Wiring a Motor Driver Without Damaging Components

Why You Need a Motor Driver in the First Place

A microcontroller pin can supply perhaps 20 milliamps. A small hobby motor can pull 500 milliamps the moment it starts, and a stalled gearbox motor will happily demand several amps until something gives. Connect a motor straight to a Raspberry Pi or Arduino and you will be shopping for a replacement board before the kettle boils. A motor driver is the middleman: it takes a low-current logic signal from your control board and switches a much larger current from your battery or power supply into the motor windings.

That separation is the whole point, and it is also where beginners come unstuck. The two sides of the driver — logic and motor power — must be wired thoughtfully. Get the basics right and your robot will trundle around the kitchen floor for years. Get them wrong and you will learn the smell of hot silicon.

Check the Polarity Twice Before You Power Up

Almost every motor driver module you can buy in the UK has clearly marked terminals, but the markings are small and the silkscreen is often printed on the underside where you cannot see it once the board is screwed down. Photograph the board before mounting it, or write the labels on a scrap of paper taped to your bench.

• Battery or supply input: positive to VCC or VIN, negative to GND. Reversing this is the single most common way to kill a driver instantly, because many boards have no reverse-polarity protection.
• Motor outputs: the two wires from a DC motor are interchangeable — swapping them simply reverses the direction of rotation. Do not worry about which goes where, but do keep the pair tidy.
• Logic pins: usually 3.3V or 5V tolerant, but check. Feeding 5V logic into a 3.3V-only driver can damage it.

Before connecting anything, set a multimeter to continuity and confirm which terminal is which. It takes thirty seconds and saves a tenner. Also check your power supply voltage against the driver's rating: a driver rated to 12V fed from an 18V tool battery will not last long.

Common Ground Is Not Optional

The logic signal from your microcontroller is a voltage measured relative to ground. If the driver's ground and the microcontroller's ground are not connected, that reference point floats and the driver sees nonsense — twitching motors, random direction changes, or nothing at all.

Run a single wire from the microcontroller's GND to the driver's logic GND. On many modules the logic ground and the motor supply ground are already tied together on the board, but do not assume it. If your board has separate GND pins for logic and power, join them. Keep that ground wire short and reasonably thick; thin jumper leads add resistance that shows up as jitter when the motor draws current.

While you are at it, keep your signal wires (PWM, direction, enable) away from the motor power leads. Motor wires carry fast-switching current and radiate noise. Two or three centimetres of separation is usually enough on a small robot.

Give the Supply Some Headroom

A 6V motor driven from a 6V supply through a driver will not see 6V. Driver chips drop voltage internally, often 1V to 2V depending on the type. Choose a supply a volt or two above what the motor wants, or accept slightly reduced speed.

Also think about current. Stall current — the current drawn when the motor is held still but powered — is typically five to ten times the free-running current. A motor that idles at 200mA might demand 2A when your robot bumps into a skirting board. Size your driver and power supply for the stall figure, not the idle figure, and add a little more for luck.

• Fit a capacitor of around 100µF to 470µF across the driver's supply terminals, close to the board, to smooth current spikes.
• Add a small 0.1µF ceramic capacitor across the motor terminals to suppress brush noise.
• Never disconnect a motor while the driver is powered. The collapsing magnetic field produces a voltage spike that can exceed the driver's rating.

Cooling and Current Limits

Cheap driver modules quote impressive peak currents on the listing, then quietly overheat at half that figure. The copper track on a small board is a poor heatsink, and a bare chip in still air will get hot quickly at anything above an amp or so.

Stick a small heatsink on the driver chip with a thermal pad or a dab of thermal adhesive. If your board has a metal tab with a mounting hole, use it. Give the driver breathing room inside your enclosure rather than burying it under a battery pack, and cut a few ventilation slots if the case is sealed.

Many modern drivers have a current-limit potentiometer. Set it by measuring the voltage across the sense resistor, or simply by running the motor under load and checking the chip temperature with a finger after thirty seconds. Warm is fine. Too hot to touch for more than a second means turn the limit down.

A Safe First Power-Up Routine

Do not simply flick the switch and hope. Work through this sequence instead:

• With power off, check continuity between logic ground and power ground.
• Confirm supply polarity with the multimeter, not by eye.
• Power the logic side alone and check the driver's status LED, if it has one.
• Send a slow PWM signal with the motor disconnected and measure the output terminals — you should see a varying voltage.
• Connect one motor, run it at low speed, and watch the driver chip temperature.

Once that works, wire the second motor and test the pair together. If something misbehaves, power down immediately and recheck your grounds and polarity. Almost every "dead driver" turns out to be a loose ground or a reversed supply, and both are easy to fix if you catch them early. Take your time, label your wires, and your robot will reward you with smooth, dependable motion.