I think I'll put "experimental" in my destination sign.
When I first started on my conversion project I decided to try 'portable' air conditioners. I decided on two Sunpentown WA1010 H units because they were specified as outstandingly efficient (EER of 15.2) and only drew 6 amps each. Well sorry to say the manufacterer plain LIED. They did draw the 6 amps but they never cooled very well, I could get a temperature difference of no more than 12 deg F. So I added a pretty efficient (EER 11) 10,000 BTU window unit in the rear, through the rear cap. Now I could cool the bedroom , no matter what the outside temp was. But the front of the bus was always too warm if the outside temp was over 85 or so. Since I was committed to no rooftops I went shopping for a ductless split. I picked a heat pump that is rated at 13+SEER, 18,000 BTU/h (19,500 on another site) but required 240 volts and was rated as drawing 5.5 amps at 240. When I got it though the tag said 6.5 amps. I made 240 out of 120 by adding the output of an isolation transformer to the 120 source. I picked an isolation transformer that was rated at 11 amps hoping that it would cover the starting surge and crossed my fingers. I mounted the indoor section as far forward as I could behind the driver's seat, ran the lines and wires down the wall and into the former condensor bay. I had to modify the outdoor unit to fit the bay, this amounted to relocating the electrical controls, rotating the refrigerant connections from the side to the rear and removing 2" from the enclosure. I mounted the transformer to the bulkhead between the condensor and evaporator compartments. I mounted the modified outdoor unit to some angle aluminum I added for the purpose. Wired it all to a 20 amp 120 volt breaker, then I called a local AC tech to add a filter dryer, vaccum the lines and turn it on. IT worked!! Well today the outside temp hit 90 and the bus was parked in full sun, no clouds, with only the front split running the entire bus was 68 and the unit was cycling 15 minutes on 5 minutes off and drawing 12 amps when on. WOW what a difference. I'm not quite done though, I'll adjust the charge a bit in the near future, as soon as I get proper superheat data from the manufacturer, because the factory charge is for a 25 foot line set and I only have 15. The correction is supposed to be .5 oz/foot but I really want peak the efficiency and no problems when it gets really hot outside, I might even get to 11 amps running. In summary the new ductless split works outstandingly and the portables were a sad mistake
Regards
Jerry 4107 1120
How do you get enough air curculation in the bay for it to work? I am considering 12k btu units that would run on 120 Jerry
Jerry,
The outside unit is situated as far left in the old condensor area as possible, there was no floor in that area as the original condensor was cooled by a 34" fan on the bottom of that portion of the bay through a very coarse screen, really a rock guard. Since my outdoor unit is but 12" deep, it's fan blows out to the left and there is about 20" x 36" of screened opening on the bottom air flow seems more than adequete. BTW my generator is on the right side of the same bay and it also exausts outward, to the right through added louvers in the tool compartment door, so it is sharing the air intake. I'll be watching the generator temp the first time I run both the generator and the front AC, but my gut tells me it'll be fine.
I sure would advocate going to 18,000 BTU over 12,000 even though you'd need to duplicate my transformer trick. Even with the transformer I'm drawing less power than the best of rooftops.
Regards
Jerry 4107 1120
Jerry,
Where did you get your isolation transformer?
I have 2 mini-splits for my coach and they are 240 volt. I have 240 V from my genset but would like the option of running on 120V, in case I get stuck in a campground with only a 30 Amp service.
Also, how much insulation do you have in your coach?
TIA, Ed.
Jerry,
That's great news. Congrats.
Help me understand the wiring trick: Is the isolation transformer also a step-up, taking 120 in and putting out 240, or is it 1-1, and you are simply ganging the output with the existing 120V supply to make the 240? If the latter, is there any wave-form delay in the transformer output, and, if so, how did you deal with it?
-Sean
http://OurOdyssey.BlogSpot.com
Of course it works, we would expect nothing less of you!
I'll try to answer both Ed's and Sean's questions. I got the transformer from an ebay seller. Though it has 2 120 volt primarys and one 120 volt secondary I paralleled the primarys and then wired the secondary in series with the primarys. So it is a 1:1 transformer but wired as a 1:2 autotransformer. This connection makes it 'in effect' an 'autotransformer' with the 120 input accross 1/2 of the output. The transformer is of a 'toroidal' type and is rated, as an isolation transformer, at 1320 VA but the autotransformer connection doubles that to 2640VA. There is no 'waveform' delay of any significance, the load sees 240 while the line is 120. Regarding insulation, In most of my bus I have 3 layers of 1/2" foam board (rated r7/"). I did use 1/2" furring strips on the walls and 3/4" on the ceiling so I have no metal ribs in contact with my wall or ceiling material. My roof is also painted with 'Supertherm' and overcoated with bright white paint which definitely helps but it's hard to say how much. I have removed the 'center' 2 windows on each side but retain the rest of the stock windows. The driver's area and the front wall has no added insulation.
Regards
Jerry 4107 1120
Sean, since you are so great at posting diagrams, if you understand this connection can you please make a drawing of it and post it. I am having trouble understanding what he did exactly. Thanks,
Richard
Jr,
I sure was a bit nervous as to wether the transformer would handle the starting of the compressor but it does it with no apparent strain. And I've even ran it for 2 cycles (1/2 our) powered by the inverter (SW2512) off of the house battery with the shore cord unplugged.
Regards
Jerry 4107 1120
Here's a try at a picture.
out
!---- <240>-----!
! !
! !
!WWWW!WWWW! the transformer
! !
! !
H<120> N
in
Regards
Jerry 4107 1120
Jerry Liebler....is this similar unit you have???
http://cgi.ebay.com/1-5KVA-115Vac-Toroidal-Medical-balance-Transformer_W0QQitemZ270122864381QQihZ017QQcategoryZ4665QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
Thanks Jerry J
Sojourner,
Yes, it's about the same shape, size and weight and should work in a similar way but mine has different windings and is slightly smaller electrically. I also didn't pay near that much for mine.
Regards
Jerry 4107 1120
FWIW:
Imformation about "Toroidal" type transformer.....a state of art version for step-up or step-down voltage transformer as well isolation.
http://www.alphacore.com/News/O-core%20latest%20article.pdf
http://www.coilws.com/Toroidal%20Power.htm
Thanks Jerry Liebler for a interesting project report. I am sure it run much cooler then older version.
Learn new things everyday.
Sojourn for Christ, Jerry J
Jerry, would you part with the information so we could buy one of those mini-splits, too? I'm confident that you researched your choice pretty carefully. We also would like to have a heat pump, and I already know how to deal with the autoformer part of your setup.
It's been my impression that most of these rooftops are worth just about what is paid for them. Thanks for the report.
Tom Caffrey
Tom,
Sure, the unit I got is 'branded' 'Celiera' and I got it from AC-World.com in Detroit. I picked it up while visiting relatives and avoided paying for shipping. It appears that the same unit, from the same manufacturer, with the same specifications, are marketed by several companies under their brand names.
From what I can tell the following 'brands' on Ebay have a unit which looks the same and has the same specifications and even the same manuals: Harbor Point, Bon-air depot, Airlux, and of course AC-World.
The key is 13+ Seer and watch the running current spec. and watts used
Regards
Jerry 4107 1120
Jerry, congratulations for your thinking "out-side-the-box".
Your drawing shows what I would have in the past called an autotransformer. One winding with three taps on it. The general purpose to step 120 volts up to 240 volts.
But you talk about an isolation transformer which I would in the past have expected three 120 volt windings (six leads). One input winding on one side of the laminations, and two output windings (or vice-versa) on the other side of the laminations. The purpose to not only step up the voltage from 120 volts to 240 volts, but also to provide complete electrical isolation between the primary and secondary windings. These devices are generally much heavier, larger and more expensive than an auto transformer.
I still do not really understand how you connected it but again I would like to congratulate you on what I consider a brilliant solution to a vexing problem.
Richard
Quote from: Jerry Liebler on May 26, 2007, 08:07:32 PM
Here's a try at a picture.
out
!---- <240>-----!
! !
! !
!WWWW!WWWW! the transformer
! !
! !
H<120> N
in
Regards
Jerry 4107 1120
Richard,
I'll try to clear up what I said. I started out with what was designed as an isolation transformer that had 2ea. 120 volt primaries and 1ea. 120 volt secondary. It's intended purpose was to isolate either a 240 volt (primaries in series) or 120 volt (primaries in parallel) source from a 120 volt load. I then connected the primaries in parallel and connected the secondary in series with the primaries. The center tap of the now 240 volt single tapped winding is connected to the neutral, the other end of what was intended to be the primary is connected to the 120 volt source's hot side which is also one end of the load connection. The remaining end of what was the secondary is now the other side of the 240 volt load. The advantage of the auto- transformer connection is it effectively doubles the current capacity of the transformer. Isolation wouldn't be desirable anyway as we really want each leg of the 240volt output to be 120 volts to neutral for safety. I wanted to make the transformer's capacity significantly more than the rated compressor current to assure that the voltage wouldn't drop too much during the startup surges. The toroidal transformers have shorter windings than more conventional transformers so they have less winding resistance for similar ratings, this also reduces the voltage drop during the startup overload.
I'm sure glad it works, my wife would really be p--d if I'd wasted the money I gambled to try it.
Regards
Jerry 4107 1120
Thanks Jerry, Now I understand. I think it was really a great idea. I was aware that an autotransformer connection had a higher rating when connected, but in 50 years I never saw or heard of anybody doing it like that. Making an auto transformer from an isolation transformer. You are a genius.
Richard
Quote from: Jerry Liebler on May 27, 2007, 10:17:02 AM
I'm sure glad it works, my wife would really be p--d if I'd wasted the money I gambled to try it.
Regards
Jerry 4107 1120
Jerry, it looks like you gambled on a sure thing ;D
We talked about this in Timmonsville, & you lost me when it came to the transformer. But I just knew you had it figured out right. Way to go! You are one handy guy to have around! Thanks for taking the time to share & explain!
Happy bussin! :)
kyle4501
I concur with all the guys above - Way to go!!!!!!!!!!!!!!!!!! You are the man!!!
It's a true gift to have you aboard and for you to share your talents and knowledge. I can't wait to meet you and see your bus in Cincy in a couple weeks.
As with some of the other guys, I am all but totally lost on how you did what you did and what you did to make it work. But if/when I get to the point of changing AC's, I'll follow in your footsteps. I'm sure a visual in Cincy will help me a great deal.
Thanx again for all you've done for me,
Chaz