using balance lead for 2S and 3S connection at the same time

[Sean_M]

Hello night flyers,

I am setting up my first night rig. It is a TREX 450 with MS composite blades and I am using a combination of green, red, and blue Turnigy LED strips.

I have found that at 2S the blue LED strips are very dim, they seem to need more voltage to come to the same brightness as the red and green LEDs. My idea is to wire the green and blue LED strips to the 2S taps on the balance lead of my 3S 850 MAH LIPO. The blue LED strip will be wired to the 3S taps on the balance lead. I tried this and it seems to work. My question is if this is electrically safe? Don't want the LIPO to blow on me.

Has anyone done this?

Thanks for your help,

- Sean

[kavic5150]

No, it will not make your lipo explode. What it will do is drain 2 cells a bit faster than the third. I get 3 flights with a 370mah 3s so you should be good for at least 5 with an 850mah.

I've heard of guys using a small brushed esc as a pwm controller to dim led strips. This can make them brighter than 2s but dimmer than 3s which is too bright for most flyers. I'm not sure exactly how this is done, but its been covered in older threads.

You could wire in a big resistor on each led strip and just change the resistor value a bit to adjust brightness. That way you would not have an unbalanced pack.

I used this: http://led.linear1.org/1led.wiz and plugged in 12.6v, 10v and 400ma (current draw for a 60led 1 meter strip) and it recommended a 6.8 ohm 2 watt resistor.

Then I bumped up the diode forward voltage to 10.5v and 11v (for the whole 1 meter strip) and got 5.6 ohms 2 watts and 4.7 ohms 2 watts respectively.

Use resistors rated for at least 2 watts so you dont burn them out.

Ebay has these in packs of 3 to 5 for a few dollars each shipped from the US.

[Sean_M]

Originally Posted by kavic5150

No, it will not make your lipo explode. What it will do is drain 2 cells a bit faster than the third. I get 3 flights with a 370mah 3s so you should be good for at least 5 with an 850mah.

I've heard of guys using a small brushed esc as a pwm controller to dim led strips. This can make them brighter than 2s but dimmer than 3s which is too bright for most flyers. I'm not sure exactly how this is done, but its been covered in older threads.

You could wire in a big resistor on each led strip and just change the resistor value a bit to adjust brightness. That way you would not have an unbalanced pack.

I used this: http://led.linear1.org/1led.wiz and plugged in 12.6v, 10v and 400ma (current draw for a 60led 1 meter strip) and it recommended a 6.8 ohm 2 watt resistor.

Then I bumped up the diode forward voltage to 10.5v and 11v (for the whole 1 meter strip) and got 5.6 ohms 2 watts and 4.7 ohms 2 watts respectively.

Use resistors rated for at least 2 watts so you dont burn them out.

Ebay has these in packs of 3 to 5 for a few dollars each shipped from the US.

Thanks very much kavic5150,

I tried it out last night and it seems to work well using the balance taps. I see what you mean about the cells getting out of balance. I may try the resistor method instead.

- Sean