Converting interior lights to LED

The exterior light discussion reminded me that I should look at changing the lights for the dining room and sconce.s  behind the couch from the 194 wedge bulb to an LED setup. Someone had recommended LEDLight and I checked with them. I had heard that there needed to be some protection in the circuit/base against overvoltage when the charger is going. LEDLight said that their bulbs are tested to work up to 13.8v but have no resistor. There is also no protection of the LEDs themselves, they are bare. I am also concerned about quantity, quality and direction of the light. The dining room lights are close to the ceiling and the sconces are not even chest high. Any thoughts, recommendations and suggestions would be appreciated.

It would be interesting to hear how they current limit the LEDs without a resistor.  They must connect several in series.

Ned said:

It would be interesting to hear how they current limit the LEDs without a resistor.  They must connect several in series.

Click to expand...

That is what bothered me. The comment was just that they work without problem up to 13.8. They don't modify the voltage. There was a single LED light but most were 3-12 LEDs in the "bulb".

Great minds seem to be thinking the same thing.

I have a lot of 912 base bulbs in ceiling fixtures such that the light from one side shines out and the light from the other side bounces off a white reflector.

I would like to replace at least some of these with LEDs.

LEDLight has some 912 replacements but they are mostly or totally "end firing".  Seems like you would lose most or all of the light.

Has anybody replaced 912 bulbs with LEDs?  Happy? 

Joel

As Ned mentioned, an LED is a current driven device and the light output is directly proportional to the current flowing through it - once the voltage is above the minimum forward voltage of the LED, usually around 2.4 volts. Anyone who says their LEDs can handle 13.8 volts without a dropping resistor or some sort of voltage regulator is not telling the true story.

LEDLight has some 912 replacements but they are mostly or totally "end firing".  Seems like you would lose most or all of the light.

Click to expand...

Directionality of the light is, or should be, a major concern. By their very nature (a cleft in the surface between the anode and cathode; the P and N junction) the light is emitted at a very narrow angle - about 6 degrees right and left of center. That makes for a very narrow beam of light. The lens part of the LED will spread it out to about a maximum of 60 degrees (left and right), but the light falloff at the edges will be severe. See the attached document. An LED is always 'end firing'. To achieve an illumination pattern similar to a regular light bulb will require either several (many) LEDs precisely positioned, or some very sophisticated optics for direct lighting, or a number of them directed towards a 'light box' which mixes the individual LED outputs into a homogeneous light source for indirect lighting. This technique is used very successfully in photograph enlargers where a single 'point' light source must be spread evenly across a full-frame section of film.

Ned,

Tak to Russ about LEDs!!  

Anyone, if you are serious about using LEDs in the MH, besure they have a vlotage regulation system, not just a resistor as if you have a charging voltage of greater than what the assembley is rated for, i.e., 13.8 volts, the LEDs will start to burn out and it will significantly shorten the life.  In Pomona, I found ONE LED vendor who really understood them and his prices reflected the additional electronics that were included along with the LEDs BUT he also had long unconditional guarantees.  Now if I can find the information on him.  :-((

joelmyer said:

Has anybody replaced 912 bulbs with LEDs?  Happy? 

Click to expand...

Wally replaced the light over the kitchen sink with LEDs. The old bulb was an 1141.
the new setup is wired directly to the switch. Without getting into all the specifics The quick rundown is the new setup is a 2 inch square of 36 LEDs. He revamped old fixture and removed original socket The light is OK but not great. Lights up the area directly under it well enough but the light does not spread out like the old one did. I used to be able to read the clock with just the kitchen light . Now I must get very close to the clock or turn on more lights. As a fill light over the sink work area it is sufficient. It is the light we will leave on when we are not in the rig because it draws so little.
We may replace or two more but not all. We will keep a mix of incandescent floresent
and LEDs,
Helaine

Jim,
A single Zener diode and a couple resistors are all that's required for an LED array up to about 1 amperes for about 25 cents (in quantities of 10 or more). Larger than that, the more the cost.

A transistor and a couple of resistors in a constant current configuration would cost about the same, and won't waste power when the voltage rises above the threshold.  After all, you are trying to limit the current, not voltage.

Helaine & Wally said:

Wally replaced the light over the kitchen sink with LEDs.

The light is OK but not great.

We may replace or two more but not all. We will keep a mix of incandescent floresent
and LEDs,

Helaine

Click to expand...

Thanks Helaine

Lou Schneider said:

A transistor and a couple of resistors in a constant current configuration would cost about the same, and won't waste power when the voltage rises above the threshold.  After all, you are trying to limit the current, not voltage.

Click to expand...

You need to regulate voltage, here is why

If you wire the led's in series, christmas tree style, then if one goes bad, (open) Of course if one shorts out, no problem with a current limited input.

If you wire them in parallel, then if one fails open, with current limited source, the others are not over-fed

But if one fails shorted.. All go out.

so your best choice is to either use one resistor per LED or one resistor per every few leds and limit the voltage.  That way if one led fails only those few leds that share that resistor are affected.

One of these days I'm going to start building my own LED arrays, I'm looking for like 50 led's on a project board

50 leds, 50 resistors and a 5 volt 3-terminal regulator or two or three

Good point, Lou. Either one will work and you do have dissipation losses with a transistor too.

LEDs in parallel sharing a single resistor is generally not a good idea. In order for it to work properly, they should all come from the same electrical binning by the manufacturer, otherwise each LED will have slightly different characteristics. If you have 3 in parallel, the dropping resistor has to be sized to provide enough current for all three, and the one with the lowest turn-on voltage will hog the current, starve the others, and possibly burn itself out.

James Godward said:

Anyone, if you are serious about using LEDs in the MH, besure they have a vlotage regulation system, not just a resistor as if you have a charging voltage of greater than what the assembley is rated for, i.e., 13.8 volts, the LEDs will start to burn out and it will significantly shorten the life.  In Pomona, I found ONE LED vendor who really understood them and his prices reflected the additional electronics that were included along with the LEDs BUT he also had long unconditional guarantees.  Now if I can find the information on him.  :-((

Click to expand...

Jim

I spent a lot of time with him at Indio and Pomona. He even let me try out his prototype replacement for the dining room light (array of LEDs with a reflector cover). It still needs work since  the socket and his wiring weren't compatible. I'll see him again at FMCA-St. Paul or Indio next January, but didn't keep his card.

Bernie,

I found the sheet he gave me with the URL on it.  http://www.lunasea.com

I looked at the items he had bu none of them fit where I wanted them.  We talked about what was needed for me and we are going to keep in touch.  Probably more by E-Mail and phone than in person.  What he has done should work well.  They are the  only ones I have found so far that recognize the over voltage problem in MHs etc.

Texas Instruments has a series of videos on this that are good but technical.  VBG

John In Detroit said:

You need to regulate voltage, here is why

If you wire the led's in series, christmas tree style, then if one goes bad, (open) Of course if one shorts out, no problem with a current limited input.

If you wire them in parallel, then if one fails open, with current limited source, the others are not over-fed

But if one fails shorted.. All go out.

so your best choice is to either use one resistor per LED or one resistor per every few leds and limit the voltage.  That way if one led fails only those few leds that share that resistor are affected.

One of these days I'm going to start building my own LED arrays, I'm looking for like 50 led's on a project board

50 leds, 50 resistors and a 5 volt 3-terminal regulator or two or three

Click to expand...

John, you might be interested in this site to get motivated. LOL

http://www.bgmicro.com/index.asp?PageAction=VIEWCATS&Category=115&Page=1

How critical is this 13.8V limit?  Are we talking about failure within an hour or two or just shortening their life from "forever" to  100,000 hours?    Incandescent bulbs have their life shortened at higher voltage too and we don't lose sleep over that.

Only rarely will your charging system exceed 13.8V (probably for short periods while in bulk charge mode) and the lights won't be on some of that time anyway.

RV Roamer said:

How critical is this 13.8V limit?  Are we talking about failure within an hour or two or just shortening their life from "forever" to  100,000 hours?    Incandescent bulbs have their life shortened at higher voltage too and we don't lose sleep over that.

Only rarely will your charging system exceed 13.8V (probably for short periods while in bulk charge mode) and the lights won't be on some of that time anyway.

Click to expand...

Gary

The person I talked to at LEDLights wouldn't indicate what would happen if the LED was exposed to 14.3-4v for any (or what) period of time.

Each LED will have an absolute maximum current rating for continuous operation. It is typically 30mA for many common types. This absolute maximum is based on the junction temperature (TJ), which is the point where the teeny-tiny gold anode wire contacts the pn junction of the diode. Too much current will generate too much heat for the junction and it will burn out. That same LED can be pulsed with a much higher current (around 100mA), but only if it's done in brief bursts of about 5% (example: 1?s on followed by 20?s off), which prevents excessive heating of the junction. But, any good design will not operate any component at its' maximum rating. A 30ma LED will still output quite a bit of light when operated at only 20ma @12.6VDC, and that 10ma safety margin will be sufficient to allow it to operate safely at over 18VDC.

The short answer is, if it's designed to operate at or near maximum at 12.6 VDC, anything above that risks failure. If it's designed to operate at 75-80% maximum, you won't have a problem with normal voltage fluctuations in a motorhome. 

I use a lot of LED lights.  here is some math

The LED itself drops around 0.2 volts when glowing, So you may consider the entire 13.6 to 16 volts as dropped across the resistor

A "High brightness wide angle" LED from Radio shack says 20 ma max (that os 20/1000 amp or .02 amp) so let's limit it to say 18MA to be safe. at 13.6 volts that's i=E/R R=E/I or 13.6/.018 or  755 ohms

Now let's see what happens to the current if we kick the voltage up to 16 to equalize the batteries..

16/755= 21ma.  20 is the max. but the .02 volt drop will make up the difference

Though they call them "12 volt" most are designed for 13.6

Now, if you want to keep them the same brillance, no matter what the battery does, you start with a 3 terminal voltage regulator, one with a FIVE volt output (or 9, don't really matter but  5 works better)

now you use 5/.02 or 250 ohms, and the bulb won't dim till the batteries are well into the DANGER zone. (Around 7 volts)

I use 12 volt LED indicator arrays, cause they are low cost and easier than building my own, I've used them on five or six volt lines and gotten good indication (Glow) so I know you can use a bit larger resistor.