Intro: Build an Analog Electricity Usage Meter
I have used a Kill A Watt (http://www.p3international.com/products/special/P4400/P4400-CE.html) electric meter for a while and I decided to build an analog one. This project went from being simple, with a single panel ammeter and an outlet, to full scale with three meters, a lamp socket, binding posts, and switches for all the outputs.
I also decided to pay attention to the aesthetics of this project and build one that had a steam punk look.
Rather than simply mount the plastic meters I decided to remove the movements and reassemble them in a wooden case and make my own numbers for the meters with a piece of tea-stained paper and an old typewritter.
From Simple to Complex
The basic design requires only 4 components. A cord, an outlet, a volt meter, and an ammeter. My design is more complex because I have two ammeters and three outputs, each with an independent switch.
Volt meters are connected across, where the current travels and ammeters are connected through the path of the current. (See picture two)
The idea of using a steam punk aesthetic meant that the plastic gauges with pre-printed backgrounds would not work. Thus it was necessary to disassemble each one and rebuild it in the new case. Avoiding this step and mounting the panel meters intact will save a considerable amount of time.
Other Design Ideas
One idea is to use an economy multi meter, often available for under $10. It would not be difficult to build a small case, add a plug or a cord and an outlet, and wire the system together. This would be considerably simpler and less expensive.
One important consideration is that to measure volatge you must connect the meter across and to measure amperage you must connect it through.
Measuring wattage directly requires expensive laboratory equiptment. Since W = V*A most devices measure voltage and amperage and multply them together. One idea would be to have the needles of a volt meter and ammeter overlap. The wattage could be read at the point where the needles cross.
The simplest answer is simply to have a multiplication chart with the rows being 110, 115, 120, and 125 for the volts and columes of 1-15 for the amps.
Step 1: Materials
1- 1/2" thick board 12" X 10-1/4"
4- 3/4" thick boards 12" X 2-1/2"
1- 3/8" thick plywood 12 X 10-1/4"
-- 0-150 V AC volt meter (http://www.allelectronics.com/make-a-store/item/PMA-150V/150V-AC-PANEL-METER/-/1.html)
-- 0-5 A AC ammeter (http://www.allelectronics.com/make-a-store/item/PMA-5A/5A-AC-PANEL-METER/-/1.html)
-- 0-15 A AC ammeter (http://www.allelectronics.com/make-a-store/item/PMA-15A/15A-AC-PANEL-METER/-/1.html)
3 on/off two position toggle switches ( at least one should support two circuts)
1 on/on two position toggle switch
1 porcelain lamp socket
1 circular outlet (recommend using a connector used for repairing an extention cord.)
2- 1" brass hinges with screws
4- 2" brass screws with matching nuts and end cap nuts
1- length of brass tubing that the shaft of the 2" bolt will fit into but the nut will not. This will be cut to make spacers.
2- 1" brass bolts with nuts and knurled knobs that will work well as thumb screws.
Step 2: Tools
Table saw (recommended)
If you do not have access to shop equipment a solid, sharp hand saw will also work.
pipe or bar clamps
C - clamps (the angle irons and C-clamps will help ensure squareness during glueing)
drill press (not necessary but highly recommended as it will be easier to have perpendicular holes)
heat shrink tubing or electrical tape
needle nose pliers
small ajustable wrench
Drill Bits: (Will vary based on your design, which meters you buy, and the size of your other hardware)
assorted small sizes for pilot holes and mounting bolts
1-3/8" flat bottom bit
high quality paper
fine point ink pen
black tea bag
typewriter (helpful but not necessary)
scanner/copier (Not necessary, I made copies of my original design for a back plate before tea staining in case I needed to redo it.)
Wood stain (I used Minwax Mohagony because i wanted a dark finish. The smallest cans will be more than enough for this project)
small stain brush
Step 3: Build the Case
The dimensions used to build this case were 10 1/4" X 12". I decided to use 12" across the top to accommodate the width of the three gauges.
The sides of the box are a simple design with two 10 1/4" rails into which are cut dados to fit the longer rails. Those rails were cut specifically to fit. The dados and rails were cut using a table saw, however, a sharp hand saw, a good layout, and careful cutting will also do the trick.
Once the pieces are cut dry clamping is the best way to check how well it fits together before gluing.
The box dimensions you use should be designed to accommodate the gauges, wiring, switches, and outlets.
Once the glue up is complete a dado in the bottom will allow a piece of plywood to sit flush. If you do not have access to a router the plywood can be tacked directly to the bottom and the edges can be rounded with sandpaper or a file.
The final step in the construction of the base is to cut a dado where the electric cord can fit through the back. I recommend waiting until the assembly of the panel is complete so you know where the cord will be.
Step 4: Build the Main Panel
It is important to construct a layout for the meter that works. A sketch will help. Layout the switches, meters, and outlets. After a good spacing is achieved use a square to draw lines. The horizontal lines were based on what looked like good spacing. The first vertical line was at 6", the half way point. The other two were 3 1/8" away on either side, enough to accommodate the meters.
If possible drill the holes starting on the front, this helps avoid tear outs. If you are drilling from the back have the workpiece on a solid, flat surface that give even support.
Drilling the Holes:
The meter I used required a 7/8" hole. This is slightly undersized, but only by a very small amount so I sanded to make up the difference. Once I had the hole through I glued and screwed a piece on the back side covering the holes. The panel I used was 1/2" thick so I use a 1/2" piece to ensure the holes were deep enough to accommodate the meters. I then re-drilled the 7/8" holes so they went all the way through.
2. Outlet, Lamp Socket, and Binding Posts
The outlet is in fact a connector used to repair the female end of an electrical cord. It mounted in a 1 3/8" hole. The lamp socket was the same size. I used my layout lines to drill the holes. Once I fitted the fixtures I backed them out and use a high strength epoxy all the way around and pressed them back into place.
The binding posts were quite simple. I drilled a hole to accommodate the shaft of the bolt. When I required a little more length I drilled counter sinks with a forstner bit.
This was the most difficult part. Toggle switches are not often designed to be mounted in thick materials. Thus I had to drill counter sinks with my 1 3/8" forstner bit. The holes also required a small amount of hand chiseling.
Drilling Tips: To get flat bottomed holes use a forstner bit. The point can be placed directly on the layout mark. Start with the biggest hole, the counter sink and then switch to the smaller bit you are going to use to drill all the way through. This way you have a center guide point for both holes.
Forstner bits are recommended for use only with a drill press because they are designed to only be used at 90 degrees and not on an angle. However, I have used them with a hand drill working on a solid surface, with proper leverage, and a good deal of caution.
Step 5: Protect the Meters
This was achieved by mounting a piece of acrylic over the gauges. It is wise to prepare this before mounting the meters. The less drilling, sawing, and adjusting done after the sensitive movements are attached the better.
1. Cut the acrylic.
This was salvage from an old computer case that I cut to size on a table saw. This material is available at most hardware stores and they will often cut it for you.
2. Drill holes.
Check your layout so that the mounts do not interfere with the meters or are too close to the sides of the box.
Start by drilling through the acrylic. Then place it on the front panel and drill the holes into the wood.
3. Insert the mounting bolts.
4. Cut spacers from brass tubing.
A small piece of brass tubing can be cut with a rotatory tool or a hack saw. These will allow space for the meters.
5. Place the acrylic
6. Use nuts to hold the acrylic in place
7. Use a rotatory tool or hack saw to cut the excess length off the bolts.
Try to ensure that you cut the same amount off each one leaving a small amount for a rounded end nut.
8. File the end and screw on a rounded end nut.
9. Once you are satisfied remove the acrylic and set it aside. then you can mount your meters.
Step 6: Rework the Meters
This is the most difficult and delicate part of the project.
1. Inspect the meter.
Open up the meter and inspect it carefully and determine the best way to move forward.
The meters I bought from allelectronics.com were all from the same manufacturer so they all had the same outside cases, mounting screws, and basic configuration.
2. Take the meter apart.:
After removing the front cover, face plate, and the back of the meter I unscrewed the movement from the case and pulled it forward. All three of these meters contained necessary electronics in the back portion of the meter by the binding posts.
I cut the wires leaving enough on each side so that they could be reattached later.
3. Remove the bushing from the meter case.
The cylindrical bushing shown in picture three is difficult to remove. Take out the movement and place it safely aside before pushing it through.
4. Mount the bushing in the new meter panel.
The hole required for these meters was slightly larger than 7/8". A small amount of sanding was necessary to fit them. It is important to achieve a tight fit so do not over sand. Once there is enough clearance use a piece of scrap wood and a hammer to tap them into place.
5. Drill a secondary hole next to the bushing.
When you inspect the meter you will notice that the wire attached to the front of the movement does not pass through the bushing but next to it. Drill a small hole to feed this wire through. Do not put it directly in line with the mounting hole as it will block you from mounting the movement properly.
See image 4.
6. Remount the movement.
This is very delicate and it is absolutely necessary that the movement is centered in the bushing and perfectly square. If not it will bind. Hold the movement in place and gently tap the needle so that it swings from one end to the other freely. If it sticks at any point you need to readjust.
Using a scrap piece of wood drill a test hole with a bit and see how the mounting screw from the meter fits. Though the screw is designed for a metal thread a pilot hole into hard wood will work.
Use the bit you determine to work best to drill holes to mount the movement.
Be careful in this step. If your holes are slightly off it will be very difficult to adjust.
7. Mount the back of the meter.
The back of the meter with the connectors and the necessary electronics should be screwed on (Image 6) so that the wires can be reattached and movement of the assembly will not put strain on the wires which could damage the movement or pull it out of alignment.
8. Reattach the wires.
Simply connect the right wires. It is important that you have the right back associated with the right movement. As you can see in image 6 the 5A meter and 15A meter have the same color wires.
I used a small amount of solder and some heat shrink tubing to splice the wires back together. (image 7)
Step 7: Wire the Parts
Use your wiring diagram to determine what to attach where. Make sure you do not have exposed wires. Keep lengths of connector wires reasonable, you want to ensure you have space to work without having excess length to get in the way.
Once you are done go back and trace over your wires to ensure that they lead to the right place and are connected properly.
Step 8: Add the Finishing Touches
1: Make a panel for the back of the meters.
Place a sheet of paper behind the needles of the meters and mark the zero point of each. Then trace the back plates that shipped with the meters onto the paper. I used a typewritter to type the numbers onto the paper and a fine tipped pen to darken the lines.
Once the paper is complete making a copy is a good way to ensure that you have a back up if you need it.
To age the paper steep a black tea bag and then dab the paper with it. Wipe up the excess water with a paper towel and allow it to dry. Thick paper will tend to curl so it is wise to place it on a flat surface and put some heavy books on it.
2: Stain the Wood
I used a dark stain because I felt it matched well with the brass fittings. If you can I highly suggest staining the case before assembly. This will make the task much more simple.
3: Assemble the Case:
Tack a piece of plywood into the rabbit cut in the bottom of the case and attach the front panel with two brass hinges.
Attach the paper with some spray adhesive. This works well because it covers the area evenly. If you use another kind of glue make sure to spread it completly to avoid lumps. Spray adhesive drys very quickly so after you spray the paper, don't spray the wood as the glue might damage the meters, immediately place it on the wood and flatten it with a ruler or paint scraper.