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# Beginner needs input

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#### cotjones

##### New Member
Hi, obviously I'm new. I don't know much more than basics about electronic components and circuits and haven't as of yet been able to get much practice.

I definitely have an interest in electronics but unfortunately my academic priorities lie elsewhere so I can't go to school for it. But I am trying to teach myself everything I can.

To start off, I have a project I'm working on.

I'm lighting the buttons on an xbox 360 Controller with 4 multi-color LED's.

So my basic understanding is that the supply voltage will be 3v ± a little if i'm using batteries, or 2.4v if i'm using the rechargeable battery I bought. I ordered the LED's but I don't have them yet so i don't have very specific info about them but here is what I do know:

1 Blue: Forward Voltage Min/Typ - 3/3.2V @If=20mA

1 Yellow: * Forward voltage: 3.3 V Typical * Forward current: 20mA

1 Red: * Forward voltage: 3.3 V Typical * Forward current: 20mA

1 Green: Forward Voltage (V) : 3.4~3.6

How would you wire these so that they light at the same time from the same power source. I was thinking they should be fine in parallel with resistors just to equalize the light output between the different color lights.

Are you lighting them from a separate power source or from the box ?

I just re-read the pwr source.

You can find all the online calculators you need.

https://tinyurl.com/lugsv9

I'm told keeping them around half of the max amp is the best for life expectancy

kv

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if you are using external power supply,then parallel connection will work.Since you need same current in all the LEDs ,so assuming same current apply nodal analysis .

alternatively you may use a constant current source.

The power source is the existing board power source. I want it to turn on when the controller turns on. No external power source. There is a point i can solder to which gives power from the battery while the controller is turned on without being in the same circuit as any other components.

My worry is that if I wire them in parallel, they will have differing resistances causing the one with the least resistance to power mostly and the others to not have the current they should.

If I use separate resistors on each LED, I should be able to get the resistances pretty equal for all 4, but then is that going to make the light un-even since they all put out different light at different power?

And yes i've seen those calculators, but the problem is that they assume the LED's will all be the same, While different color LED's have different voltage drops, foward voltage, and current requirements.

Your LEDs won't light if the battery voltage is less than about 4V so a 2.4V or 3V battery won't work. If you use two 2.4V batteries in series to give 4.8V then it will drive each LED if each one has its own series current-limiting resistor. You can adjust the values of the resistors to make the colours' brightness even.
The battery might not light 4 LEDs continuously for long before the battery is dead.

Your LEDs won't light if the battery voltage is less than about 4V so a 2.4V or 3V battery won't work. If you use two 2.4V batteries in series to give 4.8V then it will drive each LED if each one has its own series current-limiting resistor. You can adjust the values of the resistors to make the colours' brightness even.
The battery might not light 4 LEDs continuously for long before the battery is dead.

This can't be true. You must be misunderstanding me.

I've seen it done.

It's not the LED's won't light below their typical voltage, they just might not be as bright. And that technically wouldn't be such a bad thing, prolonging the life of the LED's

This can't be true. You must be misunderstanding me.

I've seen it done.

It's not the LED's won't light below their typical voltage, they just might not be as bright. And that technically wouldn't be such a bad thing, prolonging the life of the LED's

Then why are you asking seems you have all the answer's. Reading the site it also has the resistor calculator and give's the location of a working MOD ?

So, why are you asking us. Just do it.

But, remember just doing something to do it. Well that's one thing. Doing something and doing it right. Well that is another.

What guru is saying is electronically correct. Your said a battery you didn't say where it was or what it's pwr source was to re-charge or hold a charge on top of that it currently is powering a motor. We just thought it was a battery.

kv

This can't be true. You must be misunderstanding me.

I've seen it done.

It's not the LED's won't light below their typical voltage, they just might not be as bright. And that technically wouldn't be such a bad thing, prolonging the life of the LED's
They use a 5V supply, not a 3V battery that drops to 2.0V nor a 2.4V rechargeable battery.

You said yourself that your green LED might need 3.6V and did not show how much is the max voltage for the other colours.

They use a 5V supply, not a 3V battery that drops to 2.0V nor a 2.4V rechargeable battery.

You said yourself that your green LED might need 3.6V and did not show how much is the max voltage for the other colours.

I've seen it done on 3v controllers wireless controllers. I know for a fact the LED's will light below typical voltage. I'm not asking that, i'm asking if the differences in the different color LED's will be great enough to not work effectively if I wire them in parallel. I Know I can't series them, the voltage is too low.

Basically i'll reword: Will the differences in the LED's pose a problem and if so can I equalize them sufficiently with resistors?

I know they won't be as bright as their full potential but they don't need to be, just a slight glow will be satisfactory.

An LED does not have one voltage. Its voltage is a range of voltages.
They are not the same so one might need 2.8V and the next one (same part number) might need 3.6V. You said that your green LED has a voltage range from 3.4V to 3.6V. If it needs 3.6V then it will not light with only 2.4V from a rechargeable battery and it will stop lighting when a 3V battery drops below 2.5V.

Each LED needs its own series current-limiting resistor that also needs voltage that must be added to the voltage required by the LED.

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An LED does not have one voltage. Its voltage is a range of voltages.
They are not the same so one might need 2.8V and the next one (same part number) might need 3.6V. You said that your green LED has a voltage range from 3.4V to 3.6V. If it needs 3.6V then it will not light with only 2.4V from a rechargeable battery and it will stop lighting when a 3V battery drops below 2.5V.

Each LED needs its own series current-limiting resistor that also needs voltage that must be added to the voltage required by the LED.

Ok that sounds better. So in other words i'm looking at doing this?

Ignore those resistor values. i obviously won't know what the resistor values will be until i test the LED.

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Your 3V battery voltage will begin dropping the moment it is used for the first time. Then the dim LEDs will get dimmer and dimmer and dimmer and dimmer and dimmer and dimmer and dimmer and dimmer and ....

Your 3V battery voltage will begin dropping the moment it is used for the first time. Then the dim LEDs will get dimmer and dimmer and dimmer and dimmer and dimmer and dimmer and dimmer and dimmer and ....

With the LED's pulling 15-20 mA each will my 60-80 mAh load will dramatically drain the power from my 3V. 2000-3000 mAh source? the controller itself uses about 37 amps. so we'll say I have a total load of 100mA that should give me at least a 15 Hour battery life. and probably more. now what if I parallel extra batteries in? Would that by chance damage the components of the controller or just increase the available mAh. The other possibility is that I have the USB cable that supplies a 5v to the controller. I could install an on/off switch and only use the LED's when connected to the USB.

Energizer's datasheet for their AA alkaline cell shows a capacity of 1800mAh at a drain of only 25mA and a capacity of 2500mAh at a drain of 100mA. But the final voltage is only 0.8V per cell. Then your "3V" battery will be only 1.6V and will not do anything.

The 3V will be only 2V in a couple of hours.

Energizer's datasheet for their AA alkaline cell shows a capacity of 1800mAh at a drain of only 25mA and a capacity of 2500mAh at a drain of 100mA. But the final voltage is only 0.8V per cell. Then your "3V" battery will be only 1.6V and will not do anything.

The 3V will be only 2V in a couple of hours.

I just don't see where you are getting this.

With a 3v 100mA draw i'm looking at a nominal .3 watts. Well according to this Duracell data sheet One battery on a .25 watt load will not drain the battery to 1.2 volts for 6 hours. Double the battery voltage and that number gets more favorable.

So try this on for size. I run the LED's at a current of 10mA (since the brightness of LED's rated at a 20mA Max doesn't vary much from 10-20 amps. giving me around a >75mA total load. Or .22 watts. (about a 10 hr. battery life with the voltage dropping to 2.4v at 10 hrs.

Duracell PROCELL: Batteries: Overview for the MX1500...

So am I right? should that give me about 10 hr. battery life? I mean I could reduce the current more on the LED's. I'll just have to get them and see how far I can reduce the current and they still light sufficiently..

I should be able to get the current down to about 5mA, that would make my load around .15 watts. That would make my battery life fantastic. around 20 hrs. or more.

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Just as a followup, thank you for your help guru, but I think I've figured it out for myself.

I just received Some of the LED's today. I hooked up a 470Ohm resistor to the end of one of them and applied voltage from the 2.4V battery resulting in just under a .5 mA load. And they still lit. (rather brightly surprisingly.) 5mA a piece on them should be no problem, if not favorable for this particular application.

The problem is that you do not have enough voltage to properly light the LEDs.
Then as the batteries discharge the dim LEDs will get dimmer and dimmer and dimmer ...

A "2.4V" rechargeable battery is actually 2.8V or 3.0V when it comes fresh from the charger. Then the voltage quickly drops to 2.4V. Maybe your LED had 0.5mA when the battery was 2.8V or 3.0V.

A cheap LED is a dim old one in a focussed case to make it appear brighter when it is shining directly at you. To the side you can barely see it.

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