How to make a dual power supply station from a vintage Powerstat

Thread Starter

David Sanchez

Joined Dec 16, 2016
5
Hello, I have recently found real joy in making very simple analog electronic audio circuits; and it's getting more complex very raplidly... My father gave me this old Powerstat a while ago and I was thinking It could make a dual power supply with it.

As for now I'm working on simple projects like stepped tone generators, lfo´s and for my next project I want to make a variable bandpass filter, so I'm in the 5V to 15V range.

I would specifficaly need +5/-5V, +9/-9V, +12/-12V and +15/-15V, don't know if I would need certain config for each value or if I can use one config for all values and adjust voltage by the main powerstat knob (that would be ideal).

Te Powerstat specs are the following:
InV: 120
OutV: 0 - 140
A. 10
KVA: 1.4
Freq: 50/60

I´m attaching the powerstat photos and specs plate so you can appreciate it.

Powerstat01.jpg
Powerstat02.jpg
Powerstat03.jpg

I came across this image from the Make:Analog Sinthsizers book from MFOS´s Ray Wilson

upload_2016-12-22_19-45-29.png

I really don't know if this setup would work, I'd really appreciate any help.

Thanks in advance, Happy Hollydays and/or Christmass

David
 

crutschow

Joined Mar 14, 2008
24,302
You need to add an isolation transformer for safety since the Powerstat is an autotransformer that has no isolation between primary and secondary.
You could use a 120V primary transformer with a 30-40V center-tapped output (15V to 20V from ether winding to the center-tap).
Then add a bridge rectifier and filter capacitors as shown in you drawing.
That will give you a variable output voltage of 0Vdc to about 20Vdc to 28Vdc.
But note that the output voltage is not regulated with a change in load and will have some voltage ripple in the output.
That may be okay for some applications but could be problematic for sensitive analog circuit.
For that you may have to add extra filtering or a fixed voltage regulator.
 

Thread Starter

David Sanchez

Joined Dec 16, 2016
5
Thank's for the info, both very usefull. I think now is the time to let you know that I'm very ignorant when it comes to electronics, I'm self teaching myself in a very disperse manner, looking for the koledge I need to complete a specific task. That said, I have a 3° grade title, so I can read and reproduce schematics (not desing), my solder skills are getting beter and I'm willing to experiment.

By now start to guess if this powerstat is going to be usefull at all. Scott's amazing DIY power source feeds from the domestical outlet, so in this case I really wouldn't need the device, but several transformers.

But crutschow made me think that maybe I can use the powerstat set to give a fixed output of 30V so I can get ±15V and from there go down to ±12V, ±9V and ±5V.

This project, more than a "fashionable power source" is a necessity, where I live the price of power sources are prohibitive (as in very much way too expensive) and way over my household budget.

Thaks again for the replies
 

dannyf

Joined Sep 13, 2015
2,197
I would specifficaly need +5/-5V, +9/-9V, +12/-12V and +15/-15V,
what really matters is how much current you expect to draw from each voltage range.

The simplest would be to wire multiple sets of +/- regulators to a common set of rectifier + capacitors.

and adjust the transformer for designed output voltage.

Two downside with that approach:

1) it cannot supply too much current - the limit there is the regulators;
2) if the transformer is to too high of a value, it can fry the regulators.

The alternative is to fix the transformer to the highest setting. The downside is that the low voltage regulators will run hotter.
 

Thread Starter

David Sanchez

Joined Dec 16, 2016
5
Regarding the current I need, At the moment, I'm working on very simple projects, currently I'm using a 9V battery. Of course I imagine that with increasing complexity and the sum of devices I could need more Amps, but I´m not there yet.

I sure hope that when I get there I would actually be more confident and have more knowdelge and maybe be able to design a power source myself.

As for now, I would rely on this forum's member's experience.

Heat is a big deal here because of the weather, I would need to use heatsinks and fan coolers.

I tested the powerstat and up to 50V is in the 0.00 acuracy, increasing while it goes up.
 

#12

Joined Nov 30, 2010
18,190
You can use the Powerstat to power a transformer, and then use the rectifiers and capacitors to get a dual DC voltage like in the first post. You can get any pair of voltages, but only one pair at a time. It will be sufficient for a while, until you decide to build a permanent, multi-output power supply.
 

Thread Starter

David Sanchez

Joined Dec 16, 2016
5
You can use the Powerstat to power a transformer
All transformers I have seen convert from 120V to the desired Voltage, so if I set the Powerstat to 120V It would be the same as connecting the transformer to the wall outlet.

Could there be a way to rectify the Voltage coming from the Powerstat at AC 30V and convert it to DC +/-15V?

I have a bunch of 5V, 9V, 12V and 15V transformers at hand, but for use with op-amps I don't want to rely on virtual ground.

Any sugestions? thanks
 

dannyf

Joined Sep 13, 2015
2,197
if you are using them for opamps, you don't need much current.

In that case, see if the transformer you have provides a center tab. if it does, you are golden.

if not, you may have no choice but to go with a virtual grounding scheme.
 

#12

Joined Nov 30, 2010
18,190
All transformers I have seen convert from 120V to the desired Voltage, so if I set the Powerstat to 120V It would be the same as connecting the transformer to the wall outlet.
True. Are you saying you can't turn the Powerstat to a lower voltage and get a lower voltage out of whatever transformer you have laying around?
Could there be a way to rectify the Voltage coming from the Powerstat at AC 30V and convert it to DC +/-15V?
No. The Powerstat doesn't have a center tap.
I have a bunch of 5V, 9V, 12V and 15V transformers at hand, but for use with op-amps I don't want to rely on virtual ground.

Any sugestions?
Use the Powerstat to power a pair of 15 volt transformers. Wire their outputs so a center tap exists. Turn the Powerstat to a lower voltage if you want less than +/- 20 volts.
 
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