5V between stand-offs without J15 installed

Hardware related problems and workarounds

5V between stand-offs without J15 installed

Postby ajtravis » Sun Aug 24, 2014 12:31 am

Hi,

I've just replaced the 4@microUSB power connectors I was using to power my SKU101020 Parallella boards from a Maplin 5V/8.4A charging station with 4@USB->5.5/2.1mm barrel connectors and changed link 14 back to the default 1-2 position.

I want to use separate power suppy connections, so that I can power each board on and off independently during testing. I have NOT installed link J15. However, when I powered off one of the boards, the green LED's stayed on and I realised that the metal stand-offs supplied by Parallella to stack the four boards are live - I measured ~4.95V between the stand-offs in the corner next to the barrel connector and the other tree stand-offs. This is what I would have expected if J15 was fitted, but I am surprised to find it when J15 is NOT fitted. I read the warning here: http://www.parallella.org/power-supply/:
Powering a cluster with multiple PSUs

A cluster may be powered via multiple power supplies.

When using a power supply for each board:

the power supplies should be plugged into a common power strip
J15 must not be fitted AND metal stand-offs used or else damage may occur!

The board concerned did not have any USB peripherals connected, but continued to be powered up through the stand-offs when I removed the barrel connector:
IMG_2279.JPG
IMG_2279.JPG (214.18 KiB) Viewed 10749 times

IMG_2281.JPG
IMG_2281.JPG (183.13 KiB) Viewed 10749 times

I did not think it was possible to damage the Parallella boards by powering them from multiple PSU's when stacked using the stand-offs because that is precisely the configuration of the 4@SKU101020 cluster 'kit' I received from Adapteva. Nevertheless, the warning in the PSU how-to states that I should NOT install J15 if I power the cluster using multiple PSU's connected to the 4@barrel connectors. Why, then, is there ~5V on the stand-off next to the barrel connector when I have NOT fitted J15?

Bye,

Tony.
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Re: 5V between stand-offs without J15 installed [solved]

Postby ajtravis » Sun Aug 24, 2014 9:44 am

ajtravis wrote:[...]
Why, then, is there ~5V on the stand-off next to the barrel connector when I have NOT fitted J15?

Hi,

As you can see from the pictures in my previous post I fitted flat washers under the stand-offs. I've just got a Ground Electronics 4@Parallella case-kit and the flat washers were supplied with it - Previously, I did not have flat washers under the stand-offs. The following pictures show that on one of my boards the plated through-holes on the track running from one leg of the barrel connector are close enough to the square pad around the hole for the stand-off to short when a flat washer is placed over the pad. There is some variation between the boards and on the other three, this track is under the barrel connector - problem solved :-)
IMG_2282.JPG
IMG_2282.JPG (152.84 KiB) Viewed 10740 times

IMG_2283.JPG
IMG_2283.JPG (174.17 KiB) Viewed 10740 times


Bye,

Tony.
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Re: 5V between stand-offs without J15 installed

Postby 9600 » Tue Aug 26, 2014 9:38 am

Hi Tony,

Just to be clear: the supplied steel washers should be used in place of boards in order to maintain the height of the stack — i.e. if you have less than 4 Parallella — and not used in addition to boards.

Cheers,

Andrew
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Re: 5V between stand-offs without J15 installed

Postby ajtravis » Tue Aug 26, 2014 12:24 pm

9600 wrote:Hi Tony,

Just to be clear: the supplied steel washers should be used in place of boards in order to maintain the height of the stack — i.e. if you have less than 4 Parallella — and not used in addition to boards.

Hi, Andrew.

No instructions were supplied with the case-kit and the stand-offs supplied by Ground Electronics are slightly shorter than the ones supplied by Adepteva, by about the thickness of a flat washer, so I thought the flat-washers were there to make up the difference in length: I think the kit needs to have a parts-list and some instructions included to avoid this sort of confusion.

When I initially tried to build the case, without using the flat washers but with four Parallella boards, there was a gap at the top. That's why I put the washers under the stand-offs to make up the length. I've now re-used the original (longer) Adepteva-supplied stand offs and I've only put flat washers next to the perspex - It now fits perfectly :-)

I've left the rear panel off, because I want to continue using separate power supplies for the moment and I've mounted a 5V USB-powered fan externally to see if it's possible to fit e-link cables internally instead of the internal 5V fan supplied with the case (I'm using USB to power the fan because I'm not yet using the PSU supplied by Ground Electronics).

Since I had to pull my cluster apart to remove the flat washers anyway, I tried out an alternate configuration with two pairs of Parallella boards back-to back (one stand-off apart) and one of the component-sides of each pair facing towards each other separated by the long stand-off. This is equivalent to folding the flat configuration of four Parallella boards with their N-S connections adjacent (as suggested by Andreas) into a stack with alternate N-S connection pairs on the same side, which might be more practical for interconnecting them in a stack without the N-S cables having to span the boards:

Code: Select all

e-link configurations (== component side, \_/ e-link cable)

flat config:

     node1        node2        node3        node4
   __==_==__    __==_==__    __==_==__    __==_==__
   N       S\__/N       S\__/N        S__/N       S

stacked config:

   __==_==__    node1
   N       S\
             |
  /S_  _  _N/
 |   == ==      node2
 |
 |
 |
 | __==_==__    node3
  \N       S\
             |
   S_  _  _N/
     == ==      node4


This alternate stacked configuration is exactly the same height as the default Ground Electronics design, and the top two apertures for HDMI and USB still line up but not the lower two HDMI and USB apertures. I think it might be worth considering making new end panels if we can source suitable e-link cables. I've put my boards back into the case in the default configuration with four boards stacked one stand-off apart until there is some news about where to source suitable e-link cables.

Bye,

Tony.
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Re: 5V between stand-offs without J15 installed

Postby 9600 » Tue Aug 26, 2014 2:58 pm

Hi Tony,

ajtravis wrote:No instructions were supplied with the case-kit and the stand-offs supplied by Ground Electronics are slightly shorter than the ones supplied by Adepteva, by about the thickness of a flat washer, so I thought the flat-washers were there to make up the difference in length: I think the kit needs to have a parts-list and some instructions included to avoid this sort of confusion.


Ah, now I see where the confusion has come in: the product page (short link: http://gndel.ec/PACK-01 ) links to an assembly guide on GitHub. The packaging has the short link on it, but should probably be clearer and say to see this link for assembly info.

Cheers,

Andrew
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Re: 5V between stand-offs without J15 installed

Postby ajtravis » Tue Aug 26, 2014 3:14 pm

9600 wrote:Hi Tony,
[...]
Ah, now I see where the confusion has come in: the product page (short link: http://gndel.ec/PACK-01 ) links to an assembly guide on GitHub. The packaging has the short link on it, but should probably be clearer and say to see this link for assembly info.

Hi, Andrew.

Been there, got this:

Forbidden

You don't have permission to access / on this server.
Apache/2.2.16 (Debian) Server at gndel.ec Port 80


I found it at: https://github.com/abopen/parallella-cluster-case...

You can see the same potential problem with the connectors near the barrel connector on this image:
https://github.com/abopen/parallella-cluster-case/blob/master/images/ConnectFan.jpg

Nice case, though ;-)

Bye,

Tony.
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Re: 5V between stand-offs without J15 installed

Postby 9600 » Tue Aug 26, 2014 3:55 pm

ajtravis wrote:Been there, got this:

Forbidden

You don't have permission to access / on this server.
Apache/2.2.16 (Debian) Server at gndel.ec Port 80



Argh! Looks like a URL shortener hiccup. Fixed.

Cheers,

Andrew
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Re: 5V between stand-offs without J15 installed

Postby ajtravis » Tue Aug 26, 2014 4:05 pm

9600 wrote:[...]
Argh! Looks like a URL shortener hiccup. Fixed.

Hi, Andrew.

I think you could avoid any potential problems like the ones I experienced by putting a flat washer between the perspex and stand-off at the bottom of the case and connecting the wires there instead of on the first two boards. I found quite a lot of variation between the Parallella boards: two out of four of mine shorted, two didn't.

What do you think about my alternative stacked configuration?

Many of us bought into the Kickstarter campaign because of the Epiphany mesh interconnect, not just to use Gbit ethernet!

Bye,

Tony.
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