# How to determine FET switch specifications

I am working on a DIY drone, and I (preferably) need to be able to disconnect my ESCs from the battery via the transmitter (a Raspberry Pi). After looking for solutions for a while, I concluded FET switches are my best bet to automate this. However, I am not certain how to determine the requirements for the switches (I have no engineering knowledge, I am learning on the fly). Considering that the maximum current draw for the motors is 12A, the battery is 11.5V, and the RPI's pins for control are 3.3V and can take a maximum draw of 16mA, are my assumptions correct:

1. Switches need to have Vds>11.5V, and Vgs<2.5V
2. The draw on the gate can be neglected because it is ~0

Also, what considerations should be made about the S->D current draw? And am I missing other factors?

• In RC applications, the goal is to use the lowest possible $R_{DSon}$ to minimise heating which is $P=I^2R$. You probably want to use high-side switch which can be done either with PMOS and a small BJT (simpler) or with NMOS and self-oscillating bootstrap driver (cooler). – venny Sep 18 '14 at 14:51
• "Learning on the fly" -- I like that :-) – Dave Tweed Sep 18 '14 at 14:54
• Why do you need to disconnect the ESCs from the battery? WHat is it you are trying to achieve? For example, why would it not be sufficient to switch the ESCs off? – gbulmer Sep 18 '14 at 15:15
• @venny thanks for your suggestions I will research both of them :) – Mitio Sep 18 '14 at 15:16
• @gbulmer It is indeed sufficient, I am simply looking for a way to automate the process. – Mitio Sep 18 '14 at 15:19