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Let's face it: working with electronics is not every hot rodder's strong point. Some shy away from it and have the car professionally wired, while others make a go of it themselves and come out with a completed wiring system that is just as clean and well-executed as those from the professionals, and still others…well, we won't discuss those, but we've all seen the results of their efforts.
A big part of designing a quality automotive electrical system comes down to preparation and configuration — understanding why and how the components interact — to ensure the installer orients them correctly in the layout. It is essential to use relays, especially when high-amp-draw fuel pumps and other electrical accessories are in place.
MSD developed these pieces to simplify the wiring process greatly while improving the wiring system’s appearance and reducing clutter under the hood and inside the driver's compartment. There are two versions: the Stand-Alone Solid State Relay and the new High Current Solid State Relay that handles higher currents with ease. Each style is available in red or black to provide the builder with flexibility for the sake of appearances.
MSD's Merchandising Manager, Silver Gomez, clued us in on the details of how these can be used in a hot rod or race car build.
"The solid state relay is ideal for the builder who is using standard relays in their build and understands how to wire those. These solid state relays make his life easier because there's less wiring, they are easier to use, and they have diagnostics and self-protection built into them," he says.
The installed cleanliness of these relay systems is hard to beat. Instead of finding a relay mounting location near each component and then routing wires everywhere through the engine bay (or interior), the user can mount this unit in one place and route the wiring in a neat, clean manner.
Each solid state relay - regardless of standard or high-current - replaces four traditional relays and allows the user to cut down on a bit of wiring in the process.
The independent channels can be activated using power or ground. The standard Solid-State Relay provides up to 50 amps of momentary power handling per channel (for up to 8 seconds) and 20 amps continuously. The High-Current version tackles 100 amp loads per channel (for up to 8 seconds) and 35 amps per channel of continuous draw. Electric fans, electric water pumps, nitrous solenoids, lights, and anything else that needs electrical power can benefit from using these devices.
The solid state wiring arrangement does a fantastic job of reducing redundant wiring in the vehicle by utilizing a single feed wire (from the primary power source) along with a single ground wire to the relay and a suitable place close by on the chassis.
The built-in LEDs will provide the user with diagnostics to determine whether the unit is operating correctly. If the circuit trips, deactivate and reactivate the affected channel to reset it. This depiction of the diagnostic LEDs (right) shows #1 channel in Normal Off (both lights out) and #2 channel in Normal On (both lights on) condition. On the #3 channel, we have "Fault Output On," which means that 12V has been applied directly to the unit or the unit itself is faulty. On the #4 channel, we see that the unit has experienced a fault due to over-current, missing battery power, or missing ground. Reset faulted channels by deactivating and reactivating the applicable trigger wire(s).
"The solid state relay makes your life easy: connect the main power wire, the output to each unit, and the activation wires. You can put ground or power to it, and it turns the circuit on," says Gomez.
"Also, depending on the component you're activating, it may need its own ground. For example, an electric fan will have a power wire that runs to the main relay, but you ground it close to the fan itself."
The user can activate each output with a physical switch or program it through laptop-configured output selection as with the Holley EFI Dominator, HP, or Terminator engine management systems. Here, the user can program each output to turn on once they reach a specific temperature or another targeted operating variable.
"The options are endless. You can put a regular toggle switch on it, a pushbutton switch, or however you want to activate that specific channel," says Gomez.
The High Current Solid State Relays can trigger components requiring pulse-width modulation as well. MSD says that the PWM signal can be used with a maximum frequency of 150 hertz and a duty cycle range from 50% to 90% for up to 30 minutes. If the PWM circuit is active for only a few seconds — such as a nitrous solenoid used in a progressive-type drag racing application — the user can extend the operating range from 30% to 90% to gain more flexibility.
The installer must pay close attention to each relay type's operating parameters (standard or high-current). The wire gauge used must be adequate for the application to prevent any fire and overheating risks. Additionally, automotive-grade AWG wire is required to ensure fluid and heat resistance.
Be sure to follow wire size (gauge) requirements listed in the instructions for each Solid State Relay Module. All supply and load wires must be sized correctly to ensure safe and proper operation.
Pairing channels to drive high-demand electronics is simple. Wire side-by-side outputs together (correctly, of course) and ground as you would any other component.
Ground, 12V activation, and chassis ground wires can be 18-22 AWG for either the Standard or High Current relays. The user can run parallel channels to spread out the load should there be a device that requires more power than one channel can handle. Large electric fuel pumps or other high-demand components like air suspension compressors or dual electric fans are no problem for the High Current relay.
Additionally, each relay can trigger either 12V activation or Ground Activation components from the same unit using the appropriate activation channel on the relay block.
It is important to note that the relays include built-in automatic over-temp, short circuit, and overload protection to ensure safety. The built-in LED status indicators help to guide the user through diagnostics when there is an electrical issue.
These relays are ideal for someone rewiring a classic vehicle, adding accessories to a tow vehicle or off-road side-by-side, and even cutting down the wiring clutter in a complete race build. The flexibility they offer the installer to power accessories combines with the robust yet simple design to provide a level of simplicity that's hard to beat.
Make sure to follow the instructions in the installation guide to ensure you have the correct wire to support the current draw your relay block will require. This step is critical — you need to know what your components need to make sure you're powering them properly to prevent overheating. One of the neat features of these solid state relays is the ability to power both 12V and ground-activated components from the same relay. Use the upper terminals for 12V applications and the lower level for ground-activated applications. Regardless of how the component turns on, the installer must always hook up the ground in the activation strip's lower-left corner.
