Door Chime Solenoids

Solenoids are just a component of the mechanism, but as they are most frequently the cause of trouble with of old chimes, I devote a separate page to them.

The most common problem is a dirty solenoid cylinder and plunger.  On every old chime, thereís a label warning NOT to oil the solenoids Thatís because the oil will in time gum up or attract dirt which will easily overcome  the weak power of the solenoid and render it non functional.  If some of the solenoids are working but others are not, chances are that some are stuck due to gummed up oil, decades of accumulated dust, or a little corrosion.  Easy to fix.   Most solenoids have a rubber or metal cap on the back.  Very gently remove the cap, and slide the plunger out of its cylinder. Keep track of the spring which might try to get away.  Polish the plunger and inside the cylinder with metal polish and reassemble.  A little powdered graphite can serve as a suitable lubricant, though nothing is needed if the parts are well cleaned.

Solenoids can have more serious problems.  Most  plungers are made of two parts:  a steel piston and a strike pin. Very early strike pins are typically made of wood or hard leather, later ones generally made of plastic.  In chimes with plastic pins, itís common to find strike pins broken or gone missing.  The effect of a missing strike pin is that the plunger is too short, which makes it entirely ineffective. With a little finesse, new pins can be made from plastic rod or a hardwood dowel.  New plunger sets from NuTone are theoretically available though can literally take months to receive.  For other brands, NuTone parts might work, but mostly youíre on your own.  If you need to replace or reconstruct plungers, the table below may be helpful.

  

 

number of solenoids

solenoid tube i.d.

solenoid tube length

plunger diameter

plunger length

spring length

piston

pin

total

Nutone PN 69628000

3

-

-

0.308

1.060

0.475

1.535

0.80

Nutone PN 69581000

4

-

-

0.308

1.060

0.39

1.450

0.80

Nutone first generation

4

 

 

 0.308

1.50

0.06

 1.56

 

Nutone second generation

4

0.312

2.10

0.305

1.190

0.350

1.540

1.50

Nutone third generation

4

0.312

2.10

0.308

1.200

?

?

1.42

NuTone 1980ís

4

0.312

1.90

0.308

1.060

0.325

1.385

0.86

Rittenhouse 610 4              
Rittenhouse 620 4              
Ritt '39 diagonal

4

0.375

2.43

0.370

1.50

0.050

1.55

0.875

                 
                 

 

 

 

 

 

 

 

 

 

 

Beyond being gummed up a bit with old oil and dust or debris, I have also seen older units where the solenoids were locked in place with corrosion.  Iím not sure what sort of conditions would cause the problem but I suspect that a long period of storage in a damp location could do it. Stuck plungers can be removed with a few smart taps, though be careful not to damage the strike pins if approaching from the front .  Some brands have removable tube caps at the front end, which allows removal of the plunger through the front, which is less risky to the strike pins.  

Another common problem with solenoids is a hardened glob of gunk just inside the rear cap, effectively sealing the back end of the solenoid tube and contributing to the immobile state of the plunger.  This gunk had once been a shock absorber that cushioned the plunger on its return stroke and made for quiet operation.  Apparently, early models used some foam rubber that petrifies after 50 years or so.  The residue can be removed with a solvent like lacquer thinner. Later models used a wad of cotton thread.  Current plunger replacement kits include a spongy foam rubber shock absorber, presumably made of a stable modern synthetic. 

Hereís a nice solution if you need to replace end caps.  Any hardware store that sells Ace brand products will have something called 3/8Ē Tips, which I believe are made of polypropylene and intended for dressing off the ends of various metal legs. They are a perfect fit for the 3/8Ē solenoid tubes used on NuTone chimes, and perhaps other brands.  You will need to drill a hole in the rear of the cap to allow air to pass through the tube as the plunger travels.

A rare but possible problem with solenoids is that the coil can deteriorate.  The coil is made of up a spool wound with a specific number of "turns" of magnet wire of a specific gauge, which when charged, creates a specific amount of magnetic field to drive the plunger.  Magnet wire is copper with an an insulating coating, usually enamel. The insulation keeps the coil winding from shorting the electrical path through the coil circuit..  If the insulation becomes damaged enough to cause shorts in the coil, the magnetic field will be weakened , reducing the strength of the plunger's action.  The solution is to unwind the old worn magnet wire, noting the number or turns, and  then rewinding using the same gauge and the same number of turns... and of course terminating the ends patterned after the original set up.  After consulting with a solenoid expert, I have learned a few important facts about solenoid coils. The number of turns, not the gauge of the wire determines the magnetic strength.  Heavier gauge wire only serves to make the coil more rugged and more resistant to being burned out by electrical overload.  A coil can be rewound with heavier gauge wire and the same amount of turns to result in  the same magnet strength, though the physical volume will be different and perhaps not fit on the spool or in the allocated space in the device.

A   Typical plungers from a second series NuTone. The red plastic strike pin is original.  The crude wooden replacement is an improvised solution-- not pretty but effective.  It's not unusual to find plungers with missing strike pins.  Plungers are typical dull with light corrosion.

B   Here's a problem that is not so typical.  One of the strike pins melted into pool of deformed plastic.  My guess is that someone tried to clean it with a very aggressive solvent that attacked the plastic pin in a big way.  The rubber shock absorbers were also in a bad state, welded to the back of each solenoid, effectively cementing them all in place.  The good news-- the m.o. for fixing plunger problems is the same regardless of how weird or nasty the symptom is:  clean, polish and replace the strike pin.  .

C   NuTone plungers after polishing and creation of new strike pins made from hardwood dowel.

D   Brand new replacement kit from Nutone includes plungers with plastic strike pins, springs, polypropylene end caps and foam shock absorbers.  Plungers are the NuTone standard 1.5Ē long, but the springs are for the latest vintage models which have shorter solenoid tubes.

E   Parts from a third series Nutone.  The shock absorber is a wad of wound up cotton thread. The end cap is a plastisol sort of material.

F   Another inventive feature from Rittenhouse-- a cotter pin retains a washer that holds the plunger inside the solenoid tube, instead of a rubber cap.  Who knows what the original reasoning was, but 65 years later, the beauty if this feature is that there are no rubber parts to rot away and the cotter pin is a standard hardware store item if it needs to be replaced.  

G   Here's the full plunger assembly for that 1939 Rittenhouse.  Strike pins are made of hard leather. Note the big fluffy felt shock absorbers.

H   Check out the plunger from a later Rittenhouse.  It has felt rings on the plunger to assure a long life of super smooth action. Contemporary Rittenhouse advertising used the tag line "Floating Percussion", which I suspect refers to these very special plungers. Note felt shock absorber and metal end cap.  Very deluxe.  

I   Classic signs of a troubled solenoid coil:  the protective tape wrap is partially broken away and the enamel insulation on the magnet wire is visibly deteriorated. This one could be due for a rewind.

 

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