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Hi,

Just wanted to know how to convert my MTH Z 4000 3 rail transformer to use for two rail. I see rectifiers advertised on eBay and was wondering if that is all I need or do I need something more or is their a better option ?

Thank You,

Kenneth

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Last edited by Kenneth Willis
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A bridge rectifier is all it takes, but the one you posted seems pretty expensive to me.

As long as it handles 50 volts or more and 6 amps or more, it will be fine. As you become  more advanced electrically, you can add a double pole, double throw switch to reverse your train's direction without swapping wires around.

Last edited by RoyBoy

I don't think you need those jumpers I see.  Try to find one with just wire connected and no jumpers.  Here is a link explaining the switch and how it works.  Also, I  included a badly drawn sketch of what you want to do.  the dots in the sketch are the terminals on the switch.  When you move the switch the connections change in the terminals on the right side.  The two terminals on the left are typically the two in the middle of the switch.

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Here is a better diagram of how to wire a Double Pole, Double Throw (DPDT) switch to change the polarity of the  DC for reversing. This is what's called an "ON-ON" switch with no center off position. You don't want a center off position (ON-OFF-ON) for a reversing toggle. Grainger has them for $3.99.

No matter what make of DPDT switch you buy, you will have to add the "X" jumpers to the switch.

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@hokie71 posted:

I don't think you need those jumpers I see.  Try to find one with just wire connected and no jumpers.  Here is a link explaining the switch and how it works.  Also, I  included a badly drawn sketch of what you want to do.  the dots in the sketch are the terminals on the switch.  When you move the switch the connections change in the terminals on the right side.  The two terminals on the left are typically the two in the middle of the switch.

Not correct. Those jumpers are exactly what the OP needs to reverse the DC polarity and reverse the train direction.

@Bill N posted:

Why would you choose to convert an AC transformer...?

Because it's the cheapest/easiest/smartest way to go and have adequate power and voltage control and meters.

I don't know what a two rail, O gauge DC power supply and voltage controller costs, but the bridge rectifier and switch are less than twenty five bucks.

The MTH Z-4000 is already designed to run trains. All it needs is a rectifier and a reverse switch.

Last edited by RoyBoy

What is the "AMPS" reading on your Z-4000 throttle that is hooked to the bridge rectifier?

Multiply that number by 2.  In round numbers this is the WATTS of power that the bridge rectifier is generating as heat in doing its task of converting AC to DC.

So if the AMPS reading is 0.5, then 2 x 0.5 = ~1 Watt.  The bridge rectifier will feel warm.

If AMPS is, say, 2.0, then 2 x 2.0 = ~4 Watts.  The bridge rectifier will feel very warm and likely too hot to handle.

If AMPS is, say, 5.0, then 2 x 5.0 = ~10 Watts.  The bridge rectifier will likely burn your finger.

What you can/should do is fasten the bridge rectifier to a piece of scrap metal to act as a heat-sink to pull the heat away from the bridge rectifier.  If using a bridge that looks like your initial photo, that's why there's a mounting hole in the center!  You're "supposed" to use heatsink compound to make for better heat transfer to the metal plate.  But heatsink compound is annoyingly over-priced and my experience just about any kind of household Lithium grease or the like is good enough.

business opportunity

What I find amusing is the eBay listing from the original post suggests over 100 have been sold.  You can buy these bridge rectifiers for maybe $1-2 a piece in small quantities and well less than $1 a piece at, say, 100 pieces. 

So rename the bridge rectifier as an AC-to-DC converter for trains and charge $16.99 (plus shipping).  As they say, America is the land of opportunity!

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