Buck Boost XFMR

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PAUL50 said:
. It’s on a pole and I only have single phase at the pole. 2 hots and a ground. That’s all. This buck boost transformer is not three-phase it is single phase. The panel is 208/120 single phase, the object they are trying to hook up is 240 single phase. I was given the buck boost transformer and was told to feed the xfmr from the existing 208 panel into the secondary side of the buck boost transformer which is 16/32. Then was told the primary would then have 240. Ive never hooked one up backwards. It just trips the breaker and I can find no reason why unless the xfmr is bad.
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You can't use just any ol buck boost transformer. It does need VA rating selected in accordance to the load and amount of voltage change that needs to occur. But the basics of getting 240 out of 208 input are the same with a 16/32 secondary, you will need to put 32 volt coil in series with a 208 volt coil with the net across the series being 240. The fact the primary is rated 240 and not 208 probably changes actual result some but you will be in the right ballpark with actual output.

By putting 208 volts directly to the 16/32 coil the impedance is way too low and high current flows and reason you are tripping breaker. No OCPD and you would have burned it out, still possibly did some damage to it anyway.
 
PAUL50 said:
I was given the buck boost transformer and was told to feed the xfmr from the existing 208 panel into the secondary side of the buck boost transformer which is 16/32. Then was told the primary would then have 240. Ive never hooked one up backwards.
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Look at the turns ratios mentioned in this thread.
 
kwired said:
Basically you are putting 208 across the primary then putting the secondary in series with the primary and the added or subtracted effect depending on how it is connected gives you the bucked or boosted voltage.
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Basically only boosting one leg.

It's easier for some guys to think in terms of line/load instead of primary/secondary

One leg gets tied through from line to load. The windings are tied to that same line and load, connected in series, and the other line and load tapped in at different points
 
PAUL50 said:
View attachment 2554688View attachment 2554688View attachment 2554688
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That drawing looks like you are intending to feed 120/240 single phase panel with load side of this - that will not work. There is no true neutral with what you have. Such a buck boost transformer would normally be used for supplying an individual 240 volt load from a 208 volt source or vice versa.

If you did boost it to 240 and bring the supply neutral to the output panel, you would have 120 volts to the common ungrounded line but the other boosted line would be about 152 volts to neutral if using 32V coil as the boost amount.
 
kwired said:
If you did boost it to 240 and bring the supply neutral to the output panel, you would have 120 volts to the common ungrounded line but the other boosted line would be about 152 volts to neutral if using 32V coil as the boost amount.
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That's really all he needs to know about how it works. It boosts one leg. All the other technical jargon is most likely in one ear and out the other.

Then just needs to know where to hook each wire.

Anything beyond that is confusing to people who don't understand the concept.

That's why I posted a diagram way back in the thread
 
And what you are trying to do and apparently being told to do is use it like a typical isolation transformer or separately derived system. Which will work if you supplied the 16/32 volt section with 16 or 32 volts and connected your output leads to the 120/240 coil, but you would need a 3 kVA 16/32 volt source and the outupt would only be able to be 3 kVA or it will overload the transformer.
 
James L said:
That's really all he needs to know about how it works. It boosts one leg. All the other technical jargon is most likely in one ear and out the other.

Then just needs to know where to hook each wire.

Anything beyond that is confusing to people who don't understand the concept.

That's why I posted a diagram way back in the thread
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Looking at what he is trying to do he probably needs at least a 15 kVA maybe even 25 kVA single phase transformer with 208 to 120/240 capability, or utilize his 120/208 supply for any 120 volt circuits and use a buck boost appropriately sized for anything that must be 240 instead of 208.
 
As I said before, most manufactures of buck boost transformers supply multiple wiring diagrams for different configurations. You have yet to say how many amps the load is, with a 3 kva buck/ boost, it is either fairly large, or you have oversized the transformer, which is ok, because you never want to undersize it. Grainger and Square D both have online calculators to size it by.
 
Just looked at your drawing, you cannot use a buck/boost transformer to feed a 120/240 panel. Your neutral to phase voltage will be boosted also. You need an Isolation transformer as others have mentioned.
 
It is very simple.
Somebody misunderstood what was being said.

You want to connect the transformer in an autotransformer configuration, like the posted diagram shows. This is a standard routine common connection for a buck-boost application.

Just connect your 208V to the LV terminations and your 240V to the HV ones.
Buck-Boost arrangements do not really have primary and secondary connections, which is probably part of the miscommunication..

An auto
 
kwired said:
That drawing looks like you are intending to feed 120/240 single phase panel with load side of this - that will not work. There is no true neutral with what you have. Such a buck boost transformer would normally be used for supplying an individual 240 volt load from a 208 volt source or vice versa.

If you did boost it to 240 and bring the supply neutral to the output panel, you would have 120 volts to the common ungrounded line but the other boosted line would be about 152 volts to neutral if using 32V coil as the boost amount.
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The panel is only feeding 2 220 disconnects no N needed. I didn’t add that I’m sorry.
 
hillbilly1 said:
As I said before, most manufactures of buck boost transformers supply multiple wiring diagrams for different configurations. You have yet to say how many amps the load is, with a 3 kva buck/ boost, it is either fairly large, or you have oversized the transformer, which is ok, because you never want to undersize it. Grainger and Square D both have online calculators to size it by.
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I have no idea what the load is. Just doing as I was told. That was all.
 
jim dungar said:
It is very simple.
Somebody misunderstood what was being said.

You want to connect the transformer in an autotransformer configuration, like the posted diagram shows. This is a standard routine common connection for a buck-boost application.

Just connect your 208V to the LV terminations and your 240V to the HV ones.
Buck-Boost arrangements do not really have primary and secondary connections, which is probably part of the miscommunication..

An auto
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It state’s primary and secondary in the drawing. I understand that this type can be wired both ways now. Everyone has been very helpful and I’ve done a lot of reading today. I did hook it up this way. It seemed logical when it was explained in the beginning when I started the project. It still trips though. That was yesterday. I’ll be back in front of it tomorrow and check wire for wire to make sure none are marked wrong. Thanks
 
I had one years ago that didn’t show the windings, just had numbers. 277 to 120 step down. Wired it up, turned it on, let the magic smoke out of it. Returned it to the supply house, they claimed I wired it wrong. They called the manufacture, and the manufacture said it had the wrong label on it, and was being recalled. They replaced it then.
 
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