Introduction: Old-World Light Bulb Load

When working with power electronics, quite often the right piece of test equipment is an old-fashioned incandescent lamp. They make good ballast resistors and dummy loads for a variety of devices. A 100W bulb starts at about 10Ω when cold and works its way up to about 150Ω, so they even adapt well to a wide range of voltages. Plus, they are cheap, available in a several values, and generally do not explode on failure.

As I have been designing a little power supply myself of late, I decided to make myself a little box to hold a pair of light bulbs wired to standard 5-way binding posts. For some reason, I decided to make something nice, and to try to improve my woodworking skills at the same time.

I am a fan of all things steampunk, and so I decided to try to make something with a similar old-time feel.

Step 1: Electrical Parts

I started by finding the essential electrical parts. I found the small porcelain light bulb sockets at Home Depot, and I picked up the standard 5-way binding posts from Radio Shack. I have to admit that I was very tempted to use knurled brass thumb nuts instead of modern binding posts, but since this device is also meant to be useful, it has to accept banana jacks, and so I resigned myself to having a little bit of plastic.

My original plan was to simply mount all these parts to a board and get back to work on my power supply. The problem was that the binding posts expect rear connections. The light sockets are more flexible, but they do allow rear wiring.

I quickly came to the conclusion that I would need a box.

Step 2: The Box

With the idea in mind that I would need a box to mount these parts on, I started looking around my workshop for something suitable. I had plenty of plastic and metal project enclosures, but nothing had the right look. Finally my eyes came to rest on a sheet of oak craft board that I had sitting next to my scroll saw.

The board was 5.5" wide, just big enough to mount the two fixtures side by side. I measured off a piece 4" long and cut it. Then I measured a set of pieces a nudge more than 1" long, and cut those off. Two of them I left 5.5" long, two of them I cut down to 4" long.

I measured and marked the location of fingers for box joints, marking on the inside surfaces the order in which they assemble. This is important: while they are all measured the same way, they only go together in one order, as slight errors occur from freehand cutting.

I cut the slots out with my scroll saw. To make these square cuts, start by cutting two slots straight in, keeping the blade on the waste side of the line. After cutting to the final depth, back the blade straight out. Once both slots have been made, put the piece back into the blade at an angle, cutting through the waste piece while turning, reaching the bottom about half-way between the two slots. At this point, the blade should be facing in the right direction to finish half the cut, resulting in a nice sharp corner. Then just make another cut, starting from where the last cut began, but in the opposite direction, making another sharp corner.

The mating pieces will usually not fit the first time you try. I used the scroll saw to take off paper-thin curls of wood until the parts fit. You could do the same, or if you are not as comfortable with scroll saw operation, you could file them down with a wood rasp.

After the box was ready to assemble, I marked and drilled all the mounting holes.

Step 3: The Brass Plates

No old-time woodworking project is complete without a touch of brass. The shiny yellow metal complements stained hardwood nicely. This was one of the most complicated parts of the project, and not even strictly necessary, but it looks good.

I started with some craft store brass strip, which I cut to length. Brass is remarkably difficult to cut with a scroll saw. My first attempts caused a blade break, so I searched the internet for advise before continuing. It turns out that the trick is to use a backer board, so I picked a lump of pine from my scrap bin and put it under the brass. After that, the scrolling went smoothly, although slowly and noisily. I imagine that the correct tool for the job is an abrasive band saw, but I do not own such a tool.

After cutting, I rounded the corners on a stationary disk sander. I then tilted the sander table to a 45 degree angle and beveled the edge. The resulting edges were rather sharp, so I cleaned them up on the sander without using the table. When using a disk sander without a table, hold the piece at an angle away from the direction of rotation. Otherwise, the grit will catch the workpiece, and even assuming you can keep a grip on it, this will cause the piece to vibrate. Holding the piece at an angle causes the grit instead to push the piece away from the wheel, allowing fine control and reducing the amount of material it removes.

I then took the plates over to my drill press and drilled out the mounting holes. I have to admit that I made a mistake here. Brass is a slippery material. Make absolute sure that you have a good center punch before trying to drill it, and drill a pilot hole. My own center punches were not well enough defined, and the pilot holes drifted. Thankfully, I managed to mostly correct their locations before drilling the mounting holes. Mostly.

After that, one thing led to another, and I had managed to scratch the brass. Brass is, after all, a relatively soft metal. I sanded it down with 400 grit sandpaper. If I had any 200, I would have started with that, and it would have given me better results. After sanding with the 400 grit, I ran over it with a Dremel wire wheel, giving it a nice shiny brushed appearance.

Some time after I took this picture, I decided to refinish the brass parts, as I had picked up some 220 grit sandpaper. I did it the same way, but I decided to forgo the wire wheeling.

Step 4: Gluing the Box

Because friction fit is never enough, the time arrived for me to glue the box together. I used Elmer's brand "Stainable Wood Glue", because I figured that I would probably end up with glue in a few random places and a stainable glue would probably help to hide it when the time came to stain the wood.

I started by taking the workpiece to the scroll saw and enlarging a couple corners to improve the fit under pressure. If anything, I may not have been aggressive enough in doing this, but it helped a lot.

I rolled out a sheet of aluminum foil, poured a little glue out onto a corner, and used a Q-tip to apply the glue to the mating surfaces of the box joint. As the process is rather time sensitive, I wasn't able to actually get pictures of this step in progress.

After the glue was applied and the box was assembled loose, I clamped it every which way and left it to sit for a few hours.

Step 5: Surface Preparation

The next day, I removed the clamps. The box was, indeed, a single solid piece. I applied some wood filler to the surface, and scraped the excess off with a putty knife, and then left that to dry overnight.

The next day, I sanded the surface smooth with a bit of 220 grit hand sandpaper. Then, using some 80 grit sandpaper on my stationary disk sander, I cleaned up any overhangs on the box finger joints. I then rounded down all the edges and corners.

After this, I applied a second coat of wood filler and then sanded it down in preparation for surface finish.

Step 6: Surface Finishing

After filling the grain and the box joints with wood filler and sanding, I applied a coat of Minwax water-based rosewood color wood stain with a cotton cloth. I was pleasantly surprised by how well the wood filler soaked up the stain, leaving a very even finish. I then left it to dry overnight.

I waited another day for the weather to clear up, and on a nice sunny day with little wind, I applied three coats of Minwax Polycrylic matte topcoat, allowing an hour between coats, and sanding lightly with 220 grit before applying the next coat.

The results are pretty good for a first try.

Step 7: Assembly and Wiring

The last step remaining is to assemble all the parts. I had to clear the holes with a hand-drill, as some wood filler had adhered to the insides, but otherwise, this was completely straightforward. I mounted the fixtures down with some #10 screws.

I fed some 18AWG wire through the holes in the back of the bulb fixtures, and soldered them to the binding posts. I fastened the other ends in the screw terminals. After that, I put the retaining rings on the fixtures, and added some bulbs.

I made a bottom out of a sheet of mat board from a craft store, which I cut to size using a rotary cutter. I rounded the corners of the mat board on my disk sander, which worked far better than I expected. I then glued this to the box with some rubber cement.

I was out of rubber feet, so I made some with a bit of craft store self-adhesive foam sheet. I made a punch by sharpening some 3/4" brass pipe on my disk sander, and while pressing the punch into the sheet against some scrap wood, turned it until the material was cut. This seems to be a pretty easy way of making non-marring feet, although the foam is a bit soft. I applied four of these improvised foot pads to the bottom.

Step 8: Apply Power

For the purposes of demonstration, I connected the bulbs in series and then to 120VAC.

Comments

author
MarinaM25 (author)2016-04-08

Great project! Thanks for sharing! I would like to try the same but with these lamps hardware.ch/bega I wish it works great!

author
silver55 (author)2012-05-17

Dexterity 10
Safety 1
There is no protection on the wires to the terminals.
The voltage of 125 V AC is dangerous.

silver55

author
mguima (author)silver552012-11-04

I got 127 V AC shock many times and I´m still here to tell.

author
silver55 (author)mguima2014-02-10

You're lucky, many have not had the same luck.
The rules indicate 50 Vac and 30 mA limit as bearable by the human body.

author
Orngrimm (author)mguima2014-02-07

Thank god you dont live in Europa with 230V. Do that here and you wont walk away this easy... ;)

author
fretted (author)silver552012-10-16

Love this light the wood box and the porc holders are awesome

author
alames (author)2012-01-10

If the plastic is objectionable, you might consider old fashioned binding posts. Consider brass posts with horizontal holes, and a nut to bind the wire in the post. I seem to remember seeing some brass binding posts with axial holes that your banana connectors would fit into.

author
anvil_man (author)2011-04-11

Nice job. Got me thinking ... years ago I was in this old time blacksmith shop and he had this large array of different size bulbs on the wall with switches.

Being young, I had to said what in the world is that for... It was his speed control for his forge blower by turning on different bulbs in series he could change the voltage going the blower motor and the speed..

As I recall this shop was old most likely build before electrical power was common. so when he got power that was a to control his blower..

author
Mtalus (author)2011-03-21

I use a similar setup for constant(ish) current battery charging. Say 120 watts of lamp to pass 1 amp and then through a bridge rectifier with the output to the battery. Meets all the charging needs that I have. I screw in a plug adapter so that I can plug in a five bulb lamp when I need more current. When I don't need the light I plug in an oil filled motor run capacitor (24uF passes about 1 amp) to lower the waste. Right now I have a 9v alkaline charging with a neon test light as the limit. (I know, I know. Alkalines aren't ment to be recharged. The chemistry is rechargable but the package isn't designed for it. The leakage risk is acceptabel for my Harbour Freight VOM.)
Of course you have to observe voltage precautions and monitor the state of charge. (You make it a "smart(?)" charger.)
By the way, it takes about 3 days for the 9v to charge with the neon limit.

author
froggyman (author)2009-04-01

puting the lights in parrallel should make the lights brighter than is series. just my 2 cents

author
CaladanJen (author)froggyman2009-04-01

Of course it would. And the result would be much harder to photograph. I connected them in series to deliberately current-starve the bulbs, which gives them a warm orange glow that takes a very nice picture, as well as reducing the intensity and making better use of my camera's dynamic range.

author
bug on fire (author)CaladanJen2009-04-01

and it also makes it look more like something Thomas Edison would make I like it

author
CaladanJen (author)bug on fire2009-04-02

Thanks :) You have a good eye. Edison's original carbon filament bulbs were a lot more orange than the tungsten we use today, and that was exactly the effect I was trying to achieve for the photo.

author
Hycro (author)CaladanJen2010-10-06

I think clear bulbs might have also been a good choice as well, would give it an "older" look...well, to me anyways...lol.

author
Hycro (author)2010-10-06

Personally, since I don't have many power tools at my disposal (aside from drills, electric impact gun, angle grinder, and soldering gun) I would have cut with a hacksaw or snips, and rounded the edges either with a file, or the snips again...(whether I use the snips or not really depends on the thickness)

author
sickdog74 (author)2010-05-02

Dang. That's beautiful!

author
Capt. Howdy (author)2009-04-08

INSPIRING. Nice joints i havta dust off my delta "thumb remover" and make one of these. i might put a bottom on it rout a couple key holes in it and mount it over my workbench. when not in use for electronics projects it would add some light to my work area.

author
CaladanJen (author)Capt. Howdy2009-04-08

Thanks :) Which type of saw do you count as the "thumb remover"? I used a scroll saw to make mine. I use mine strictly for electronics projects, but it's gotten a fair bit of use since I built it. I did actually make a bottom for it, as I mentioned in step 7, but it wouldn't work for holding it upside-down.

author
Capt. Howdy (author)CaladanJen2009-04-09

some time ago i built a jig for my table saw for cutting that type of joint. i've never lost a thumb to it but i always figured that would be the best tool for the job.

author
CaladanJen (author)Capt. Howdy2009-04-09

As a general rule, I avoid table saws. Although I do own a router table, go figure.

author
Rob K (author)2009-04-02

What kind of voltages do you run theses on?

author
CaladanJen (author)Rob K2009-04-02

That depends on the particular test that I'm conducting. I've used it on 5V, 12V, 60V, and 120V, some DC, some AC so far. For some tests, the voltage changes during operation.

author
blugyblug (author)2009-03-29

Nice and Clean. This could really come in useful for some people though (not me, im not an electronics guy)
I hope no one starts ranting about how incandescents are bad for the environment...
Not many people on instructables who yell "1st comment!" =D

author
wolf555hound (author)blugyblug2009-03-29

I would think we'd all want incandescent bulbs, seeing as those long tubey ones*im drawing a blank here* have mercury in them. I just cant get my mind off it. The miracle tubey thingy filled with mercury that we're throwing away... I think i ate too much mashed potatoes...(IDK if you'll get this)

author
CaladanJen (author)wolf555hound2009-03-29

Yes, they are full of mercury vapor (which is a rather tiny drop of liquid), and yes, it's a problem. That's why so many fluorescent recycling bins have started popping up in some stores. With that said, the estimates of the environmentalists say that, in an area where most electricity is generated by coal, the amount of mercury released by the coal burned for the extra power used by incandescent lamps exceeds the mercury used in fluorescents. I'm not sure if I buy that, but their numbers are convincing.

author
cd41 (author)CaladanJen2009-03-31

:D I just throw the fluorescents away in my garbage, :D But luckily i have only burned out 4 since i started using them, which is weird because it says they should last for 5 years(probably some small print somewhere to mess with that number) and they burned out in 2 months, rip off

author
CaladanJen (author)cd412009-03-31

If they burn out that quickly, you might want to check your electrical wiring. Compact fluorescent bulbs don't wear out as quickly as incandescents but they are far more susceptible to line noise, which can damage or destroy the sensitive ballast electronics.

author
blugyblug (author)wolf555hound2009-03-29

Lol????

author
CaladanJen (author)blugyblug2009-03-29

My home lighting is all fluorescent. CF bulbs are full of electronics, though, and make rather bad loads (very nonlinear), especially since they are so efficient (which is bad, when burning power is what you want to do).

author
Uncle Kudzu (author)2009-03-29

don't know much about electronics, but i think i get the concept and can appreciate that the completed device is a beautiful marriage function and finish. very nice work!

author
CaladanJen (author)Uncle Kudzu2009-03-30

Thank you.

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w8znx (author)2009-03-29

works and cheaper than a variac

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CaladanJen (author)w8znx2009-03-29

Referring to the old TV repair trick of putting one in series with the device under test? I actually have a couple variacs already, but while they do a good job of changing the voltage, they aren't so good for changing line impedance or for burning power.

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Bio: Geek of all trades. I love building stuff. Electronics is my passion. Software is my trade. I dabble in several forms of art.
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