| Author | Message | ||
| Roger Baughman (Roger)
Registered Member Username: Roger Post Number: 54 Registered: 11-2006 Posted From: 69.232.71.118  Rating: N/A |
I would like to get some considered openions as to the advisability of installing an alternator in place of my REO air conditioning compressor to power my roof air while on the road. My REO compressor is no good. Also there is a leak in the system some where that is very hard to find. So before I spend another $2,000.00 on the old system I am considering a new alternator to power my existing four house batteries then through the inverter to power the roof air. A few specs, The roof air is a Duo-Therm 600 series Penguin, 13,500 btu, 115 ac volt, 20 amp, requiring a 3.5 to 5.0 AC Generator capacity. My inverter is a Freedom 20 100 amps DC, 2000 Watts made for deep cycle batteries with a modified sine wave. I would appreciate any information anybody can give me on this. Roger I made a mistake and posted this on the flea market too, sorry. | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 696 Registered: 8-2006 Posted From: 12.69.89.106 Rating: N/A |
Roger, Some of these numbers don't come out right. If the A/C is 10 SEER, which isn't very high, it would need 1,350 Watts to RUN, which would be about 12 amps of 120VAC. Starting Wattage requirement would exceed 2000, but most inverters have a surge rating which SHOULD handle it. MSW is not as efficient as pure sine wave, so the current draw may be a little higher. The number game? 100 amps of 12VDC is only 10 amps of 120VAC, theoretical perfect, which a MSW inverter isn't. 10 amps of 120VAC is 1200 Watts, so somebody's published numbers are way off. Could your A/C 20 amp requirement be a minimum circuit breaker size? My considered opinion would be at least a 3 KW inverter. You still got your original bus alt? If so, get a 3-4 KW 24V inverter, put it in a well vented space, and enjoy. George | ||
| John MC9 (John_mc9)
Registered Member Username: John_mc9 Post Number: 759 Registered: 7-2006 Posted From: 72.146.76.23  Rating: N/A |
One of the guys at our local Harbor Freight stores, is using the HF 2000 watt (4000 peak) inverter to power his 13.5 AC unit, atop his van. He says he only runs it when the engine is running, but it works fine. He gave me a demonstration, and yeah, it worked! I bought one ($149), but sold my bus, and haven't hooked it up in my diesel van yet. I plan to power a 5kbtu window-type unit with it, and hopefully have a small battery bank to use it during short 1 hour stops. It's cheaper than the $2,000 fix you're talking about, and if it works, you can brag about it here! You might want to add a "easy start" capacitor to the AC unit, tho... | ||
| James Robinson (Jjrbus)
Registered Member Username: Jjrbus Post Number: 184 Registered: 12-2000 Posted From: 70.10.100.194 Rating: N/A |
Several years ago I had a knowledgeable friend run the numbers and I bought an inverter to run the fridge. Numbers all added up, but it would not start the fridge, somebody was fudgeing numbers. Jury rig your inverter to the roof air and see if it works would be an option. I have a Trace DR2436 which i run off the 24 volt bus alternator it runs one roof air effortlessly. | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 645 Registered: 10-2006 Posted From: 64.241.37.140 Rating: N/A |
The usual hassle is not running the AC , its getting it started. With a time delay , so it wont attempt a start within 3 min of the last run , and a larger set of start capacitors , they can be run well from an inverter. Big next hassle is the wave form , only Sine Wave will fully power the unit , although it will "run" on chop chop power. To me a good $1000-2000 sine wave inverter will do more than just solve down the road air , and should be a viable choice. FF | ||
| Ed Roelle (Ed_roelle)
Registered Member Username: Ed_roelle Post Number: 71 Registered: 3-2005 Posted From: 71.0.165.140 Rating: N/A |
One reason that you want a larger inverter than the numbers suggest, is heat. For example, a 2000 watt inverter may produce that at ambient temperatures. However, during use, the inverter heats-up and heats the inverter compartment. As the temperature rises, the inverter performance deteriorates. The manufacturers have graphs on their web sites that will show you this. A second reason is the future needs. Consider if you may change to a household refrigerator in the future, or want to run 2 A/Cs. Ed Roelle Flint, MI | ||
| Debbie and Joe Cannarozzi (Joe_camper)
Registered Member Username: Joe_camper Post Number: 131 Registered: 10-2006 Posted From: 70.195.56.127 Rating: N/A |
I think spending 2000 on repairing the OTR A/C would be money well spent. It is designed to keep 50 people cool in extreem heet. I spent north of 5000 fixing ours and it was worth every penny. I would only run an a/c off a inverter as a redundent system and choose to get power from the generator instead. | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 806 Registered: 11-2005 Posted From: 208.54.200.30 Rating: N/A |
Roger, You have two AC problems; one for underway and one for parked. You can't power the one AC from four house batteries while parked for very long. One 13.5 AC won't cool the bus except at night. Inverters have a pretty high loss factor, around 20%. You sure don't want to keep the bus engine running to power the AC. Nothing will cool the bus like the original AC but it will probably be too much. If you're determined not to repair it then you should get a good genset of 6KW or larger and another roof AC. The genset will fit nicely into the old AC equipment space. | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1299 Registered: 10-2003 Posted From: 71.58.110.9  Rating: N/A |
That coach ac has plenty of overcapacity, but you won't enjoy it if it can't remove enough humidity on those cooler but still ac needed days. Ever cool a room with too big an AC? Be more like a swamp cooler. Whether you spend the money to fix it is going to depend on how you are actually going to use it. Flexibility is important. | ||
| Jack Conrad (Jackconrad)
Registered Member Username: Jackconrad Post Number: 929 Registered: 12-2000 Posted From: 68.26.181.237 Rating: N/A |
Before spending money on the Bus AC, ask yourself how much of the time you spend in the bus will the bus engine be running. Since we do mostly weekend to 1 week trips with no more than 150 miles each way the bus engine is running less than 10% of the time. We could not justify the expense for something that could only be used less than 10% of the time. Your use may be differnet. Jack (Message edited by JackConrad on January 21, 2009) | ||
| John MC9 (John_mc9)
Registered Member Username: John_mc9 Post Number: 762 Registered: 7-2006 Posted From: 74.230.99.46 Rating: N/A |
"So before I spend another $2,000.00 on the old system " Another $2k ?? Two grand will buy four rooftop airs. We kept very cool, regardless of the Florida heat (even in the Keys during the hottest part of the summer), with only two roof air conditioners in an old commercially built 37' motorhome. I planned to use only two in the 40' MC9. A decent 6.5kw genset will run both ac units just dandy. If you bought two of those el'cheapo Harbor Freight 2kw/4kw peak at 149 ea., you could run both ac units going down the road using a decent 12vdc alternator. Use the genset when you stop. With the bus AC, you have to run the engine. That doesn't fare well if you plan to park in other than a campground, and want to keep the bus cool while you're gone (not to mention the questionable legality of an running, unattended vehicle). I agree with Jack 200%. Unless you plan on doing a ton of driving in hot weather rather than camping, forget dumping cash into the OE AC. (just opinions, of cuz) | ||
| Roger Baughman (Roger)
Registered Member Username: Roger Post Number: 55 Registered: 11-2006 Posted From: 69.232.71.118 Rating: N/A |
Thanks to everyone for all of the info. To George: Here is the here are the specifivations from the Duo-Therm owners manual. Normal Capacity (btu/hr) 13,500, Electrical rating - 115 VAC, 60 Hz 1HP - Compressor Rating 11.5 - Fan Motor Rated Load Amps, 3.1 - Compressor Locked Rotor Amps, 50.0 - Fan Motor Locked Rotor Amps, 8.8 - Heater Amps/Watts @ 120V AC, 12.7/1530 - Minimum Wire Size 12AWG Copper up to 24 ft. - AC Circuit Protection, 20 AmpTime Delay Fuse or 20 HACR Circuit Breaker - Minimum Generator with two units, 5/0 KW. Now I have two of these air conditioner units. I also have a 12.5KW Diesel powered generator for the off shore power needs. I do have the orginal bus 24v alternator. The 100 Amps I mentioned was for the inverter battery charger, that is for 12 volts. The maunal says it is rated at 50 Amps for 24 volts. John says a 2000 watt inverter could work for one air unit. My inverter manual says that there is "a low battery cutout circuit and considerable surge power is available for starting electric motors". The manual also says that The 2000R adds the ability to control an engine driven alternator. The problem is I do not know if my inverter is a 2000R unit. To Gus: When I had the REO air working it would be too cold then I would have to turn it off and it got too warm. The thermostat did not work well enough. It is just too expensive to get all of these things fixed when I am not that good at these types of electrical controls. I really do need a back up system. Diesel generator and the roof airs. My wife will get very sick if she gets too hot. She has high blood preasure and it can be very dangerious for her to get over heated. To Jack: I need good air conditioning no matter how much or little I use it. I am still trying to decide which way to go. Thanks for all of the help. Roger | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 648 Registered: 10-2006 Posted From: 64.241.37.140 Rating: N/A |
"We kept very cool, regardless of the Florida heat (even in the Keys during the hottest part of the summer), with only two roof air conditioners in an old commercially built 37' motorhome. The summer heat in FL is down the center of the state , the Keys are vacation land because the ocean keeps them so much cooler! The SEASON in the keys is the summer! not the winter . "I think spending 2000 on repairing the OTR A/C would be money well spent. " I think it will be the first of a huge pile of cash for very little. 50% of all the maint time Hound spent was on the air cond. In the "old days" a 5 lb shot of Freon every week was a TIGHT !! system. If you really prefer mechanical air,an auto "hot rod" setup can be installed fairly inexpensivly Welch Ind. Atlanta, and will giVe aUTO LEVELS OF SERVICE , NOT THE BUS CRAP LEVEL. Even if you smuggle it in from Mexico or the Bahamas a 30lb can of F-12 is over $200. FF | ||
| John MC9 (John_mc9)
Registered Member Username: John_mc9 Post Number: 766 Registered: 7-2006 Posted From: 68.18.13.21 Rating: N/A |
I had the Welch auxiliary air conditioner in my MC9. It used cheap r134, didn't leak like all hell, and would put ice on the windows for the back 3/4 of the bus. There's a local guy (a friend), that might be interested in selling one, and I'll be happy to ask, if you'd like. The Welch runs off an added pulley assembly that sits atop the radiator blower assembly. The auxiliary system is only usable when the engine's running. There's been some speculation that it might be possible to run it off a small gas engine, but an electric motor with enough torque, would be too large and expensive for any serious RVer. The system is great for an auxiliary system in a commercial bus, but the cooling won't reach the front windshield area well enough to matter (even with fans). The cooling unit is mounted at the rear of the bus, with the air blowing directly out and over the last row of seats.  http://www.welchindustries.com/auxacsys.html Some individuals have run lines from the Welch unit, to the OE defroster at the front of the bus, and were quite successful doing so. The tech at Welch can't offer instructions, but might offer names of those that have made that modification (I didn't push the issue). All in all? I would stick the two roof air conditioners on the roof, run them with the genset, and try that el'cheapo 2kw/4kw peak inverter for over-the-road use (generator/alternator running). (one for each AC unit) It would be the most cost-effective solution to the most common question regarding "keeping cool". During the period of time I had my bus sitting in the heat of east central Florida, working my butt to the bone tearing out that stupid toilet, I ran one rooftop AC unit using a 3kw construction generator, or the storage facility's meager 15 amp power. I obviously didn't bake my brains, right? During the period of time I had my bus sitting in the heat of east central Florida, working my butt to the bone tearing out that stupid toilet, I ran one rooftop AC unit using a 3kw construction generator, or the storage facility's meager 15 amp power. I obviously didn't bake my brains, right? During the period of time I had my bus sitting in the heat of east central Florida, working my butt to the (Message edited by john_mc9 on January 22, 2009) | ||
| Roger Baughman (Roger)
Registered Member Username: Roger Post Number: 56 Registered: 11-2006 Posted From: 75.3.207.153 Rating: N/A |
One question. What is the AMP OUTPUT of the REO MCI engine mounted alternator? Thanks, ROGER | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 811 Registered: 11-2005 Posted From: 208.54.200.57 Rating: N/A |
I agree with John, I wouldn't even consider using the old bus AC system in your case. A 12.5 KW genset is way overkill from what I can tell from your posts. It will not have much of a load on it with your present setup. 6.5 - 8.0 is probably plenty. I run two 13.5 BTU ACs and the rest of a modest electrical load with a 6.0 KW Honda gas powered genset and it seems to be just right. It works hard but doesn't loaf on the job. Diesels like to work hard more than gas. | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 699 Registered: 8-2006 Posted From: 12.69.89.106 Rating: N/A |
Roger, Thanks for the updated info, now we can make more informed advice. Your A/C will draw about 14 amps, adding the compressor current and the fan current, and figuring them at 120VAC instead of their listed 115VAC. 14 Amps of 120VAC will require 140 Amps of 12VDC, if the inverter were 100% efficient, pure sine wave. A MSW inverter is probably in the 85-90% range, and then because motors don't run as well on MSW, I would figure on about 170 Amps of 12VDC to run the one 13.5 roof air. If I understand correctly, what you want to do is run a roof air off your engine while driving, and you have plenty of genset while boondocking, and a 50 amp shore service to run two roof airs when in a park? If so, AT LEAST a 3000 Watt 24 Volt inverter off the main engine alternator and chassis batteries will do very well for OTR operation. The listed draw of your A/C (14.5 Amps @ 115 Volts) is 1668 Running Watts, which is TOO close to your present inverter's 2000 Watt rating for my comfort level, not to mention very little left for starting surge. Adding capacitors isn't the answer either. More capacitance in the start winding will indeed provide more starting torque, but then will consume more run current. The suggestion should have been a "hard start kit," which has a potential relay that takes the extra capacitor out of the circuit as soon as the compressor starts. HTH, George | ||
| John MC9 (John_mc9)
Registered Member Username: John_mc9 Post Number: 773 Registered: 7-2006 Posted From: 68.18.13.21 Rating: N/A |
With all respect, OM... At the famed Harbor Freight store, I went outside with the employee, and he gave me a demonstration of his 13.5 Coleman roof air conditioner running on the Harbor Freight 2kw inverter, and his van engine running. He said he wouldn't attempt running it on battery power, since he only had one battery.. (har) We sat and talked about it, and the unit cycled quite well. It cooled his van down within minutes, and the change in engine idle was almost insignificant. The air unit indicated absolutely no droning, or difficult cycling sounds. He said he's been running it for over a year, and had friends that have been doing the same thing. I have yet to use mine, and it's still in the unopened box, perhaps this summer I'll give it a try.. It's 2kw rated, with a 4kw peak rating. I respect engineering, and theory, but it worked for that guy, and it's been working for others, too. As a side note..... Theoretically, the pyramids couldn't have possibly been built by man. | ||
| Roger Baughman (Roger)
Registered Member Username: Roger Post Number: 57 Registered: 11-2006 Posted From: 69.232.71.118 Rating: N/A |
To George: You have it right as for how I plan to use the air while driving/boondocking/in park. Thanks for you advice on the inverter running off of my engine alternator. I think that is the way I want to go on this. Harbor Freight has an inverter that is rated 5000 watt continuous and 10,000 watt peak power for 500.00. I am concern about the Harbor Freight quality though. I guess for the price it is worth a try. If it dies maybe they will replace it. And thanks to John for the Harbor Freight lead. I have one of there stores near me. | ||
| Tom Christman (Tchristman)
Registered Member Username: Tchristman Post Number: 54 Registered: 1-2006 Posted From: 66.218.33.156 Rating: N/A |
I think that an inverter should only be used as an intermittant power source-like for making coffee, microwave, and for continuous outputs where the inverter is way bigger then the load, like for a refrigerator (again only about 50% run time). When I bought my inverter, it could be stacked to double the output and was considering running the roof A/C's going down the road. The gal that sold me the inverter asked if I had a Diesel genset, I said I did, and rather then selling me another inverter, talked me out of it. I run two of the three roof A/C's going down the road with the genset. No problems, perfect electrical sine waves, and keeps the bus at 75 degrees in over 100 degree weather (also have 2.25" of sprayed foam insulation). Good Luck, TomC | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 814 Registered: 11-2005 Posted From: 208.54.200.87 Rating: N/A |
My experience with HF over many years has been that some stuff is good and some is not so good. I've even received brand name stuff once in a while, but not often. I only buy tools from them that I won't be using day in and day out. Most of their stuff won't hold up to daily use. | ||
| John MC9 (John_mc9)
Registered Member Username: John_mc9 Post Number: 777 Registered: 7-2006 Posted From: 72.146.79.49 Rating: N/A |
Roger - Gus, and Tom are right. HF imports a ton of junk. But, they guarantee the junk pretty well, and take returns. Still, I wouldn't use anything from China or a third world country, with total faith. I hope I wasn't wrongfully assuming that you had a genset as the main supply for the AC units, and just wanted some redundancy..? You did say: "I also have a 12.5KW Diesel powered generator for the off shore power needs." So, having a 12vdc alternator (of sufficient amperage) to power an Inverter, to run the rooftop air conditioners while going down the road, as redundancy, doesn't seem to be that bad of an idea! It redundancy, it's cheap, and it's free power. And unlike the OE system, it can be used while at the power-pole with the engine off.. with the inverter down the road, or with the genset any old damned time you feel in the mood. I don't think I'd start with the 5000 watt, $500 model, though. In my ridiculously humble opinion, I would go with a cheap $149 model, and see how it powers one AC unit. If I am satisfied, I'd buy a second $149 one and power the other AC unit. You won't be losing too much (everything's returnable anyway), by buying one at a time for one AC at a time, and if one did fail, the other will keep going. Call it "more redundancy". The "modified sine wave" models will power the AC unit, perhaps not as well as a true sine wave model, but it will work. When I bought mine, I figured that 149 smackers was worth the try. The kid at the store ran it, and I witnessed it. I wouldn't use it as the only means to an end, but as another alternative? Why not. | ||
| Roger Baughman (Roger)
Registered Member Username: Roger Post Number: 58 Registered: 11-2006 Posted From: 69.232.71.118 Rating: N/A |
To John, I like your reasioning on the $149 inverter. I was thinking that it might cause some problems with the air unit not getting the correct amount of power over time. Rumming it foe a short run is one thing, but running it for several hours maybe 5 or 6 hours seams like pushing it. what do you think about the intermittant use that Tom mentioned? | ||
| John MC9 (John_mc9)
Registered Member Username: John_mc9 Post Number: 781 Registered: 7-2006 Posted From: 72.146.79.49 Rating: N/A |
Intermittent use of anything, is better than full usage, unless it's a diesel. The guy I talked with, said he had his running for as long as he and his wife were riding in the van.... about 10 hours at any one time, according to him. He really didn't have any reason to lie; they don't work on commission basis at Harbor Freight. But of you're running it and have a backup in case it fails, what's the problem? The AC unit shouldn't suffer.. There's much said about sine wave vs modified sine wave, and mostly all in theory alone. The genset in our Winnebago would run sick at times, and provide less than 80 vac. The frequency was equally as sick, with lights pulsing at a slow rate. The AC units kept right on chugging along. Will a modified sine wave kill the same AC unit? I sincerely doubt it. But all the sincerity in the world, isn't going to put your hard-earned cash back in your wallet. Weigh it all out, do the figures (cash-wise), and make an educated decision. I can't speak with experience, since I haven't tried it yet. But if I have the time and energy, I will. I have a carrier window unit I plan to use in our Ford E350 7.3 diesel van. It will be a redundancy to the OE system; I don't have much to lose..... Do you? | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 658 Registered: 10-2006 Posted From: 64.241.37.140 Rating: N/A |
Will a modified sine wave kill the same AC unit? I sincerely doubt it. The question actually is will the reduced output from chop chop electric run the unit to your satisfaction. Cold enough? Chop chop power is fine. FF | ||
| Roger Baughman (Roger)
Registered Member Username: Roger Post Number: 59 Registered: 11-2006 Posted From: 69.232.71.118 Rating: N/A |
Thanks John and Fred for you openions, I do appreciate them very much. Roger | ||
| Cullen Newsom (Cullennewsom)
Registered Member Username: Cullennewsom Post Number: 51 Registered: 2-2009 Posted From: 98.201.161.214 Rating: N/A |
I've been told that it is inductive loads like motors and transformers that have the most trouble dealing with MSW. With that notion in mind, and given that a particular unit starts and runs fine, maybe you will shorten the compressor motor's life. But, maybe not enough to account for the price difference in an MSW inverter vs a "Pure" Sine Wave inverter. As Fred said, adding a capacitor may help. I suspect that if your load doesn't change much, you might even be able to find a value for capacitance that allows you to approach the performance of a SW inverter. Of course this won't be ideal since the compressor will cycle while the fan runs constantly. But, in truth, ideal circuits don't exist anyway. Sometimes good enough is good enough. So, it's been a few months. Have you tried it? Is it "cold enough"? |