at the information sheet on the transformer to see which colours would be between the end of the 120 volt winding and the start of the 240 volt section. When I got back to the end of the thread I realised you were suggesting the same thing. I suggest that the TS measures the resistance between the black and orange wires and if he gets a sensible reading (I would guess at between 50 and a few hundred ohms.) that he tries connecting the 120 volt supply to the black and orange wires and an checking the voltage between the red and green wires.

Les.
 
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