How to Generate Off Grid Power using a Car Alternator and an exercise bike.

This project goes into the building of a DIY pedal-powered generator out of an old car alternator and a bike. This generator is useful for powering your devices and gadgets in case of a grid-down scenario.


The materials you need to build this generator are bike, MDF for the base plinth, magnetic trainer stand for bike, Alternator, drive belt, 12V battery, cable connectors, 12V socket, multimeter, screwdriver, and insulation tape.



The rear end of the bike and the rest of the components are mounted on a one-inch thick MDF board. This has a good amount of stability that keeps it away from moving around. We add an extension bit on the front. The extra height there just compensates for the fact that the back wheel is in a stand.

The alternator is mounted nice and secure onto the base using brackets. Bolts connect the alternator to the brackets and screw the brackets down to the base. Once you are pedaling, and you have got an electrical load in the circuit, there is quite a bit of force pulling the alternator forwards. So it does need to be really securely bolted down.



Make sure that the wheel of the bike is in line with the alternator pulley. With any wheel, we have a rim bed and rim walls. Here what we need is a drive belt that fits purely in the rim bed. Make sure you measure the internal width of the rim bed.

Also, measure the width and depth of the alternator pulley grooves and get a belt that fits accordingly. Also, make sure you have got a belt that is long enough because a typical drive belt that is used in a car is not going to be long enough because it is only made to go around a pulley on the engine.



The car alternator used here has three wires coming out of them.It has a main power thick output wire, it supplies main power to the devices. Then there are two small cables, one for voltage sensing and the other for field coil ignition. The voltage sensing wire goes straight to the 12V lead-acid battery in our case. To get the alternator to generate power you first need to apply a small voltage through the field coil and that is because an alternator doesn’t have any permanent magnets in it.

The way that any generating device works is by moving either electrical charges through a stationary magnetic field or moving a magnetic field around a charge. So the field coil inside the alternator is attached to the field coil ignition cable, and putting a voltage generates the magnetic field, which enables the alternator to generate power when you turn the shaft via the drive belt. You don’t need to keep applying a voltage to it as it’s running, because it will generate its own power. The negative from the alternator is connected to the negative of the battery.

The positive connection from the alternator is connected to the positive of the battery. The third connection coming from the alternator is the field coil activator. This is connected to a switch. The connection goes back to the alternator to activate the field coil.



A standard cigarette lighter socket is connected to the battery terminals. It will draw power off the battery first, and once you start charging power because the alternator is connected to that, it is going to draw it from the alternator, and the alternator will simultaneously power whatever is connected to that socket, and recharge the battery.

The alternator used here has a voltage tolerance of 11 to 14V. A Modular splitter is connected to the cig power socket to charge multiple devices. Make sure that the plug comes with a fuse or whatever you plugin needs to be rated to the right power for what you are going to charge.



To run alternating current devices, we connect a 150W Power inverter to the circuit. The alternator actually generates alternating current. But it’s got a rectification circuitry built into it, which changes it to DC. The inverter changes the DC output from the alternator to AC.

Finally, we add a master switch that switches the battery on. The Power switch stops any drain from the battery through the field coil. The switch also connects the multi sockets that charge various devices. It isolates the battery from the circuit. It isolates the alternator from the circuit, and it isolates the remote switch and the battery from the field coil completely.

The AC generating device like an alternator has a minimum speed of operation in which they are stable. So do check for your alternator, what is the recommended minimum speed for it. If you spend it below that speed, what happens is because of the way it works, you get a periodically varying force that acts as a resistance to your pedaling.

Image Credits : Systemic Creative

Leave a Comment