Two lists that never match
A controlled door has a hardware list and a power list, and the two are counted by different people at different times. The hardware list is the lock, the reader, the request to exit, the door position switch and, if the lock is in the leaf rather than the frame, something to get cable across the hinge. Five items per door, four of which are small and easy to leave off an order. The power list is what those items draw, which is where the supply and the battery come from.
This page does both from the same door list, because they are the same doors, and the commonest way an access control job stalls is that somebody counted one list and not the other.
Fail-secure and fail-safe cost completely different amounts
An electric strike that is energised to release draws nothing at all until somebody presents a card. Over an hour with four releases of five seconds each, a 350 mA strike averages under two milliamps. A magnet that is energised to stay locked draws its full current continuously, and 500 mA is 500 mA at three in the morning on a Sunday.
On the default door list that is three magnets at 1,460 mA against three strikes averaging 6.1 mA between them. The magnets are 63 percent of a 2,316 mA standing load and the strikes are a quarter of one percent of it; the rest is readers and the controller. That is the whole reason the standby battery figure looks the way it does, and it is why one extra magnetic lock changes a battery size while one extra strike does not. Which type a door gets is decided by what the door has to do when the power fails, and that is a question about people leaving a building rather than a question about amp-hours.
The far door is the one that misbehaves
Lock current is large by low-voltage standards and the cable is often small, so the drop is real. A 500 mA magnet on 150 ft of 18 AWG loses 0.96 V before it arrives, which is fine. Put the same magnet on 22 AWG and it loses 2.42 V, from a supply that only had twelve to give, and the lock sees 9.6.
An underfed lock does not fail cleanly. It buzzes, holds weakly, releases late, or works all afternoon and refuses at seven in the morning when the rest of the building has just switched on. Chasing that fault at the door is unrewarding because the door is not where the problem is. The page prints the arriving voltage per door next to the minimum you entered, so the long runs are visible before anybody pulls cable.
The battery is sized by the standing load, not the peak
Take the standing figure in amps, multiply by the standby hours you are working to, divide by whatever fraction of the battery you are prepared to count on, and that is the capacity. Nothing subtle. What makes it go wrong is the write-off: a sealed lead acid cell that has been in a cupboard for three years, at whatever temperature that cupboard reaches, does not give its label capacity, and the difference is not small.
The standby period itself is not a number this page can supply. It might be set by your own specification, by an insurer, by a monitoring agreement, or by the authority inspecting the building, and those disagree. Enter yours.
The part that is not arithmetic
A door held shut by an electromagnet is a door that will not open when the electricity is doing something unexpected, and that is a life-safety matter governed by rules adopted where the building stands and enforced by somebody who inspects it. What such a door has to release on, whether it may be there at all, and what has to be tested and how often are outside anything worked out here, and no result on this page is an argument that an arrangement is permitted. Inrush is also outside it: a coil takes a brief current well above its holding figure at the instant it energises, that figure is on the device data sheet, and how much of it a supply will source is on the supply data sheet.
Questions people ask
How much current does an electric strike draw?
Whatever its data sheet says, and this page takes that figure rather than supplying one. What matters more is the mode: a fail-secure strike is energised only to release, so over an hour with a handful of releases it averages a couple of milliamps, while a magnet energised to stay locked draws its full figure every second. The difference between those two is the difference between a small battery and a large one.
What size battery does an access control panel need?
Standing current in amps times the standby hours, divided by the fraction of the battery you are prepared to count on. On the default door list, 2.3 A for four hours with a quarter written off comes to 12.4 Ah, which is why the 7 Ah battery in the form covers only 2.3 hours of it. The standby period is not something this page can supply, because it may be set by your own specification, an insurer, a monitoring agreement or the authority inspecting the building, and those do not agree with each other.
What wire size should I use for a maglock?
The page shows what each gauge does rather than picking one. A 500 mA magnet on 150 ft of 18 AWG loses 0.96 V of a twelve volt supply; on 22 AWG over the same run it loses 2.42 V and the lock sees 9.6. Compare the arriving figure against the minimum operating voltage on the lock data sheet, remembering that the supply itself sags on battery, which is when the lock is least able to give anything away.
Why does a door lock work sometimes and not others?
On a long thin run, the usual cause is that the voltage arriving is close to the lock minimum and something moved it. More load on the supply, a warm cable, a battery part way through a power cut, or several doors firing at once will each take a few tenths of a volt. The symptom is a lock that buzzes or releases late rather than one that plainly fails, which is why the fault gets chased at the door instead of at the run.
What does each access controlled door need?
A locking device, a reader or keypad, a request to exit device, a door position switch, and a power transfer if the lock is in the leaf rather than the frame. That is five items per door and four of them are small, which is why the count is the thing that holds up an install. Whether a particular door may be locked at all, and how it has to behave in a fire, is decided by the rules where the building stands.