The Powered Rail is a block that is used to stop or increase momentum of moving carts. It was added as response to bug boosting. It is noteworthy that the glitch boosters currently still function but it is recommended to use either per track and not to mix them. It's operated by Redstone currents, whether this comes from a lever, a button, another circuit or even a detector rail or otherwise although the redstone dust needs to be attached to it similar to a noteblock or redstone repeater.
In its unpowered state, it acts as brakes for any minecart which crosses its tile. In its powered state it will accelerate the cart passing over them. A notable exception to this rule is a Powered rail which has a solid block on either end which will boost a cart from standstill when activated. Although currently it is not confirmed if this is a glitch or intended behavior.
The speed of a cart which is boosted using Powered Rail is calculated to be at a maximum speed of 8 m/s, however there seems to be a difference between the momentum and the maximum speed it travels at. Or more specific, the speed a cart travels at appears to be fixed on a distinct maximum value regardless of the available momentum; thus if you build up enough momentum you travel at a great distance at the same speed before all the momentum is used and you start to slow down.
Confusingly Powered Rail in your inventory is still referred to as Powered Rail by the tooltip, although at that point for obvious reasons it actually is unpowered. The icon is that of powered rail as well. Generally when referring to the rail in it's off position as 'unpowered rail' and otherwise powered rail typically implies 'powered Powered Rail'
Powered rails, much like redstone wire, have two possible states: on or off.
A rail that is "off" slows any passing minecart by applying a frictional force. The force is generally strong enough to bring a moving minecart to a complete stop, or to hold a minecart in place on a slope.
A rail in the "on" state will accelerate a minecart if any of the following is true:
The minecart is already moving, in which case the cart is accelerated in the direction of motion
The minecart is stationary, but one end of the powered rail is up against a solid block. In this case, the cart is accelerated in the direction that is not blocked.
The minecart is stationary, but the powered rail is on a slope. The instant the powered rail is activated, the brake is released and the cart will start moving down due to gravity. As the cart is now moving, rule (1) applies and the cart is accelerated in that direction.
A simple launcher using four Powered Rails, a Button and a solid block
The second and third cases can both be used to create simple stone button-activated launchpads. When the powered rail is off, carts are held in place, providing a safe way to load and unload carts without them derailing like they would on pressure plates.
Powering
Power can be transmitted to the rail from any of the six adjacent positions (above, below, or any side) in the same ways that redstone wire is powered. Strangely, the rail can also receive power from the five positions immediately above those adjacent positions. In other words, the rail acts as if it is two blocks high, and can receive power through any of eleven adjacent spaces, just like a door. This works whether the upper space is occupied or empty. However, powering the rail through the upper space currently exhibits more bugs related to updating.
Powered rails will propagate power to each other if they are adjacent and part of the same track, for up to 9 blocks from the power source (1 being powered directly which is propagated to 8 adjacent rails) . They will also receive power from any adjacent detector rail (when a cart passes over it), even if they are not part of the same track (which follows from the rules above).
Because the detector rail powers attached rail it could be used to activate power rails only when necessary:
For one-way travel, place a detector rail before the powered rail
For two-way travel, place a detector rail on both sides of the powered rail
In practice it is far more efficient to have powered rails constantly active using other means:
Place a Redstone Torch either next to the powered rail or two blocks underneath it or use powered Redstone wiring to achieve the same effect
Place an activated Switch next to the powered rail
It needs to be noted that currently the rail needs to be placed before the power source for it to work. If you dig a hole 2 blocks down and place a redstone torch inside followed by a block on top any rail you place on top will not appear to be active; however there are some workarounds for this.
Optimal use
A (single, sloped down) powered rail boost gives an occupied cart enough momentum to travel 64 tiles on a flat surface, or 8 tiles for an unoccupied cart. It is usually impractical and expensive to place powered rails one after the other. Instead, space powered rails out at regular intervals once the cart is traveling at speed [1]. When using the regular interval technique its worth noting that people suggest to get the maximum speed from the start versus increasing the distance between powered rail,for example four powered rails in a row is sufficient to boost a cart to the speed it easily reaches a next Powered Rail - although keep in mind that this kind of track is best kept free of unoccupied carts.
Using the exception of a blocked off track to the acceleration of moving carts, and joining this with the regular interval technique it this might be an example of a simple cart track with 2 stations.
First make a launcher by placing a block, a single powered rail, a regular rail and attach a button to the block that blocking one end of the track.
Place four powered rails to gain momentum to cover the interval technique. Activate these four rails so that they are always on, for example by a simple lever or a hidden redstone torch. The activated button will launch the cart toward the group of four rails and will quickly reach top speed.
The track itself will then be a row of normal track combined with the occasional powered rail and eventually leads to another station on the other end of the track. Which is a mirrored version of the first station. An example of this type of station is shown in the Effects section, above.
This above station has certain benefits such as the launcher and the speed it gets to. But would be impractical in multiplayer because a collision will occur if two people use it at the same time. However, once at speed, the optimal spacing of powered rails on a level track is to use 1 every 26 blocks (that is, a repeating pattern of one powered rail followed by 25 normal rails, then another powered rail, and so on) which maintains a constant minecart speed of 8 m/s.[2] If gold is in short supply, it is possible to use powered rails with more space between them at a cost of a reduced overall speed:
One powered rail every 30 blocks: 7.8 m/s–2.6% speed decrease
One powered rail every 32 blocks: 7.2 m/s–10% speed decrease
By using 1 powered rail every 26 blocks, you can easily match this with using one standard torch every 13 blocks which keeps the entire track at light level 7 and above since hostile mobs can spawn on tracks (non-hostile mobs will only spawn on tracks if the track is on dirt with green grass).
Diagonal travel
Because 'diagonally' laid down tracks (meaning a track consisting of the pattern; left corner attached to a right corner attached to a left corner ... and so on) already showed a difference with normal rails on the distance and speed there was reason to test the properties of such tracks when the cart was powered by powered rail.
For diagonal tracks on level ground, the optimal spacing of powered rails is 1 every 36 blocks (counting orthogonally, if you count diagonally instead it is 1 every 18 blocks). It is worth noting that 36 is roughly equal to 26 multiplied by the square root of 2, which is the actual distance one would travel diagonally (by Euclidean math) if a player moved 26 blocks on both coordinate axes.
Momentum
It has been proven there is a difference in momentum and speed. For example if you place a long line of powered rail you will still travel at the 8 m/s speed for quite a distance but the distance is further as you would with only a few powered rail. The suspicion is that the developers implemented a limit on the speed the carts accelerated by powered rail travel at to reduce the load on servers. It is worthwhile to note that speed and momentum can differ quite substantially. In real life examples the momentum of an object is based on weight and speed, inversely if you release something at more momentum it will travel further and faster. Practical examples show that it is possible in minecraft to build up momentum with a small 3x3 loop and get a considerable boost in momentum, resulting in a very long travel distance while still cruising along at the speed limit until all the surplus momentum gets used and the cart returns to a balance of speed and momentum.
Tests show that slopes impact the momentum severely, and thus the speed plummets fast but if there is enough surplus momentum it is viable to travel up slopes with ease.
The chapter below assumes carts that do not have this surplus momentum and is to get some benchmark values.
Climbing slopes
Six blocks up without additional boosting
Launching from rest via four powered rails, an occupied cart has enough to climb a 1/1 slope six blocks high without further boosting and then travel horizontally at a very slow speed for at least a dozen blocks before coming to a stop. Such a cart does not have enough momentum to climb a seven block high slope. An unmanned cart in a similar setup will only climb three blocks and then travel a few blocks horizontally.
A pitfall that people might initially fall into could be placing a powered rail every (other) block to maintain the speed. This means that when using this example for every two blocks of height climbed, a gold ingot is required and this has likely been the cause for complaints about the powered rail being 'broken'. There is however a great way to travel higher up a slope and that is to have more momentum to begin with.
Inversely to the fact that sloped up tracks decrease the momentum rapidly, sloped down tracks add more momentum to the boost by comparison. For example 3 sloped down powered before a slope up consisting of normal track gives approximately the same elevation as 6 level powered rail.
However it is worth to note that the trick to overcome slopes is to make sure there is enough momentum before the slope up. When building a roller coaster this is of course a lot more easy to overcome than when you already start from bedrock level. A discussion in the minecraft forum[3] shows it is possible to reach a remarkable height with just using 4 powered rail.
The example shown is a 3x3 loop with 4 powered rail, a cart is placed on the track and allowed to spin around for a few seconds to build up momentum beyond the speed limit. The best practice is to have a pressure plate close the loop. When the cart has sufficient momentum the player steps inside, because the pressure plate is deactivated the loop switches so the cart goes onto the normal track and subsequently the player starts to move onto the sloped part of the track. With just a few seconds of building up momentum it is very much possible to reach cloud level with sea level as starting point by using only 4 powered rail.
A Detector Rail will power the 4 blocks adjacent to it as well as the 2 blocks below it when a minecart (both occupied or empty) is over it. It is thus possible to activate powered rails inline without the use of redstone torches or wiring. This lends itself to one-way powered rail lines by placing a detector rail before the powered rail (with respect to the desired direction of travel). This way, occupied carts will only be boosted if they are traveling the proper direction. Carts coming from the "wrong" way will be quickly brought to a stop by the inactive power rail. A two-way line can be inefficiently created by placing detector rails on either side of the powered rail. Notice however that when using this as described there will be a cart stuck on the track and might block or repel the cart that is going the correct way.
Placing alternate powered and detector rails up a 1/1 slope will not propel a cart more than 3 blocks upward if there was little momentum to start with, because in fails to clear the booster before it returns to the "off" state. The cart will become stuck unless it is in a "train" of two or more carts, in which case the last cart in the train will become stuck.
In general it is possible to include a detector as a source to get the power to activate an adjacent powered rail but this is not recommended as best practice. For example if you place one detector and 6 subsequent powered rail you will see the cart gets stuck on the third or second powered rail since the moment the detector stops detecting the cart the power will get cut instantly and the powered rails return to their braking behavior.
A better example to use detector rail would be have something activated or changed based on where the cart is in your track, or as failsafe devices. For example if you have a station with a cart waiting if may be a good idea to release the cart waiting at a station in case a next cart arrives instead of having both collide.
Curved power rails currently only exist in the case of a T-junction.[4] They do not currently function like regular rails in a curve (without being in a junction). It is possible to make a one-way curved railway using power rails, but not a bi-directional one.
When placing rails, regular rails prefer to curve towards the powered rail. In cases such as these, the south-west rule applies.
A cart traveling on a powered rail that collides with an object (wall, single block, player, other cart) will reverse direction. It will not reverse direction if it collides with a translucent block, such as Stone Slabs or Glass. If a track including powered rails is bordered by blocks acting as "buffers", the cart will indefinitely continue back and forth along the track. Having carts interact with each other on a short track designed this way can be used to chain multiple carts together as a "train". Once aligned, they will all move together at relatively the same speed.
How far the charge passes down adjacent rails is independent of the length of redstone wire. Even if the rails are connected to a redstone torch by 15 blocks of redstone dust, the 8 adjacent rails will still be powered normally despite the fact that they should be out of range for the torch.
Powered Rail Mechanisms
Stop Points
It is possible to make points in your track where a cart is stopped and then jumpstarted again by player input. This can be useful for creating checkpoints to certain sites of interest in your world. This can be done by using two powered track pieces on a one block incline, by having the first powered track piece going down, with the second powered track piece at the bottom and a button placed alongside the second powered track piece, so that the button is directly above the track. You can see an animated example of this stop point if you click on the image
Animated Gif of said example,click for the animated version
When the cart comes to this point it will stop On the incline, allowing the cart to use gravity to start the boost when the button is pushed. Players can then either stay in the cart and carry on to the next stop, or leave the cart at the station for themselves/other players to use later.
Starting boost
Creating a simple initial boost device using 2 powered rails. Dig a hole 1 block deep and 2 blocks long. Place the powered rails inside the trench, connect one end to the track that you wish the mine cart to exit. Finally place the mine cart on the powered rail. Once power is applied to the rail the mine cart will be boosted out.
Bugs
If a Powered rail is only powered by another Powered rail diagonally up or down, you can destroy the rail powering it and it will continue to look and act like it has power until the block is updated. This can be used to have little to no power sources in your track design and up to 2/3 less powered tracks for uphill parts.
When you power a track, 8 tracks in both directions (excluding the track being powered) will be powered. If you have a 19 Powered tracks in a row [1,2,3...18,19] and you Power track 10, tracks 2-9 and 11-18 will receive power. If you add power to track 9, after powering track 9, track 1 will not be powered, even though it is within the 8 tracks. After this, if you remove power from track 10, power will be taken from track 9, however, the same tracks will be stay powered (tracks 1 which should be powered is not, and track 18 which is powered, should be unlit). If you power track 2, (or 18), you will get power in the next 8 blocks.
Doing this, you can power infinite tracks with only 3 torches. 1) If you power track 1, up to track 9 will be lit. 2) Power track track 9 (or last lit track) and 10 (the last unlit track). Putting power in track 9 will keep the previous tracks lit, and 10 will power the next. 3) Then unpower 1, it will still be lit, as 9 is lit, and in the 8 range. 4) Now unpower 9. 1 is still lit. Jump back to step 2.
This also means you can't power tracks in steps of 1 (unless you make something fancy with redstone circuitry). You would have to unpower everything, then power the one 8 steps away (you need n carts + 8 for the number of tracks)
There are currently no textures for curved power rails. However, they still work when placed at T-junctions powered by Redstone.[4]
Trivia
For comparison of speeds, walking speed is about 4 m/s (4.27 exactly), thus using powered rail to speed up will almost double your traveling speed.
Powered rails will always show as powered in the inventory even if destroyed and collected while it was unpowered.
Noting that it takes 6 Gold Ingots to make 6 Powered Rails, it might be more resourceful to use bug boosters. However, bug boosters will no longer function in the upcoming patch 1.6. [5]
When a powered rail with power has another powered rail added next to it, the second rail will not light, until the power is reset.[6]