The Westinghouse MU control system for electric cars relies on a number of control resistors to reduce the voltage applied to the electropneumatic contactors. Unfortunately, it seems impossible to keep them from failing over time, at least under museum conditions of operation. And they are unlike any other resistor in design.

The Illinois Railway Museum Car Department is running out of spares, particularly the 40 ohm type. So we're getting desperate. We would like to know if anyone knows of a supply source, or has come up with a workable substitute. Any information you have will be most helpful. There are lots of trolley museums out there with Westinghouse controls of various types (HL, ABLFM, etc.) and sooner or later we're all going to need a solution to this problem. Thanks!

(I don't have a good picture of these resistors available, but those of you who have worked with this system will know what I'm talking about. And I can get a picture soon if it would help.)

Don't know if you need "exact" replacements (shape and mounting holes), but there are lots of modern high power wire wound resistors to chose from.

Try Digi-Key (tm) a major distributor of all things electronic. There are several possible choices;

Ohmite (tm) "270 Series";

https://www.digikey.com/catalog/en/part ... eries/5843

Ohmite (tm) "250 Series";

https://www.digikey.com/catalog/en/part ... ckohm/5842

Digi-Key has lots of values in stock and they generally do not require minimum orders.

Cheers, Kevin

Are they failing because of your operation, or because the units are new old stock that is just deteriorating with age?

The Western Railway Museum has at least two cars with these "blade" voltage divider resistor assemblies. We are also very low on spare parts.

All the elements in a car's voltage divider are running whenever the car's control power is turned on. Their shelf life as spares is not the issue, they just burn out from years of usage.

The individual resistor elements which are failing are really interesting technology for their time. I'll try to get some photos later this week unless someone else does it first.

I've been told that when Westinghouse discontinued them circa 1960, they just told customers to make some sort of new device using off-the-shelf components.

I think a matrix of some sort of Chromalox strip or tubular resistors could make a robust replacement which would be serviceable with standard parts. The problem is getting someone to design it.

Are these the cast iron resistors? Photo would help. Also would help to know how many watts it needs to be rated at. (Can easily figure this out, if we know the ohms per element and the max voltage these elements will ever see)

I and others have looked at reproducing the Westinghouse Electric Type 197 controller resistor elements for many years. It would be difficult and expensive, and so far that is not where the limited resources have gone. Westinghouse gave up on this device and advised customers to contact their Engineering Department for assistance in finding suitable replacement resistors.

Several museums have made replacement units out of ceramic tube resistors in a configuration similar to the GE control resistor and many headlight resistors. The unit I am most fimilar with has 16 elements. Six are used for the over current reset relay. Since these are rarely used, they are usually not a problem. The other 10 are the voltage divider that provides power to the magnet valve coils. They are energized when ever the car is running and can be a problem.

In your case there are probably ten 40 ohm resistors across 600 volts. That would draw 1.5 amps continuously. That works out of 900 watts. Each of the 10 elements is generating 90 watts. To replace these with ceramic tubes, I like to use a tube rated at twice the continuous power that will be seen. In this case that would be 180 watts. However I think the next standard size would be 250 watt tubes.

A replacement resistor would require 10 250 watt, 40 ohm tubes. These could be mounted in sheet metal frames. Since ceramic resistors no longer come with the ends molded to insert into sheet metal frames, WRM inserts hard fiber or reinforced phenolic tubes into the resistor tube and glues them in place with high temperature Sauereisen cement. Only insert the tubes in about an inch and use the largest practical ID to allow air to flow through the ceramic tubes for cooling. If this puts the resistor terminals too close to the metal end frames, spacers can be added over the mounting tubes. Use four tie rods to hold the end frames in place. It 10 tubes in one frame seems like to much, split the resistors into two assemblies. Plan the wiring to keep interior connections as simple as possible. I normally use bare wire as it will get hot around the resistors. When insulation is needed wire beads can be used, which we have purchased from LSP Industrial Cemerics. They are the appropriate hardware, but can get expensive. For bushings to get the wiring inside the resistor assembly we have used ceramic tubes from old household knob and tube wiring. People who work with ceramic tile can cut these short. They can be cemented into holes in the end frames with Sauereisen cement. Make sure to put a piece of cement board above the resistor assembly to protect the underside of the car from the heat.

I would suggest leaving the Type 197 control resistor in place and use the terminal box as a junction box to run leads to the new control resistor. In most cases all the wires from the control resistor can be connected at any of the Type 426 junction boxes, but one or two wires may have to be run back to the switch group junction box. Do not forget to disconnect the control resistor wires in the control resistor, except for the overload relay reset wires. When this is all installed I would suggest checking the voltage on each of the magnet valve coils to be sure everything came out properly. The voltage should be between 100 and 150 volts.

At the Pennsylvania Trolley Museum as the restoration of West Penn 832 (curve side) was progressing it was discovered we had no headlight resistor or even anything close. So the writer got busy and used the Electric Service type DP units as a model. From the Electric Service catalog it was obvious they were a "cookie cutter" design as to the number of tubes. The tubes were a standard design then and are still readily available from several sources. We happened to use Ohmite. The unit we needed was a DP-14 (number of tubes) but they made a fair number of line items where the number of tubes varied. We also had on hand a DP-5 and a DP-3 from which many of the common parts could be measured.

With CAD if you have one size, you can spend some hours making another size as most of the underlying parts are the same. It took quite a few hours to get the first one correct as the writer is an EE and not the best sheet metal design guy.

The unit also requires ceramic inserts for the resistor mounting and ceramic terminal blocks. Since they are the same for all sizes with only the number required changing, these were drawn up and made by a ceramic company. We purchased enough for five units has we have a number of cars needing exactly the same unit.
The sheet metal fabrication was performed by a local company who does it as a donation. They asked for the DXF files of the details which saved a lot of time for them with their sheet metal CNC equipment.
The resistor fill was tinkered with a little to avoid tapped units with exposed ni-chrome as in the writers 40 years experience in a steel plant knew this reduced reliability. Also I wanted to used standard of the shelf tubes.

We did have a couple of issues:
I was unable to get a finished photo as on a Wednesday it was a pile of parts on a workbench and Saturday it was under the car. Also, it looks too good. The quality of the raw sheet metal was much better than in the 1920s.

I'm attaching the main drawing but not the five sheets of details. They are the property of the Pennsylvania Trolley Museum.
Dennis Bockus

Is there some reason that designing a switching power supply that actually transverts the voltage directly without wasting All That Heat is not an 'engineering' solution?

Thanks to everyone who contributed. However:

We know about the modifications that North Shore did when Westinghouse stopped making them, and we could certainly design something that replicates the function using ordinary commercial resistors. The problem is in maintaining the appearance of the old part. So what we want to know is:

- Has anybody managed to repair bad ones, or
- Has anybody created new ones, either by replicating old ones or by
designing something new that looks the same.

One of our electrical experts says: I have a design in mind to create drop-in replacements using modern parts, but before I go about prototyping it I wanted to know if someone's already done it. Getting into one to consider repairing it isn't terribly difficult; the problem is in what materials to use in making the new winding. I don't know what the original resistance metal was, but nichrome or a nickel- or chromium-alloy steel would seem to be likely. I looked up nichrome, and it was first used in 1906. It'd be a possibility. I'd guess the insulator was sheet mica; there's certainly something modern that could be used if the existing material was no good or new sheet mica couldn't be found.

Entering a quick search... at the big ole green book place, 27 additional leads pop up to explore:

https://www.thomasnet.com/nsearch.html? ... +Suppliers

John

"- Has anybody created new ones, either by replicating old ones or by
designing something new that looks the same."

Well, if you want to reinvent the power resistor I say; go for it....

Sure, you could come up with a design that looks like the old designs (the ones that don't last)....

And you could figure out how to make a few dozen "good ones", not counting the couple hundred "trial ones" you throw out along the way...

But why would you want to recreate a part design and manufacturing method that is routinely failing in your application ???

If Westinghouse had the most perfect resistor ever created why did they stop making them decades ago ???

Read the Ohmite product description. All welded construction; the terminals are spot welded to the heater wire. No vibration leading to arcing leading to failure. Sealed inside a fired enamel coating. No corrosion on the wire when it is hot, no corrosion when moist air condenses on the wire after it cools down. Ceramic tube as the structural support for the wire, very stable over a wide temperature range, able to handle rapid heating and cooling.

Patient; "Doctor It hurts when I have to keep replacing the same failed resistors....." Doctor; "Stop replacing failed resistors with more resistors that are just waiting to fail...."

Cheers, Kevin

The resistance element is a thin metal foil strip (possibly nichrome, but would need metallurgical analysis to confirm).

The metal strip is cut through from alternate edges so that is a continuous very fine long ribbon. I think that making the die to do that cutting is the most difficult part of the job.

The ribbon is wrapped in sheet mica for insulation. Resistance value could be controlled by width of the cut ribbon, thickness of the foil, or possibly alloy, I guess.

We have several dead elements at WRM, I'll try to get some photos on Wednesday.

Sounds like a toaster element. Wonder if that'd work?

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

If it is Nichrome you should be able to confirm with a sample. The link has the resistivity formula, calculate resistance using length and area of the sample. Then confirm with a good resistance meter.

Another method, use 40 Ohm as the answer and guesstimate the length and area of the ribbon in your resistor. Plug in the nichrome resistivity value and see if the equation roughly balances.

http://www.endmemo.com/physics/resistance.php

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