Power requirements for Hubs

[keithr]

power requirements:  If a hub requires 60amps of power (if all strings are 80% +) will that hub need a dedicated electrical outlet?

[shaunkad]

It depends on the current draw of your DC power supply you may be able to use two hubs on one outlet. Your hub power supply should tell you the amp drawn.

[rrowan]

Nope

Don't confuse AC amps with DC amps

Check your Power supply input amps needed. It will most likely be 15amps or less

Cheers

Rick R.

[keithr]

Thanks guys  did not take in the idea of AC  to DC amps,

[Trepidati0n]

Things can get a bit confusing on this.

1.  A typical VAC home outlet is 15 or 20 amps.  However, in reality, if you excersie that level, you will tirp.  You need to be ~80% otherwise you are heaidng towards the breaker going "click"

2.  Since we are converting "POWER" from AC to DC, we have to figure out the least amount of power you get from an outlet.  In typcal home that is somewhere between 100-120VAC.  I always assume low..therefore 100V.  However, since most people will be running their show at night, the voltage at the outlet tends to be a bit higher.

3.  If I take the 80% from #1 and the low level from #2, you get 1200Watt (100*15*80%) and 1600Watt (100*20*80%) respectively.

4.  For RJ's system, 99% of the power is from 12V so we will ignore everything else.

5.  A PC power supply is typically 80-90% efficient.  Lets go with 85% assuming the people here are buy decent supplies.

6.  Therefore you get 1200W/12V*85% = 85Amp or 1600W/12V*85% = 113Amp of DC current you can work with out of one AC circuit breaker. The number of supplies you need to use that much is up to you.

7.  A node is ~29mA of DC current.  Therefore, you can support 2900nodes (85A/.029A for a 15A outlet) and 3900nodes (113A/.029A for a 20A outlet) respectively.


Of course all hte numbers above are based upon YOUR setup.  I just gave a pretty conservative estimate. 

If I had to just give a simple rule of thumb, I would say you can support approximatley 200 pixel nodes per amp of AC current out of the wall.

[deplanche]

I recently did a similiar computation, but came at it a slightly different way...

For 100 nodes, you need:
100*0.029 amp DC = 2.9 amp DC
(2.9 amp DC * 12VDC)/0.85 = 40.9 Watts
40.9 watts/100 VAC = 0.41 amps AC

So for 100 nodes, you need 0.41 AC amps
          200 nodes, you need 0.82 AC amps
          244 nodes, you need 1.00 AC amps
         2928 nodes, you need 12.00 AC amps

To keep from tripping a 15A AC breaker, you'd want to stay below the 80% of 15A or the 12 amps and 2928 nodes shown above, which is very close to what Trepidation calculated.

You will notice that I have calculated that I can power 244 nodes per AC amp, as oppsoed to 200 nodes per AC amp that he calculated.  This is becuase I use the 80% at the end, where he uses it at the beginning.  Just different ways of doing the same thing.

[Trepidati0n]

Nope...it is becaused I used 80% pretty much twice.  You need a 80% for the breaker, and then another derating for the supply efficiency.  PC supplies, are not 100% efficient 

[deplanche]

You used 80% for the breaker and 85% for the power supply.

I used the 85% in my calcs at the beginning for the loss of efficiency.  But held off on the 80% breaker limit until the end because if I am well below the limit, it doesn't matter.. at least to me.

[WWNF911]

Thanks to Both of you. Good info.