Rectifier for locomotive

[rockershovel]

I’ve just acquired an early 90s, 3-rail MTH O Gauge K4 locomotive which, like most such devices is designed to run on 20v AC, rectifying this to 12v DC for the can type motor. It has some rather curious electronics which are best described as “pre-DCC pseudo-DCC” and as seems common, they have long since ceased to work reliably, if they ever did work that is; this one doesn’t seem to have seen much use. 

 

Another loco in the same box, looks like this inside; the previous owner has apparently lost patience and stripped the electronics, replacing them with a rectifier (the loco runs nicely on AC or DC, but won’t reverse direction). 

 

 

I’d like to convert the electronics on the K4 to run on AC or DC, although just DC would be acceptable, especially if it would reverse on DC. So, I need a rectifier, and I’m open to suggestions. 

 

I don't understand electronics and have less than no inclination to educate myself on the subject. This isn’t a DCC conversion project, nor am I interested in endless debate on the subject; any such posts will be deleted. I am looking for a rectifier, consistent with my “black box” level of understanding. Any suggestions? 

 

[sncf231e]

25 minutes ago, rockershovel said:

 

 

although just DC would be acceptable, especially if it would reverse on DC. So, I need a rectifier, and I’m open to suggestions. 

 

 

 

Just connect  a wire from the center rail pick-up to one side of the can motor and a wire from the wheel pick-up to the other side of the motor and you can run DC and reverse by reversing the voltage. No rectifier needed.

I have done the same with my MTH Berkshire when the electronics stopped working. Runs OK as you can see:

 

Regards

Fred

BTW: with only a rectifier and no extra electronics or switches it will not be possible to run on AC in two directions.

Edited February 13, 2020 by sncf231e

[rockershovel]

That’s probably what I’ll end up doing. It runs nicely when it runs, and it’s primarily a loco for club outings like NAROGG where losing the sound effects, isn’t important. 

 

The loco I illustrated appears to have a rectifier fitted to power the headlight and firebox glow, but in the process has ended up losing its reverse in consequence. If I do this to the K4 as a temporary measure, I’ll separate the power supply so it will reverse from track current on DC

[sharris]

There's quite an involved discussion of the reversing and sound effects control system on another forum - it's a lot more complex than I was expecting!

 

https://ogrforum.ogaugerr.com/topic/which-3-rail-trains-will-run-on-straight-dc

[rockershovel]

29 minutes ago, sharris said:

There's quite an involved discussion of the reversing and sound effects control system on another forum - it's a lot more complex than I was expecting!

 

https://ogrforum.ogaugerr.com/topic/which-3-rail-trains-will-run-on-straight-dc

 

That’s heavy stuff, even by OGRR standards... the crux of my problem is, that MTH tried to run too many features, from a power supply with an insufficient number of insufficiently differentiated commands, resulting in a loss of functionality and reliability, and a tendency to become locked into loops. 

 

DCC, powered by modern electronics, provides the command system necessary to run so many features. 

 

 

[rockershovel]

1 hour ago, sncf231e said:

Just connect  a wire from the center rail pick-up to one side of the can motor and a wire from the wheel pick-up to the other side of the motor and you can run DC and reverse by reversing the voltage. No rectifier needed.

I have done the same with my MTH Berkshire when the electronics stopped working. Runs OK as you can see:

 

Regards

Fred

BTW: with only a rectifier and no extra electronics or switches it will not be possible to run on AC in two directions.

 

Is that a Williams brass Scale Hudson? 

[melmerby]

1 hour ago, rockershovel said:

That’s probably what I’ll end up doing. It runs nicely when it runs, and it’s primarily a loco for club outings like NAROGG where losing the sound effects, isn’t important. 

 

The loco I illustrated appears to have a rectifier fitted to power the headlight and firebox glow, but in the process has ended up losing its reverse in consequence. If I do this to the K4 as a temporary measure, I’ll separate the power supply so it will reverse from track current on DC

Can't see the point of a rectifier for the lights, unless they are LEDs

You could power the motor direct from the track as has been suggested for DC operation, if the lights are LEDS, connecting them through a bridge would maintain the correct polarity.

[rockershovel]

1 hour ago, melmerby said:

Can't see the point of a rectifier for the lights, unless they are LEDs

You could power the motor direct from the track as has been suggested for DC operation, if the lights are LEDS, connecting them through a bridge would maintain the correct polarity.

 

They are indeed, LED lights. 

 

The loco illustrated has combined power, ie it will run on AC or DC, so the train current passes through the rectifier. For the K4 I’ll have two separate circuits - the existing one for lights and markers, and a separate tapping for DC traction current. That way I retain reversing function, at the expense of AC running 

[sncf231e]

11 hours ago, rockershovel said:

 

Is that a Williams brass Scale Hudson? 

Yes, the video description is:

"A New York Central 4-6-4 Hudson being an older Williams 3-rail AC brass model and a Nickel Plate Road 2-8-4 Berkshire from MTH with all electronics removed and running on DC with a mixed good train running in the garden."

So I changed power supply between running the two locomotives; easy with a power supply cart like this:

 

 

Regards

Fred

 

[rockershovel]

I do like the power supply cart, I must do something like that! 

 

For some reason the full description you quote, doesn’t appear in the link? 

 

I have a Williams brass USRA Pacific with no sounds fitted, runs fine on either 12v DC or 20v AC. So does my Williams diecast Hudson.