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BTU/power question

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  • hijumpnsams@aol.com
    HI, What size genny will I need to run rooftop air, will a 3000 watt do? I am not sure if the unit is 12,500 or 15,000 BTU unit, how do I check and where do I
    Message 1 of 16 , Aug 15, 2007
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      HI,
      What size genny will I need to run rooftop air, will a 3000 watt do? I am
      not sure if the unit is 12,500 or 15,000 BTU unit, how do I check and where do I
      look? I am thinking of the quiet Honda model, any comments? I want to be
      able to run the air ALOT.
      Thanks,
      Merrilee



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    • Bill
      I would but two 2000 and a parallel kit instead of a 3000. There about the same money. You only have to use one of them if your not running the air, less
      Message 2 of 16 , Aug 15, 2007
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        I would but two 2000 and a parallel kit instead of a 3000. There about the
        same money. You only have to use one of them if your not running the air,
        less gas. You can lift a 2000 buy yourself. A 3000 is pretty heavy. You
        have 4000 w instead of 3000 if you need it. I had a 3000 and changed to two
        2000. The 3000 was just to heavy to get out of the truck by myself. With
        the two 2000 I can run the air and anything else I want all at the same
        time. I couldn't with the 3000.

        Bill


        Bill
      • Lynnie Whitefield
        Reading from my Onan handbook, it says the power average requirements for an air conditioner are 1400-2200 watts power and 12-18 amps. and says a 13500 BTU AC
        Message 3 of 16 , Aug 15, 2007
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          Reading from my Onan handbook, it says the power average requirements for an air conditioner are 1400-2200 watts power and 12-18 amps. and says a 13500 BTU AC will use 2200 watts and 18 amps.

          If I figured correctly from the above, that is approx. 6.13 btu per watt, and a 3000 watt generator should handle approx. 18,390 BTU., and approx 27 amps.

          Lynnie


          ----- Original Message -----
          From: hijumpnsams@...
          To: classicrv@yahoogroups.com
          Sent: Wednesday, August 15, 2007 7:51 AM
          Subject: [classicrv] BTU/power question


          HI,
          What size genny will I need to run rooftop air, will a 3000 watt do? I am
          not sure if the unit is 12,500 or 15,000 BTU unit, how do I check and where do I
          look? I am thinking of the quiet Honda model, any comments? I want to be
          able to run the air ALOT.
          Thanks,
          Merrilee

          ************************************** Get a sneak peek of the all-new AOL at
          http://discover.aol.com/memed/aolcom30tour

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        • Lynnie Whitefield
          Just wondering how the noise level compares between the two 2k units running and the one 3k unit running? Lynnie ... From: Bill To: classicrv@yahoogroups.com
          Message 4 of 16 , Aug 15, 2007
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            Just wondering how the noise level compares between the two 2k units running and the one 3k unit running?

            Lynnie

            ----- Original Message -----
            From: Bill
            To: classicrv@yahoogroups.com
            Sent: Wednesday, August 15, 2007 9:59 AM
            Subject: Re: [classicrv] BTU/power question


            I would but two 2000 and a parallel kit instead of a 3000. There about the
            same money. You only have to use one of them if your not running the air,
            less gas. You can lift a 2000 buy yourself. A 3000 is pretty heavy. You
            have 4000 w instead of 3000 if you need it. I had a 3000 and changed to two
            2000. The 3000 was just to heavy to get out of the truck by myself. With
            the two 2000 I can run the air and anything else I want all at the same
            time. I couldn't with the 3000.

            Bill

            Bill






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          • Dutch
            Your figures do not allow for the compressor starting load, that will run 3 times or more the running current. The i type inverter generators are
            Message 5 of 16 , Aug 15, 2007
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              Your figures do not allow for the compressor starting load, that will
              run 3 times or more the running current. The 'i' type inverter
              generators are particularly bad at handling motor starting surges. A
              conventional 3KW generator will handle a 13,500 BTU/H AC just fine,
              but a 3KW inverter type could be a bit "iffy". I would want to try it
              with my AC before buying one...

              Dutch

              --- In classicrv@yahoogroups.com, "Lynnie Whitefield" <birdman1@...>
              wrote:
              >
              > Reading from my Onan handbook, it says the power average
              requirements for an air conditioner are 1400-2200 watts power and
              12-18 amps. and says a 13500 BTU AC will use 2200 watts and 18 amps.
              >
              > If I figured correctly from the above, that is approx. 6.13 btu per
              watt, and a 3000 watt generator should handle approx. 18,390 BTU., and
              approx 27 amps.
              >
              > Lynnie
            • adam coote
              Hey Dutch, I m fairly new here at the Classic RV group but I had a question for you or whomever could help me. I recently obtained an ONAN generator/arc
              Message 6 of 16 , Aug 15, 2007
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                Hey Dutch,

                I'm fairly new here at the Classic RV group but I had a question for you or whomever could help me. I recently obtained an ONAN generator/arc welder combo under the name miller. Do you know where I can get engine parts for the ONAN? it's a twin, opposed cylinder engine. If you or anyone else can help me out, please let me know ok? my personal email amc19812002@... thanks.

                adam

                Dutch <yahoo.mail@...> wrote:
                Your figures do not allow for the compressor starting load, that will
                run 3 times or more the running current. The 'i' type inverter
                generators are particularly bad at handling motor starting surges. A
                conventional 3KW generator will handle a 13,500 BTU/H AC just fine,
                but a 3KW inverter type could be a bit "iffy". I would want to try it
                with my AC before buying one...

                Dutch

                --- In classicrv@yahoogroups.com, "Lynnie Whitefield" <birdman1@...>
                wrote:
                >
                > Reading from my Onan handbook, it says the power average
                requirements for an air conditioner are 1400-2200 watts power and
                12-18 amps. and says a 13500 BTU AC will use 2200 watts and 18 amps.
                >
                > If I figured correctly from the above, that is approx. 6.13 btu per
                watt, and a 3000 watt generator should handle approx. 18,390 BTU., and
                approx 27 amps.
                >
                > Lynnie






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              • Dutch
                I ve emailed you off-list, Adam... Dutch ... for you or whomever could help me. I recently obtained an ONAN generator/arc welder combo under the name miller.
                Message 7 of 16 , Aug 15, 2007
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                  I've emailed you off-list, Adam...

                  Dutch

                  --- In classicrv@yahoogroups.com, adam coote <amc19812002@...> wrote:
                  >
                  > Hey Dutch,
                  >
                  > I'm fairly new here at the Classic RV group but I had a question
                  for you or whomever could help me. I recently obtained an ONAN
                  generator/arc welder combo under the name miller. Do you know where I
                  can get engine parts for the ONAN? it's a twin, opposed cylinder
                  engine. If you or anyone else can help me out, please let me know ok?
                  my personal email amc19812002@... thanks.
                  >
                  > adam
                • Lynnie Whitefield
                  I was just quoting from my Onan generator handbook. The BTU/Wattage calculation was mine from their example. I did some more research and question the
                  Message 8 of 16 , Aug 15, 2007
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                    I was just quoting from my Onan generator handbook. The BTU/Wattage calculation was mine from their example. I did some more research and question the BTU/Wattage relationship listed. I did see on a couple of sites that the starting current of their units was 1.8 times the running current. If this is the case it seems that a current range on a 13500 btu unit of approx. 12-18 amps would a little short on the top end (21.6).

                    If three times the running current is normal for starting wouldn't this mean well over 30 amps and how does the fusing handle this?

                    Just an old guy with an old RV,
                    Lynnie

                    Not trying to be argumentave here, just trying to get clear in my mind the starting and running current relationship.


                    Dutch said:

                    Your figures do not allow for the compressor starting load, that will
                    run 3 times or more the running current. The 'i' type inverter
                    generators are particularly bad at handling motor starting surges. A
                    conventional 3KW generator will handle a 13,500 BTU/H AC just fine,
                    but a 3KW inverter type could be a bit "iffy". I would want to try it
                    with my AC before buying one...

                    Dutch

                    --- In classicrv@yahoogroups.com, "Lynnie Whitefield" <birdman1@...>
                    wrote:
                    >
                    > Reading from my Onan handbook, it says the power average
                    requirements for an air conditioner are 1400-2200 watts power and
                    12-18 amps. and says a 13500 BTU AC will use 2200 watts and 18 amps.
                    >
                    > If I figured correctly from the above, that is approx. 6.13 btu per
                    watt, and a 3000 watt generator should handle approx. 18,390 BTU., and
                    approx 27 amps.
                    >
                    > Lynnie






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                  • Dave P
                    Ordinarily, motors are protected with slow-blow fuses that ride through the current rise when the motors start. I agree that 3x is high for a fractional
                    Message 9 of 16 , Aug 15, 2007
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                      Ordinarily, motors are protected with slow-blow fuses that "ride through" the current rise when the motors start. I agree that 3x is high for a fractional horsepower motor under moderate load such as in an air conditioner compressor. One-and-a-half to two times is probably more realistic. Not to confuse the issue, but I would be more worried about a small generator not being able to supply enough VARs to the A/C. The genset and the A/C could be damaged when poor power factor leads to a voltage sag and current spike that will most likely occur faster than the generator breaker can operate. This damage will be cumulative and irreversable....so yes, it'll work the first time, maybe even the first 30 times, but eventually those thin motor or generator windings are going to go. As Dutch said, inverter-type generators don't handle dynamic loads well in the first place.

                      Good engineering is all about margin. Race car drivers can run their engines at the ragged edge because they expect to do major repairs very often. Leave some breathing room in your calculations and you'll sleep better at night.

                      All that being said, I have heard of people running single rooftop A/Cs off Honda 2kw portable generators with no problem. I wouldn't try to run much else in parallel though...especially inductive loads like motors and large electronics.

                      Dave

                      ----- Original Message ----
                      From: Lynnie Whitefield <birdman1@...>
                      To: classicrv@yahoogroups.com
                      Sent: Wednesday, August 15, 2007 5:41:59 PM
                      Subject: Re: [classicrv] Re: BTU/power question

                      I was just quoting from my Onan generator handbook. The BTU/Wattage calculation was mine from their example. I did some more research and question the BTU/Wattage relationship listed. I did see on a couple of sites that the starting current of their units was 1.8 times the running current. If this is the case it seems that a current range on a 13500 btu unit of approx. 12-18 amps would a little short on the top end (21.6).

                      If three times the running current is normal for starting wouldn't this mean well over 30 amps and how does the fusing handle this?

                      Just an old guy with an old RV,
                      Lynnie

                      Not trying to be argumentave here, just trying to get clear in my mind the starting and running current relationship.


                      Dutch said:

                      Your figures do not allow for the compressor starting load, that will
                      run 3 times or more the running current. The 'i' type inverter
                      generators are particularly bad at handling motor starting surges. A
                      conventional 3KW generator will handle a 13,500 BTU/H AC just fine,
                      but a 3KW inverter type could be a bit "iffy". I would want to try it
                      with my AC before buying one...

                      Dutch

                      --- In classicrv@yahoogroups.com, "Lynnie Whitefield" <birdman1@...>
                      wrote:
                      >
                      > Reading from my Onan handbook, it says the power average
                      requirements for an air conditioner are 1400-2200 watts power and
                      12-18 amps. and says a 13500 BTU AC will use 2200 watts and 18 amps.
                      >
                      > If I figured correctly from the above, that is approx. 6.13 btu per
                      watt, and a 3000 watt generator should handle approx. 18,390 BTU., and
                      approx 27 amps.
                      >
                      > Lynnie






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                    • Dutch
                      Coleman lists the starting locked rotor current for their popular Mach 3 13,500 BTU/H AC at 48.3 amps, and even the little 9,200 BTU/H Polar Cub at 45.6
                      Message 10 of 16 , Aug 15, 2007
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                        Coleman lists the starting "locked rotor" current for their popular
                        "Mach 3" 13,500 BTU/H AC at 48.3 amps, and even the little 9,200 BTU/H
                        "Polar Cub" at 45.6 amps:

                        http://www.rvcomfort.com/pdf_documents/rv_ac.pdf

                        Household circuit breakers are designed to handle the momentary
                        overloads from motors starting in AC's, refrigerators, freezers, and
                        such. If a fuse is used instead of a breaker, a special time-delay
                        design is required...

                        Dutch

                        --- In classicrv@yahoogroups.com, "Lynnie Whitefield" <birdman1@...>
                        wrote:
                        >
                        > I was just quoting from my Onan generator handbook. The BTU/Wattage
                        calculation was mine from their example. I did some more research and
                        question the BTU/Wattage relationship listed. I did see on a couple of
                        sites that the starting current of their units was 1.8 times the
                        running current. If this is the case it seems that a current range on
                        a 13500 btu unit of approx. 12-18 amps would a little short on the
                        top end (21.6).
                        >
                        > If three times the running current is normal for starting wouldn't
                        this mean well over 30 amps and how does the fusing handle this?
                        >
                        > Just an old guy with an old RV,
                        > Lynnie
                      • Steve Elms
                        I have a 76 Midas with roof air. I m pretty sure it s the origional one. I think it s a 15,000 btu but I m not positive about that. I first tried an old Honda
                        Message 11 of 16 , Aug 16, 2007
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                          I have a '76 Midas with roof air. I'm pretty sure it's
                          the origional one. I think it's a 15,000 btu but I'm
                          not positive about that. I first tried an old Honda
                          2200 watt generator. It would run the AC but just
                          barely and wouldn't even maintain 110 volts while
                          running. Next I bought one of the cheap 3000 watt
                          generators. I think it was only $300 or so brand new.
                          It worked okay but was very noisy and only lasted one
                          season. No parts were available that I could find. So
                          I then got a new Yamaha 3000 watt, the one that will
                          surge up to 3500 watts. It works great! It's quiet,
                          electric start, and is really just about perfect
                          except it's really heavy. A friend let me try his two
                          Honda 2000's with parallel kit. Each one is not too
                          heavy to load and they're small enough to actually
                          carry inside the motorhome if I don't want to pull a
                          trailer. The only disadvantage I see is you have two
                          generators to mess with, oh, and no electric start.
                          The noise level might be slightly higher than the
                          Yamaha but just barely.

                          I hope this helps,
                          Steve
                        • JerryK
                          Many campers are quite satisfied with their $300 Generators here s a link to an on going forum that discusses the pros and cons. It s located on RVNet.
                          Message 12 of 16 , Aug 16, 2007
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                            Many campers are quite satisfied with their "$300 Generators" here's a link to an on going forum that discusses the pros and cons. It's located on RVNet.
                            http://tinyurl.com/25ecj2
                            JerryK

                            Steve Elms <selms@...> wrote:
                            I have a '76 Midas with roof air. I'm pretty sure it's
                            the origional one. I think it's a 15,000 btu but I'm
                            not positive about that. I first tried an old Honda
                            2200 watt generator. It would run the AC but just
                            barely and wouldn't even maintain 110 volts while
                            running. Next I bought one of the cheap 3000 watt
                            generators. I think it was only $300 or so brand new.
                            It worked okay but was very noisy and only lasted one
                            season. No parts were available that I could find. So
                            I then got a new Yamaha 3000 watt, the one that will
                            surge up to 3500 watts. It works great! It's quiet,
                            electric start, and is really just about perfect
                            except it's really heavy. A friend let me try his two
                            Honda 2000's with parallel kit. Each one is not too
                            heavy to load and they're small enough to actually
                            carry inside the motorhome if I don't want to pull a
                            trailer. The only disadvantage I see is you have two
                            generators to mess with, oh, and no electric start.
                            The noise level might be slightly higher than the
                            Yamaha but just barely.

                            I hope this helps,
                            Steve





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                          • Elizabeth
                            I was talking to an onan dealer he told me minimum 4,000 watts to run an just one AC. Elizabeth Many campers are quite satisfied with their $300 Generators
                            Message 13 of 16 , Aug 16, 2007
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                              I was talking to an onan dealer he told me minimum 4,000 watts to run an
                              just one AC.



                              Elizabeth





                              Many campers are quite satisfied with their "$300 Generators" here's a link
                              to an on going forum that discusses the pros and cons. It's located on
                              RVNet.
                              http://tinyurl. <http://tinyurl.com/25ecj2> com/25ecj2
                              JerryK





                              [Non-text portions of this message have been removed]
                            • JerryK
                              Did you ask him what size the smallest generator he carried was? :-) :-) Jerry Elizabeth wrote: I was talking to an onan dealer
                              Message 14 of 16 , Aug 16, 2007
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                                Did you ask him what size the smallest generator he carried was? :-) :-)
                                Jerry

                                Elizabeth <aegearhart@...> wrote:
                                I was talking to an onan dealer he told me minimum 4,000 watts to run an
                                just one AC.

                                Elizabeth

                                Many campers are quite satisfied with their "$300 Generators" here's a link
                                to an on going forum that discusses the pros and cons. It's located on
                                RVNet.
                                http://tinyurl. <http://tinyurl.com/25ecj2> com/25ecj2
                                JerryK

                                [Non-text portions of this message have been removed]






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                              • Jack Rabon
                                The Onan 2.8 kw generators are designed to run a 13.5kbtu air conditioner & have a little left over for misc loads, see this ad for example:
                                Message 15 of 16 , Aug 16, 2007
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                                  The Onan 2.8 kw generators are designed to run a 13.5kbtu air conditioner &
                                  have a little left over for misc loads, see this ad for example:
                                  http://www.generatorjoe.net/product.asp?3=311

                                  In general, the portable generators have ratings which are similar to the
                                  HP ratings of cars during the 1960s. It seems that the test engineer set
                                  everything up right, then watched for a fleeting peak of power, so he could
                                  rate the genset.

                                  Not so for the more robust (and expensive) gensets like Kohler & Onan,
                                  which can actually deliver rated power for a long time.

                                  I read the book on a portable genset in Home Depot, and it showed that the
                                  3250 watt rating which was boldly printed on the side of the unit, was
                                  actually a "surge" rating. Probably taken as the load was slowing the
                                  frequency & steeling energy from the engine's flywheel. The actual rating
                                  was 2900 watts.

                                  To get the electrical load of anything, look at the data plate on the unit.
                                  Or use Google and save some time.

                                  Jack

                                  -----Original Message-----
                                  HI,
                                  What size genny will I need to run rooftop air, will a 3000 watt do? I am
                                  not sure if the unit is 12,500 or 15,000 BTU unit, how do I check and where
                                  do I
                                  look? I am thinking of the quiet Honda model, any comments? I want to be
                                  able to run the air ALOT.
                                  Thanks,
                                  Merrilee
                                • Elizabeth
                                  He carries everything. They are an RV parts and repair place and they do not sell RV s there. They are supposed to be the best place in Atlanta. Elizabeth ...
                                  Message 16 of 16 , Aug 16, 2007
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                                    He carries everything. They are an RV parts and repair place and they do not
                                    sell RV's there. They are supposed to be the best place in Atlanta.

                                    Elizabeth

                                    -----Original Message-----
                                    From: classicrv@yahoogroups.com [mailto:classicrv@yahoogroups.com] On Behalf
                                    Of JerryK
                                    Sent: Thursday, August 16, 2007 10:45 AM
                                    To: classicrv@yahoogroups.com
                                    Subject: RE: [classicrv] Re: BTU/power question



                                    Did you ask him what size the smallest generator he carried was? :-) :-)
                                    Jerry

                                    Elizabeth <aegearhart@bellsout <mailto:aegearhart%40bellsouth.net> h.net>
                                    wrote:
                                    I was talking to an onan dealer he told me minimum 4,000 watts to run an
                                    just one AC.

                                    Elizabeth

                                    Many campers are quite satisfied with their "$300 Generators" here's a link
                                    to an on going forum that discusses the pros and cons. It's located on
                                    RVNet.
                                    http://tinyurl. <http://tinyurl. <http://tinyurl.com/25ecj2> com/25ecj2>
                                    com/25ecj2
                                    JerryK

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