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    Buck boost transformers

    I need to install a buck boost transformer on a natural gas filling station (no prior experience with these transformers). The supply voltage of the equipment is listed 208/240 volts 1 phase. The unit draws about 8 amps at full load. It has an electronic control board and a compressor. The supply voltage dips to 197 volts under load and shows 207 volts with no load. The transformer I have ordered will boost the voltage by 10%. This will put the voltage without load at +/-228 volts. If it wasn't for the dual voltage ratings on the nameplate I would have been leary due to being so far over 208 volts without load and what it might due to the electronic board. By the way this equipment is about 400 feet from the source with #12 wire. Obviously the wire size should have been larger from new (I didn't install it). I am only using this transformer as a short term solution and will look at the bigger picture because I can see more problems arising in the future in this corner of the building. Anything else I should be concerned about.

    #2
    The best way to learn anything beyond a fast post here would be to read this.

    http://www.sola-hevi-duty.com/support/index.htm
    Brian John
    Leesburg, VA

    Comment


      #3
      Jing, I do have one recommendation: place the BB at the source end of the run, rather than at the load end. The reason is that you want the long run to be at the highest voltage, and thus lowest current, possible.
      Master Electrician
      Electrical Contractor
      Richmond, VA

      Comment


        #4
        Probably the most difficult thing for installers to understand is how to wire a buck-boost transformer. I is common for a singe B-B transformer of set of 2-3 B-B transformers to be provided with a number of wiring diagram configurations. It's trying to figure out which diagram to use and then wiring the tranforemr(s). When you don't do that many of have done none at all that can be difficult.
        The wiring diagram on the transformer itself alone isn't going to make it happen.

        Comment


          #5
          Actually for me the drawings are the answer. Pre-Internet I had to wire buck boost XMFR's I got the Hevi-Duty catalog read the info on buck boost study the drawings looked at the available conductors and their tags. Not that complicated IF YOU DO NOT LET IT BAFFLE YOU.
          Brian John
          Leesburg, VA

          Comment


            #6
            I remember the first buck boost transformers I ever wired, and I was so ticked off. "They sent me the wrong transformers", I declared. "These are only 24 volt transformers". :grin:

            Life's road is funny.

            Comment


              #7
              I would like to know exactly a 'buck boost' transformer' is or does?? is it just a low voltage power supply?? like taking 120 v ac and stepping it down to 12v or 24v ac for low voltage wireing.??

              Comment


                #8
                Originally posted by jameselectric
                like taking 120 v ac and stepping it down to 12v or 24v ac for low voltage wireing.??
                +/or used as an autotransformer - depending on how it is connected - a certain voltage above or below 120. Commonly used also to go from 208 to 240. (or there bouts...)
                [COLOR=blue]Electric heretic[/COLOR]
                [COLOR=white]It's always gonna be in the last place you look....[/COLOR]

                Comment


                  #9
                  Originally posted by jameselectric
                  like taking 120 v ac and stepping it down to 12v or 24v ac for low voltage wiring.??

                  No.

                  Typically you use a BB Trans to move the voltage up or down just a small percentage.

                  For me this often mean boosting 208 to 230, some 230 volt equipment can not run on 208.

                  The advantage is the BB transformer will be very small, inexpensive and easier to install compared to a standard transformer.

                  They are typically name plated as 120/240 to 12/24 transformers and can be used that way when wired 'normally'

                  But when connected as an "autotransformer," they can handle loads up to 20 times the nameplate rating.

                  Check out this site


                  Here is one way to wire a buck boost, notice that the primaries (H) and the secondaries (X) are wired together and that one circuit conductor more or less just passes straight through.



                  Compare that to conventional transformer connections where primaries and secondaries are only magnetically connected.

                  Last edited by iwire; 02-17-08, 07:21 AM.

                  Comment


                    #10
                    I have looked at the wiring diagram that goes with the transformer that I have ordered. It is a simple four wire diagram with two primary leads and two secondary leads, the same as the diagrams in the recent post. The transfomer I ordered will give me a fixed 10% boost which puts my voltage in an acceptable range for the equipment in question. Why did I pick this transformer over an autotransformer with multiple taps? Power of suggestion from the service tech that noticed the problem? Are there any advantages of a buck/boost compared to an autotransformer?

                    Comment


                      #11
                      Originally posted by jinglis
                      Are there any advantages of a buck/boost compared to an autotransformer?
                      Used in that context they are one in the same. Do you have a multi-tapped isolation transformer? Got a link?
                      [COLOR=blue]Electric heretic[/COLOR]
                      [COLOR=white]It's always gonna be in the last place you look....[/COLOR]

                      Comment


                        #12
                        No, I don't have a multitap isolation transformer. The reason for the buck/boost was cost (under $100) and 2 day delivery. This is only a short term solution to get the equipment up and running properly in a short period of time. The long term solution is probably $10,000 to install another service at this end of the building. Roughly 450 feet and probably a 600 volt feed, transformer and panel due to the fact I anticipate other problems in this area over the years.

                        Comment


                          #13
                          I must point out that B-B transformers have 2 separate windings. As iwire pointed out primaries are commonly 120/240 with secondaries of 12/24, 16/32.
                          If you looked at the NP of a transformer that is intended for B-B application you wouldn't have a clue as to how in the world to wire it unless you had a separate wiring diagram to do so.
                          The wiring diagrams will show that a given Transformer will have a multiple of wiring configurations for various B-B voltage requirements.
                          The neat thing about this application is that it allows you to purchase an affordable transformer to make an incremental voltage adjustment. That is only enough transformer kva is require for that adjustment not that the transformer must carry the entire load as a common "isolation transformer" where a separate source is established. The most common use is to buck (lower) or boost (raise) the supply voltage a small amount, usually 5 to 27%.
                          Remember that A B-B transformer or 3ph-transformer bank does not provide isolation. It is extremely important that the overload protection be applied according to art. 450 of the NEC. Should OCP be applied incorrectly the load can be exposed to an extremely high voltage should a fuse blow in an unacceptable location in the B-B circuit.

                          Unlike a B-B and an autotransformer a transformer with only one winding.
                          This single coil has one or more extra taps or electrical connections in various positions along the winding. Each tap corresponds to a different voltage so that effectively a portion of the same inductor acts as part of both the primary and secondary winding. Depending on the application, that portion of the winding used solely in the higher-voltage (lower current) portion may be wound with wire of a smaller gauge, though the entire winding is directly connected.

                          Autotransformers are usually economical only with turns ratios no higher than about 4:1. For a given power rating, they can be made smaller and more compact than transformers with two windings.

                          As with a B-B transformer the autotransformer does not provide isolation and, therefore, doesn't derive a separate source.

                          Comment


                            #14
                            Originally posted by iwire
                            No.

                            Typically you use a BB Trans to move the voltage up or down just a small percentage.

                            For me this often mean boosting 208 to 230, some 230 volt equipment can not run on 208.

                            The advantage is the BB transformer will be very small, inexpensive and easier to install compared to a standard transformer.

                            They are typically name plated as 120/240 to 12/24 transformers and can be used that way when wired 'normally'

                            But when connected as an "autotransformer," they can handle loads up to 20 times the nameplate rating.

                            Check out this site


                            Here is one way to wire a buck boost, notice that the primaries (H) and the secondaries (X) are wired together and that one circuit conductor more or less just passes straight through.



                            Compare that to conventional transformer connections where primaries and secondaries are only magnetically connected.



                            thanks for the link, however i do see on that website that it can be used for the 12v 24v etc.. low voltage for lighting too.

                            Comment


                              #15
                              Originally posted by jameselectric
                              thanks for the link, however i do see on that website that it can be used for the 12v 24v etc.. low voltage for lighting too.
                              Yes, the same transformer that can take 120 or 240 volt primary and create a 12 or 24 secondary can be used as a buck boost.

                              The difference is in how you make the field connections.

                              There are at least 3 or 4 ways to make the connections as a buck boost depending on the voltages and if you are boosting or bucking.

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