The story How i converted hot blower into bench power supply 35 volts/15 amps

Dear friends Based on the demand i am writing this article on bench power supply which delivers up to 35 volts/15 amps.
We came across many articles on bench power supply in internet by simply  using computer SMPS and ordinary step down transformer etc. They are  useful only for beginners and hobbyist not for professionals. This present story is very useful for professionals.
High voltage and currents power supply are very expense starting  from 5k to more then lakh rupees  depending up on the brands, model, voltage and current ratings. Manufacturers will fix price very expensive depending up on their Models.
Bench power supply play very important role in powering AVR  based inverters/voltage stabilizers/ups repairs  and variable  AC  and DC voltage /Current controlled power supply.
Below is the story how I made it and even today working fine in  my repair activity.

In my Junk i found an Un-repairable Hot air blower. Made my mind to make use of that for variable power supply.

Started to fix the components inside the chassis by making satiable cuttings for digital ammeter/ volt meter as shown below, pls go through the photo below for your understanding.

Hot air blower chassis made empty 

Chassie is been cut and fixed volt meter and ammeter as in the photo below.Now coming to the working principle and electronic theory of an instruments is a  very simple rectifier circuit which converts AC to DC.

Volt meter size cutting done

Now question in mind is how to vairy input to step down transformer  and again to get veriable  35 volts AC to rectifier circuit  because hear instrument what we are making is a veritable DC power supply.

Yes, the Technic hear is very simple varing 230 volt ac to step down transformer  35-0-35/15 Amps  between 0 to 260 volts ac up to desired level.

Step down transformer fixed with bridge rectifer

Below are the components selected to design the circuit 

1) 35-0-35 / 15 amps step down transformer 1#

2) 500 watts  ac bulb Dimmer 1#

3) 6800mfd 35volts  electrolytic capacitor 1#

4) High current rectifer doides 4#

5) 10k 10 watts fixed resistance as a load resister

Please go through the circuit diagram presented below for your understanding 

CIRCUIT DIAGRAM

Bulb dimmer:-

Below is the typical variac type dimmer  which is used to control the ac loads and is very cheap when compared to Costly  lab variac.

In my project  as per  above circuit diagram you can use to vary 230 volt ac starting from 0 to 260 volts and control the step down transformer output accordingly and set the final output ripple free DC output and same can be monitored in the respective volts/current panel meter.

Important to be noted this project will work on only by using variac type dimmer because in market will be available triac based dimmers still cheap but won't work on transformer loads and ultimately miss lead you resulting failure.

Typical bulb dimmer

Every one knows working principle of rectifier .Hear logic what i made is just varing the input voltage level  using ac bulb dimmer it just acts as Variac and controls the input ac voltage to the rectifier circuit and produces the ripple free DC and can be used to run various dc loads for repair working and parallely we can monitor the out put voltage and current status  in the panel after powering the bench test equipment's.

Volt meter and ammeter fixed front view

Appearance an power on condition

One more thing here short circuit or over load protection circuit is not included. If you are export in electronic circuit designing one can create their own design for the safety propose.

To the best of my knowledge what i presented here is more enough and act as a good bench test instruments.

Hope this article may be useful to you in constructing the  needy test equipment instead of purchasing costly DC source. And i again  hope you enjoyed this i will be back with one more interesting topic in the next episode. 

With best Regards

Basavaraj BM