This article provides a step-by-step guide to building a DC generator capable of charging 12V, 24V, 36V, and even 48V batteries. This project repurposes common components like an Old Treadmill Motor and a small gas engine to create a charging station for off-grid situations.
STEP 1 : The Materials Required
- Discarded treadmill with DC motor
- Small engine (e.g., 3 HP Predator engine from Harbor Freight)
- V-belt pulleys,5/8″ bore 3.5
- V-belt,1″ bore 3″
- Metal brackets and hardware
- Welding equipment
- Angle grinder
- Drill
- Victron charge controller, 250/100
- Circuit breakers,125A Nader Circuit Breaker,16A, DC circuit breaker
- Choke
Step 2 : Motor Extraction and Inspection
Unplug the treadmill and remove the cover.Locate the DC motor. This is usually found underneath the running belt. Carefully inspect the motor for any visible damage. The motor in this project had a label indicating it’s a 2.5 horsepower motor, running on 130 volts DC.To ensure the motor is functional, connect its leads to a power source that matches its voltage. Once the motor is confirmed to be working, detach it from the treadmill frame.
Step 2 : Preparing the Motor Shaft for a V-belt Pulley
Clean the Motor Shaft: If the original pulley was welded, you’ll need to clean the shaft to prepare it for a new V-belt pulley. You can use an angle grinder to remove any welding residue.
Select a V-belt Pulley: Choose a pulley that fits the motor shaft snugly and accommodates the desired V-belt size. In this project, a 3-inch pulley with a 1-inch bore was selected. You may need to modify the pulley’s bore size to fit the motor shaft.Once the pulley is prepared, carefully install it onto the motor shaft, ensuring it is securely fastened.
Step 3 : Assembling the Generator
Cut and weld metal pieces from the treadmill frame to create a support structure. Reattach the motor with the new pulley to the treadmill frame using its original mounts.Securely mount the gasoline engine to the treadmill frame, ensuring its pulley aligns with the treadmill motor pulley.
Connect the two pulleys with a V-belt, adjusting the engine’s position to achieve the desired belt tension. You can use a straight edge across the belt to assess the tension. Aim for approximately 1 inch of deflection in the belt.
The treadmill likely has a linear actuator used to adjust the incline of the running belt. You will repurpose this for adjusting the V-belt tension. Remove any wiring or components related to the treadmill’s control board from the actuator, keeping only the mechanical parts necessary for adjustment.
Determine a suitable spot on the frame where the linear actuator can be mounted to effectively adjust the tension of the V-belt.Securely attach the linear actuator to the chosen location on the treadmill frame. You may need to cut and weld additional metal pieces to create suitable mounting points.
Step 3 : Wiring and Electrical Components
Identify the positive and negative leads of the treadmill motor. Connect these leads to the appropriate terminals on the charge controller.Install a 16-amp circuit breaker between the motor and the charge controller, and a 100/25 amp circuit breaker between the charge controller and the battery.Connect the charge controller and circuit breakers to a din rail box for a clean and organized setup.
To prevent AC spikes from the brushes reaching the charge controller, install a suitable inductor in the wiring. incorporating an inductor choke into the circuit, the high-frequency AC spikes generated during commutation are suppressed. The inductor effectively acts as a low-pass filter, allowing the desired DC current to flow while blocking the unwanted AC noise.
Locate the wire coming directly from the positive (+) terminal of the DC motor. This wire carries the motor’s output current.Carefully cut this positive lead, creating two separate segments.Connect one end of the inductor choke to the segment of the positive lead still attached to the motor’s positive (+) terminal.
This connects the inductor directly to the source of the AC noise. Connect the other end of the inductor choke to the positive (+) input terminal on the charge controller. This ensures all the motor’s output current, now filtered by the choke, flows into the charge controller.Connect the negative (-) lead from the treadmill motor directly to the negative (-) input terminal on the charge controller. This completes the circuit for the motor’s output to reach the charge controller.
Step 4 : Testing and Evaluation
Connect a 12V battery to the charge controller and start the gasoline engine. Observe the voltage reading on the charge controller to confirm the system is generating power.
Connect different voltage batteries (e.g., 48V) to test the versatility of the charger.Observe the engine speed, amperage output, and charging time to assess the charger’s efficiency.
Image Credits : DavidPoz
