Group Actions
Engagement
  • Author Author: jw0752
  • Date Created: Date Created
  • Views 2018 views
  • Likes 10 likes
  • Comments 20 comments
Related
Recommended

An Extreme Ripple Power Supply Build

jw0752

I usually like to build my projects before I blog about them. This is probably due to the number of times the initial plans do not lead me down the envisioned path. The simplicity of this build along with a good pile of solid resources and the fact that I must wait for my panel meters to arrive has made me decide to blog a preview.

 

In my shop almost never a week goes by with out the need of an AC voltage source. I use the AC source to test motors, lights, power supplies, and circuit boards as well as a substitute for transformers. Since I have built several DC bench supplies and blogged about them over the recent years I decided that it was about time to build an AC power supply suited to my needs. I am currently using a Variac that is plugged into an isolation transformer for my applications but it doesn't monitor the voltage or the current so there is always a lot of patch wires and a couple meters to clutter the bench.

 

Here is my wish list for the new bench AC power supply:

 

0 to 160 volts no load output

2 to 3 Amps capable

Isolated from the mains

Binding post and AC receptacle Output

High Voltage warning light

Meters for indication of Output Volts and Current

 

Initially I found the following items in my parts grave yard:

 

image

This will be the isolation transformer. I can put 115 volts on the primary and it will have 130 volts on the secondary. This will drive the small Variac pictured below.

 

image

 

The case will be from an old Dental Cavitron Scaler. I have used this same style case before to build a Bench Power Supply and a DC Electronic Load.

 

imageimage

 

The Plexiglas blank control panel was cut a couple years ago in anticipation of an application for this case. The case as seen in this picture it still needs a cleaning and a coat of paint.

 

image

 

The case has been painted and I have the tentative control panel layout on the sheet of paper next to the case.

 

image

 

The chassis has had some modifications. The metal that the variac is mounted to was originally part of the chassis deck but it has been cut and folded up to provide additional support for the relatively heavy variac. The cut out on the right side of the chassis came with the original piece of equipment. Anomalies like this often dictate where components and controls need to be placed. In this case it will be the recess needed to allow the mounting of an AC line Output jack on the front panel.

 

I have also produced a tentative Schematic for the power supply. I say tentative as I do not yet have the digital AC panel meters and so I am guessing at their requirements. Nothing ever runs true to plans so I will very likely have to take back a few of the things I told you here when I blog about the completion of the build.  Here is the tentative schematic.

 

image

 

One advantage to giving a preview of what I am building is that I can welcome any advice that anyone is willing to send my way. In the past ideas and advice from my many friends here on element 14 have resulted in renovations and improvements in subsequent builds.

 

Sorry about the title but sometimes it helps to get people in the door when I leave them asking what the heck is he talking about now.

 

Thanks John

 

 

Parents

  • - I don't claim to be an expert, but there are a number of notes and suggestions I would make.

     

    1. Consider putting fuses on both primary and secondary sides of the Variac. They are expensive and deserve to be properly protected - consider the possibility you have a 1A rated Variac input of 120V fused at 1A on the primary. If set to step down to an output of 1V, does this mean you can draw 120A at 1V from the Variac? Of course not. Due to the shared winding, the winding is limited to 1A, so whether output is 1V or 120V, the output should be limited to the rating (or slightly above as short term abuse can be tolerated). Of course, the primary fuse wouldn't blow in this example as at 1A/1v, the primary fuse sees 1/120A of load - so best to have a fuse on the secondary or both sides (my preference).

     

    A second reason is in case whatever you plug in is powered and applies significant DC to the winding which could burn the insulation and destroy the Variac. Best to be safe as fuses are cheap.

     

    2. Consider scraping off some insulation from the side and tapping the Variac to provide your low voltage supply for panel meters - could save a transformer but the cost could be a tiny load on your Variac at all times that you might need to think about.

     

    3. Perhaps also consider circuit breakers instead of fuses if you're prone to accidents.

     

    - Gough

Comment

  • - I don't claim to be an expert, but there are a number of notes and suggestions I would make.

     

    1. Consider putting fuses on both primary and secondary sides of the Variac. They are expensive and deserve to be properly protected - consider the possibility you have a 1A rated Variac input of 120V fused at 1A on the primary. If set to step down to an output of 1V, does this mean you can draw 120A at 1V from the Variac? Of course not. Due to the shared winding, the winding is limited to 1A, so whether output is 1V or 120V, the output should be limited to the rating (or slightly above as short term abuse can be tolerated). Of course, the primary fuse wouldn't blow in this example as at 1A/1v, the primary fuse sees 1/120A of load - so best to have a fuse on the secondary or both sides (my preference).

     

    A second reason is in case whatever you plug in is powered and applies significant DC to the winding which could burn the insulation and destroy the Variac. Best to be safe as fuses are cheap.

     

    2. Consider scraping off some insulation from the side and tapping the Variac to provide your low voltage supply for panel meters - could save a transformer but the cost could be a tiny load on your Variac at all times that you might need to think about.

     

    3. Perhaps also consider circuit breakers instead of fuses if you're prone to accidents.

     

    - Gough

Children