Transformer Help

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Little Bill

Little Bill

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I was asked by a friend to aid him in wiring a transformer. He told me it was a buck/boost (auto transformer).
It is to be wired to a dental imaging machine. I was told it was to keep the voltage within a tolerence.

The input voltage is 240V, and the way I understood him, the machine needs the voltage to stay as close to that as possible within their tolerence spec.

He just sent me a picture of the transformer and I got the cat. # and looked it up. It is called a "general purpose transformer".
I don't think it is a buck/boost, but I could be wrong. In any case, I can't see how it can be wired for the primary and secondary to both be 240V.
That sounds more like an isolation transformer is needed to me, but I'm not a transformer expert by any means.

I am adding this link for you transformer gurus to look at and see if you can help with this.

http://download.schneider-electric....e=CAD&p_File_Id=65868464&p_File_Name=3579.pdf
 
Little Bill said:
I was asked by a friend to aid him in wiring a transformer. He told me it was a buck/boost (auto transformer).
It is to be wired to a dental imaging machine. I was told it was to keep the voltage within a tolerence.

The input voltage is 240V, and the way I understood him, the machine needs the voltage to stay as close to that as possible within their tolerence spec.

He just sent me a picture of the transformer and I got the cat. # and looked it up. It is called a "general purpose transformer".
I don't think it is a buck/boost, but I could be wrong. In any case, I can't see how it can be wired for the primary and secondary to both be 240V.
That sounds more like an isolation transformer is needed to me, but I'm not a transformer expert by any means.

I am adding this link for you transformer gurus to look at and see if you can help with this.

http://download.schneider-electric....e=CAD&p_File_Id=65868464&p_File_Name=3579.pdf
Click to expand...
That is an isolation type (for purpose at hand)... but an isolation type transfomer doesn't necessarily hold the voltage to any tolerance. That's mostly controlled by the primary voltage.

Tell your friend and get more info on the machine and available power...
 
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Smart $ said:
That is an isolation type (for purpose at hand)... but an isolation type transfomer doesn't necessarily hold the voltage to any tolerance. That's mostly controlled by the primary voltage.

Tell your friend and get more info on the machine and available power...
Click to expand...

Are you saying that what I described would be an isolation transformer, or the actual transformer that I linked to is an isolation transformer?
If the latter, I don't see how that can be wired 1-1 ratio.

I agree and planned on asking him for more info on this machine and requirements.
 
Little Bill said:
Are you saying that what I described would be an isolation transformer, or the actual transformer that I linked to is an isolation transformer?
If the latter, I don't see how that can be wired 1-1 ratio.
Click to expand...
The linked transformer is isolation type for the purpose at hand. For 240 in and out, the primary would be wired as shown for parallel while the secondary as shown for series. I'm not quite sure what it is you described since you mentioned both buck/boost and isolation transformers.

Ultimately, if the available voltage is 240V nominal and the machine requires 240V but regulated to a tighter tolerance than utility/system provides, neither a buck/boost or isolation transfomer is going to help. To hold a tighter tolerance, he'd best be served with an appropriate UPS.
 
Smart $ said:
The linked transformer is isolation type for the purpose at hand. For 240 in and out, the primary would be wired as shown for parallel while the secondary as shown for series. I'm not quite sure what it is you described since you mentioned both buck/boost and isolation transformers.

Ultimately, if the available voltage is 240V nominal and the machine requires 240V but regulated to a tighter tolerance than utility/system provides, neither a buck/boost or isolation transfomer is going to help. To hold a tighter tolerance, he'd best be served with an appropriate UPS.
Click to expand...

I described what I know about the two different transformers, or maybe partly implied.
I do know a buck/boost is not an isolation transformer, but that is what the guy was saying he had.
My question, in part, was what type transformer it is that was linked to. I don't think it is a buck/boost.

The confusion on my part is what he described and what the actual transformer as shown actually is.

I still need to get more info on what the machine actually needs as far as voltage and tolerances, etc.
 
Little Bill said:
I described what I know about the two different transformers, or maybe partly implied.
I do know a buck/boost is not an isolation transformer, but that is what the guy was saying he had.
My question, in part, was what type transformer it is that was linked to. I don't think it is a buck/boost.

The confusion on my part is what he described and what the actual transformer as shown actually is.

...
Click to expand...
I can't quite tell whether you are still confused or not. As stated at the beginning of my last post, the linked transformer is an isolation transformer.

The thing about a buck/boost transfomer is that in many cases, it looks just like an isolation transformer, is actually built just like an isolation transformer, and the schematic representation also looks just like an isolation transformer. The difference is the turns ratio and thus the secondary voltage, then how it is connected. The rated secondary voltage is comparatively low, usually like 12 or 24 volts, depending on one or two windings and whether wired series or parallel. From there, it is connected in a manner to operate as an autotransformer.

Given that, the linked transformer is an isolation transformer intended to be used as an isolation transformer.
 
Last edited:
130425-1202 EDT

Little Bill:

Any transformer with two separate coils and no low impedance connection between the coils is an isolation transformer. Thus, the secondary could be at any potential relative to the primary within the insulation capability of the transformer. How the windings are connected can alter this. An isolation transformer can be used for all sorts of applications.

An auto-transformer has just one winding with one or more taps on the winding. There is no electrical isolation between the input and output. An isolation transformer can be connected so that it performs the function of an auto-transformer. I would suggest that the usual application of a buck or boost transformer will make it look somewhat like an auto-transformer, except connected as a buck it is functionally equivalent to an auto-transformer, but from a winding perspective it wastes copper space.

If you require voltage regulation, then you need a ferroresonant transformer, a servo driven Variac, or some electronic device.

If you need noise isolation then a transformer with a Faraday shield between primary and secondary may be needed, and other filtering.

You need a proper definition of what this transformer is required to do.

If you actually have 240 and 240 is what is required, then you do not need a voltage changing transformer. If tight regulation is required, then that is a different story. But the manufacturer of the equipment should design for a reasonable variation in input supply voltage. At home my voltage is 123 much of the time, ranges from 120 to 126 in general.

At figure 9.8.3.2 on my web page http://beta-a2.com/energy.html you can see my home voltage with 1 second resolution averaged in 1 hour periods for the period from 8-15-2011 thru 9-14-2011. In fig. 9.8.2.2 you can see voltage with 1 second resolution for 1 day.

.
 
Smart $ said:
I can't quite tell whether you are still confused or not. As stated at the beginning of my last post, the linked transformer is an isolation transformer.

The thing about a buck/boost transfomer is that in many cases, it looks just like an isolation transformer, is actually built just like an isolation transformer, and the schematic representation also looks just like an isolation transformer. The difference is the turns ratio and thus the secondary voltage, then how it is connected. The rated secondary voltage is comparatively low, usually like 12 or 24 volts, depending on one or two windings and whether wired series or parallel. From there, it is connected in a manner to operate as an autotransformer.

Given that, the linked transformer is an isolation transformer intended to be used as an isolation transformer.
Click to expand...

I'm not still confused, and probably not that confused to start with, but more needing reaffirmation.
I have connected a few buck/boost transformers and I was totally confused on the first one with the 24V secondary listed on it.
But I have since learned how they work and somewhat understand the low secondary listing on them.

I wanted to make sure of what I was aware of concerning buck/boost transformers before I corrected my friend. Being as he told me the machine mfg sent the transformer to him as a buck/boost. I also think I remember seeing a buck/boost once that said "general purpose transformer" on the nameplate once. That was one thing I wanted to be sure of as the linked transformer said "general purpose" on it, but the diagrams didn't represent what I know to be a buck/boost.




gar said:
130425-1202 EDT

Little Bill:

Any transformer with two separate coils and no low impedance connection between the coils is an isolation transformer. Thus, the secondary could be at any potential relative to the primary within the insulation capability of the transformer. How the windings are connected can alter this. An isolation transformer can be used for all sorts of applications.

An auto-transformer has just one winding with one or more taps on the winding. There is no electrical isolation between the input and output. An isolation transformer can be connected so that it performs the function of an auto-transformer. I would suggest that the usual application of a buck or boost transformer will make it look somewhat like an auto-transformer, except connected as a buck it is functionally equivalent to an auto-transformer, but from a winding perspective it wastes copper space.

If you require voltage regulation, then you need a ferroresonant transformer, a servo driven Variac, or some electronic device.

If you need noise isolation then a transformer with a Faraday shield between primary and secondary may be needed, and other filtering.

You need a proper definition of what this transformer is required to do.

If you actually have 240 and 240 is what is required, then you do not need a voltage changing transformer. If tight regulation is required, then that is a different story. But the manufacturer of the equipment should design for a reasonable variation in input supply voltage. At home my voltage is 123 much of the time, ranges from 120 to 126 in general.

At figure 9.8.3.2 on my web page http://beta-a2.com/energy.html you can see my home voltage with 1 second resolution averaged in 1 hour periods for the period from 8-15-2011 thru 9-14-2011. In fig. 9.8.2.2 you can see voltage with 1 second resolution for 1 day.

.
Click to expand...

Now the part in red above confuses me, as I thought a buck/boost was an auto transformer!:?
 
You guys let me hit the 2000 post count with my previous post and it didn't trip the confetti or balloons or anything!

I guess I'll have to settle for some ice cream!:D
 
130425-2342 EDT

Little Bill:

Strictly speaking an auto transformer is going to be a single winding with a tap part way down the winding. The winding is all in the same direction on the core.

If this is a boost unit then the input will be between one end and the tap, and the output will be from said one end to the other end. The number of turns will be optimized for the one end to the tap for the input voltage. In other words to get normal flux density for the transformer material based on the input voltage, number of turns, and core material.

If it is to perform the buck function then optimization will be for the input voltage across the total coil.

What is typically done is to use two coils. One is a primary, optimized for some input voltage. Then the secondary is connected to either add to or subtract from the primary voltage. So the same winding always is the primary. Whereas in the auto-transformer the primary is either between the tap and one end, or across the whole coil. A Variac is a good example of an auto-transformer where the primary is one end to a tap, and outputs possibly 0 to 140 V from 120 V. But may be connected to the outside ends, and then outputs is 0 to 120 V.

.
 
Little Bill said:
I thought a buck/boost was an auto transformer!:?
Click to expand...

gar said:
130425-2342 EDT

Little Bill:

Strictly speaking an auto transformer is going to be a single winding with a tap part way down the winding. The winding is all in the same direction on the core.

If this is a boost unit then the input will be between one end and the tap, and the output will be from said one end to the other end. The number of turns will be optimized for the one end to the tap for the input voltage. In other words to get normal flux density for the transformer material based on the input voltage, number of turns, and core material.

If it is to perform the buck function then optimization will be for the input voltage across the total coil.

What is typically done is to use two coils. One is a primary, optimized for some input voltage. Then the secondary is connected to either add to or subtract from the primary voltage. So the same winding always is the primary. Whereas in the auto-transformer the primary is either between the tap and one end, or across the whole coil. A Variac is a good example of an auto-transformer where the primary is one end to a tap, and outputs possibly 0 to 140 V from 120 V. But may be connected to the outside ends, and then outputs is 0 to 120 V.

.
Click to expand...

gar said:
130426-0928 EDT

Little Bill:

See http://en.wikipedia.org/wiki/Autotransformer for a discussion on auto-transformers.

.
Click to expand...

Little Bill said:
I was just always taught that buck/boost transformers were autotransformers because of the different taps.
Click to expand...

Well according to the info that I will link to below, I was right in saying a buck/boost is an autotransformer.

3) What is the difference between a buck-boost transformer and an autotransformer?
When a primary lead wire and secondary lead wire of a buck-boost transformer are connected together electrically, in a recommended voltage bucking or boosting connection, the transformer is in all respects, an autotransformer. However, if the interconnection between the primary and secondary winding is not made, then the unit is an insulating type transformer.
Click to expand...

http://www.electrical-contractor.ne...cs/101699/Questions_Answers_about_Buck_B.html
 
Little Bill said:
Well according to the info that I will link to below, I was right in saying a buck/boost is an autotransformer.
Click to expand...
One thing that distinguishes the two, at least in terms of what you stock, is that a buck-boost transformer can be built with either an autotransformer or an isolation transformer, while an autotransformer cannot be converted to an isolation transformer if that is what you need.
A bigger difference internally is that a buck-boost transformer usually has a much higher current rating on the low voltage winding, since the full load current does not have to flow through the high voltage winding.
To get the same economy in use of copper, an autotransformer would have to change the diameter of the wire at the tap point. Whether that was done or not, it could still be used for either buck or boost.
 
gar said:
130425-1202 EDT


An auto-transformer has just one winding with one or more taps on the winding. There is no electrical isolation between the input and output.
.
Click to expand...

Gar, typically the transformers we use as buck boost are single two winding transformers that get wired into an auto transformer configuration. Often they will have 120/240 primaries with 16/32 or 12/24 secondaries.

See diagrams below.


buck_boost-wiring.jpg
 
Little Bill said:
I was asked by a friend to aid him in wiring a transformer. He told me it was a buck/boost (auto transformer).
It is to be wired to a dental imaging machine. I was told it was to keep the voltage within a tolerence.

The input voltage is 240V, and the way I understood him, the machine needs the voltage to stay as close to that as possible within their tolerence spec.
Click to expand...
I'm with the others. The transformer in your link will not make the voltage tolerance out any better than the input supply. No simple transformer will.
If the tolerance of the voltage is critical you might need some regulating device.
Maybe something like a CVT would do the job.
 
Besoeker said:
I'm with the others. The transformer in your link will not make the voltage tolerance out any better than the input supply. No simple transformer will.
If the tolerance of the voltage is critical you might need some regulating device.
Maybe something like a CVT would do the job.
Click to expand...

Thanks Mr B! I've already explained to my friend that (as I suspected, but was looking for assurance) that the transformer he has will do nothing for voltage regulation.

BTW, what is a CVT?
"control voltage transformer" just a guess.
 
Little Bill said:
BTW, what is a CVT?
"control voltage transformer" just a guess.
Click to expand...

Constant Voltage Transformer
It uses a tuned resonant circuit and a saturated portion of the core (ferroresonant circuit) to deliver an output sine wave that is almost independent of the input voltage over a range of as much as 40%.

Unfortunately for some uses, the output voltage is very sensitive to input frequency, so do not try to use them with a poorly regulated generator.
 
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