The previous posts showed how to use an inexpensive voltage converter module to be able to get variable voltage from a fixed DC power supply. This post is one more variation and is the last build of these modules that I planned to do (build no. 3).
This unit is a step up step down DC buck converter module. The unit uses an LM2577S for boosting the voltage up and an LM2596S for stepping the voltage down. It has an input range of 3.5 – 28 volts and an output range of 1.25 – 26 volts. Both the input and output is rated at 1 amp stable and 3 amps maximum.
It is similar to the adjustable boost voltage module discussed in a previous post only this one doesn’t come with a built in voltmeter. When I bought the unit I also bought a mini voltmeter so I would have a way to check the voltage in real time.
The unit is a 3.2 to 30v mini voltmeter and is shown connected to the output voltage screw terminals in the above photo. The two heat sinks affixed to the ICs did not come with the unit. They are 11mm x 11mm x 5mm heat sinks with thermal adhesive. I bought those separately and the “peel and stick” thermal adhesive was included.
The unit that I bought came with mounting hardware – 4 female threaded standoffs and 4 screws (3M metric threads). The unit still required 4 more screws for mounting the standoffs to the enclosure box (3M x 5mm Phillips head metric screws).
The whole point of trying out a variety of these modules was, for me, a matter of experimentation and seeing what works and what doesn’t. I noticed some slight variation in output voltage on one of the units so I have two other units to work with.
This particular unit was designed for voltage regulation for solar panels. It is supposed to maintain a steady output even with variations of the input supply voltage. It should work fine for breadboarding and other low current circuit tests.
Just as in the previous builds, this unit will be mounted in a rigid clear plastic storage box with a hinged lid. This project is only a little bit more complex with the addition of the voltmeter and a switch to select between input and output voltage display.
Before going much further, I wanted to check the unit with a multimeter.
The unit checks out okay. Below is a photo of the parts needed for the build – back row: step up step down DC buck converter module, mounting hardware, plastic box (3 9/16″ x 2 9/16″ x 1 1/8″) front row: mini voltmeter, 2 black banana jacks, 2 red banana jacks, a 2.1 mm coax panel mount DC power jack and an SPDT sub miniature toggle switch (on – on).
Before obtaining the SPDT switch or making the wiring diagram I had to check something on the unit. I wanted to know if there was a common negative polarity (ground) that ran through the unit. If there was a common connection for the negative screw terminals on the input and output side, then I knew I would be able to use an SPDT switch instead of a DPDT switch.
I checked the connection with a multimeter and it showed that there was continuity between the negative input and negative output terminals. If the test would have shown no connection between them then I would have had to use a DPDT switch instead.
Below is the wiring diagram for the project:
Next all the holes were drilled in the plastic case. I used a sharp 1/8 inch drill bit for all the holes except for the two holes for mounting the voltmeter. A taper reamer was used to enlarge the holes where needed. The box was made from styrene plastic, which was very brittle. This was the best way to drill the holes without cracking the plastic.
I measured out the hole locations and made markings on plain white paper then trimmed them with a utility knife. The paper markings were affixed to the box with repositionable adhesive and a roll on glue tape dispenser. The markings for the bottom holes were affixed to the underside of the box (photo below).
The paper markings for the side panels were affixed to the inside of the box.
The box was placed over a small block of wood to drill the holes in the base.
A smaller block of wood was used to drill the holes in the side panels.
The holes for the voltmeter were drilled with a smaller bit. The diameter depends upon the size of the holes on the voltmeter and the mounting hardware.
The holes for the one of the side panels is shown in the photo below.
After the holes are drilled, simply peel off the paper markings. It should come off clean if repositionable adhesive is used.
The photo below shows the mounting hole for the switch being enlarged with a taper reamer.
The toggle switch has a locking ring for anchoring the switch and preventing it from rotating. The locking ring fits into a keyway notch on the threaded mounting bushing on the switch. The locking ring required a second hole to be drilled in the panel.
The switch was temporarily mounted in the hole to mark the location for the anchoring hole for the locking ring, then the hole was drilled (below).
We want to make sure that the switch maintains a lateral orientation. When the switch is toggled left, the input voltage displays and when the switch is toggled right, the output voltage is displayed.
Enlarge remaining holes with a taper reamer where needed and temporarily mount all the parts into the holes to check alignment and proper fit (below).
Make sure everything fits and then remove the parts that need soldering. The voltmeter was not removed because the leads were previously soldered to it. Cut leads from red and black hookup wire and solder them to the components. All the leads were tinned to make the job easier.
Pay careful attention to the solder lugs on the switch to make sure that the correct leads are soldered the them. When finished, re-mount everything except for the circuit board back into the box (below).
The last step is to connect the leads to the screw terminals on the input side and then the output side of the circuit board. Tighten the screws and then mount the circuit board to the box with standoffs and screws.
I checked the DC power jack by connecting a 12v AC adapter. The voltmeter displays the input voltage.
Then check both left and right switch positions for the input and output voltage display on the voltmeter. That checked out okay.
The last check was to make sure the banana jacks were working. Below is a photo of the unit connected to a DC bench supply. The input voltage displays 24.4 volts.
The unit is ready to connect to a project board or circuit. The output voltage can be adjusted with the trimmer pot screw. Just make sure not to exceed the current capacity of the unit or the power supply.