What controls amount of current?

Question

If increasing voltage proportionally increases your current (assuming no change in resistance), then voltage really 'controls' but does not itself define the power output of something, and an increase in voltage means an exponential increase in power output. But what is it that determines current? Why would a situation create high current but low voltage? Why high voltage low current? What do you use to convert voltage to current or current to voltage and how does it work? What is it about a battery's composition that determines current? I get that placing a load on the connection will increase resistance and therefore draw more amps to continue working. Does this mean there is a sort of base level of current a battery will put out, and resistance will just draw however much additional current to allow itself to operate?

Thanks for any answers

Answer 1

Voltage across a resistance controls current in that resistance. It's that simple. Ohm's law, I = E/R. Double voltage across a resistance, you double current through it.

Note, this is an ideal answer, in practice things change a bit, because resistance is not just confined to a fixed resistor in a circuit.

Connecting wires also have resistance, and batteries have "internal resistance", usually considered as a fixed resistor in series with the battery.

Any given battery will only supply a maximum current depending on size and type, so what happens is that IF more current is expected of it, its TERMINAL VOLTAGE will fall to match the voltage to the current max. it can supply. That's that "internal resistance" at work, the voltage "drop" (lost) is across the "internal resistance". Who really cares about why? You choose the most appropriate TYPE, and terminal voltage, of a battery for the particular application.

Yes, power increases exponentially.

High current, low voltage, high voltage, low current can both be the same power, because power by Watt's rule is voltage x current. So 100V. at 10A. is 1,000W., and 10V. at 100A. is 1,000W. Same power.

I think you are overthinking too much, and confusing yourself.

Answer 2

~ My comments are enclosed with a ~ If increasing voltage proportionally increases your current (assuming no change in resistance), then voltage really 'controls' but does not itself define the power output of something, and an increase in voltage means an exponential increase in power output. ~true~ But what is it that determines current? ~the circuit resistance added to the source resistance determines the current. 6 volts at 1 ohm source; 2 ohm load = 3 ohms; I = E/R = 6/3 = 2 amps. Why would a situation create high current but low voltage? Why high voltage low current? ~High current at low voltage is the result of low source resistance 0.08 ohms and low load resistance 0.02 ohms = 0.1 ohms with a 3 volt source = 30 amps~ What do you use to convert voltage to current or current to voltage and how does it work? ~A dc to dc converter coverts the dc to ac then back dc at a different voltage and current. The newer ones turn the input power off and on thousands of times per second to reduce the voltage and current by the desired amount at efficiencies as high as 99%~ What is it about a battery's composition that determines current? ~It increases with the dimensions of the battery and decreases with the millimeters of spacing between positive and negative. The chemicals used make a difference. Lithium ion batteries have close spacing, low internal resistance and can deliver higher current than other batteries of the same size~ I get that placing a load on the connection will increase resistance and therefore draw more amps to continue working. ~not correct~ Does this mean there is a sort of base level of current a battery will put out, and resistance will just draw however much additional current to allow itself to operate? ~No, a load resistance of zero will result in maximum battery current = sometimes enough to damage the battery or even explode the battery. Neil~

Answer 3

Your question covers at least two topics.

(1) Water analogies are often used to describe current

and Voltage. Consider a 1,000,000 gallon water tower

with two outlets: the first ¼" inch in diameter and

the second 12" in diameter.

Which pipe will drain the tank faster?



Here pipe diameter compares to resistance at fixed Voltage.

Voltage compares to height of tank which is proportional to

pressure.



(2) Power does increase geometrically with current (P=I²R)

Assuming a remote generating station which sends power to

a city 100 miles away, the power lost to transmission

is the resistance of the wires (fixed) × (Amperage)².

Sending 1,000 Amperes at 120 Volts will consume 1,000,000

times more transmission energy than sending 1 Ampere at 120,000 Volts..