Hooking up a 12v DC LED strip box to Automotive wiring?

[electricview]

Hey guys, new here and a questiona bout wiring an led control box to my car!

I've in the past had some super cheap LED strip lights and a control box in my car for a few months then the box stopped working, I assume its becuase it preferred 12v and the way i had it wired up was probably giving it anywhere from 12-15 volts depending on if the car engine was on or accelerating or not. anyways i'm buying a new box from a website and i want to try to expand its life a little longer than 6 months this time..

I have it hooked up leaching off the glove box lightbulb wiring, so it only is on when my parking lights/headlights are on at night. I've read one person used a 7812 inline to keep the voltage down, I am aware the 7812 wouldn't protect against larger spikes, but I asume these occasional spikes are not what was killing my old box just the constant 14.8v while driving.

so here's the specs.

From what i understand my 1 meter of lights, consisting of 3 colors, each color line uses 300mah of power, so the total draw of the lights should be less than 1amp i believe. But the box i'm getting supposedly has these specs:

Voltage: DC 12V
- Output: 3 CMOS drain-open output
- Static power: < 1W
- Max output current: 2A each color
- Output power: 5V<30W; 12V<72W; 24V<144W

the picture of the controller box says "Output 12v 3*2A

So i'm not sure if that means this controll box is going to draw 6 amps even tho my particular lights are only going to use 900mah? or if the control box will only draw 900mah therefore making the 7812 possible to use? I realize if the car is off and i wanted to turn on the lights my battery would be supplying around 13.70-13.90 volts and it might not be enough for the 7812 to do its thing? (or would the lights just be real dim?).

I'm trying to avoid spending tons of cash on this solution. The replacement control box is only costing me around 8 or 9 bucks, so spending 30 on some kind of voltage converter/limiter/capcitor concoction isn't really an attractive option for me. Heck i was just gonna throw a resistor in line just before the box assuming most of the time my power would be at 14.5volts and hope it would work!

I didnt post any links to the actual box in case its frowned upon here, but its from Dealextreme (chinese).


Anyways any advice or thoughts on this would be much appreciated!

Thanks knowledgable peoples!

 

[Reloadron]

A link to the box would be fine and is encouraged.

The biggest problem you face is that a 7812 is a 1 amp (with heat sinking) regulator with a dropout voltage of two volts. That means it will not work below 14 volts or better. This is where automotive LED projects become a problem. The data implies 2 amps times 3 outputs for a 6 amp (6 * 12 = 72) watt maximum as I read it anyway.

Ron

 

[electricview]

Does drop out mean that it just completely wont function below 14 volts? or that it will just be very low power? I think the lights will light up with around 8 volts.. (i've hooked up a 9volt battery and it powered them for testing purposes, albiet dimmer than usual).

Here's a link to what I "Originally" Bought: **broken link removed**

The box from that burned out (or rather just doesnt seem to function, I'm not sure why, I have basic multimeter skills, the resistors all seem to respond correctly for their values, i suspect the ' 3 pronged jobbies in there ' (are those gates?) might be dead and i'd replace em but wasn't sure if that was possible or not).. ANYWAYS...

The lights still work, but since the box died, i went and purchased this: **broken link removed**

With the assumption that I could hard wire 2 wires to the circuit board for power (instead of using the A/C slot hole that appears to be in there). That might have been a bad assumption on my part but i figured I could make it work.. And i think it should be enough to power the lights..

So a 7812 is not gonna work cuz when the car is off and its just battery power i.e. 12.60 ish volts, they wouldn't turn on? (but would it work okay when the car is on and i'm getting around 13.90-14 volts? is there any other cheap options that might just help prolong the life? I'd probably be pretty happy with a year maybe 2, but 6 months is kinda short..

 

[ronv]

You might still be able to use it. It is just that when the battery is at 12 volts the output will be 10 volts. How much current does your led strip take?

 

[electricview]

Best I can tell? 12 volts. it's these: **broken link removed**

But as i said, I needed to test if the lights were dead when my first controller box stopped working, so i took a regular 9volt battery out to the car and wired one end up to the 12 section of the strip and then the negative lead to each individual color, They each (1 at a time, i didnt try to power all 3 with the single 9 volt battery) lit up just fine, they were probably about 70-80% of their max brightness but definately bright enough to see during bright overcast daylight.

You guys are awesome for your quick replies and helping me out on this! I learn as I go, and i'm still a novice at this stuff

 

[ronv]

Should work. One maybe 2 strips per 7812. You might want to put it on a small heat-sink if it gets hot when the car is running.

 

[Boncuk]

Here are some values of an ideal 7812 regulator:

Input (V) - Output (V)

12 - 10.8
13 - 11.8
13.5 - 12.0

There is little chance the LEDs will be damaged even without voltage regulator.

My stepdaughter uses four LED strips on her motorbike all connected directly to the battery. They flicker at low rpm, getting steady at higher.

Boncuk

 

[electricview]

Ronv: When you say one maybe 2 strips per 7812, do you mean strip of light? I only have 1 strip (that i've cut in half to seperate to the driver and passinger side, then spliced together with 13 inches of wires), So one 7812 might do? Also when you say a possible heat sink, do i need something large? would it be silly to consider something like a copper penny?

And how would i wire this? positive from the power source to the first lead i assume, then the output to the boxes positive lead, but where do the neg's go? they both connect to the negative pin of it?

I'm asuming this is what i'd be getting right? http://www.electronicecircuits.com/...age-Regulator-lm7812-IC-pin-configuration.jpg

Boncuk: well i'm using a control box with the lights, and i'm just more concerned it's the thing thats dying (since the first one stopped working) It seems the LEd's themselfs are FAR more resilient than the control box

 

[Boncuk]

Hi electricview,

it would be nice if you had a schematic of the control box or take a good photo of it to study the parts used in it. Maybe there are CMOS chips involved which are very sensitive to voltage spikes as caused by the car alternator.

Regards

Boncuk

 

[KeepItSimpleStupid]

The automotive environment is basically hostile. Some reverse engineering could help.

I remember a thermocouple scanner with a Wall Wart power supply with CMOS devices. We were using it near some 500 to 100O W IR lamps and the scanners kept dying. Inside, they had the silk scree locations for a full regulator. Added a Transorb or TVS and a fast reverse diode and all was happy for many years.

At a minimum, you should add 3 parts:
1. Transorb for about 18V
2. Fast reverse diode across the power supply input. Fuse first.
3. Fuse.

The reverse diode does two things: 1) Protects against the -200 V alternator dump and if someone powers the unit backwards.
The 18V fast clamp protects against positive transients.

These components aren't cheap and I've been having trouble finding TVS stuff lately. Could cost you >9 with shipping. Fuse, fuseholder etc and hope you can mount it in the same case.

 

[electricview]

I would need a seperate fuse and couldn't rely on the one that the glovebox light was already using? is that becuase the glovebox fuse is probably a 5 or 10 amp and that would blow the box itself or something?

Boncuk at this time i only have the first (not working right now) box, I could take a picture of though it has a picture on deal extreme : https://img.dxcdn.com/productimages/sku_14962_6.jpg

the new box i dont have just yet, it's on its way from china, I just wanted to check ahead before i got to be informed. but i can definately take a picture of it when i get it open and post it here.

I guess i got lucky when i put regular LEd's with just resistors in place of my old bulbs in my dash then and they haven't blown yet?

 

[KeepItSimpleStupid]

Classic example where the transistor blows in order to protect the fuse. The diodes are the most important. Fuses are usually sized for the wiring because they protect the infrstructure. Sizing the fuse for the circuit, helps protect the circuit. Two different purposes.

Having fuses that a consumer can replace invites problems because it's likely that they will be replaced with any value handy. They used to be replaced with pennies.

 

[4pyros]

Looking at the pictures from the DX website and the fact that ti uses AT89C2051 MCUs. I think it already has a voltage regulator. I don't think your car voltage killed it. Looking at the build quality of the unit you may have a bad solder joint or a snapped wire.

 

[electricview]

Looking at the pictures from the DX website and the fact that ti uses AT89C2051 MCUs. I think it already has a voltage regulator. I don't think your car voltage killed it. Looking at the build quality of the unit you may have a bad solder joint or a snapped wire.

I'm not a pro with the multi-meter but i did try to test the output leads for each line when i had this thing hooked up to my car (after it fried) it looked like it was only outputting around 3 volts to each line, but some power was being output. I tested each resistor on the board and they all correctly registered values within 5%. I did not know how to test the 3 pronged guys with heat sinks (are those the transistors?) and didn't think it was possbile to test the IC's in the middle of the bored.

To be honest my first thought was to find out what went bad in my original box and just try to buy replacement parts, becuase heck if it was cheap enough, i'd be okay with replacing a part in there every 6 months or so, if it only costs like a buck each time, but when my novice problem sovling skills couldn't find a defunct part, i gave up on that idea and ordered the new box (slightly different brand/model).

If its true that my car voltage didnt kill the old one (not sure if the new one is going to have that since it looks like its designed for an A/C adapter, and the #1 box wasn't designed for that). How could i better trouble shoot the rest of the parts that i either a. dont know how to test properly, or b. cant test properly? (i can always take more pictures if it helps.

 

[4pyros]

yes post a pic, we need to see the numbers on the parts.

 

[electricview]

Okay here is a picture of the older box the one thats 'not working' currently (the new box should be here in a few days). If you need a close up of any parts let me know.


**broken link removed**

 

[KeepItSimpleStupid]

As suggested, we need to see the part numbers. There are at least 3 drivers, 2 things that use a processor and what looks like a voltage regulator.
The processors may be sensitive devices. Since they are likely programmed by the manufacturer, it's not likely replacing them will do anything.

Checking the output of the regulator is your first test. It can tell you, if it's working or whether some device is shorted.
From ground (the black lead), measure the voltages on the 3 pins of the regulator and report back. The number would help too, but it's probably a 7805 or similar.

 

[4pyros]

The transistor looking thing in the middle of the right side where the power comes in is a 7805 liner voltage regulator in a TO-220 package. The the tab on top with the hole in it, is common or negative, the pin on the right is the input, closest to the power wire, it should be getting 12 volts from the car. The pin on the left is the output it should be 5 volts. the pin in the middle is common or negative, its the same as the tab. Get your meter and check the input and output of the 7805 regulator.

 

[4pyros]

I dont like the way the diode looks in the upper right corner. Is it chared or does it have glue on it or something?

 

[electricview]

YEah the diode was covered in solidified hot glue when i got it, so i chipped it all off, its probably residue left over from that, I thought i tested the diode and it was working a-ok, but i'll do that again shortly here..

For the 7805 is the only way to test it properly, to hook up the box to the car power source again, and then measure the output and ground lead and see if its 5v?


*** edit

Okay I just tested it how i think it should be tested, I put the black lead of my multimeter on the middle pin (i also tried the top part with the hole as well same readings that way) and the red lead from the multimeter on the 3rd pin (or better yet, the pin that is just under that little circle symbol with what looks like "e3" written inside it)

the readings were varied, from anywhere around 1.2 to up to 1.70 volts, I dont believe i ever saw it reach 2 volts at all..

Just for the heck of it i also put the leads on the solder dabs where the + and ground come in from the car source and attach to the PCB. I was only getting about 3.5 to 3.7 volts right there, I tested the actuall leads from the car they were registering at 11.60v so i'm not sure if this is correct or not, i guess I assumed it would be 11.60 at the solder points on the pcb where those cables attach to it, i guess not?