Are transformers efficient?

[Scott & Heather]

If I were to consider buying a 240 V mini split air conditioner for our coach, could I use a T240 transformer to step up the voltage to 208 V? Would I lose efficiency by doing this? Does that defeat the purpose of having an efficient mini split?


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[ArtGill]

I am planning to do the same.  I'm looking at using a mini split with two heads.  Each head would be 12,000 btu's but the outside unit would be only 18,000 BTU's.  I am looking at using a trans former to go from 120vac to 240 vac.  You have some loses to heat but my advisors say it should work.  The mini splits are inverter based should be tolerant to voltage droops.  We used an amp probe on a comparable unit and found the amp draw ramps up slowly, no spikes.  At present, I have made the decision to go ahead with my plan, but I am working on funding it.

Art

[bigred]

Would be a lot easier with the 120/240v transformer since these are easy to find .Not so easy to find with 208/240 especially in the lower kva ratings .Despite my lack of knowlege on converting btu 's to amps/wattage ,how many amps are you looking at?? About forgot all this stuff since retiring ,I think that if you are 3 kv (3000 watts) you can reverse hook the transformers with no loss in KVA rating.

[TomC]

They make mini-splits up to about 14,000btu at straight 120v. You'll be much happier without the step up transformer. Just buy two units and put one on each leg. Good Luck, TomC

[luvrbus]

Just stick to ducted roof tops you full timing and starting a family you are going to need the bay and wall space

[Seangie]

Scott,

Stick with 120v.  Youll thank me later.

We had straight 240 from the generator and it was a pia.  This also greatly limits the places youll be able to stay.

The transformer will work initially but I think over time it will be troublesome and down the road youll have issues with not only the transformer but also the mini-split.

Call me if you want to talk about minisplits.  Ive had plenty of success and failure in that department.

-Sean

[bevans6]

A simple step up center-tap transformer will be around 97% efficient, depending on the model.  Close enough to 100% that you can about ignore the loss.  It will put out single phase center-tapped power, and normally you look for 2:1 on the voltage, so 120 in you get 240 out, center-tapped for two 120 volt legs exactly the same as a house.  208 volts is usually found with three phase power where the legs are 120 degrees apart, not 180 like house current.  You won't get 208 volt three phase out of a normal step up transformer that is fed with 120 vac.

Brian

[Jim Eh.]

Call me if you want to talk about minisplits.  Ive had plenty of success and failure in that department.

-Sean

Do tell, do tell. Or would it be better in it's own post so as to not jump the post.

[buswarrior]

Do tell, do tell.

Yes, please share, I am also interested in this realm. I hate roof warts.

happy coaching!
buswarrior

[TomC]

Roof warts do look bad-but show me a $2 million band bus with anything but 5 roof tops. You can't because they need the storage space, the roof tops are easily replaced and now most high end buses have roof liners (fences) around the perimeter where you don't see the A/C's

[Lee Bradley]

My bus is set-up with 12/24 and 120 systems; Trace 4024 and Honda EV6010. I went with mini-split 24,000 btu compressor, 9,000 btu in the bedroom, 12,000 btu in the kitchen/living room and 18,000 btu over the driver. I run it off a 5,000 watt 120/240 transformer on the road and camping where 50 amp isn't available and switch it to a 240 circuit where 50 amp is available. No problems in 4 years.

[buswarrior]

Every build, every decision, is a compromise, biased towards the builder's particular wants, needs or delusions?

The transformers are intriguing. Whether powering a mini-split, or other 240 volt appliance, such as an electric drier, electric cooking units, etc...

keeping the generator wired for 120 (another set of reasons), and the ability to make 240 at a 120 campsite is a whole 'nuther set of fascinating variables for the busnut theorist to ponder?

If thinking was money, we'd all be rich!!!

We need more typing about the selection and use of transformers!

happy coaching!
buswarrior

[bevans6]

As with all things electric, start with power.  I'm getting a new heat pump installed in my house, and it has a 20 amp fused supply (it's a 1 ton unit).  So if I wanted to use a transformer to run it, I would look at compressor draw being less than 20 amps at 240 volts, so 4800 watts, and starting loads of less than 3 times that, so I might buy a 10 KVA transformer.  Now I might look at available supply.  I have a 30 amp generator, and my typical plug in at home or campsite is also fused at 30 amps.  That's 3600 watts, and it will transform into 3600 watts less a bit for efficiency at 240 volts, so that is 15 amps at 240.  I still might look at the 10KVA unit, or I might downsize a bit to 6500 or 5000 KVA.  You want the whole thing to have quite a lot of headroom so you minimize voltage sag when the compressor motor is starting, although selecting a modern Mini-split with inverter driven and variable speed motors will really lower the power requirements.

As with everything, you get what you pay for.  A nice thing to have is a regulated or protected output, you can get ones that can boost low campground voltage or that have surge protection and output breakers.  At the size you would be looking at they don't have outlet plugs but need to be hardwired on the supply and output side into distribution boxes.

Example of a unit that would probably be typical is here:  http://www.220-electronics.com/10-000-watt-diamond-series-voltage-transformer-with-regulator.html

This step up and step down transformer thing is done all the time.  I'm looking at a step down transformer right now that steps around 7K volts single phase to center-tapped 240 volt, it's bolted to a pole on the street outside my house.  Typical transformers, if they are dry (some are full of oil) are massively reliable.  You open up a 60 year old piece of electronics and you don't even worry if the transformers still work.  The tubes, the capacitors, the resistors can all be toast, but you are going to have voltage!

[bigred]

The only thing that will kill a dry transformer is a Direct lightning hit !!!

[Scott & Heather]

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


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