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.

Comments

[silver55]

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

silver55

[mguima]

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

[fretted]

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

[alames]

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.

[anvil_man]

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..

[Mtalus]

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.

[froggyman]

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

[CaladanJen]

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.

[bug on fire]

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

[CaladanJen]

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.

[Hycro]

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

[Hycro]

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)

[sickdog74]

Dang. That's beautiful!

[Capt. Howdy]

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.

[CaladanJen]

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.

[Capt. Howdy]

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.

[CaladanJen]

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

[Rob K]

What kind of voltages do you run theses on?

[CaladanJen]

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.

[Uncle Kudzu]

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!

[CaladanJen]

Thank you.

[w8znx]

works and cheaper than a variac

[CaladanJen]

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.

[blugyblug]

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

[CaladanJen]

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).

[wolf555hound]

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)

[CaladanJen]

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.

[cd41]

: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

[CaladanJen]

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.

[blugyblug]

Lol????