Capacitors in coil signal outputs

[cmonref]

Bruce wrote: "I have a circuit that manages the capacitor so that it slowly charges up then connects to the mains which eliminates this problem (can post if people want)."

Does your circuit manage both the charge-up and the "bleed-off" (for want of a better term) of the capacitor? I'll take you up on your offer to post it for general use.

Brian

[Bruce Bowling]

Does your circuit manage both the charge-up and the "bleed-off" (for want of a better term) of the capacitor? I'll take you up on your offer to post it for general use.

Brian

The circuit is something I was playing with for a next revision of the relay board, I plan on putting this option in along with some filtering circuits to provide a nice, clean 12V supply. It manages the charging rate, only hooking it up when it reaches nearly full charge, and has a small bleed resistance to slowly discharge over many days (depending on capacitance, bleed current is less than a milliamp). Here is the circuit:



Its pretty simple, when the battery V1 is first applied the large stereo capacitor C2 is charged up thru the bank of four 330-ohm resistors (R6-R8 - these are 1/2 watt). The capacitor is disconnected from ground path via U1 MOSFET, until the voltage across the cap is nearly equal to the battery voltage, at which point the FET is turned on and it applies the capacitance to the battery mains. Diode D1 is really a LED (mis-drawn in this schematic) which you can use to see if the caps are in charge mode, it will glow bright at first (45ma flows int he beginning thru the diode, use a suitable one) and it will get dimmer and dimmer, and turn off when the MOSFET is active.

The capacitor can be anything from 1/2 farad to 3 farad or more. If you use more than 1F capacitance then you should use 1W resistors for the 330-ohm ballast resistors or they will get real hot.

Disregard the OUT signal net on the schematic, I put this in on this to run a circuit simulation, there is nothing special about it.

You want this to be hooked up to the +12V rail all the time, not switched. Hook this in under the dash wiring at the point before the ignition switch, its better there than hooking up direct at the battery terminals.

- Bruce