[Milsurplus] dynamotor brushes ?

[Bruce Gentry]

Carbon brushes are a sophisticated and developed art  almost lost today. 
To answer the immediate question, using a substitue in the low voltage 
part of a dynamotor is not a serious issue. The important things are 
that the material is compatable, dimensions are proper, the counductor 
to the carbon is suitable, and the spring is comparable. Now for some 
explanations. "Carbon" brushes usually aren't pure  carbon. They will 
have various amounts of graphite, lead, silver, and copper dust, as well 
as (GASP!) sometimes asbestos blended in. For occasional use in the low 
voltage portion collectable equipment, almost any brush that is black or 
dark grey is fine. It is perfectly acceptable to sand or file an 
oversize brush. Work slowly, check the fit often so you don't go too 
far. Keep the brush body true and the faces perpendicular and square. 
The brush must slide freely in the holder without excess slack. Work 
them to size outdoors and wash your hands afterwards and definately 
before eating. Some brushes rely on the tension spring to carry the 
current to the carbon. I have never seen a brush in anything military 
that did this, however. Be sure the lead or shunt is adequate for the 
current being carried. The tension spring should be large enough to fill 
the space for it in the brush holder but not bind up. The brushes in the 
high voltage portion of the dynamotor are far more exacting, substitutes 
must be watched carefully to be sure there is no excessive sparking or 
heating, and the dynamotor does not draw excessive current and overheat. 
It is usually ok to use a high voltage brush from one dynamotor in 
another so long as it fits or can be made to fit. In all cases, the 
communtator must be in good condition and clean, and the brushes seated 
properly for good operation. Heavy sparking is not correct, and "ring 
fire" partially or completely encircling the communtator is the sign of 
serious problems such as a shorted communtator or armature winding. One 
good source for substitute brushes is elevator technicians. Brush type 
motors and generators are still in use in elevator installations, and an 
older well experienced technician (or mechanic, as they are referred to) 
can often be a source for brushes and advice. Find out where they tend 
to hang out at coffee time, buying them a drink and a snack will free up 
a lot of parts and help. Find and speak to them directly, NEVER!- to 
their offices or supervisors!

     Bruce Gentry, KA2IVY   IUEC Local 62, retired


On 8/31/18 1:52 PM, Hubert Miller wrote:
>
> With all the various dynamotors out there, are the brushes 
> standardized at all, so you could hope to find say, brushes for some 
> old boat radio dyno ?
> -Hue
>
>
> Sent from my Verizon, Samsung Galaxy smartphone
>
>
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