Okay, let's break down why directly connecting a 115V DC motor to 120V AC is a bad idea and what you'd need to do to make it work (if it's even feasible).

Why it's a Bad Idea (Don't Do This!) Different Voltage Types

DC (Direct Current) flows in one direction, while AC (Alternating Current) changes direction rapidly (typically 60 times per second in the US). A DC motor is designed to receive a constant voltage in one direction.

Voltage Mismatch

Even if you could connect it, 120V AC often has a peak voltage higher than 120V. Also, a 115V DC motor is rated for 115V DC. Applying a higher voltage, even if it were DC, could damage it.

Motor Design

DC motors have different internal components (like the armature and field windings) designed for DC operation. AC will induce unwanted currents and magnetic fields, leading to overheating, arcing, and rapid failure.

Lack of Rectification

You're essentially trying to force alternating current into a device that expects direct current. Without converting AC to DC, the motor will likely just vibrate and fail quickly.

How to (Potentially) Make It Work (But Consider Alternatives)

You would need to convert the 120V AC into approximately 115V DC. This requires several components:1. Transformer

Step down the 120V AC to a lower AC voltage. You would need to calculate the appropriate transformer output voltage based on the voltage drop in the rectifier and filter circuits. A reasonable guess would be a transformer that outputs somewhere around 90-100 VAC. You need to ensure the transformer is rated for sufficient current (at least 10 amps on the secondary side, preferably more for headroom).2.

Rectifier

Convert the AC voltage to pulsating DC voltage. A bridge rectifier is the most common and efficient choice. It uses diodes to allow current to flow in only one direction. You'll need diodes rated for the voltage and current requirements (at least 200V and 10A, with a safety margin).3.

Filter Capacitor

Smooth out the pulsating DC voltage from the rectifier into a more stable DC voltage. A large electrolytic capacitor is typically used. Calculating the required capacitance is complex and depends on the load current and desired ripple voltage. A reasonable starting point would be a capacitor in the thousands of microfarads (e.g., 4700 uF or 10000 uF) with a voltage rating of at least 160V.4.

Voltage Regulator (Optional but Recommended)

This helps maintain a constant 115V DC output, even if the AC line voltage fluctuates or the motor load changes. You could use a linear regulator (like an LM338) or a switching regulator. A switching regulator is more efficient.

Important Considerations and Warnings



Safety

Working with AC power is dangerous. High voltages can cause electric shock and death. If you are not comfortable working with AC circuits, do not attempt this. Consult a qualified electrician. Always use appropriate safety precautions, including proper grounding, insulation, and circuit protection.

Component Selection

Choosing the right components is critical. You need to consider voltage, current, power ratings, and heat dissipation. Undersized components can fail catastrophically.

Heat Dissipation

Rectifiers and voltage regulators can generate a significant amount of heat. You may need to use heat sinks to prevent them from overheating.

Motor Type

Is this a brushed or brushless DC motor? Brushed motors are more common and will work with a simple rectified and filtered DC supply. Brushless motors require a more complex electronic controller.

Alternatives



DC Power Supply

The simplest and often safest option is to buy a pre-made 115V DC power supply rated for at least 10 amps (and preferably more). This is the recommended approach.

Variable Frequency Drive (VFD)

VFDs are typically used for AC motors, but some can be used with DC motors (though less common). Check the VFD's specifications.

Simplified Example (Illustrative, Requires Careful Design)

120V AC --> Transformer (120V AC to ~90-100V AC) --> Bridge Rectifier --> Filter Capacitor (Large Value, High Voltage) --> (Optional) Voltage Regulator (to output 115V DC) --> 115V DC Motor

In Summary

While technically* possible to convert 120V AC to 115V DC for your motor, it involves designing and building a power supply, which requires electrical knowledge and carries safety risks.

Buying a pre-made 115V DC power supply is almost always the better, safer, and more reliable solution. If you insist on building your own, proceed with extreme caution and consult with someone experienced in power electronics. Flag for review