Power supplies

Electronic circuits need power. The simplest power supplies are batteries, and 5V USB power banks or adapters.

Stand-alone LiPo batteries are not suitable for experimentation, because they will deliver too much current when shorted. This can damage components or vaporise fragile connections such as PCB traces, even with just a few volts.

This page describes three ways to create simple but practical power supplies for use in the electronics hobby lab. With low-cost parts from China, useful power sources for experimentation can be built for just €20 .. €45.

PS1: LiPo’s + Regulator

This project was described on the weblog, see Quad 18650 power supply:

Benefits

  • low-cost, under €20 with parts from eBay
  • self-contained, the custom battery holder is 3D-printed
  • useful adjustable range for simple projects: 0..13V
  • continuous display of the current being drawn

Drawbacks

  • no current regulation, several amps can flow when shorted
  • adjustment is a bit tedious, the up/down buttons are sluggish
  • construction with unprotected LiPo’s requires some care
  • can’t be plugged in while in use (different ground voltage levels)

PS2: Dual Fixed

This supply has two independent fixed outputs: 12V @ 5A and 19V @ 3.4A (or 31V @ 3.4A when connected in series). It’s made from standard “power bricks” which are fully enclosed, quiet, and produce almost no heat:

Benefits

  • low-cost, around €25 with parts from eBay
  • standard 4mm banana jacks and pluggable screw terminals
  • continuous display of output voltage and current
  • mains-powered, yet very easy to build

Drawbacks

  • no current regulation, several amps will flow when shorted
  • when switched off, output voltages will only gradually drop off
  • slight inaccuracy due to a low-side shunt, within 1..2 counts

Bill Of Materials

  • 19V 65W adapter (eBay)
  • 12V 60W adapter (eBay)
  • two 100V 10A panel meters (eBay)
  • four 4mm banana sockets (eBay)
  • 4-way pluggable screw terminal (eBay)
  • rocker switch (eBay)
  • 25x18x5 cm plastic case, 2 half-shells, origin unknown
  • power cords for both adapters

Construction

The housing is a split plastic case, with 2 plastic insets as front and back panel. Here is the internal layout, before hot-glueing everything in place to fix it to the case and front panel:

All the nasty AC mains power and supply electronics are inside the power bricks. The only 230V wires are the power cord (top left), the connections to both power bricks, and the power switch. All wires carrying AC mains are securely fastened and insulated. The power cord has a strain relief, in this case by wrapping the cord’s internal metal braid around one of the internal case housing mounts:

If this supply ever gets dropped, many things may happen, but the power cord should not detach or be exposed.

AC mains voltage is lethal. This supply has a grounded plug and is enclosed in plastic - it should be safe when used properly.

A view of the front panel, now with hot glue applied:

Panel meters

The displays are panel meters which sense 0..100V and 0..10A. They need to be connected in a specific way when powered by the same supply they are used on, because they have a low-side current monitoring shunt: the “–” input side is slightly below the “–” level presented on the output. This will lead to a +0.1V display error at 5A:

In this dual power supply, everything is duplicated. The 12V and 19V outputs are completely independent.

PS3: Adjustable & Limited

This power supply is based on the widely available DPSxxxx switching power modules. It has finely adjustable voltage and current-limit settings, as well as up to 9 presets. Another nice feature is that the unit starts up with the same settings after a power cycle.

Benefits

  • low-cost, around €45 with parts from eBay
  • adjustable from 0 .. 22V, with 0 .. 3A output current limiting
  • standard 4mm banana jacks and pluggable screw terminals
  • continuous display of output voltage, current, and power
  • mains-powered, yet very easy to build

Drawbacks

  • every setting is hidden behind 3 push buttons and a knob
  • when switched off, the output will stay on a few more seconds
  • no remote control or reporting (but check out the OpenDPS project)

Bill Of Materials

  • DPS3003 power module (eBay)
  • 24V 72W “cage” power supply (eBay)
  • two 4mm banana sockets (eBay)
  • 2- or 4-way pluggable screw terminal (eBay)
  • rocker switch (eBay)
  • 25x18x5 cm plastic case, 2 half-shells, origin unknown
  • power cords for both adapters

Construction

The housing is a split plastic case, with 2 plastic insets as front and back panel. Here is the internal layout:

The power cord has a strain relief by wrapping all the wires around a stand-off inside the case. See PS2 above for more construction details, it’s very similar to this one.

AC mains voltage is lethal. This supply has a grounded plug and is enclosed in plastic - it should be safe when used properly.