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Old 06-02-2018, 04:17 PM   #1
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Changing over to LED Bathroom fixtures

Our large 12V fat boy bulbs on the Medicine Cabinet are a pain... I hit and break them when I try to open the cabinet door.. and I wanted to switch them over to LED's... Wife didn't like the style of gold fixture so we looked and looked and finally I found one at Ikea that would do. I cut off the power supply from the circuit and hooked up the leads to power and nothing. Reversed.. Nothing. I bought some LED light strips that I've used elsewhere in the bus and still nothing works... I hooked up the old fixture and there's still power.. 12V... pain in the backside. Is there something special with that cabinet and 12V?
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Old 06-06-2018, 11:09 PM   #2
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Interesting conundrum, Mike. We have made the conversion to LED's throughout our rig except for those little exterior running lights. For us, it has been plug and play. I think you are tracking well to suspect the medicine cabinet and/or its 12v supply.

To make a short story long -- We did quite a bit of remodeling (apparently the new phrase is upscaling) on our sticks-n-bricks recently. Built in '89. The range hood SWMBO wanted was a discontinued floor model. We installed it, but LED bulbs would not work in it. Nor would they work in the new recessed lighting fixtures we had installed. Or the ceiling fans. But they would work in free standing lamps. Had a long conversation with the electrician at the design center. Caught a bad case of MEAGO (my eyes are glazing over). The gist seemed to be that the old light switches were not compatible with LED?????????? Being broke from the remodel (and thinking I was being sold a load of wolf cookies, so didn't want to pay his labor rates) went down to the hardware store to buy new wall switches. The big box guy agreed with the design center guy! Installed the new switches -- all LED lights are bright lights.

Talk to a lighting electrician.

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Old 06-07-2018, 07:30 AM   #3
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Every time I read forums like this I learn something else. This is indeed a new one for me. Thanks for posting this, will certainly keep it in mind.
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Old 06-11-2018, 06:36 AM   #4
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With LED lights, you cannot likely use an older switch that has dimming capability built in. Recent vintage switches with dimming capabilities should indicate if they are compatible with LEDs - if you want a dimmer/switch. Obviously, a straight on/off switch should work anywhere. Not really sure you need to get an electrician to find this out but glad you got yours working.
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Old 06-11-2018, 02:27 PM   #5
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The OP found a light from IKEA that's 12v?
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Old 06-11-2018, 06:36 PM   #6
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Originally Posted by 4x4van View Post
The OP found a light from IKEA that's 12v?
That's similar to my first thought also.
OP, are you SURE the new fixture is 12 volt. That seems mighty specialized for IKEA.
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Old 06-16-2018, 07:37 PM   #7
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One thing to keep in mind when you buy LED fixture, and cut off the power supply plug to wire them into your 12V wiring from your old fixture, is that LED lamps are polarity sensitive, and unless they have a build-in polarity guard (diode), if you connect them backwards, you will not even see a wink, as they burn out. If they have an internal blocking diode, then they simply will not work with reverse polarity.

I suspect that the OP's fixture from Ikea, when first connected to his 12V wiring, may have had the polarity reversed, and fried the lamps. If that is the case, then they are done. Best to have plugged the original fixture into an outlet, switched them on, then checked with a multimeter, to see which wire was positive, and negative AND that they are actually getting 12-14 VDC from the power supply. With that information, then connect up to the RV 12V wiring, observing polarity, and they should work. And yes I agree, that wall-mount dimmers may not work LED lighting, but should if the dimmer was all the way up, as that should deliver full 12V to the fixture.
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Old 06-28-2018, 05:19 PM   #8
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Most decent lights will have protection against reverse polarity. I know even the cheapies that I slap on my motorcycle for accent lights do.

As for the dimmers - the issue is that LED requires PWM (Pulse Width Modulation) to dim. It's not actually dimming the lights by cutting back on the electricity like a normal dimmer. It's actually flashing them at certain rates of off to on (longer off to on for dimmer).
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Old 07-03-2018, 04:39 PM   #9
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Unless the voltage is too high, hooking up an LED (even a cheap one) backwards won't burn it out, it simply will not light. An LED is a Light Emitting Diode; a diode is like a one-way valve. Current will flow in one direction, but not in the reverse direction.

I still question how the OP got a light from IKEA that is 12vdc rather than 120VAC. And if the IKEA light had a wall wart power supply that the OP cut off, was it a 12vdc power supply, or something different? I've seen wall warts that output various dc voltages, as well as some that even put out low voltage AC.

We know that the original light works on 12vdc. We know that the circuit still has 12vdc (no blown fuse). We know that the IKEA light, sans cord/power supply(?) doesn't work. And we know that an LED strip used elsewhere may or may not work (depending on if the OP tried reversing the polarity). Here is my guess:

The OP got a nice light from IKEA that was actually 120VAC. He hooked it up to 12vdc, and of course it didn't work. Then he tried some LED light strips used elsewhere, and inadvertantly hooked them up with reversed polarity, so they also did not work. Reinstalling the original 12vdc lights did work, of course, because the polarity was correct.
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