Page 1 of 2 12 LastLast
Results 1 to 10 of 18

Thread: Phase Converters - 240/1 to 208/3

  1. #1
    Join Date
    Dec 2007
    Location
    Dayton, OH
    Posts
    131

    Phase Converters - 240/1 to 208/3

    Good morning.
    We have an upcoming application (restaurant reno and expansion) where the existing service is 240/1. There is a planned service upgrade to 208/3. But, that upgrade will take place maybe 6 months AFTER the completion of the reno/expansion. So...I think that the HVAC equipment (the only stuff that needs 3-phase) will need to run from Phase Converters before the upgrade. There will be 3 AHUs and 3 Condensing Units. I think 10 tons each.
    I plan on designing the new Elec equipment with 3-phase distribution and using only two phases in this interim period.
    This gets a little tricky, but I think we can make it happen.
    I've not specified Phase Converters before, and am looking for a little guidance. Anyone have preferred manufacturers? Anyone ever RENTED them for 6 months? Rotary? Static? One for each piece of HVAC equip?

    Thanks In Advance for any insight/advice.

  2. #2
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    33,733
    My experience with rotary and static converters is there is unbalance voltage and current in most instances - not so much of a problem if motors are oversized, but if running a motor near it's full load rating or even into service factor can be a problem. Problem is worse if the motor load varies as it is hard to compensate for changes in load on the fly. Rotary might be better, in such cases but will still have some of this issue. Static converters are best suited for steady loads as you fine tune them by adjusting taps in the capacitors to achieve as optimal balance as possible, but a change in load needs re tuning to get optimal balance again.

    Keep in mind you will not have 120 volts to neutral in either case on your derived phase.

  3. #3
    Join Date
    Jul 2006
    Posts
    2,442
    Seems like an expensive way of doing things. If you can spend the same amount of money* and get the new service now, I'd do that. Is only the building's service equipment single-phase and the 3-phase just needs to be run down a pole or does the PoCo need to install transformers/etc?

    * buy, install, and remove the converters, plus whatever would be spent on the new service equipment.

  4. #4
    Join Date
    Dec 2007
    Location
    Dayton, OH
    Posts
    131
    building is served (underground) from a 1 phase transformer on a nearby pole. So the utility (PG&E, this is in San Fran) has some work to do. All would LOVE to get a new service now, but, need to wait for the utility to do their work first.
    And, our client does not wish to wait (sound familiar?).
    So I need to find a way to get them up and running on 1 phase.
    And, just for kix, I also need to make sure that there is adequate kw capacity in this guy....HVAC guys think they need a lot.

  5. #5
    Join Date
    Dec 2007
    Location
    Dayton, OH
    Posts
    131
    and, fortunately, there is 3-phase on the nearby pole line

  6. #6
    Join Date
    Jan 2016
    Location
    PA
    Posts
    4,174
    Can you use vfd's or perhaps the equip already has them?
    they need oversized by ~sqrt 3



  7. #7
    Join Date
    Sep 2008
    Location
    UK
    Posts
    10,355
    Quote Originally Posted by Ingenieur View Post
    Can you use vfd's or perhaps the equip already has them?
    they need oversized by ~sqrt 3
    I don't know what rating the OP needs (or I missed it) but there are a number of mainstream drive companies that do single phase in, three phase out.
    Si hoc legere scis nimium eruditionis habes.

  8. #8
    Join Date
    Jul 2007
    Location
    Clark County, NV
    Posts
    629
    Quote Originally Posted by Besoeker View Post
    I don't know what rating the OP needs (or I missed it) but ...
    A typical 10-ton HVAC package or condensing unit would need about 12 kVA.

    Now, he says these are split systems, so in addition to the condensing units, we have three air handlers that also need power. A 10-ton air handler will probably be 3-phase equipment as well, about 2 kVA each.

    Air handlers might complicated the matter greatly because whereas condensers are often located near one another and fed from the same panel, it is quite common that air handlers will be close to the space they condition, and are often fed from their nearest panel.
    Last edited by MAC702; 10-05-17 at 02:27 PM.

  9. #9
    Join Date
    Dec 2007
    Location
    Dayton, OH
    Posts
    131
    10 ton Splits. And TWO systems, not Three, as I had previously thought.
    CUs are 45 MCA, 208/3 (16kw)
    AHUs are 67 MCA, 208/3 (24kw), which includes 10 kw each for elec heat.
    Totals about 80 kw.

  10. #10
    Join Date
    Jul 2007
    Location
    Clark County, NV
    Posts
    629
    Quote Originally Posted by raberding View Post
    ...AHUs are 67 MCA, 208/3 (24kw), which includes 10 kw each for elec heat...
    I'm assuming these are heat pumps with auxiliary electric heating? If so, you may be able to get by for the hopefully-only-six-months without needing the auxiliary heating strips. This would reduce your AHU requirement drastically.

Posting Permissions

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