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What dose PD mean (Power Dissipation)? What PD do i want, and dose it really matter? I am gessing lower is better, as it means how much power is LOST? Someone please tell me! Also, what is the most likly higest ampage i would run with an xmod? Like 5 Amps of so?
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The higher the power dissipation the better. That is why I went with TO-220 and TO-262(tabless TO-220's). You'll probably be pushing 1 or 2 amps continuously, maybe more if you have a hotter motor, but the higher the current rating of the FET, the better. R(DS) is an important factor. R(DS) is the resistance the FET will present to the current flowing through your motor when the FET is on. Another important spec is V(GS) on. That is the voltage needed to fully turn the FET on/off. If you don't achieve that voltage, then the FET will always be resistive(half on/half off) and will short your cells through the FET's, thus seriously robbing your motor of current, and causing your FET's to heat up and your cells to die quick. In other words, it'd be terribly inefficient.
IC1 is the integrated circuit inside the xmod that signals the FET's to turn on/off. IC1 will only provide 3.4V to drive the FET's. Higher wattage FET's usually need V(GS) levels of 10V to fully drive the FET, or at least as high as the voltage it will be switching on/off. So if you have 7.2V from drain to source, it's best to have a V(GS) signal of at least 7.2V. If you have 7.2V from drain to source, but only have 3.4V signaling your gate(V(GS)), then that's where you're going to be running into FET's heating up, motor's hardly driving, and cells heating up and dying quickly.