Are transformers efficient?

[eagle19952]

Ok reading between the lines here, it could be done, but it sounds like the 3 phase could be an issue. I want to run something like an 18,000 BTU unit with two zones. Bedroom and rest of coach. Multi zone splits only come 240 volts


Sent from my iPhone using Tapatalk

but the 3 phase is not a part of your discussion. any 220 volt appliance single phase will run on 240.
208 will too, just single phase single phase
208 just happens to be common to 3 phase also, as well as 377 IIRC.

[bevans6]

Three phase power is only available in industrial areas, as a rule, and powers large industrial motors.  I'm not aware of any residential mini-splits that would require three phase power.  220 or 240 VAC in residential use in North America (not positive about Mexico) is what I call center-tapped 240 VAC.  The transformer that feeds your house has two live outputs and a neutral.  The neutral is the center tap position, and is referenced to ground, or zero volts.  The two legs are 120 volts each with reference to neutral, and add up to 240 volts between each other. 

Brian

[bigred]

You can do three phase but a transformer will not convert single phase to three phase.You would need a rotary phase converter available from Ronk.

[eagle19952]

You can do three phase but a transformer will not convert single phase to three phase.You would need a rotary phase converter available from Ronk.

still not a bus/mobile option.. it would consume a lot of storage space, more then a busnut would want to sacrifice.. not for me.

[bigred]

Actually a phase converter probably would not be any bigger than a transformer.

[ArtGill]

Ok reading between the lines here, it could be done, but it sounds like the 3 phase could be an issue. I want to run something like an 18,000 BTU unit with two zones. Bedroom and rest of coach. Multi zone splits only come 240 volts



Scott,  The only three phase is coming out of the inverter in the mini split.  I'm going to use a two zone unit.  I found the same you did that they only come in 220/240 vac.  You must have watts in to equal watts out, therefore it takes twice as many amps at 120 vac as the unit is rated for at 240 vac.  My friend the HVAC engineer and myself put an amp probe on an acutal, installed and operating unit to read the amp draw.  We found that the unit used less amps than the manufacturer specified, but more important to us is that it didn't have "spike" when first coming on the current draw "ramped" up over a period of time.  I feel both of these characteristics are because of the inverter technology.   The inverter is single phase in and three phase out.  The fans and compressor are three phase because the speed of the compressor and fans is easier to control three phase and the units will be lighter.  Also, the remotes BTU's can add up to more than the outside units BTU rating.  They will compensate automatically.
I talked to my business neighbor, the motor rebuild and repair shop about the transformer and he saw no problems.  He did recommend that I over size by 50%.  I don't have my data at home, but the transformer that I selected is around $100.00.
Art

[Scott & Heather]

Ok. I'm in way over my head on the phase power thing here. Guys, remember I'm just a former computer tech consultant turned singer lol.


Sent from my iPhone using Tapatalk

[eagle19952]

Ok. I'm in way over my head on the phase power thing here. Guys, remember I'm just a former computer tech consultant turned singer lol.


Sent from my iPhone using Tapatalk

now i understand, ....  Art has it. a 100$ transformer is probably the size of a shoe box...the 3ph is on the out not the in..o no roto anything is needed.

you could figure a 220 pole/rv park source and a secondary 110v/ transformer alternative when the 220v park pole was not available. I would.

[Oonrahnjay]

    I am the original S in KISS so I'm following this with interest but not a lot of understanding ... but I kept everything on my coach 120V for the simplicity of it.  Is 240V worth the complication of transformers and additional circuits and breaker boxes and wiring?  I'm thinkin (may be wrong, don't forget the "S" part) that many quality inverters can be "stacked" or combined to get 240V out of two inverters but again, more complication.
    What is my weary little brain missing here???

[blue_goose]

How did the 3 phase get into this are transformers efficient.  I don't know of anything that you would put on a coach that would be 3 phase.  I would think all large coach,s are wired for 220 volts 50 amp. 
My coach is all electric and has a 220 volt stove top (now you can buy 120 stove tops). If we only have 110 volts we use an electric fry pan or start the generator.
Jack

[buswarrior]

Art, please share the numbers in your plan.

If a $100 transformer lets me avoid wiring for 240, but lets me have a 240 appliance....

a whole new world opens up....

Unfortunately, transformers were on the curriculum of that high school electrical course that got cancelled due to low enrollment, long ago and far away.

Very interesting!

happy coaching!
buswarrior

[Scott & Heather]

Ok so ignore 3 phase. My
Muddled mind. Here's my actual finally question:

Can I somehow make a mini split set up to run on 208v input power run on 120volts? Not a big one, just something in the 15,000 BTU range


Sent from my iPhone using Tapatalk

[bevans6]

If you read the informative reply from Art Gill, you see that in some literature or from a technicians point of view, the motors inside the Mini-split might well be three phase motors.  Why?  Because three phase motors are smoother, quieter, more efficient, more reliable than single phase motors.  More why?  Because the mini-split uses inverter technology (similar to but different in application from the pure sine wave inverter that you use to produce high quality AC from your batteries) to take in the incoming power and change it to something that really efficiently drives the compressor and condenser/air handler motors very quietly and at variable speed.  The fact that the motors happen to be three phase is irrelevant, they could as well be any number of phases including zero for a DC motor.  It just totally doesn't affect a thing as far as powering a mini-split AC unit is concerned.  Any mini-split type AC unit sold in North America for residential use is going to have an option for single phase power, either 120 volts or 240 volts nominal, the only difference being the amount of current and hence the wiring gauge needed to hook them up.  End of story...  I hope!  

This actually answers a question I had for quite some time.  My buddy had a fan motor fail in his heat-pump at home, a 5 ton unit with variable speed this and that, inverter controlled.  The new motor was close to $1,000! until the dealer got involved and it was under warranty.  I could not figure out how a fan motor could cost that much.

Scott, please share the make and model of your unit that requires 208 volts.  Do you already have it, or are you shopping?  Every single one I looked at has a voltage input range from 208 - 230, 60 Hz single phase.  Every single one could be powered with a step up transformer like the one I posted a day or two ago.

[bevans6]

OK, I thought I would continue confusing the heck out of people and explain why the voltage input range is 208 - 230 volts, and why I keep saying 240 volts is the normal residential supply voltage.

In the USA and Canada, the national standard for AC line voltage at the source is actually 120 volts  plus or minus 5%.  It's supplied to a house at anything from 110 volts to around 125 volts, depending on the region and the distance from the source - the power pole transformer.  All of these voltage levels are acceptable and equipment is designed to accommodate the range.  In the olden days the standard for voltage was anywhere from 110 to 115 to 117 to 120, and they are effectively interchangeable.

In a normal residential hookup, power is delivered to the house with a single phase 240 volt feed that has three components - two 120 volt live feeds that are opposite in phase (but still the same phase) and neutral, which is tied to ground and is a reference.  So you get your two 120's and if you connect across them you get your 240.  That is the nominal voltage - it's usually lower, has around a 5% tolerance and equipment people put 230 on their spec sheets.  Which is all fine.

In a light or heavy industrial situation, the power feed to the building will be three phase.  It's supplied over four wires - one for neutral, and three live feeds to carry the three phases.  Each phase is 120 degrees apart from the other two, so instead of a power pulse every 1/60th of a second (60 Hz), a motor would get a power pulse every 1/180th of a second, three pulses per rotation.  Hence smoother, quieter and more efficient.  In a typical light industrial building the power feed will be 208 volt three phase, other standards are 440 volt, 480 volt, 575 volt.  A big building will have a power plant with transformers to take in the high voltage and divide it down to whatever the machinery or equipment happens to need, and it gets quite complicated.  But there is always a need for plain old 120 volt 60 hz power.  If you take a 208 volt three phase system and measure the voltage from one hot leg to neutral, it will be 120 volts.  If you measure from one leg to another leg it will be 208 volts (they don't quite add up because the two legs are only 120 degrees apart, not 180 degrees apart like they are in a single phase system.  All buildings with three phase power coming into them will normally have an option to supply 120 volt for all normal desktop type stuff, and 208 volts for higher power but non-industrial things like air conditioners.

So that is the sad story of why you see both 208 and 230 volt specifications on residential type air conditioners - because they might be installed in a building where the power is derived from an industrial three phase supply, so they are built with the option to use that type of power.

[Oonrahnjay]

... So that is the sad story of why you see both 208 and 230 volt specifications on residential type air conditioners - because they might be installed in a building where the power is derived from an industrial three phase supply, so they are built with the option to use that type of power.

    So if they're used at 208, it's still a single-phase service.  And if a 120V unit is used and it's wired in properly, it's single-phase and half-a-full-phase sine wave - just like it would be if it were wired into a single leg of normal 240V service?
    I live in a 50 year old house in a little country town; everything here is old-fashioned, behind the times, and low-tech.  Every time I measure voltage anywhere, I see 119.5-121V (or 240V +/- a fraction).  I'm happy to call it 120 and 240 volt.