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From: terryS on 9 May 2010 10:20
On May 8, 7:23 am, Jasen Betts <ja...(a)xnet.co.nz> wrote:
> On 2010-05-04, eromlignod <eromlig...(a)aol.com> wrote:
>
> > Hi guys:
>
> > I'm an ME and I'm trying to drive a large number of circuit boards in
> > a confined area.  The circuits are all identical and pull about 150 ma
> > at 5V each.  The problem is that there are almost 100 of the circuit
> > boards spread over about a 48-inch distance.  The power supply is big
> > and can handle the total current, but I'm getting a terrible voltage
> > drop as I get farther and farther from the supply.  The current gets
> > to be so much that the IR drop is significant, even for fairly heavy-
> > gauge wire.  My voltage is dropping so much that it is causing logic
> > circuit problems.
>
> > Is heavier-gauge wire my only option?
>
> if resistive loss is the wire is the cause then increasing the amount
> of copper is the solution.
>
> If you have the system wired so that the second unit is powered by
> short wires from the input terminals of the first and the third is
> likewise powered from the second  your 90th unit has 89 short wires
> (that probably total much more than 48" ) and also 90 mechanical joins
> that probably have higher resistance than than short wires themselves
> between it and the power supply.
>
> Adding power feeds that go direct to the supply every 10 or so units
> (like Phil suggested) will alleviate most of that.
>
> As others have suggested swapping to a bus-bar system where each unit
> connects directly to metal rods would also work, but at 15A smells
> like overkill to me.
>
> --- news://freenews.netfront.net/ - complaints: n...(a)netfront.net ---

Am wondering if the problem is not with the 5 volt 'feed' side???????
Maybe it's with the 'return' side? maybe the wire gauge or metallic
path of the return needs to be looked at?
100 units at 150 ma is only 15 amps (total) and normal gauge wire Such
as 10AWG or 12AWG; unless something stupid like 26 AWG has been used
to a carry the whole 15 amps, has very low resistance per foot etc.!
Something weird about this question.
Assuming the 5 volt supply, is, say the positive? How is the negative
side wired; through a frame 'ground' or equipment case or something
with a significant resistance path?
This perhaps somewhat similar to a motor vehicle when there is a 'bad'
ground to the vehicle frame due to corrosion etc.
Suggestion anyway!
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