Setups basic electronics question on dropping voltage

[tommyjw6206]

I wasn't sure where to put this but since it related to an FPV, thought i'd start here. Moderators, of course move this to more relevant forum if exists.

I'm using a 4s (16.8v at max voltage) battery to power a TS832 transmitter that is rated at either 7-15v or 7-16v (depending on what part of the manual you look at. don't you love that?) I could buy a cheap voltage regular that would drop to 12 volts but that would be an overkill as I really don't need voltage regulation since the TS832 already has one. I just want to drop the input voltage by 3 volts. Been a long time since DeVry (lol. 30 years) so I've lost my electronics know how. What resistor would i need to put in series with this transmitter's power input to limit the current to the rated 220mA?

Thanks.

 

[tommyjw6206]

Let me ask it this way... If one saw a transmitter rated at 7-15v or 7-16v, would you worry about powering it from a 4s battery?

 

[tommyjw6206]

To conclude this discussion, if you have a device that already has a voltage regulator (most do in the rc areana if they support a wide range of voltages), you only need a voltage drop resistor in series with the circuit if the maximum voltage of your device is below the voltage of your battery. so to calculate your resistor value, if you want to drop 3v on a device rated at a maximum of 220mA, the resistance is calculated as volt / current = resistance of your resistor. in my case 3v / .22A = 13 ohm resistor. the wattage of the resistor is volt * current = watts * 2 (to be safe). in my case, it was 1.2 W resistor.

it's been referred to as a poor mans bec but it's one component that can be seemlessly integrated in to your circuit with the bulk of a BEC.

 

[Tasajara]

I just use a Pololu 12V, 600mA Step-Down Voltage Regulator D24V6F12 to power my gimble and one on the Vtx.
It is a switching regulator so it will be pretty clean voltage and not get hot. Costing only $5.95 and about the size of a dime it is a good deal.
You can get them with a maximum output current of 600 mA. Where the TS832 has a working current of 220mA.