Buck Boost transformers.

[K2X]

We did a lab in class the other night with Buck Boost transformers and the class got out a hour and a half early so i really feel like I didn't get enough. Soo I've been looking on ebay and i'm willing to buy a BB xformer just to play with and share with at least one other classmate. Looks like on ebay they go about $75 plus shipping . I was thinking that if someone here had a beater Buck Boost that would work for a couple of students, i could buy it and maybe save a couple of bucks. I'm not looking for anything free, just a good deal.. Thanks. pm me.

 

[Volta]

As far as I know, all that differentiates a regular (isolation) transformer from one rated for buck-boost (auto transformer), is that the secondary conductors are rated for the higher voltage. Other than that, any transformer will operate as buck or boost if wired that way, but the secondary conductors' insulation may not be rated for say, 240 volts, if the seconday output is 12/24.

Sounds like a good project to learn from, you can set it up to see a few different final voltages.

 

[jim dungar]

As far as I know, all that differentiates a regular (isolation) transformer from one rated for buck-boost (auto transformer), is that the secondary conductors are rated for the higher voltage. Other than that, any transformer will operate as buck or boost if wired that way, but the secondary conductors' insulation may not be rated for say, 240 volts, if the seconday output is 12/24.

Sounds like a good project to learn from, you can set it up to see a few different final voltages.

There is no physical difference between a buck-boost and a regular transformer. A transformer becomes a buck-boost based on how it is connected not how it is built.

The windings are built with an insulation appropriate for their voltage level, not the voltage level of the overall installation.

 

[Volta]

There is no physical difference between a buck-boost and a regular transformer. A transformer becomes a buck-boost based on how it is connected not how it is built.

The windings are built with an insulation appropriate for their voltage level, not the voltage level of the overall installation.

I should have borrowed your signature line. :grin:

Are you saying that (almost) all transformers have insulation on the seconday conductors rated for the voltage of the primary?

 

[jim dungar]

Are you saying that (almost) all transformers have insulation on the seconday conductors rated for the voltage of the primary?

Not at all.

And there is no need for them to. In a buck-boost autotransformer connection, the low voltage windings never have the high voltage applied to them.

 

[Volta]

Not at all.

And there is no need for them to. In a buck-boost autotransformer connection, the low voltage windings never have the high voltage applied to them.

Well the primary voltage is not applied to the secondary, but it is run through the secondary, which should then be insulated for it.

 

[jim dungar]

Well the primary voltage is not applied to the secondary, but it is run through the secondary, which should then be insulated for it.

Voltage does not run through the secondary.

The primary winding is connected in series with the secondary winding. The HV is applied, or delivered, across this series connection so each winding only 'sees' the voltage it was designed for.

 

[winnie]

Transformer insulation has to deal both with the voltage between coils and voltage to ground.

When connected as a buck-boost transformer, the interturn voltage is the same (or lower) than the normal interturn voltages that the transformer is designed for. However the voltage to ground may be much greater than in the normal 'isolated' configuration.

I certainly would not want to connect the a 7.2KV to 120/240V transformer as a buck-boost; the secondary coil is not insulated for 7.2KV to ground.

Likewise, if I were taking some random 240V to 32V transformer and connecting it as a buck-boost, I would want to know that the 32V coil was designed to tolerate 240V to ground.

-Jon

 

[gar]

100219-0917 ES

Electronic type transformers that I am familiar with will have Hipot specifications that I believe apply to all windings.

For much useful transformer information visit
http://signaltransformer.com/

Here is the datasheet for one model with many variations
http://signaltransformer.com/Data/Datasheets/DL-Rectifiers.pdf
This has a 1500 V Hipot test spec.

Some more useful pages
http://signaltransformer.com/Data/Datasheets/DU-SU.pdf
http://signaltransformer.com/Data/Datasheets/ICT.pdf

The following have their primary and secondary on essentially two separate bobbins and would have equal breakdown voltages between each separate item.
http://signaltransformer.com/Data/Datasheets/241-MT-DMT.pdf

You do not need to work with large transformers in order to study the general characteristics of transformers.

For some interesting information on inrush current to incandescent lamps and transformers for different turn on times in the AC cycle see the photos at my web site
http://beta-a2.com/EE-photos.html

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