Third brake light for my 64

[Yadkin]

Here's the lit assembly (no resin yet) on a battery charger.

From a upper angle:



And straight on:



Tomorrow I'll stop at the shack and get a fuse for my VOM tester and a pot.

[scumdog]

What happens if an LED fails to work - can it be easily replaced?

[simplyconnected]

Most solid state devices go through a 'burning-in' period, where they are run for a time. Normally, if a solid state device fails, it will be sooner rather than later. LEDs are no exception.

Most LED devices make it nearly impossible to replace a single LED without tearing into the whole thing. But the flip side is, LEDs normally last for decades.

Back in 1983, I made numbers for my 1949 wooden front door. I routed out the center and drilled a hole to the hinged side. Then I put sandwiched plexiglas with my house numbers in the hole. I made this during down time at work.

I connected the wires to my doorbell transformer and made a small voltage regulator because the LEDs were too bright (lit up the front porch). That part is screwed to my floor joist in the basement.

These have been crankin' for thirty years without a single failure. It stands out from the street at night:


I used telephone handset wire at the hinge. I think I replaced it twice. I can't count the number of folks that asked me to make one for them (mostly neighbors). - Dave

[Yadkin]

Wow that's an old door. Hinges on the outside?

[Yadkin]

Dave,

I wired it up and powered the circuit by the Jeep, engine warm and idling, directly on the positive battery terminal and good ground. Through the diode the current is 50 mA, if I feed after the diode it is 130 mA.

Running 50 mA/ 28 bulbs = 1.8 mA/ bulb. That's about 9% of the rating.

Steve

[simplyconnected]

Wow that's an old door. Hinges on the outside?

Well, I'm old too. Yes, hinges can be on the outside of storm doors. Oh wait, you guys in the South don't have storm doors. Look in the last picture, through the glass, and see the REAL front door (hint: it's open).

We do things differently in Michigan. See that long thing above the LEDs? That's a Mail Slot. Our Mail Person actually climbs up on our porches to deliver mail to everyone's house. Houses here, are raised a few feet off grade level because we have full basements underneath. Most all my neighbors have a mail box attached to the front of their house. Our daily newspaper is delivered to our front porch as well. It's been that way since before I came around.

Here's what it looks like in daylight at Halloween, complete with two porch dogs...


Ha! The front door is left open in this one, too. We leave it open a lot. - Dave

[Yadkin]

Oh don't go on and on about The South. I grew up in metro Boston and we had a door slot for mail. Our German Shepard would try to take the mailman's fingers when he inserted mail. And we had an oil boiler converted from coal, and a work shop converted from the coal bin. The gas meter was in the basement and the poor guy had to knock on the front door, get my mother to lock the dog upstairs then go around to the basement entrance to read the meter. We had galvanized water pipes, screw-in electrical fuses and had to replace all of it. Our house had at least one electrical outlet in each room. And a garbage pail buried in the ground outside with a step-on lid that some guy collected twice/ week to feed his pigs. One time I went to toss the day's garbage in there to find an enormous raccoon looking back at me.

Like many Northerners, your view of The South is probably from I-95 which is flat with a high water table, and homes are built on stilts, crawls spaces or slabs. Here in the Piedmont or mountain regions most homes have basements. Mine's buried on the front and one side with a walk-out at the rear and a two-car garage on the right side. There used to be a windowless room between the garage and finished area so I knocked down a wall to enlarge the garage and that's where my project car resides.

I also have a storm door on the front but took it off the back since it makes it easier to get to the gas grill with both hands full.

And yes my mailbox is on a post next to the street.

[simplyconnected]

My folks are from anthricite country in PA (because they mined coal in Wales), I was born in Chicago, but I absolutely love the South. In fact, Dare County is very prominent in North Carolina's Outer Banks. It was named after my people (yes, I'm related to Virginia). Dad lived in Lakeland, FL (straight down I-75) for 20-yrs. My brother lived in Louisville, KY forever (working at Lousiville Assembly). Robin has many Navy rel's in VA, and last time we were there we took in a great NASCAR race at Martinsville Speedway. We're all over the US.

Back to your situation. Yes, it's a situation. Just to clarify your measurements:
You have paralleled four series circuits with one series diode.

• The diode (1N4004) should have dropped the supply voltage by about a volt. But the real purpose of the diode is to protect the LEDs from Counter Electromotive Force (CEMF) up to 400-volts. I do not recommend using a battery charger because it is an AC device and we have no idea how much ripple it produces. Again, use a car battery.
  • Current measurements for each series branch should be less than 0.02a.
    • Series circuits share the same current flow.
    • Parallel circuits share the same voltage.
    
    So, 4 (parallel branches) X <0.02a (series branches) = <0.08a TOTAL.
    0.15a is twice the current you should expect, and may damage your LEDs.

Follow my suggestion using the potentiometer to bring the current down.

[Yadkin]

Dave I think we have our units messed up. The bulbs are good for 20mA. 4 x 20 = 80 mA. I only have 50 mA through the diode.

[simplyconnected]

Yes, I see that. I wanted to know if you are using the diode and what do you think of the light intensity?

From the pictures, they look white. That could be from the camera washing out from 'looking' directly into the lights. Anyway, it looks like you are all set.

I still didn't get my order, so I called MPJA in FL. They said it shipped on the 16th and should be here Mon. They also said their computers all crashed last week and they 'lost' a day, trying to get back up and running. That's MY kind of luck. - Dave

[Yadkin]

Yes I'm using the diode. I'd like the bulbs a bit brighter as they are running at 62% of their rated amperage. But with this set up I can skip the potentiometer and not worry about burn out.

Or I can rewire to 7 sets of 4 with the potentiometer and dial it in to closer to the rated maximum.

Just approximating, but that should get me 62% x 7 ÷ 4 = 109% without the potentiometer.

[simplyconnected]

Man, if it's not one thing it's another. My order finally came in. I connected a car battery (with a charger to bring it up to 14-V) with seven LEDs and two VOMs, one for voltage (on the left) and the other for current (on the right).

Using the least components, we have four branches of SIX LEDs and one with FOUR, giving us 28 LEDs. Here's the circuit:

As you can see, I took one LED out and added a resistor in each branch to get less than 20mA. Here's the branch for SIX LEDs:

...and FOUR LEDs:

These LEDs are so bright, my camera couldn't get much detail. The brightness washed the picture out but you can see what's going on.

After grabbing all these great pictures, I tried posting. Oh, no... the server was full, and wouldn't let me post. I thought the worst because our server lives about ten miles from me and it's been cold (ten degrees F), windy, and many houses are without power.

It looks like we're up again. Cross your fingers.

Got questions or concerns? Shoot them by me. - Dave

[Yadkin]

Wouldn't it be easier to set it up with 7 sets of 4 and a single resistor after the diode?

[Yadkin]

My dad is here for a few days, he's a retired electrical engineer and looked this over.

The LEDs are rated at 5v maximum reverse polarity. Since they are wired in series of 7 that's 35v. Even wired wrong, the 12v battery won't fry them. He suggested I nix the diode.

When I take the diode out the circuits brighten up per the original plan. No resistors or other junk needed.

DONE!

[simplyconnected]

...just a word of caution: LED's are current devices. That means OHM's law doesn't quite work with LEDs. Use THIS CALCULATOR for your circuit. If they have a 20ma rating (0.02a) I would run them at fifteen milliamps. They will last MUCH longer that way.

I realize that you are using them for simple brake lights that don't come on or stay on for very long. But LED's can fade quickly if driven hard (using threshold current) and they aren't very forgiving if someone reverses your battery leads, even momentarily. How likely will this happen? Probably not very likely but if it ever does you're really going to be mad. That's the reason for the diode. Another 'trick' I do is, make a simple bridge from four 1N4004 diodes. That way you cannot get the polarity wrong and it safeguards your LEDs.

Resistors and diodes are cheap. If you need any I will send them to you. - Dave