Please help with LED power consumption!!!!!

dayve

Member
Oh, wow! Those circuits are a bad example of how to use LEDs properly. That single high-power LED should work on 4.5V with that orange-white-gold (3.1 ohm) resistor. Is that the one that it was originally using? It looks to be undersized, but it would be about the right value. That resistor is going to get hot, though, so don't put it up against anything important.

If you can't come up with some different resistors and/or rewire the LEDs in the wings, those aren't really going to work right. That one big brown-green-gold (1.5 ohm) resistor only just sort of works with 4 parallel strings of 6 parallel LEDs running on 4.5V. That's a very poor way to drive LEDs.
 

cdfigueredo

Elite member
[QUOTE = "Piotrsko, post: 546250, member: 41952"] ¿Qué tal poner leds en serie? Cada uno reducirá el voltaje en aproximadamente 3 voltios, por lo que 2 en serie comen aproximadamente 6 voltios, 3 comen 9 voltios ....... mi luz de cocina tiene 10 en una cadena en serie con 5-6 cadenas conectadas en cadena a través de la red eléctrica de 120v . La desventaja es 1 falla, la cadena se oscurece. [/ QUOTE]

This is what i am thinking due to i cant deattach the LEDs of the wings.... Could this work??? i thinks is neccesary to add some resistors in somewhere but i don;t know where??? any ideas???
diagrama1.png
 

cdfigueredo

Elite member
Oh, wow! Those circuits are a bad example of how to use LEDs properly. That single high-power LED should work on 4.5V with that orange-white-gold (3.1 ohm) resistor. Is that the one that it was originally using? It looks to be undersized, but it would be about the right value. That resistor is going to get hot, though, so don't put it up against anything important.

If you can't come up with some different resistors and/or rewire the LEDs in the wings, those aren't really going to work right. That one big brown-green-gold (1.5 ohm) resistor only just sort of works with 4 parallel strings of 6 parallel LEDs running on 4.5V. That's a very poor way to drive LEDs.

So? there is not way to make it work propertly with the resources i have? :oops:
 

Piotrsko

Master member
I would take the 3 in series of leds in your picture and add 1-2 more in series since the 11.1 battery is nominal and goes up to 12.6 or more fully charged. I'm not so sure what voltage your bulbs need since they can vary from 2.1 to 3.7 and may tolerate up to 5. How about making a power resistor out of steel wire about 2-3 foot long and sliding one connection from the far end until they light up? Toaster wire is preferred, but bailing wire works also, just needs to be longer.
 

myxiplx

Member
I think dayve has more electronics knowledge than I do, but I don't think you should wire them like that.

The problem with running LEDs in parallel without a resistor to limit current is that you tend to blow the LEDs and have the failure cascade through everything, taking out all the lights on the model.

Without a resistor to limit the current what tends to happen is that the LEDs warm up due to the current flowing, and as they warm up, the internal resistance of the LED drops, which allows more current to flow, which warms them more.... and the cycle continues until you get so much current the LED fails. The problem with a bunch of LEDs connected in parallel like that is that the LEDs are rarely well matched, so some will have lower resistances than others, and will heat faster. Whichever heats fastest draws more current, heats more, then pops. Then the next in the chain pops, etc...

I've only basic knowledge of electronics, but whenever I followed guides on making night blades for RC helicopters, every guide had a resistor attached to each LED, with the combinations of resistors and LEDs then wired in parallel.
 

myxiplx

Member
Double check this, but I believe that given you've already wired the wings this is the best compromise. Wire each wing, the body, and the large lamp as their own circuits, with the appropriate resistors in place to limit the current flow.

Use a 5V BEC as the input, total current draw is under 0.5A so most BECs should handle it.

Wing Circuit.png


Body Circuit.png


High power lamp circuit.png


Wiring diagram.png
 

Bricks

Master member
Make it simple just get some male JST connectors ( these connector are the same as your balance connector for your charger ) and connect it to your balance battery lead and you can pick voltage by which pin you connect your LED`s too. I did a quick search and you can use something like these I did not take the time to just find the male ends which are cheaper. I connect all my LED`s thru the balance lead.

https://www.amazon.com/dp/B07K43J2QJ/?tag=lstir-20
 

myxiplx

Member
Even using the balance leads and JST-XH connectors, you still need to include resistors. The current which flows through a LED rises massively with voltage, pushing 4.2V from a fully charged LiPo cell through them without a resistor could very easily fry the LEDs.

And even if it doesn't, allowing that much current to flow will mean the circuit pulls far more mAh from the pack than is necessary.

1582185671560.png
 

cdfigueredo

Elite member
Double check this, but I believe that given you've already wired the wings this is the best compromise. Wire each wing, the body, and the large lamp as their own circuits, with the appropriate resistors in place to limit the current flow.

Use a 5V BEC as the input, total current draw is under 0.5A so most BECs should handle it.

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Looks like this could be a good solution. Actually, my knowledge of electronics is very basic. So i can;t say if this is wrong or right, but looks like u know what are u saying ;). the only problem i see with that is that i don;t have any BEC... could i use another ESC for powering the lights? On the other hand, could be possible to power this circuit with 3 AA batteries... this will be 4.5V???
 

cdfigueredo

Elite member
Make it simple just get some male JST connectors ( these connector are the same as your balance connector for your charger ) and connect it to your balance battery lead and you can pick voltage by which pin you connect your LED`s too. I did a quick search and you can use something like these I did not take the time to just find the male ends which are cheaper. I connect all my LED`s thru the balance lead.

https://www.amazon.com/dp/B07K43J2QJ/?tag=lstir-20

Pardon my ignorance, but if I connect the LEDs to balance battery lead, specifically to one of the cells, this would not make that cell discharge faster, unbalancing the battery?

Also, I always fly with a voltage checker connected to the battery that tells me when to land. Could i connect this in parallel with the lights? Will the sensor still warn me correctly?
 

Bricks

Master member
Pardon my ignorance, but if I connect the LEDs to balance battery lead, specifically to one of the cells, this would not make that cell discharge faster, unbalancing the battery?

Also, I always fly with a voltage checker connected to the battery that tells me when to land. Could i connect this in parallel with the lights? Will the sensor still warn me correctly?

You are not going to notice a difference.
 

myxiplx

Member
Looks like this could be a good solution. Actually, my knowledge of electronics is very basic. So i can;t say if this is wrong or right, but looks like u know what are u saying ;). the only problem i see with that is that i don;t have any BEC... could i use another ESC for powering the lights? On the other hand, could be possible to power this circuit with 3 AA batteries... this will be 4.5V???

How are you powering your servos and receiver? Don't you have an ESC with a BEC there?
 

myxiplx

Member
Personally I wouldn't add an extra BEC, just power them from your normal ESC. You have 2A to play with and the LEDs are only pulling 0.5A at most.