Power supply for multiple boards

[JAY X]

I have to power multiple boards for a custom project. 16 boards. Each board draws 43ma aprox. so total draw is 688ma.@ +/-17v.
My idea is to use IDC cable to power all boards to provide gnd return and rails. So it ocuured to me to use the same scheme as modular synths are using. A 10 pin IDC connector, with the central 6 pins for GND and the 4 side pins for +/- 17V. My question is if this is enough GND regarding return current path to the linear PSU, and noise.

Jay x

 

[user 37518]

I have to power multiple boards for a custom project. 16 boards. Each board draws 43ma aprox. so total draw is 688ma.@ +/-17v.
My idea is to use IDC cable to power all boards to provide gnd return and rails. So it ocuured to me to use the same scheme as modular synths are using. A 10 pin IDC connector, with the central 6 pins for GND and the 4 side pins for +/- 17V. My question is if this is enough GND regarding return current path to the linear PSU, and noise.

Jay x

why are pins 3-8 connected together? if you are going to use multiple GND cables, keep them separated till the very end.

 

[JAY X]

Hi!. I think they would like to show thermal relief connections at board level. Not tying each wire to each other...

 

[user 37518]

Hi!. I think they would like to show thermal relief connections at board level. Not tying each wire to each other...

Thermal relief by showing pins connected together? if that is the case, that diagram is very sketchy. How is thermal relief accomplished by showing pins connected together, I don't get it, do you have an example of this?

 

[Newmarket]

Hi!. I think they would like to show thermal relief connections at board level. Not tying each wire to each other...

It seems fairly obvious to me that that diagram is intended as a wiring/connection schematic.
There's no sign that it is intended to relate to pcb footprint or layout. And it just doesn't make sense as thermal reliefs.

 

[JAY X]

Hi!

The point is:

In a 10 pin IDC cable ¿6 pins devoted to GND is enough? given the current draw (688 ma aprox).

 

[user 37518]

Hi!

The point is:

In a 10 pin IDC cable ¿6 pins devoted to GND is enough? given the current draw (688 ma aprox).

Are you going to power each module with a separate cable? or one single cable for all? if the latter, then the power supply cable is your biggest worry rather than the GND cable, a thin IDC cable might handle 688/6 mA because you have 6 grounds, specially if its short, but I wouldn't bet on a single IDC cable being able to provide 688mA without a penalty.

Check this webpage for the current capability

http://www.mosaic-industries.com/em...evelopment/cables/ribbon-cable-current-rating
It depends on the gauge, a 28AWG seems to have a maximum rating of 1 A. So you are still within the limits, but, as I said, it is not adviceable.

Quote for that webpage: "the manufacturer's maximum current rating, when applied to all wires in the cable, produces a power dissipation of about 2 W/ft (or 6 W/m). Presumably, at the maximum current there will be a temperature rise of the order of 30 °C"

 

[Matador]

The same current that flows in via the +12V line returns to ground in each module: why not 5 pins for power and 5 pins for ground?

Even a single modest 22 gauge wire is only around 15 mOhms per foot, meaning a loss of 10mV across 1 foot of conductor.

 

[ccaudle]

Hi!

The point is:

In a 10 pin IDC cable ¿6 pins devoted to GND is enough? given the current draw (688 ma aprox).

There are only four pins devoted to positive power. The same amount of current flows in both sides of the power, so if six isn't enough for ground, four probably isn't enough for power.

 

[tkaz]

Many semi-pro mixers have power and ground done in a similar way. I remember seeing an article, was it by Eddie Celetti? about rewiring a Soundcraft mixer by
running separate ground and power to each channel. Lots more work & wire that way, but he achieved a noticeable improvement in noise.

 

[Newmarket]

Many semi-pro mixers have power and ground done in a similar way. I remember seeing an article, was it by Eddie Celetti? about rewiring a Soundcraft mixer by
running separate ground and power to each channel. Lots more work & wire that way, but he achieved a noticeable improvement in noise.

I think I recall such an article and IIRC it was indeed Mr Celetti.
He used to publish a lot of good stuff particularly on digital tape stuff ADAT / TASCAM / DAT.

 

[JAY X]

Many semi-pro mixers have power and ground done in a similar way. I remember seeing an article, was it by Eddie Celetti? about rewiring a Soundcraft mixer by
running separate ground and power to each channel. Lots more work & wire that way, but he achieved a noticeable improvement in noise.

Interesting...so each channel has their own +/- gnd wire back to the psu?. This means 3 wires x number of channels...so 16 channels means 48 +v 48-v and 48Gnd...back to the psu...maybe through a bus bar...

 

[JohnRoberts]

I am not a fan of second guessing console designers unless there is an obvious problem. Over the decades I've killed many brain cells pondering console design. There are multiple popular but sub-optimal approaches ranging from heavy bus bars to individual wires.

Large console design (in fact all engineering) is a calculated trade off between cost and performance. A 50+ strip console will already be a rats nest of internal wiring (often shielded cables). We could add individual wires for every channels PS if it was necessary (IMO it isn't).

Identify a real problem then address it.... Don't look for easy answers (that is the design engineers job).

JR