Replacing tungsten and halogen bulbs with modern LED bulbs is becoming popular with many RV owners since it reduces the power load. However, you have to be careful that you’re installing LED replacement bulbs into DC powered fixtures, and NOT AC powered fixtures.
Recently, editor Chuck Woodbury has been receiving letters from RVtravel.com readers about replacement LED bulbs overheating and melting the fixtures. Here’s just one of them:
“Chuck,
I purchased LED replacement bulbs for the reading lights in my Coach House motorhome. The item said, ‘LED RV Boat Car Home Marine Cabinet Lamp Light Reading Bulbs.’
“Having replaced lights in previous RVs with LEDs without problems, I didn’t expect problems with these. However, minutes after replacing and turning on the lights, they heated up and started smoking and they were too hot to touch. The smell of burning plastic filled the coach. I quickly turned off the lights, and when they finally cooled down, I removed the LEDs.
“Going back to the page where I ordered these, I found this warning:
Warning: Please note this G4 LED must be powered by a 12V DC circuit only. If you use these bulbs on an insufficient AC circuit you will burn out the lamps due to excess heat being applied causing the solder points on the LEDs to melt away. If used on a correct 12V DC circuit you will not have any of the mentioned problems.
If you wish to change your existing G4 under cabinet lights from halogen to LED, you must ensure to change all halogen transformers to 12-volt DC LED Drivers. You do not have to change the complete fitting. Just find the halogen transformer and replace with 12v DC LED Driver.
Apparently, the lights where I used these new bulbs had halogen transformers. Who knew? Anyway, be careful when replacing lights with LEDs. If the fixtures are not 12 volts DC, problems can occur.” —Bill Myers
Hey Bill,
Thanks for the heads up. And yes, it’s certainly possible that a 12-volt DC LED bulb installed in a 12-volt AC fixture can overheat and possibly cause a fire. That’s because the actual polarity of the power is reversing from positive to negative 60 times a second. And a lot of DC powered components will “short out” on negative polarity. What this will do is allow the LED bulb to turn “on” 60 times a second during the Positive half of 60 Hz AC, but during the Negative half of the 60 Hertz power cycle it’s shorted and drawing a huge amount of current that’s turning into heat.
Now I don’t know just how many RVers are out there are powering their cabinet lights with a 12-volt AC halogen transformer fed by an inverter, but there must be at least a few of them to cause all these problems. So I’m going to ask my writing colleagues Gary Bunzer and Chris Dougherty if they can identify any RV brands and models that might be suspect. And I’ve already ordered a 4-pack of these G4 LED bulbs to test on my bench with 12-volts AC to see exactly what happens and how hot they get. According to the warning on the website they can get hot enough to melt solder, and that’s pretty hot.
I
n the meantime, if there’s any possibility that your cabinet lights are running on 12-volt AC rather than 12-volt DC power (you can test that with a voltmeter set to DC volts), then DO NOT replace the existing Halogen bulbs with LED versions. And always confirm that any replacement LED bulbs are running cool to the touch before you put the covers back on the lights.
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.
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I also think so. I have read some information like that here: https://vogeltalksrving.com/how-to-change-rv-interior-light-bulbs/#more-1229 and it really useful. There are certain safety rules implemented along with tips to help you realize when the right time is to get your LED bulbs replaced.
I agree. Too many suggestions of test with voltmeter without instructions on where to place probes and what to look for. Very frustrating!
I’m a little suspicious of this, since LEDs are used on AC circuits all the time as a modern pilot light replacement for all those neon lamps we oldies recall. Because an LE*D* is a diode, it runs only 50% duty, but proper 4V and 50ma (current limited) levels should not swamp the breakdown (reverse blocking) voltage… Its simply off (non/semiconducting) in reverse polarity, not heating like a resistor. My 4V LEDs are happy on 4V AC, just slightly flickery.
When replacing 12V incandescent with 12V LEDs, the bulb has to reduce voltage to the nominal 4V/LED level, the common way to do that being triplets of 4V LEDs in series, and N triplets in parallel for brighter light. 120V AC bulbs use strings of 30 similarly, and may add a smoothing capacitor for 60hz flicker, but only a few brands bother to rectify AC to DC (which just flickers at 120hz).
If you put a 12V intended bulb into 120V supplied ficture, you WILL heat/burn… A new DC to DC converter (“buck” down or “boost” up) doesn’t make any sense if 12V battery is going to 12V bulbs. Much more likely, they are (clumsily) telling users not to use 12V DC bulbs in existing 120V (or any other odd voltage) fixtures. Don’t go with a new 120 to 12V transformer either – 12V battery power doesnt flicker or require 120V inverter / shore power in transit. I’d never have inefficient 120V lights in an RV, but if you do, cap the AC and tap into 12V DC.
One thing that WILL get people in fiery trouble is installing 12V “CANBUS compatible” bulbs as cabin lighting. Strictly, ONLY use “non CANBUS” bulbs, which will NOT heat up in use.
What is Canbus?
That sounds like a great idea for an article. I’ll write it up soon and post it here.
This is scary. Sounds like it may be difficult for a novice to know if their halogen lights are ac. You mentioned testing with a voltmeter but failed to describe the test, what to look for. Please get more info out soon.