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5U power distribution woes
MUFF WIGGLER Forum Index -> 5U Format Modules  
Author 5U power distribution woes
umma gumma
dammit, I have had a bunch of 5U modules sitting in boxes, for over a year, because i can't decide on a power distribution setup!

I don't like the messy cables of the dotcom stuff

I'm having a hard time finding a reasonable distribution board...and then I'd also have to buy all the connectors etc

the aluminum bus bar concept makes the most sense, from a cost standpoint, because wire is cheap, and alu is cheap. But I need a drill press to drill the bars out, and I am worried about connections coming iunfastened during moves, and shorting something out

I feel like Conan, contemplating my sorrows upon the tree of woe...

sduck
You don't need to drill holes in the aluminum bars. That's just one approach of many. And a properly done wiring isn't going to have issues with coming undone.

It's not 5U, but here are some pics of a bus bar euro system I built recently. Maybe you can get some ideas from it. This is actually a fairly inexpensive sytem except for those busboards, which are expensive and probably overkill.



JohnLRice
Since you can't decide, I would suggest going with the cheapest/easiest method right now so you can get your modules up and running! thumbs up Buy the Synthesizers.com QDH20 or QDH40 power harness, hook it all up and GO! Driving

Then, down the road if you feel you need/want distribution boards or rails just install at your leisure. Plus you could recycle the DotCom power harness by cutting it apart and putting crimp ends on the cables. (or sell it if you want to use heavier cables).

I don't think having the cables come loose from bus bars would be too much of a worry, especially if you use lock washers? Graham or Rex etc can answer this better. I'm assuming Loctite compound would be a bad idea since it would partial insulate the connection? hmmm.....
Rex Coil 7
I'll be as brief as I can:

** No loctite.
** Use #8 crimp on eyelets.
** Use #8 (8-32) stainless steel screws.
** Use #8 stainless steel outside star lock washers.
** Use #8 (8-32) stainless steel nuts.
** Use gas tight paste on both sides of the eyelets.
** Use 6101 T61 aluminum bars (that alloy is specifically used as bus bars in industry and power distribution for millions of people).
** I used 1.00" x 0.250" rectangle bar "full round edge" .. see link:

LINK = https://www.onlinemetals.com/en/buy/aluminum/aluminum-full-round-edge- 6101-t61-extruded-full-round-edge/pid/18142

** #8 stainless screws can be tightened down plenty tight enough to prevent anything from coming loose in transit. Let's remember that Graham builds top notch modular synth systems for touring professional musicians. If it were a ~worry~ he would have gone another route a long time ago. His reputation depends on the success of that "stack" of fasteners. No worries, it works!

** You do not need a drill press. Member *EricTheRed made all of his bus bars for his LARGE system (5 PSUs!) with a hand drill motor without even centerpunching the holes first. I'm picky, so I used my drill press, did layout prior to centerpunching as well. But it's not required at all.

** I use 0.500" spacing of the eyelet holes in the bus bars (0.500" center to center). That's just enough space between the eyelets to allow doubling up two eyelets on each hole (in the event I need to connect two module power cables to the same hole on the bus bar for whatever reason).

** As John said, you can use the Dot Com squid as an interim solution until the bars are ready to mount up. Then you can cut the squid apart and install the eyelets on the cables. You can also remove one to two feet of excess cable on each one since the Dot Com squid has some 24 inch long cables, and some 36 inch long cables. I've got some that are only 8 inches long. The longest ones are 12 inches long. Do your best to keep the cables no longer than 18 inches.

** If the bare/exposed bars worry you, you can place a layer of felt over the bars after your connections are made. A-La vintage tonewheel Hammond .....





Should you elect to go this way I'll give you all the help that I can should you have questions. Component sources, methods, etc ...

cool







JohnLRice
Rex Coil 7 wrote:
** You do not need a drill press. Member *EricTheRed made all of his bus bars for his LARGE system (5 PSUs!) with a hand drill motor without even centerpunching the holes first. I'm picky, so I used my drill press, did layout prior to centerpunching as well. But it's not required at all.
thumbs up Drilling by hand is not a big deal through thin material but through thicker material even a slight angle will cause the bolt head, nut and connectors etc to not sit flush, and besides not looking nice it wont be as good of an electrical connection.

A little jig that I didn't even know existed until a couple years ago that can really help drilling straight holes through thick material is a Big Gator Tools V-Drill Guide. Even if you have a drill press it's handy to have when you need to drill or tap a hole into something that wont fit under a drill press.
https://smile.amazon.com/BIG-GATOR-TOOLS-STD1000DGNP-V-Drill/dp/B0061F Y004



umma gumma
thanks for all the advice!

I guess I had to vent a bit: haven't had much spare time to mess with anything either very frustrating
Faustgeist
Rex Coil 7 wrote:



For a second I thought this was your new power distribution and I yelled in my office "WHAT HAS HE DONE!", LOL
Eric the Red
Hey now! I have a centerpunch now...
Sugarfree
Rex Coil 7, how about brazing or welding aluminum busbars and T-bars for a system with multiple power supplies? would this provide better conductivity than screws?
Rex Coil 7
Sugarfree wrote:
Rex Coil 7, how about brazing or welding aluminum busbars and T-bars for a system with multiple power supplies? would this provide better conductivity than screws?
No, I wouldn't think so. Welding/brazing will only make the two pieces as tightly connected as the clamps were when it was welded. I'm assuming you mean using TIG.

Screws put a constant and more manageable pressure on the two pieces being connected. If the correct screws are selected (the shape of the heads makes a difference) they should provide very solid contact, with the added advantage of using gas tight paste impregnated with metal crystals (zinc crystals) that cut through the very thin layer of oxidation on the aluminum which forms inside of just a few milliseconds. So the crystals cut through the oxidized surface, while the gas tight substrate paste "seals" the surface from oxygen. The whole combination of cutting through the oxidation and then sealing the surface improves conductivity and is highly recommended for this application. You can't use that paste if the joint is welded. And no matter how well you clean the surfaces prior to welding, the oxides form in milliseconds after the aluminum is machined (sanded, filed, ground, acid etched, whichever) clean. That layer of oxidation prevents the flow of electricity, creates more impedance, and adds resistance to the area ... which is all completely counter to what bus bars offer (lower impedance, and less resistance)

TL;DR .... No, welding is not better than using screws.

cool
umma gumma
good tip & explanation, about the paste!

thx again
sduck
I'll second the gas tight paste suggestion - on Rex Coil's recommendation I got some from Lowes (yes!) for that large system above, and it's cheap, easy to work with, and even though you can't tell if it makes a difference or not, it does - maybe you can't tell now, but in 10 years maybe.
Graham Hinton
sduck wrote:
It's not 5U, but here are some pics of a bus bar euro system I built recently. Maybe you can get some ideas from it. This is actually a fairly inexpensive sytem except for those busboards, which are expensive and probably overkill.


Sorry, sduck, but this system is actually not a good example. You've missed the whole point of using busbars and haven't taken onboard everything I've been trying to explain about power distribution for years. I know imitation is supposed to be the sincerest form of flattery, but this is more like cargo cultism.

The pcbs are just a waste of money, one of the points of using busbars is to totally eliminate pcbs and ribbon cables. Any advantage those pcbs might have over other pcbs has been lost by the lightweight distribution supplying them.

The PSUs should be wired to the busbars using the sense terminals otherwise you have a common impedance coupling problem in the wires feeding the busbars which sum all the module currents.

There should only be only one 0V busbar, not two joined together with wires. Either bend one or bolt two together. It should also be Earthed and I don't see any wiring to the mains earth pin.

Consider the 0V path between two modules in opposite corners of the case. There is far too much resistance in the way. Don't pick a nice looking busbar from a catalogue, instead say "I want 1milliohm maximum resistance across my system, how much metal do I need to achieve that?". There are online calculators to work out the resistance of bars. The busbars you chose are not intended for this use.

I bet that case makes an excellent soundboard for the nasty buzzing transformers in those power supplies.

Your choice of wiring colours is an expensive accident waiting to happen.

On a positive note, at least you got the system powered up.

Quote:
I'll second the gas tight paste suggestion - on Rex Coil's recommendation I got some from Lowes (yes!) for that large system above, and it's cheap, easy to work with, and even though you can't tell if it makes a difference or not, it does - maybe you can't tell now, but in 10 years maybe.


Of course you can tell, just test the system measuring the voltage drops on load with any multimeter that can read mV. If you use a power resistor as a dummy load, 12 ohms for 12V, then you know 1A is flowing and can work out the resistance of each section and each joint. When the whole system is loaded measure the voltage drops in each bar and wire and if they are over 10mV there is room for improvement and the lower you can get them the better.
umma gumma
thanks for the input Graham!

busbars it is

I left a removable back panel on my cases, so should be able to access the nuts underneath, like Rex' example, when moving/connecting modules to busbars
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