Under The Hood: Lionel 91 (1930-33) and Marx 425 (1950s) Circuit Breakers

[M. Mitchell Marmel]

The eBay listing read, "Lionel no. 91 and Marx circuit breakers converted to red blinkers"...

http://www.ebay.com/itm/Lionel-no-91-and-Marx-circuit-breakers-converted-to-red-blinkers-/251601080426

And lo, that was what was delivered unto me this week!  'Course, me being who I am, I wondered:  Could I get these blinking things back into working order? 

The 1930-33 vintage Lionel 91 circuit breaker as delivered.  Despite the seller's careful packaging, a corner of the 80+ year old casting broke off in transit; however, a touch of Loctite ACC gel put it to rights.

Interior of the 91.  Note that it only has two lugs, making it the earlier version (more on this later).  When I got it, the works were rusted shut and the coil, while live, was also gummed up.  A bit of cleaning, oiling, spring tightening and rewiring later, it worked fine!  This is the mechanism in the "on" position. 

Here's the mechanism in the "off" position.  When a short circuit occurs, the relay snaps, the feed to the track opens (note the gap at right) and power flows to the light bulb instead.   Normally, the bottom wire of the coil grounds to the chassis directly; I found it necessary to solder a jumper from the coil to the chassis (I tapped a hole in the chassis to take a 6-32 screw). 

And here is the 91 cheerfully lit! 

The Marx 425, by contrast, was considerably more spartan inside, as befit its lower price. 

Like its Lionel counterpart, the Marx circuit breaker shunts track power to the lightbulb when there's a short circuit.  Unlike its complicated counterpart from two decades earlier, the Marx breaker uses a simple thermal breaker such as is found in many transformers.

The bulb is rewired directly to the breaker contact...

And the Marx breaker is ready for service!   The orange-painted RW, incidentally, is the subject of my earlier article on mounting a zener diode into a Lionel transformer. 

In service, both the Marx and Lionel breakers did a good job on short circuits, popping before the RW's internal breaker had a chance to do so.  However, the Lionel proved sensitive to the extra voltage provided when the whistle button was pressed;  my guess is that it was actually built that way in the pre-whistle tender age, as later models (1934-42) were equipped with "High"  and "Low" terminals, allowing some flexibility:

http://pictures.olsenstoy.com/cd/b123%5C001025.pdf

The Marx, on the other hand, took the whistle in stride.  :-)

In any event, formerly disabled blinking scenery is now working accessory!  Hoorah! 

Mitch

[dsmith]

Mitch, Thanks for the detailed analysis of both circuit breakers.  It's great to see the old technology working again.

[lionelsoni]

Mitch's post is a good example of the advantage that thermal circuit breakers have over magnetic types for running toy trains.  The purpose of the circuit breaker is of course to limit the current to a safe value.  The problem, which he experienced, with the Lionel breaker illustrates that that circuit breaker does a poorer job of modeling the behavior of the wiring that it is meant to protect, compared to the Marx thermal breaker.  The reason for limiting current is really to limit heat in the wiring.  The thermal breaker does a reasonable job of keeping track of the wiring temperature, while the magnetic breaker trips immediately when the current exceeds its setting, even though the wiring may still be cool and no harm has been done yet.  This behavior is called "nuisance tripping", and it is not usually considered to be a good thing.