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From: eromlignod on 3 May 2010 22:23
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? Is there a way to "goose" the
voltage along the way, like with a DC-DC converter or something?
Other tricks?

Any replies are greatly appreciated.

Don
From: Phil Allison on 3 May 2010 22:27

"eromlignod"
>
> 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? Is there a way to "goose" the
> voltage along the way, like with a DC-DC converter or something?
> Other tricks?
>
> Any replies are greatly appreciated.


** You need to have multiple DC power feeds to all those modules - not
just a single bus.

Break them up into groups of say 10 or so and run a cable back to the PSU
for each group.


...... Phil


From: George Herold on 3 May 2010 22:32
On May 3, 10:23 pm, 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?  Is there a way to "goose" the
> voltage along the way, like with a DC-DC converter or something?
> Other tricks?
>
> Any replies are greatly appreciated.
>
> Don

Wow, this is great! I'd try and lay things out so that each circuit
has about the same amount of resistance between it and the power
supply. Then you can add a sense line back to the PS to adjust the
voltage. (but only one and it might not be necessary.)

George H.

From: George Herold on 3 May 2010 22:34
On May 3, 10:27 pm, "Phil Allison" <phi...(a)tpg.com.au> wrote:
> "eromlignod"
>
>
>
>
>
>
>
> > 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?  Is there a way to "goose" the
> > voltage along the way, like with a DC-DC converter or something?
> > Other tricks?
>
> > Any replies are greatly appreciated.
>
>  ** You need to have multiple DC power feeds to all those modules -  not
> just a single bus.
>
> Break them up into groups of say 10 or so and run a cable back to the PSU
> for each group.
>
> .....   Phil- Hide quoted text -
>
> - Show quoted text -

Can you mix more than one 'sense' feedback line?

George H.
From: John Larkin on 3 May 2010 22:58
On Mon, 3 May 2010 19:23:05 -0700 (PDT), eromlignod
<eromlignod(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? Is there a way to "goose" the
>voltage along the way, like with a DC-DC converter or something?
>Other tricks?
>
>Any replies are greatly appreciated.
>
>Don

It's only 15 amps. How are the connections being made between the
supply and the boards? How are they grounded?

The best wey to distribute power like this is to use a higher voltage,
24 maybe, and use a "point of load" switching regulator on each board.
But that may not be feasible at this point and, at 15 amps, isn't
really necessary.

#10 wire is about a milliohm per foot. Four feet at 15 amps will drop
60 millivolts, not enough to bother logic. So your problem isn't
purely wire resistance.

John



John

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