LED's require correct polarity - Fiberglass RV


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Old 06-28-2015, 03:37 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, 03:48 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, 04:32 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, 04:34 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, 03:29 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, 06:24 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, 09:57 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, 10:20 AM   #8
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more to check polarity of our lights LOL
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Old 06-29-2015, 11:16 AM   #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, 11:24 AM   #10
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Remember when life was simple???
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Old 06-29-2015, 07:25 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, 09:04 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, 10:44 PM   #13
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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, 07:38 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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Old 06-30-2015, 08:24 AM   #15
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I seem to recall that someone posted awhile back that they purchased a box of inexpensive LED's in bulk off the internet and only some of the bulbs had reversed polarity. Resulting in some of the bulbs worked fine in one light while a couple of others from the same box, did not in the same light without the wiring being swapped. Which would suggest to me that perhaps it was an error in manufacturing process. Due to the low costs of the bulbs it would be a good bet there was little quality control. ;-)
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Old 06-30-2015, 10:14 AM   #16
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I seem to recall that someone posted awhile back that they purchased a box of inexpensive LED's in bulk off the internet and only some of the bulbs had reversed polarity. Resulting in some of the bulbs worked fine in one light while a couple of others from the same box, did not in the same light without the wiring being swapped. Which would suggest to me that perhaps it was an error in manufacturing process. Due to the low costs of the bulbs it would be a good bet there was little quality control. ;-)
There is always plenty of "cheap junk", and the word is: buyer beware, but in my case polarity reversal was in the wiring of the fixture, not the LED's. I think in general they are getting not just cheaper, but better. I hope I can say in a few months that I timed the market well.
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Old 07-09-2015, 02:23 PM   #17
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In the interest of making my TV's lighting control module happier I've been changing the exterior lights on our '92 casita over to LED.

Discovery #1 - the polarity thing - the side marker sockets in back at least were wired backward. As I was bodging in some #194 LED replacments I had lying around (wedge bases) my solution was just to change which wire went to the base contact and which went alongside the wedge and was pinched to the side contact.

Discovery #2 - They got the tail lights right, but my cheapie 1157 LED replacements were wired OK for polarity but backward for brightness. I had to unsolder the bulb base, rotate 180, and then resolder. Also fixed a cold solder joint on one plank of the 'christmas tree' while I was at it.

Result: they're nice and bright and current draw is about 80% less than it used to be. It'll be better still once I get the front side markers replaced as well. I'd already had the soldering iron out anyway making my freetastic fan, so the hassle factor was greatly reduced over what it might have been.

Conclusions: 1. Check the polarity at the sockets. 2. cheap LEDs are indeed cheaper for a reason.
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Old 07-09-2015, 06:41 PM   #18
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I noticed that a number of people are changing the marker lights, brake lights or directional bulbs to LED's. Is it for brightness and longevity?

My motivation to go with LED lighting inside the Scamp is to have my battery last longer when camping without shore power. While on the road, the LED lights or incandescent will make no measurable difference. Is there something else to consider other than the above mentioned brightness or longevity?
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Old 07-09-2015, 08:54 PM   #19
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Is there something else to consider other than the above mentioned brightness or longevity?
Absolutely! The exterior bulbs in my Casita looked like they might be the originals from 1992. Longevity (of the bulbs) isn't an issue.

One factor is response time - if you hit the brake lights or turn signals, LEDs are about 300 milliseconds faster to light up. That doesn't sound like much, but human reaction time under ideal circumstances is in the 600-800 ms range. Anything you can do to clue in the human behind you sooner is a good thing. That's why high mount brake lights were adopted - they were documented to reduce rear-end collisions because the people following noticed the lights coming on sooner.

But for me, what is specifically an issue is the lighting control circuitry on the tow vehicle. Back in the day you could just hook the running and signal lights up to the TV wiring and you were done.

Then along came electronic lighting controllers. Now there's a pretty strict current limit. Go beyond it and you cook something, the computers get unhappy, or both. All this is fine if you have the factory tow package - I don't. Uhaul will sell a little box full of relays that switches power from somewhere else with signals from the tail lights. I've avoided that because it's one more thing to break, and they're kind of expensive for what you get.

My TV is an old enough design that it expects to use incandescent bulbs for everything itself. That's the good news, as it means that it has a pretty stout current capability. The bad news is that exceeding design specs by 50% by adding more bulbs isn't good for longevity.

The off-the-shelf solution is to put some LEDs in. Loads on everything are suddenly just about where they were before the trailer was plugged in, but the trailer is actually brighter than it was with incandescents.

No filaments to break is just another bonus. My total outlay on LEDs is about $5 right now - I bought them straight from China. Minor QC problems are figured in the price...
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Old 07-09-2015, 10:47 PM   #20
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Quote:
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I noticed that a number of people are changing the marker lights, brake lights or directional bulbs to LED's. Is it for brightness and longevity?

My motivation to go with LED lighting inside the Scamp is to have my battery last longer when camping without shore power. While on the road, the LED lights or incandescent will make no measurable difference. Is there something else to consider other than the above mentioned brightness or longevity?
One has to be careful about LED tail lights. The very bright day time, full sun lights are nice, but at night they blind the driver behind you. There are laws and rules about how bright tail lights can be at night. Some car manufacturers have gone back to incandescent because of this. They need to incorporate some sort of dimmer for night time use.
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