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After doing the calculation of the watt output on the 12V rail.

What power does each antminer need?

How much for 1 antminer and for 2

Maybe try this topic: https://bitcointalk.org/index.php?topic=671189.0

Tried reading through it but its nearly 200 pages long and just wondering if someone had an easy answer.

I know a CX500 Corsair will run 1 antminer s3
will a CX750 run 2 antminer s3

No need to read the whole 200 pages. Just ask the question there and people will reply.

Antminer S3 at stock clock of 218.75Mhz runs at 30.5 Ampere on +12V single rail.
That's roughly about 366watts from a +12V rails of power supply.
Sizing of power supply units can be done by going through its datasheet or specs which is available at the manufacturers website and also printed on the back side of PSU.
Look for the single +12V rail in the datasheet or specification label in PSU, there will be an Amperage rating.
Multiply the 12*Ampere of +12V rail and the resultant is your maximum power you can connect to that psu on that +12V rail.

When you what to know how much load you can connect to a PSU, just go to its specification and look for +12V single rail.
Take out the amperage rating on that +12V rail and multiply it to amperage will give you the maximum you can load.
On a safer side to run 24hr, every day, do not full load the +12V rail. Keep a limit of 80% as a good practice.
There will be some current overload than the specified from any load.
Especially in case of Antminer S3 I doubt there is some more load sometimes than the rated like the hashrate jumping over and below specified 441Ghs.

So, always set 125% as load when doing sizing. For example the Antminer S3 is specified as 366W but you do sizing for 366*1.25 = 457.5 to be in a very safe zone.

Coming to the matter, CX500 the +12V is rated at 38A, that is a maximum of 456W can be loaded in idle conditions.
So one S3 can be loaded at maximum were we did out math and found 457.5 as S3 power consumption.

In case of CX750, CORSAIR website says its 12V @ 62A. So, 12*62 = 744W.
744/2 = 372W. So in idle conditions 2 Antminer S3-es of 366W can be connected to this power supply unit.
But as per our safety calculations we need 457.5*2 = 915W or ~ 76A required in +12V rail.
Now rest depends on you to whether load two S3s in CX750 even though its possible.

You have other PSU model options to safely run for a small amount of additional money.
Power Supply Units will not go worthless like Mining hardware.

for my upcoming S3, I had ordered a Segotep GP700G (600 W total)... 48 A & 576 W on the +12V rail... it can provide enough juice for the S3...

an update, since, there was no stock on the Segotep GP700G PSU, I changed and purchased one Antec NeoEco 650M (650 W total)... 50A & 600W on the +12v rail... both the S3 and the Antec NeoECO 650M are running 24/7 now... also, I had purchased one Segotep RP Plus 650 (550 W)... 45A and 540W at the +12V rail... its now waiting for my 2nd S3...