buck and boost

[lowvoltman]

what size buck and boost would you use on 50a 120/208v 1 phase service
need to boost to 240v. I understand they are capable of alot more than the nameplate rating. thanks

 

[drbond24]

What amperage do you need @ 240 V?

Every transformer is capable of more than its nameplate rating. You're just killing it faster than necessary, though. Better to stick with the nameplate.

 

[brian john]

240-208=32 volts X 50 A= 1.6 kva. Check the math I'm no wiz kid heck I am not an wiz old fogey either.


BUT THE NAME PLATE IS THE RATING check the catalog number against the manufacture data sheets for the particular unit.

 

[philly]

240-208=32 volts X 50 A= 1.6 kva. Check the math I'm no wiz kid heck I am not an wiz old fogey either.


BUT THE NAME PLATE IS THE RATING check the catalog number against the manufacture data sheets for the particular unit.

So you use the voltage difference across the transformer as opposed to the ouput voltage to size the transformer? I would have thought that you needed to use the secondary voltage times the seconary current to size, in this case 240V * 50A = 12kVA. This seems awful high for a boost transformer so I'm thinking that I'm incorrect

 

[augie47]

So you use the voltage difference across the transformer as opposed to the ouput voltage to size the transformer? I would have thought that you needed to use the secondary voltage times the seconary current to size, in this case 240V * 50A = 12kVA. This seems awful high for a boost transformer so I'm thinking that I'm incorrect

you're looking at it as a standard step-up transformer. Buck & Boost are a different animal.

Here is SqareD's calculator link:
http://www.schneider-electric.us/su...-tools/buck-and-boost-transformer-calculator/

 

[jim dungar]

Remember, if you use a buck-boost to raise the Line-Line voltage you will also be raising the Line-Neutral voltage. 120/208V boosted will yield about 133/236V.

 

[LarryFine]

This seems awful high for a boost transformer so I'm thinking that I'm incorrect

Your thinking is correct. :wink:

The buck-boost is not a magic box. Its energy isn't free. It adds to the output voltage by using additional current from the supply circuit. The same with an auto-transformer or a transformer with voltage-adjustment taps.

The primary current simply energizes the secondary, which is placed in series with the primary; the two windings in series become an auto-transformer, which is connected as either a step-down (buck) or step-up (boost) unit.

But, the only current that the secondary imparts to the load is its proportion of the total load-side voltage. If it's contributing 10% of the load voltage, it only has to supply 10% of the load current. Thus, only that much power.