Best Of New Brass EP-2 assembly & Mod clinic

[u18b]

Dang electronics are just as involved as building the locomotive. 

LOL. Chris, you are exactly right.
I kind of dreaded it, but space is so tight, it was necessary.

[u18b]

Spent some time on the B Cab.

Here is the decoder for the B end.
Note the yellow wire since this decoder goes in the rear.  We don't need the white wire.



And the B end now works!

[Bob Horn]

Ron, you are unreal!! Keep up the good work. Bob.

[peteski]

Ron sent me a PM relating to my earlier post (about calculating the LED resistor value).  I'm glad that you found it helpful.

Instead of replying directly to him, I thought I might as well explain myself publicly.  When I mentioned that figuring out a safe resistor value only requires grade school math skills (and the smileys I used) were not meant to imply a low level of his (or anyone else's) intelligence.  I was not trying to put anyone (including Ron) down.  I was simply indicating my puzzlement that someone as meticulous as Ron, who not only did a super job of making a gem of a EP-2 model from what is a diamond in the rough, and who also is doing a superb job of documenting this process in this thread, would say "I didn't feel like doing all the math to go from 3.2 volts to 5 volts."  Phew, that was a long sentence! 

As far as the 5V output on the decoders, I think that some decoders do have a regulated common-positive 5V output (but not any of the N scale decoders I'm familiar with). Other decoders (again, not N scale ones, provide a regulated common-positive 1.5V output. That is for directly powering the 1.5V micro-bulbs.

But most (probably all) N scale sized decoders simply provide the higher common-positive voltage I mentioned in my earlier post.

I have another comment about your LED install Ron:  The resistor you used is rather large (physical size).  You could have safely used a much smaller resistor. The size is often important in N scale LED installation (as there isn't much room inside our models).  To demonstrate a bit more of that simple math (I hope that you don't mind), once you chose a resistor value, you can calculate the power dissipation of that resistor.

Citing the example in my previous thread, voltage across the resistor (6.8V) multiplied by the current passing through the resistor (0.0014A) gives 0.0095 Watts of power dissipated by the resistor.  To be safe, using a resistor rated at the twice of the dissipated power is a good idea. That is 0.019W.  You could have safely used a 1206 size resistor (0.12" X 0.06"), which is rated at 0.25W or even smaller 0805 size resistor (0.08" X 0.05"), rated at 0.125W.

Here is a photo of the same decoder you are using, next to couple of home-brewed circuit boards holding 0603 LEDs and 0805 (1k ohm) resistors.  The space was tight (Atlas N scale Shay) and the small 0805 resistors were safe to use as far as power dissipation goes.

(full thread of the install http://forum.atlasrr.com/forum/topic.asp?ARCHIVE=true&TOPIC_ID=54040 )

SMD resistors aver very inexpensive.  Having bunch of the common values used for use with LEDs is very helpful.   For example, every standard resistor value from 470 ohms to 10k ohms comes in very handy.  SMD resistor kits are available on eBay, or can be purchased from electronic suppliers like Digikey or Mouser Electronics. I usually buy 50 resistors of each value (at that quantity they cost about 4 cents each).

I also have to agree that using flux is vital, and it makes huge difference, when doing the kind of miniature soldering/desoldering work you are doing.

[u18b]

Thanks Bob.
Believe it or not, a whole lot more to go.

Peteski,
Thanks for your informative comments.

As for size, here are a few of my thoughts.  I'm afraid it has nothing to do with math.

My experience of several locomotives and decoders (not just a few) is that after some continuous running, the resistors in some of these gets pretty hot-- enough to burn your finger if you left it there.

This has happened with a few of my own home brews too.

Now, as your math indicates, in these situations, the problem may be not so much the under-rating of the wattage of the resistor, but maybe the resistor value is too low.  I don't know.  All I know, is that they sometimes get hot.

So a while back when I was placing (what for me was) a sizable order from Digikey (by the way- GREAT customer service.  I had a problem (long story) and the customer service people were wonderful.).

I was leary of 1/8th watt resistors-since I felt there was a greater chance the 1/8th watt heat dissapation would make them get really hot.  But when I ordered resistors in several sizes, I was looking for:

1/4 or 1/2 watt
cheap

On that second point, it is amazing the price differences between parts and manufacturers.  I'm sure quality is a factor, but why pay 38 cents each when you can get them for 17 cents.

So when looking for cheap in those sizes in many different resistors, sometimes they were out of stock of what I really wanted.

LOoong story.... so yes, those 4.7 K resistors are a little on the large side.  They are 1/2 watt.  But that was probably because at the time I ordered, it was all they had in my price point.

And in this particular instance, the 1/2 watt size was OK since it is the same with as the decoder itself.

[peteski]

Ron, the math doesn't lie.   You mentioned hot resistors in some electronic circuits you purchased (not home-made). They might not be designed properly. I don't know. If a resistor value was as you say "too low" in value, then too much current would be flowing through it, causing it to dissipate more power (and get hotter).  But if the simple calculations are done (as I demonstrated in the last couple of posts), and a resistor is chosen capable of double of the calculated power dissipation then it will not overheat.  No ifs or buts about it. 

This is all I'm trying to say: if some basic calculations are are made, and proper components are chosen, the guesswork is taken out of the equation. 

For example, I have a similar setup on the photo in my previous post. Using DZ125 decoder and a white LED. I am using a 1k ohm resistor (which passes more current than the 4.7K ohm resistor you are using). I calculated that a much smaller (physical size) resistor would be safe to use. No problems with it overheating.  But  of course, there is nothing wrong with using a resistor with a much greater power dissipation rating. However in N scale space is usually at premium. I'm not asking you to change your installation - I just wanted to show to other Railwire members that if they have limited space, a smaller resistor could be used without any ill effects.

Going back to my original post, the 1.4V I mentioned being dropped across the bridge rectifier inside of the decoder is actually across 2 diodes (in that bridge rectifier). Single silicon rectifier diode usually has a voltage drop of 0.7V across it.

[Sokramiketes]

I used to do a lot of calculations until I figured out 1k ohm worked pretty well for every surface mount resistor I've needed to run off a decoder.   

[u18b]

I've spent a LOT of time tweaking today.
You'll hear more in the coming days.

But for now, here is one simple but helpful thing I did.

Remember, I got these things running in analog mode.

But the wiring harness is designed to be quick and efficient - even for DCC.

Well, remember this shot?
It shows the little jumper wires I made for running this in analog mode.
I'm jumpering the Red-Orange    and   the Black-Gray.



But those pins are small, so I sacrificed a plug and make an Analog plug.



Here is the finished product.



Decoders are great for speed matching.  But they are a real pain for just getting the mechanism to run well.  To simply test the running smoothness, I need analog mode.

Well, with this modular harness, I just plug this little plug in.... and test all I want with my old MRC power pack.

[u18b]

Today's instalment is called:  A Quest for Perfection.... or Ron's Neurotic Obsession.

The new EP-2 runs very well overall.   But one of the Cabs in particular just.... somehow I knew it could be better.

My guess was the inner bearing.
I really don't like some aspects of the design KMT gave me.
One is that I would have preferred the motor shaft to be really long and have an OUTBOARD bearing that was held tightly (no wiggle).

This short shaft business simply does not seem optimal.

So I decided to remove the inner bearing and find a way to support the motor at exactly the correct height.



Another reason to walk though this is that it shows how effective building the modular wiring harness is.  In what follows, know that I disassembled and assembled this loco probably about a dozen times as I made experimental tweaks.

So here is the Cab.  Remove the three screws to the shell and lay the shell to the side-- watching those LED wires.  I don't want to pull them or scratch the coating off.



Pull the decoder plug.



Pull the red boiler room jumper wire.



The shell is now free.



Pull the wire from the front truck pad.



Remove the power truck and the gearbox.



Lift the heatsink off the motor. (this is actually my frame connection.)



Remove the two screws to the motor.



Pull the motor assembly free.



Now the idea here is that I need some kind of shim to go under the motor.

Here is my calliper and a LOT of experimentation.

80 mil was too big.  40 + 10 was too small.  60 mil was close.



After a LOT of experimentation and searching, I found I had some fat two-sides perfboard.
I cut a piece off.



Ok, let's measure this.



Into the calliper.



As you can see, it measure a little over 64 mil.  I'll add something to this.



Cut a triangular piece.



Trim the sharp tips.



This size is good for support under the motor while not covering the hole for the red wire.



Superglue.  Getting just a little on the tip.



Add glue around the base.



Pieces of paper range from about 3 mil to 4 mil.  here I am adding a piece of 4 mil.
Superglueing it down.



So now, I am right about at 68 mil.



Now to remove the inner bearing.  USed a NWSL gear puller.



Install the motor.



Here you can see the shim.



Reassemble to test in analog mode.



test run shows that this worked.  Just right.



Reassemble with decoders.  Reset the decoder to be sure and start from scratch.
Run both Cabs to see the speed matching.
in this case, the A cab ran faster.  So the B unit was my reference.
I programmed the B Cab to run a a good top speed.



Then with experimentation, I programmed the A Cab to match.
This was just a rough estimate using the Vstart, Vmax,  and Vmid  variables.
Experimentation (and recordkeeping!) allowed me to get them very close.



It worked!  Both decoders are programmed to #3 and the loco is run as one.  But the speed matching of the decoders is just what this pair needed for maximum efficiency.

[u18b]

I recently received an original 1983 EP-2 for repair.

The paint job is very nicely done.  But it is a basket case electrically.

The owner said he paid someone to get it running and they couldn't.

Well, not only did they not get it running, they clearly had no idea how these admittedly complex locos work.

1.  There was no pick up at all from the front idler trucks.  Remember from my design revisions for this new EP-2 that the pickup wire is predestined to break.  Unless it sits in a box and never touched, those two wires are GOING to break.

2.  The jumper ire that runs through the boiler room.  Someone soldered one of the plug in!  Yikes.

3.  The wheels are all jumbled.  Even if there was a jumper wire to the front truck, this loco would have a short since the wheels are not lined up properly.

4.  Lead putty was actually fouling the drive shaft.

A lot of the information in this new EP-2 clinic applies to the old one.

In the coming days, I post a few photos of this repair.

Having the old and new side by side help show off the differences between the two.

[u18b]

The loco just looks a little naked.

Time to move to the pantographs.

As is consistent with the kit, they are not finished.



The pins are too long.



You will notice that there are two kinds of pins.
Fixed soldered pins (right side of each pair) and pinched unsoldered pins.



Here is a closer shot.  The moveable pin is folded over.



We will start with the soldered pins.  Trim them all fairly close.  As long as the solder joint is not changed, there is no problem.



Better.



The moveable pins could be folded over.



or trimmed.  As long as there is a flared portion that won't go through the hole.



Now mounted on the Cab shell with it's two mounting pins.



Now we are getting somewhere.

[u18b]

YouTube video coming later tonight.

You will be AMAZED.

 

[davefoxx]

Awesome, Ron.  I can't wait to see it in action.

DFF

[Ian MacMillan]

Epic work. Can't wait to see the video.

[u18b]

Well, it's not the Super Bowl....

But this is the fruit of the last 11 pages of work and 3 months.

As you know, I'm kind of a performance nut (as you have seen in this thread).

But this 5 minute video comparing the Old brass NJ EP-2 from 1983 (stock- except wonderfully painted) and this new EP-2 I've been building.... makes the work stand out.


Please turn your cell phones off, and no more talking until the film is ended.
And thank you for your support.