O22 Switch Contacts Burning Out?

[msacco]

yep, that's what mine look like!

 

 

mike S.

[Birds]

Neil,

Thanks for the picture.

I don't have anything that looks like that on my switches. 

Chris 

[Neil Poersch]

Chris .....Thanks for your help in posting the pictures.

Mike...... I'm glad but also sorry to hear that your switches have the same erosion as mine.

This certainly appears to be a ticking time bomb for Lionel. Theroetically all of their switches built like this will ultimately have this problem. It really depends on the amount of use thatnthey get as to how quickly a problem appears. It will be very interesting to see what they do.........try to ignore the problem or shift blame onto the users or do the right thing and own up to their mistake. I will post my results with them.

Neil

[Birds]

Neil,

I checked my switches again.  After wiping away some of the grease I saw that I do have the same thing just starting on to form on the very edge of one or two of the four contacts.

My older switches are out of warranty.

Here are two upgrades I was going to do to the switches:

• install the TVS discussed earlier in the thread
• solder small plates of hobby brass over the contacts so that they are thicker 

Chris

[lionelsoni]

"While you've still got some foil left, you might try reflow-soldering or even gluing suitably thin brass strips over the foil."

Chris, you may already know that it's easy to separate the foil from a printed-wiring board by overheating it.  So consider my suggestion of reflow-soldering or gluing (with no more of a solder connection than you need for electrical purposes).

[Birds]

Bob,

Is there a glue you would recommend?

The items I am familiar with are non-conducting thermal adhesives, but for all I know KrazyGlue would work.

I am using a 35 watt iron, but overheating the board is a real concern of mine given my limited experience soldering on printed boards.  I have more experience with jewler's soldering torches and metals.

Thanks,

Chris 

[lionelsoni]

Not really.  Krazy Glue sounds promising; but you would have to be fast and accurate with the placement.  Perhaps an epoxy.

Don't worry about the conductivity of the glue.  You can solder a short jumper to make the electrical connection.

[Anonymous]

I was thinking about our problem with these switches, and I think I discovered the source of the problem.  I think the problem maybe caused by the point that rides on the foil contact pad.  My theory is that the point is too sharp. As a result, the contact patch between the point and the foil is very small.  The patch is only the width of the scratch in the foil.  This results in excessive arcing, which destroys the foil pad.  If the contact point was filed down, the contact patch would increase and the arcing would be greatly reduced, if not eliminated.  This should, in theory, stop the deterioration of the foil contact pads.

[Birds]

I looked at the points of my newer O22 switches and the older pre-O22 switches from the early 1990's.  Both of them use the same size points.

The early 1990's switches have metal contact plates instead of foil plates.  While the 1990's switches show evidence of arcing, the metal is thick enough that it isn't getting damaged.

I picked up some hobby brass tonight and have finished adding brass plates to one and a half switches.  I decided to solder the plates over the original contacts, and managed to do this without ruining anything.

One procedure I found to be a key to doing this is to completely tin the side of the brass plate that is going to be the underside.  This lets you plate it in position, hold it in place with a tool, and then apply the soldering iron to remelt the solder.

I tested the completed switch out and it functions as it should.

The plate size that I am cutting is .5 cm x 1 cm.  I originally started with a jewelers saw, but the cuts weren't straight.  I switched over to using a utility knife and scoring the brass a lot of times until it was thin enough to bend the strip over and snap it off.  The edges were then smoothed out with a small flat file.

Only 34 contact plates to go....

Chris

[lionelsoni]

Congratulations!  That's a difficult soldering job.  You have re-invented reflow soldering.  I mentioned it a couple of times, but should have explained what it is.  Others with the same problem would probably like to know what thickness of brass you are using.

[Birds]

This thread came at a good time for me.  I greatly appreciate everyone being so willing to share.

The brass I am using was picked up at the local hobby shop.  A craft store such as Michaels may also carry it.  It is:

K&S Engineering Stock Number 251

It is called: ".010 Sheet Metal, Brass"

This appears to be thicker sheet metal than was used on the 1990 switches (the pre modern O22 switches) I mentioned in my earlier post as not having problems with contact plates erroding.

K&S Engineering also has a 0.015 thickness sheet metal.

Here is a photo (click on photo to enlarge it):

•  New plates are on the top left and right
•  The brass turns a pink color when heated, but this comes off with steel wool
•  I have not done a final cleaning on the plates in the photo
  

•  The contact plate on the bottom left is the OEM silver foil
•  The contact in the bottom right corner has some solder on it.  This is a reflow that didn't work because I had too much solder on the bottom of the new plate.

 

Chris 

[msacco]

Chris,

thanks for posting this. Although I have ripped these switches out of my layout and replaced with trusty 022 postwars, I will use this fix for my damaged switches and save them for future lighter duty use.

 

Mike S.

[Neil Poersch]

Chris,

Great work on the brass strips solution.  Given that the new brass strip is thicker and is also on top of the original strip it would be higher than the level of the original strip. Does the sliding point contact have any difficulty in moving off and onto the new strip?

Neil

ps no word from Lionel yet on my switches

[Birds]

Neil,

Thanks.  You all provided a lot of great suggestions on where to start.

I have completed three switches now and have the plates cut and filed for a fourth.  I try each switch manually before putting it back together, then I try it with a transformer set to 12v and then 14v.

The contacts don't appear to have any difficulty moving over the new plates.

The contact points appear to be rounded so they appear to ride up and over over the plates.  When I tried the switch manually, very slowly, there was no resistance that I noticed once the point hit the new plate.

I also filed the surface edges of the new plates to remove any burrs or lips on them.

There is still arcing that occurs, so I will still add a TVS to each coil but will size them for a maximum RMS voltage of 14 volts.

The switches operate as they should at both 12 and 14 volts with the new plates. 

Chris

[Neil Poersch]

Sounds pretty good Chris.

I had originally suggested a MOV but in retrospect a TVS makes more sense.

What TVS did you settle on? a 30 volt rated unit?

Neil

[Birds]

Neil,

I decided that I would go with a 20 volt rated TVS - the SC20CA.

I don't plan on running my switches past 14 volts.  They have plenty of snap for me at 12 volts.

I will use a star (aka "home run") topology using a terminal strip as the bus bar.   The wires will be 14 gauge with spades on the ends.

Chris 

[lionelsoni]

Chris sent me this by e-mail.  I hope he won't mind my answering it here, so that everyone can benefit:

Bob, I have a couple questions about installing TVS's on switch motors. The switch thread is getting pretty long and old, so I thought it best to e-mail you directly with these. 1) When the TVS's are soldered to the coils can they be added into the existing soldered mass of wire connections (so that the TVS bridges the existing solder points from one point on the coil to the other point on the coil), or does one need to unsolder the wires at the coil and redo everything? 2) Will a TVS rob any power from the switch requiring one to increase the switch voltage to compensate for a reduction in power? Thank you for all your help. Chris

You shouldn't need to unsolder anything if you can make a reliable connection on top of what's there.  If it's properly sized, the TVS shouldn't draw any current until the coil shuts off, and then only briefly while the coil's magnetic field collapses; so no supply voltage increase.

[Birds]

Bob,

Thank you for your answer.

I wasn't sure if you were following this thread anymore, and I appreciate you posting your answer to the thread.

Chris 

[Birds]

Update and an electrical question for Bob.

I just finished installing the last of the brass contact plates over the silver foil on my switches.  I used a 40 watt soldering iron because I found this heated the plate quickly.  A 25-30 watt iron took more time and I ended up having the plate slip a bit waiting for the solder to reflow.

All switches work correctly with the new plates.

One important point I discovered while doing this was to make sure that the amount of solder used to tin the bottom of the new plate was minimal.  Just enough to cover the bottom, but not mound.   When too much solder was added then it wouldn't reflow, or it wouldn't bond correctly and the plate would come up.

While everything was apart, I was also able to fix one switch that was sluggish, and one that hung on some throws by rebending the four arms that hold the contacts.  The explanation below will make sense if one looks at a schematic of the O22 switch.  These arms are located on the "moving contact assembly" (part 711-216), and act as springs that lift the whole "moving contact assembly" up off the "fixed contact assembly" (part 711-37) below it.  The problem I found was that if the arms applied too much pressure, then this caused the moving assembly to do two possible things:

1. have too much pressure against the two retaining pins / rivets (part 711-65) that hold the unit in place and cause the assembly to bind and move slowly
2. lift the end of the arm of the assembly located at the "lock hinge" (part 711-113) too high and cause the squared off tabs on the end of the arm to hang up on the lock hinge

I was able to adjust the tension on the four arms by gently bending them, and was able to get these two switches snapping and working as well as the others.

 

Question for Bob:

The Vishay SA20CA TVS has a PD rating of 3 watts.  Vishay's spec sheet defines PD as "Power dissipation on infinite heatsink at TA = 75 °C".

Q: What does "Power dissipation on infinite heatsink" mean, and is it applicable in this scenario of adding a TVS parallel to a coil?

Chris 

 

[lionelsoni]

The "infinite heatsink" means that the outside of the device is kept strictly at 75 degrees.  In that situation, the inside of the device will not get hot enough to destroy it if it is dissipating 3 watts (3 joules per second) continuously.  This rating doesn't matter to us.  The coil will deliver only a very small fraction of a joule each time it is switched, with many seconds between operations.  So it won't be anywhere close to 3 watts.

[Birds]

Thank you Bob.

The TVS's were ordered, and they will be here in a few days.  I'll post an update when they arrive and I get a switch completed.

Chris

 

[lionelsoni]

Be sure you don't exceed your 14-volt limit, or you will begin to heat up the TVSs.

[Birds]

The TVS's arrived and I was able to get a few switches completed.

Question: How can you tell if a TVS is working?

The switches still arc at the contact plates.  I put a volt meter across two plates to check the voltage both before and after the TVS installation.  I did not see a difference in voltage before or after the TVS was installed.

One point to make note of is that I found the leads for the to coils are joined in the middle.  They both come out at the third contact (the fixed voltage post contact).

Chris 

[lionelsoni]

You could put an incandescent lamp in series with one and apply a variable voltage to the series combination.  Below 14 volts, there should be no light from the lamp.  Somewhat above 14 volts, you should begin to see some glow in the filament.

The TVS doesn't get rid of all the arc voltage, just the peaks above 20 volts.  So it is possible still to see some sparking.