This week I’m going to circle back and continue the discussion about LED bulbs that were designed for CAN Bus use, and which overheat in an RV interior light application.
But first, here’s a quick heads-up on the poll we took last week asking if you’ve ever encountered power at a campground that showed high or low voltage, or grounding problems. To read that article again or get in on the poll please click here.
As you can see from the almost 600 readers who participated in this survey so far, 58 percent said you had indeed encountered one of these problems, and many of you left detailed descriptions in the message area. So if you haven’t done so already, please take the poll and add your vote to the survey. I’ll write an article discussing what this all means in a future column.
Now, back to the LED bulbs designed for CAN Bus use. Here’s the first part of an email I received from long-time RV Travel reader Wolfe Rose warning us about the danger of using CAN Bus rated LED bulbs in your RV’s inside lights.
Mike, I wanted to alert the RV Travel readers to a seriously dangerous product category I’ve encountered…
The short and non-techie summary: NEVER use “CAN Bus compatible” LED bulbs for RV lighting. Never. Ever. You can tell they are the “wrong” LED bulbs because they get burn-your-RV-down hot, while proper energy efficient bulbs stay quite cool in use…. —Wolfe
(Wolfe then adds a very detailed explanation of what he discovered.)
Wolfe, thanks for the heads-up and warning. Here’s my explanation for the rest of our readers.
CAN Bus starts with the acronym CAN, which stands for Controller Area Network, which implies wanting to Control a bunch of things in a local Area that are hooked together in some kind of Network, in this case a motor vehicle. Things you would like to control in a vehicle include headlights, stoplights, turn signals, fuel injectors, starter motors, brake controllers, etc.
Back in the old days before computers there would be HUGE wiring harnesses connecting all these things together with hundreds of color-coded wires. So there was a wire that went directly from the light switch on the dashboard to each of the running lights. Another wire went from a switch under the brake pedal to each of the brake light bulbs in the lighting housing. As you can imagine, there were HUNDREDS of wires going every which way, with dozens of connectors hooking it all together. These old school wiring harnesses were always specific to each vehicle and were not only heavy, they cost a lot as well.
What if there was a better and cheaper way to do this that weighed a lot less. Enter the “CAN Bus”. For those of you in the computer industry this is old news, but for the rest of you just follow along. Imagine a city bus that runs from 1st Street up to 99th street and then back. And along the way there’s a bunch of bus stops, maybe on 10th Street, 20th Street, 30th Street, etc. Now let’s imagine you want to deliver a written message from 1st Street to 40th Street. You write the note, hand it to a rider who jumps on the bus and begins traveling on the route. He ignores the 10th, 20th and 30th Street stops because the note says “deliver to 40th Street.” When he gets to 40th Street he jumps off the bus and delivers the message to someone waiting at the bus stop. Maybe that message says “turn on the brake lights.”
A CAN Bus works exactly the same way. There’s a single wire that starts somewhere in your car’s computer system which loops all around your vehicle in a circle like a big commuter bus route. And at dozens of places along this wire (route) there are bus stops, which are actually the things we want to control. So there will be a bus connection to the tail lights, headlights, door switches, brake controller, etc. — literally hundreds of them in an average car. And each of these bus stops can not only receive instructions from the car’s computer, they can report back information such as “this tail light bulb is burned out,” which is how your car’s computer knows to alert you to a dead bulb or a tire with low air pressure.
Now this sounds like a pretty slow process if you’ve ever ridden a city bus. But a computer communication bus runs at the speed of light, and it does thousands or millions of these round trips every second. So there’s really no noticeable delay from when you push on the brake pedal, which sends a message on the CAN Bus to the back of the car, and then turns on a transistor, which then sends voltage to the brake bulb to make it light up.
So why would they make a brake light bulb with an extra resistor that can heat up and cause a fire in your RV’s overhead lights? Well, the CAN Bus light controller in your vehicle was designed to sense a certain amount of current from a normal bulb. And if you swap it out for an LED bulb, that LED will draw so little current that the sensor will assume the bulb is dead and report that info back to the car’s computer, which will give you a dead bulb warning. To correct that problem any retrofit LED bulb designed for an earlier version CAN Bus needs to have an extra resistor across it to draw the same amount of current as a regular tungsten bulb. And, of course, that resistor gets hot enough to melt plastic and possibly catch your lighting fixture on fire if left on for several minutes or more, something your brake lights probably won’t experience.
That means you’ll want to avoid using any retrofit LED bulbs that are rated for CAN Bus use in your RV interior lights, since it will not only draw a lot more watts than an LED should, it will also get hot enough to melt your fixture and maybe cause a fire.
I’ll cover more on AC-DC LED bulbs overheating next week. But in the meantime, let’s play safe out there. —Mike Sokol
Mike Sokol is an electrical and professional sound expert with 40 years in the industry. Visit NoShockZone.org for more electrical safety tips. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.