The following describes my latest enclosure. It incorporates some of the ideas of Brad, Professor Randy, Floyd and others who have contributed their knowledge on enclosures. I posted a sketch of my design in this forum about 6 months ago. This is the final product with some modifications from that original sketch. I have posted this info in the 3000W Chinese Gensets forum but decided that it should also be posted here because the original design sketch was posted in this forum.
Materials were “re-purposed” as much as possible while building this iteration. It has been in use for the last couple of months. I concluded that this enclosure was good to about 100 degrees ambient at 2000 watts generator output. This is enough to run my 5ver’s 15k BTU A/C unit. At this ambient temperature, it is necessary to shut the AC off to run the microwave. The combination of the two requires about 3200 watts. Testing showed that my Champion genset reached its maximum output of 2900 watts at 100 degrees ambient. Running both loads together resulted in the engine rpm lugging down and the voltage dropping from 120v to 103v. Frequency also was reduced due to the loss of engine rpm but was not measured.
Now, the disclaimer:
THIS ENCLOSURE WAS BUILT SOLELY FOR THE USE OF THE WRITER. OTHERS WHO ATTEMPT TO BUILD A SIMILAR ENCLOSURE DO SO AT THEIR OWN RISK. VARIATIONS IN THE DESIGN AND USE OF THE ENCLOSURE INCLUDING BUT NOT LIMITED TO AIRFLOW, GENERATOR LOAD, AMBIENT TEMPERATURE, ALTITUDE, EXHAUST TEMPS, AND NOISE ABATEMENT WILL AFFECT THE ABILITY OF THE ENCLOSURE TO SAFELY HOUSE THE GENERATOR.
The main reason for this latest iteration was to move the gas tank out of the enclosure and have it located in a lower temperature environment. Last winter my wife’s microwave oven decided to quit working. I disassembled the corpse for useful parts. The outer housing was steel measuring 25” long, 17” deep and 14” high or just the right size to house the engine and generator head of my Champion genset. The fuel tank and control panel were raised 6” to allow clearance to the top of the new enclosure. Miscellaneous openings in the rear panel of the re-purposed microwave housing were covered with metal foil tape except for one opening located below of the engine air cleaner inlet to allow intake of cool engine combustion air.
The fuel hose and electrical wiring were routed through the rear panel of the enclosure. The rear panel separates from the rest of the enclosure and stays with the generator when the enclosure is removed. This allows for quick removal of the enclosure for any work needed on the genset or to operate the generator without the enclosure. With the enclosure installed, the front enclosure panel slides sideways to allow for checking the oil, operating the choke and using the recoil starter.
To improve airflow and reduce cooling air re-circulation, the bottom of the enclosure was closed and air intake ducts were fabricated for the engine and generator head. The generator head duct inlet also had a booster fan incorporated to improve the cooling airflow through the generator head. Tests confirmed that the 300 cfm exhaust fan produced a negative pressure inside of the enclosure. Enclosure openings and clearance slots were sealed to force almost all of the air to enter through the cooling air ducts except for the air cleaner intake air opening in the rear of the enclosure.
The exhaust piping inside the compartment was insulated with high temp fiberglass insulation re-purposed from an oven to reduce heat load in the compartment. The muffler was insulated and wrapped to reduce heat transfer and noise. A piece of 1/4” thick hardbacker board was added between the insulated exhaust pipe and the genhead to reduce the exhaust heat load on the generator windings.
Tests were conducted to measure the capabilities of this enclosure. These were completed at an average ambient temperature of 98 degrees at 1470 feet above sea level. The unit was in a shaded environment to eliminate sun load, which in Arizona can add 30 degrees to the surface temperature of an enclosure or fuel tank. Electrical loads were 2600 watts and 1600 watts for the first test and 2200 watts for the second test.
During the first test, the generator ran for 30 minutes at 2600 watts before it started to stumble. The load was immediately and arbitrarily reduced to 1600 watts by turning off the leaf blower and leaving the air compressor load running. The test continued for another 30 minutes without any further problems with the maximum temperatures dropping and stabilizing. At 1600 watts, the air temp above the engine stabilized at 160 degrees, above the genhead at 140 degrees and enclosure exit air at 150 degrees. Test time was 60 minutes under load, 15 minutes running with cooling fans load (110watts) and 15 minutes with the engine off and cooling fans running. Enclosure cooling was extremely effective after the engine was stopped and the cooling fans continued running.
The second test was completed at an electrical load of 2200 watts. It was terminated after temps were stable for 4 consecutive readings taken at 5-minute intervals. Total test time was 45 minutes under load and 15 minutes for cool down with the engine off and the enclosure cooling fans running. The stabilized engine air, genhead air and exiting air temperatures were 156, 145 and 152 degrees respectively measured in the same locations as the first test.
The fuel tank temperature after the tests was between 110 and 118 degrees. Under direct sun load, it would have been in the 140 degrees range and probably 150 degrees if it was still mounted inside of the generator enclosure.
Temperature graphs and other data from the tests are included along with the pictures. The pictures were taken while the generator and enclosure were mounted on a temporary test stand base.
This design was a success for me in that it allowed me to operate my RV air conditioning at 100 degrees ambient with the enclosed generator. At a 75-80 degree ambient, both the A/C and the microwave can be run together for short periods probably due to reduced air conditioning power requirement and increased generator output. The maximum electrical load at high ambient temps should be limited to about 1800-2000 watts. My 5ver’s A/C and enclosure cooling fans use about 1800 watts at 100 degrees ambient. Of course, the refrigerator and hot water tank are on propane and the battery charger is turned off while the generator is being used for the A/C at high ambient temperatures.
Someone may have noticed that I continue to run the 120v cooling fans after stopping the generator. This is accomplished by using a 2500-watt inverter and RV batteries. The inverter is wired into the generator control panel. The 3 way toggle switch on the panel acts as a transfer switch with one position for the 120v generator, center position off, and the other position for the 110v inverter. This also allows me to use the inverter to run the microwave and entertainment system in the RV through the same wiring that the generator uses.
Sound reduction was not a priority with this enclosure. I am satisfied that it is in the low 60’s dBA (by subjective evaluation). If I would try to lower the noise level further, I would add ¼” thick hardbacker to all of the enclosure’s surfaces. This would add about 20 lbs. to the enclosure.
Future improvements will include a 160-degree enclosure air temp automatic generator shut down switch and improved exhaust piping temperature insulation. Brad noted that his exhaust pipe insulation was cool enough to touch. Mine isn’t. If I can get the insulation surface temperature cool enough (like Brad’s), I will remove the hardbacker heat barrier between the exhaust and the genhead.
Finally, I will consider switching to a dual fuel system of propane and gasoline following Professor Randy’s instructions in his propane conversion thread.
Now, here is a request for temperature data.
The generator head temperatures were measured during the second test just after the 2200-watt load was removed. The temperature was a respectable 123 degrees near the AVR but 190 degrees on the sheet metal windings cover near the top of the genhead by the long mounting bolt on the exhaust side of the genhead.
I am requesting that forum readers with the Champion 3500 watt generator in its original factory configuration measure the temperature of their genhead at this same location (see picture for the exact location) after about 30 minutes of operation and either send their temp info to me in a PM or just report it in this forum.
I would like to confirm that the 190-degree temp at this location is typical of the OEM configuration due to both the engine and muffler heat load on the genhead. If this temp is not typical, I will address the exhaust pipe insulation improvement soon.
2600/1600 WATT DATA
2200 WATT DATA
GENERATOR OVERVIEW
COOLING EXHAUST FAN
FUEL TANK ROTATED
BACK OF ENCLOSURE
HOT AIR EXIT (ORANGE)
EXHAUST PIPE INSULATION
ENGINE AIR INTAKE DUCT
DUCT MOUNTING
GENHEAD AIR INTAKE DUCT
GENHEAD AUXILIARY COOLING FAN
GENHEAD HEAT SHIELD
Bob and Cathy
2002 Montana 3655FL
2006 Chevy 2500HD Duramax/Allison
PullRite 16k Superglide
Just a Great job Bobandcat.........
It's really interesting to see your temp/output gragh. I find my temperatures run real close to yours. Thanks,
Brad
After adding sound lowering panels to my C46540 it is now back as a OEM unit except the muffler is wrapped with 1" 400 degree insulation received from Brad.
On a 88 degree day here are my temp findings. A heater was used for load and with a clamp on meter the reading was 16.10 amps.
Valve cover 115
Dip stick 133
Genhead cover/ muffler side 182.2
Genhead cover/front side 118
* Genhead bolt with arrow (Bob) 240
Manifold 420
Exhaust end of Muffler 380 (Wrapped)
I have sound lower panels and a 1150cfm fan used for inside air exhaust, I located under the genhead air exhaust with the fuel tank raised 6" (idea came from Bob) and modeled on the design from Brad.
See DuroPower DP3500EC electric start installed in a previously owned MH factory genset compartment. Very low dBA. Now we have Bob with a design of the future.
Well done Bob. Maybe someone else will also give us their design. And/or add suggestions.
Brad, got any updates. Anything new? Don't hold out on us
Floyd,
Thanks for the temp info. You confirmed what I expected. The muffler heats up the side of the genhead to a very high temperature. The windings apparently can take those temps over an extended period of time. Otherwise, these generators would have a high failure rate.
one of the reasons built in RV generators from onan etc.. have larger higher HP engines per KW rating is the need to Drive the big squirrel cage blower used to keep the thing cool, the other reason is too have enough HP left for the genny head after heat de-rating.
my 4500 generiac had a 10hp motor and I think the 6.5 kw onan had a 12 hp motor, running on memory here , so my numbers might not be correct
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As long as I stay arround 16 amps or less my compartment stays arround 160 degrees. Seems not to matter much what the outside temp is..which is strange. If I try to pull over 16 amps then the temp seems to kind of go into a cascading type effect and continues to rise. I beleive I have a fix and will post it when I am done. Total load with the AC running is 13-14 amps as long as my Batt. are not too low. This temperature is measured on the cylinder head.
Brad
The factory control panel. Generator is running(1/2 hour, no load). You can't tell from the pictures but the red run light is on and the back light in the gauge is glowing green. I replaced the hour meter with a temp gauge. Sensor is mounted on the head in the location illustrated in previous pictures. I can shut it down from here but cannot hook up the start untill I install an electric start on the ole CHAMP. (Stay tuned for that one...should be fun)
Here, I believe, is the reason I am limited to 16 amps. I will be replacing and reconfiguring the bottom of this install. The Black material by the fan blades was my attempt to reduce the distance between the edge of the blades and the wall of the duct. It helps...just not enough.
Brad
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