LEDs With 4s

[RCJim]

I put some LEDs on my tricopter with a Turnigy receiver controlled switch so I could turn them off and on. The thing I was concerned with is that I’m using a 4s battery for my setup and the LEDs are of course for 12v. Will they be alright or do I need something to lower the voltage to them?

[GAntonjo]

Good morning, RCJim.

I cannot tell if you safely can run your LEDs directly on 4S. It all depends on the voltage tolerance of your LEDs. The LED strips I use on my tricopter are for 12V, but I have successfully connected them directly on my 4S LiPo (no switch). One solution would be to connect them to the balance plug of your LiPo, only using “3S”. Look at this Balance Connectors description to get an idea on how to use the Balance plug for tapping less than 4S off the battery. Between any 2 adjacent wires on the balance plug you should get 1S voltage (i.e. 3.7V).

IMPORTANT NOTE: If you choose to connect the LEDs to the balance plug, you will un-balance the battery charge. This should be OK for a low-current load as the LEDs, but if you use this for loads that draw more current, you may damage your LiPo. In any case, use a LiPo alarm that can check all LiPo Cells individually and alert if they fall below the 3.0V on any cell.

I would also add a fuse on the cables to the LEDs to be on the safe side.

[marcoose]

It depends 🙂 4s tops out at 16.8v (4.2 x 4). Most “12v” LEDs are designed for automotive use, where the charging 12v system is typically more like 14. So 4s is really only a couple volts too high. Depending on the safety margin in your LED you could be ok. The best way to be sure is put an ammeter in series and see what your current draw is compared to the rating.

Alternately you can put a couple diodes with high enough current rating in series to get .7v drop each. Most diodes should be fine. Or install a suitable resistor. To calculate the right one you really need the forward voltage drop and current specs of the LEDs used, but you can always run them a bit dim if you don’t want the max brightness to be safe.

[RCJim]

I’m using a 4s 3000mAh for the battery. If I were to use a couple diodes would they need to be 3A diodes? What I’m trying to do is power 3 strips of 3 LEDs. I can’t power them with a balance plug since I already wired it all. In order to do so I would have take the whole thing apart. For this reason using a UBEC would be difficult as well, using a resistor or diodes would be the best option since I can get to the LEDs positive terminal. Any more advice would be great since I know very little when it comes to electricity.

[marcoose]

No, you (most likely) do not need 3A diodes. They only need to handle enough current to power your LED strips. Without knowing what the strip is I would be guessing at the rating, but unless each LED is bright like a flashlight they are probably <100mA each and should be fine on a typical 1N4001 (1A) diode.

Is it something like the Diatone strips ? They already have enough series resistance to handle 4s so you should be ok without anything.

[RCJim]

No, I got them on Ebay but they are more like the Hobby King strips.

[RCJim]

If that’s what you mean they say the working current is 400mA/meter, I’m using about a sixth of that. So would I just put a few of those diodes in series between the LED positive wire and the battery?

[RCExplorer – David]

I would do just like marcoose suggested, one or two 1n4001 diode in series with the LED’s. Drops the voltage a couple of volts per diod 🙂

[RCJim]

OK. Thanks guys.

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