SOLVED: Bachmann E-Z DCC controller, High Track Voltage, and N scale..

[learmoia]

So.. a few questions..

I'm wrapping up construction for a Christmas present first time layout for my nephew, who loves trains but this would be first 'Model train'...

I'm doing the layout in N Scale, and (assuming he enjoys it) he will eventually want to run multiple trains.  To avoid the overall PITA of toggle switches, I wired the layout for DCC, but I wanted a simple DCC system to start so I chose the Bachmann E-Z DCC system.

One problem I'm running into is track voltage..

I found as I was installing decoders into his locomotive, the decoder was getting really hot really quickly, but not burning out..

So after a bit of research, I found out that the Bachmann system puts out alot of voltage.. (16V to the track..) measured on an Tony's Train Exchange DCC volt meter.
(My Digitrax Zephyer is putting out 13.1V and everything is fine.. )

High for HO, WAY too High for N scale.

I've found 2 methods to reduce track voltage..

Method 1:
Replace the power input to the DCC system with a lower voltage, (and the system will supposedly take it (and still work) and then output lower track voltage.)

Method 2:
Build a diode bridge placed between the track power output and the DCC bus to lower the voltage.

In the grand scheme of things, I prefer Method 2, but am not sure how to obtain the parts needed in a post Radio Shack Era, and I don't think I will have the solution complete by next Friday.
Method 1 can probably be accomplished this weekend.

Any thoughts, comments, ideas..?

Thanks ~Ian

 

[djconway]

There was a diode matrix discussed on the old Atlas forum for lowering the voltage on their system. I'll go looking for the thread.

[jagged ben]

I'd probably just go with method 1. 
You asked for thoughts and comments.   

[peteski]

I would also say that method 1 would be preferred.

If there was a Radio Shack within reasonable distance then you could pick up some bridge rectifiers to to the job.  If there are none around then Digikey or Mouser Electronics will ship parts overnight or next-day.  But it the fast shipping will cost you.

I mentioned bridge rectifier because those greatly simplify the circuit construction.  Each bridge rectifier contains 4 diodes and a typical silicon rectifier will drop 1.4V across it.  If you need a hookup diagram, I can draw one up for you.

I'm also a bit puzzled that a decoder would heat up that much from extra few volts at the track. Decoders do not dissipate much power since the motor and function outputs use PWM (the driver transistors do not work in analog mode where they would dissipate lots of extra power and heat up).

[learmoia]

I would also say that method 1 would be preferred.

If there was a Radio Shack within reasonable distance then you could pick up some bridge rectifiers to to the job.  If there are none around then Digikey or Mouser Electronics will ship parts overnight or next-day.  But it the fast shipping will cost you.

I mentioned bridge rectifier because those greatly simplify the circuit construction.  Each bridge rectifier contains 4 diodes and a typical silicon rectifier will drop 1.4V across it.  If you need a hookup diagram, I can draw one up for you.

I'm also a bit puzzled that a decoder would heat up that much from extra few volts at the track. Decoders do not dissipate much power since the motor and function outputs use PWM (the driver transistors do not work in analog mode where they would dissipate lots of extra power and heat up).

The decoder is only getting hot on the board near the LED.. and by hot, I mean too hot to touch within seconds of turning on power.. if I use the Digitrax Zephyr with 13 volts, everything is fine.  I'm not sure who's decoders they are.

What bridge rectifier part(s) would I be looking for?  There are a couple Radio shacks on the way in my travels tomorrow, I might stop and see what they have.

Thanks -ian

[peteski]

What bridge rectifier part(s) would I be looking for?  There are a couple Radio shacks on the way in my travels tomorrow, I might stop and see what they have.

They only have about half a dozen of rectifiers listed on their website.  Depending on how much current the system supplies will determine which rectifier to use.  Always use one rated higher than the maximum current the system can supply. Radio shack has a 1.5A rectifier listed (Catalog #: 2760268) but I would go with the next one up which is rated 4A.  Here are couple:
Catalog #: 2761146
Catalog #: 2761173

They also have 8A and 25Arectifiers (a bit of an overkill), but if those are the only available at the store, they'll work fine. Catalog #: 2761185 and Catalog #: 2761181.

The voltage for all of them is plenty high (50V or higher).

[nscaler711]

I've got the EZ DCC system, and I run N scale.
But I have never had any of my decoders blow up, or get hot enough to notice.
So I don't see what the problem is with the systems voltage.
Seems to work just fine for me, when I'm not using my MRC Prodigy Advance....

[cgw]

Digitrax makes a diode reducing module for Z scale  UP6Z.  It reduces track voltage by 4 or 6 volts at 3 amps for safer  locomotive operation.   If you search Atlas Web site they listed instructions on how to reduce the track voltage down.    The lenz compact system (rebranded as Atlas) cranked out 16+ volts to the track and would let the smoke out of decoders.  The diode reducer would knock it down to a safe 12~13 volts.  MRC sold a small diode  reducing board but it is not longer available.

The diode bridge would be the fastest and cheapest way to do it.

[peteski]

I think that Ian is just overly cautious, but it is his prerogative .  From his description it is most likely the headlight current limiting resistor which is getting warmer than he is used to.  But there is nothing wrong with wanting to run his trains using a lower voltage.

[learmoia]

I think that Ian is just overly cautious, but it is his prerogative .  From his description it is most likely the headlight current limiting resistor which is getting warmer than he is used to.  But there is nothing wrong with wanting to run his trains using a lower voltage.

Yeah, I want everything to be user friendly..  the decoders are getting warm enough that they warped nearby plastic while I was testing, so it's an issue I want to address.

No luck at radio shack.. because there was no radioshack..    And it was still listed on the company website.

So..   I don't think this will get resolved before christmas..

I think I'm going to go the bridge rectifier route.

It appears this would be the drawing diagram.

http://www.atlasrr.com/voltage.htm

[peteski]

Like I said, Digikey or Mouser Electronics have what you need (and then some). They offer many shipping options (2-day shipping might be a good option).

That diagram is correct. 

[learmoia]

I called a local mom+pop electronics store (not radioshack) and they can get 400v 5a bridge rectifiers (smallest they couldnorder) on Wednesday, so I put in an order.

Down to the wire but making progress.~Ian

[C855B]

... From his description it is most likely the headlight current limiting resistor which is getting warmer than he is used to. ...

Based on my experiences, the heat in this case is probably from a good ol' fashioned brute-force regulator (78xx family and descendants). These get stupid hot if you attempt to pull down more than double their rated output, regardless of actual output load. Without having it in front of me, I would guess this is the main regulator for the microcontroller logic. Yes, the right thing to do is lower the supply voltage, and eating up a few volts in diode drop is as good a way as any.

[peteski]

Mike, in my experience I never seen a decoder using that type of voltage regulator. ALos, most of the microprocessors on decoders run off 3 volts.  That is why decoders can run starting on fairly low analog DC voltages. Only the microprocessor section of the decoder needs somewhat regulated voltage. Rest of the decoder (functions and motor drive) run off the raw rectified voltage.

The microprocessor (microcontroller) uses a tiny amount of current (microamps or at most most  few milliamps).  No need for a brute 78XX series voltage regulator.  Most decoders use a simple resistor and a  Zener diode to regulate the voltage and a small tantalum cap to smooth it out  That circuit doesn't really get warm, even with higher track voltages.

[C855B]

[shoulder-shrug]

Just a SWAG. Yeah, a zener, etc., would make sense with the very low currents of the uC. I've just had a fair amount of firsthand experience with 78xx/79xx regulators where increasing the source voltage very little changed it from "warm" to finger-burning HOT. Had to do two-step regulation to tame that stuff.