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Splitting DC Power / Sharing an Adapter
Old 22nd January 2020
Here for the gear

Splitting DC Power / Sharing an Adapter

Forgive me if this is a dumb question, but when power requirements are low, is it reasonable/safe to use a splitter with a DC adapter?

e.g. I've got 8 budget wireless receivers which each require 12V/0.3A, and it seems overkill to use every plug on a 15A conditioner for them.

I noticed some precedent, in that Shure sells/sold a 4-way cable with their PS124 supply, but it appears to be wired in sequence rather than split, and I imagine there are other aspects to the design that I'm missing.

Assuming I don't want to fry my gear, is this something that can be done?
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Splitting DC Power / Sharing an Adapter-spt-power-supplies-adapters-93-p102a-64_1000.jpg  
Old 23rd January 2020
Lives for gear

I don't see why not, provided the power supply is adequately sized for the full load it needs to power. You could also use a plain old power strip from your power conditioner.

I'd be utterly shocked if the Sure unit wasn't wired in parallel internally, and just has the connecters physically in series for ease in making the connections.
Old 26th January 2020
Lives for gear
Richard Crowley's Avatar
IN THEORY it is a very simple and easy thing to do with a high chance of complete success.

HOWEVER, IN PRACTICE, there are many pitfalls, some of them dangerous, injurious and damaging.
If you want to power multiple loads from the same source, there are some rules/guidelines that must be observed if you wish success.

tl;dr Powering two identical loads is one of the easiest to accomplish safely and successfully.
By definition they are both AC (or DC), and use the same voltage.
But they each draw some amount of current, and you must find a power supply that provides double (or triple or whatever) the current.
So if each piece wants 1 Amp (1A), then you must find a power source that is rated to deliver 2A if you are powering two gadgets.

There are several VERY different standards for external power supplies which are show-stoppers to powering multiple loads from a single supply:

First, some gear wants AC (alternating current), while some wants DC (direct current).
Feeding DC into a load that wants AC is unlikely to damage it (assuming you don't exceed the rated voltage).
However, there are many examples of gear that wants AC that will simply not operate on DC.
(Technically, because it is common to use op-amps in audio circuits, and typically op-amps want a positive and a negative power voltage.
And the gear uses the AC power input to "split" into both positive and negative voltage supplies internally.
So, if you feed only positive power into it, it will be unable to make the negative power voltage which is requied for normal operation.)
And feeding AC into a device that wants DC will have a very high risk of failure and likely even damage to the gear.

Much modern gear is designed with the negative side of the DC power connected to the circuit ground.
(This is generally because of the predominance of Silicon-based NPN semiconductors in the modern age.)
However back when they first started making guitar effects pedals with Germanium PNP transistors, Positive ground was the standard.
And 9V DC Positive-Ground continues to be the standard here into the 21st century.
So you must be very concerned about whether the loads you are trying to power are both Positive-Ground (+G), or Negative-Ground (-G).
Powering a +G gadget and a -G gadget from the same power supply will likely short (and KILL) the power supply if the +G gadget is interconnected to the -G gadget.
ALWAYS double-check whether the gear is +G or -G before trying any tricking powering solutions.
If you don't understand the issue, and/or you can't determine whether the gear is +G or -G, then just DON't DO IT!

As yet an extra layer of danger and confusion, some gear is designed so that NO part of the incoming power connection is connected to ground.
In fact they are designed on the assumption that the incoming power will be FLOATING from any external ground reference.
Trying to connect two pieces of gear that want FLOATING power will be a disaster of varying degrees.
At best, you will get a loud hum that makes the gear unusable.
And at worst, you will toast/fry/blow-up the power supply circuits in one or BOTH of the gadgets.

For these reasons, you must use extreme diligence before attempting to operate multiple gadgets from the same external power supply.

There are two commecial solutions to this problem. One of them is essetially a big empty rack-mount box where you can plug in all your wall-wart (and line-lump) external power supplies. It hides and organizes and contains all those separate, annoying power supply things and end up with a single power cord to plug in to mains power. It has essentially a special kind of power strip in the box. Special because it is typically designed to allow enough space around each outlet to plug in all your wall-warts without running in the the adjacent power supply, etc.

The other commercial solution is a power supply with multiple, ISOLATED outputs so that it will, for example, power a dozen guitar effects pedals with power that is isolated from the other power outputs. That eliminates any of the hazards enumerated above. Internally, it is a large-ish power transformer with a whole bunch of separate output windings, each of which feeds a separate power circuit (to make 9V DC, for example). Because of the complete isolation between the outputs, it also circumvents any of the hazards listed above.

The difference between "wired in sequence rather than split" is completely mechanical and makes assembly easier/cheaper. It has no electrical significance.

Of course we aren't even mentioning the unfortunate fact that there are literally dozens of different kinds/sizes of power connectors in current use. In the round "barrel jack" type, the most common are the 2.1mm/5.5mm kind and the 2.5mm/5.5mm variety. They are commonly called "2.1mm" and "2.5mm" because that is the diameter of the inside pin, while the outside barrel on both is 5.5mm diameter.

Because of the same 5.5mm outside barrel dimension, they look so similar that they are easily confused with the other. But while you could possibly mate a 2.1mm plug (male) into a 2.5mm jack (female), it would create a connection that will be VERY likely to be intermittent with the slightest movement. And you would not be able to plug a 2.5mm plug in to any kind of 2.1mm jack because the inner pin is simply too big. Here are a few of the more common sizes:

Old 26th January 2020
Lives for gear
Richard Crowley's Avatar
More trivia you didn't want to think about.

It would be uncommon for a gadget that wants 1A power to come with an external supply rated at 1A. We typically use power supplies that are rated slightly higher than the expected load. So that they aren't running full-out at the maximum rating. So a gadget that wants 1A might be supplied with a 1.2A power supply just as a small measure of safety.

So, for example, If you wanted to power TWO of these 1A gadgets, you might want to look for a 2.4 or 2.5A power supply. Of course the voltage and AC/DC would be identical to the original supply.

A load will only draw as much current (Amps) as it needs, regardless of how much is available from the power source. So, using a higher-rated power supply is typically not a problem. But you would NEVER want to use a power source that is rated for a higher (or lower) voltage. There may be practical exceptions to this rule. Some gear can tollerate slightly (10% max) higher or lower voltage. But don't just assume you can get away with that.

Remember also that many external power supplies (typically small "wall-warts") are unregulated and will have a measured output of significantly higher voltage than they are rated for when measured without being connected to the load. So, you might have a wall-wart specified at 12V that measures 15V before being connected to the load. These unregulated power supplies are typically not suitable for multiple-power schemes becaue their voltage depends on the exact nature of the (combined) load.
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