Trying to make use of older MTH engine with bad boards via Bridge Rectifier and Cap?

You can get aftermarket reverse units from Dallee and other sources.

Welcome aboard Dave, 

It would probably be useful to some of the more knowledgable folk to say what the model number is of your engine, but I'm going to go really generic.  

Assuming all you want is for the engine to move, and don't care about the lights or smoke or anything else, you can probably get away with just the bridge rectifier, and maybe even a single diode. In either case you'll want one rated for more current than the motors can possibly take.  You can measure this with an amp meter and by stalling the motor at full power, but I will guess any single can-style motor won't take even close to 5 amps.  A typical 6 to 8 amp bridge rectifier should do fine, be more than enough, and be easy to find.  

You'll want to check the proper voltage for the motor, if it is a 24v motor than the bridge will be needed to get the full speed from it, but if it is a 12v motor, a single diode may be enough to get it to work without damaging the motor.  

JGL

Hello Again,

Not sure how etiquette works on a forum so I'll respond to both that replied to my question.

Gene H.

 Thanks for the information. I'll look into that Dallee company as an alternative to Electirc RR. Right now I'm saving up....

JGL

The MTH unit is a 20-2241-1, Lehigh Valley, FA-2 ABA. It has two DC motors in each A unit.  I am only going to kluge up the second A unit so I can run it on an outer loop. I like to keep things moving...

I have a 50volt 25amp rectifier in my junk box. I'll give a try with that tomorrow.  I was thinking there was a need for a cap. I guess it might give it a little of a flywheel effect if I did put one in. But that is not needed. I may hook up the interior lights if only to see what happens.

Thanks to you both for taking the time to respond.

Dave

I have done a number of conversions with 8 amp bridge rectifiers, no capacitor. Have hundreds of hours of run time on some of them.

Steve

You can use a bridge rectifier with a 6 amp 50 volt rating and wire the can motors to it. Don't use a single diode! It won't regulate the AC properly. A capacitor isn't needed to run just the motors.

Lee Fritz

Once you have the rectifier, you can use a 3 position E-Unit out of your parts bin if you want to have F-N-R operation while waiting on ERR equipment.

Dave -email me I have a circuit on a PCB that will work perfectly for you. Won't even cost you a penny!

Steve "Papa" Eastman posted:

I have done a number of conversions with 8 amp bridge rectifiers, no capacitor. Have hundreds of hours of run time on some of them.

Steve

Yep it's pretty easy, The bridge rectifier has 4 connections, 2 AC connections  that go to the track, and 2 DC that go to the motor.   

     Interesting post from  jon above.. go for it.

phillyreading posted:

You can use a bridge rectifier with a 6 amp 50 volt rating and wire the can motors to it. Don't use a single diode! It won't regulate the AC properly. A capacitor isn't needed to run just the motors.

Lee Fritz

Lee,

I've obviously not tested anything, but I'm curious why half wave rectification wouldn't work.  The thought only popped into my head because of a recent discussion on triacs and the DCDR in lionel engines, which sends half wave rectified power to the motors in legacy engines, and it seems to work fine.  

JGL

JohnGaltLine posted:

phillyreading posted:

You can use a bridge rectifier with a 6 amp 50 volt rating and wire the can motors to it. Don't use a single diode! It won't regulate the AC properly. A capacitor isn't needed to run just the motors.

Lee Fritz

Lee,

I've obviously not tested anything, but I'm curious why half wave rectification wouldn't work.  The thought only popped into my head because of a recent discussion on triacs and the DCDR in lionel engines, which sends half wave rectified power to the motors in legacy engines, and it seems to work fine.  

JGL

Half wave works but isn't efficient, you end up throwing away half the power. The motor might tend to clock or buzz because there will a switch on followed by a switch off followed by a switch on again in cadence with the 60 Hz input.

Bogie

Does anyone remember the Williams   Die cast GG-1.  Large motors with no fly-wheels and no reverse unit. Just a big diode from the center rollers to the motors .   . Terrible runner. 

In line with what Bogie mentions; AC power cycles from negative to positive 60 times a second here in the USA, so full wave protection is required.  DC power is constant voltage and don't change polarity like AC.

A comment about Lionel engine with Legacy; Lionel must have a special set-up to run with the Legacy engines and I would not attempt to follow that set-up unless you know a whole lot about electrical & electronic work.

Lee Fritz

TonkinWerks posted:

Hello,

New member here.

I was told in passing that I might be able to use an older MTH engine with bad control boards by using a bridge rectifier and

a capacitor. Granted this will only allow one direction operation. At some time in the future I plan to use replacement boards

from Electric RR but for now I would like to use the engine even if only one direction.

Does anyone have any idea of the components / values that might work for an application like this.

Thanks

Dave

My first question to you is, do you understand basic electricity and have you done any electrical work before? If so, it's relatively simple to take out the original electronics and use a bridge rectifier to convert the AC track power to DC for the loco motor. You can also use a manual switch for reversing instead of having to buy an E-unit. I've done this on some O-gauge locos myself.

Can you show us a photo of what you're working on?

OldBogie posted:

Half wave works but isn't efficient, you end up throwing away half the power. The motor might tend to clock or buzz because there will a switch on followed by a switch off followed by a switch on again in cadence with the 60 Hz input.

This was actually the entire point... if the motor is a 12VDC standard can motor, then you want to throw away half the power.  Running a 12VDC motor on 18-24VDC is not a good idea.  Of course with the full bridge, chances are it will fly off the track around a corner before you do much harm to the motors at full power... if you have lighted cars or other things on the track, however, you might want to turn the voltage up a little.  

phillyreading posted:

In line with what Bogie mentions; AC power cycles from negative to positive 60 times a second here in the USA, so full wave protection is required.  DC power is constant voltage and don't change polarity like AC.

A comment about Lionel engine with Legacy; Lionel must have a special set-up to run with the Legacy engines and I would not attempt to follow that set-up unless you know a whole lot about electrical & electronic work.

Lee Fritz

Bogie and Lee, the only difference between full and half wave would be half wave will cycle on and off 60 times a second, and full wave 120 times a second.  Whether half wave or full wave the power is still switching on and off, you need a large capacitor to actually turn that cycling power into DC.  OR... the induction of the motor can be used to store energy between cycles, the motor it's self acting as a capacitor, which is why you don't need true DC to run a motor, 60 or 120 cycle on and off will work just fine.  A motor is not going to care about either once it is receiving enough power not to stall.  

The entirety of lionel's 'special setup' is a small capacitor across the motor.  otherwise it is track power running through a triac to the motor, the triac performing the same function as a diode, with adjustment of how much of the wave is allowed to pass through.  It's really nothing fancy.  

JGL

Anybody else get a bit jealous of those two-rail DC guys, one side of the motor goes to one rail, the other side to the other, and its done?

Hello Everyone,

Again thanks for all the information. It gave me that push to try a few things. Here are the highlights.

1. Put in that 50volt 25amp bridge and it is working great!
    Put on the un-powered B unit and  13  cars and it pulled them without issue.

2. Then wired in the incandescent bulbs for the cab, headlight and engine numbers, Seems to work fine.
    Looks good. This is rectified track voltage after the bridge.

3. Then put in a 7805 voltage regulator (5volt) to drive the Green LED lights(x2). Again looks to be
    working fine also. (NOTE! Watch for ground loop. This and its heat sink are isolated from the
    chassis.)

4. Put in a 2000uf cap to see the effect.
        a. It seems to give or emphasizes the flywheel effect when power is cut and it is winding down.
        b. Again it seems to allow the bulbs to dim off gradually. Kinda cool.

5. But in a fuse holder and for now a 10 amp fuse. An abatement attempt against magic smoke
    generation. I fully acknowledge that all of the above could end up as a molten puddle by the
   end of the day. Would not be the first time!

This should be fine till I get the new board(s) with direction control and maybe even a
sound board.

I have a few more questions you'll see from me in the future.

 My setup is a 5x9 ping pong table I got off Craigslist(broken). Its kind of cheesy but I like it.
3x O gauge loops and a N gauge in the middle.

Two engines I have are Railsounds that I like, the third is a K-line whose sound board source
I'm not sure of.  Maybe Proto?

Thanks Again!
Dave

SantaFeFan posted:

Dave -email me I have a circuit on a PCB that will work perfectly for you. Won't even cost you a penny!

 

Hello Jon,

Looks like I have it for now (as I watch for fumes). I appreciate the offer and would be interested in what the PCB you

mention consists of?

(I gotta confess, I don't really know how to email directly. Still learning the ropes here.)

Thanks

Dave

Here is an attempt to post a picture of the engine as it is currently set up.

Second attempt to post a picture.......Used attachment, the "Insert/edit image" did not have success.

If this was a PS-1 engine you probably could have left the bottom board in, wired in a switch with jump wires and had it run off the bottom board, retain directional lighting and had a switch for selecting direction.  G

Hello,

Thanks for the suggestion.

In this case it is a PS2.

While I am really please with the result so far, your comment for a reversing switch is definitely going on my

next to do list. I think that also is in my junk pin.

Also, If i may ask, since you are a O Gauge / MTH person of knowledge, do you know off hand the

nominal operating type(ac/dc) and voltage level for both the MTH Smoke heater element and the

attached blower motor.

My best guess so far is 3 to 5 VDC for the motor, but the heater element is a toss up. I did get some

good smoke volume on 6.5 VDC pulling about .65 amp. during a short test. Am I close?

I want to use it in a building smoke stack I'm thinking of putting on my table.

Thanks Again!

Dave

Exact voltage is variable by PWM depending on engine.  But a PS-2 smoke unit is two 16 ohm elements in parallel for an effective 8 ohms.  So keeping voltage around 6V or less is about right.

A PS-1 smoke unit is a single 16 ohm provided DC power rectified from track power until about 13V at which point the second resistor is put in series to limit current in the 13-18V range.  Not that a PS-1 engine would be run on that type of voltage.

Fan is about 5V or so.  Slightly lower voltage would be good.  All depends on how much smoke out you want.  G