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Please help with LED power consumption!!!!!

cdfigueredo

Well-known member
#1
Hey guys, i am working on this project https://forum.flitetest.com/index.php?threads/tundra-rc-from-scratch.61971/ and i need some help with the power LED consumption. I am planing to conect the lights to the chanel 5 on my Rx (See the diagram bellow)
281580_2bce0b8d17ed2ade31c32ad1aa5d160b.png
These are the LEDs. I took them from an old broken lantern.
9.jpg 6.jpg 7.jpg

I've tried them all and they work perfectly by connecting them to the receiver. But I have doubts. In the end I calculate that they would be approximately 15 LEDs in total connected in parallel.
I am worried that they will drain the battery too fast or simply that it will be too much load and the ESC will not be able to feed the servos.

What do you think????? please, could someone help me????
Thanks in advance
 

Grifflyer

WWII fanatic
#2
You could run an external BEC and use a separate battery for just the lights.
How much volts are your lights rated for? Mine are rated for 12 so I splice them in so they get power directly from the battery without drawing power from the BEC.
 

cdfigueredo

Well-known member
#3
You could run an external BEC and use a separate battery for just the lights.
Grifflyer, my resources are limited, so i don't have anything else than a ESCs. :cautious:

How much volts are your lights rated for? Mine are rated for 12 so I splice them in so they get power directly from the battery without drawing power from the BEC.
To be honest, i don;t really know. As i said, i took them fom an old 3 x AAA lantern... so... it must be something under 3x1.5V=4.5V :unsure:. I guess i can run some test, leaving the lights on for a while and check the battery charge. I will use a 3s 2200mAh 25c.
In the worst case, i will use 3 AA batteries just for the lights. But i will try to avoid it to save weight.
 
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#4
A 2200mAh pack isn't going to be bothered at all with what look like standard 5mm LEDs. If that's what they are, those are typically driven at about 20mA (although sometimes higher to produce more light at the expense of lifetime). You may run up against the limit of your 1A-2A integrated BEC if you have 15 LEDs pulling 20-30mA each + a few servos.

Are there some resistors somewhere in your wiring? Even just driving them at 5V would destroy a typical LED without having some sort of current limiting resistor in place. I don't think AAA cells would have a high enough internal resistance to keep from destroying the LEDs. With some minor calculations, you could add a resistor that would allow you to safely run the LEDs directly off the battery pack. This would eliminate the load on the BEC. It would be crucial to get that resistor value right, though.

Do you have a multimeter? If so, set it to the A or mA range and stick it in series with at least a few of your LEDs. That would tell you how much they're really drawing.
 

cdfigueredo

Well-known member
#5
A 2200mAh pack isn't going to be bothered at all with what look like standard 5mm LEDs. If that's what they are, those are typically driven at about 20mA (although sometimes higher to produce more light at the expense of lifetime). You may run up against the limit of your 1A-2A integrated BEC if you have 15 LEDs pulling 20-30mA each + a few servos.

Are there some resistors somewhere in your wiring? Even just driving them at 5V would destroy a typical LED without having some sort of current limiting resistor in place. I don't think AAA cells would have a high enough internal resistance to keep from destroying the LEDs. With some minor calculations, you could add a resistor that would allow you to safely run the LEDs directly off the battery pack. This would eliminate the load on the BEC. It would be crucial to get that resistor value right, though.

Do you have a multimeter? If so, set it to the A or mA range and stick it in series with at least a few of your LEDs. That would tell you how much they're really drawing.
Are u telling me that i can use the 3s 2200mAh battery without problem through my receiver???? and it will work fine???
I don;t use any resistor, but the old lantern had one that i can use. i will try to upload some pictures later. And yes, they are 5mm LEDs. No, i don;t have a multimeter. :cautious:
 
#6
Are u telling me that i can use the 3s 2200mAh battery without problem through my receiver???? and it will work fine???
I don;t use any resistor, but the old lantern had one that i can use. i will try to upload some pictures later. And yes, they are 5mm LEDs. No, i don;t have a multimeter. :cautious:
NO! The receiver needs to be connected to the BEC.

It is possible to to power the LEDS directly from the battery by using a proper resistor, though. See http://ledcalc.com/#

LEDs need to be current limited. If they aren't, they will typically destroy themselves. That site will help you pick the correct resistor and LED configuration (series vs. parallel).
 
#8
As mentioned above you absolutely must have a resistor attached, otherwise the LEDs will pull too much current and fry themselves pretty quickly. Worse, when that happens it can create a cascading effect.

But in terms of current draw, you're fine. I'm about to build my first FliteTest night fly model, but the picture below is what I'm running at the moment, there are around 230 colour changing LEDs on there and the lights at max brightness only draw around 100mAh from a 2S lipo in a 4 minute flight. :)

Plane Insane Evolution with 224 NightWave LEDs.jpg
 

cdfigueredo

Well-known member
#9
NO! The receiver needs to be connected to the BEC.

It is possible to to power the LEDS directly from the battery by using a proper resistor, though. See http://ledcalc.com/#

LEDs need to be current limited. If they aren't, they will typically destroy themselves. That site will help you pick the correct resistor and LED configuration (series vs. parallel).
Are my imputs right???? This is for makeing a Y harnes with xT60 conectors and power the ESC and the LEDs form the same battery????? is that the idea????
1223.png
 
#10
PS. I power that model from two 2S 300mAh packs. If you're running a 3S 2200 you have about 10x more mAh available than I do :)

And I'm also powering all of these, plus the servos straight off the BEC of a 15A ESC :)
 

cdfigueredo

Well-known member
#11
As mentioned above you absolutely must have a resistor attached, otherwise the LEDs will pull too much current and fry themselves pretty quickly. Worse, when that happens it can create a cascading effect.

But in terms of current draw, you're fine. I'm about to build my first FliteTest night fly model, but the picture below is what I'm running at the moment, there are around 230 colour changing LEDs on there and the lights at max brightness only draw around 100mAh from a 2S lipo in a 4 minute flight. :)

View attachment 158468
wow, that looks pretty.... how do you conect your LEDs to the battery?
 
#13
Are my imputs right???? This is for makeing a Y harnes with xT60 conectors and power the ESC and the LEDs form the same battery????? is that the idea????
View attachment 158467
Yes, the general idea is to power both your ESC and the LEDs directly from the battery. Keeping the LEDs in parallel is not the efficient way to do that, though. It's calling for a relatively massive 3W resistor in that case. Most people won't just have those laying around. If you leave the calculator on "The Guru" setting, it will tell you the most efficient way to do what you want to do. The circuit below draws less than 1/4 of the power and uses readily (and cheaply) available 1/8 or 1/4 W resistors.

Click the little "?" next to each setting to learn more about that setting. The voltage drop across white LEDs is typically around 3V. It's only 2V for typical red LEDs, though, so you can't just go mixing red and white LEDs without knowing what you're doing.

Screenshot_2020-02-18 Current limiting Resistor calculator for leds.png
 

cdfigueredo

Well-known member
#14
Yes, the general idea is to power both your ESC and the LEDs directly from the battery. Keeping the LEDs in parallel is not the efficient way to do that, though. It's calling for a relatively massive 3W resistor in that case. Most people won't just have those laying around. If you leave the calculator on "The Guru" setting, it will tell you the most efficient way to do what you want to do. The circuit below draws less than 1/4 of the power and uses readily (and cheaply) available 1/8 or 1/4 W resistors.

Click the little "?" next to each setting to learn more about that setting. The voltage drop across white LEDs is typically around 3V. It's only 2V for typical red LEDs, though, so you can't just go mixing red and white LEDs without knowing what you're doing.

View attachment 158469
dayve, i saw the "guru" mode yesterday but it is late for me because i covered both wings and there are 4 LEDs on each conected in paralell :oops: so i can;t change that.
All the LEDs i am using came from this lantern
a.jpg b.jpg
and all are white, i just paint them with red and green bookmarks, so the consumption and voltage are the same for all the LEDs.

For the landing light i am planing to use this LED form another 3 AA battery lantern. (this one is super super bright)
c.jpg d.jpg e.jpg

This is what i have now. I wolud like to find a good way to connect the remaining LEDs to be able to power ESC and the LEDs directly from the battery. Any advice????
diagrama.png
 
#15
That wiring could cause you problems with runtime. From the calculations in the circuit above could be drawing around 440mA for each wing.

Since you already have the LEDs and wires in place, you would probably be best running these from your receiver or a separate BEC. I'm going to assume these are typical white LEDs and need a 3.3V voltage drop to operate. If that's the case, you can reduce the power consumption considerably by driving them from a 5V BEC:

LED calcs 5V supply.png


For the remaining LEDs you've not yet wired up you would be best wiring resistors in series with each individual LED, following the diagram the LED Guru calculator throws out. With 6 LEDs connected a 5V supply when I run the calcs it's recommending 68Ohm 1/8W resistors.

I don't have any experience with super bright LEDs I'm afraid, but if that was running at 4.5V before and you have all the electronics still connected you might already have everything you need contained within that reflector. It's possible that will run just fine if connected directly to a 5V supply.
 

cdfigueredo

Well-known member
#16
That wiring could cause you problems with runtime. From the calculations in the circuit above could be drawing around 440mA for each wing.
There are 4 LEDs in parallel on each wing instead 3. How did u get this value "440mA"????
123.png


Since you already have the LEDs and wires in place, you would probably be best running these from your receiver or a separate BEC. I'm going to assume these are typical white LEDs and need a 3.3V voltage drop to operate. If that's the case, you can reduce the power consumption considerably by driving them from a 5V BEC:
i don't have any BEC, the ESC i am using now is this one http://www.valuehobby.com/gforce-30a-esc-4576.html whcich has an integrated BEC: 2A / 5V (Linear mode). Would it work to power at least the wing LEDs form the receiver safetly?????

For the remaining LEDs you've not yet wired up you would be best wiring resistors in series with each individual LED, following the diagram the LED Guru calculator throws out. With 6 LEDs connected a 5V supply when I run the calcs it's recommending 68Ohm 1/8W resistors.
Are u excluding the bigger LED (the super bright)??? that ;s why are 6 LEDs instead 7? Also u are using 5V as power source, that implies i should use a BEC or i could use the linear BEC on my ESC???
 

Piotrsko

Well-known member
#17
How about putting leds in series? Each will drop the voltage by about 3 volts, so 2 in series eats approximately 6 volts, 3 eats 9 volts.......my kitchen light has 10 in a series string with 5- 6 strings daisy chained accross the 120v mains. Downside is 1 fails, the string goes dark.