MOTM

Paul et al, 

I recently exceeded the 12 module limit on my 900 PS due to the  addition of
some Blacet & PAIA devices. According to specs the current draw of my
current collection of modules is well below the capacity of the 900. 

I took a look at the MTA connectors and it appears that with a slight
modification you could create a cable with MTA connectors in the middle,  as
well as on each end. Not unlike an internal power cables on a PC. This
entails drilling four small holes that allow the cable to pass thru the
connector.

The benefit would be you could power an entire row of module with a single
cable...
What I'm wondering is if there are any potential problems with doing this?

jmw

I think that might deep-six the "star ground" configuration that Paul
created which eliminates ground loop problems in the MOTM system. Maybe not,
but I wouldn't fool with his design myself.



		-----Original Message-----
		From:	jmw [mailto:evening@...]

		What I'm wondering is if there are any potential problems
with doing this?

Only if *all* of the modules in the cale are *low current* ones. Like the
800
700
120

Sticking a 300 or a 420 or a 410 in there is a *bad* idea. Why? With such
a cable, there is no "star ground" and the current "sloshes" up and down the
cable.
Sensitive modules *will* pick this up. But sticking 6 MOTM-800s together is
not a big deal.

AMP does make a *specific* MTA-156 to do this. Allied has them.

I suggest getting a MOTM-900-PCB for $16 (see the PDF catalog) which is the
connector
pcb used in the MOTM-900. You stick it somewhere with double-sided foam tape
or screw it down, and chain
off of that.

Paul S.


-----Original Message-----
From: jmw <evening@...>
To: motm@onelist.com <motm@onelist.com>
Date: Friday, October 29, 1999 10:03 AM
Subject: [motm] power cable modification...


>From: "jmw" <evening@...>
>
>Paul et al,
>
>I recently exceeded the 12 module limit on my 900 PS due to the  addition
of
>some Blacet & PAIA devices. According to specs the current draw of my
>current collection of modules is well below the capacity of the 900.
>
>I took a look at the MTA connectors and it appears that with a slight
>modification you could create a cable with MTA connectors in the middle,
as

>well as on each end. Not unlike an internal power cables on a PC. This
>entails drilling four small holes that allow the cable to pass thru the
>connector.
>
>The benefit would be you could power an entire row of module with a single
>cable...
>What I'm wondering is if there are any potential problems with doing this?
>
>jmw
>
>>

> From: "jmw" <evening@...>
> I recently exceeded the 12 module limit on my 900
> PS due to the addition of some Blacet & PAIA devices.
> According to specs the current draw of my current
> collection of modules is well below the capacity of the 900.
> snip <

> From: "Paul Schreiber" <synth1@...>
> snip <
> I suggest getting a MOTM-900-PCB for $16 
> (see the PDF catalog) which is the connector
> pcb used in the MOTM-900. You stick it somewhere
> with double-sided foam tape or screw it down, and chain
> off of that.
> snip<

I use these MOTM-900 PCBs in my MOTM set up.  I have three of them.  I
would certainly agree with Paul that they are the way to go.  Each PCB is
star connected back to the output of the power supply (I am using a case
supply, not the 900).  These 900 PCBs come with "power in" spades for
connection of larger wire to the power supply.  The crimp style connectors
are available everywhere (even RS).  I have my 900 PCBs connected to the PS
with # 14 wire.  Although the wire is much bigger than needed, it let me
locate the 900 PCB a bit away from the PS (so MOTM power cables will easily
reach modules) without fear of modules interaction as Paul mentioned.

If you install these in a metal rack (as I have done until my case project
is done) you need to be careful that the bottom of the circuit board does
not short out.  I bolted mine down inside one of those cheap RS plastic
project boxes (4 X 6 I think) and did not use the lid.  It keeps the board
well isolated from potential shorts (pun intended) and still leaves all the
connectors easily accessible.

I have some very nice industrial grade # 14 stranded wire that we use at
work for wiring switchboard panels.  Essentially anything less than 20 feet
is a piece of scrap, so I help myself to what would otherwise hit the
recycle bin.  I like it over what you normally find in the store as the
insulation is thinner yet tougher.  If you (or anyone else on the list)
wants some just let me know how many feet and I will send you 3 pieces that
long to wire from your PS to your 900 PCB.  $0.00 per foot  :)

Larry Hendry

It looks like the 900 PCB is the way to go.

Thanks for everyone's input.

jmw