Refuse To Fuse

Say good-bye to traditional fuses, and say hello to Intelligent Switches.

At Autosound 2000, Richard and I have been writing about performance and high-end car audio for over ten years. One of our long-standing problem areas has been with the use of fuses on power cables for “high performance” car audio systems. The word “fuse” comes from the French and means “to melt.” In order for a fuse to melt, there must be a difference in potential across the fuse element. As more current is passed through the fuse, the voltage drop across the fuse increases, and the fuse element continues to heat. On a car’s fuel line, this is like using a valve that decreases the fuel as the throttle is increased. When the most current is needed, the most restriction is added to the power circuit. After 200+ years of using high current fuses, technology has come up with a solid-state replacement — the Intelligent Circuit Breaker.

Back in 2001, we began testing devices known as Intelligent Switches for a company called IntraUSA in Seattle, WA. These microprocessor-controlled switches are constructed with parallel MOSFETs and then encapsulated into relatively small extruded metal enclosures. The reason for the small size is that there is little or no heat sink required because the voltage drop across the switch is on the order of milliVolts — even when carrying 100, 250, 500 or 1000 amps! By clever programming and packaging, Intra’s Intelligent Switches soon became SoundGate’s Intelligent Circuit Breakers, or ICBs, and were recently introduced into the car audio market.

Intelligent Circuit Breakers
Basically, an ICB looks and functions like a mini dual-battery isolator, however, the voltage drop across a dual-battery isolator at 500 amps would surely limit a “high-end” car audio system. Also, a dual-battery isolator under such conditions would require massive heat sinking fins and large cooling fans. Additionally, the diodes in a dual-battery isolator build up more and more heat as the current increases. This is the same situation as for a fuse. Just when the most current is needed, the dual-battery isolator consumes a maximum amount. The ICB solves this problem because the voltage drop across the semiconductor devices is incredibly small.

Let’s say that the goal is to connect a car’s battery to a secondary battery that powers the car stereo equipment as soon as the engine is started. An ICB with a 100-amp threshold would certainly handle this task for most vehicles. Connections require that one terminal of the ICB connect to the + battery post of the car’s battery, the other ICB terminal connects to the + battery post of the secondary battery, then there’s a small connection to chassis ground, and a control lead. As soon as the control lead is connected, or the manual RESET button depressed, the ICB’s solid-state switch closes.

Each ICB has a pair of microprocessor-controlled blue LED status indicators that continuously monitor the operation of the device. By blinking specific codes, status functions such as On, Off, Over Temperature, Severe Overload, and Short Circuit conditions can be displayed remotely and on the ICB.

Short Circuit or Catastrophic Overload
The SoundGate ICB-100 is factory programmed to automatically open if the 100-amp limit continues for longer than 15 seconds. When this occurs, the intelligent switch contacts open and the blue LED repeatedly blinks nine times, indicating the overload. A quick press of the reset button returns the ICB to normal operation. The reset button is located on the ICB-100, or can be remotely controlled. The pre-programmed, 100-amp limit is normal overload and could be used to protect power amps and other vehicle equipment. It’s important to note that the current through the ICB is accurately gauged by the microprocessor’s internal current and voltage sensors.

There’s another, more serious, condition that we must never overlook in aftermarket car audio. This condition is the short circuit or catastrophic overload that could happen in the event of a vehicle collision. Competitive car audio mandates a main power fuse, or circuit breaker, be placed a short distance from the + battery post(s). In the event of an accident, this fuse protects the car, and the passengers, from the tremendous energy stored in the car’s battery. If the main power cable of an ICB is short circuited to chassis ground, the switch will open within 5 mS (.005 seconds). Again, the ICB must be manually reset to restore operation. Installation for this situation would be to place the ICB close to the car’s battery, just like with a main power fuse.

Versatility
There are currently four ratings for SoundGate’s ICBs: ICB100, ICB250, ICB500, and ICB1000. The most popular is the 100-amp ICB-100 which retails for around $249.95 and can be interfaced to a $24.95 ICBCABLE for remote control and monitoring. Other uses include an automatic high-temperature disconnect that opens the switch contacts when the ambient heat becomes excessive. The ICB can also be used to charge Stiffening Capacitors quickly and safely without the small resistor.

Up at the IntraUSA plant, we observed a huge diesel truck started with one of the solid state switches. The truck’s mechanical solenoid was replaced with the electronic switch which was connected to an automatic sequencer. The system was programmed to start the truck every few minutes for many months. The ICB has never failed.

Seasoned car audio competitors Mark Eldridge and Gary Biggs recently went “fuseless” and equipped their award-winning vehicles with several ICBs. This upgrade really makes sense for competition and for all high-performance systems.