how to stop excessive current from overloading the wrong parts of a circuit

[jos]

Suppose I want to make a circuit with 60 parallel circuits, 5V, and .06 Amps per parallel circuit, totaling 3.5 Amps being split between all of the parallel lines. Now suppose I want to add one last parallel circuit along with the others, so 61 parallel lines between the positive and negative terminals. If I were to happen to supply that circuit with 5V and 15Amps, I'd have about 11.5 Amps extra running the circuit. What can I do to make sure that all that excess amperage gets sent through the last parallel circuit instead of one of the parallel lines that draws .06 Amps because of a load?

drawing of my supposed circuit (more or less):
_______ +
|Power |--------------------------------------------------------------------------------------------|
|source | 0000000000000000000000000000000000000000000000000000000000000 |
------------------------------------------------------------------------------------------------------|
-


sooo the zeros are the .06A loads, and that last "|" connecting the positive and negative currently is depicted as just a wire, but I'd like to know if something can be put there which can assure me that none of the "0" loads are taking the excess 11.5 Amps which are somewhere in the circuit. If it needs to be, the wire could easily be placed to the left of the nodes, although I don't know what difference it would make.

 

[Dave_H]

Your circuit will not draw excess current unless there is a design problem or a fault. The circuit will only draw
as much current as it needs (3.5A), not the 15A limit of the supply.

If you don't need 15A you could get by with a supply with less capacity. Sometimes it makes sense to use
a supply with lower capacity because if a fault such as short circuit does occur, there is less available
current to do damage. A 15A supply may be able to supply more than 15A before its over-current protection circuit
cuts in (if it has one), or fuse blows.

Dave


I assume/hope that the loads are current-limited and you are not relying on the PSU's current limit to control the
overall current, which would be a bad idea.

 

[PhotonWrangler]

What Dave said.

Let's say your smartphone needs 5 volts at 1 amp to charge. You could plug it into a 1 amp charger or a 2 amp charger and it will draw only 1 amp from either one.

 

[Lynx_Arc]

If you do know the current draw expected and are wanting to be sure of no overload adding a fuse inline is a simple process. For a 3.5A circuit a 5A fuse should suffice such that any short in the circuit would blow the fuse.

 

[DIWdiver]

Jos, think of it like the water supply in your house. Say you have 60 PSI and your supply line into the house can supply 15 gallons per minute (GPM). This is analogous to a 60V supply that can source 15A. If you shut off all the water in the house, the flow goes to zero. There is capacity that is not being used, and you could call this 'excess', but you don't have to dump it on the ground. Now open the kitchen faucet, which is designed for 2 GPM. Now your main inlet will be at 2 GPM and you have 13 GPM of excess capacity. Now your sprinkler system comes on and wants 10 GPM. Not a problem. It takes 10 and the kitchen still takes 2. Electrical circuits work just like this.

As long as they are designed for the voltage you are supplying, you can connect any number of similar or different loads to the supply, and each will draw only what it wants.

Actually, the wiring of your house works like this too. In my house I have a 100A service. I can plug in a 120W lamp that draws 1A, and it will work regardless of what else is plugged in - nothing (0A), oven (30A), disposal (8A), microwave (12A), etc. As long as you don't overload the system, everything is fine.