The Basics

The Bachmann power pack consists of a plastic body, in either black or brown, with a knob with a flip lever in either corresponding red or cream.

The pack itself converts household 120VAC into roughly 12V variable DC, with an additional pair of leads providing constant AC for lighting accessories or activating Tyco action accessories.

The unit I shall be digging into is a Model 6607.  On the pack it stated this unit handles an input of 200VAC @50-60Hz, and provides an output of 17VDC and 20VAC, with a maximum output of 7VA [watts?] total.

This unit has a slight issue in that the knob travels further than it should in one direction, so seeing as how it's already a known bad unit, perhaps we can find some nifty parts inside - at the very least, a potentiometer would be great!

From Careful Surgery to Outright Demolition...

Things started out easy enough; to ensure that I'd never be tempted to use this unit again, I chopped off the cord and discarded it.

Then I pulled out my favorite pry bar, an old butter knife, and when to work removing the bottom from the pack.  It appears to me the unit is assembled using a heat press, so you can be sure I found out quite soon just how difficult disassembly is.

After five minutes I only had one corner popped up, and even that wasn't coming up well, and then there was bloodshed, as I slipped and caught the plastic.  Finally, I levered the knife one last time and heard a simple *crunch* in side and I knew it was done.  Out came the snips, and I very directly removed the base in little pieces!

And so we can see the item that went crunch appears to be a light bulb of sorts, a resistor by all means.

Pulling the board...

I now snipped the leads to the output posts, removed the screw that holds in the knob, and pulled the inner board - would there be treasure on the other side?

NO!

Aha!  All the Bachmann power pack is, is a printed circuit board with on large transformer, a couple resistors, and this wheel with contacts.  As the wheel turns, the contacts complete the circuit through a different set of printed tabs, hence the Bachmann transformer really is an incremental variable DC power pack and not a continuous variable DC power pack.

Up top we can see that the reason the knob failed is because a stop has fractured off the knob.  So regardless, we have really lost very little taking this journey.

Anyhow...another mystery solved...and I'm back to the drawing board for finding a potentiometer for my project...

Thanks for the dissection

Thanks for the pictures, Benny.  It's always interesting to see how something is made, and to learn whether there might be any useful parts inside.  I've done something similar with the newer square power packs, trying to install a phone jack to make a walkaround throttle (it worked, by the way).  What I found interesting was that there are multiple connections that seemed to have no purpose.

Hope you had fun...

It's always fun to dissect stuff when it breaks!  Hopefully you were not injured too seriously.

So you had to hack it open.  Gee, I hope the "no user serviceable parts police", don't come around to harass you!

In most cases you will find that the DC power packs, especially older Tyco, Bachmann, Life-Like etc. packs, have no potentiometer inside.  I have found rheostats, or more like something resembling the design of a rheostat, in all of the packs I can remember taking apart over the years.

What do you need the pot for Benny?  Whatcha buildin? :o)

It's a hoot, that's for sure...

The next project...well, I'm hoping I can sell it...but first, I have to get all the parts together, assemble it, and make it wiork!! 

Yesterday I created all my schematics, they're rough at the very least, for my project.  When I get done, I will have a rather nice Modern schematic...for more than just this project!!

Ahhh...

Project for sale, OK gotcha!

Now I can sleep at night.

Thanks so much, Benny.  This was a very timely project you're reporting on.  It was really bothering me as to what was inside that darn little black box.  Now I can rest easy.

Well...

It's been sitting here in front of us all along, has anyone else actually ever done it?

Some good news

I didn't grow up with Bachmann trains, so have never owned one of their throttles.

I was pleasantly surprised to see that they use a multi-tapped transformer, rather than a pot. That gives much better stability of control at the lower speed settings. (no series resistance).  And I suspect costs them more to make the transformer.  (BTW, the "light bulb" is probably a bi-metallic thermal overload cut-out).

So you have the option of 5 different voltage outputs in parallel, if you decide to use the transformer for other projects.

{bi-metallic thermal overload cut-out} moment...

Andy...

I spent about 30 minutes under the layout one day, trying to get the wall wart as close to 12VDC as humanly possible with a multimeter and simple adjustments.

And the damn thing kept Jumping from one unit to the next, with no in between the two settings...

Now it's all falling together - HA!!!

It's not a bad transformer, all in all.

Walk Around Throttle?

Ken,

Did you use this as a DCC jump throttle on the zephyr? If so How did it work?

Regards,

John

Walkaround

Actually, I made two of them, for use on a friend's layout.  He uses them to switch a short line, and they work quite well.  We ended up using phone jacks on the fascia and 7' phone cords to connect everything.  While we were concerned about running both AC (16V, not line current) and the track power through the small phone line, it has worked flawlessly.

I have considered using them on a jump port, but at the moment I'm thinking of doing something even simpler.  I do have a homemade throttle of very similar design which I am currently using on a jump port.

I've got to say, those newer square Bachmann power packs are as good as the one in this thread is bad.  they're well made, have a real potentiometer, and are easy to work on.  They're not comparable to much more expensive throttles, of course, but for the price and what they are, they are surprisingly good.

Shortline...

As Ken mentioned above, The the newer power packs have worked flawlessly on my little shortline!  They fit well in your hand and with making them into walk around throttles they are about perfect for the job.  

The only draw back I've found is that they are a bit too small for running multiple locomotives on a train, but for a single engine and slow switching speeds.  No complaints!

You can get a potentiometer

You can get a potentiometer from old radios with vol knobs. Thanks for posting this I just found my old Bachman unit exactly like this and was goign to tear it apart.

no audio pots for throttles

Be careful raiding audio components for pots; they frequently have audio taper instead of linear and will not work as you expect in throttles, etc.

Not just non-linear

Even if you managed to find a linear potentiometer from some old electronics equipment, it would still have a very low current rating and usually several thousand ohms of resistance.  So it would only be good for a transistorized design, needing a substantial current amplifier to supply the 1 amp or so a DC loco might need.

Please be aware, DIY throttle design needs some electronics know-how up front.

walkaround throttle

Ken, Could you provide info as to how you put together the walk around. It could be something I could use on my layout. Currently I'm only to the room preparation and could easily put this in from the start. Have you discovered any problems with this system? I'd rather learn from your mistakes instead of inventing them over for myself. Does the train keep it's speed when you unplug to move to a new plug in?

I kind of have the concept envisioned but am looking for you to help fill in some blanks. And at my age the blanks seem to reproduce faster than they can be filled in.Thanks if you can give me any help.

Bing

R.I.P. RR The Route of the Buzzards 

My memory is a little fuzzy,

My memory is a little fuzzy, as it's been a while, but I'll see what I can do.

As mentioned above, we used phone jacks.  Lowes (and I assume other similar stores) sells a box of jacks meant to snap into a panel (which can take up to 6 jacks of various descriptions).  They're the smallest jacks we could find, and that's kind of important.  I cut a square hole in the top of each throttle, eliminating the 16VAC terminals.  Inside, I ran 4 wires off the back of the jack.  Two go to the 16VAC pads on the circuit board, and two more to the pads where the track power wires connect.  As I recall it took a little probing and testing to figure out which pads were the best, but in the end it was a pretty simple job.  About the most difficult part of the whole thing was dealing with the potentiometer, as the wires are very fragile and easy to break at the point where they connect to the board - and it's a bit of a challenge to re-solder them.

Of course, at the other end of the cord is a phone jack mounted to the fascia.  Nothing fancy, just a normal single phone jack in a wall plate.  Keep track of which wires are AC and which are DC, or things could get interesting!  WE tried both a short phone cord, and a coiler receiver cord.  The coiled cord is neater, but the jack is too wide for it, and needs .030" spacers on each side in order to keep the cord tight.  I believe that he's using a short (7') phone cord now, and since it's so short the fact that it is not coiled or retractable is not an issue.

Because of the way I added the wires to the circuit board, the throttles still function with the stock connections as well (minus the accessory terminals, of course).  In essence, all I did was add a secondary means of connecting them to the layout - one that is a little cleaner and more convenient.  The train stops if the throttle is unplugged, since it is completely self contained.  All that is on the layout is a power supply and the wiring needed to connect everything.  Overall, I would say it's a simple and effective modification, and it works well - within the limits of the Bachmann power pack.

pictures

I will get some pictures posted of the power packs as soon as I can.  Its been a pretty crazy week for me and my basement time has been cut short.  As Ken mentioned the throttle is completely self contained and if the cord is unplugged the trains will stop.  This has not been as issue for me as I only have them mounted on my little branchline.  If I were using these on a mainline, I could see where you would want memory throttles. 

What's Inside a Bachmann Power Pack?

Ah...

A small step for you, a giant step for the model railroaders community!

I enjoy your small project!

Reminds me of an old sketch, ending with:

".. and next time I wil tell you about the troll monster in the milk!"

The old sketch

became an hilarious movie. "the Troll Hunter" (US title).

Power pack

I posted a link in the Bachmann forums but it was pulled and the thread locked. Bachmann did not want any kid attempting to open one of these packs.

Rich