G Scale Model Train Forum banner
1 - 2 of 32 Posts

· Premium Member
Joined
·
113 Posts
RE: "Hybrid" Power?

Gentlemen, Bill Swindell is quite correct. You can think what you will, but capacitors have been around for a long time; they ain't rocket science and very little math is needed to understand them.

What is important is the RC Time Constant: Resistor value multiplied by Capacitor value gives Time in seconds. If a resistor (or resistor equivalent) is placed across a charged capacitor, it discharges to 37 percent of original value in one RC time value.

The RC time constant is in seconds if the capacitor is in farads and resistor is in ohms. So a 1 farad capacitor and a 20 ohm resistor has an RC Time Constant of 20 seconds. And of course if the capacitor value is in microfarads and the resistor value is in megohms, the time constant is still in seconds. And 37 percent of 20 volts is 7.4 volts.

A 1000 microfarrad capacitor and a 20 ohm resistor has a time constant of 0.02 seconds. One half cycle of the AC voltage is 0.0083 seconds long.

A 20 ohm resistor across a 20 volt source draws one amp. So you can approximate the equivalent drain of an engine. And a one farad capacitor is huge.

The inductance of a motor will have an effect on the RC Time Constant, but only if it is high and if there was circuit continuity.

The reason music will last a bit longer is because the circuitry's resistance is high.

Art
 

· Premium Member
Joined
·
113 Posts
RE: "Hybrid" Power?

Had to learn this stuff back when the Navy got me in 1945, jimtyp; I think it's easier to learn when you're young. Neither batteries or large capacitors come in 'AC', so backing up presents an additional problem. This can be solved by rectifiers but the hazards of exploding capacitors - or batteries - are really not good.

While working for IBM back in the 50's, I had the end covers off a big power supply, larger that a side-by-side freezer/refrigerator, when one in a bunch of capacitors blew. Fortunately, the plastic shield held; I just aged a few months. These 'safety-covers' had just been recently installed as several employees had been injured by exploding caps.

Art
 
1 - 2 of 32 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top