Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

12V power source for leds

Status
Not open for further replies.

poolman966554

New Member
hey all, looking for a bit of advice here. Im pretty inexperienced, but trying my best to figure things out.

Im looking to install some 5050 leds on a vehicle, but not sure how to power it up..

The leds have resistors onboard, that are specified for 12v usage. Unfortunately batteries can run up to 12.7V and much greater while engine started.
Running while engine is on is not the plan, but would have to make the mistake and forget and put 14.4v though the strand

My first thought was a 'quick n dirty' LM7812 and caps, but quickly realized by datasheet that it can only provide up to 1 amp out. The strand could pull up to 5A @ 300 leds .

Any suggestions here would be appreciated.
 
I have never heard of "5050" LEDs. Can you post their datasheet or a link to it?
Maybe they are made for a 12.0V power supply not a vehicle battery that charges at 14.4V.

The minimum input for a 12V regulator is 14.5V for a 7812 or 15V for an LM338 (it can supply 5A) so they will not work if the input is only 12.7V when the battery is not charging.
 
The strand could pull up to 5A @ 300 leds
Are you sure about the current? From my limited research it seems some LED strips are wired with all LEDs having respective current-limiting resistors, whereas other strips (e.g. as supplied by Maplin) comprise LED groups, each group having 3 LEDs in series with a single resistor. The latter arrangement would draw less total current.

Edit: I don't know which country you're in, but in the UK at least there are strict regulations about vehicle lighting. Also, vehicle modifications are likely to invalidate your insurance.
 
Last edited:
Vehicle lighting is also regulated in Canada. Car owners are not allowed to modify the lighting the car was made with.
But they allow fairly new Chrysler cars and Jeeps to blind oncoming cars with their full brightness high beams used for daytime running lights. When it is dusk, cloudy or raining then the Chrysler and Jeep daytime running lights are unbearable.
 
Can you post their datasheet or a link to it?
Im not sure if i can post a link here, but if you were to search ebay for" RGB 5050 Waterproof leds" im sure youll get the exact same led strip.

Are you sure about the current?

That i am not. As i haven't put an ammeter in series to verify current.. The specs on ebay says .2A per led, 300 led per strand though.
As for law, im not to concerned about that portion as i wont drive with them on. I just dont want to make the mistake and remote start the vehicle with lights on. also im pretty sure cars are not allowed, BUT motorcycles are! i do have rgb on my bike, but controlled from an atmega328, and transistors..
 
i completely agree Guru, but again, im def being responsible here.. this mods for parking lot scenarios.. I definitely dont need police trying to stop me lol.

That said, we have the lighter end of enforcement here in Erie,PA..
As i said motorcycles are allowed as much as they want by this code:
http://www.dmv.state.pa.us/pdotforms/vehicle_code/chapter43.pdf.

The last page, "4310. Motorcycle Lighting" says we riders may add led, and strips to our bikes so we can be seen.
 
The strip of LEDs comes with a 12V/5A power supply which is probably voltage regulated so the LEDs might burn out if powered from the variable voltage of a vehicle.
 
Limiting the current might be a better bet .....providing you know how much current the LEDs are rated for.
 
Since the spec's for the LED strips have no details then we do not know anything about them. We are simply guessing.
The photo shows that each group of three RGB LEDs has 3 resistors so I guess that the three red LEDs are in parallel then have a series resistor and the same for the green and blue.

The spec's say the 300 LEDs use 60W (12V x 5A= 60W) disregarding the power wasted in the resistors.
Then the current in each LED of one color is 5A/300 LEDs= 16.7mA then three of them draw 16.7mA x 3= 50.1mA.
Assuming that the green and blue LEDs have a forward voltage of 3.2V then the current-limiting resistor for each group of three green or blue LEDs has a voltage of 12V - 3.2V= 8.8.V. Then the resistor value is 8.8V/50.1mA= 176 ohms (probably the standard value of 180 ohms).
If the supply is 14.4V then the voltage across the 180 ohm current-limiting resistor is 14.4V - 3.2V= 11.2V, the current in each triad of one LED color is 11.2V/180 ohms= 62.2mA and the current in each LED of one color is 62.2mA/3= 20.7mA which is only 25% higher than if the supply is 12V so the LEDs might not get fried, but the resistors might burn out.

The increased current in the red parts of the strip is the same when the supply is 14.4V.
Assuming that the forward voltage of the red LEDs is 2.0V then with a 12V supply assuming that the current is also 50.1mA for each triad of red LEDs, the resistor value is 12V - 2V/50.1mA= 200 ohms.
Then when the supply is 14.4V the 200 ohm resistor has a current of (14.4V - 2V)/200 ohms= 62mA and the current in LED of one color is 62mA/3= 20.7mA.
But the current-limiting resistors for the red LEDs have a higher voltage across them and therefore get hotter and might burn out sooner.

I hate guessing about missing spec's for cheap Chinese junk sold on ebay.
 
If you wanted to build your own low drop-out regulator you could try this. Note that the FET can dissipate up to 15W, so would need to be on a substantial heatsink (electrically insulated from the vehicle metalwork).
LEDstripRegulator.gif
 

Attachments

  • LEDstripRegulator.asc
    2.7 KB · Views: 131
thanks for the responses!

guru, i hate china stuff too, but theres something about browsing ebay at 3am that always seems to get the best of me lol.
The strip comes with a controller, that handles PWM for the fade, and creating different colors.. not sure how that would respond to an increase in voltage,as i havent opened it up. thats why i was thinking of a dc-dc regulator or some sort.

Alec, thanks for the schematic! ill def keep that in mind.. i already have most parts on hand
 
The voltage regulator circuit from Alec is perfect for the LED strip product in a vehicle.
Where will you put 300 LEDs on a motorcycle?
They would look cool on the wheels but how would you make connections when the revolve?

EDIT: The LM324 is a quad opamp (it has four opamps in it) in a 14 pins package but an LM358 is a dual opamp in an 8 pins package with the same opamps. I think there is or was a single opamp the same but I have never seen one.
 
5050 LED's are used in SMD striplights which you see on ebay.
It is a code number. These LED chips look yellow but are actual white
 
link attached to one of these 5050 SMD lights.

**broken link removed**
 
Circuits like Alec's have major stability problems. You can add a resistor between the 431 and the minus input and connect a cap from output to minus in and hope for the best. I have frequently found that the cap value that is right for one load still allows oscillation at a different one. I don't like to admit it, but I usually give up with this circuit because I don't have the math skills anymore to solve the heavy duty equations needed to determine the optimum compensation scheme.
 
5050 LED's are used in SMD striplights which you see on ebay.
It is a code number. These LED chips look yellow but are actual white
Most white LEDs are a blue LED with a yellowish see through phosphor on top. The yellow phosphor has enough red and green light so the total combined with the blue make white light.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top