Battery Substitutes for MTH Engines
 

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Battery Substitutes for MTH Engines

Shared by Sam Dillon aka rrman on OGR Forum in November 2011

3 Volt - See assembly process here.

For 3V cell:
2) 647-JUMT1335MPD $3.04ea $ 6.08 3.3F@ 2.7V capacitor
1) 78-1N5227B $0.07ea $ 0.07 3.6V zener diode
TOTAL $ 6.15
Wire capacitors in series and place a 1N5227B diode across total, band end towards capacitor +. Removed the 3V battery pack from loco, opened sleeving, unsoldered connector wires then soldered red lead to capacitor + and black lead to capacitor -. Cover with 3/4" heat shrink tubing and done.

3V 1

More detailed view of 3V top connections 3VtopCloseup

3V 2

3V 3

3V 4

9 Volt

Mouser components:

For 9V cell:
4) 647-JUMT1335MPD $3.04ea $12.16 3.3F@ 2.7V capacitor
4) 78-1N5223B $0.07ea $ 0.28 2.7V zener diode
1) 534-81-8TB $0.35ea $ 0.35 9V battery connector with leads
TOTAL $12.79
Wire capacitors in series and placed a 1N5223B across each one, band end towards capacitor +. Connected the 9V snap connector red wire to negative and black wire to capacitor positive (because we are now reversed in how current is flowing i.e. we are sourcing current rather than receiving power.) [See Q & A] Cover with 3/4" heat shrink tubing and done.

9V 1

9V 2

9V 3

9V 4

 

Q & A Concerning Socket Polarity

Question - I am a little confused about the polarity. You say in the directions:
"Connected the 9V snap connector red wire to negative and black wire to capacitor positive (because we are now reversed in how current is flowing i.e. we are sourcing current rather than receiving power.)" for the 9 volt.
And for the 2.4 volt: "unsoldered connector wires then soldered red lead to capacitor + and black lead to capacitor -"
The pictures show the same. This seems to me that one or the other is incorrect.
Could you please verify which is correct?

Answer -
For Radio Shack 9V connector (or what ever generic off the shelf 9V connector used), internally the red wire is connected to the snap that goes to the battery + terminal, the black goes to connecter snap that goes to battery - terminal. Because we are now using this Radio Shack connector "backwards" to connect to our capacitor cell to MTH 9V connector, we have to connect the capacitor cell + terminal to the 9V connector black wire and connect the capacitor cell - terminal to the 9V connector red wire. This is done so the capacitor cell + polarity "lines up" with the MTH 9V connector + snap, and the capacitor cell - polarity "lines up" with the MTH 9V connector - snap.
For the 3V cells, I simply removed the connector with attached wires from the battery + and - tabs then connected them to the capacitor cell + and - respectively since this connector's polarity is already correct for battery so it can be directly connected to the respective capacitor cell terminals that functions as battery.

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