LED's require correct polarity - Fiberglass RV


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Old 06-28-2015, 04:37 PM   #1
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LED's require correct polarity

A few days ago I received my $20 ten-pack of replacement LED lights. I could not resist at that price. Now all lights in the Scamp are LED, some I replaced last year with the adhesive tape strips, which were already quite cheap.

All worked fine, except one. I suspected that the polarity of that fixture was wrong and confirmed it by trying a second "bulb". The center contact is normally the +12 V, the bayonet is ground. I wonder if anybody else has run into this. Of course, in 2004 (the year of my Scamp), with resistive load only, it did not matter how the fixtures were wired and keeping the +12 on the center contact makes for a slightly safer arrangement, but nothing more.
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Old 06-28-2015, 04:48 PM   #2
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LED's require correct polarity

It depends on what you buy. The " better" led fixtures include a regulator circuit to make them immune from voltage variations and a full wave bridge to make them non polarized. At $2 per I suspect you got an led and a resistor?? Could be the led was bad or inserted backwards. A bigger concern with the cheapies is dumping. Components that don't come up to spec are sold cheap. It's a little like gambling. Some times you win..... Raz
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Old 06-28-2015, 05:32 PM   #3
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I would be very surprised if Scamp, or anybody else, would be installing light fixtures with rectifiers built in, even now when LED's are becoming common. The cost of wiring correctly (matching colors) is virtually zero, the cost of fixtures with rectifiers is a finite value.

Here is the link to the replacement lights, I think that these are the same that were mentioned in another thread:
http://www.amazon.com/gp/product/B00...491325-9803156

They are all good, whether they are putting out the lumens they promise I have no way of measuring, but they seem just as bright as the incandescent bulbs I replaced. They have multiple LED chips as well as resistors, all chips light up. The light color is definitely bluish, rather than the incandescent reddish, but that is fine with me.
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Old 06-28-2015, 05:34 PM   #4
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Oops, wrong link - here is the right one:

Amazon.com: HOT SYSTEMâ„¢ 1156 7506 1003 1141 LED SMD 18 LED Bulbs Interior RV Camper White 10-pack: Automotive
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Old 06-29-2015, 04:29 AM   #5
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I would be very surprised if Scamp, or anybody else, would be installing light fixtures with rectifiers built in, even now when LED's are becoming common. The cost of wiring correctly (matching colors) is virtually zero, the cost of fixtures with rectifiers is a finite value.
Perhaps a poor choice of words on my part. You are calling what Scamp installed the fixture. I used the term "fixture" to differentiate between the led component and what you are calling an led which is really an led with additional biasing components. The rectifier is included in the biasing circuitry along with some sort of voltage regulation on the more expensive units . For $2 per the biasing circuit will most likely be just a resistor. Sorry for the confusion. Raz
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Old 06-29-2015, 07:24 AM   #6
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It makes sense that somebody would sell fixtures with the full wave rectifiers built in. (Just four diodes, after all.) As I type, it dawned on me that those LED lights in my first link do not have a bayonet, but are reversible, therefore the polarity of the fixture socket would not matter.
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Old 06-29-2015, 10:57 AM   #7
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yes! the techie-guy who does our work found the polarity was wrong in two instances in our 1984 Scamp 5th Wheel.
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Old 06-29-2015, 11:20 AM   #8
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more to check polarity of our lights LOL
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Old 06-29-2015, 12:16 PM   #9
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more to check polarity of our lights LOL
One step forward. Two steps back.
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Old 06-29-2015, 12:24 PM   #10
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Remember when life was simple???
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Old 06-29-2015, 08:25 PM   #11
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I bought some for a friend too and then found out that his lights have two poles on the bottom of the light plus the connection the side makes. Mine only have one. I thought the only two types were with the pins on the side were either level or offset. Yes I long for simplicity too.
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Old 06-29-2015, 10:04 PM   #12
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Smile Polarity & offset lugs

The offset lugs are for double contact bulbs, so the polarity is correct. Typically combination tail/stop/signal or parking/signal lights. One contact is for the low wattage tail light, the other for the bright stop/signal light.
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Old 06-29-2015, 11:44 PM   #13
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Quote:
Originally Posted by Paul O. View Post

All worked fine, except one. I suspected that the polarity of that fixture was wrong and confirmed it by trying a second "bulb".
Yup I had it happen. Not with some rather pricey LED replacement bulbs I had purchased but with two relatively cheap ones a friend gave me that they had purchased in bulk off the internet.
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Old 06-30-2015, 08:38 AM   #14
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It could be that those "rather pricey" LED replacements had the full wave rectifier built in and the new cheap ones do not.

The rewiring of the fixture in question was simple, but the access to it was tight, inside one of the cubbyholes in the loft.

I measured the current draw and found that the incandescent bulbs draw almost 1.5 amps, the LED's draw about eight times less and give off about the same amount of light. Great improvement in the future life of our battery!
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