[sdiy] Powering a second bit of kit from same PSU (wiring options)

[Tom Wiltshire]

Does it give you a *maximum* per rail? That'd be more useful.

But yeah, it sounds enough to me. If they're drawing between 0.35A and 0.5A, then you can still run two of them off a 1A supply - just. That negative rail will be the limiting factor, since the 3A positive side is going to have plenty of grunt for the job.

In practice, I'd hope that the current draw isn't quite as symmetrical as they make out, and that the negative side won't be quite as tight as 0.7-1A makes out.

If the supply is ok up to 42W, that should be ok. 0.35A x 12V = 4.2W, so each SynthDriver is 8.4W or so (two rails). That would put two units somewhere around 15-20W, which sounds safe enough.


On 18 Feb 2015, at 16:29, random variate <randomvariate at hotmail.co.uk> wrote:

> Thanks for the replies.
> 
> So, the SynthDrivers need a minimum of 0.35A per rail (+12v/-12v).  
> 
> The PSU I bought is the XP Power PCM50UD07, which delivers 3A and 1A respectively on each output, to 42W max power output.
> 
> Do you think that has enough oomph to drive two Synth Driver Units?
> 
> Cheers
> 
> Tim
> 
> 
> 
> 
> 
> 
> 
> 
> ----------------------------------------
>> Date: Wed, 18 Feb 2015 10:14:21 -0500
>> From: nate at paperproductsmusic.com
>> To: chris at chrismusic.de
>> CC: synth-diy at dropmix.xs4all.nl
>> Subject: [sdiy] Powering a second bit of kit from same PSU (wiring options)
>> 
>>> (Well, I'm assuming a simple 2 pin PSU - if you have a "real" PSU with
>>> +/GND/-, things are looking much more benign.)
>> 
>> If the proposed power supply has plenty of current for two boxes, it's
>> probably not a wall-wart :)
>> 
>> Besides, if:
>> "Say for example, both units use a voltage regulator for an artificial
>> center ground between both power pins, and use that as a signal ground.
>> If both centers are not at the same voltage, you may have kind of a
>> short circuit via signal ground."
>> 
>> That would be done in the individual boxes/units/synths/etc and the
>> only thing that would be affected would be overall current draw. The
>> grounds are otherwise inherently isolated by the voltage dividers and
>> regulators. Well, not isolated, but drawing current back through the
>> supplies. This is the whole reason NOT to use a DC wall-wart, because
>> the power is usually dirty, and hard to calculate overall current draw
>> (and therefore supply voltage). At least with an AC wall-wart, the
>> supplies are symmetrical. So, as you draw more current the supply
>> voltages decrease equivalent amounts.
>> 
>> As you said, this is all besides the point because if it's a
>> legitimate power supply (linear transformer based design) it should be
>> capable of driving anything you want. As long as you don't exceed it's
>> current specifications, of course.
>> 
>> I say go for it. I'd run the other box power cord separately with
>> similar gauge wire. If your individual boxes aren't equipped with a
>> fuse, that might be a good idea.
>> 
>> Nate
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