Electrical Assistance Please - Wiring up UV Exposure Unit

holmburgers · Dec 13, 2011

Hi all,

This should be an easy set of questions for anyone versed in electricity, which I am not!

Ok, in short (get it??), I'm going to be mounting 7 lamp sockets into a board which will have 2.5' legs on it (resembling a TV tray) and the contact frame will be placed below this. I'm using CFL black-light bulbs, so no ballasting or anything fancy will be required. So if I I'm not mistaken I can just connect these lamps sockets straight into "the mains" via a normal AC plug. I do intend to include a switch, and not yet, but maybe a cooling fan down the road depending on how hot it gets.

So my questions are:

1- Do I need to wire this in series or in parallel? The extent of my wiring experience is with speaker cabinets, which, depending on your ohm requirements, can be wired in series or parallel. But since I don't think they'll be any resistance to speak of, does it matter with this circuit? Or lets say I want it to work with a bulb unplugged, I assume a series circuit will require all bulbs to be present to complete the circuit. Depending on the answer to this, further inquiry may arise!

2 - What type of wire (gauge, braided/solid) is considered safe for 120V applications? Would it be wise to include a fuse in this circuit, and if so, what amperage?

3 - Is a 2-prong plug sufficient? If in theory I were to use a 3-prong, where would the ground even go??

Thanks in advance for preventing me from burning down my house, electrocuting myself or a combination of the two!

and p.s., I'll post pictures once it's done.

BrianShaw · Dec 13, 2011

I can't (won't) offer much advise because IANE (I am not an electrician) but soon I'll be doing same/similar. I'm planning parallel with a separate cooling fan circuit. I belive that any hardware store can supply the proper solid wire. color counts. Two-prong or three-prong is OK (I think) as long as either is properly grounded. I'm not planning a separate fuse/circuit breaker but do plan on uising it in an outlet that is not on an already heavily loaded breaker.

Here's a web site I think might help... or maybe it just confuses, but I find I need this kind of aid whenever trying to burn my house down using DIY electrical work:

http://www.thecircuitdetective.com/electrical_wiring_connections.htm

Mike Wilde · Dec 13, 2011

120V north american-centric advice placed here.

I built one using 9 BLB compact flourescents, with bases up in a box that the printing frame gets slid under the lights.

I used 'screw shell' lamp sockets, and wired them all together in parallel with 'lamp cord'.

Lamp cord is 2 conductor stranded copper wire. One side of the pair has a ridge or ridges. Wire that side up to the silver screw of all of the sockets, and the wide blade of the plug you plug in.

If you add a switch, place it in the other than ribbed line, that is connected to the narrow plug blade.

I added about 6 3/4" holes in the back of my unit at the top and the door at the front leaves a gap when closed.

That seems to be sufficient ventilation to dissapate the modest heat these lamps generate when left to run for an hour, which is the longest cyanotype exposure I use, when dealing with overly dense enlarged negatives.

BrianShaw · Dec 13, 2011

Although this isn't my thread... thanks, Mike. That is a lot mroe elegeant (inexpensive too) than I had in mind. Good to hear that you actually have done it!

Do the 9 bulbs cover 8x10 evenly? I was thinking 12 bulbs... but, again, I have no experience so that's all just thoughts.

Peter Simpson · Dec 13, 2011

holmburgers said:
Hi all,

1- Do I need to wire this in series or in parallel?

2 - What type of wire (gauge, braided/solid) is considered safe for 120V applications? Would it be wise to include a fuse in this circuit, and if so, what amperage?

3 - Is a 2-prong plug sufficient? If in theory I were to use a 3-prong, where would the ground even go??

1 - Parallel, almost everything should be wired in parallel.
2 - Assuming 60 watt bulbs, you'll be drawing approx 500W or around 5 amps - use 18AWG stranded (lamp cord) for your wall cord, inside can be solid or stranded, whichever is easiest to connect to your fixtures, no fuse needed.
3 - 2 prong would be sufficient. If the housing is metal, attach the ground to the metal housing.

A 110V muffin fan would be a good idea, an enclosed volume will get quite warm quickly. Digikey.com has them . Don't forget an air inlet as well as an exhaust.

It might be easier to wire if you bought a crimper and some ring terminals. You can get the wire, crimper and terminals at Home Depot or Lowes.

holmburgers · Dec 13, 2011

Hey everybody, thanks very much! This is coming together.

One note; the CFLs are only 13 watts, so I'll be dealing with 91 watts, and potentially 182 if I were to get Y-adapters and doubled the # of bulbs (no plans at present, though I'd like to "overbuild"). How many amps though? Where does this put me with AWG?

The design will be fairly open, not really enclosed. I'm going to put a reflective foil behind the bulbs to increase reflectance, and I'll plan to connect the ground to this.

Can a 110V fan plug in just like the lights, w/o other needed components?

Thanks again!

holmburgers · Dec 13, 2011

oh, I forgot to mention that before I've been using just 2 CFL black-lights suspended about 1.5" above my frame. No exposure has been overexposed, and this is with an hour long exposure. So I'm hoping that with 7, arranged in an equidistant pattern with roughly 10 inches between the furthest placed bulbs and suspended about 2 feet above the frame, I'll get reasonable exposures and excellent coverage up to 11x14", though that might be a stretch. 8x10" will be sufficient, though I suspect that our friend the inverse square law will mean that slightly larger formats are easily covered.

holmburgers · Dec 13, 2011

One more thought... does anyone know where to find, or exactly what the following are called...

I'm looking for dowel rod legs and corresponding bases to screw into my board. The bases are little metal sockets with threads to accept threaded dowel rods that act as legs. I believe I've seen these on cheap decorative tables (designed to have a table cloth put over them, 'cause they're particle board and flimsy) and they're usually threaded at a slight angle so the leg splays out slightly.

Ring any bells? It's amazing how hard it is to find simple things when you don't know exactly what they're called...

Mike Wilde · Dec 13, 2011

I have had good coverage and uniformity for 10x10 placing 9 13W spiral BLB bulbs within a box not larger than 28x28" with a height of 6" from the bulb bottom to print top.

The inside of the box is all white.

Sides and top are melmamime particle board, as I recall, because I built it from the remians of an old cheap Ikea style desk I had disassembled and was redy to take to the dump after getting wiggly loose one tiime to many.

holmburgers · Dec 13, 2011

Mike, I assume you have the bulbs pointed straight down, right? As long as you have a reflective background, do you think that's any less efficient than having the bulbs, say, positioned horizontally? The latter would make more surface area of the bulb facing the print, but it makes for a much more complicated design.

Just curious,

holmburgers · Dec 13, 2011

Here are the leg connectors I was referring to.. still can't find them for sale just yet.

http://www.lollychops.com/.a/6a00e553eafb068833013484aba03f970c-popup

jeffreyg · Dec 13, 2011

I didn't notice a reference that your project will enclosed. If not, be sure to get UV protective glasses. I have a lightbox from Edwards Engineering through Bostick & Sullivan which will handle up to 11x14 that has eight black-light fluorescent bulbs and approx. 2in clearance from the printing frame. The fan is always on when the lights are on. Exposure times vary with individual negatives, paper and emulsion.

http://www.jeffreyglasser.com/

holmburgers · Dec 13, 2011

Found the leg mounting bases (angled top plates).

Good call on the glasses Jeffrey. I could add a velvet curtain that drapes around the sides though.

vpwphoto · Dec 13, 2011

Good adice above, I am not certified, but do a lot of successful electric work.
It is easer to think of electric like plumbing. Black (hot) is the high pressure water.. (just like a fire hose). A switch is simply a valve to turn the water on and off. The current goes in one side of the device and goes out the other side on the white (drain). It can also just go out the ground (messy just like a bad drain).
Paralel man! Series and you get dim bulbs! Take a deep breath do it and you will soon understand not as complicated as it might seem.
Green wire... use it. connect all the green wires together to the ground circuit, ground the metal frame to this if your project is metal. I know some old codgers will tell you you don't need no stinking ground. I like the idea, and think it can save you some pain or death.

holmburgers · Dec 13, 2011

Wow, I think it's as good as built!

About the ground though... I'm not planning on having any metal to speak of, except for maybe a reflective background, but white paint or reflective paint sounds good enough for that. I do want it to be safe though; what do I need in a ground?

Mike Wilde · Dec 13, 2011

I just thought of a typical make up table in a dressing room that I have improvised numberous times.

The ones I have helped to throw together with various community theatre companies out of sundry backsatge storage rooms to create 'proper' make up stations.

We make the back board about 3-feet wide, put a string of 3 screw shells each side of the mirror, and one along the top, and then run a short return of about 6-8" out from the backboard on each side to separate one make up staion from the next. Actually this frame also helps to stabilise the vertical rear backframe. Ppaint the whole thing with white paint, to make the chip board look a little more pleasant, and then also improve the diffusion of the lights. Stick half of a back of bedroom door plastic mirror in the middle of the backboard at a slight down angle so the person can get a good view of face and hair while seated.

Screw in 7 60w old fashioned incandescant lights and everyone is happy. Good diffuse lighting.

So for this project I just threw things together kinda the same way - no mirror, two lights where the mirror would go, and then fiddled with the screw shell spacing while temporarily fitted with 25w incandescant footlight bulbs for visible output.

I stuck my integrating dome refective light meter at a constant height over the edge of the box while it was inverted and played with distance from the side wall, and distance between lamps while the screw shells were held in place temporarily with masking tape to see what gave the most uniform output. Then I screwed them into place.

The lights ended up further from the side wall than I thought they would- I guess a lot of the side output of all of the lamps bounces off the side wall more than I expected. Turning them sideways may have put more light out, but it would have been heaps more of a PIA. I presumed that UV would be refelcted the same way that vsible was, and so far this presumption appears to have held true. I tried with aluminum foil on the top behind the bulbs agiast the socket tops, but it gave me worse uniformity.

Good luck with this project.

L Gebhardt · Dec 13, 2011

Take a look at rockler for the leg adapters. These and these look promising.

Wire things in parallel as others have said. If any part of the frame is metal, such as the reflector then you want to ground that in case one of your wires comes loose and touches it. Without grounding it you won't know until you touch it. I would try to avoid any metal in the frame so I could not worry about grounding it. If your light sockets have ground screws use them.

Steve Smith · Dec 13, 2011

holmburgers said:
One note; the CFLs are only 13 watts, so I'll be dealing with 91 watts, and potentially 182 if I were to get Y-adapters and doubled the # of bulbs (no plans at present, though I'd like to "overbuild"). How many amps though?

That's easy to work out. Divide the watts by the volts. So 91 watts at 110v is less than 1 amp.

Steve.

BrianShaw · Dec 13, 2011

vpwphoto said:
It is easer to think of electric like plumbing.

Ha... I saw a white van on the freeway yesterday -- y'know, the kind with ladders -- belongingto an electrician. His license plate read "NOTPLUMNG".

polyglot · Dec 13, 2011

holmburgers said:
Wow, I think it's as good as built!

About the ground though... I'm not planning on having any metal to speak of, except for maybe a reflective background, but white paint or reflective paint sounds good enough for that. I do want it to be safe though; what do I need in a ground?

No offense, but seriously this is the point where you should be deciding not to do it. If you don't know the difference between parallel and series and why you would choose one over the other, nor what is required to achieve electrical safety, you should not be constructing anything using mains power. If you know that you don't know whether the result will be safe, you're a fool to build it.

As an electrical engineer, I can not in good conscience give directions on how to do this even if it is extremely simple in the grand scheme of things electrical. Do you know, for example, the proper screw tension required to hold a copper wire securely without damaging it and having a live end come out? How the ends should be looped and twisted before inserting in the terminal to make a safe connection? So there's plenty that you don't know that you need to know to achieve safety, on top of the stuff you already know that you don't know.

I will say that you should have an earth-leakage circuit breaker (commonly known as ELCB or ground fault interrupter / GFI) professionally installed in your house. They're mandatory here in AU now and they have a reasonable chance of saving you from a DIY project gone subtly wrong. Won't save you from an electrical fire though.

"Do not meddle in the affairs of [wizards] for they are subtle and quick to anger".

BrianShaw · Dec 13, 2011

polyglot said:
As an electrical engineer, I can not in good conscience give directions on how to do this even if it is extremely simple in the grand scheme of things electrical.

You sound a bit like my father, who was also an electrical engineer. Except his words of wisdom were often closer to, "... and when you get yourself in trouble, don't call me."

The good thing is that smart people can learn new skills. While your warnings are quite valid, perhaps a little faith that sufficient learning will be done prior to building the project. Electrical work does require knowledge, but its not something that requires advanced degrees to learn. Trust me... I'm not the most intelligent guy but I learned to do lots of electrical work. Electronic work is a different story.

I respect your conscience though.

ME Super · Dec 13, 2011

The switch needs to be in series with the lights, which must be in parallel with each other. As for figuring out how much current is drawn, add the wattages of the bulbs together, then divide by the voltage and you'll get current (basic Ohm's Law: Power = Current * Voltage, or Current = Power/Voltage.)

I can draw up a schematic later tonight on how you'd wire this up in case a picture is needed. Tried doing an ASCII-art drawing and it just didn't work.

ME Super

polyglot · Dec 13, 2011

BrianShaw said:
You sound a bit like my father, who was also an electrical engineer. Except his words of wisdom were often closer to, "... and when you get yourself in trouble, don't call me."

The good thing is that smart people can learn new skills. While your warnings are quite valid, perhaps a little faith that sufficient learning will be done prior to building the project. Electrical work does require knowledge, but its not something that requires advanced degrees to learn. Trust me... I'm not the most intelligent guy but I learned to do lots of electrical work. Electronic work is a different story.

I respect your conscience though.

Absolutely smart people can learn and degrees are not required. I'm just asking that people do the learning first and don't go ahead and build things that they already know have a good chance of being quite unsafe. While I know from the OP's history here that he's a reasonably smart guy and could easily learn how to do this safely, the questions in this thread tell me in no uncertain terms that this lighting box has a good chance of ending up a deathtrap if built right now.

Peter Simpson · Dec 13, 2011

Simple electric circuits shouldn't be hard for those of average intelligence. Just remember two things: it can kill you if you touch a live wire, and to always unplug before you work on it.

The fan goes in parallel, just like all the lamp holders -- black to black, white to white.

The switch goes in the "hot" wire -- black (brown in EU) is hot, like burned stuff, white (blue in EU) is cold (neutral, return) like water, ice and snow and green like grass (with yellow stripe, like my lawn) is ground.
Now, with lamp cord, the one with the stripe should be hot, but only if you have a polarized plug on the end. That may be the only reason to use a 3-wire cord: so you always switch the hot. It's OK to leave the ground unconnected if you have no metal to connect to. Bring the cord in, connect the black wire from the cord to one side of the switch and the black wire from all your light fixtures and the fan to the other side of the switch. All the whites connect together and to the line cord.

You'll do fine.

holmburgers · Dec 14, 2011

polygot, I think your warning is a bit over the top.

True, I've never built anything electrical from scratch; just fixing broken things by soldering or reconnecting wires. But to abandon this project right here and now because I asked for advice is a totally ridiculous suggestion.

I'm not going to burn down my house, I'm not going to kill myself, and I guarantee I'll make a perfectly safe device. Maybe you should be warning about the dangers of potassium dichromate, since I've never had lab training either.

Sorry, don't mean to sound harsh, and I do appreciate your concern, but think back to earlier times when people cobbled together all kinds of apparatuses, and a darn good percentage of them lived to tell about it.

Electrical Assistance Please - Wiring up UV Exposure Unit

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