both negative and positive rail from 2 bench power supply

Thread Starter

jacopo1919

Joined Apr 12, 2020
85
Hello Everybody.
Looking around for Bench Psu, I found some nice products for reasonable prices. the ones I checked were 1x output
The point is that i need +-15V.
After checking again, i saw that 2 or more outputs Bench PSUs become much more expensive so i thought the following:
Is it a good and safe solution to buy 2 units and link one positive with the negative of the other unit (which would become the 0V) and then get positive and negative rail from the other leads?
In this way i will safe good money (at the expense of the space consumed on the desk) but saving money will be stupid if this can be dangerous.
 

LowQCab

Joined Nov 6, 2012
2,357
It will work just fine as long as the Power-Supplies are Transformer-Isolated.
Virtually all are Isolated, but I would double-check just to be sure.
How do You do that before You purchase one (2) ?,
don't worry about that, just imagine how much Money you'll save.

"Sometimes" You might get what You paid for.
.
.
.
 

Ian0

Joined Aug 7, 2020
5,945
I only need ± supplies if I am doing small signal audio, in which case the voltage can be anything between ±10V and ±15V, usually at <100mA, so I have a small ± supply for that, then a 3A bench supply for everything else.
 

MrChips

Joined Oct 2, 2009
26,807
Depending on what you plan on doing with ±15V power supply, there may be other solutions.
If you are experimenting with bipolar op-amp circuits then very often you don't need more than 100mA.

It might be useful and educational to build your own PSU. It is not a difficult project.
 

Thread Starter

jacopo1919

Joined Apr 12, 2020
85
VOLTCRAFT LPS1305 is the one that looks good and affordable to me (here).
@LowQCab Unfortunately I didn't get what you meant in the last 3 lines of your answer, but the Manual says at PG.4: " The DC output of the power supply unit is electrically isolated and features protective. separation from the mains voltage", so i guess will be fine.

@MrChips I already built a +-15V Linear PSU but i wanted to have reliable gear with precise and adjustable outputs + current limiting.

I also used a small SMPS but it has the same limitations mentioned above.
 

crutschow

Joined Mar 14, 2008
30,463
One advantage of having a dual-voltage supply, is that they usually have an option to have both output voltages track from one control knob.
Also both voltages will come up together at power on so the possibility of having only one voltage on, which sometimes can damage a circuit, is minimized.
 

DickCappels

Joined Aug 21, 2008
9,105
I used to do that with some nice HP linear power supplies (one for positive and one for negative) in the late part of last century. As precaution I place reverse polarity protection diodes from each output to ground, you might consider that.

To expand on @MrChips ' post #4:
Since the early 1980's my home bench supply has been in a couple incarnations an LM317 and LM337, a transformer, rectifiers, and capacitors. All in a grounded metal box. Very reliable and almost bullet proof. Good for a few hundred millaimps and about ±20V this is all I need when debugging circuits. When real current was required I use the off-the-shelf computer and printer power supplies that were going to be sold with the product anyway. Why re-invent something being made all over the world?

For many tests I just use a 12V wall wart to feed regulators on the boards.

Nothing fancy, nothing to be proud of, but they get the job done reliably.
 
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