Here's a method of dealing with rotary switches that make contact with two poles for each switch position.

 

There should be a pdf attachment that represents the basic circuit. I used K1 to K4 switches to represent my 4-way switch. K-5 is the main power switch.

The R-1 to R3 represent my resistor arrays (there are 3x3 resistors per array) with their cumulative resistance values used as the ohm value in the table at the bottom of the pdf. Watt tolerance for each resistor array is 4.5W. The wire coming off the 1st terminal on the switch represents the coil circuit in operation with no limiting resistors.

R4 is the square coil itself (18" long per side) which should have just shy of 100 ohms resistance and achieve maybe 1 to 2 Watts. Without anything else in line, it should be running the circuit at about 13 V and 0.23A.

R5 is just a light bulb (of unknown wattage from a vintage radio) I will put in parallel in the circuit so I can tell when it's on. The voltmeter is there as more visual evidence of functionality. There will also be a 315mA fuse in the system (there was no symbol for fusible link).

I tested the circuit in the little free software package I downloaded and it worked. Individual tests of each resistor array in a simple circuit setup (no components except fuse installed) provided the following magnetic field values in the center of the coil:

No resistor = 390 mGauss
47Ω = 266 mG
150Ω = 163 mG
4700Ω = 10 mG

These values are pretty darn close to what I was looking for.

Questions:
1) Should I install the voltmeter in series or parallel? (I'm thinking it needs to be parallel).

2) Does it matter if the wall plug for the transformer is polarized?

3) Given the above answers, does it matter where the fuse is located?

 

Rats. Looks like the PDF cut off the R5, but it's what's in the little parallel circuit on the right side of the diagram.

 

PS. Cool switch trick. Thanks, but it turned out to be one pole per click. WHEW.

 

Snip:

I unsoldered my gear and tested it yesterday to confirm that the switch only selects one position at a time. I was doing my continuity tests in the wrong location, it turns out. After I re-brained myself, I could see what I did wrong.

This is weird. I would swear that this post didn't exist when I posted the rotary switch schematic. I wouldn't have bothered.

 

Questions:
1) Should I install the voltmeter in series or parallel? (I'm thinking it needs to be parallel).

2) Does it matter if the wall plug for the transformer is polarized?

3) Given the above answers, does it matter where the fuse is located?

Voltmeters are always connected across the source or the load. Ammeters are always connected in series with the source or load.

You don't necessarily need a polarized plug with a transformer but using a 3 wire cord and plug does help protect you from any leakage or short from the primary side to the core of the transformer.

Put the fuse in the primary side of the transformer.

 

No worries. I notice things pop up sometimes later than they should. Probably a screen refresh issue. Still handy information.

Thanks for your comment. However, since I'm a total noob, you'll have to help me figure out where the fuse and the voltmeter should be in that schematic. How do I know which is the primary side of the transformer? Not sure what "across the source or load" might mean in the context of my circuit.

Regarding the transformer, it only has two terminals on the plug attachment side. I chose a 2-prong plug. Is there a safe way to attach a 3-way plug?

WHEE!

 

If you use a two wire cord it won't matter which wire gets connected to either terminal of the transformer primary. If you use a three wire cord it will have a Black, White and Green wire. The green gets connected to the chassis or metal enclosure of your project. The black and the white can go to either terminal of the transformer primary.

BTW, I didn't understand your question regarding Primary and Secondary. Since you've been powering your coil with it you must already know which connections are the primary and secondary windings.

 

Ah, the gizmo has a wood chassis. So 3-wire cord is a no-go.

The coil is just 600 feet of magnet wire wound around a wooden frame. So there are only two terminals on that component. There's the cluster of resistors on the switch, which could be grouped together as another component (one wire goes into the switch, and all of the resistors are soldered together and connected into one output wire) The voltmeter is another component. The fuse is another. I don't know if things have to go in a particular order.

So, I'm guessing the load is the coil? Or is it the resistors and the coil? Or just the resistors? If I'm supposed to connect the voltmeter "across the load", what load do I choose?

You indicated to "Put the fuse in the primary side of the transformer", and I'm not sure what you mean by primary side.

Sorry to be confusing, I'm not up to speed on common terminology.

 

Are you saying that the Helmholtz coil you wound is being connected directly to 120V mains? Has all the tests you've been doing not used an isolation transformer?

Edit: Never mind. I re-read your first post, which makes your questions even more confusing because you seem to know how you're hooking everything up in that post.

 

I have hooked the coil up directly to the transformer with a fuse in line and plugged it into 120 mains after calculating the number of winds I'd need in the coil to create enough load to get appropriate voltage and amperage. I have done additional tests by installing each resistor array in the same circuit.

I did all of this in baby steps--including using safety switches, safety glasses, fire extinguishers, IR thermometers, and a fabulous assistant. I started by turning the unit on in progressive 5 second increments and worked my way up from there. I am comfortable with the product thus far. All items operate within a few degrees of room temperature for minutes at a time, so I call that a success.

It's possible that it sounds like I know what I'm doing. Admittedly, I get the larger concepts, but I'm flailing around in the dark regarding certain things, like whether the placement of certain components matters. This stuff isn't always made clear in electronics books.

Now I just need to get the fuse and the volt meter in their proper order in the circuit so I can test it again before I solder it together and mount everything in its final location in its wooden project box.

Going back to my 3 questions, one of them has been answered, and that's whether the plug needs to be polarized (which is no, and that's excellent).

That leaves two of my original questions:
-Should I install the voltmeter in series or parallel? (I'm thinking it needs to be parallel)?

-Does it matter where the fuse is located?

Also, now there's a new, third question:
3) What part of this circuit is considered "the load"--which could be rephrased as "where do I connect the terminals of the volt meter? If it's right in my circuit diagram, then, WOO HOO!

I should let you know that whatever happens, when I'm done with this thing, I'll be taking it over to the university and plopping it in the lap of an electrical engineer for confirmation that I did it right. If he wasn't so busy, I would have pestered him with all of this little stuff. Unfortunately, he's not very available, so I have turned to books, google, and you amazing folks. My goal here is to make this thing as complete as possible and understand the basic concepts before I go have him look it over for its final safety check.

 

I'll post a complete schematic before I hit the sack tonight.

 

I appreciate your time!
M

 

I didn't feel like drawing a 4 pole switch but it's irrelevant here. This circuit was re-drawn from your last circuit. I wired the switch so that max current to the coil is at (clockwise) position 4. This means that position 2 (R1) is your largest resistor and R3 is your lowest in the switched network. Position 4 goes directly to R4 that's always in the ciruit, as you drew it.

 

Oooh! Thanks! Of course, I now have more questions for you.

Now, the plug that I have has no large pin on it. They are both the same size. From your description RE: the insulated case, this shouldn't be an issue?

The fuse is .315 A. I've been using it on the 12 V side of the transformer. I presume this will still be okay if it's located on the mains side of the transformer? If not, please explain why and suggest a proper fuse (would it be 3A if my transformer is rated for 3A?).

I'm also running on 12 Volt, which I presume doesn't matter.

AND I have a little 2-pole rocker switch/power switch that I forgot to mention that I will put in the circuit as well (ugh--too many parts). Does it matter where that goes?

I have no ammeter, just a volt meter. I understand they serve similar functions. Is your diagram intended to show the difference between how a voltmeter and an ammeter would fit into the circuit? If not, do I need an ammeter and why?

R4 as I had it in my diagram is a lamp. If I install it in series, it will disable the circuit if it burns out. Is there any reason not to keep it in parallel like I had it?

Sorry to be such a pain.

 

Oooh! Thanks! Of course, I now have more
questions for you.

Now, the plug that I have has no large pin on it. They are both the same size.
From your description RE: the insulated case, this shouldn't be an issue?

As I indicated on the schematic (Notes) ... No.

The fuse is .315 A. I've been using it on the 12 V side of the transformer.
I presume this will still be okay if it's located on the mains side of the
transformer? If not, please explain why and suggest a proper fuse
(would it be 3A if my transformer is rated for 3A?).

I doubt very, very much that your fuse is rated at .315 Amps. That would
translate to 315 milliamps and would surprise me that you had one.
They're not exactly something your local Radio Shack or hardware store
would carry. Unless you got your fuse from NASA.
You can try your .315 A fuse on the primary side as shown but I can't
guarantee that surge current won't pop it occasionally, if not often.
Slo-Blow fuses are sometimes required on the primary of transformers.

I'm also running on 12 Volt, which I presume doesn't matter.

No, your fuse value is based on max current.

AND I have a little 2-pole rocker switch/power switch that I forgot to
mention that I will put in the circuit as well (ugh--too many parts). Does
it matter where that goes?

If it's rated for 120VAC then you can use it as the Power switch indicated
on my schematic.

I have no ammeter, just a volt meter. I understand they serve similar functions.
Is your diagram intended to show the difference between how a voltmeter and an ammeter would fit into the circuit? If not, do I need an ammeter and why?

Yes, they were put there and labeled to show proper hookup.

No, they are totally opposite sexes of each other. A Voltmeter measures
Electrical Pressure (In Volts) like a water pressure meter does in PSI.
An Ammeter measures Electron Current (In Amps) like a water Flow Gauge
measures the flow rate in GPM. The design of Voltmeters and Ammeters
are also opposite of each other. A Voltmeter is designed to be used across
(in parallel with) the circuit being measured. An Ammeter, on the other hand,
is designed to be inserted in series with the circuit under test.
Besides accuracy, the prime requirement of electrical instruments is to look
as invisible as possible to the circuit under test. This is because an instrument
is also a circuit, so when connected to the circuit under test it's now part of that
circuit. This means that a Voltmeter should present the highest possible internal
Resistance to DC and the highest possible Impedance to AC. An Ammeter, on the
other hand, should present the lowest possible Resistance to DC and the Lowest
possible Impedance to AC.
Whether or not you need an Ammeter or a Voltmeter is up to you. I thought you
were building a standard of sorts to check your Gauss meter against. I think you
should at least provide a Voltmeter or jacks to plug one into. The Voltmeter in my
schematic measures the voltage across the (Load) Helmholtz Coil as that's what
we want to measure.

R4 as I had it in my diagram is a lamp. If I install it in series, it will disable the
circuit if it burns out. Is there any reason not to keep it in parallel like I had it?

Your pdf schematic shows R4 in series and that's why I drew it that way.
If you have it wired in parallel with the 12V secondary it will simply serve as a pilot
light. If you have it wired across (in parallel with) the Load it will function as a
relative voltage indicator and change brilliance with your rotary switch positions.
Edit: Probably not a good idea to put the bulb across your coil at this point as
it will effect the required resistor values in your circuit.

 

WHEW! Excellent descriptions and very helpful.

I stole that low amp fuse out of a Radio Shack pocket multimeter when I was looking for something to protect my coil from getting overloaded during my tests. I'm a pro at finding the things that I need lying around the house. I now understand its limitations. I'll check into some slow blow fuses for future use.

I'm sorry, I miscommunicated on my R4. R4 in my diagram is the coil. R5 is the parallel installation on the right side of my diagram, which got lopped off in the post, and that was the lightbulb. So, yes, I'll run it as a pilot light in parallel.

Oops! I didn't see your switch on the diagram, but I see it now. The switch I have is rated 10A, 125/250 VAC. So I'm okay.

Again, thanks so much. I'll post a photo of the thing when I'm done sticking it all together.

You folks are my heroes!

 

Progress made. Light soldered in. Final assembly pending. YAY!

 

Can you measure the primary resistance (120V side) of the transformer for me? Knowing this may give me insight of max possible surge current.

 

Sure. I will try do that later today. Am I measuring ohms from one 120V terminal to the other?

I still have a ton of testing to do, and need to build a bracket to center the meter in the coil on its three axes. Also need to enclose and protect a few things that could electrocute an unwary user. Then final sanding and varnish, safety notes, instructions for use, and a pocket for the log-book.

I just got the control box mounted on the lid. Broke the teeny coil wires off yesterday without thinking and improved their connections significantly this morning and re-confirmed that they work.

I will post some photos and videos as well in the next few days. I feel like I just scaled Mt. Everest.

Now I can go work on my VW and the yard and do some other stuff that I've been wanting to do for weeks. WHEE!