Need some help. I am looking to make an led light pod with 5 leds with a 12v battery (continuously charged) . Which leds will work better (less heat and better illumination). 3v or 6v.

 

Welcome to AAC.

LEDs configured to operate at either 3V or 6V, on their own, will simply make a cracking sound and some smoke–of course.

This means you will have to arrange the LEDs in series and/or parallel circuits. There is no heat advantage for either option, however with the 3V LEDs you can have two for each of the 6V ones possibly offering the chance to physically distribute them in a more advantageous way for more uniform light.

The 6V option, by default would use a 2SnP arrangement where 2S refers to two LEDs in series and nP refers to paralleling the 2S pairs where \( \mathtt{n = \large{LED_{pieces} \over {2}}} \).

The same holds true for 3V but since \( \mathtt{{12\div3}}= 4 \) the series part will be four LEDs for a 4SnP configuration.

Bear in mind that each of the S groups will require an appropriate current limiting resistor.

 

You could put all five of the three volt LEDs in series across the 12volts and they would not be operating at the maximum power, so the heat would be less. OR you could either have 4 LEDs or six LEDs and the arrangement would be much simpler for either 6 volts power or 12 volts power.. Isit toolate to revise the design??

 

You could put all five of the three volt LEDs in series across the 12volts and they would not be operating at the maximum power, so the heat would be less. OR you could either have 4 LEDs or six LEDs and the arrangement would be much simpler for either 6 volts power or 12 volts power.. Isit toolate to revise the design??

Yeah, I can see where putting five 3 V LEDs in series and then powering the string with 12 V would definitely produce less heat. Of course, we will need a flashlight to find it.

 

Need some help. I am looking to make an led light pod with 5 leds with a 12v battery (continuously charged) . Which leds will work better (less heat and better illumination). 3v or 6v.

Are these individual LEDs, or LED modules designed to operate from a specific voltage? Do you have a manufacturer's part number or a link to the data sheet. you could share.

You could put them all in series and then use a constant current driver to provide the voltage needed from the 12 V supply. You could get a somewhat similar, but not quite as good, solution by putting them in series and powering them with a battery eliminator circuit that outputs something like 18 V to 20 V along with a series current-limiting resistor.

 

Yeah, I can see where putting five 3 V LEDs in series and then powering the string with 12 V would definitely produce less heat. Of course, we will need a flashlight to find it.

Are these really diodes rated at 3.00 volts?? That is not a common LED voltage rating.
What is the source of these LEDs?? How much current or power are they rated at??

The fact is that LEDs will illuminate at less than the rated voltage. How much less is variable, because like most diodes the current per voltage is not an instant jump. Diodes are quite non-linear as they go into conduction. And contrary to the belief of some, they do illuminate a bit at less than the rated voltage.

Do you already have the LEDs, or is this project still in the decision stage? If you have them already then a temporary series connection of all five will provide a useful bit of information.

 

Unfortunately, there are three distinct things that people call LEDs.

1. An actual LED component. This is simply a single light emitting diode with no other components. Call these raw LEDs. These are specified to operate at a specific current, and they list a voltage range Vf min to Vf max that the LED will have at that current. These cannot be reliably powered simply by a voltage. Minimally, they can be powered by a voltage of about 1V or more above Vf max with a resistor in series. The voltages specified will typically be in the range of 1.2V (IR) to 3.6V (white or blue)

2. A device that contains an LED and other components (sometimes, simply a resistor) that is designed to operate at a specific voltage. Call them LED lamps.

3. COB LEDs are raw LEDs in series / parallel. These are high powered and typically soecify a higher voltage, more like 30-50V. These really should have a constant current driver.

How you run these from 12V will depend on which you have.

So, which are you talking about, raw LEDs or LED lamps, or (unlikely) COB LEDs.

 

Are these really diodes rated at 3.00 volts?? That is not a common LED voltage rating.
What is the source of these LEDs?? How much current or power are they rated at??

The fact is that LEDs will illuminate at less than the rated voltage. How much less is variable, because like most diodes the current per voltage is not an instant jump. Diodes are quite non-linear as they go into conduction. And contrary to the belief of some, they do illuminate a bit at less than the rated voltage.

Do you already have the LEDs, or is this project still in the decision stage? If you have them already then a temporary series connection of all five will provide a useful bit of information.

DigiKey has 445 Blue or White LEDs rated at a Vf of 3.0 V. They only have 4 rated at 6 V, but they appear to be arrays, usually with three LEDs in series and with no current-limiting diode.

Yes, like any diode, they will conduct some below their rated Vf, but it falls off exponentially at roughly an order of magnitude for every 60 mV to 120 mV. So if you run them at 2.4 V instead of 3 V, that could be between five and ten orders of magnitude less current (and light) than at their "proper" Vf.

 

FIRST, my suggestion was to do an experiment! many of the on-line sellers are vastly less accurate than Digikey!! Thus results may vary quite a bit. Second, the TS has stated that the battery is under constant charge ( a 12v battery (continuously charged) . So we do not know the actual voltage that will be available, except that it will be greater than 12.00 volts.
The simplest thing would be to add one more 6 volt LED and have three sets of two six volt LEDs in parallel, possibly with a single resistor to provide a small voltage drop.

 

FIRST, my suggestion was to do an experiment! many of the on-line sellers are vastly less accurate than Digikey!! Thus results may vary quite a bit. Second, the TS has stated that the battery is under constant charge ( a 12v battery (continuously charged) . So we do not know the actual voltage that will be available, except that it will be greater than 12.00 volts.
The simplest thing would be to add one more 6 volt LED and have three sets of two six volt LEDs in parallel, possibly with a single resistor to provide a small voltage drop.

If you put two 6 V LEDs in series and connect those to 12 V, then the actual current you get becomes highly variable and unstable, due to minor differences in the diodes and the actual supply voltage. So the three strings have a pretty good likelihood, particularly if the LEDs are not from the same wafer lot, to be very noticeably different. A small resistor improves this, but also quickly kills the current and still leaves a lot of uncertainty in the current in the three strings due to Vf variation. You want enough overhead voltage so that the voltage across the resistor is significantly larger than the variation in Vf.

We don't know the reason for five LEDs -- it may be that that's all that will fit. If a DC/DC converter is not an option, then I'd recommend putting three 3 V LEDs in one string and two in the other. Then using appropriate current limiting resistors in each string. With at least 3 V of overhead, you can get pretty stable control of the current. Even the variation in voltage due to the charger (which may or may not actually be continuously charged even if it is continuously connected to the charger, depends on the charging circuit) will probably not result in very noticeable variations in illumination, since humans are pretty insensitive to a factor of two in intensity.

 

I was suggesting two SIX VOLT LEDs in series across 12 volts. or FOUR of the 3 volt devices.

 

I was suggesting two SIX VOLT LEDs in series across 12 volts. or FOUR of the 3 volt devices.

Yes. And if you do either, the ability to control the current becomes almost non-existent because you have no overhead to work with. Small differences in the individual Vf of the LEDs can result in not only big changes in total current, but also big variations in the splitting of current between the strings.

 

Need some help. I am looking to make an led light pod with 5 leds with a 12v battery (continuously charged) . Which leds will work better (less heat and better illumination). 3v or 6v.

This would go much better with links to the LEDs you have in mind.

Ron

 

Yes. And if you do either, the ability to control the current becomes almost non-existent because you have no overhead to work with.

Something sold as a “6V LED” is very like a single LED in series with a resistor. These could be put in series as long as each draws nearly the same current at 6V. But, as Ron said, we need to know what the really are.

 

I have purchased and used a few "LEDs" sold as 12 volt items and never had to "control the current" one bit.
Aside from that, with a 12 volt source and two in series it is not likely to need a lot of control. so the benefit of "Headroom" is not obvious.

 

I have purchased and used a few "LEDs" sold as 12 volt items and never had to "control the current" one bit.

Because they have a resistor already.