The following is part 1 of a guide on ship capacitor management. This content is derived from a syllabus for a class that I teach at EVE University. I wrote the original syllabus in 2010, and it has been improved considerably since then, thanks to revisions by professor Kivena and other teachers at the UNI - my heartfelt thanks to them.
Last updated: December 6, 2014
This guide is designed for pilots who want to maximize the performance of what is the most important piece of equipment on your ship: your capacitor, also generally known as a "cap" in EVE jargon. Your capacitor supplies energy to your modules, enabling you to fire some types of weapons, engage EWAR, maneuver your ship, and maintain an active defensive tank. If your capacitor empties, then your ship becomes potentially impotent and immaterial. A drained capacitor in a fight can translate quickly into finding yourself floating in space in a pod.
Your capacitor, quite literally, is life.
Your Ship's Reactor
Every ship includes a reactor, which provides electrical power. Each race uses a different type of reactor - Amarr: Antimatter; Caldari: Graviton; Gallente: Fusion; Minmatar: Nuclear - though they all operate exactly the same way.
Power from your reactor is routed to two uses: your powergrid and your capacitor.
What is a Powergrid?
Many people confuse capacitor and powergrid, but they are two completely different features of any ship.
While the capacitor stores power from the reactor for use on demand by modules, the powergrid is a static, constant flow of energy used for fitting modules on your ship. Most (but not all) modules require a minimum amount of power just to be installed and maintained "at the ready" on a ship - that is, to be "plugged in" to your ship's systems.
In short, capacitors are used for module operation, while powergrid is used for module fitting and readiness.
Powergrid is measured in megawatts, and can be seen by selecting "Show Info" on your ship, and looking at the powergrid section. You can also find this information in the ship fitting window.
There is no direct relationship between your capacitor and powergrid. You can increase your powergrid with certain modules, skills, implants and rigs, but increasing your powergrid has no effect on the size or recharge rate of your capacitor. A larger powergrid simply enables you to fit bigger and more power-hungry modules.
What is a Capacitor?
The capacitor is a power storage unit that is tapped to activate fitted modules on a ship. While your reactor supplies a flow of electrical power, such energy is difficult to store. Imagine trying to store electricity from the outlets in your home. Your ship's capacitor has the ability to store a certain amount of power, and to draw that power from your reactor at a certain rate. Capacitor management is therefore all about maximizing these two factors - capacitor capacity and the recharge rate - while minimizing modules' consumption of power out of your capacitor.
Capacitor is measured in gigajoules. When you activate modules, the amount of cap required is deducted from your total cap, which you can see in the middle of your heads-up display (HUD). Hovering your cursor over the capacitor icon in our HUD gives you more information in a pop-up window.
Generally, the larger the ship, the larger the amount of capacitor capacity. Capacitor capacity can be increased by certain skills, modules, and rigs, and also by some booster drugs.
Capacitor recharge rate can likewise be improved by skills, modules and rigs, and also can be affected by some implants.
The capacitor has a natural recharge rate, replenishing its energy (from your ship's reactor) over time. If you use this energy faster than it can replenish, you will eventually drain your capacitor and not be able to activate any modules (and you may not be able to warp to your intended destination, because warp drive requires an amount of capacitor energy proportional to the distance to travel).
Capacitor function is more fully explained in the in-game fitting screen. The first line is simple: it's the total capacitor capacity, followed by how long it takes to recharge it from empty to about 98%. (Note that it takes a very long time – much longer than the time stated here – to fully recharge it to 100%.)
The second line first shows the excess recharge rate. This is essentially the difference between the usage rate – the rate at which you use energy, assuming all fitted modules are running continuously – and the recharge rate. A negative number implies that you are using more energy than you can recharge. This rate is measured in gigajoules per second.
The numbers in parentheses show the same thing, except in percentage form. This is your excess or deficit recharge rate, as a percentage of your peak recharge rate.
Finally, the top right corner tells you if you are cap stable, or if not, how long it takes for your capacitor to run out of energy (again assuming all fitted modules are running continuously).
Hovering your cursor over the small capacitor icon to the left of these values shows you at what capacity level your capacitor will stabilize (if you are cap stable) – or how long it takes for your cap to run out, if not.
Your ship capacitor does not recharge at a constant rate. As illustrated in the following graph, the highest recharge rate occurs when your capacitor is around 25 percent of total capacity. If you pass below this level, then you will run out of cap swiftly as the recharge rate drops off. Remember: this rate assumes no other factors in play – if enemies are draining your cap with energy neutralizers or energy vampires, it will drop off even faster.
What does "cap stable" mean?
A "cap stable" ship is one in which the power demands of your modules will not exceed your capacitor's recharge rate, when your ship's fitted modules are operating. In other words, the aggregate rate of power drawn from your capacitor by your operating modules will not exceed the capacitor's recharge rate, so your capacitor will never empty.
In general, your ship will remain cap stable if the energy in your capacitor does not fall below 25 percent of your total capacity. This is because the highest recharge rate occurs when your capacitor is at about 25 percent of full capacity.
Is being cap stable good?
A cap stable configuration means that you can engage all fitted modules, and unless disrupted by energy weapons, your capacitor will be able to keep your modules operating indefinitely.
Note: you can be cap stable and still run out of cap, if people use energy neutralizers on you. Overheating modules can also make you no longer cap stable, because overheating can make some modules cycle faster and thus use up more cap.
So, should you always be cap stable?
Not always. In PvP (player vs. player) engagements, having a cap stable configuration is not required. In fact, a cap stable configuration can limit the damage per second (DPS) potential of your ship, and make your vessel less effective in combat.
In order to achieve a cap stable configuration, you must limit the size and energy requirements of any active modules: weapons, shield, armor, EWAR, sensors, or any module that consumes power from your capacitor. In addition, you must often fit modules that expand capacitor capacity, recharge rate, or both - such as cap rechargers, power diagnostic systems, capacitor flux coils, and capacitor power relays - which then occupy fitting slots that could be used for offensive and defensive capability enhancements.
Also, PvP ships very often fit microwarpdrives – it's very difficult to be cap stable with a MWD, because it both reduces your capacitor and uses a lot of cap when active.
When deciding whether to make your ship cap stable, take into account how long your combat encounters will last. Most PvP fights are over relatively swiftly, so striving for cap stability is usually pointless. Incursion rooms only last around 10 minutes maximum – so if your cap can last that long, you don't need to be cap stable. Missions are probably the longest combat encounter, with Level 4s sometimes lasting 20-40 minutes – or more. For these, being cap stable can be very useful, as you can then maintain an active tank for the entire engagement.
Your fitting window assumes you run all your modules constantly. If you don't, then you might be cap stable anyway. By switching modules off in the fitting window, you can see if you are really cap stable in practice.
Next post: Part 2 - Improving Capacitor Performance
Fly safe! o7