Battery switching without tears

On Tuesday, April 7, 2020 at 8:58:53 PM UTC-7, 2G wrote:
On Tuesday, April 7, 2020 at 8:06:46 PM UTC-7, Andy Blackburn wrote:
I put a power resistor in the circuit to keep the current surge down. I undersized the capacitor so if I mess up on the with rotation I can lose power. Typically I'll shut off some non-essential equipment to lower the draw if I really don't want a computer reset.

Andy

On Sunday, April 5, 2020 at 8:45:30 AM UTC-7, jfitch wrote:

What is the inrush current when you first switch the power on? Must not be enough to blow the fuse, but that'd be something I'd want to O'scope with a current probe.

You didn't say what the resistor size was. There is already a resistor in the circuit - it is called the internal resistance of the battery,wiring resistance, switch contact resistance and the equivalent series resistance (ESR) of the capacitor.

I forgot to mention that aluminum electrolytic capacitors have very significant inductance at frequencies above 10 KHz. Inductance (also called a choke because they choke off current) limits inrush current. The joules of energy being transferred is pretty low (about 0.6 J), but I have no problem with adding a small series resistor (1 ohm - don't worry about the wattage as very little power is supplied by the cap).

Tom