AC/DC (not the band, mind you)

[rthmjohn]

I've never fully understood the difference between alternating current and direct current. What is the difference? Could someone explain in simple terms and then maybe in more detail?

[swansont]

I've never fully understood the difference between alternating current and direct current. What is the difference? Could someone explain in simple terms and then maybe in more detail?

 

In AC the voltage and current vary in time. In DC there is a fixed voltage and constant current. Each has some advantages and disadvantages. The main advantage of AC is that it's very easy to step the voltage up and down, because transformers need AC (changing current means a changing magnetic field, and a changing magnetic field in a pickup loop generates a voltage/current) so you can transmit power at high voltage (and lower current) and then convert to lower voltage at the far end and get more current.

[5614]

In AC the voltage and current vary in time. In DC there is a fixed voltage and constant current

Can't really add to that.

 

The mains (ie. a plug) is AC, whereas a battery is always DC.

 

There are methods to make AC into DC and vice versa.

[Phi for All]

DC tends to be easier on the devices it powers (Edison made DC powered light bulbs with filaments that are still burning today), but AC can be pushed much further away (we could never have power plants supplying DC current).

 

I remember hearing that Edison's original idea was to have everybody generate their electricity personally from small home generators so we could use DC current. I wish someone would come up with an affordable unit that was environmentally friendly but it would probably topple the economy since you wouldn't have to replace bulbs and blow dryers all the time.

[rthmjohn]

What exactly are the advantages of DC current?

[swansont]

What exactly are the advantages of DC current?

 

It's a bit safer; you're still prone to getting a nasty shock, but AFAIK AC is more likely to stop your heart.

[Phi for All]

What exactly are the advantages of DC current?

The flow of electrons in the DC current are one-way and continuous, so it's less stressful on whatever it's powering. AC goes back and forth between the source and what it's powering more than 50 times per second. This tends to burn equipment out faster.

 

But DC current can't be stepped up or down, as swansont mentioned. Power stations can send out AC electricity in extremely high voltage to cover long distances and then transform it down for safe use in the home or office.

 

In both AC and DC current, danger is a combination of many factors, including voltage, ameperage and resistance. I've had shocks playing around with furnace transformers and D batteries that were very high in voltage, but very low in amperage (and duration).

 

It has been argued that the added pollution and cost of personal DC generators would be offset by longer lasting electrical equipment. I'm not sure if some of our modern equipment could be made to run off DC current (although computers can run on batteries, and all batteries are DC current). We're also not in a market condition that would survive very long if you only bought one set of light bulbs in your lifetime.

 

Batteries are very interesting as a source of DC current. You should never throw away batteries that are making your flashlight dim or your cassette player sound funny, because those batteries will power a radio or a calculator or a clock for weeks to come.

[lauron]

It's a bit safer; you're still prone to getting a nasty shock, but AFAIK AC is more likely to stop your heart.

 

may i ask why this is? i suspect it's something to do with the signals produced by the myogenic tissue in the heart but i'd love to have a definite answers.

thanks

[swansont]

may i ask why this is? i suspect it's something to do with the signals produced by the myogenic tissue in the heart but i'd love to have a definite answers.

thanks

 

I'm not a physician or a biologist. I've seen the claim in a number of places that it generally takes more DC current to cause fibrillation that AC, but not exactly why this is the case.