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Multiplexing Wiring Kit - Multiplexing For Hot Rods
Simpler, Lighter, And More Reliable: ISIS Multiplexing Electrical Technology Is Now Available For The Performance Market. January 01, 2010
By Marlan Davis
Photography by Marlan Davis
www.hotrod.com In an effort to improve reliability, reduce costs, lighten cars for improved mileage, and ease diagnostics, new-car manufacturers are radically redesigning their electrical systems, embracing a technology known as multiplexing. Thanks to solid-state microcontrollers and logic devices, wiring engineers are able to design a multiplexed system wherein multiple analog or digital inputs are combined (or multiplexed) at one master logic center, transmitted over one pair of wires to a remote module, and then distributed (or demultiplexed) for output to various electrically operated devices. The new ISIS (Intelligent Silicon Integrated System) brings the same technology to the aftermarket for hot rodders and racers alike in a user-friendly, reprogrammable package.
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Multiplexing Wiring Kit - Multiplexing For Hot Rods The ISIS multiplexing wiring system could revolutionize the way hot rods are wired, saving time and weight, easing diagnostics, enhancing vehicle security, and eliminating most daisy-chained electrical relays and in-line switches.[/align]
Why Multiplexing? Fuel injection, electric fuel pumps, electric fans, cruise control, multistage nitrous systems, antiskid brakes, high-zoot sound systems, electric power steering, and power windows, seats, and door locks have vastly increased the complexity of many modern hot rodders' wiring needs. Even with a more basic old-school hot rod or race car, the number of remote relays and daisy-chained circuits and controllers takes up space and adds weight-from all the add-ons, as well as from the added weight of the heavy-gauge wiring needed for their interconnection. And no matter what the application-from no-frills to power everything-custom wiring is one of the most time-consuming and expensive parts of any project, requiring days to lay out wires from separate control switches to components, routing power lines, and testing and troubleshooting circuit integrity.
With ISIS, wiring becomes dramatically easier because multiple wires no longer run all the way from an electrical switch, through the fuse box, and out to each individual accessory. It takes the average weekend mechanic about 40 hours to wire a car. ISIS maintains that its system cuts that time up to 70 percent. And with shorter and fewer wire runs, you're looking at about a 40 percent weight savings compared with a traditional wiring harness. That's a big deal in a weight-conscious race car.
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Click Image For Larger View A typical three-cell ISIS starter kit includes one Mastercell; two Powercells; input and output harnesses; a CAN interconnection cable; main power input cables; a bunch of extra terminals, fuses, and miscellaneous interconnection parts; and comprehensive instructions. The add-on inLINK key fob is a popular security-enhancing option[/align]
How It Works ISIS' original architecture was designed for mission-critical, cannot-fail police, fire, and emergency vehicles, so it's tested to a reliability standard far beyond most typical hot rod parts. The basic system consists of a Mastercell control unit, which can be mounted behind the dashboard or inside the passenger compartment, and at least one slave unit or Powercell installed at a point near a cluster of electrical components. A Controller Area Network (CAN) bus cable connects the Mastercell unit to each subservient Powercell. One Mastercell can control and coordinate up to 50 inputs and 50 outputs. Each separate Powercell can power up to 10 components. You can run up to five Powercells installed at different remote locations.
Each Powercell can support up to 125 amps overall with each of the 10 fused outputs rated at 25 amps. If a current-drawing component eats more than 25 amps (typically, electric cooling fans or high-output electric fuel pumps), an available Mastercell and Powercell input and output circuit may still be used to control the low-current side of an external relay. For just about all other circuits, separate relays and high-current-capable bulky switches are no longer needed, as the Powercell itself acts like a relay but with lower inherent resistance and degradation over time than a traditional mechanical unit because the solid-state ISIS has no moving parts.
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This is a basic ISIS configuration. The Mastercell receives inputs from switches or sensors. Based on its program, it communicates through a single CAN cable to one or more Powercells, which in turn output to a device or load. Direct high battery current is present only at the Powercells[/align]
Instead of the usual practice of running battery current from a switch, through the device, and then to ground, on the ISIS the typical circuit path operates in reverse: Low current flows out from the Mastercell to a switch or sensor and then on to ground. Based on its programming and the sensor or switch position, the Mastercell communicates through the CAN cable to a Powercell to activate or deactivate the component (such as lighting or ignition). With the switches or sensors now located on the low-current, ground side of the circuit, their amp rating is no longer critical. It takes less than 1 milliampere to turn on an input to the Mastercell. Switch life is virtually unlimited, and you can use miniswitches for even the most electrically demanding consumers. If the alternator or battery fails, ISIS still operates on just 5.5 volts. Special order options include the ability to selectively and hierarchically disable noncritical electrical components or enable a master disconnect in the case of a low-voltage condition.
Unlimited VersatilityThe ISIS system can perform special functions beyond simple On/Off circuit control. Because of their solid-state, MOSFET architecture, Mastercells can cycle hundreds or even thousands of times per second, allowing pulse-width modulation or varying-intensity lighting schemes. Mastercells can accept 0-to-5-volt analog input for proportional control of an output: The same light can be set to blink as a turn signal or stay lit as a running light. Interior lighting, the headlights, and the cooling fans could be set to stay on for a set amount of time after you leave the vehicle. Daytime running lights could be set up so the headlights are allowed to illuminate at different intensities depending on the ambient lighting conditions.
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Mounted on the center console, the Mastercell is the boss unit, receiving info from switches and controls, then relaying it to the Powercell(s) through the yellow plug and CAN cable. Note the thin-gauge wires coming out of the gray harness connector-there are no high-power connections directly to the Mastercell; it runs off a wire in the CAN cable (yellow connector). The fuses shown are for the Speartech EFI system, not the Powercell.[/align]
There is no longer a need for separate time delays on a staged nitrous oxide system. You won't need any turn signal flasher modules, LED taillight load resistors, daisy-chained ignition system retards, or race car fuel pump primers, either. With ISIS, the potential control possibilities are limited only by your imagination. As long as the circuit is controlled by a switch or sensor, functionality can be integrated directly into ISIS.
Diagnostics and Security Electrical troubleshooting is easy with ISIS. In a traditional wiring system, each separate electrical circuit must be painstakingly diagnosed point to point with a multimeter and test light. ISIS builds self-diagnostic capability directly into the system.
A separate security system is no longer needed. The optional inLINK wireless control module and its associated key fob allows the owner to lock out the fuel pump, the ignition, and the starter-not at the switches or devices, but through the Mastercell itself just by pressing a button on the key fob. Hot-wiring the ignition switch does nothing. InLINK can also be used to control remote actuation of courtesy lights, parking lights, or a horn panic button.
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The integrated blue LCD screen in each Mastercell indicates overall system status and provides comprehensive system details and additional detailed diagnostic information.[/align]
There is yet another available option: About the size of a handheld GPS unit with a portable touch screen, the inTOUCH wireless device offers even more remote functionality than the basic inLINK key fob. It snaps into a dash-mount cradle for recharging and vehicle control, but the vehicle owner can take the portable unit with him when leaving the car-which means he essentially has all the vehicle switches with him as well.
Programming The basic programming that comes with the kits will cover a majority of vehicle applications. If the end user desires some special function or control, it can be accommodated at the factory before the system is shipped. By the time you read this, end users will be able to generate their own code via ISIS' Internet-based programming interface that allows the use of virtually any Web-capable platform: a Windows-based PC, a Macintosh, a
CPU Great God's Linux special, JPL's mainframe, or even a Smartphone. But at least initially, a Windows-based PC plus an optional inCODE interface module will still be needed to send the new code to the Mastercell's programming header.
Typical InstallationMost hot rods will probably end up with one Mastercell plus two Powercells-one at the front and one at the rear-as shown in the photos of Bruce Douglass' custom '57 Chevy 210 hardtop being wired by McMillan's Speed & Fab. This high-end, no-compromise car features a Car Creations custom frame with Corvette C5 suspension front and rear, a 6.2L LS2 engine, and a 4L70E auto trans. The headlights, parking lights, front turn signals, engine computer, electric fan, windshield wipers, horns, HVAC (heating and air conditioning), electro-hydraulic brake power booster, and gauges are connected to the front Powercell. The rear Powercell outputs to the audio system, taillights, license plate light, interior lighting, rear turn signals, electric fuel pump, fuel level sender, door latches, and power windows.
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No power goes to the dash; all the current switching is done in the remote Powercells. The original '57 switches (such as this master light switch) are still present, but they only ground the circuit. The switch's outputs now serve as inputs, and the original B+ terminal is now used for ground.[/align]
Pricing The typical three-cell starter kit used to wire the '57 Chevy goes for $999 as this is written, plus another $179 for the inLINK key fob. Compare that with a roughly equivalent conventional wire harness ($450) and a typical antitheft system ($200), and it's seemingly about double the outlay to step up to ISIS. But that's not the whole story: Extra heavy-duty switches, relays, time delays, and analog ignition and boost-control devices found on many of today's sophisticated hot rods can easily raise the price up near the cost of an ISIS unit. And then there's the time and labor savings, both during installation and later in diagnostics. Early ISIS adapters simply love the unit. We'd say if you have the bucks, it's well worth the price.
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Each Powercell circuit is protected by a Mini Fuse of appropriate rating for the load controlled by the circuit. LEDs next to the relevant fuses aid in troubleshooting: At a glance, they indicate whether the circuit is off (no light), on and functioning normally (bright light), or has a problem (dim light).
The '57 Chevy mounts the rear Powercell behind the package tray on the other side of a bulkhead that supports the '57 Chevy's trunk-mounted battery. The CAN cable terminates in a large yellow plug. The Powercell farthest from the Mastercell also gets a terminal resistor plug (marked with an R). The illustrated instructions and typical schematics included with the ISIS make all these hookups a breeze
The high-current (input side) cables (A) are protected by modern Mega Fuses (B) instead of old-school fusible links. This is the front Powercell, mounted here on the firewall. Vertical mounting is recommended for best cooling. Note the main power input © coming off the starter's BAT terminal.
The fused, output-side harness comes preterminated at one end with industry-standard Delphi Metri-Pack 280 sealed connectors. The opposite end is left unterminated for custom connection by the end user.
The Flex-a-lite variable fan controller (arrow) draws 50 amps, so it still needs a separate in-line relay, with the low-current side of the relay controlled by the ISIS system. Once the inner fenderwells are installed, all this wiring will be hidden.
The inLINK wireless control key fob module has five control buttons-four on the face, plus a side-mounted shift button. It lets you remotely control up to 16 different vehicle functions. The daughter board needed to interface with the inLINK plugs into the Mastercell.
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