, any movement of carriers, such as subatomic charged particles (e.g., electrons having negative charge, protons having positive charge), ions (atoms that have lost or gained one or more electrons), or holes (electron deficiencies that may be thought of as positive particles).Electric current in a , where the charge carriers are electrons, is a measure of the quantity of charge passing any point of the wire per unit of time. In (q.v.) the motion of the electric charges is periodically reversed; in (q.v.) it is not. In many contexts the direction of the current in electric circuits is taken as the direction of positive charge flow, the direction opposite to the actual drift. When so defined the current is called conventional current.Current in gases and liquids generally consists of a flow of positive ions in one direction together with a flow of negative ions in the opposite direction. To treat the overall effect of the current, its direction is usually taken to be that of the positive .

A current of negative charge moving in the opposite direction is equivalent to a positive charge of the same magnitude moving in the conventional direction and must be included as a contribution to the total current. Current in semiconductors consists of the motion of holes in the conventional direction and electrons in the opposite direction.Currents of many other kinds exist, such as beams of protons, positrons, or charged pions and muons in particle accelerators.Electric current generates an accompanying , as in electromagnets. When an electric current flows in an external , it experiences a magnetic force, as in electric motors. The heat loss, or energy dissipated, by electric current in a conductor is proportional to the square of the current.A common unit of electric current is the , a flow of one of charge per , or 6.2 × 1018 electrons per second. The centimetre–gram–second units of current are either the (esu) per second or the absolute electromagnetic unit (). One abamp equals 10 amps;

mercial power lines make available about 100 amps to a typical home; a lightbulb pulls about 1 amp of current and a one-room air conditioner about 15 amps.The CMC series AC over current monitor with reversing relay and fault detector counter from the ATC Diversified Electronics division of Marsh Bellofram is designed to detect a motor jam, providing the equipment with an opportunity to self-clear before going into a lockout and alarm mode, protecting machinery from damage due to a motor burnout condition.home ac window unit Control voltage is continuously applied to the CMC series. how to set up an ac unitUpon application of the control voltage, both the forward and alarm relays initiate. ac unit check upWhen AC current is initially applied, the inrush time delay initiates to disable the over current sensor during the inrush period.

On over current, the forward relay de-energizes and the unit has a 5-second dead band, then the reverse relay energizes for the selected time delay. Finally, the reverse relay de-energizes, rests for the dead band and the forward relay energizes completing one full cycle. After one cycle is complete, the forward relay remains energized if conditions have returned to normal. If an AC over current condition remains, the unit will go through the same operating sequence as before until jam is corrected or the number of preselected cycles has occurred. The number of cycles that occur before lockout is field selectable from 1 to 9 cycles to prevent the faults from accumulating and causing nuisance alarms, a time band is initiated upon sensing the first fault. Then, successive occurrences equaling the number of faults within the time band will cause alarm. When the number of cycles reaches the pre-selected count, the Forward, Reverse and Alarm Relays lock into the de-energized state. Reset is accomplished by pressing the reset button.

The LED indicator glows when the forward relay is energized. The CMC series operates in the fail safe mode as the relays are energized in normal conditions. An external CT may also be used to extend the range of the current monitor. AC over current monitor with reversing relay Expressly designed to detect motor jams Current demand level monitoring Conveyor or motor load jam detectionFor many people, it doesn’t matter. DC is faster, and that is all that they need to know. But for the curious, this is a simplified explanation of the difference between AC and DC charging. Technical details are intentionally glossed over here. The reason we have two types of charging is that there are two “types” of electricity, AC and DC; so we shall start by discussing them. DC is the simple positive-and-negative type of electricity that you probably experimented with in 7th grade science. A key advantage is that it is easy to store in batteries. That is why portable electronics – flashlights, cell phones, laptops – use DC power;

they have to store it. Plug-in vehicles are portable so they use DC batteries too (although most of them have AC motors – a complicating step we may consider another day). AC electricity is a little more complicated because it switches back and forth, but a key advantage is that it can be transmitted economically over long distances. That is why AC power comes in through the power lines to your home, and is what is available at power outlets. Stationary appliances that use electricity directly from an outlet – lamps, refrigerators, washing machines – use AC power. Because the electric grid provides AC, the electricity must get converted to DC when you want to charge a portable device. This conversion is done by a “rectifier”. Portable electronics that recharge from wall power all have one: it is usually in a black box in the charging cord, along with some other components we will ignore. You’ll notice that the more power the device uses, the larger that box is. The key to understanding AC versus DC charging is learning where the box is, and why.

Here is the DC charging solution for my tablet computer. It is simply a USB cable, which allows my tablet to charge from a DC USB port in a car or laptop. Both sides have DC, so no conversion is required. Now, here is my tablet’s AC charging solution. The same USB cable plugs in to a little black box that plugs in to an AC outlet – the box converts AC to DC. Here is a simplified diagram (can you tell I didn’t take art classes?) of how AC and DC charging work with a plug-in vehicle: When you plug in to AC power – whether you plug in to a 120V or 240V outlet, or use J1772 charging equipment – your car converts the power to DC. When you use a DC charging station – CHAdeMO and Supercharger are the varieties in active use, with CCS coming soon – the power is converted by the station, so DC goes straight in to your battery (not really, but close enough for this discussion). Note that in both cases the power starts as AC and ends up as DC; the only qualitative difference between “AC charging” and “DC charging” is whether the conversion is done before or after it goes in to your car.

Why bother with two types of charging – why not choose a single place to convert the power? AC is more readily available at power outlets, but despite AC lines carrying vast amounts of power, outlets are limited. Dedicated DC charging stations provide more power, but being expensive to install and dedicated to plug-in charging, availability is limited. AC outlets are ubiquitous, so to make charging convenient your car should be able to plug in to them. That means every car has to be able to convert AC to DC. The conversion equipment in current plug-in cars varies; most can convert up to 3.3, 6.6 or 9.6kW of power. For comparison a typical household outlet can continuously provide up to 1.4kW, and “high-power” 240V outlets sometimes found in garages and RV parks can provide up to 9.6kW. It is technically possible for a car to convert far more power than that, but the equipment would be bulky, heavy, expensive, and hot – and anything over 9.6kW would see infrequent use because higher-power outlets are not available.

To illustrate this point: the Tesla Model S offers a $1,500 option that allows the car to convert up to 19.2kW. Twice-as-fast charging is obviously an enormous benefit when you can use it, so some owners swear by it – but you can only get that much power if you use special hard-wired 240V charging equipment. The West Coast has a few such chargers along popular travel routes, but such equipment is hard to find, not needed for overnight charging, and still far slower than DC charging. Many owners skip this option to save money and weight. DC charging stations have special grid hookups so they can get and convert far more power. DC stations are big, expensive and have a lot of cooling – it wouldn’t be practical to put that equipment in every car, even if there was a way to plug directly in to the grid. CHAdeMO chargers vary from 25 to 60kW, and Superchargers are 90 to 120kW – almost 100 times faster than a standard 120V household outlet, and more than 10 times faster than 240V AC outlets.

At higher cost, the grid could supply even more power; but these limits are largely set to avoid harming the car batteries while charging. (Many factors determine how fast batteries can charge, but currently cars that use Superchargers have significantly larger batteries than cars that use CHAdeMO chargers. All else being equal, larger batteries can accept more power without harm). An easy way to visualize the AC/DC charging differences is to consider how Tesla handles charging for their Model S sedan. They make large quantities of boxes they call “chargers” that include a 10kW rectifier to convert AC to DC. Every car they build gets one for AC charging, and so can handle all the power than any outlet provides. Plugged in to the right outlet, this can charge a car at up to 24 mile of range per hour. If you buy “twin chargers”, you get two boxes in the car and can now handle high-power hard-wired charging equipment as well. This can charge the car at up to 50 miles of range per hour.