Pennsylvania A3 Switcher (Kozo)

[Kim]

Kim’s Extra Stuff: Switch Bracket

As I was ruminating on how I wanted to make the switch bracket, I decided I needed to make a few modifications to the battery holder.  First, I enlarged the hole through the cap to the battery compartment so the wire I wanted to use could fit through.  Then I carved a recess in the top of the battery holder bracket so I could make a ground contact using a 1-72 screw.  The top of the bracket has to sit flush with the underside of the running board that it’s mounted to, so the recess was necessary.  The ground terminal of the battery is connected to the battery case, so this screw terminal should get me a good ground.


Kozo recommends using a chassis ground for the light circuit.  I considered this, but I’m worried that my powder coating will insulate some of the parts and prevent a solid ground.  So I’m opting to run two wires to all the lights. Might not be needed, but it won’t be that much more trouble than running just a single wire.

Here’s the bottom side of the cap with the positive lead sticking through.  When I’m ready to commit, that positive terminal will be soldered to the brass spring-loaded pin sitting there in front.


I also enlarged the hole in the running board that passes the positive terminal.  I made it big enough that the little connector I want to use for the battery will fit through the hole – just barely.


Then I started on the bracket for the switch.  Here are the three parts I made for this.  They are made from steel (1/16 sheet, and 1/8” x 3/8” bar).  While Kozo doesn’t document how he mounts his switch, you can see it in a couple of the photos in the book. He uses a very simple angle bracket.  I opted to make it a little more complicated.  I wanted to have a bit of protection between the wires and the boiler.  I want to make sure the wires don’t touch the side of the boiler, so I made a bracket with a large shield.  That notch in the large plate piece will fit over the edge of the base of the reversing lever.


Here’s what it looks like after I soldered it together.


You can see the notch along the bottom that fits over the reversing lever.  During soldering, I got a bunch of solder in that notch so I had to mill it out.  I did a little over-milling on the corners to make sure it would fit right.  And it does.


Here it's mounted to the running board, just next to the reversing lever.  This is the same place Kozo shows it in his pictures, but like I said, my bracket is a little bigger with that shield there. I also plan to mount a few clamps on that shield to hold the other ends of the conduit runs.


And here’s what it looks like with the cab back on.  Just fits!  You can see the end of the conduit run coming from the front headlight just sticking out around the edge of the boiler.  This will be bent up to deliver the wires behind the shield plate there.


I’d have liked to make the switch panel extend over to the side of the cab, and also put a top over the switch area so you didn’t see any wires.  But because of how the cab connects to the running board too, I couldn’t figure out how to get a wider switch panel in there.  All my attempts made it impossible to lower the cab into place.  So I’m just going with this.

Guess we’ll see how it goes, eh?
Kim

[crueby]

Looks great! 




Rather than the little toggle switch, how about a miniature version of the old Dr Frankenstein  knife switch!

[cnr6400]

 

[Kim]

Thanks Jeff!

Rather than the little toggle switch, how about a miniature version of the old Dr Frankenstein  knife switch!

I dunno, seems like a real safety concern - using a knife switch with this kind of high voltage! 

Kim

[kvom]

Rather than a hollow handrail in brass, what about a stiff insulated black wire serving as one of the handrails?  Paint the other black to match.

[kvom]

Another thought is to insulate the holes through the stanchions and use the metal rails as the conductor.

[Kim]

I like those ideas.  I don't think I'll be doing that for this engine, since I'm pretty happy with the solution I've got at the moment.  But maybe next time?

Thanks for all the ideas and suggestions!
Kim

[Kim]

I needed to make one more short conduit run – from the rear of the engine to the switch bracket.  This is for the connection to the light on the tender.

I also had to make three more brackets to hold the conduit in place.  I made these just like I did the others, but this time, I took some pictures to show how I did it.

I started with some K&S 1/8” x 1/64” brass strips I happened to have on hand.  That made the job pretty easy to do.  I just bent the end around a 1/8” rod using non-mar pliers.  I left the end over long so that I had something to hold onto when drilling in the next step.


Then drilled the mounting hole for the screw.   I did two at a time – one on each end of the brass strip.


I cut them off the parent stock with a pair of side cutters (you can do that with 1/64” brass ) then rounded the ends on the belt sander.


Here’s what it all looks like together.   The top tube is the one coming from the headlight at the front of the engine.  The lower tube is from the rear of the engine for the wires coming from the tender.


One more shot with the switch and air reservoir in place, just to make sure I didn’t encroach on their space when running the conduit.  You can see the conduit sticking out the back of the engine just below the rear bumper/bolster thing. 


Well, I think that’s all I’ll be doing on the wiring for the headlights at this point.  I’m going to wait to run the actual wires till after everything is painted and I’m doing the final(ish) assembly.

Next up is the water tubing.
Kim

[crueby]

Nice!   

Is the insulation on the wire you are using able to handle the heat from the boiler being so close? Sorry if you've already covered this!
Chris

[Kim]

Well, my hope is that having the wire inside the conduit will help protect it from most of the heat.  Yeah, it'll get hot, but hopefully not over a few hundred degrees.  And most insulation should withstand that (he says optimistically).  I know it will melt if you get it to soldering temp, but that's over 400F, and I don't think the outside of the boiler will get that hot.  Guess we'll see, eh?  If my lights start to short out to the conduit, then I'll know something's wrong! 

Kim

[Roger B]

So much fine detail     

PVC wire will start to soften over 250°F but unless there is any significant pressure it won't flow. A fluoropolymer or crosslinked insulation would be better but I can't recall what you were planning to use.

[Kim]

Thanks Roger! Good info.

I'm planning on using 30ga wirewrap wire.  It's gotta be small to fit through my little conduit!

I just googled it and came up with this:

Code: [Select]

WesBell Kynar wire wrap has a solid silver-plated copper conductor with PVC insulation. Kynar has a very thin insulation thickness of .004 inches and a temperature rating of 105 degrees Celsius.
Not sure that's the same brand of wire I'm using, but it's likely a good indication.  And 105C = 221F.  That's the range I was picturing and hopefully, I'll be OK.  Otherwise, I won't be ruining the lights! 

Kim

[Roger B]

Confusing    Kynar (PVDF) is a fluoropolymer and has a continuous temperature rating of 135°C, it's not the same as PVC which at the best has a continuous rating of 105°C as they quoted.

[cnr6400]

Just an FYI Kim, food for thought - McMaster Carr carry a number of types of high temp wire. See link below. Of course none of it is inexpensive. I have used their silicone jacketed low voltage hookup wire which is rated to 400 deg F, it worked fine at over 450 deg F for a short time, until I noticed the overheat condition. Didn't seem to affect the jacket or the conductor. Good stuff. 

https://www.mcmaster.com/products/high-temperature-wire/

[Kim]

Great link, Jeff, Thanks!

They have some 36ga wire with FEP insulation rated for up to 400F that is only 0.01" in diameter.  Or, for slightly less money, 36ga wire with silicone rubber insulation rated up to 390F that is 0.02" in diameter.  I think the 30ga wirewrap wire I'm planning to use is about 0.024" in diameter.

Hmm... is it worth doing it right first? Or seeing if I can get away with what I've already got on hand... Hmm....

Kim