I have a 1F Stinger HPM cap with the digital meter and wondering when / what actually makes the cap active for lack of better wording. When the car is running / driving the meter is always showing between 13.9 and 14.4. With the car not running and just on it show 12.0 to 12.6.

Sounds stupid but Im wondering when, how, or what makes the cap do its job and how can you tell if it is. Is the cap always running and maybe thats why Im not sure. Or does the volt level have to really drop for it fire up?

Sorry to sound like a complete dumb *** but I guess I had a different understanding or thought about caps before I put it in

 

First off - awesome cap - the HPM cap is one of the sexiest caps out there right now.

Secondly - to understand when the cap works you have to know understand what the system is doing.

Your alternator only produces x amount of current. Obviously the battery only has so much as well. Under heavy electrical loading it's very easy to exceed the potential amount of current available between the battery and the alternator. When this happens you'll get a serious voltage drop. The capicator works by storing electricity (which is why prior to using the cap you have to charge it) and when there's a large drop in power the cap discharges it's electricity. Typically caps will discharge their energy when there's a large quick drain on power from subs hitting and from the use of high current amplifiers. The amount of energy stored in a cap isn't much and under most circumstances it's used when the vehicle is in idle and the alternator is not producing full output power.

It's hard to actually say it's always working (when in reality it sort of is) and it's hard to say it only works under full loading (because that's not true as well). Current is always flowing through the cap (so it's always working) but the benfits are only when there's a heavy load on the system and the alternator and battery aren't enough.

hopefully that makes some sense.

 

Is there any "simple" way to calculate how much voltage your system is using - to determine if a cap is required?

Or better put:

If you've just added an amp, and it uses up "X" volts, and "Y" is the amount of extra available voltage that can be accessed before it dips into battery charge voltage from the Alt, what is "Y"? That number should be a near constant across all Z's, right?

 

Rule of thumb is 0.5 farads for every 500 watts of RMS power.

 

I would have disagree with this. 1 Farad is a lot... most capacitors you will find in modern day TV's and such are much, much smaller in capacity.

If you discharge 1 Farad through your body... it will probably kill you. If you blowup a 1 Farad cap you can cause some serious bodily harm (hence why most caps have a safety release in case you cross polarity).

For those installing cap... be extremely careful... it's a lot of power there once stored ( you always need to charge your cap before installing it ).

 

Farads, fumdingles, and Fobos. I'm a mental midget when talking about electrical standards and conversions.

Lets make this simpler for us (me) dumbos here. Can I assume that if my little volt meter in my car does not dip below 14V, that I am ok?

 

Oh you'll know if your cap isn't enough or isn't working. Just crank up your system at night... turn on all your lights (including cabin lights).... and play some heavy bass music. If the lights dim everytime you hit some heavy bass notes... you need a cap, or a larger capacity one.

But usually the cap is only wired for the sub amp since that's the #1 power hungry thing in most car audio systems. So let's say you get a 1000 watt JL Audio monoblock amp. That means at a minimum you should need a 1 farad cap.

No need to check out the volt meter.

 

nwind - true, a 1 farad cap is big compared to say a 300 microfarad cap found in most modern electrical circuits but then again they are dealing with very small currents. In a car stereo with say 100amps being pulled, the amount of energy stored in a cap is small. We're talking about the same thing really but in different terms and different ways .

My general rule of thumb is for every 100amps being pulled under full load on a sub amp I use 1 farad cap. The reason I say this is because in my Z I'm pulling over 750watts yet I don't need a cap at all (because only 300 watts are for the sub). Now in my Honda I'll need probably at least 2 farads of capacitance when I'm running 2200+ watts (250amp possible pull) to one sub when I start building it.

 

The amount of power stored in a capacitor will not make your system "hit harder", but what the cap will do is smooth out the peaks and lows in your alternator voltage. Due to the nature of alternators, they generate power in short bursts, and the capacitor merely fills the lows, but also attenuates the highs. The plus to this is a reduction in noise (due to the smoothing out of the power)

I don't believe in capacitors and their associated marketing ********. If your lights dim when your bass hits, you are obviously drawing too much power, and a simple fix like a capacitor is only hiding the bigger problem - not enough alternator power.

In response to the voltage question: a car battery makes approximately 12 volts. The alternator is usually around 14.5 or so, and the reason for this is that the alternator has to charge the battery, and electrical current works much like water: It goes to the place with the least resistance.

So, to summarize: a capacitor will not enable an alternator making 60 amps to power a system drawing 150 amps, but what it will do is give cleaner power to the amplifier connected to it.

 

Speaking of one farad. I have only seen a single one farad capacitor and it was the size of a three story house. It was used to fire the accelerators at Fermi Lab in chicago.

Farads relate to how quickly that the caps can be discharged/charged not necessarily the capacity of the cap. Like if you had a 60 hz sine wave like wall power you would want a cap that charged in .5 sec and discharged in .5 sec to smooth out the "ripple" in the supply. Of course with AC you need rectifiers to flip the negative part of the AC sine wave.

Short answer? Caps clean your power supply while under load. They are like having a line of credit attached to your checking account. You can write a check for more than your account, and the credit will cover it, but you gotta pay that money back before you can bounce another check.

 

Love the analogy. Couldn't have put it any better words for non-EE people like me.