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Old 05-05-2010, 06:00 PM   #192
Ran D. St. Clair
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Join Date: Apr 2009
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I wanted to quiet down my generator a bit, and possibly also provide insulation between the generator bay, under the truck, and the living quarters. I blocked up the openings between the metal floor joists and drilled some holes through the wooden floor above the generator bay. I then injected foam to try and fill the space. This time I used a canned foam that is intended to seal around windows and doors. They claim it will not bow the door frames, and that it remains somewhat flexible for life. I sprayed some water in through the holes just to make sure it was good and moist in there before injecting the foam. Unfortunately in these hidden applications I have no way to know how well I filled the space. When foam starts oozing out of the cracks I figure it is full, but I don’t really know.

I also don’t know if it really quieted anything down. I realized later that much of the noise was coming up through an open air vent related to the toilet. It sits about 4’ from the generator exhaust and was projecting sound directly into the interior. With nothing but hard walls inside (for now) the noise bounces around pretty good. That vent provides for combustion air to the toilet, and will eventually be covered by the toilet. I would be worried about hot exhaust gasses from the generator entering the living quarters but the toilet itself is mostly sealed, from the inlet vent all the way to the exhaust flue. Of course if I open the toilet lid it isn’t sealed and any seal is never going to be perfect anyway.

It remains an issue of concern, which is why I will be installing a Carbon Monoxide detector. With so many things in such a small place it is difficult to insure that exhaust fumes don’t find their way back in somewhere. I know that some RV’s have a generator exhaust that extends up well over the roof line, and I think that would be a fine solution, but it doesn’t work very well with the small portable generator I am using, (Honda Eu2000i).

Depending on where I am camping, I may be able to remove the generator from the generator bay and chain it to a tree or something. That would reduce the noise and the fumes. As a stealth camper, I need to be able to operate in an urban setting as well, so I also need to be able to charge batteries when the generator is on board. I can do that, but I will have to put up with the noise.

The Honda generators are relatively quiet, but the total perceived noise inside the living quarters relates to many factors. I am not saying that it is really loud or anything, but it could be better. The air conditioner (a standard Coleman Polar Cub roof top unit) is also a bit loud. I thought all the ceiling insulation would quiet it down a bit (and it probably did) but it is still a bit loud. For the moment it comes back to having an empty room with hard walls. Once I have bedding, curtains, and other soft surfaces it may calm down. Fortunately I don’t personally mind a bit of white noise. It tends to mask the more startling sounds that wake me up or otherwise annoy me.

I have been using my batteries and inverter on a regular basis while building the truck. All the tools, lights, vacuum cleaner, etc. that I have been using are running off the inverter with no problems so far. I just plug the truck in via extension chord to the battery charger and put the energy back in as fast as the inverter takes it out.

I did notice that the air inside by inverter bay was getting nice and warm though. That bothers me, because it has been mostly cool outside, and I went to a lot of trouble to make sure I had good airflow through the inverter bay. Once it gets hot out, or even really hot out, like 105F in the California dessert, and I am running the generator, battery charger, air conditioner and Inverter all at the same time, I don’t want to see much temperature rise between the inside of the inverter bay and the outside air.

After looking at the situation, I think I know what the problem is. I designed the battery charger and inverter to use their internal fans to draw fresh air into the bay, and then push the hot air out through a separate opening. The air path is sealed so the hot air can’t circulate back around to the input side within the bay. What I didn’t consider was that the battery charger might be running hard while the inverter was loafing (or the other way around). Both the battery charger and inverter have fans that run hard or not at all depending on how hot they are. I think what is (was) happening is that the battery charger was running full tilt but the inverter was doing almost nothing. The hot air would exit the battery charger and then sneak backwards through the inverter, then loop back through the battery charger again (not good).

To fix the problem I added an air baffle between the battery charger and inverter. Now the exhaust air from the battery charger (or the inverter) has no choice but to go straight outside. Once outside it could try to sneak back in through the inverter exhaust filter, but hopefully once in the open air outside it will mostly blow away and dissipate. Also, in order to sneak back in, it would have to overcome the resistance of the exhaust filter, which isn’t much, but hopefully helps to reduce the backflow. When air exits the bay it has to come in somewhere else, which is intended to be through the filtered inlet, which is physically a few feet from the outlet. Hopefully it won’t loop back that way, at least not much. If I have to I will add a temperature controlled fan to the inlet air vent and force the issue. I would rather keep things simple though.

As soon as I get a really hot day this summer I will have to run a full test with the air conditioner, generator, and everything else running all day long. I am sure my neighbors will love that. They are already bitching about me making too much noise with my table saw in the garage. I guess I can try to park the truck down the block while I run the test. It’s important not to piss of your neighbors because they know where you live….

To be continued….
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