Variable voltage portable power supply

Variable voltage portable power supply, 2-32V

Legionlabs

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Description

By connecting a variable DC-DC step up converter to a variable DC-DC step down converter you can cheaply build a 'good enough' portable power supply.

Details

A variable power supply is a basic piece of test equipment.

I am a nomad, so a portable solution was necessary.

By setting a cheap step-up dc-dc converter to accept a range of inputs and output 32 volts, then connecting it to a variable step-down converter, we get a power supply that accepts a wide range of DC inputs, and outputs anything we want between about 2-32V. It's a simple solution and I'm sure thousands of people have done it, but I'll document it anyway.

These DC-DC converters are available from dx.com, bangood, and electronics markets in various developing countries.

In my case, the converters are from Ban Mo in Thailand, the wires and LiPo (not shown) from Nhat Tao in Viet Nam, and the case and dials from Ahikabara, Tokyo.

A display could be added but seemed unnecessary as I already have a portable multimeter and oscilloscope that can do that.

Components

1 × DC-DC step up converter wide range of input, fixed or variable output.
1 × DC-DC step down converter Variable output
1 × potentiometer same value as the trimpot in the step down converter
1 × case (optional) helps getting through airports
1 × barrel jacks so you can mak modular attachments

Project Logs

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An Uneventful Day
Legionlabs • 10/18/2015 at 14:53 • 0 comments

I have electricity, nothing is on fire, nearby politics are stable, and nothing nearby has exploded recently.
Each of these things has been not true for me at various points, so I took advantage of this quiet period to expand the utility of the LiPo RC battery I always keep charged as an emergency power source by building this variable output power supply.
Beyond it's utility as a tool, 24 watt-hours is a lot more than nothing when the power cuts, and I can connect most power sources to it including small solar arrays, and most types of battery.
I hope it is not as useful to you as it is to me!

View project log

Build Instructions

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1

Step 1

Look at the front and back of your step-down converter and note where the trimpot connects, as well as the value of the trimpot. In this cake it was 50kOhm
2

Step 2

Remove the potentiometer either by desoldering it properly, or lacking tools, by bending it back and forth until it snaps off. Now solder the potentiometer in place of the trimpot. The order of the wires is the same as the trimpot was: if in doubt it probably goes the way you think it does.
3

Step 3

Install in a case. I used an RC LiPo battery clip as input as I have a spare battery lying around I don't use, it's physically impossible to plug in in the wrong polarity, and it's easy to find replacements.
As you might expect, turning the potentiometer sets the output voltage.
Now go make some tea and call it a day.