MOTM

On 3/22/07, jamesabaxter put forth:
>
>Paul advised me to ditch our Power One HDCC 150W (3A) in favor of two
>CP131As:
>
>5VDC@8A w/OVP
>+/-15VDC@1.5A
>Max Current/Fuse Rating 3A@120V

I don't know why he would say two 1.5A supplies would be better than
one 3A supply, especially if you already owned one.

>I was hoping to get some guidance and reality checks before I get
>started . . . .
>
>First, fuses:  I see that there is a 4A fuse in the AC input connector
>drawer.  I plan to replace it with a 1.5 Amp fuse and do the same
>thing with another AC input connector for our second power supply.
>Does this sound right?  Are these the only fuses necessary?

Yes, you only need to fuse the AC.  However, a 1.5A fuse might not be
large enough, considering in rush current and energy lost by the
regulator.  I would go with Power One's recommendation.  Nevermind,
in the event of a short or catastrophic failure, it's going to draw
way more current than the fuse rating anyway.

>Second, wire gauge:  I understand that 12 gauge wire should be used to
>bring power from the supply to the distribution boards and to daisy
>chain other distribution boards.  However, I notice that 18 gauge wire
>is being used to connect the AC input connector to the power switch
>and the power switch to the transformer on the power supply.  I would
>have thought that 12 gauge wire would have been required there, as
>well.  Is it not?

No, the reason you use heavier wire for the regulated DC is to lower
its resistance.  In comparison, the impedance of the AC wire compared
to the transformer primary is negligible, and its exact voltage is
neither critical nor regulated.

>Third, I understood from Paul that it would be OK to daisy chain the
>distribution boards as long as I use 12 gauge wire.  We're talking
>990, 960, and 900 on one supply, and a 960 & 900  on the other.  From
>what I've been reading it seems it might be better to use barrier
>strips.  Is this true?  I don't really understand how this would work
>(I've never dealt with barrier strips) -- Is it sort of like a mult
>and works with jumpers?

A barrier strip is a piece of insulator with metal lugs or screw
terminals mounted on it.  You could also use wire nuts.

>Last, just to double check:  I wire to the terminals on the power
>supply that say +12V, -12V, +-RTN (for analog GND), 5V.RTN (for
>digital GND), and either of the +5V terminals.  I ignore all the rest,
>which have 'S' in front of them (for remote sensing?).

Yes, you do not need to use remote sensing.