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From: George Jefferson on 4 May 2010 02:02


"eromlignod" <eromlignod(a)aol.com> wrote in message
news:b7d87d53-648e-4f06-9b21-7231208b6ccd(a)p2g2000yqh.googlegroups.com...
> 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.
>

A quick hack maybe to try to equalize the voltage using resistors. Attempt
to add a small resistance to the closer loads to drop the voltage to about
the same as the furthest ones then up the voltage from the supply slightly
if you can. This may be next to impossible to do effectively if the topology
if the circuit does not facilitate any easy estimations of the resistances.

Alternatively you can divide the circuits into several groups and go from
there... as phil has suggested.

Or if you got a lot of copper to spare, use the same length wires, one for
each circuit. The is effectively the above suggestion but with groups of
size 1 but doesn't require any calculations or anything since every circuit
board will have the same drop due to the same length wire(and guage of
course).

Really it's going to depend on your topology. If it a bus with very short
stubs then the drop should be relatively linear and can be computed by
finding the relative distances. The resistance to add would be quite simple
to do(although it depends on the final power supply voltage which is unknown
but can be estimated).

Of course the optimal way would have been to add regulators/converters on
the boards from the getgo.



From: Sjouke Burry on 4 May 2010 12:39
eromlignod 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
What I have done in those cases is mount copper rails(~3mm by 20 mm)
like they use in power stations.
then you only need 2 or 3 short wires the each connector.
From: whit3rd on 4 May 2010 14:51
On May 3, 7:23 pm, eromlignod <eromlig...(a)aol.com> wrote:

> 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 current gets
> to be so much that the IR drop is significant

> 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?

As others have pointed out, point-of-load regulators solve the
problem nicely but your system is of such small scale that shouldn't
be necessary. Using thicker wire for a trunk line (10 gauge copper)
and letting the last-few-inches stay at a more convenient size will
work well. You can also configure the trunk as a loop (put ferrite
beads on if the ground-loop pickup or radiation is a problem); this
doesn't use much extra wire, but halves the copper resistance.
From: gearhead on 5 May 2010 12:16
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


Is this for your self-tuning piano?
http://www.amica.org/Live/Publications/Past-Bulletin-Articles/SelfTuning-Article.PDF
According to the article at that link, a piano could pull as much as
500 or 600 watts. That's a lot of power and you will get a voltage
drop in inverse proportion to power supply voltage, as I'm sure you
know.
Are you running the heater current through the same wires that power
the logic chips?
Maybe you should try to find a way (power-wise) to separate the brawn
from the brain, as it were.
You could run your wire-heaters at a higher voltage than the logic and
use local voltage regulation for the logic.
Or use remote voltage sensing -- a dedicated wire between the power
supply and the load that doesn't carry any power.
From: Jasen Betts on 8 May 2010 05:23
On 2010-05-04, 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?

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 termials 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 powerssuply.

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.


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