"Because this is for a MUSEUM, not a tourist railroad. There is a difference."

Yes Dennis, I got that part. And I might be a bit snippy but at some point you have to choose between something that "works" or something that is "on display". And you need to make decisions about how much effort to put into relatively mundane uninteresting components and how much effort to put into a car that operates much of the time and generates some excitement (and donations).

A museum with a trolley car with "worn out" resistors is a wonderful exhibit of how manufacturing techniques from 50 years ago did not produce a car that can still operate decades after the service life it was designed for. Great learning experience; stuff designed 50 years ago was not expected to be operating in the next century. And indeed here it is on display not operating since it exceeded it's design lifetime.

Don't get me wrong, I restored a 1920's gasoline engine powered Plymouth Locomotive (at a museum) to operational condition. I made some "modern day" upgrades; the original gasoline fuel tank was positioned about a foot in front of the operators seat at eye level with nothing between the operators face and the tank but air.... This was just inside a wooden cab wall that could have easily been penetrated by something in a collision..

And it had gravity feed, no fuel pump that could be automatically disabled if the engine quit running. One small collision could have broken a fuel line and sprayed gasoline on the operator and potentially the passengers just a few feet behind the cab.

I restored the original fuel tank as a "non-operational" replica of the "old days" and then I discreetly hid a modern safe fuel tank and pump as far away from the operator (and passengers) as possible...

Just saying, winding your own resistors to match 50 year old techniques that have not stood the test of time just because they "look like" the old ones seems like a waste of time. I would create a static display of the "good old days" in a "stuffed and mounted" trolley car and use modern parts to make your operational cars less effort to maintain.

Also, just so you are aware, Mica is now considered a Hazardous Substance in many States and requires proper protective equipment for handling it.

No disrespect intended, good luck if you decide to replicate old resistors. If I can help specify new components feel free to ask. I am a degreed Electrical Engineer with several decades of experience.

Cheers, Kevin.

"You can buy nichrome flat heater wire in lots of different values. To attach it you need to rivet or screw it down."

And that is one of the failure modes for "old school" resistors. No matter how tight you rivet or screw down a piece of metal that is going to expand and contract with temperature changes you cannot get it tight enough to last forever.

As the temperature rises the wire expands and forces the rivet (or screw joint) apart just a tiny little bit. After many years the joint starts to open and electrical contact is lost, then arcing occurs and the resistance wire and/or contact metal fails.

Modern high power resistors intentionally weld the resistance element to the contact element. This is a much longer lasting bond. Easy to do with the proper spot welding equipment.

Learn from the failures of the past, don't repeat them.

Cheers, Kevin.

The control resistors that are failing are probably somewhere between 60 and 100 years old. I do not think anybody is saying that they are a poor design. They are just a complicated design that probably required a lot of specialized tooling to make. If Al can post pictures of the dissembled unit in the next couple of days everyone will have a better idea of the problem.

Has anyone contacted Homewood Products Company in PA? Homewood was Westinghouse's renewal parts supplier/manufacturer. They are still in the business of supporting Westinghouse electrical apparatus. Today its mainly for power grid. They have many original Westinghouse drawings on file. If they have they drawings, they may be able to make it. Sometimes you might get lucky, and there might be old stock of parts gathering dust in the warehouse. I was able to order some contactor tips. I cleaned out the last dozen or so of stock before I got the we can make them quote, but it wil cost you xx dollars.

Its worth a shot. or maybe you can also work with them to see if they can make something modern, yet can drop in the old control resistor frame, so it as least looks original. All they need is the stock number of the unit, or the individul piece number.

Call Jim Pastir 1-412-665-2721

j.pastir@homewoodsales.com

Randy,

We came across this problem a number of years ago with our Cornwall (ex UIC) BW loco with HL control.

I also had extensive correspondence with Dave Johnston (a walking encyclopedia of electric railway knowledge!) at the time.

I concluded that it would be *possible* to make an exact replacement but prohibitively costly. Perhaps if many railway museums got together for a group order. These flat units are of a very unorthodox design. The resistance material is silver colored. It could be german silver, nichrome, or something similar. The original pattern was most likely produced as a stamping from a solid sheet. Today it might be possible to make this via laser cutting. Another problem would be obtaining a sheet of the correct material having the correct resistivity and thickness.

So, we wound up doing exactly as others: replace with generic 225W off-the-shelf resistance tubes mounted to a GPO3 backboard and placed in some out-of-the-way place. We left the original resistance units in place and just disconnected them and ran the wires to the new resistor assembly.

Here are photos of this type of resistor bank. The detailed photos of the resistance ribbon are from a failed element, hence their dirty brown color. The original material is silvery metal.



A "blade" resistor module, the element inside, and the resistance ribbon wrapped in mica:

I have dealt with Homewood Products in the past, however not on this specific item. I never purchased anything from Homewood as the costs were very high. It is my understanding that this part, or some portion of it, was made by Chromalox. Westinghouse Electric discontinued supporting parts for this unit when Chromalox would no longer supply the parts. I have talked with Chromalox, but have never found anyone there who knew anything about these units.

From Al's photos above you can see how fine the element is. It is not clear how to handle the resistance element without damaging it. The material is only a few thousandths thick. The outer sleeve is probably tin plated steel. As I recall it is soldered together. The inner case is formed sheet metal. The lower part has the edges folded up and crimped over the flat cover plate. This retains the mica sheets that are folded up around the resistance element.

Thanks for posting the photos. I looked at one yesterday and was curious as to the inside arrangement. The silvery lead material was warped in thick copper foil to avoid heat building at the terminal screws.
I’m surprised at how long and thin the actual internal resistive element is. Was the photo of a 40 Ohm unit? If so the material must have much less resistance than nichrome, may be Iron??
I too found it hard to imagine how to fix or sub the individual flat steel resistors. However after seeing the box they are in, if it were me, I’d replace all with new ceramic tube type resistors within the same box.

I'm not sure of the failed units' resistances, they failed years ago.

As to the color of the resistance strip, several years ago a new element was damaged in such a way that the end was pulled out of the sheet metal jacket. It was bright silver, just like a new nichrome or other high-temperature element material.

I think I'll send a piece of the material to a metallurgist for analysis (cut from a larger area at the end of the strip).

Does a strong magnet attract the element? Iron would be attracted to the magnet and nichrome would not. Any local college or university that has a scanning electron microscope with x-ray spectroscopy can tell you the elemental composition for sure.

Thanks to those who have contributed so far. At least we seem to be learning as we go along. I would certainly agree that this appears to be a poor design -- difficult to manufacture and prone to eventual failure. But it's what the cars were equipped with.

Have you considered useing DC DC converters to bring down the voltage?

See here (for example), 225 W, 40 Ohm, approx 10" long, $87 each, 10 pcs in stock.

https://www.mouser.com/ProductDetail/Vi ... biCQ%3d%3d

Other wattages and resistance values readily available, try Mouser, Newark, DigiKey, Allied. All of those have online catalogs, for really odd values you may have to place a minimum order and wait a few months.

Yes someone could reproduce the old resistors, looks like a die cut resistance element wrapped in mica and encased in steel. You could make a workable replacement by mounting modern resistors inside the old exterior frame. Nobody would notice, except for real rivet counters.

They make special spring clips to support these by the ends, or long bolts to attach them to a flat chassis surface. Just don't tighten them down too hard, they need to expand and contract without being stressed. And there are flameproof versions available.

Note; they make special "non-inductive" versions, these are wound in such a way that the magnetic fields cancel out and there is little inductance. Probably not a concern for a Trolley. The old ones being sealed inside a steel can keeps the magnetic field inside the resistor.

Edit: here is a "modern" version of the "cased" resistors shown in the photo. I would bet these are $$$ and take a while to get;

https://www.powerohm.com/pdfs/CRCAT00.pdf

Also, they make "strip heaters";

https://www.omega.com/pptst/MSH.html

These are basically the same construction as the control resistors shown in the photos.

Unfortunately since these are designed to be heaters they are sized for the common AC voltages 120 & 240 Vac. They may not handle much higher voltages and your choices of resistance value may be limited. But custom parts maybe an option.

There is just an off chance that one of those strip heaters would fit inside your existing steel "blade" cases AND have the proper resistance/wattage/voltage ratings. Then you could make a functional unit that from all appearances looks like an original factory unit but has affordable and available replacement parts. If I can help PM me, I'd be glad to see if that is feasible.


Cheers, Kevin

I think the 1910-1930 BLW 50 and 60 tonners all had control resistors in a case as described above. IATR is still running one or two of these types, however, there are two that have had a group of Ohmite type resistors mounted vertically in a fabricated frame.

The 1920's Class C's get line power for a control box in the "Run" position. The wire from there to the controller drum I called "X7" for lack of a better name. If the drum was in any position except "OFF" it connected to wire 77, also known as you trace it to wire 5. Wire 5 was the feed to the control resistance series string, the major points being 140 ohms, 70 ohms, and 70 ohms to ground.

Between the 140 ohm and first 70 ohm resistor was wire 6, common to the R1, RR1, R2, RR2, R3, and RR3 magnet valves that when energized shorted out their respective grids. Wire 7, between the two 70 ohm resistors, went to the controller providing a circuit to the other side of the above mentioned magnet valves. Also, wire 7 provided the circuit to the remaining magnet valves with ground the other side.

When any magnet valve is energized then you have the resistance of the magnet valve (about 35 ohms each measured) in parallel with the appropriate 70 ohm control resistor. This causes a change in resistance calculated by 1/Rt = 1/70 + n/35 where n is the number of magnet valves energized on the circuit. When all magnets valves are energized you can calculate the current flowing. If it is about 4 amps, with Ohmite 225 watt resistors you can determine the number of resistors and ohms necessary to obtain the voltage division and watts developed in the worst case. Don't forget a heavy safety factor.

The control resistor box also had a second set of resistors connected to wires 8 and O (or zero) that was used to supply momentary voltage to the overload relay reset solenoid. This could only be activated if the controller was in the "OFF" position. Wire 82 from the reset position of the control switch went to the drum and came out wire 8 which went into the control resistor box. Wire O came out and went to the reset solenoid coil. The other side of this coil to ground. The coil appears to be low resistance thus momentary contact should be used.

Maybe all this more than one wants to know.

You could try asking an expearenced elevator mechanic as electric railways and electric elevators had a lot in common.