Need Help buck 240 open delta to 208 wye

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The buck-boost diagrams posted, are for auto-transformer connections. Autotransformers require that the HV and LV winding configurations are identical.
 
electriguy said:
I cant figure this diagram out. Figure DD is what I need to use, cant figure out the connections.
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Welcome to the forum.

The diagrams are pretty straight forward, everywhere there is a dot put all those wires under one wire nut.

Your thread title is a different matter. What is it you are hooking up? What is the supply voltage? Why does what you are hooking up need a different voltage?
 
Should have added more info.. I need to just lower the voltage for a condensing unit from a high leg 120/240 to 120 208. Whats confusing me is b phase.. The line and load both connect to the same wires?
 
electriguy said:
Should have added more info.. I need to just lower the voltage for a condensing unit from a high leg 120/240 to 120 208. Whats confusing me is b phase.. The line and load both connect to the same wires?
Click to expand...


Did not look at the schematic before replying, but remember this is an autotransformer not an isolation transformer or SDS. All that matters in the end is voltage to the supplied load.

Even a simpler single phase buck-boost application will have input and output tied together on one side , it is the difference in number of turns between the other input and output leads that makes the change in voltage.
 
electriguy said:
Should have added more info.. I need to just lower the voltage for a condensing unit from a high leg 120/240 to 120 208. Whats confusing me is b phase.. The line and load both connect to the same wires?
Click to expand...
Yes, in an autotransformer connection, it is common to have one line serve as the 'reference leg', and as such it passes straight through the transformer.

If you need 120V at your load, you will need to be careful with which line is chosen as your reference. In particular, do not connect your system high leg (usually B phase) as the straight through leg.
 
electriguy said:
Should have added more info.. I need to just lower the voltage for a condensing unit from a high leg 120/240 to 120 208. Whats confusing me is b phase.. The line and load both connect to the same wires?
Click to expand...
Please clarify which of the following the load requires:


  1. 208V 3? 3W (3 hots, no neutral)
  2. 208Y/120V 3? 4W (3 hots, 1 neutral)
  3. 208V 1? 2W (2 hots, no neutral)
  4. 120/208V 1? 3W (2 hots, 1 neutral)

In cases 2 or 4, can you determine whether 120V internal loads are tied to any particular hot(s)?
 
All most afraid to chime in, afraid some one will bite my head off again.

So if I am wrong please, I am apologizing now.

But the OP. said he wants to reduce the voltage not increase it.

I think that the DD is a boosting configuration.

Needs to use either CC or EE. configuration

Ronald :)
 
ronaldrc said:
All most afraid to chime in, afraid some one will bite my head off again.

So if I am wrong please, I am apologizing now.

But the OP. said he wants to reduce the voltage not increase it.

I think that the DD is a boosting configuration.

Needs to use either CC or EE. configuration

Ronald :)
Click to expand...

An auto transformer has a HV side and a LV side.
To buck: line in to HV, load out of LV
To boost: line in to LV load out of HV

Often, the winding configuration is not important. You use what ever is needed to accommodate the desired voltage change.
The most common arrangement is 2 transformers connected in an open delta, with a 10% or 13.3% change.
The 3 transformer wye connection is usually used for larger kVA ratings.
 
ronaldrc said:
All most afraid to chime in, afraid some one will bite my head off again.

So if I am wrong please, I am apologizing now.

But the OP. said he wants to reduce the voltage not increase it.

I think that the DD is a boosting configuration.

Needs to use either CC or EE. configuration

Ronald :)
Click to expand...
Polarity isn't marked so hard to tell which diagrams are buck and which are boost.
 
Smart $ said:
Polarity isn't marked so hard to tell which diagrams are buck and which are boost.
Click to expand...
We can guess by their arrangements... as Jim Dungar pointed out (though I think he got it backwards)... but it's not as certain as the manufacturer stating which configuration is which, or indicating polarity.
 
Smart $ said:
We can guess by their arrangements... as Jim Dungar pointed out (though I think he got it backwards)... but it's not as certain as the manufacturer stating which configuration is which, or indicating polarity.
Click to expand...


Sorry, I didn't know different Transformers Numbered there Lines differently.
I was always taught that they where suppose to be a certain way.

This DD transformer should be a boost transformer. H1 through h4 + x1 through X4
should be additive.

H1 through H4 + X4 through X1 would be subtractive and would be a actual buck configuration.


Ronald :)
 
ronaldrc said:
Sorry, I didn't know different Transformers Numbered there Lines differently.
I was always taught that they where suppose to be a certain way.

This DD transformer should be a boost transformer. H1 through h4 + x1 through X4
should be additive.

H1 through H4 + X4 through X1 would be subtractive and would be a actual buck configuration.


Ronald :)
Click to expand...
After a little investigation, that diagram appears to be from Acme. Here's a link to their documentation:

http://www.acmetransformer.com/~/media/inRiver/322941-13868.pdf

It also says diagram DD for bucking 240 to 208.
 
ronaldrc said:
This DD transformer should be a boost transformer. H1 through h4 + x1 through X4
should be additive.

H1 through H4 + X4 through X1 would be subtractive and would be a actual buck configuration.
Click to expand...

The additive versus subtractive connection of the windings changes the final ratio of the transformation only. it has no affect on if the transformer is used for bucking or boosting. The final transformer ratio is dependent on the final connections, which is why you can get some relatively strange looking ratios such as 208:229.

If the source is connected to the LV terminals then the output has been boosted to the HV.
If the source is connected to the HV terminals then the output has been bucked to the LV.
 
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