Intro: Enclosure for a Generator
This Instructable is all about building a box for my new generator. We couldn't really afford an inverter type generator to run the stuff we want to (airconditioner, fridges and freezers), so it a standard older type wired into the house. The box's main purpose is to help redirect/muffle the sound a little and also to help protect it from the weather. I chose to pour a concrete slab for it to sit upon and make the walls out of concrete blocks with the cores filled in with concrete to help make it denser and should reduce the noise a little.
Things I also had to consider included; placement, how well blended in it would be, airflow around the generator, weatherproofing and exhaust gases.
This unit is designed to be wired into the fuse box of the house, I hired an electrician to do this part and put the input power outlet near where I was putting the box. Its on the beam in the corner behind the box, you may see it in some pics.
The end result is as per the attached picture.
Stuff you will need:
Cement, sand, aggregate and water
wheelbarrow or cement mixer
concrete smoothing device such as trowel and piece of wood
something to hold the form-work, stakes, pegs etc
blocks to make walls
wood of some sort to make door and roof
ventilation type fans
earthing rod (available from electrical supplies shops)
some cable to wire to the earth
Dust mask - cement powder can be a little nasty
Gloves - again with the cement powder, I didnt use them, but I had a hose and washed off anything that got on me
Water - needed for the concrete mix, but also good to replace fluids as you work
Tarp - shade, rain protection etc
A great way to start something like this is with a plan.
First up, choose a site. I had this little corner near the house that was the furthest point from both our house and the next door neighbours. It was also sheltered a little under the eave of the house. It also had no plants of note (save for an elephant ear plant that was nice and easy to cut down), and was kind of neglected. Perfect!
Next, measure up the generator. It was 800mm x 600mm. So that gives a nice easy rectangle to work with. I drew this as on paper so that Id have the measurements all the way through. After that I figured that 100mm of gap between the generator and wall sounded like enough, so added that and drew another box. Finally, after a quick trip to the place that makes concrete blocks, I picked a block type that was 90mm wide. So I added a final box around that. Sadly I seem to have thrown this piece of paper out, so imagine three drawn boxes on a piece of paper with the dimensions scribbled in. these dimensions will vary depending on the size of bricks you choose and the size of your generator.
This then gives the dimensions of the slab that will be required. Make sure that it will fit in the area you want to put it.
I went with enough bricks to make the box about a metre high. In the plan I also included a layer of half height blocks sideways at the bottom to allow for airflow intake with the plan being to have the top exhausting air to give a positive airflow path that should keep the temperature down and also vent the exhaust gases safely into the atmosphere.
*** Edit*** Found the plans! Attached as per pictures 3-6. Photos only Im afraid, but they are easy enough to read :)
Once a slab size has been chosen, the next step is to build some formwork. Essentially this means 'barriers to hold the liquid concrete in'. Mostly its made from wood, but you can in theory use plastics or metal as well if you have it lying around. I used wood as I had some lying around from a previous project that wasnt being used currently.
The wood should be put in the intended area to the outside of the planned slab size. So my slab was going to be 1200mm x 1000mm, as the wood I had was 19mm thick, to be able to attach it together, one of the pieces needed to be 19mm longer then the other. So I cut a piece of wood 1000mm long, and the other 1219mm long. They were then fitted in an "L" shape up against the existing concrete of the patio and carport. Spray the inner edge of the wood with cooking oil spray, or smear oil on. This will stop the concrete from sticking to the wood. I probably should have sprayed the pegs with it :(
Normally you would use wooden stakes as outside barriers to hold the formwork in place, but i had plenty of camping pegs lying around so used them instead. Whatever you use should be put on the outside of the wood where the concrete will not be going. Whatever you use will probably end up covered in a light layer of concrete. Wooden stakes could be thrown away whereas metal pegs would need to be cleaned.
The wood is then placed down as in the picture and the pegs driven into the soil with the head holding the wood steady. The wood is then checked with a level and hit with a hammer until it is level, though removing some soil helps if its a big difference.
Next up, laying the concrete.
Due to the small size of the slab and the low weight (35kg generator + Walls and concrete filler) that was expected to be placed upon it, I didnt see the need to put any reinforcement bars in the concrete, if it was for a driveway or something, then it would be worth using though.
Calculating the concrete mix required I did online, there are plenty of calculators out there that you put the dimensions in and get the number of bags needed. Mine ended up at 6 bags of concrete, plus the sand and aggregate. I popped down to the local place that sold that sort of stuff and returned with 6 bags of concrete and a trailer full of premix (1/2 cubic metres). All up about AU$100.
Mixing up this much in a wheelbarrow (about 8 wheelbarrows worth for mine) is hard work if your wondering, especially in 40 degrees celcius heat and 90% humidity (I lost 4 kgs of body weight, mostly sweat in a few hours). If you can afford to hire a cement mixer then do it, it would make it a fair bit easier. Make up the mix as per the back of the packet, mine was about 4:1 premix:cement.
Once its mixed up, pour it in until there is enough to progress to the next step... leveling the concrete.
Once the concrete is up to the top of the formwork, it needs leveling so that its flat. If you did the formwork correctly, then it should still be level once the concrete is in it. It makes it easy to see then if the concrete is level as it lines up with the formwork. Using a piece of longish wood, the idea is to scree (flatten) the concrete in line with the formwork by sliding the edge of the wood your using to flatten the concrete over the top edge of the formwork. , since the pegs I used stick up over the top, I used a hand trowel to flatten it all.
Once flat, let it sit for a little bit until the surface has a thin layer of water on it. It should be hard enough that poking it lightly with your finger will leave a mark, but not sink into it. Then go over it again lightly until its as smooth as you want it.
To let it dry, you can either let it air dry, or you can add some water to the top to slow down the drying process. the second option is meant to make stronger concrete, at the trade off that it will take longer to dry. I left it a week, and put a bowl of water on it the first 2/3 days to help it dry slower.
Once dry, remove the formwork, its hard to tell how dry it is from the surface, thats why I left it the week.
Once I pulled the formwork off, I saw that it had been pushed out by the weight of the wet concrete. Visible in the second picture, it has a slope to it that should not be there. The concrete slab itself was all level once dry, just that side was crooked. Ah well, it will still suffice for my purposes!
Next up, adding the brickwork.
I had a plan written down, so had exactly the bricks I would need for each layer ready to go. I mixed up the mortar (Sand, Line and cement powder, mixed as per the pack recommendations) in a small plastic tray that I had in the shed. This allowed me to make the mortar in small batches as I went along, so that I didnt have any wastage or drying happening.
Start by making the base layer, this particular design went all the way around for the first two layers, and then only three sides from then up. Put down a layer of mortar, not too much and not too little, but just enough. As this was the first time I have done blockwork, my mortaring was shocking! Id look up some videos on youtube as to the technique that those in the know use.
In the plan there were full length bricks, half length, quarter length and half height. Most of the half height were to be laid as the first layer on the bottom sideways as air intake holes.
First picture has all the bricks that I got
Second picture has the first two layers done. I stopped at this point and let the mortar dry overnight.
My plan was to make a door and top so the third picture shows the brick layouts for only three sides. This was completed the next day.
The particular sequence that I used was a complete wrap of full length bricks, then the next layer had half length ones in it to make it match, and offset against the layer underneath. Repeat until the top is reached.
Once the mortar is all dry, its time to fill the holes in the wall with concrete to increase the density of the walls a bit and make them stronger. I used three wheelbarrows full of concrete mix in the holes, and basically just poured it into the holes until it was all full.
If your mortaring is as bad as mine and you have holes in the walls where the mortar should be, then there is a silicon type product thats available thats designed to look like mortar and fill gaps. I used two tubes of the stuff!
Once its all done and dry (I waited another week) then time for a lick of paint to help seal it against the weather and help it to blend in to the background and not be so obvious. I used a generic green colour and painted it on with a brush to the outside only.
You could now stop at this point if it suits your purposes to just redirect the sound and there is adequate cover over the box area that the generator wont be affected by torrential rain. In theory, the generator should have plenty of ventilation, and the dense concrete filled bricks will redirect the sound toward the opening side very well. I wanted to add a roof and door type setup though and also forced ventilation.
Moving onto the front door.
Sadly I dont have any pictures of the setup being made as it was raining and I didnt want my camera to get wet. The tarp I had up over the top all the way along helped prevent most of it, but i still got wet!
To make the front door, I clamped a piece of vertical wood to the inner sides of the space where the 4th wall would be, then I pretty much screwed planks onto that from the bottom upwards until I covered the opening. I did this as I was using scrap wood that I already had lying around. Then i put a piece of plywood across the top, attached some hinges at the back and at the front to make a upward folding design. This was all using scrap that I already had, so if your doing something similar and buying the bits, then you may do it differently.
Into the top, I put two bathroom ventilation fans to provide the suction in the theory that heat rises, and creating a positive flow of air, entering in the bottom, and exiting out the top. To put these in, I traced around the top of a bucket that matched the dimensions of the fans perfectly, then cut it out with a jigsaw. Then i cut a hole with a forstner bit next to them big enough to drop the power cords through so they are inside the box and out of the weather.
All the wood was given a layer of paint to help prevent weather and water ingress.
Final bits and pieces!
The first picture shows the gap at the top front between the top piece and the front wood wall. As this needs top pivot outwards to start with and then inwards as the whole setup folds up, I couldnt put a piece of wood over this. I ended up using some scrap rubber from an old boot liner and screwed it down onto a flat piece of wood to stop water and weather coming in. Visible in Picture 2.
Picture 2 also has the weather proofing that I did for the fans, Its just half a plastic barrel that I had lying around, painted green with a cut out on the back side to let the fans vent. This should stop most of the weather from hitting the fans and causing lots of electrical nastyness! Picture 3 shows the back side of it. Its just sitting on top so that it can be pulled off to open the lid, then put back on top easily.
Handles are great! hence I put some on in a nice easy to acess spot that helps me to open the lid as shown in picture 4.
Picture 4 also shows some weather stripping that I put down, this is foam that comes in rolls with a sticky side to it. I just ran a line of it along where the wood comes close to the bricks. In theory it will help with the airflow and also reduce some noise.
Picture 5 shows the latch piece that I put on the front left corner, the box is going to hold a generator after all so I want to make it as hard to steal as possible.
Finally Picture 6, 7 and 8 show a magnetic door catch that I purchased to stop the wood bits falling on my head while I start the generator.
Almost time for the generator!
Picture 1 shows the earth rod. As the generator is running into the house power, and I have safety switches installed, its a great idea to earth the generator like the manual says. I got the rod from an electrical place, its about 2.5 meters long, but as its only a generator and not a house, I chopped it shorter, then hammered it in next to the box. Then I ran the cable through the vent hole nearby and into the generator earth socket. The power cable also goes from the generator through a vent hole and into the inlet socket.
Picture 2 shows the generator installed in its new home. The powerboard is a temporary method of checking the fans all work as they are supposed to. As the fans are only to be run when the generator is running, may as well plug them into it ey? The cables will be clipped to the wall so they arent near hot exhausts or engines and are out of the way.
Picture 3 shows a small addition that I made after it was all done. As we have cane toads around here, the nasty little buggers like to hide in out of the way spots. So i got an old ironing board from the tip (we have a shop where they resell stuff cheap), cut the mesh off and cut and bent it into a shape that would fit the vent holes. Then I put a piece of wood across the top and hammered it in. No cane toads in my generator anymore!
The finished product! The tarp is a new heavy duty square one thats folded in half that I bought and its going to stay there to provide additional protection from the weather (we get lots of rain here). The green blends in well, and the whole box does not stand out.
Final step is to redo that garden and put in some hedging plants to muffle the noise even more, and also to screen it all out from view. Thats a job for the dry season so the weather is milder when we do it.