Page 2 of 3 FirstFirst 123 LastLast
Results 11 to 20 of 24

Thread: Second set of eyes for 480 delta delta to 240/120

  1. #11
    Join Date
    Jul 2007
    Location
    Clark County, NV
    Posts
    184
    Quote Originally Posted by Robert4709 View Post
    ...Q1. How do I get the required 208-230 to the A/C ?
    Addressing this only.

    I work with "208 - 230" HVAC equipment everyday, installing and repairing. These are nominal voltages to let you know that the same equipment is rated for both nominal 208 systems and nominal 230 systems.

    Here, a nominal 230 system is an actual target of 240, with some specific sites measuring up to 243 at times.

    Everything works fine.

  2. #12
    Join Date
    Dec 2012
    Location
    Placerville, CA, USA
    Posts
    18,176
    You use a buck transformer. A transformer with a 480 primary (that can tolerate 490 long term) and two isolated 24V secondaries can be put in series with the two output secondary ends to get roughly 110/220 center tapped and balanced. Or use two 12V secondaries instead to get very close to 120/240.
    That additional transformer can be sized just to deliver the power associated with the voltage difference times the load current instead of the full load power.

    Sent from my XT1585 using Tapatalk

  3. #13
    Join Date
    Oct 2017
    Location
    Houston, Texas, USA
    Posts
    10
    First of all Thank you all for giving so much input in this, this thanks should have been at the top of my last reply but passed the 15 minute edit deadline fixing typos. I really do appreciate the time and experience your sharing here.

    Quote Originally Posted by MAC702 View Post
    Addressing this only.

    I work with "208 - 230" HVAC equipment everyday, installing and repairing. These are nominal voltages to let you know that the same equipment is rated for both nominal 208 systems and nominal 230 systems.

    Here, a nominal 230 system is an actual target of 240, with some specific sites measuring up to 243 at times.

    Everything works fine.
    Im assuming though that the current ~263V is a bit too high

    So currently my quandary is are all of the "240/120" delta type(if I got a 3 phase) and or single phase transformers like this where their secondary voltage actuals are 10% or so over and if so if I get a 208Y/120 instead of a delta delta will that be equally high by 10% and be a 225/130ish output. I havent bought the new transformer yet Im just trying to understand the system so I dont burn money on the transformer and end up burning out my electronics such as the A/C by being to far over/under but I admit I have no working understanding of the tolerances of all these things Im running mostly on a conceptual understanding from engineering classes years ago so pardon my ignorance in much of this.

  4. #14
    Join Date
    Jun 2006
    Location
    Ohio
    Posts
    21,259
    Quote Originally Posted by Robert4709 View Post
    ...
    Q1.How do I get the required 208-230 to the A/C ?
    Your interpretation of this [nameplate?] value is what perplexes me. A NEMA motor or motor compressor is [nominally] rated 230V when it is intended to be connected to a [nominal] 240V supply.
    I will have achieved my life's goal if I die with a smile on my face.

  5. #15
    Join Date
    Oct 2017
    Location
    Houston, Texas, USA
    Posts
    10
    Quote Originally Posted by Smart $ View Post
    Your interpretation of this [nameplate?] value is what perplexes me. A NEMA motor or motor compressor is [nominally] rated 230V when it is intended to be connected to a [nominal] 240V supply.
    Im not at the site atm I can get an image of it tomorrow to follow up.

  6. #16
    Join Date
    Oct 2017
    Location
    Houston, Texas, USA
    Posts
    10
    Quote Originally Posted by GoldDigger View Post
    You use a buck transformer. A transformer with a 480 primary (that can tolerate 490 long term) and two isolated 24V secondaries can be put in series with the two output secondary ends to get roughly 110/220 center tapped and balanced. Or use two 12V secondaries instead to get very close to 120/240.
    That additional transformer can be sized just to deliver the power associated with the voltage difference times the load current instead of the full load power.

    Sent from my XT1585 using Tapatalk
    Im hoping just to select the appropriate single large transformer to replace this one to both increase my capacity and give the desired voltages I just was surprised at seeing the elevated voltage after his and am somewhat worried that if i go get a used transformer with incomplete documentation i may see a similar plate and wrongly assume it will be 120/240 out when its not.

  7. #17
    Join Date
    Jun 2006
    Location
    Ohio
    Posts
    21,259
    Quote Originally Posted by GoldDigger View Post
    The note in the bottom right corner of the label says it all:

    "The primary voltage ratio of 240/480 is available only at 60Hz with a secondary voltage of approximitely [sic] 130/262." It is delivering exactly as promised.
    BTW, the dots on the windings strongly suggests that the four windings are on a common core, so open delta is not an option. `
    Still a matter of loaded vs. unloaded voltage. A 3kVA transformer doesn't take much to load up... and there is actually a matter of voltage sag along with motor starting voltage. Now if you go back the the OP you'll find he is actually talking about a 20kVA transformer and using this one for comparison.
    I will have achieved my life's goal if I die with a smile on my face.

  8. #18
    Join Date
    Oct 2017
    Location
    Houston, Texas, USA
    Posts
    10
    Quote Originally Posted by Smart $ View Post
    Still a matter of loaded vs. unloaded voltage. A 3kVA transformer doesn't take much to load up... and there is actually a matter of voltage sag along with motor starting voltage. Now if you go back the the OP you'll find he is actually talking about a 20kVA transformer and using this one for comparison.
    I did do the voltage measurment with an 8 amp load on the 263V which gave me the 263V reading was connected with a 50ft 10 AWG line at the time which if it was 12 or 14 AGW would have had a more pronounced voltage drop. If the issue persisted in the next transormer one idea was to just use a 14 AWG for the 15A load and use the Line resistance to drop the V(though probably not the best solution) but you are absolutely correct that Im not trying to fix this 3kv into working im trying to learn from it in selecting the bigger one so I dont have to 'fix' the larger one.

  9. #19
    Join Date
    Jun 2006
    Location
    Ohio
    Posts
    21,259
    Quote Originally Posted by Robert4709 View Post
    I did do the voltage measurment with an 8 amp load on the 263V which gave me the 263V reading was connected with a 50ft 10 AWG line at the time which if it was 12 or 14 AGW would have had a more pronounced voltage drop. If the issue persisted in the next transormer one idea was to just use a 14 AWG for the 15A load and use the Line resistance to drop the V(though probably not the best solution) but you are absolutely correct that Im not trying to fix this 3kv into working im trying to learn from it in selecting the bigger one so I dont have to 'fix' the larger one.
    A 240V 8A load will not heavily load a 3kVA transformer to the point of voltage sag... so it is still performing as the note says. But the whole point for it even having a 130/262 actual output is to compensate for the nuances experienced when heavily loaded. Taking it to this level is not commonplace IMO.

    Also, the disparity between a 230V motor voltage rating and a 240V nominal voltage supply isn't meant to be literal, i.e. forced. You do not have to use smaller gauge wire to ensure voltage drop. A 230V-rated motor will operate just fine on a nominal 240V system with minimal voltage drop. It'll just draw slightly less current when fully loaded.

    I think you are overthinking the situation...
    I will have achieved my life's goal if I die with a smile on my face.

  10. #20
    Join Date
    Oct 2017
    Location
    Houston, Texas, USA
    Posts
    10
    Quote Originally Posted by Smart $ View Post
    A 240V 8A load will not heavily load a 3kVA transformer to the point of voltage sag... so it is still performing as the note says. But the whole point for it even having a 130/262 actual output is to compensate for the nuances experienced when heavily loaded. Taking it to this level is not commonplace IMO.

    Also, the disparity between a 230V motor voltage rating and a 240V nominal voltage supply isn't meant to be literal, i.e. forced. You do not have to use smaller gauge wire to ensure voltage drop. A 230V-rated motor will operate just fine on a nominal 240V system with minimal voltage drop. It'll just draw slightly less current when fully loaded.

    I think you are overthinking the situation...

    so if we scale the 3 kv to a 20 kv it is likely not to sag even given a 35A load so then I guess my question is is it ok to give the A/C 263V long term?

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •