LED operation, care & feeding of

[Mike90250]

....

you can use a dc dc converter to be sure that the voltage sent to the lambs is close to that value...

and you are done enjoy

And here, is the end of your knowledge.

LED's (much like PV panels) are CURRENT devices, not Voltage. You do not regulate the voltage to the LED, your control the Current (amps). LED's have a threshold voltage where they start to conduct, but voltage is a minor part of the total requirements.

[ANIKHTOS]

And here, is the end of your knowledge.

LED's (much like PV panels) are CURRENT devices, not Voltage. You do not regulate the voltage to the LED, your control the Current (amps). LED's have a threshold voltage where they start to conduct, but voltage is a minor part of the total requirements.

led is voltage related
the different voltage you apply the different ah they will draw
and since leds have a very narrow tolerance in voltage you need to be sure that the voltage will be in that operating limit

and for the best efficiency you need to go to the min values of the led

so when you talk about leds all the talk is about voltage not ah
and there is where your knowledge to led ends
you know nothing about them

all your concerns in running leds for long life is about providing them a stable regulated voltage
of course all devises consumes amp but in led the only concern is your voltage


Lumen min.: 139
Lumen max.: 488
mA min.: 350 mA
mA max.: 1500 mA
V max.: 4 V

at min efficiency was 137 lumen per watt
going to max 4 volts you go down to 81lumen per watt
but at the same time your current is 4.3 times more

so how it made it a current??
leds is all about voltage
a

[Mike90250]

LED operation

First, I'm going to split this off the OP's thread.

Second, unwritten forum rules - Moderators are always right, unless you have substantial documentation to back
up your views.

Third - here is the simple explanation on driving LEDs

http://electronicdesign.com/components/understanding-led-application-theory-and-practice#single

Driving Single LEDs

It seems as if driving LEDs ought to be simple. They’re diodes, they have a certain forward voltage drop, and their light output depends on current, for which there is a do-not-exceed value for any given diode. That seems like a manageable set of parameters, doesn’t it? But then it starts getting complicated. As with conventional diodes, LED current varies exponentially with the voltage, i.e., a small change in voltage can cause a large change in current. That’s why, in most cases, LEDs are driven with constant-current sources.

https://en.wikipedia.org/wiki/Light-emitting_diode#Power_sources

Power sources

The current–voltage characteristic of an LED is similar to other diodes, in that the current is dependent exponentially on the voltage (see Shockley diode equation). This means that a small change in voltage can cause a large change in current. If the applied voltage exceeds the LED's forward voltage drop by a small amount, the current rating may be exceeded by a large amount, potentially damaging or destroying the LED. The typical solution is to use constant-current power supplies to keep the current below the LED's maximum current rating. Since most common power sources (batteries, mains) are constant-voltage sources, most LED fixtures must include a power converter, at least a current-limiting resistor. However, the high resistance of 3 V coin cells combined with the high differential resistance of nitride-based LEDs makes it possible to power such an LED from such a coin cell without an external resistor.[126]

(I added the bold)

And for a real life example of how Current is the factor for LED's, take any simple LED that does not have internal resistors, and connect it to a high current voltage source, and set the voltage for the max LED voltage.

Use lead acid cells, large NiMh cells, something that will not allow voltage sag when the LED is connected.
Try it first with an incandescent light bulb, on a 12V car battery. A 12v brake light just lights up.
Voltage, with unlimited current.

Now with an LED, you will, when the circuit is powered up, see a brief flash of light as the LED vaporizes itself, as it wants to suck every amp from the batteries it can. A forward conducting diode has very little resistance and requires current control to prevent burning out.

So you just do it your way and enjoy replacing LED's

[sensij]

To be fair, his suggestion was to use this series of LED, 6 strings of 4 leds in series. Based on the data sheet, forward voltage is 2.9 V @ 350 mA and 3.25 V @ 1500 mA. With a tightly regulated 12 V supply, the LED string has a chance of not burning up, as long as it doesn't get too hot. However, the amount of light emitted would not be as steady as it would be with a proper LED driver (current control), given the thermal coefficients and other margin of error that surely exists between the actual lamp and the data sheet.

[jflorey2]

led is voltage related
the different voltage you apply the different ah they will draw

You are referring to the V-I curve for the LED. Unfortunately this curve depends on part-to-part variation and temperature. That means if you drive two similar white LED at (say) 3.6 volts, you might damage device A while only driving device B to 70% of its maximum output power. However, if they are both rated to 700ma, and you put them in series and drive them both at 700ma - you get maximum power from both without overdriving them.

Many people think LED's are voltage rated devices because they are used to using them with ballast resistors. If you use a ballast resistor you can make some simple assumptions and operate LED's very reliably from voltage sources - but then you are losing a significant fraction of your power to the ballast resistance.

so when you talk about leds all the talk is about voltage not ah

"All the talk" is about current, not voltage (and not ah, which is amp-hours.) All LED's have a rated CURRENT and a voltage RANGE they are likely to need.

Lumen min.: 139
Lumen max.: 488
mA min.: 350 mA
mA max.: 1500 mA
V max.: 4 V

OK cool. From the above if you exceed 1500ma you will damage the device. If you apply 4V you MIGHT damage the device. So what voltage do you use?

[inetdog]

What I see as one bottom line point for this thread is that when working with LEDs you need to know in advance (before applying power) whether you have:

1.Raw LEDs in any combination of series and parallel, without any ballast resistor or driver. For those a limited (appropriate) current source for the light level you want is imperative.
2. LEDs or LED arrays with an internal ballast resistor and a voltage drop across that resistor of at least 3 volts in normal operation. For them a regulated voltage may be perfectly appropriate. But going too high (as, for example, when powering the LEDs directly from a battery that is being equalized, can reduce the life of the LEDs (and the ballast resistor) significantly. If you have a nominal 12V LED array which consists of 8V of diode drop and 4 volts across a ballast resistor, then changing from 12V to 16V will double the current through the array and quadruple the power dissipation of the ballast resistor.
3. LED arrays with a built-in driver circuit which will accept a wide range of voltages and provide a limited current to the LEDs. If you have one of these, you can apply any voltage in the specified input range. But you should not try to dim the LEDs by reducing the voltage.
4. Any other major scenarios??

When one member is talking about one scenario and the next member is talking about another, confusion and flaring tempers can ensue.
It is not always easy to look at an add for LED arrays and tell which you are getting.

[azdave]

I know way more about LEDs than I do about solar.

I built this fully customized, animated LED array for my 98 Eclipse almost 10 years ago. It has close to 1000 series-parallel wired Cree LEDs driven by a custom micro-controller and PWM boards, all installed with allowances for current and thermal management to survive through Phoenix summers. It was an awesome project.

Project thread

http://www.hidplanet.com/forums/showthread.php?4189-98-Eclipse-Tail-Light-Conversion-Project

Two-minute video of final install animation.

https://youtu.be/K6sZg3iL5EY

[Mike90250]

To be fair, his suggestion was to use this series of LED, 6 strings of 4 leds in series. Based on the data sheet, forward voltage is 2.9 V @ 350 mA and 3.25 V @ 1500 mA. With a tightly regulated 12 V supply, the LED string has a chance of not burning up, as long as it doesn't get too hot.

However, the amount of light emitted would not be as steady as it would be with a proper LED driver (current control), given the thermal coefficients and other margin of error that surely exists between the actual lamp and the data sheet.

A tightly regulated supply is pointless with LEDs, until the supply also limits current, unless you are under-voltage driving the LED's and starve them.

Reverse voltage 5v
Forward voltage (@ 350 mA, 25 °C)v 2.9
Forward voltage (@ 700 mA, 25 °C)v 3.05
Forward voltage (@ 1000 mA, 25 °C)v 3.15
Forward voltage (@ 1500 mA, 25 °C)v 3.25

The Vf is only controlled by the inherent resistance of the diode. Strings of LED's generally are not matched or balanced, and will perform poorly in Parallel without specific driver circuits or current swamping (lossy) resistors.

[Mike90250]

I know way more about LEDs than I do about solar.

I built this fully customized, animated LED array for my 98 Eclipse almost 10 years ago. It has close to 1000 series-parallel wired Cree LEDs driven by a custom micro-controller and PWM boards, all installed with allowances for current and thermal management to survive through Phoenix summers. It was an awesome project.

Project thread

http://www.hidplanet.com/forums/showthread.php?4189-98-Eclipse-Tail-Light-Conversion-Project

Two-minute video of final install animation.
https://youtu.be/K6sZg3iL5EY ......

Awesome !