current rating of a power supply

[SanjKrish]

Give me an example where two power sources which has same voltage ratings but different current rating..


Why does the wire heat up when a device exceeds the current rating of something

why are all the source voltage sources.. and not current source..

 

[jiripolivka]

Give me an example where two power sources which has same voltage ratings but different current rating..


Why does the wire heat up when a device exceeds the current rating of something

why are all the source voltage sources.. and not current source..

1. A 6V motorcycle battery and a set of 4 AA cells in series: both have 6V but the first can light up a 25W lamp which the other cannot. Reason: current capacity.

2. Any conductor heats up by a current. The current density in a given cross section is to be known to define the heat loss. A thin wire can be melted (in a fuse it is required when a current limit is exceeded) while a thick wire will only get warm by the same current.

3. In electronics most circuits need a constant voltage with a variable current. Special circuits are known that keep the current constant over a specific voltage range.

 

[SanjKrish]

Thank you jiripolivka..
Now I could figure out hw things work..
I don't have an idea about motorcylce battery though..

jiripolivka tell me one thing..
If i connect two batteries in parallel then will their current capacity double?? I mean if the load requires tat much amount of current..

 

[jiripolivka]

You can also take a half of a car battery to get 6V. Paralleling two batteries should generate a sum of their current capacity, but there is a problem in that batteries do not generate exactly equal voltages as needed. THen the "stronger" battery pushes current into the "weaker" one, and the result is that both discharge even without a load. So it is not recommended to leave two batteries connected in parallel.

 

[SanjKrish]

Okay perfect..
Now can it be compared with water tank scenario where two batteries in parallel would mean a water tank with twice the dimensions of regular tank and placed at the same height of the regular tank..
Since bigger the tank would imply larger the water it can supply without a change in the potential..
In such case since the tank is placed at the same height(potential) the voltage of the regular and the bigger tank remain the same.. Just an example for understanding...

 

[SanjKrish]

Ok i think i'm asking too many questions which u feel is irrelevant or i am confusing too much instead of sticking with the definition..

 

[KerimF]

In theory only, two identical batteries have the same voltage (same tank height in your example).
Practically speaking, when we connect two batteries rated at the same voltage, a current (small or not) flows between them till their internal voltages become exactly the same (like in water case).
Also every battery has an internal resistance. In theory, identical batteries should have equal internal resistances. In reality, they don't have. Therefore, when two similar batteries supply a current to an external load, the current of the battery that has the lower internal resistance is higher than of the other one. In other words, they don't discharge (or be charged if they are rechargeable) at the same rate.