Atlas GP7 w/ESU LokSound (photos and video)

[peteski]

No, do not hook them up to the motor leads!

I haven't dealt with ESU decoders for a while, so I don't remember the specifics. Check the decoder's manual - there should be some mention of hooking  up external caps.

Usually, the positive side of the caps (the dark band side of the caps) hooks up to the common positive terminal of the decoder. Usually that is the blue wire (same as used for common positive for the decoder functions). The negative side of the caps has to be attached to the decoder's ground or common.  There might be a wire designated as such (uncertain of the color) or you might have to attach the cap to one of the components on the decoder which is ar the ground potential.

[mu26aeh]

I think Dave was just asking in general if John solders wires directly to the tabs or takes the leads out of motor, solders, and reinstalls with brushs etc.  And asking separately where to wire in the tantalum caps
 

[davefoxx]

I think Dave was just asking in general if John solders wires directly to the tabs or takes the leads out of motor, solders, and reinstalls with brushs etc.  And asking separately where to wire in the tantalum caps

Yep, this.  Sorry, if that wasn't clear.

DFF

[peteski]

In my experience I try not to disturb the brush holders. Usually there are thin brass strips trapped under the round brush holders. I usually trim those brass leads within about 1/8" of the brush holders, then quickly solder the wires to those leads. Soldering leads directly to the brish holders is risky. The soldering process can heat up the holders enough to melt the the plastic which holds them.

Looking at the photos in the initial thread it appears that John left the brass stripe full-length on the motor (they both travel up to where the original light board was), and he probably soldered the decoder to the ends of the brass strips.

[jdcolombo]

@davefoxx

As Peteski observed, I solder the motor wires to the phosphor-bronze strips that are already in place to contact the light board (on a DCC-ready unit). I wrap some kapton tape around the frame halves at that area to guard against shorts.

The positive side of the caps is wired to the blue wire.  The negative side is wired to a pad on the "back" side of the decoder, directly opposite the blue wire pad.  You will have to cut away a bit of the plastic insulation (if you haven't already cut it all off) to get to this pad, which is at the very edge of the board at the front.  It's hard to see where this wire goes from my GP9 photos, so here is another photo that shows the connection point better:

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John C.

[davefoxx]

@jdcolombo,

Thanks for that response.  I think I understand the tantalum caps now.  I also found your picture of the "tantalum caps "sandwich," which showed how you wired it together.  Very helpful.

Last question (probably not): do you have a picture of your homemade circuit board and the resistors?  I think this is the last piece of the puzzle that I'm not clear on.

Thanks again,
DFF

[peteski]

@jdcolombo,

Thanks for that response.  I think I understand the tantalum caps now.

It is always helpful to understand how things work when using them. I googled  "capacitor explaned" and  here is a nice down-to-earth explanation:
https://learn.sparkfun.com/tutorials/capacitors

In this application we use them to store energy (derived from the track voltage inside the decoder) and release that energy during brief power interruptions when traveling over dirty track.  With the capacitance value we are using they only store enough energy for less than a second of model's operation, but that is enough in most instances for uninterrupted running and sound.

Most decoders have similar caps already installed on the board, but with much smaller capacitance (to keep their physical size smalle). Those can only supply energy for milliseconds.  The caps added by John supplement the on-board caps.

Tantalum cap is polarized which means that if they are installed in reverse polarity to the circuit they will literally explode and burn.  Same goes for exceeding their voltage rating.  Hooking up multiple caps in parallel will result in the total capacitance being the sum of all the individual capacitance.

[jdcolombo]

@jdcolombo,

Thanks for that response.  I think I understand the tantalum caps now.  I also found your picture of the "tantalum caps "sandwich," which showed how you wired it together.  Very helpful.

Last question (probably not): do you have a picture of your homemade circuit board and the resistors?  I think this is the last piece of the puzzle that I'm not clear on.

Thanks again,
DFF

Photos of my resistor boards:

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I use 1K, 1/8W smd resistors for these and 1/32" single-sided copper clad board.   After soldering on the resistors, I trim the boards to final size by simply clipping of excess from the ends with a pair of flush-cut nippers.

John C.