Current vs. load

[Badar]

When using Air Conditioners or any other heavy load we require a heavy pair of wires (Big Dia).This is becaue the more the load the more current it draws.

Doesn't this fact contradict with the other?
We have a battery connected with a resistance (in this case simply resistive load).The supply drops all the voltage on the resistor whatever is its value.
The less the resistance (Load) the more is the current.

If it doesn't contradict then how?

 

[j.p.bill]

The terminology is possibly confusing. Loads should be understood in terms of power consumed, rather than as resistances. So a large (or heavy) load will be one that pulls a lot of current. Power is calculated as the voltage times the current drawn. That's why a heavy load needs larger wire.

 

[Leftyretro]

When using Air Conditioners or any other heavy load we require a heavy pair of wires (Big Dia).This is becaue the more the load the more current it draws.

Doesn't this fact contradict with the other?

Not at all, ohm's law applies.....

We have a battery connected with a resistance (in this case simply resistive load).The supply drops all the voltage on the resistor whatever is its value.
The less the resistance (Load) the more is the current.

Keep in mind that the voltage source sees the 'total load', however I2R loss in the wire leads to the actual load is wasted energy being dropped so that the actual load sees less voltage then the source voltage.

If it doesn't contradict then how?

Ohm's law will allow you to analyze why larger wire between source and load are needed for highest efficiency and safety...

Lefty

 

[dch222]

Lower resistance = heavier (higher) load. Think current (or power)

 

[Badar]

The terminology is possibly confusing. Loads should be understood in terms of power consumed, rather than as resistances. So a large (or heavy) load will be one that pulls a lot of current. Power is calculated as the voltage times the current drawn. That's why a heavy load needs larger wire.

That is absolutely true and i had that in mind but does this mean higher wattage corresponds to a lower resistance of the load.if no than how a higher resistance can draw high current at a given voltage.
Wattage is simply a term that depends upon both voltage and Current.
Higher V.I means higher wattage but first i want to know from where does this current come at this high load.

 

[CheapSlider]

does this mean higher wattage corresponds to a lower resistance of the load ?

YES


Low Resistance = High Load
High Resistance = Low Load


P=IV (using ohm's law I= V/R)

P = VI = V x V/R

= V^2 / R

The value of P will decrease as R gets bigger, and P will increase as R gets smaller

 

[ThermalRunaway]

If you think of it in terms of plumbing, then if you have a pressured water system and there is a valve in the middle posing little resistance, you will get a large water flow. In a similar way, if you have a high current supply and you connect a small resistance across it, high current will flow.

If you wind the valve in so that it now poses a large resistance, you'll get less water flow and using the same analogy again if you have a high current supply but you connect a high resistance across it, you'll get a low current flow.

Brian

 

[Badar]

I think now i m getting this.
But can you make me visualize that low resistance corresponds to high load beacuse if so then how the A.C or any other appliances use this heavy current as it sis just passing through it and is not utilized.

 

[3v0]

You have been told everything you need but let me give it a try.

I think now i m getting this.
But can you make me visualize that low resistance corresponds to high load

As above all you need to know is in Ohm's Law.

A resistor is like a valve that controls the current flow.

Think of it like this. You hook a fire hose up to a fire plug (the mains). On the end of the hose is a valve (a resistor). The water want to flow from the fireplug to the street/drain which is a good analogy for electrical ground.

With the valve wide open there is little or no resistance and the valve allows all the water the hose can carry to escape (A large load lots of water flow because the valve has little/no resistance).

With the valve half shut less water comes out because there is more resistance to flow ( A smaller load less water flow due to greater resistance).

With the valve fully shut no water flows at all (very very high resistance results in no load no water flow, as in the switch is off).

if so then how the A.C or any other appliances use this heavy current as it sis just passing through it and is not utilized.

You should understand from the above that an appliance (which is in effect on resistor) only allows the current that it actually uses to flow through it. Just like the valve on the fire-hose.

 

[Hero999]

Where ever there's a current flowing through a resistance there is a voltage drop.

The higher the current the higher the voltage drop.

The higher the resistance the higher the voltage drop.

The thinner the wire the higher the resistance.

The thicker the wire the lower resistance.

Therefore the thinner the wire the higher the voltage drop and the thicker the wire the lower the voltage drop.

The compressor requires between 220VAC and 240VAC to work properly and if there is a large voltage drop in the cable there won't be enough voltage left to operate the compressor.

 

[ThermalRunaway]

When you place a low resistance across the output of a source; be it A.C. or D.C. or whatever, then you demand high current from it. It becomes more and more difficult for a source to maintain it's output voltage as you increase the current you demand from it. Therefore when you place low resistance across the output of a source, it can be said that you're loading it. The lower the resistance, the higher the current demand, and the greater load you are placing on the source.

You're thinking of it the wrong way. You're wondering how it is possible that a lower resistance is causing a higher load. But you should be thinking in terms of current - the more current you draw from the source, the more you're loading it and the smaller resistance the higher load you'll place on the source due to the higher current you're demanding.

Brian

 

[ThermalRunaway]

By the way, when you place a small resistance across the output of a source the energy IS utilised (normally wasted). You draw high current due to the small resistance you've placed across the output, and most of that is converted into heat in the resistor itself.

If you place low resistances across high current outputs then you need to use devices that can withstand the heat that is generated. Wirewound resistors are common in these applications, and they're normally huge. Sometimes heatsinked too.

Brian

 

[Badar]

Ok.Thank you all very much.I now understand it.