I want to use a power supply of 5v x 20A . I want to 4 strips of led lights each one draws 5A of current. I can't afford to buy all 4 strips all at the same time and seems stupid to buy 4 separate power supplies at 5v x 5A.so I was wondering if I use a current splinter circuit at 5A per leg that I can use one at a time. Then add the strips when I'm able to receive them. If that makes sense to you all. Any suggestions will be appreciated. I can make the circuit but wondering if I needed a load on the other three legs to keep 5A on the other legs.
Ampere rating on power supplies are a max, not rating not a fixed quantity. Look at Ohms law: If voltage and resistance* is fixed, current automatically comes out as a fixed value.
Most power supplies fix voltage. So your power supply is actually a 5V 0-20A** power supply. The voltage is fixed, current is set by the load resistance.
There are also constant current supplies, which will be e.g. 5-20V 1A. They will adjust the voltage such that a certain current flows. You need them for high power LEDs, but not for strips.
That said, 20A is pretty massive. You will need pretty thick cables for that - more than the 1,5mm²~=15AWG that is commonly used in mains wiring in Germany. Americans seem to have rather 12AWG, which makes sense since they have lower voltage, i.e. higher current for the same power.
- Plain LED resistance is not fixed, but your strips are one or the other way, at least in first order.
** There are three reasons not to always by huge power supplies: 1) price, 2) they will be less efficient under lighter load, aim for around 70-80% load for best efficiency. 3) they can be more dangerous. If you make a mistake and send 20A over a connection that was built 500mA, bad things will happen (something between massive damage and fire). A 1A supply will have much less drastic effects.
I really think we should have a sticky thread that explains these basics.
A piece of advice when using this forum.
Do not hi jack threads
Do not post a question more than once
Otherwise people get very pissed off with you.
Offending thread
http://forum.arduino.cc/index.php?topic=516934.msg3527602#msg3527602
Where your question was already answered.