Nobody has to know about the GFCI back in the service panel :)

If properly maintained knob and tube is safer than "modern" wiring. This is because the wires are separated and dissipate heat better. The real danger is where the wires come together at a fixture or an outlet and of course anywhere a person could contact them. BUT MOST IMPORTANT. VOLTAGE DROP! For a given size of wire size and load at 32 volts you can only use one third the length of the run you would use with 110 volts. Demonstrate yes, but I wouldn't go to over board on something that will go over most peoples heads.

Mikechoochoo

It is also pretty easy to current limit wherever this 32 VDC is coming from, so the wire never gets pushed, even with a short.

But still, inspect every inch of those old wires...

--
Will

At the risk of over simplifying things, a bulb is a bulb is a bulb. As Dave has stated, no one can see a volt. (Not withstanding the discussion on DC rated bulbs for trolley cars, which would go over 99.9% of EBT visitor's heads. I did find that interesting and informative, though.)

The real attraction here should be the POWER SOURCE for the electricity, regardless of voltage and/or current. As EBTRR pointed out, restoration of the power plant may not be practical. So, why not offer a scaled down substitution?

Take some generic miniature steam engine and small generator, perhaps Mamod makes something suitable. Put it in a plexiglass case in front of the real generating plant, and with the components in the same orientation. Pipe compressed air to it, through a suitable FLR and solenoid valve. Control the SV with either a coin switch, or a pushbutton with a donation box alongside. Use the power generated to run some small bulbs.

What you have done is made a miniature working "schematic" of the real powerplant, and at what should be minimal cost. Having been to the Franklin Institute and similar museums many a time, I dare say that visitors will be more impressed with something actually in motion, than with a glowing light bulb.

Having brought up the Franklin Institute, I also have to mention the Hagley Museum, just outside of Wilmington, DE. They do have a machine shop that runs on line shafts, powered by waterwheels. They also have water powered gunpowder grinding mills, and an operable stationary steam engine, that used to be used when the river was too low to run the waterwheels.

While I understand the thinking behind using the original wiring and 32VDC bulbs from an historic standpoint, I feel that it would take a lot of effort to do something that so very few people would appreciate and understand. And in terms of practicality (and health) no one is wrapping pipes with asbestos today, or using it for boiler insulation on their locomotive restorations. How about cloth covered wire on diesels? I know I've used lots of Exane.

Why do railroad museums have this rather sloppy attitude about electrical gear? Why do we like to count rivets and get all worked up about making sure the correct [insert favorite steam loco part] is correct and the paint job perfect for a restoration, but then completely let restoration standards slide for the electrical equipment? Why do we not spend the time to find good vintage wire, original relays, and actually dress the cables properly? Why do we instead just get off the shelf parts and zip ties?

It is not a valid reason to say that "too few people care". In a museum environment, the fact that something is not of interest at the present time is not important, as it may become important in the future. There are people interested in the "nuts and bolts" of electrical systems, and if the trend continues (especially if railroads completely electrify when the oil runs dry) the interest will only get stronger. The problem is that too many railroad museums rip to shreds all the historic fabric of the electrical gear just to get a restoration complete - and once it is gone, it is gone.

Back when all this railroad gear was being built, there were quite a few engineers spending a lot of effort getting the electrical systems working - perhaps we should start treating their work as important.

--
Will

That's a good point, Robert. I was assuming that new vintage-style wire didn't exist. If new wire is available that closely-resembles the old stuff, then there's really no reason to keep the old wire in place. BUT in the course of pulling out the old wire, make sure the old wiring's routing and joints are replicated as closely as possible. And re-use as much of the old fixtures and electrical equipment as possible.


Well, true, 32 VDC is less likely to arc-over than 120 VAC. On the other hand, once a DC arc is struck, it won't tend to self-extinguish like an AC arc will. (That's why switches carry a lower DC voltage rating than they do an AC rating-- a DC arc will sizzle steadily inside the switch because the voltage driving it doesn't vary, while an AC arc will tend to die because the voltage driving it falls to zero every half-cycle.)

As for current draw, it's true enough that the wires can't carry the same power at 32 VDC that they could at 120 VAC because they can only carry so much current. In fact, the problem of voltage-drop is aggravated by the use of low-voltage DC. To pull an example out of thin air, #12 wire would handle 20 amperes safely at 120 VAC, and deliver 2400 watts of power with only the customary 3 to 5 percent voltage drop over a run of 80 feet. That same 80-foot run of #12 wire, used in a 32 VDC system and held to the same 3 to 5 percent voltage-drop, would only be able to deliver about 160 watts of power using a current of 5 amperes.

(That reduced current suggests that bad joints may not be an immediate problem, as heating is proportional to the square of the current-- 1/4 of the current means 1/16th of the heating.)

Still, the problem of bad joints needs tackling. The turn-of-the-century books I have on electrical engineering suggest that joints back then were more substantial than modern-day wire-nutting gives. If the old joints are well-made and the tape or sealant is undisturbed, it may well be worth leaving alone. If nothing else, measure the length of the wiring with joints in it, and determine the size of the wire. From those two pieces of information, you can calculate what the resistance of the wire run should be. Then pass a substantial current through it (don't exceed one ampere for every 300 circular mils of cross-sectional area!!) and measure the voltage that appears at the ends of the wire. If that voltage significantly exceeds what Ohm's Law says it should be, you've got a bad joint somewhere.

OK, do I get my two cents now? :-)

More pontifications as they occur to me, or as Sandy Mitchell prods me.....

Here is a small electric plant I made for elementary school presentations. The generator is a drive motor out of an inkjet printer. The driver motors are surprisingly high quality in inkjet printers. Repair shops will give you broken printers. Look for the drive motor, not the stepper motor.

This picture is at speed. Note the bulb is lit.

If I might add some to this - on houses I've been in that have had knob and tube wiring, the wires are attached together by firmly twisting about 1" of stripped wire together very firmly, optionally soldering them together, then wrapping with either cloth or liquid electrical tape. Much, much more secure than wire nuts and it gives you a lot more contact between the wires.

So, absolutely correct on this point.

http://www.riwire.com

They make fabric covered wire for antique automobile restorations. You can get it in any color combination.

Where does one get vintage DC bulbs for trolleys?

The goal is for people to get the idea about how the system worked, right?

Fake it until you hit the lotto. Take your generator to an armature works and have them document and remove the windings. Replace or bush the bearings so it spins right. If you have the documentation on the rotor windings, you can have it rewound when the money comes in for a full system restoration. This makes the rotor lighter so you don't need as much power to run the simulated generator. Hook up a small hidden motor to turn only the portion of the drive line which is belted to the gutted generator. You don't have to run a genuine full load capable belt either.

affordablequalitylighting.com has 25-100 watt, 12V "A" bulbs which screw into 'regular' fixtures. Some new 10 GA wire and a 12 V transformer...you're good to go. You might be able to run everything off one generator.

I have purchased 32 volt bulbs from http://www.aamsco.com (follow the site to railway light bulbs) and http://www.go2marine.com (follow the site to electrical, replacement marine bulbs). If you want clear 32 volt bulbs, you are pretty much out of luck except for large headlight bulbs and thumb-sized water glass bulbs, both from Aamsco. You can also use the RYPN site search function, as the source-of-32V-bulbs topic has been discussed before.

I agree with Will. If the lights were originally 32 VDC, they should stay at that. The history and development of electricity is just as important to preserve as any other aspect of industry, and we should not just throw it aside for the sake of convenience. I believe 32 volts was chosen ecause that is what a turbogenerator put out?

What would really be great is if I could generate some 25 cycle AC power so all the lights in my building would flicker!

One issue that we must remember is that if we don't start hoarding incandescent bulbs soon they will become rather difficult to get in a few years ever since "the enemy within" outlawed their sale.

While it's true that several states, including Rhode Island, Connecticut, North Carolina and California, have seen legislation proposed to ban the sale of incandescent light bulbs in the next few years, it's actually Phillips, the major producer of such bulbs, which proposes to phase out production. That's a business decision, perhaps driven by politics, but a business decision nevertheless. There are still a number of specialty manufacturers who will continue to produce runs of incandescent bulbs for niche markets such as ours.

It is also not too hard to actually make smaller incandescent bulbs. There are a small number of guys making working handmade 1920ish vacuum tubes that work very respectfully - and those must be a magnitude harder to pull off than a simple lightbulb (more complex base, more internal parts, much greater vacuum, etc.). There is a good video kicking around youtube from one of the guys showing how it is all done.

So when the last incandescent bulb is made, and the stocks have all dried up, there is still hope.

--
Will