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Old 10-07-2011, 09:43 AM   #1
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Exclamation DIY LED Afterburner HELP!

Not sure if this is the right thread for this but here it goes...

Looking to make a led afterburner on one of my planes. I want the led brightness to coincide with the throttle. I know that one way to do it is to connect the led's to a low amp brushed esc inline with the brushless esc then connect both esc's to the throttle channel via Y-harness and voila.

I'm looking to skip the whole extra low amp brushed esc. Would I be able to just connect the led strip to an open channel on my rx and mix it in with the throttle? Or would the voltage be incorrect? Any help is greatly appreciated.
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Old 10-07-2011, 12:09 PM   #2
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Originally Posted by raitheslacker View Post
Looking to make a led afterburner on one of my planes. I want the led brightness to coincide with the throttle. I know that one way to do it is to connect the led's to a low amp brushed esc inline with the brushless esc then connect both esc's to the throttle channel via Y-harness and voila.

I'm looking to skip the whole extra low amp brushed esc. Would I be able to just connect the led strip to an open channel on my rx and mix it in with the throttle? Or would the voltage be incorrect? Any help is greatly appreciated.
No.

The rx only gives a PWM signal with short pulses differing a bit in length and with no power at all. In any case you need some kind of electronics. And a brushed ESC should be quite cheap nowadays (ebay...).

RK
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Old 10-07-2011, 12:33 PM   #3
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Originally Posted by r_kopka View Post
No.

The rx only gives a PWM signal with short pulses differing a bit in length and with no power at all. In any case you need some kind of electronics. And a brushed ESC should be quite cheap nowadays (ebay...).

RK
Yeah just tested an led strip on my rx. Not enough juice to light it up. Was super dim and only 3 out of 24 lit up.

Now my question is this. I will be running 4s batteries so how do I attach a voltage regulator to the led strip? What kind of voltage regulator would I need?
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Old 10-07-2011, 07:16 PM   #4
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Here's what I use.

I have a string of Leds controlled by a Castle Creations, Pixie-7P with the red wire cut to disable the BEC.

It can handle 7 amps and up to 21Volts with red wire cut, but you will need to put a resistor in series with your leds to drop the voltage down to something they can handle without burning up.

Ohm's law can help you figure the value for the resistor.

My led strip pulls 400 ma at 12 volts. If I want to run it from a 4s pack, I am going to assume the pack is putting out about 16 volts. (at full charge it would be 4 x 4.2 = 16.8) That means I am 4 volts too high. I need to find a resistor that will have a 4 volt drop across it at 400 ma.

In electronics, E represents Voltage, I represents Amperage, R represents Resistance
(all in full units)

Ohm's law is
volts equals -- amps times resistance -- or E = I x R
Amps equals -- voltage divided by resistance -- or I = E/R
Resistance equals -- voltage divided by amps -- or R = E/I

So in my example to find the resistor, I will use the amount of voltage I need to drop (sort of get rid of) which is 4 volts,
and the current the leds pull when operating at the voltage they are designed for, in my case 400 ma,

since 1 ma means 1/1000 of 1 amp, 400 ma = 0.400 amps

Put all this into the formula and it is --- 4 / 0.4 = 10 ohms

So I would put a 10 ohm resistor in series with the leds, and then I could run them from 16 volts without burning up.

Since watts equals I x E in my example I will also lose 0.4 x 4 = 1.6 watts, not enough to bother with a fancy voltage reg.

Hope this helps

If I knew the voltage your leds require, and the total current at that voltage, I can figure the resistor for you.

Dave R, Proud PGR rider.
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Old 10-07-2011, 07:35 PM   #5
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Originally Posted by Wildflyer View Post
Here's what I use.

I have a string of Leds controlled by a Castle Creations, Pixie-7P with the red wire cut to disable the BEC.

It can handle 7 amps and up to 21Volts with red wire cut, but you will need to put a resistor in series with your leds to drop the voltage down to something they can handle without burning up.

Ohm's law can help you figure the value for the resistor.

My led strip pulls 400 ma at 12 volts. If I want to run it from a 4s pack, I am going to assume the pack is putting out about 16 volts. (at full charge it would be 4 x 4.2 = 16.8) That means I am 4 volts too high. I need to find a resistor that will have a 4 volt drop across it at 400 ma.

In electronics, E represents Voltage, I represents Amperage, R represents Resistance
(all in full units)

Ohm's law is
volts equals -- amps times resistance -- or E = I x R
Amps equals -- voltage divided by resistance -- or I = E/R
Resistance equals -- voltage divided by amps -- or R = E/I

So in my example to find the resistor, I will use the amount of voltage I need to drop (sort of get rid of) which is 4 volts,
and the current the leds pull when operating at the voltage they are designed for, in my case 400 ma,

since 1 ma means 1/1000 of 1 amp, 400 ma = 0.400 amps

Put all this into the formula and it is --- 4 / 0.4 = 10 ohms

So I would put a 10 ohm resistor in series with the leds, and then I could run them from 16 volts without burning up.

Since watts equals I x E in my example I will also lose 0.4 x 4 = 1.6 watts, not enough to bother with a fancy voltage reg.

Hope this helps

If I knew the voltage your leds require, and the total current at that voltage, I can figure the resistor for you.
The voltage is 12v but i do not know the current :/
Purchased this from eBay. Not much info on it. Any recommendations?
http://www.ebay.com/itm/180687140964...ht_3493wt_1163
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Old 10-07-2011, 09:40 PM   #6
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Originally Posted by raitheslacker View Post
Now my question is this. I will be running 4s batteries so how do I attach a voltage regulator to the led strip? What kind of voltage regulator would I need?
Better take 3s from the balancer cable. The current is not so high so it won't disbalance the battery much.
Typical BECs don't give you 12V.

RK
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Old 10-08-2011, 02:41 AM   #7
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Pulling the 12v or 3s on the balancer cable will work just fine. It's simpler than a resistor, just watch the balance of the battery, because you will be discharging some cells a tiny bit faster than others, if the leds are wired correctly. I have seen some suggested wiring diagrams that would pull much more current than necessary.

If you don't have a good digital meter to read volts, amps & resistance, I would highly recommend getting one, also a inline wattmeter is almost necessary when setting up a good flying plane, it will help you choose the right prop, without burning up the motor.

Good luck if you need more help, we are here.

The basic electricity lesson I posted first, may come in very handy, when you can't tap into the battery's balance plug. I do some custom work with just bare leds. Some need very different voltages and currents, than others, so I just gave you what I do all the time, didn't mean to bury you in tech talk.

Dave R, Proud PGR rider.
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