MOTM

a) you only need 1 fuse (in the AC socket)

b) the grounds from the 2 CP-131s *must* be tied together, at *one point only*. 
this can be on the barrier strip, you need 2 more "positions". This is the +-15V 
ground. You already have the earth grounds connected. This is NOT THE SAME 
GROUND as the +-15V ground. DO NOT tie earth ground to the +-15V ground.

c) use a Slo-Blo type fuse (Littelfuse 215 or 218 series).

Paul S.

----- Original Message ----- 
From: "jamesabaxter" <motm@...>
To: <motm@yahoogroups.com>
Sent: Monday, March 26, 2007 9:21 PM
Subject: [motm] Re: Power Supply Fusing & Wiring


> Hi, again -
>
> I'm getting ready to commit to my new power scheme and before I start
> drilling holes and spending money on wire, eurostrips, etc., I just
> wanted to double-check my scheme with you all.
>
> I've put up a PDF with a diagragm of what I'm tryin to do:
>
> http://www.freeclyde.com//guest/FreeClyde_MOTM_Power_Scheme.pdf
>
> I've gotten some conflicting ideas about whether this is the right way
> to fuse . . . .  I've been told that the fuse in the AC input
> connector is all I need, but I've also read that each power supply
> needs a fuse after the switch as well.
>
> The other issue I'm fuzzy on is tying grounds.
>
> For the earth grounds to the power supply chassis:  The most
> convenient thing for me is to place one power supply right next to the
> AC area (input connector, switch, and AC eurostrip).  The other supply
> would be 5-6 feet away.  Should I a) just make sure the earth wires
> from the AC terminal block to each of the chassis are the same length,
> b) wire one chassis to the mains' AC earth and tie the two chassis
> together, or c) something else altogether?
>
> If it would be better for the power supplies to be next to each other,
> that can be arranged.
>
> Also, what about the two analog commons and the digital ground?  Are
> they all supposed to be tied together?
>
> Last, I was told to use 12 AWG if I was going to daisy chain
> distribution boards, but since I'm going to do a star configuration, I
> should be OK with 14 AWG, right?  The runs will be 2-4 feet (at least
> if I separate the power supplies).  Should I cut all the cables to be
> the same length (from the power supplies to the distribution boards)?
>
> Thanks for any thoughts!  Sorry to newb out on you like this ...
>
> - James
>
>
> --- In motm@yahoogroups.com, "jamesabaxter" <motm@...> wrote:
>>
>> Hi -
>>
>> I've inherited responsibility for maintaining a >40 module MOTM.
>>
>> Paul advised me to ditch our Power One HDCC 150W (3A) in favor of two
>> CP131As:
>>
>> 5VDC@8A w/OVP
>> +/-15VDC@...
>> Max Current/Fuse Rating 3A@120V
>>
>> 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?
>>
>> 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?
>>
>> 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?
>>
>> 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?).
>>
>> Thank you so much for any advice you can offer.
>>
>> - James
>>
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