2-8-0 shorting out

[Yampa Bob]

Shawneehawk

In my first post, I briefly mentioned an inconsistency in the tender wiring and wheel orientation, my error for not elaborating with greater emphasis.

Taking a cue from Jim, those who are already well versed in tender wiring may skip the following narrative and jump to the diagram at the bottom.

I have worked on 7 tenders, both Vandy and USRA, that I run on my 2-8-0 Connies.  All but one had the front wheels with insulator left, rear wheels insulator right.  The odd one had the wheels reversed, but the wires from the trucks were wired differently on the pc board.

The usual convention for DC wiring is red for positive, black for negative.  It therefore follows that the "right rail rule" is that the right rail, as viewed from the engineer's perspective looking forward, is positive. (for forward loco movement) Any time the right rail is not positive, the loco will move backward.  This is why (on DC power) two locos will always move in the same direction regardless of their related orientation (nose to nose, tail to tail, or nose to tail)

I have a new 2-8-0 on my bench.  Looking at the 2 wire harness on the bottom of the loco, the red wire is connected to the right wheel wipers, the black wire to the left wheel wipers. So far it appears to be wired as it should be, at least to my satisfaction. 

Now the tender, with the shell off, connector plugs forward. On my version, the red wire from the two conductor plug at the front (left side) is connected to the left solder terminal at the back of the board, which is labeled "power input".  The black wire is connected to the right solder terminal.

There is a red wire leading from the left solder lug to the front truck bolt.  Another red wire is connected from the right solder lug to the rear truck bolt. 

The front tender wheels have insulator left, so the wheels pick up power from the right rail.  The rear wheels have insulator right, picking up power from the left rail. Again, the right rail rule is being followed. 

Now about that oddball that was different. One red wire was from left solder lug to the rear truck bolt, another red wire from right solder lug to front truck bolt.  Apparently a worker soldered them wrong, and just turned the wheels around to compensate, or perhaps they had the wheels wrong, and decided to switch the wires.  Who knows?  The rear wheels were picking up power from the right rail, the front wheels from the left rail.  But since the wires were switched, it works ok. 

The important thing is that you verify the wiring in relation to the wheel orientation, keeping in mind the "right rail rule" as you proceed. Since both the loco pickup wires, and the tender pickup wires all go to the two solder terminals, if either the tender wheels or the wiring is wrong, you will have a short between the rails.  As Jim mentioned, it might be a dead short or a "resistance" short depending on the contact between the wipers and axles, or contact between the wheels and rails, all of which could be intermittent.

Incidentally, on the oddball tender, I changed the wiring and the wheels to match my other tenders. 

Others may not agree with my "convention", but it is the way I do it to keep everything uniform and avoid confusion and/or mistakes.

Sorry about the long winded explanation, but I have learned that you can't assume the factories always follow a standard procedure. I drew diagrams of the tender wiring (both ways that I have observed).  I'm not claiming that either way is correct or not, all my tenders are wired as on the left.

[shawneehawk]

Bob, long winded explanations are fine with me, as I do feel I am learning something here.  I do appreciate everyone's patience with me.

Patience is something I lack.  Last night, even though I knew better, I returned to the basement to give the Connie a final look.  There, at the edge of the layout, in poor light, and with tired eyes...you guessed it...the motor block and chassis ended up in the floor.  The motor block came open, and I had to collect the motor, bearings, worm, screws, and plastic mounts.  This morning, I worked on the chassis, which surprisingly did not appear damaged.  After some effort (and profanity) I was able to get the the motor parts back together and repositioned.  I did have to resolder the red wire to the motor.  Initially there was some grinding, and I feared I had stripped the plastic gear.  Then I realized I had not put the final 2 screws in the bottom of the block, did so, and tested the loco.

The bottom line:  It ran good in both directions, although a little noisier in forward.  Perhaps gear noise, I'm not sure, but nothing appeared binding.  I ran the loco for 30 minutes in each direction and it did not stall.  Once, the tender rear truck wiper and screw fell out...this has also been a problem...and the loco continued running fine on just the grossly contorted front truck pickup.  Perhaps the problem has been in the trucks and wipers all along, as I had to bend the front wiper under the wheels to make contact. 

I just finished examining the tender wiring.  Jim, I am going to skip snipping any more wires for the moment, due to the fact the Connie ran good for an hour.  Bob, I have traced the wires as you suggested.  The front wheels are insulated left and the rear ones on the right. The red and black wires go to the solder terminal as you described.  Then I found the 2 red wires which go from the solder lugs to the truck bolts are reversed.  The red wire from the left lug goes to the rear truck, and the red wire from the right lug goes to the front truck.  Sounds like I should reverse these, right?  I also like everything uniform.

Thanks...I do feel we are getting someplace finally.  At a minimum I will still need to replace the trucks and wipers...just hope I can get the front truck, the one with the melted screw, off without tearing anything else up.  It does not swivel well at all and is a derailment waiting to happen.

[Yampa Bob]

If the lugs are wired as you describe, and you don't match the wheels to the wiring, you may still have a potential for a short.  Study the diagrams and use the plan you like best. From my experiences, the score is 6 to 1 in favor of the left diagram.

It would  help if the factory used red and black wires from the solder lugs to the trucks for easier tracing, and included a diagram. As seen above, a picture is truly worth a thousand words.

A major part of troubleshooting is isolating the problem, "Is it the loco or the tender?"  I recently scrapped a Vandy tender for all the parts.  Using the male connector from the tender front, I spliced the black and red pickup wires over to the wires leading back to the motor. By plugging the loco into this adapter, the loco will run on DC without the tender.  In lieu of the connector, you can jumper the plugs from the loco with tiny wires, similar to the jumper plugs that come with the loco in a small bag.  Just be sure the wires are small enough so as not to spread or damage the female connectors in the plugs, insulated from each other with tape, and tie the wires up so they don't catch on the rails or turnouts.

Welcome to the "Learning the hard way" club, the largest brotherhood in the world.

[richG]

Hi Bob

Nice explanation and drawing. Much better than I could ever do. I have seen this Spectrum tender issue in a couple different forums. Some modelers are not aware of the change from tender wheels picking up from only one rail to what the Spectrum does now. I have wanted to draw something like that but never took the time. Good job. I would like to use your information if I ever see this issue in a different forum. Actually, I can just like to this forum since you do not have to login to read like you have to in the Yahoo groups.

Rich

[Yampa Bob]

Thanks, Rich.
The diagram was hastily drawn in the wee hours, I'm sure someone could improve on it. Feel free to use it any way you like, hopefully it will help others to avoid a meltdown. 

When I got my first Spectrum 2-8-0 I was anxious to get it running. I only noted the variant while adding weight to one of the tenders.

Rule number two of Murphy's Law states that if there is a way to do it wrong, someone will do it.

[shawneehawk]

While we're on tender wiring, it has always irked me that this loco does not have a backup light.  Any suggestions on connecting one?

Looks like I will be ordering replacement trucks from Bachman.  The small brass washer I found is not even shown in the parts diagram.  Does it go on top of the wipers?

The Connie continues to run well this evening, except for the motor noise when going forward.

[Yampa Bob]

Looking at the tender I referred to earlier today, there is a small brass washer under the bolt head, on the bottom.  It might be for better contact between the wiper and bolt, however I wouldn't count on the washers being present on all tenders. You might ask service when ordering the truck.

I have also considered adding a backup light. A friend added a great looking brass light, but didn't disclose the details. Jim Banner has done lighting mods on locos, so he would be best qualified to answer this question.

One of my Connies is noisy going forward, possibly the gear rubbing on the casting. This thread has some information.

http://www.bachmanntrains.com/home-usa/board/index.php/topic,4506.msg37905.html#msg37905

[shawneehawk]

Thanks for the link, Bob.  I spent some time working on the Connie this evening.  I was able to determine that the forward noise was coming from the motor itself, not the gears.  I removed the motor from the block and took the belt off and tested it.  No noise, but when I return it to the block, the noise returns, and I can't find the reason for it.  Could it be that it just needs run more?

It took awhile, but I was able to get the front truck off the tender.  The truck itself looks ok.  I don't know why I did not think of this earlier, but I realized that I've had a MDC Santa Fe Prairie since the mid 80's that is not being used (I model L&N), and I could use the wipers and and probably the trucks from it.  Anyway, I was able to get the truck repositioned and ran the loco in both directions for about 15 minutes.  It is running ok and not stalling or derailing.  It is not shorting and I see no sparks.  Perhaps the motor will quieten once I put the decoder back in.

Now the big question, as I don't want to fry the Tsunami...I hope the motor on this loco is isolated ok, and that I did not miss anything when I got the parts out of the floor and reassembled it.  The exploded view helps, but I know it doesn't cover everything.  I know there are 2 white plastic spacers or screw mounting pads that go between the halves of the diecast block and these are in place...am I missing anything else? 

[Yampa Bob]

Well, it appears you have removed all the gremlins and have reached the "moment of truth", but the decision to reinstall the Tsunami is yours to make.

I would be inclined to run the loco on DC power for awhile with the decoder installed to make sure there is no binding or other problems.

You might want to run without the shell on the tender so you can check for excessive heat buildup in the decoder. When running a DCC loco on DC, I always have a DC ammeter installed in one track power lead to monitor the current. 

Good luck

[pdlethbridge]

Bob, isn't the 'learning the hard way club' one of the after school clubs from the School of hard knocks?

[Yampa Bob]

Yes, and after 70 years I have lots of scars to prove it.   

[shawneehawk]

I've just returned from a trip, and have been running the Connie in both directions.  It continues to run well, although the noise is still present.  I did put the Tsunami back in and placed the loco on my PowerPax equipped programming track, and was able to read the manufacturer ID and version, so I take this as a good sign.

I've removed the Tsunami and am going to continue running in both directions on DC for another evening or two, then may plug the decoder back in and see how it does running on DC like Bob recommended.

Thanks again, and I'll keep you posted.

[Yampa Bob]

I should clarify one statement I made earlier.  With the decoder installed, and running on DCC power, check the decoder for heat buildup.  Running on DC with the decoder installed, you probably won't get any extra heat, as the decoder is essentially bypassed when on DC power.

[richG]

I should clarify one statement I made earlier.  With the decoder installed, and running on DCC power, check the decoder for heat buildup.  Running on DC with the decoder installed, you probably won't get any extra heat, as the decoder is essentially bypassed when on DC power.

DCC decoders running on DC can still generate heat, The decoders are not bypassed when running on DC or I have misunderstood what you mean by bypassed.  The logic circuits are still being used to control the motor and lights. The motor gets pulses from the decoder logic even when the decoder sees pure DC. Some functions no doubt will not work.
The input to all decoders is at a full wave bridge rectifier so this bridge can handle DC and DCC. The motor will not get any pulses until the decoder sees a little over  5 volts DC, the operating voltage for a lot of logic circuits.
The NMRA requires this for the decoders. I have used an Oscilloscope to verify this. Hope this helps.

Rich

[Jim Banner]

The only way to truly bypass a decoder is to unplug it and plug in a dummy plug.  Otherwise, as Rich points out, it is still part of the circuit and still produces heat when you run the locomotive on dc.