Function of Capacitors?

[Ed McGettigan]

What is the function of the capacitor on the voltage regulator and under the dash by the ammeter?

My 1964 Corvette 327/300 4 speed with the radio delete option has a capacitor attached to the voltage regulator but I couldn't locate one attached under the dash by the ammeter. Is that correct?

[John H.]

Re: Function of Capacitors?

Ed -

Those two capacitors (and about six more in various places) were there to reduce "pop" noises in the radio caused by relay contacts opening and closing, low-voltage spikes, etc. - no other function but radio noise suppression. So few cars were built without radios, many no-radio cars still got some of the capacitors anyway, just out of assembly line habit.

[Klaus Friedrich]

Re: Function of Capacitors?

Hi Ed,

the capacitors on non-radio cars have the function to suppress radio noise, too. Not the noise of the radio in the car but the noise in radios nearby (other cars, houses etc.)

STW
Klaus

[Bryan L.]

Re: Function of Capacitors? think of them this way

The act like a condom. They hold the charge and pass the effect.

BL

[Jack H.]

Re: Function of Capacitors?

What others have told you is correct. Capacitors in these areas are there for noise reduction.

Capacitor (archane term = condensor) is an electrical storage component. It stores electrical charge much the same as a bucket holds water. The governing equation is q = CV where q is electrical charge in columbs, C is the fixed storage capacity rating of the part (Farads) and V is the voltage applied to the part.

If we take the time derivative of the equation (d/dt), we get dq/dt = d/dt[CV]. The entity dq/dt (change in electrical charge per unit time) is an electrical identity; current flow, I or amperes. Since, the storage capacity of a given capacitor is typically constant (time invariant) the opposite side of the equation reduces to C dV/dt.

This says the current flowing through a capacitor is proportional to the CHANGE in voltage across it. Or, the component blocks DC current flow and passes AC current flow....

When electrical disturbances happen (generator turns ON, you hit the brakes and the tail lights turn ON), two simultaneous solutions to the circuit equation occur: a steady state solution (DC current flows to the tail lights and they illuminate) and a transient solution (there's a momentary fluxuation of electrical current flow that quickly dies out & goes away). The transient solution produces AC current flow of various frequencies.

By 'tacking' capacitors here/there on various electrical wires to ground, no DC current flows (short circuit). But, in the event the wire is carrying AC current from a transient disturbance, the capacitor looks like a convenient way for the AC current to go to ground (crawl off and die vs. go down the wire and broadcast and/or disturb other items sharing that line).

That's about as simple as I can make it without a 4-year degree in electrical engineering! You'll see capacitors (caps) strewn here/there in rather large quantities in cars to 'slurp up' or 'eat' switching transients VERY frequently.

[John M.]

Re: Function of Capacitors?

Jack, How would a MOV compare for noise reduction? I would think that the very tight clamping curve of a MOV would lead to much better transient protection, no? I am not planning on removing the correct capacitors on my 60, but inquiring minds want to know..... Regards, John McGraw

[Dale Pearman]

Bout Five Years Ago

I wrote for the Restorer about capacitors. You might want to check it out.

Dale.

[John M.]

Re: Bout Five Years Ago

Hi Dale, Do you remember what month and year? Thanks, John

[Terry M.]

And the CD says.... *TL*

Volume 21, Number 4 - Spring 1995. Unfortunately the CD complete Restorer collection does not give pages. Maybe someone has the paper copy on their night stand.
Terry

[James F.]

[John M.]

Thanks Guys *NM*