| Author |
Message |
Norm Edlebeck (66.60.197.52)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 07, 2002 - 12:34 am: | |
I have a 5.0 Propane Onan and have been told it should run 2 roof mount Duo Therm Air Conditioners (I believe they are 13,500 each). Problem is, it will for about 5 minutes or so, but then pulls down from 120 volts to the point where everything kicks out, or if I shut one off it's back up to 120 volts again. I've tried adjusting governor, changing propane back and forth from lean to rich, you name it, I've tried it, and am about at my wits end. I purchased the coach with these two Duo-Therm units. The previous owner said the front one was only a couple years old, but the back one (an automatic "Penguin") was older. I have absolutely no problem running each one individually with other 120 volt appliances, but this is bugging the hell out of me. Any suggestions or similar experiences??? Thanks in advance for any and all help. We are leaving on a 10 day trip on July 12th and hate to have to only run one at a time during these 100 degree days. |
Peter Broadribb (Madbrit) (170.215.36.92)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 07, 2002 - 5:35 am: | |
Norm,
personally I think that the 5.0 is borderline or under powered. Especially as it is propane powered. Most "dual fuel" gensets are listed with a lower output if run on propane over gas. Can the unit be converted to gasoline, how many more Kw would this unit gain?
My Apollo has a 6.5kw Onan and it will run both 13,500 a/c roof airs, and the microwave but only just. It has been known to stop for no apparent reason, probably old age as it's all from around 1977.
Lots of people go on about getting away with a small genset, well as the old saying goes..... "There ain't no substitution for cubic inches" holds well. The ones who say that it is bad for a genset to run light-loaded are probably right, but in most RV cases no matter what size genset you have, it will not run under anywhere near full load apart from the odd time you need the a/c running in summer. If you are not a full-timer, and just use the RV for the occassional long weekend, etc. how many times is that?
Just my opinion, probably not the one you wanted to hear though. I have just negotiated the purchase of a 12.5 diesel Onan and am planning on either 3 roof a/c or basement, and when I have all the a/c on and want to turn on something else, I want it to work just like it does at home.
I am not spending all this time and money to rough it unneccessarily......... LOL.
Peter. |
FAST FRED (65.56.26.123)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 07, 2002 - 7:13 am: | |
The air units only pull about 3KW , and the normal problem with a "too small" gen set is not starting the second unit.
I would keep trying to find the flaw in the gen set that is causing the overload.
Can you operate with the compartment open , or the unit slid out on a slide , to see if its a cooling problem?
Can you load down the system with a similar load of electric heaters to see if its the gen set or one of the air units?
A amp measuring device should be clamped on to the air units , as well as the gen set to see what is actually happening during those 5 min.
FAST FRED |
neil (198.81.17.153)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 07, 2002 - 9:22 am: | |
I run my 2 13.5 AC's using my 5 KW genreck propane genset. Thats all you can run on mine. I start them about 5 min. apart so the starting load for both is not at the same time. Bottom line is yes it will but it's borderline.
good luck. Neil |
Ross Carlisle (Ross) (216.107.197.16)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 07, 2002 - 9:46 pm: | |
I've been running 2 13.5's on a 3.5KW Honda construction generator with a little to spare. I seriously doubt they consume 3KW each...Unless you are counting start current as well. I think most of these AC's consume no more than 15 amps. The newer units are probably more like 12 amps. 15 amps equates to 1800 watts.
I'm installing an 8KW diesel genset. I have 3 roof AC's. I think 8KW is about the minimum I would go with. I went with diesel because I don't do campsites. I plan to be running the genset most of the time.
Ross |
peregrine (206.25.50.5)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 08, 2002 - 12:46 am: | |
Granted 15 amps @ 120 V = 1800 watts, but! That is at 100% efficentcy. Ad in that we are talking about inductive loads and then take into account the phase angle lag time. 2K watts would be more like the actual power factor. Also a 120/240 volt gen set handles the split loads better than straight 120 sets.
Semper Fi,
Al |
Doug (65.161.188.9)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 08, 2002 - 9:56 am: | |
I have to make a small comment about Peregrine's post - a 120VAC only gen set will actually be more efficient a power source (number of usable watts of power) as the total output is available on one 120VAC leg of the gen set. A combined 120/240 unit will provide half the 120VAC output on each leg. For a coach with 3 AC units, this means that HALF of the 120/240 version will have to handle 2 AC units PLUS the starting current and the other half would have one AC plus other loads I assume to try to balance the loads.
To show some math on the subject - a 120/240 gen set would have to be 1 AC (1500W) + 1 AC (1500W) + starting current (2200W) for a minimum of 5200W on one side of this example. The gen set size would have to be 10,400W to carry the coach load with the 3rd AC on the other leg of the gen set. If you were to use a 120VAC only gen set, you could run 3 AC units, plus starting current for an AC (since rarely do 2 units start at one time) plus a modest 900W of other stuff for a total of 7,500W. Now, a diesel generator, using FFs input would ALWAYS be underloaded by a good bit. Having experience with diesel generators (40KW size) FF is right - you kill a unit by underutilizing it. I too really like the idea of a single liquid fuel source, and a sound of a quiet diesel, but I can't argue with FF's and my own experience. Gasoline is a lot cheaper to operate a gen set under MOST conditions in an RV.
Now for the conditions to the above - this assumes you have a load that is NOT 240VAC such as an electric range. Most coaches without electric cooking are 120VAC arangements - they are just split loads across a 240VAC line. By re-combining loads the above generator information is valid.
All this is IMHO - just some more food for thought. |
Henry R. Bergman, Jr. (Henryofcj) (63.224.197.10)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 08, 2002 - 3:07 pm: | |
Also need to consider that you will be using both AC units during the summer when it is very hot. Plus maybe at high altitude. Much less juice.
Plus, like already said, propane reduces the output of the set. Plus other stuff you will want to use at the same time. Blender?
Need to figure all that in, PLUS another factor of only using about 80% of the available maximum power. This loads the set at a reasonable level.
All said and done, plus future expansion, you may want to get a bigger generator. Remember, things always work someless less than expected. Thanks. |
|