The most frequent cause of burnt out speed controls that I have seen is user error. The user gets the plus and minus leads reversed and the control is burnt up in a couple of seconds or less. The owner's manual recommends using a fuse on the input, but a lot of people don't bother. The second most common cause is water; the boat sinks or gets swapped and water gets into the control. Although pure water will not conduct electricity, most of the water we sail our boats in is a lot less than pure. Water causes a short in the circuit and once again, the control burns up. Our solution to the input protection problem is to build the fuse right into the control.
Our SCO-30 (above) was the first Smartcontrol to feature an on board fuse, followed by the SCT Mk2 a couple of years later. Now the SCO-10 and 20 controls also have input fuses.
The fuses used on the Smartcontrol are the same automotive fuses used in today's automobiles. That means you can buy them at any service station or auto parts store. It is easy to tell a blown fuse from a good one, even without a meter. Simply hold it up to a light as shown below. The fuse on the left is the good one, the one on the right is clearly blown.
Another way to damage a control is a short on the output side or a stalled motor. If the motor stalls because the prop is fouled, the electrical resistance of the motor drops down to almost zero. Smartcontrol has always featured automatic current limiting, even our very first model, the SC-5 (long out of production). Once the current reaches the limit, the control will automatically shut down. The user must move the stick on the transmitter to the center (off) position to restart the control. The current limiting has a start-up delay period of 1/10 of a second (2/10 on the SCO-30). During the first 1/10 of a second after moving the stick from the off position the current limiting will not activate. This allows for high current surges when the motor is starting.
Click on the picture above to view a video of me shorting the motor terminals together with a screwdriver while the motor is running at full throttle. This is just part of the normal testing on a Smartcontrol. Don't try this on a your speed control unless it is a Smartcontrol!