lol to above!


That other thing's true though - Wouldn't normally need a capacitor for a 300 watt amp.
300 watts / 12 volts = 25 amps MAXIMUM current draw

Might mean there's a poor connection somewhere or a thin power / ground cable.

I'm going to put new power cables to the amp in at the same time, so hopefully by the time done it'll be working fine and he'll be ahppy.

Just so you don't forget.

Rather than starting a new thread...

Just bought a 2 farrad Cap today for next to nothing, otherwise I wouldn't have bothered.

What's this about having to charge the cap before wiring it in or something???

Also... the cap I bought has a bunch of pretty little flashing lights and a voltage display on it which I'm presuming will be on whenever it's connected to the battery (i.e. all the time!) ... Is this true and how would I go about "turning it off" when the ignition is off..?

Would I be able to wire in a relay so that the main power line to the cap is shut off whenever the ignition is not on...?

I think you will find the cap has some smarts in with the lights and display, it will turn off when the voltage sits stable at 12.5 or near enough for a few minutes...

As for charging, do a google but i never bothered with my 1 farad with flasthing lights and wank factor, just hooked it up and the smarts in the top did the rest...

Nah caps with lights and displays etc, have enough resistance in them so special charging techniques aren't needed.

They also self discharge quickly enough after disconnecting them, so no need to worry about specifically discharging them either.

See my comment further up about charging.

My capacitor has a voltage display in it. The display turns off if nothing happens for a few minutes. The capacitor package actually came with a small light bulb for charging and very specific instructions about doing it to ensure the capacitor isn't damaged by the massive power spike it would receive if you didn't.

And because of this, no you couldn't really disconnect it with a relay, because you would need to charge it before you could turn the relay on again.

If I was parking somewhere for more than a few days I would disconnect. I've never investigated but my system (assuming cap) draws a fair standby current which makes starting a strain after a few days.

It won't damage the cap, they're made for near instant charge/discharge (that is after all what they're supposed to do). If they indeed have no internal limiting, they'll possible blow your fuse. But as already said, if the cap has any lights or deplays on it, it's got more than enough internal limiting to prevent any problems.



Cap should have no current draw, once at the same voltage as the rest of the system, there's nothing for it to do, "it can't suck any more once it's full".

I am in the same boat, picked up a free 2 farrad capacitor when i bought all my amps, 2 farrods should be 2000wrms? i am running 540wrms (4*130) & 1*500wrms (bridged), so pretty much only 1000wrms

Having a capacitor that is to high in farrads, can that kill or suck the juice out of your battery.

I have no voltage issues, thought may as well put it in the car instead of the garage!

ok ive got 4 gauge wiring (earth and power) 8gauge rem and i have this same problem...

(1200w rms system)

wat do i do 2 fix the power drain?

Google capacitor and study up mate as you don't seem to fully understand what they do or how they work... In simple terms, a capacitor is a mini battery.

A farad (PLEASE NOTE THE CORRECT SPELLING!) is a measurement of "electrical capacity". A capacitor with a higher capacitance (higher farad rating) simply holds more charge. And therefore takes longer to charge and longer to discharge.

Like data_mine said up above. Once the capacitor is charged it's not going to discharge unless there's an electrical component draining the charge.

Get to know your multimeter and go looking!

Took me ages to find what was draining my power. In the end I just added a manual isolator on my main power line and now, whenever I know I won't be using my car for a few days I simply switch it off and isolate the battery.

A cap is NOT a mini battery it is a storage device where as a battery produces electrical energy via a chemical reaction.
Cheap caps and massive value caps usually have high internal resistance and a lot of them place a load on the electrical system which makes them absolutely useless for their intended purpose.
If a cap doesn't require a resistor for the purposes of charging place it in the appropriate receptacle (garbage bin) as you will be wasting your time.

Thus my wording "in simple terms"

A cap is like a mini battery IN SIMPLE TERMS... you charge it up and it discharges quickly. For the average joe this analogy suffices.

I know exactly how a cap works. Two years of electrical engineering does it...

Think of a cap as a bucket of electricity, the battery constantly keeps it topped up, and when the amplifer needs a big hit, you basically throw the bucket of electrons at it. lol. It's there to provide electricity quickly (much quicker than a battery can).

Some terms/definitions (off the top of my head)
whole heap of electrons (electricity) = coulomb
1 amp = 1 coulomb of electrons moving over a period of a second

1 farad = 1 coulomb worth of electrons in storage (not moving)

Now a farad may seem big (and a 1F cap is pretty big). But from above you can see, that a 1F cap can only supply electricity at 1Amp for only 1 second. Change that around about, and you can have half an amp for 2 seconds, or 2 amps for half a second. A amplifier on the other hand takes MUCH more than an amp whe it's really pumping. So a cap will only be able to smooth out those instantaneous loud bass hits, or high highs (i.e. small fractions of a second).

This is where debate rages if caps are needed or useless. We can see a cap won't (can't) fix an electrical problem* (it only lasts a tiny fraction of a second), but it can help smooth out the power input to your amplifier so those loud notes can be played loud without distortion or clipping.


*So if your headlights dim, adding a cap, won't fix the problem, it'll merely hide it (maybe). Check and improve all the earth points.

The earth wire between the battery and the body, is undersized if you want to run a stereo. I heavily suggest replacing this with a length of wire as thick as your power wire (or thicker - doesn't hurt). Make you're earth wires to/from the amps as short as possible, and anchor them to solid parts on the body (seat anchor bolts are good). Some people recommend sanding back some of the paint around the bolt for a better connection, I haven't found this necessary. Failing all of that, you may need to run a earth cable all the way back to the battery.