Motor Circuit Diagramsvoltage converter

Converting a DCM Motor Schematic Circuit Diagram

Recently, we purchased a train set from a well-known company and couldn’t resist examining the locomotive’s interior. Despite featuring an electronic decoder, the DCM motor inside was actually introduced 35 years ago. It’s probable that financial constraints led to the use of this motor, considering Märklin (as you might have guessed) also offers a modern 5-pole motor in their lineup. Interestingly, they have recently introduced a brushless model as well. The DCM motor in our locomotive remains an outdated 3-pole series motor utilizing an electromagnet for propulsion.

Converting a DCM Motor Schematic Circuit Diagram

Introduction to Motor Modification

The new 5-pole motor features a permanent magnet, prompting the exploration of enhancing driving characteristics by separately powering the field winding. Utilizing a bridge rectifier and a 27 Ω current-limiting resistor was considered to create an effective permanent magnet, improving low-speed driving characteristics while maintaining initial acceleration.

Initial Experimentation and Challenges

While the modification led to improved driving at lower speeds. A constant 0.5 A flowing through the winding raised concerns about track power wastage. To address this, a small circuit was devised to reduce the current to less than half, rendering the technique more efficient. Disconnection of the field winding from the rest and the addition of a freewheeling diode (D1, Schottky) across the entire winding were pivotal steps in the modification process.

Operation and Continuous Current Regulation

The circuit operates by turning on FET T1, gradually increasing the current in the winding until it reaches 0.5 A. At this point, the voltage drop across R4-R7 exceeds the reference voltage across D2, causing the opamp to turn off the FET. Current continues to flow through the winding via D1, gradually decreasing. When the current drops by approximately 10% due to hysteresis from R3, IC1 turns on T1 again, restarting the cycle. This continuous process maintains a fairly constant current through the field winding, effectively imitating a permanent magnet.

Efficiency and Power Consumption

One of the advantages of this circuit is its minimal total current consumption. Approximately 0.2 A, despite the continuous 0.5 A current flow through the winding. This modification was pursued to facilitate the conversion of the locomotive for DCC decoder use. A new controller was necessary because changing the rotor winding’s direction of rotation requires reversing its polarity. A task handled in the original motor by using the other half of the winding. While a non-electrical solution involving a permanent magnet was viable. The availability of electronic components from the spare parts inventory made the electronic modification a practical choice.

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