Control transformer in reverse

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180909-1107 EDT

Sierrasparky:

Your questions and comments seem inconsistent.

If your hangup is listing, then there are many perfectly workable circuits that you won't be able to use.

If the question is will the transformer work, then the answer is probably yes. But there could be other problems.

The numerical values you provided make no sense.

The VA rating of a transformer does not define the input current to a transformer with a particular load. Rather it is sort of a maximum average capability of the transformer that will provide good transformer life.

The current seen at a transformer primary consists of a load component and a transformer loss component.

We believe you have now specified a load current of 0.05 mA at 120 V. This calculates to 120*0.05 = 6 mW, 0.006 W. Not much of a light. If you meant 0.05 A or 50 mA, then power is 6 W. This could be useful, where 6 mW would not be useful.

If we assume the transformer ratio is 120/24 = 5 to 1. For a 6 W load on the 120 V winding, and 24 applied to 24 winding, then the 24 V winding has an input of at least 4 A.

.
 
GoldDigger said:
Here in the US we use "trouble light" in two different senses:
1. A temporary with a cage shield and/or reflector light on a long cord used as a portable worklight, or
2. An indicator light showing that there is a problem.
.06VA would not do much for 1, but might be fine for 2.
Also, .5A instead of .5mA gives a much more believable result for 1.

Sent from my XT1585 using Tapatalk
Click to expand...

The panel mounting 22mm indicator lamps we used are rated at 20mA. That's 400 times what the op says he wants.
Seems to me that something doesn't add up.
 
Besoeker said:
The panel mounting 22mm indicator lamps we used are rated at 20mA. That's 400 times what the op says he wants.
Seems to me that something doesn't add up.
Click to expand...

I was relaying what the contractor / customer stated to me.
Looking at the project Saturday the control circuit for signaling is fed from a 30va 120v to 24v.
The load of a the trouble circuit is actually .06 @120v and I found a piezo horn that is .058 also @ 120v which they did not tell me.
The control circuit powers a few proximity sensors and a control board. The label of the sensor system says up to 3w a 24v. So I believe the control power 30va @ 24v is sufficient.

24v 40va (trans) → reverse fed trans 20va 24v input -120v output → light/horn (.12a @120v)
 
drcampbell said:
If all you're doing is lighting up an indicator lamp, why not skip the transformer altogether and use a 24-volt lamp?
Click to expand...

Because the light is a special one and they do not want to replace the fancy housing.

Plus it blinks and also has a horn that I found in my inspection.

If a simple transformer can be used that would be better than rewiring a ( conduit and wire 100')
 
Sierrasparky said:
I was relaying what the contractor / customer stated to me.
Looking at the project Saturday the control circuit for signaling is fed from a 30va 120v to 24v.
The load of a the trouble circuit is actually .06 @120v and I found a piezo horn that is .058 also @ 120v which they did not tell me.
The control circuit powers a few proximity sensors and a control board. The label of the sensor system says up to 3w a 24v. So I believe the control power 30va @ 24v is sufficient.

24v 40va (trans) → reverse fed trans 20va 24v input -120v output → light/horn (.12a @120v)
Click to expand...

LarryFine said:
So, what is the total 120v load?
Click to expand...

.12@120v
 
Sierrasparky;1942291[B said:
].12[/B]@120v
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So not 0.05mA as you previously stated.
Nor 0.005 mA?

Most of us here try to be helpful but if you continue to provide conflicting/duff information you must understand that makes it difficult.
 
Besoeker said:
So not 0.05mA as you previously stated.
Nor 0.005 mA?

Most of us here try to be helpful but if you continue to provide conflicting/duff information you must understand that makes it difficult.
Click to expand...

Thank you all for your inputs.


Sorry , My OP was about was it ok to use a control trans in reverse , nothing more nothing less.
I gave the current requirements as was told to me.
I verified in person only yesterday.
What more do you want from me. Blood or something.
 
Sierrasparky said:
Thank you all for your inputs.


Sorry , My OP was about was it ok to use a control trans in reverse , nothing more nothing less.
I gave the current requirements as was told to me.
I verified in person only yesterday.
What more do you want from me. Blood or something.
Click to expand...

If you find it difficult to perfectly say what's in your mind, please try posting a schematic diagram instead,or a picture.:D
 
Sierrasparky said:
Thank you all for your inputs.


Sorry , My OP was about was it ok to use a control trans in reverse , nothing more nothing less.
I gave the current requirements as was told to me.
I verified in person only yesterday.
What more do you want from me. Blood or something.
Click to expand...
Speaking for most, if not all of us, we tend to try to be very specific and accurate, so we ask for the details we feel we need to give the correct answer to a generalized question.

We're only trying to be helpful, not belittling. It's no always easy to give a yes-or-no answer to a yes-or-no question, especially for those of us who are (even quasi-) engineers.
 
180909-2432 EDT

Sierrasparky:

Any ordinary tightly coupled electromagnetic transformer can be driven from either the primary or secondary side. But you must stay below core saturation (volt-time integral), and within the power dissipation capabilities of the transformer.

You may not get quite the results you expect, but should be somewhat close. For example for a stepdown transformer the transformer turns ratio may be lower than the rated voltage ratio would indicate. This is to provide full output voltage at full load. When this transformer is run in reverse, then the output voltage will be less than what you might expect. But you won't exceed the volt-time integral if you provide somewhat greater input voltage.

.

.
 
LarryFine said:
Speaking for most, if not all of us, we tend to try to be very specific and accurate, so we ask for the details we feel we need to give the correct answer to a generalized question.

We're only trying to be helpful, not belittling. It's no always easy to give a yes-or-no answer to a yes-or-no question, especially for those of us who are (even quasi-) engineers.
Click to expand...

It does seem like belittling. All I wanted to know is was it plausible. Then I asked a formula and all you folks wanted to do was do the math for me.

Looks like Gar has info that is more on the lines of my ask.

gar said:
180909-2432 EDT

Sierrasparky:

Any ordinary tightly coupled electromagnetic transformer can be driven from either the primary or secondary side. But you must stay below core saturation (volt-time integral), and within the power dissipation capabilities of the transformer.

You may not get quite the results you expect, but should be somewhat close. For example for a stepdown transformer the transformer turns ratio may be lower than the rated voltage ratio would indicate. This is to provide full output voltage at full load. When this transformer is run in reverse, then the output voltage will be less than what you might expect. But you won't exceed the volt-time integral if you provide somewhat greater input voltage.

.

.
Click to expand...

Thanks Gar that is good information.

topgone said:
If you find it difficult to perfectly say what's in your mind, please try posting a schematic diagram instead,or a picture.:D
Click to expand...
I thought my OP was to the point. I am sorry if it confused some. I only knew what was told to me from the client over the phone. I asked for him to take a picture but he never did. I did the site visit and posted the corrected numbers. :?
Will do next time if possible, I did not have access at the time to draw a pic.
 
Besoeker said:
Just sound information.
Click to expand...

I was never asking anyone here about current , just if was legitimate.
All these years and now you are being a pain. I really don't understand the issue. So what if the client gave me the wrong current needs, My first objective was to know if a reverse transformer was a option. The First!
Below was my original post.
"I was approached to use a doorbell type 120v to 24v transformer in reverse to power a 120 volt trouble light fed from a 24v control circuit.
I said it was hokey and not proper listed use of the transformer. "

The necessary current was not at issue! So next time i'll just say "not at issue" or none of your business"

kwired said:
Other option is a relay with 24 volt coil to control the 120 volt indicator.
Click to expand...

The reason for not going that way was there is no 120v power within about 100'. The length plus bends plus junction boxes and running across the company mural was not what the client wanted. The client was looking for a cheap solution as all clients.
 
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