capacitor confusion

[joeyd71]

i've had a 500 watt system in my car for a few years now, and the dimming lights are starting to become a problem. so i've decided to break down and buy a capacitor. but i am a little confused about the whole charging method of one.

i understand that the capacitor must be charged before connecting it to anything. and you can use a resistor or a lightbulb to do that. but does the capacitor discharge whenever the car is off? or does the capacitor remain charged, as long as there isn't a drain (headlights left of, etc.)

please let me know

Thanks,
Joe

[Perry Babin]

The capacitor is directly connected to the battery. The capacitor's voltage is essentially exactly the same as the battery voltage. It will not discharge unless the battery is drained or it's disconnected from the battery.

A capacitor doesn't have to be charged prior to connecting it to the power/ground but it reduces the arcing which can damage the terminals when initial contact is made.


I'd suggest that you save your money and buy whatever alternator you need to properly power your system. Even with a good quality alternator, you may never completely eliminate the dimming. In many instances, the only solution is to have one alternator for the vehicle's electronics and another one (isolated from the first) to power your amplifiers.

Since you only have 500 watts (which most alternators should be able to handle), you may have a defective alternator or possibly a defective battery. You can have both checked at AutoZone or a similar automotive parts retailer.

[mikee55]

Sorry for butting in, Perry, I find sometimes its good just undo earths and clean them. Use a fine gritt and polish the terminals smooth and shiny. I've seen wire brushes and coarse paper used. Think about it, imagine blowing what you see up with a microscope? Coarse paper and the like will create a jagged face say to a brass eye and bulk head, polish it and the entire surfaces will mate together provide better conection. A jagged conection will arc at the spikey peeks as current flows through.

My theory anyway.

What do you think?

Mikee55

[mikee55]

Money wasted on a cap can always be better spent, I bet you can fix the problem and spend the money on your missus, or buy some music.

[jol50]

I was always under the impression that any restrictive connection to equipment would limit the power it consumed, and therefor lessen the car's voltage loss (as well as limit the amp's abilities). I suppose you get some loss in heat.

A new battery would be cheapest, common if the battery is smaller or 5yr old or more. Beyond that you just don't have the power, but near any car alternator should run a 500w amp without issue unless you have some other big draw in the car. If you have bad dimming a cap is not going to fix it.

[tsmith1315]

Perry:

A capacitor doesn't have to be charged prior to connecting it to the power/ground but it reduces the arcing which can damage the terminals when initial contact is made.

You *could* disconnected the battery before installing the cap. Arcing would then happen upon connecting the battery cable.

[ppia600]

Just disconnect the battery's ground terminal and connect the capacitor completely. Once you are finished with the cap, put a single element turn signal bulb between the battery ground terminal and the battery, to charge the cap. After the bulb goes out it will be charged and no more arcing. This is of course if you decide to use a cap.

[AndrewT]

forget the capacitor and overhaul your vehicle's electric circuits.

You are going down the dark road on dipped headlights.
Turn on 5 pairs of spotlights (10 * 55W ~=550W).
That will be the same load as your amp is trying to draw as it nears peak output and taking account of the losses in both the amplifier and in the PSU supplying that amplifier when it is trying to deliver 300 to 400W to your speakers.

[joeyd71]

Originally posted by tsmith1315
Perry:


You *could* disconnected the battery before installing the cap. Arcing would then happen upon connecting the battery cable.

whoa whoa whoa.

so you are saying i could just disconnect the battery, then put the capacitor all hooked up, then reconnect the battery with no problems? i understand that it would still arch, but would it explode or anything?

[Perry Babin]

joeyd71:
The only way that there would be a chance of an explosion is if you have a fuel leak. Batteries can produce hydrogen gas when overcharged but it only accumulates in very confined spaces.

As ppia600 stated, you can charge with a signal lamp (sylvania 1156 or equal). This can be done by connecting the lamp across the fuse holder before placing the fuse in the holder.

tsmith1315:
If it doesn't cause other problems, that would be a good solution.

ppia600:
I've heard stories about the newer vehicles where some would not start after the battery was disconnected. They had to be towed to the dealer to have the computers reset (or whatever they do). Have you had this happen on any vehicles? Or is this a non-existent problem?