| Author | Message | ||
| Pete (205.188.208.39)
Rating: N/A |
Hi guys.. I know we have gone over this subject before but i cant find it. I finally got my onan generator. its a 6500 desiel, watercooled. a nice unit i got from Bernhard Bus in Pa. We all have space problems..does anyone know how big a box i keed to make for this in one of my bays..and is there a rule of thumb withan inclosed area and the unit breathing? thanks BTW for the last 6 or 7 week i have been traveling the northeast from philly to mass, rt's 84, 95,87,287 The rigs that i have seen on those roads have been amazing..if any of you were there..thanks for the case of whiplash as I looked  Pete | ||
| Marc Bourget (209.142.38.81) Rating: N/A |
Dear Pete, I think the major point of interest, aside from access, is sufficient clearance to get cooling air through (in and out of) the sound box. This just relates to the physical dimensions of the genset space. More significant is the reversing duct areas for intake and exhaust of the cooling air through the soundbox. They'll take up the space that's necessary for keeping things whisper quiet and are frequently overlooked when evaluating the space necessary to install the genset. A well designed soundbox has intake and exhaust ducts that are sized correctly for the genset and the alternator's needs. The ducts themselves are lined with A/C duct liner. The reason the ducts reverse upon themselves is that sound doesn't "go around corners" well. Do this correctly and you can get some incredibly quiet genset installations. Finally, remember sound can be transmitted to the chassis through the genset mounts. Don't sabotage your quieting efforts by forcing the genset into such a small box that you forego good vibration isolation. Onward and Upward Marc Bourget | ||
| John G Root Jr (Johnroot) (66.82.9.46)
Rating: N/A |
Hi Pete, I made the box for my Onan 6500 Propane generator -- which is air cooled -- too small and now I have to enlarge it by a half an inch all around. What I did to size the box was call Onan and ask how many CFM the generator needs. Then I asked how big a duct that is and sized the air in and air out ducts accordingly. They take up half the height in the bay next to the generator compartment. The installation manual calls for a half inch air space on three sides, but for some reason it is not enough. It gets too hot for me to be comfortable (240 degrees) but which Onan says is probably ok. So with another half inch (One inch on each of three sides) I should be ok). Make sure you are generous with the specifications in the installation manual and call Onan with questions, they have been very helpful 800 888 ONAN (6626) What bus do you have? John G Root Jr PD 4106 1638 | ||
| pete (205.188.208.39)
Rating: N/A |
John..I have a 56 4501 scenicruiser ill be removing the old generator out of there tonight and getting ready to sink the new one in this weekend. still scetchy on the size of the bod but was going to bgo the dimentions of the frame that the rig is on..roughly 3x3 i have a 12 volt circ fan out of a jetta that i am going to hook up as a cooling fan..and the unit i have is water cooled and is desiel i have pleanty of room for a larger box but 3x3 seems to be a good size with the high rpm fan | ||
| CoryDaneRTSIIIL (4.17.253.83) Rating: N/A |
For John G Root We seem to have the same GenSet, What size did you end up having to make those air ducts? Did you have to make them a specific length, or I suppose I am asking, what is the LONGEST, or how short can you get away with to diminish the sound from going down the duct? I'm told the GenSet is pretty quiet all by itself before adding the sound insulation or the reversing air ducts. Did you see a great improvement with your installation? Am I to understand, that the air cooling from the GenSet Ducts is NOT ENOUGH to keep the GenSet Cool that it needs air flowing around the outer box (green shell) too? Give me an insight you might have with your installation, if you don't mind. "Imagine Your Dreams" cd | ||
| Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A |
I have a question about these boxes...specifically for a 6500 Onan... do you guys simply take the generator, stick it into a big enclosed box, feed it air from a blower-powered duct, and have another duct take air away? Or do you take into account the Onan's cooling air inlet and outlet, baffle them so they can't circulate to each other, and perhaps even let the Onan's fan do the air moving work? I'm curious to see some actual plans or drawings that work. My Onan is currently right out there in the open...I'd love to box it but I'm very unclear as to the airflow patterns you guys are all using...it would sure seem to me you'd have to duct the Onan's hot outlet air away all by itself, but maybe I'm making things too complex in my mind... Cheers Gary | ||
| John G Root Jr (Johnroot) (66.82.9.42)
Rating: N/A |
My installation is NOT successful. the plywood under the cement board caught fire today after five hours of running. The temperature in the box (not in the generator itself) kept climbing. When I smelled smoke I opened the compartment and found smoke so I doused it with water and scratched my head! My installation: I have a 4106. The heating and ventilating bay just behind the front wheels houses the Inverter and 6 AGM batteries. (There are two 85 pound propane tanks on the curb side of the compartment in their own 18 inch deep compartment made of plywood. In the drivers side there are two ducts 10 inches by 5 inches across the bottom of the compartment, with the batteries above. One duct brings the cool air in from under the bus and the other duct brings the hot air out into the wheel well. The ducts are made out of 3/4 inch pressure treated plywood and the hot air out duct is lined with aluminum foil and aluminum tape. I determined (maybe wrongly) that the 500 CFM that the air cooled Onan 6500 LP Generator needs is probably an 8 inch diameter duct or 5" by 10" . Secondly I determined that at least 3 90 degree changes in direction are needed to baffle the sound and ended up with about 5 baffles in each duct. The ducts go into the next compartment (where the big hydraulic fan for the airconditioning in the original bus was)The fresh air duct widens out and ends under the generator air intake with about 9 inches free under the generator. The exhaust duct starts under the exhuast space under the generator according to the installation instructions. The top of the duct which the generator rests on is cement board and walls are insulated with foam board and cement board. The exhaust pipe from the generator runs through the exhaust duct and into the free bay next to it (drivers side) The exhaust pipe is wrapped in EHP wet blanket to where it goes into the free bay. The exhaust goes through the bay wall in 3" stove pipe. It makes a 90 degree turn up and through the bus to the roof. The exhaust pipe is inside 3 inch stove pipe from a tee so air can get in and rise up the exhaust cooling it. This works. The stove pipe gets hot to the touch at the bends and stays warm on the straight runs. The exhaust at the roof is as hot as one would expect. The exhaust is not getting too hot. Where it gets too hot is in the compartment, and in the exhaust duct. The installation instructions call for a half inch between the generator housing and the wall of the compartment on at least three sides. I have about an inch on the back, top and left side, and less on the right side. There is a half inch on the front side where the compartment is closed in with an insulated sandwich (plywood, foam board, plywood, ehp roll board with foil). The burn happened below the exhaust pipe where it makes a 90 degree bend to go into the free bay. The compartment has a meat thermometer sticking into it with the wires and the temperature rises steadily, reaching 260 degrees after five hours running both air conditioners. I will bring the bus to Onan in Springfield, MA when I am done with everything else and hopefully they can help me out. The only thing I can think of at the moment is that the baffles slow the air too much or that they are not big enough. How big a duct is 500 CFM? and what affect do the baffles have? I hope someone can help. By the way, the generator when sealed up is quiet. It sounds about as loud as the roof air conditioner and that is a lot quieter than when the compartment is open, although the generator is a lot quieter than most I have heard. John G Root Jr PD4106 1638 | ||
| CoryDaneRTSIIIL (4.17.253.136) Rating: N/A |
John Glad you were able to find the problem before it became a loss of larger proportions. Your installation sounds interesting, I think only one part of the installation is the culprit, but I cant decide if it is the ducting or the clearance. If you can force enough air through, I am betting on the ducting, but it sounds like it will be a trial by error. I dont think Onan will be too excited to hear about your sound proofing idea. The time I spoke with them, they said the gensets were quiet enough and should not be put in sound boxes. Thats easy for them to say. Good luck and thanks for the info, I will study it while figuring mine out LOL. Keep us informed if you can. "Imagine Your Dreams" cd | ||
| FAST FRED (67.75.111.197) Rating: N/A |
Sounds like most of the heat problem IS from the exhaust pipe. There are asbestos like wraps that keep the heat in the pipe. Might try that before a $1.25 a min for the OHNO guy to scratch his head. FAST FRED | ||
| Marc Bourget (209.142.38.81) Rating: N/A |
Dear Johnroot, If the Temp steadily climbs until it reaches 260 deg, then it would appear that the airflow through the box is insufficient. The problem with the exhaust may be to a minor leak or the localized effect of the heating from the exhaust elbow. While more "corners" are better, the typical "duct" I've seen reverses 180 deg. (at least once) and the duct sections are about 3x the width of the duct, as a minimum. My memory serves that the duct section is as high as the box, the opening was as wide as the box, as were the internal openings. The soundbox would then have something resembling a "maze" at each end with a minimum of one 180 deg course reversal. If your box is 20" wide and the opening 5" high, the complete path should accept a 5 x 20 template and the air would have a 5 x 20 path all the way through- (not counting in the engine compartment 1" all around the engine might add up to be more than 5 x 20 = 100 sq. in, for example). Consider standing off a sheet metal shield 1/2" to 3/4" in the area below the exhaust elbow. The ducts, both in and out, should be lined with sound absorber. If the out duct is so hot that you want to line it with aluminum, this is another reason I would suspect your cfm is too low. Marc Bourget | ||
| jmaxwell (66.42.92.12) Rating: N/A |
From what I read, the exhaust pipe is the culprit here. FF mentions insulating it. There is a ceramic blanket insulation product made that I have used that works extremely well. It is good to 3100 degrees. It is expensive, in the range of $2.50 sq.ft. You can find it in high-end race car fab shops. It's used in NASCAR as a cockpit heat shield and fire barrier. On a pipe, you would wrap the pipe and then secure the wrapping with stainless tape or bands. Or, simpler yet, maybe u can find a way to exit the bay sooner with the exhaust. | ||
| John G Root Jr (Johnroot) (66.82.9.23)
Rating: N/A |
Hi Guys! Thanks. I have decided that the exhaust pipe is creating more heat than the exhaust air can take away. I will run the exhaust straight down and under the bus and then back up to the stack through the bus. This will expose only 6 inches or so of the generator exhaust to the exhaust air. I'll wrap that six inches in EHP wet blanket. But what I don't understand is why the exhaust pipe would generate so much more heat than the generator is designed to deal with since the muffler is inside the generator's own compartment and the exhaust pipe in my installation runs below the muffler. It may be that the baffles are restricting the air flow more than necessary so if moving the exhaust out of the soundbox in as short a distance as possible doesn't do enough I will then remove some baffles and or make the ducts bigger. The exhaust is wrapped in an EHP wet blanket, but it obviously isn't enough. Maybe the six inch run with no bends instead of 22 inch run with two 90 degree sweeps will make a big difference. Thanks guys, I'll figure out how to post pictures someday -- but not until it is working! Ah what we'll do to get a quiet generator! I should have known there was a good resason the commercial motorhomes haven't figured out how to do a quiet generator! What do you do with all that heat? On the next bus (is this one the trial bus?) I'll figure out how to use the generator heat for the hot water and to heat the bus. A diesel generator running on waste vegetable oil with a heat exchanger heating water in a 50 gallon well insulated tank should do the job. The trouble is it's fun to figure out what would be great to have and a royal pain to make it work! Thanks John | ||
| FAST FRED (67.75.106.160) Rating: N/A |
Heat transfer is very dependant on surface area, insulation just slows down the process. IF you relocate the muffler out of the gen compartment you will have loads less area radiating. This may take up room elsewhere but atleast no fires! FAST FRED | ||
| John G Root Jr (Johnroot) (66.82.9.29)
Rating: N/A |
So, running the exhaust under the bus did not help. I had a thermometer in the hot air out duct and when it got to 300 I shut it off. So I assume that I am not getting 500CFM through the generator. Does anyone know how big a duct I need to get 500CFM through the generator? Does it make sense to add a fan in the duct? In which duct? Does it matter? Thanks John | ||
| Stephen Fessenden (Sffess) (65.154.176.187)
Rating: N/A |
I'm sure you need a blower to move air through the compartment. The onan blower is for cooling in an open area. Try using a used air conditioning blower (110 volts) powered off the generator so if the generator is running the blower is running. Ask your air conditioner repairman for one. | ||
| Pete (64.12.96.235)
Rating: N/A |
John, I started this thread a week or so ago..i put everything everyone said together and camer out with this.. The box im making ( finishing it today ) is going to be 3 feet cubed. I cut in a 4x8 air duct that forms a 6 inch round outlet. I am going to make the 6 inch outlet rounded off to a 12 inch final port and I got a 12 volt waterproof cooling fan out of I think a Jetta. We trhink with the high CFM from that fam it should provide enoughpulling of the hot air to keep up with the genset. I also cut a 9 x 14 hole in the floor directly below the rad and fins of the moter to allow cool air to get in. I used wonderboard to close the interior walls of the box with a removable top. I am using ridged air vent duct on the outside of the box for soundproofing. There is also a vent cut in the door of the bus for more air to get in. the exause was vented under the bus..I am hitting a performance store a freiend of mine has and will be wrapping the exaust pips with the fireproof insulation for the pipe to keep that heat in. I hit an auto store..got a muffler from some sort of import and am venting it back...not sure where..lol..ill let you know over the weekend... thats about it for now.i am going to fire the whole thing up this afternoon..if you dont hear a big bang..it worked ! Pete | ||
| Geoff (Geoff) (66.238.120.25)
Rating: N/A |
When you go to buy a muffler get one for a mid-eighties Chevy Chevette Isuzu diesel-- the small automotive ones for gas engines will get clogged up with soot. I ordered one from my local NAPA store. | ||
| pete (205.188.208.39)
Rating: N/A |
lmao now you tell me | ||
| Geoff (Geoff) (66.238.120.25)
Rating: N/A |
Sorry-- I got into this one a little late. I learned by throwing away a gas engine muffler after my exhaust started popping after putting 75 hours on my diesel generator. | ||
| John G Root Jr (Johnroot) (66.82.9.38)
Rating: N/A |
Well, now I have to accept the heat. I put a 500CFM duct fan in the duct that brings cool air in and sealed it all up. Without starting the generator the speed of the air coming out of the exhaust duct (between the front wheels) was stronger than the flow from just the generator fan. Then I fired up the generator and even with both fans blowing after an hour and a half (it took 5 hours to burn the plywood) the exhaust duct was up to 300. So now I will take out all the plywood and replace with concrete board (durarock) and live with the heat. I hope the propane hose can take 240 degrees over many hours(which is what the box measures when the exhaust duct is 300). I sure hope I can keep the generator boxed up -- it is so quiet people wonder what that noise is, nobody has guessed that the genrator is running. John | ||
| drivingmisslazy (24.196.191.70)
Rating: N/A |
John, I would be more concerned over the capability of the alternator (generator) windings to withstand this temperature. I would suggest you look at the nameplate and determine what the rating is. Could be as low as 160 degree F for continous operation at rated load. i.e. 40 degree rise over a 120 degree ambient. Richard | ||
| John G Root Jr (Johnroot) (66.82.9.27)
Rating: N/A |
Onan told me that the generator has a high temperature cutoff at 238 degrees. If it doesn't shut itself off then it isn't too hot! I hope! John |