heat sinks / Can a 12V LED chip be installed directly into a car?

primuspaul · Feb 2, 2018

Can a 12V LED chip (the ones sold from China for $0.80 / pc) be installed directly into a car? Obviously the risk is from overvoltage since car batteries can supply anywhere from 11 volts when the car is off and the battery is powering multiple accessories (or one big one) to 14V when the alternator is running.

Obviously it will need a heat sink such as this:

https://www.ebay.com/itm/10pcs-40mm...eatsink-Fin-For-LED-Chip-Cooling/111737412513

I was just wondering if that would be enough to cool the LED to avoid premature failure due to heat.

Is that a good price for the heat sink? Anyone use scrap metal instead? I was just wondering if it's more cost effective to just buy a block aluminum ingot and use that instead of an aluminum heat sink.

rsk_productions · Feb 3, 2018

You can but will work powerful. And the voltage mount before led a diode.

primuspaul · Feb 3, 2018

rsk_productions said:
You can but will work powerful. And the voltage mount before led a diode.

What spec diode?

The led chip is 10w.

rsk_productions · Feb 3, 2018

primuspaul said:
What spec diode?

The led chip is 10w.

A Diode Zener. Search at Google diagrams and specs.
Diode Zener rear mounted work like a Voltage limiter. But don't rectificate the amparage.

ssanasisredna · Feb 3, 2018

If you are thinking of making or modifying your own car headlight ... don't. (it's illegal virtually everywhere).

Zener Diodes are clamps. Put one across a car battery and it will go "pop". I suggest buying an off-the-shelf driver if you don't know what you are doing.

DIWdiver · Feb 3, 2018

In general, you cannot expect a COB led to work very well in a car without some additional components. The voltage variation you mentioned is only one of the reasons.

Another is transients. Every time you turn something on or off (light, wipers, vent fan, AC clutch, etc) it creates a very short burst of high voltage that travels through the electrical system. These can be very damaging to electronics, including LEDs. A transient suppressor is an electrical component designed to block these from reaching your sensitive device. There are several types, with the zener diode type probably the most appropriate for this application.

The worst thing though is that the "12V" LED may actually want 10V, and 12V could severely overdrive it. The main problem here is that you don't actually know what voltage you should use, and it's pretty important. In an ordinary 12V light bulb, if you put 11V on it, it would be slightly less bright, and last slightly longer. If you put 14V on it, it would be somewhat brighter, and have a somewhat shortened lifetime. An LED is very different. If you had one that performed to spec at exactly 12V, then at 11V it would be significantly less bright and have a significantly longer lifetime. But at 14V it would be quite a bit brighter, and have a severely shortened lifetime.

To get the specified performance, an LED should actually be driven with a specific current, not a specific voltage. To get 10W at 12V, you'd need 0.833A. So you might think a 12V, 10W LED would specify a current of 0.833A or 833 mA. But you'd be wrong. Just for a reference, I looked up two available on eBay. Both specified 900 mA. One said 9-11V, the other said 12-14V. Both are advertised as 12V, 10W leds, even though 900 mA gives you 8.1W at 9V, 9.9W at 11V, 10.8W at 12V, and 12.6W at 14V!

The main thing to keep in mind is that if you apply a voltage within the specified range, you can't expect what current to get, while if you apply the specified current, the voltage should be within the specified range.

This is why there are LED drivers. They are current sources; they apply a fixed current and let the voltage do whatever it needs to do (within limits). This requires electronics. There are some workarounds (like limiting resistors), but they involve performance compromises.

Depending on what your expectations are, I would say the bare minimum components are: fuse, transient suppressor, limiting resistor, heatsink, and, of course, the LED.

primuspaul · Feb 4, 2018

rsk_productions said:
A Diode Zener. Search at Google diagrams and specs.
Diode Zener rear mounted work like a Voltage limiter. But don't rectificate the amparage.

ssanasisredna said:
If you are thinking of making or modifying your own car headlight ... don't. (it's illegal virtually everywhere).

Could you expand on this? I know adding some light colors (like blue) or adding strobe lights can be illegal, but I have not heard of DIY repairs being illegal, which is what I want this for. If I have a headlight or taillight burn out, it's comforting to know that I can fix it with superior, cheaper parts I already have. LEDs are superior because they can provide the same amount of light while drawing less current and putting less strain on the car wiring. That's why I was thinking about underdriving the LED, since I don't need it to work at 100% power and since the low beams are all you need and they're primarily to let other drivers see you, not to illuminate the road.

Zener Diodes are clamps. Put one across a car battery and it will go "pop". I suggest buying an off-the-shelf driver if you don't know what you are doing.

DIWdiver said:
In general, you cannot expect a COB led to work very well in a car without some additional components. The voltage variation you mentioned is only one of the reasons.

Another is transients. Every time you turn something on or off (light, wipers, vent fan, AC clutch, etc) it creates a very short burst of high voltage that travels through the electrical system. These can be very damaging to electronics, including LEDs. A transient suppressor is an electrical component designed to block these from reaching your sensitive device. There are several types, with the zener diode type probably the most appropriate for this application.

The worst thing though is that the "12V" LED may actually want 10V, and 12V could severely overdrive it. The main problem here is that you don't actually know what voltage you should use, and it's pretty important. In an ordinary 12V light bulb, if you put 11V on it, it would be slightly less bright, and last slightly longer. If you put 14V on it, it would be somewhat brighter, and have a somewhat shortened lifetime. An LED is very different. If you had one that performed to spec at exactly 12V, then at 11V it would be significantly less bright and have a significantly longer lifetime. But at 14V it would be quite a bit brighter, and have a severely shortened lifetime.

To get the specified performance, an LED should actually be driven with a specific current, not a specific voltage. To get 10W at 12V, you'd need 0.833A. So you might think a 12V, 10W LED would specify a current of 0.833A or 833 mA. But you'd be wrong. Just for a reference, I looked up two available on eBay. Both specified 900 mA. One said 9-11V, the other said 12-14V. Both are advertised as 12V, 10W leds, even though 900 mA gives you 8.1W at 9V, 9.9W at 11V, 10.8W at 12V, and 12.6W at 14V!

The main thing to keep in mind is that if you apply a voltage within the specified range, you can't expect what current to get, while if you apply the specified current, the voltage should be within the specified range.

This is why there are LED drivers. They are current sources; they apply a fixed current and let the voltage do whatever it needs to do (within limits). This requires electronics. There are some workarounds (like limiting resistors), but they involve performance compromises.

Depending on what your expectations are, I would say the bare minimum components are: fuse, transient suppressor, limiting resistor, heatsink, and, of course, the LED.

What about this?

https://www.ebay.com/іtm/DC-DC-5-40...Down-Convеrter-Voltаge-Regulator/1527О4811482

It says it can handle a wide voltage input and you can specify your output with the potentiometer. Can do 1.8A output, which translates to over 20W (should be enough for a 10W LED).

I'm thinking about that $0.80 item, this 10" bar which should be good for 10 lamps ($1 / pc)

https://www.amazon.com/Rеmingtоn-Industrіеѕ-О-5ОX1-5FLT6061T6511-10-Aluminum-Extruded/dp/BО1M24T7Z5/

Thermal grease which I already have, $0.80 for the LED chip. Works out to about $2-3 a piece. I'd get a driver like you suggest, but I am having trouble finding the right item for a good price. Most of the stuff on ebay is for converting mains current, not 12VDC.

nbp · Feb 4, 2018

Moved to Automotive lighting subforum.

-Virgil- · Feb 4, 2018

…and closed, because your ideas for homemade/modified vehicle lighting are illegal and unsafe. Rule 11 of this board prohibits advocating illegal or dangerous activity. If you want to build it yourself, or follow wherever your imagination leads you in terms of modifying lights, keep it to flashlights, household lights, and other non-safety-crucial, non-safety-regulated lights. Car lights aren't on that list.

I know adding some light colors (like blue) or adding strobe lights can be illegal, but I have not heard of DIY repairs being illegal

You're not talking about repairs, you're talking about modifications.

If I have a headlight or taillight burn out, it's comforting to know that I can fix it with superior, cheaper parts I already have

The modifications you think you have in mind will not make your car lights work in a "superior" manner, quite the opposite in fact.

LEDs are superior because they can provide the same amount of light while drawing less current

Number one, most of the LEDs you already have probably do not put out the same amount of light as most of the bulbs in your car. Number two, that goes double for cheap generic crap ordered over the internet from China. Number three, LEDs do not emit light in the same pattern as filaments, which means even if you manage to cram an LED where a bulb belongs, it will not be optically compatible with the lamp, which in turn will not produce the right amounts of light through the specified angular ranges. Car lights are a whole lot more complicated than "Yep, it lights up".

since the low beams are all you need and they're primarily to let other drivers see you, not to illuminate the road.

Absolutely zero percent of this is true, correct, or accurate.

The problem here is that you are substituting guesses (bad ones) and assumptions (ignorant ones) for knowledge that you clearly completely lack. If you had this knowledge, you would understand immediately why your "LED retrofit" ideas are non-starters. Car lights are life safety devices, not toys. They have to work correctly, as measured objectively according to very detailed technical safety standards. You cannot bodge this on your workbench, no matter how enthusiastic you are.

Alaric Darconville · Feb 4, 2018

primuspaul said:
I have not heard of DIY repairs being illegal, which is what I want this for. If I have a headlight or taillight burn out, it's comforting to know that I can fix it with superior, cheaper parts I already have.

No, you're not repairing a failed headlamp with some 80-cent LEDs.

Closed for Rule 11.

heat sinks / Can a 12V LED chip be installed directly into a car?

primuspaul

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rsk_productions

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primuspaul

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rsk_productions

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ssanasisredna

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DIWdiver

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primuspaul

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nbp

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-Virgil-

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Alaric Darconville

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