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Author Topic: Mini Splits  (Read 2878 times)
Kristinsgrandpa
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« Reply #15 on: January 11, 2007, 03:38:00 PM »

Actually 240 VAC is 120 Deg. out of phase. It is two of three available legs from a three phase system.

With an exception, I'm told, on a 240 VAC genset. I've heard that they are 180 out of phase.
If so, the 240 V motors don't seem to mind.

House current might also be 180 out since there is only a hot and a neutral going to my house transformer.

Ed
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Jerry Liebler
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« Reply #16 on: January 11, 2007, 04:28:49 PM »

Captain Ron,
        If you want it to do any air conditioning you need to have air flow over the outside (condensor) coils.  These units normaly have all but the front 5 or 6 inches hanging outside.  When they are hanging out a window the outdoor fan draws air in through louvers on the sides and top of the metal case and pushes it through the condensor then exausts it out the back.  When one puts one into a bus most of the designed air flow has to be maintained for it to work.  In my case I have a plenum behind the cabinets to provide air into the top and sides of the AC  unit, with air flowing into this 'plenum' from louvered vents on the sides of the cap.  I also have a duct from the rear of the unit through the rear surface of the cap and a louver in the rear opening in the cap.   I designed my rear cabinets to create the 'plenum' by making the cupboards, on each side of the air conditioner, relatively shallow, leaving over a foot behind their rear wall.  I have Drawers under the air conditioner and these are much deeper. Because of the window type air conditioner I really have no closet space over the engine.  This wasn't a big deal to me as I have plenty of closet space in the 'rollback' closet over the bathtub.
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Jerry 4107 1120     
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DrivingMissLazy
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« Reply #17 on: January 11, 2007, 05:04:49 PM »

Actually 240 VAC is 120 Deg. out of phase. It is two of three available legs from a three phase system.

With an exception, I'm told, on a 240 VAC genset. I've heard that they are 180 out of phase.
If so, the 240 V motors don't seem to mind.

House current might also be 180 out since there is only a hot and a neutral going to my house transformer.

Ed

Ed, you are correct. Generally two hot legs are brought into a home. These two legs are 120 degrees out of phase with the third phase of a three phase system.

The odd thing is that if you look only at the two legs brought in, they are actually 180 degrees out of phase with each other, so the 240 volt power in your home is always 180 degrees out of phase with each other.
Richard
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« Reply #18 on: January 11, 2007, 05:16:30 PM »

Richard,
     While 2 phase conductors are brought into a residence they are 2 phases of a 240 volt line to line delta connected three phase transformer set AND the transformer has a center tap that's grounded, it's the neutral.  The third phase conductor would be 208 volts to ground or neutral and it would be 120 degrees ahead of or behind  the lines used by the residence.
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Jerry 4107 1120
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Stan
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« Reply #19 on: January 11, 2007, 05:40:04 PM »

I have never lived in an area where the public utility company distributed low voltage three phase, especially to residential. I have always had three phase at high voltagae (commonly 25kv) feeding the distribition transformers. The voltage on any winding is always 180 degees out of phase at opposite ends so each secondary winding pair of whatever voltage is 180* out of phase and may have a center tap.  You are only concerned with phase to phase angle if you want to use the three phase and use more than one winding. If you take one leg of three phase, the two wires are 180 out of phase with each other. I can't figure out how you can get two wires for single phase that are 120* out of phase and then try and run a single phase motor on it. If you put a scope on these two wires, what do you see? Possibly two half cycles that overlap or have a space between them, both positive half cycles or both negative half cycles. I hope someone can explain this conundrum to me because I have never seen anything but a sine wave of a public uility system.
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Dallas
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« Reply #20 on: January 11, 2007, 06:06:46 PM »

I have never lived in an area where the public utility company distributed low voltage three phase, especially to residential. I have always had three phase at high voltagae (commonly 25kv) feeding the distribition transformers. The voltage on any winding is always 180 degees out of phase at opposite ends so each secondary winding pair of whatever voltage is 180* out of phase and may have a center tap.  You are only concerned with phase to phase angle if you want to use the three phase and use more than one winding. If you take one leg of three phase, the two wires are 180 out of phase with each other. I can't figure out how you can get two wires for single phase that are 120* out of phase and then try and run a single phase motor on it. If you put a scope on these two wires, what do you see? Possibly two half cycles that overlap or have a space between them, both positive half cycles or both negative half cycles. I hope someone can explain this conundrum to me because I have never seen anything but a sine wave of a public uility system.
Actually 240 VAC is 120 Deg. out of phase. It is two of three available legs from a three phase system.

With an exception, I'm told, on a 240 VAC genset. I've heard that they are 180 out of phase.
If so, the 240 V motors don't seem to mind.

House current might also be 180 out since there is only a hot and a neutral going to my house transformer.

Ed

Ed, you are correct. Generally two hot legs are brought into a home. These two legs are 120 degrees out of phase with the third phase of a three phase system.

The odd thing is that if you look only at the two legs brought in, they are actually 180 degrees out of phase with each other, so the 240 volt power in your home is always 180 degrees out of phase with each other.
Richard

This makes my head hurt!

I know this about electricity:
  If I try to strip the wires on a lamp cord with my teeth while its still plugged in, it lets the smoke out of your head. (Long Story)
  If I stick my finger in the light socket to remove the base of the broken bulb, it turns your finger nail black for a loooong time.
  If you believe your friend that he shut off the power to the irrigation system while you are on an aluminum ladder, in the mud working on a 480V motor, you are a really big idiot! (It feels like someone hits you in the armpits with 3" iron pipes).
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NJT5047
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« Reply #21 on: January 11, 2007, 06:33:24 PM »

One advantage to the mini-splits is the heating and cooling capacitiy is about the same.
I have two miuni-splits with 12,000 btu cooling and 12,000 btu heating capacity.
With rooftop units you usually have to install more heat.
Ed

FWIW, I have two Dometic rooftop heatpumps and they work very well.   15K cooling and 12K heat per unit.  These units work fine down to freezing.  One unit heats my bus....but I have a open floor plan..a narrow area between the front and rear of the coach would require two units running to heat and cool.     
They are 110VAC and one will operate on a 20A outlet.  They use more power on heat than on cool...about 15A @ on heat....11A on cool.  I don't understand this but that's the way it is.    
The strip heat Colemans and Dometics were almost useless for heat...but, those are not heatpumps.    
Downside to rooftops is noise (ducted rooftops are not noisy), and raised roof coaches. 
I would be surprised if any small heat pump works efficiently at much below 30*...with home style heat strips they would...with a good 240V supply.
JR
 
  
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JR Lynch , Charlotte, NC
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« Reply #22 on: January 11, 2007, 06:43:50 PM »

Stan,
    I lived on a farm that had 3 phase power available, we used it for irrigation pumps.  It was 240 volt line to line, delta connected and there was a 4 th wire that was grounded, it was a center tap between two of  the phase conductors. Between the grounded connection and 2 of the phase conductors was 120 volts but between the grounded conductor and the third phase was 208 volts.  There are three phase 'Y connected systems where there is a common point(neutral) at the 'center' of the 'Y and the voltage from this common to any of the phase conductors is 120, this system gives 208 volts line to line and there is a phase angle of 120 between any 2 line to neutral voltages.  The Y connection is often found on generators and can be rewired to provide 2 120 volt wires that are at 180 degrees to each other.
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Jerry 4107 1120
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DrivingMissLazy
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« Reply #23 on: January 11, 2007, 06:53:03 PM »

Richard,
     While 2 phase conductors are brought into a residence they are 2 phases of a 240 volt line to line delta connected three phase transformer set AND the transformer has a center tap that's grounded, it's the neutral.  The third phase conductor would be 208 volts to ground or neutral and it would be 120 degrees ahead of or behind  the lines used by the residence.
Regards
Jerry 4107 1120

The center tap that is grounded at the center of one winding, for example between phase A and Phase B. This provides two 120 volt legs that are from each end of one winding so they are 180 degrees out of phase.
Richard
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« Reply #24 on: January 11, 2007, 11:07:03 PM »

Ron
 I have two mini-splits heat pumps 12000 btu each, we are very happy with them.The units are 120 volt ,and they are very quiet inside as well as outside. I was able to get mine from United Refrigeration about 2 yrs. backfor aprox,$ 530.00 ea. I know the price has gone up as it has with copper , and everything else . My bride an I both agree this is the best spent money on our bus yet!!! These units are not made in the states ,but they are made very well. Most all mfg. use a rotory compressor . You may want to check e- bay at one time ther was a seller on with a complete line of these.   Hope this helps !
               Dwayne M.
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Stan
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« Reply #25 on: January 12, 2007, 05:59:44 AM »

Gerry: I think you and I both understand three phase distibution but just explain it differently. There are comments on this thread that indicate that some others do not (" 240 consists of two 'legs' of 120 that are out of phase by 180 degrees.  Just stepping up the 120 with a transformer to 240 will only give you single phase 240 which I don't think the motors in the air conditioner will like" also "Actually 240 VAC is 120 Deg. out of phase. It is two of three available legs from a three phase system.")

Your farm service three phase came from distribution transformers either on farm or down the road to a point where several farms were fed from one location. I now live in a city with underground service. The primary is 25kv three phase and each distribution transformer serves eight houses. Single phase 240 goes to each house and if I wanted three phase I would have to pay for the underground installation from the transformer location. Transformers can be wound to give any voltage desired and distribution transformers usualyl have taps for voltage adjustment and to get the configuration (single phase 240 and Delta or Y three phase) that is required. Your explanation of the Delta and Y connection is quite clear and to simplify the phase relationship on the Y connection, just visuslize the the points  where you take off 240 volts as one long winding with a center tap.

If everyone can remember that opposite ends of a winding are 180* to each other and no matter how many taps you put on the winding, between any two taps there will be a sine wave with 180* beteen them. Using some other point as a reference means nothing. Your reference point has to be one of the conductors you use for the load.

Dallas: If this makes your head hurt, try and visualize this three phase wave in three dimension.
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captain ron
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« Reply #26 on: January 12, 2007, 07:22:46 AM »

 Hey, Thanks guys for the actual info on mini splits.  Grin  It's kinda hard keeping up with the latest "PHASE" of this topic and I'm sure it will  turn "180 degrees" and go into another "PHASE" in the near future.  Grin  Have fun guys I'll check back periodically to see if there's any more useful (for me) knowledge on Mini Splits.  Roll Eyes
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Stan
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« Reply #27 on: January 12, 2007, 07:58:50 AM »

Ron: Sorry your thread got hijacked, but got off on a tangent as frequently happens. As soon as someone started posting about minisplits using 240 volts, a lot of confusion showed up and I was trying to clarify the situation. Maybe I did a poor job on the electrical explanation, and not needed by you, but you were lucky enough to get a lot of info on minisplits. There was even a couple of suggestions on how to run 240 volt units on 120 volts.
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DrivingMissLazy
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« Reply #28 on: January 12, 2007, 08:25:22 AM »

Gerry: I think you and I both understand three phase distribution but just explain it differently. There are comments on this thread that indicate that some others do not (" 240 consists of two 'legs' of 120 that are out of phase by 180 degrees.  Just stepping up the 120 with a transformer to 240 will only give you single phase 240 which I don't think the motors in the air conditioner will like" also "Actually 240 VAC is 120 Deg. out of phase. It is two of three available legs from a three phase system.")

Your farm service three phase came from distribution transformers either on farm or down the road to a point where several farms were fed from one location. I now live in a city with underground service. The primary is 25kv three phase and each distribution transformer serves eight houses. Single phase 240 goes to each house and if I wanted three phase I would have to pay for the underground installation from the transformer location. Transformers can be wound to give any voltage desired and distribution transformers usually have taps for voltage adjustment and to get the configuration (single phase 240 and Delta or Y three phase) that is required. Your explanation of the Delta and Y connection is quite clear and to simplify the phase relationship on the Y connection, just visualize the the points  where you take off 240 volts as one long winding with a center tap.

If everyone can remember that opposite ends of a winding are 180* to each other and no matter how many taps you put on the winding, between any two taps there will be a sine wave with 180* between them. Using some other point as a reference means nothing. Your reference point has to be one of the conductors you use for the load.

Dallas: If this makes your head hurt, try and visualize this three phase wave in three dimension.

Very good explanation Stan. It is really hard to explain the differences with words only. Really need an electrical diagram to show everything.

One thing I would like to make clear. To my knowledge there is no such configuration as a 240 volt three phase Wye connection. At least in my 50 years of work in the commercial electrical field, I have never seen it. Any time a Wye connection is discussed the phase to phase as well as the phase to neutral voltage should be listed.

For example in the low voltage area the nominal voltage is 208/120 volts Wye. Any phase to phase voltage is 208 volts, and any phase to neutral is 120 volts. In the higher voltage it is 480/277 Wye. The higher voltage being the phase to phase voltage and the lower voltage being the phase to neutral voltage.

If there were a 240 volt Wye configuration the voltage would be 240/139 (I believe) and that line to neutral voltage would be of no use for any known application.
Richard
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Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body. But rather to skid in sideways, chocolate in one hand, a good Reisling in the other, body thoroughly used up, totally worn out and screaming:  WOO HOO, what a ride
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