Car Large capacitor charge controllers

Posted on Jun 27, 2012

One-farad capacitors require some care. It`s a common knowledge that they must be pre-charged with a current-limiting resistor before plugging in. It is less common knowledge that those fifty-dollar `smart cap controllers` are in fact very simple devices, two dollars for parts and labor. Here`s a basic cap switch that will connect capacitor to ground only when it`s charged to within 0.4-0.7V from battery voltage (otherwise, it`s charging through a 22 Ohm resistor, which can be a low-power 12V lightbulb, too).

Car Large capacitor charge controllers
Click here to download the full size of the above Circuit.

Note that when the circuit is open, and a high current draw starts dicharging the capacitor, T1 (N-MOS with low channel resistance - IRF1010, IRFP054, IRF048, P60N06 etc) is actually conducting in reverse direction (as in syncronous rectifiers: S->D no

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