Power Trigger

Watts up with relays on motorcycles?

AMA News Author (no byline)

By James Holter

Today’s big adventure bikes require riders to be mindful of power management, and not just the power managed with the right wrist.

I am talking about the power described in amps, volts and ohms that flows through the wires networked across our machines. It’s often necessary to tap into these networks -- or create our own -- to juice the electronics that connect us to society (and facilitate our safe exodus from it).

The good news: You don’t have to be an electrical engineer to make this power work for you.

The bad news: I probably have just enough understanding here to be dangerous (so be forewarned).

Before we get to the how-to, though, let’s review some basics. There is more to tapping into your bike’s electrical power grid than cutting and splicing. You need to know where to cut, where to splice and how to go about it.

To better understand why, consider a motorhead-friendly analogy. Think of volts as torque and amps as rpm. In each case, you need both to create the power (“watts” or “horsepower”) to make something happen.

Maybe you’re familiar with these formulas:

  • Power (watts) = voltage (volts) x current (amps)
  • Power (horsepower) = torque x (RPM / 5252)

With 12 volts delivered at 2 amps vs. 12 volts delivered at 20 amps, the same amount of potential power is available as volts (or torque, in the case of an engine), but the 2 amps (or relative low rpms) are less likely to generate the necessary watts (or horsepower) to accomplish what needs to be done.

Accessories might go dead. Way points may be missed. Communication might go silent. And you may never be heard from again.

Or, something like that.

This little bit of knowledge was front-of-mind when I considered how to power accessories for my 2017 KTM 1090 Adventure R.

From a wiring standpoint, KTM’s Adventure line makes this relatively simple. For years, KTM has provided un-used factory power leads for powering non-factory stuff you add on your own. My bike has four of these factory-provided leads: two in the left side of the fairing, and two hidden under the seat.

Even cooler, one in each location is switched on and off with the ignition (these leads are known as “ACC2”), while the other provides constant power (called “ACC1”). Options are good.

What isn’t good, at least with the 1090, is while the two ACC1 lines provide a fat 10 amps of 12 volt power, the switched ACC2 lines are just 1 amp. Wimpy. I’m not comfortable relying on 1 amp of current to, say, keep a cell phone charged while pumping Twenty One Pilots and navigation guidance through a Bluetooth headset and simultaneously powering a full-featured GPS unit that no self-respecting adventure rider would dare adventure without.

(My GPS is a Trail Tech Voyager Pro 2. According to the support line, I should plan for a 3.5-amp draw to keep the unit charged. In my case, the GPS alone out-draws ACC2.)

Using one of the 10-amp ACC1 lines would do the job, but those lines are not switched with the ignition. This creates the very real (and 100 percent certain, in my case) likelihood that the devices would be left on while the bike was not running, allowing them to drain the battery at the worst possible time.

Here, I’ve plugged everything together outside the fairing to show how what goes where. Both of the factory ACC2 (factory switched 1-amp circuit) leads connect to the relay, as does the positive ACC1 (factory 10-amp circuit) lead. Exiting the relay is the now-switched 10-amp power, which we split into two, one for the USB charger and one longer wire that will power the GPS. The other split line is the negative ACC1 lead.

The answer, fellow adventurers, is the humble relay.

A relay is just a switch, like the light switch on your wall, that completes a circuit. Rather than being physically activated to complete the primary circuit, however, a relay is electronically activated by a secondary circuit. Relays come in various types. One of the most basic is a single-pole, single-throw (SPST) normally open (NO) automotive relay.

A SPST NO relay has four terminals:

  • Two terminals (marked “85” and “86”) where you connect the existing switched circuit. It doesn’t matter which terminal receives the positive voltage and which terminal receives the negative voltage.
  • The terminal (marked “30”) that receives the constant power from the battery.
  • The terminal (marked “87”) that delivers the power plugged into 30 to the device (or devices) when the switch providing power to terminals 85 and 86 is switched on.

So, I can take over where the Austrian engineers left off and use the factory 1-amp ACC2, which is switched with the ignition, to trigger a relay that completes the 10-amp ACC1. I will use this now-switched-by-relay ACC1 to power my electronic devices.

Devices? There’s still just one terminal, right? We can simply split the power at terminal 87 (as well as the ground that accompanies it and bypasses the relay) to provide two switched circuits delivering 12 volts at (theoretically) 5 amps.

This shows the USB charger in the factory hole in the left-side fairing compartment. It will be pushed into the fairing and secured with the threaded ring visible inside the fairing cavity. The relay will also tuck inside the cavity and the longer leads providing the power from the now-switched ACC1 power will extend out the bottom of the fairing.

I use this approach to power two devices: a marine-grade dual USB charger for my phone and a Trail Tech Voyager Pro.

Here are the steps for a 2017 KTM 1090 Adventure R:

Step 1: Buy a relay (make sure it’s rated for at least 10 amps, more are fine), some wire (I got 16 gauge), some wire shrink, and male and female spade connectors. This set me back roughly $10 total at an automotive retail chain store.

Step 2: Take stuff off the bike until you expose the inside of the left fairing.

Step 3: Poke out the stock plug in the factory-drilled accessory hole in the left fairing.

Step 4: Connect the positive and negative leads of the factory-switched 1-amp ACC2 line to the 85 and 86 terminals. (On my bike, I had to trim back some of the protective rubber over the factory female connectors on both ACC2 and ACC1.)

Step 5: Connect the positive lead for the constant-power 10-amp ACC1 line to the 30 terminal.

Step 6: Cut and strip the ends of four pieces of wire, two should be about 2 inches long and two should be about 6 inches long.

Step 7: Twist one of the 2-inch wires to a 6-inch wire, crimp the twist in a single female plug (protect it with some wire shrink) and plug it onto relay terminal no. 87. Crimp a female plug onto the other end of each wire.

Step 8: Twist the other 2-inch wire to the other 6-inch wire, crimp the twist in a male plug (wire shrink it!) and plug it into the 10-amp ACC1’s negative lead. Crimp a female plug onto the other end of each wire.

Step 9: Poke the 2-inch wires up through the accessory hole in the fairing and plug them into the USB charger (note that the charger will have a positive terminal and a negative terminal, so match them up).

Step 10: Seat the USB charger in the accessory hole, and tuck the relay up inside the fairing from the bottom, while extending the 6-inch wires out the bottom of the fairing.

Step 11: Put your fairing back together.

Step 12: Mount the dock for your GPS unit. (I used KTM’s factory GPS bracket that positions the dock above the gauges.)

Step 13: Plug the GPS unit dock’s positive and negative leads into the correct positive and negative power lines from under the fairing. You may need to crimp male plugs onto the ends of these wires.

Step 14: Set your GPS, if so equipped, to activate when it receives power through the dock.

Now, when I turn on the ignition, my GPS comes to life, accessories charge, and I don’t have to ride in silence because my phone died and took Twenty One Pilots away.

While your bike might not make things as simple as the KTM, with its factory ACC1 and ACC2 connectors, another option is running the main power directly from the battery and identifying a secondary switched source to trigger the relay. If you go this route, connect an inline fuse in the main power line to protect your gadgets.

James Holter manages the communications and marketing departments of the AMA.