Are transformers efficient?

[eagle19952]

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

yes.
with the proper transformer.
are you absolutely sure that the unit is restricted to 208v. it is relatively uncommon for an electrical device not to be operable in a voltage range.
ex: 208v/220v or 220v/240v 0r 208v/240v etc.

exactly what unit are you wanting ?

[Seangie]

Brian is spot on.

These AC's will run on 220v (230, 240...all the same, 180 degrees) all day long with no problems.

Here are some power issues you'll need to think about when you go to a mini-split -

1. Construction - Most of these mini-splits (That we are looking at anyways) are cheap and affordable because the electronic components in them are not high end.  They are designed to be hooked up to a 220v service that is constatnly supplying good power 99% of the time.  A power outage wont kill them but power off/on/Off/on/off/on does not contribute to the longevity of the electronic components in these devices

2.The issue you could have with a transformer is that you need to make sure its a heavy duty transformer capable of delivering clean power to both legs 100% of the time.  A 120v unit could pull as much as 12-15 amps on startup, A 220v unit is going to pull about 8-10 amps on startup.  Your going to want to get a 4000-5000 watt inverter.  Most of the wattage listed on these inverters is the wattage for 110v electrical.  

3. Power quality is another issue why you might not want to take this road. Usually you cannot tell what type of power you are getting from a park pedastal.  It could be solid 220v tested when you hook up on Thursday afternoon but by the time Saturday night hits and the park is full and everyone is running 2 or more AC units in the middle of July you could see a voltage drop that might be big enough to add quite a bit of heat to the circuitry in your mini-split.  Even if you have a power regulator that adds voltage from your battery bank to correct the voltage its still not the type of power these mini splits are designed to run on.

4.  Using a 220v Mini Split gives you a single point of failure.  If you have a 2 head or 3 head unit and the single outside unit fails, you can't run anything until you get it fixed.  And if it does fail you know it will be that 100 degree day with 60 percent humidity in August.  Unless you spend a good ton of money, this outside unit is not made to be replaceable nor does it have field replacable parts on it.  They are meant to be tossed.  The first unit I bought was sent with slightly newer evaporator/head units than the compressor, I'm talking the next model number up.  Yet the outside unit wasn't compatible with those newer evaporator units.  I ended up having to ship all of them back (After installing and paying AC guy to come up and setup) and get something different.  So within 2 months the brand new parts that I ordered were out of stock, no longer available, no parts to replace or repair and not backwards/Forwards compatible with the new model.

5.  Airflow, Airflow, Airflow - You cannot get enough air to flow through these 220v units.  They get hot quick.  They are made with just enough fan to keep them running.  By putting these units in a bay expect that you will probably have to keep a bay door open to keep the outdoor unit from overheating.  The best way to do it would be to build the outside unit right to the exterior of the bus and have a tunnel through to the other side of the bus to pull fresh air in.  other than that you just are not going to be able to get enough air through the exterior unit to cool it.  120v 9000btu units don't get as hot.  120v 12000btu units are going to get pretty warm, its a 9000 btu unit beefed up to 12k.  

6. Fixtures - Not designed to be bounced all over at 70mph.  Cracks in the copper inside the unit and at the attachment on the exterior of the unit can appear. They are not designed with shock absorbers. If you have the screw on connectors, make sure you sweat them on so they dont back off.

7.  They are badass.  These mini splits are sooooo effecient.  I ended up with a 24k btu (2x12k) unit and on our first trip we had no open windows, driving to Florida on a 96 degree day and within 15 minutes of being at the park it was ICE COLD on that bus.  They are very quiet and work extremely well.  I just don't think that they are ready for fulltiming on a bus.  

I know there are quite a few bus nuts out there that use them.  How many of those bus nuts are fulltiming, constantly putting miles down and running their units 12 months of the year?  I know that Dave & Amy (TIKVAH) have a unit on their bus.  It works very well.  Dave has lost a unit to park power (we were in the same park and tested that power and didn't see anything unusual, may have been a spike or slump) but had to figure out how to get another unit to replace it. It was a stressful day for them. They only have one unit and it keep their entire but very comfortable.  How long until they loose the new unit?  I'm hoping it lasts 5-6 years. Trust me, i want to see these mini-splits work, I'm cheering for all you guys that run them.

You just gotta make sure you understand the risks that come along with a project like this.  You can make all the changes and modifications to make it work but as soon as you loose it, there is no insurance, warranty or anything else that is going to cover your 1200 - 4500.00 investment.

Thats my 2 cents.  

-Sean

PS - On my next bus build I'm going to engineer the mini-splits into the bus, but I;d stick with (2) 120v units.

[eagle19952]

in service 25 years..by me for 14. new condenser fan motor 2007, new compressor 2011, new A coil 2012. the a coil was fine but the condensate pan rotted/rusted out so i decided to replace it..


in this photo you can see the air handler/medicine/broom/storage closet. and a small portion of the duct work.



the duct is behind/integral to the cabinets curb side seen here:

[Seangie]

in service 25 years..by me for 14. new condenser fan motor 2007, new compressor 2011, new A coil 2012. the a coil was fine but the condensate pan rotted/rusted out so i decided to replace it..


in this photo you can see the air handler/medicine/broom/storage closet. and a small portion of the duct work.



the duct is behind/integral to the cabinets curb side seen here:

Don - Thats not a cheapo 700$ mini-split.  Thats awesome though   Ive seen those pics before.

Curious - Do you have to leave the bay door open when you run it?

[eagle19952]

Don - Thats not a cheapo 700$ mini-split.  Thats awesome though  Ive seen those pics before.

Curious - Do you have to leave the bay door open when you run it?

No... but when i feel sympathetic... i do we both know that heat is the death of compressors
i have often run it going down the road.

i had no idea the mini-splits were a $700.00 deal

the new a-coil installed was 1300$. but i decided it was a good investment the day is coming when a SEER rating will make rebuilding/parts for R-22 systems impossible if not illegal.

but..if you consider the 2 million dollar coach with 5 roof tops... then the price is comparable and i have never found a residental HVAC guy who didn't want to work on it ... beats the heck out of an attic installed air handler repair in Florida in July

[Scott & Heather]

This is all so fascinating to me... Ok, shanks is like a brother to me so I take any of his advice to heart. Heck, the guy helped me change brake calipers on my truck in front of his bus in Texas. I desperately want a higher seer a/c and heat system. Heating with propane or electric resistance is expensive. Seriously, our rv park power bills are regularly in the $200 a month range summer and winter. It really stinks to me that we are somewhat prisoners to the lame rv industry's roof tops that have got to be the biggest power jobs in the climate control business. Not to mention they look hideous and add height to our already tall bus. Sean's right, we have an intense schedule and having something somewhat exotic break down on me in the summer or winter would be lame. So if I wanted to install the most efficient a/c heat pump according to the KISS principle in my coach, what should I be focusing on?


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[ArtGill]

I would find out if 220-240 is an option rather than 208.  The 120 to 240 transformer is a standard where a 120 to 208 maybe a special order.  My design keeps my coach all 120 vac and the transformer will only serve the mini-split.  As with most things you buy you get what you pay for and that is true with mini-splits.  There is/was some cheap imported mini-splits that had no support.  The unit I have had for a number of years has given me good service.  I made sure the copper refrigerant lines were well attached and supported.  My HVAC friend will not sell me anything but a Diakin AC because that what he sells and supports and we eat lunch together a number of time a week and if it fails he will hear about it at lunch every day.  So buy a brand name that has his support.

My application is a little outside the box.  My Eagle has a large compartment over the engine that had contained all the fans and coils for the over the road AC and heat and that is where I have my present outside unit and plan to install the replacement outside unit. They make a inside unit designed to fit in a 24 x 24 ceiling grid and we plan to put one in each old escape ceiling hatch.  That will require a cover of some type on the roof over each unit.  My plan is to run the refrigerant lines down the roof to the outside unit in the compartment over the engine.

We studied the manufacturers specifications for current draw at 220 vac and then we ran a real world test on an unit of the same size that was installed in the garage of my HVAC friend.  We found that the current draw was less than specified and that they was no spike of current in rush on startup.  We have decided on a 4000 watt transformer.  That will be 33 amps in at 120 vac and 16 amps out at 240 vac.  A transformer is inert as far as electronic components go.  It is two coils of wire, in this case, one has twice as many coils as the other and a core of steel.  A transformer only works on AC current.

Art

[Scott & Heather]

What are your thoughts on these new kingtec solar air conditioners? http://kingtecsolar.com/products/


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[eagle19952]

back at square one... what percentage of your life is boon docking ?
there is nothing as dependable/efficient as all electric.
there is zero risk of carbon monoxide.
two fan motors and a hat full of limit switches fixes almost any problem.
but..3-4 1200 watt electric cubes are almost as effective... for heat.
i feel your distress

i hate it when my SO is not warm ...

to anyone who wants to answer ... why are you opposed to wiring a 220v service coach ?

[eagle19952]

What are your thoughts on these new kingtec solar air conditioners? http://kingtecsolar.com/products/


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where were you going to source 48v DC ... ? Reliably ?

[Seangie]

Scott - Do 1 rooftop and 1 120v mini-split.  Youll most likely only ever need the mini split and you can have the rooftop as a backup.

We ran both rooftops most of April in Texas and our electeic bill was 65$.  I think your fridge is the other 135$.

-Sean

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[Scott & Heather]

Don it comes with a 110v power supply for pole usage. It just appeared to me that they put more effort into making the unit more efficient. But as shanks mentioned, maybe I'm chasing Pennies and it's costing me dimes. Those solar units are almost $3000


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[Oonrahnjay]

...  They make a inside unit designed to fit in a 24 x 24 ceiling grid and we plan to put one in each old escape ceiling hatch. ...

    Art, I thinkl you might have just solved my biggest A/C problem.  What's the brand/model of this 24 x 24 ceiling grid.  How thick is it?

Thanks,  BH

[sledhead]

I have a 9 k split up front that cools the coach 90 % of the time up until it is over 99 f ( parked ) on the road  then I turn on the roof rattler in the bed room for added cold  this is in the mci
on the featherlite I have 3 roof a/c 's but I am shocked at how quiet they are ( well the front 2 our original the rear is 2 years old and is loader ) all are the 13.5 btu units ducted , yes I would like to have a split unit again but I can't see replacing them for no reason

you should find that with the help of the spray foam insulation it should be easer to heat and cool

dave 

[Scott & Heather]

BH, Google "minisplit ceiling cassette"


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