PowerTech 0-24V bench top power supply teardown

 Here's my newest toy, a 0-24V, max 18A PowerTech branded switch mode benchtop power supply. In this blog we'll take a peek into the supply and see what makes it tick!


On the front panel there's a simple analog volt and amp meter, the amp meter having two scales, likely for 12 and 24V usage. The voltage adjust knob is a single turn potentiometer, with a bump in the middle of the rotation to indicate that it is at about half way.

This unit is a relatively bottom of the range model, with no digital readout or control implemented. It can be found at Jaycar in Australia listed as the MP-3800. The unit is fused internally at 3A so if you happen to kill the overload protection the most that will happen is the fuse blowing. It's only a 220-240VAC model, so not very useful in places with 110VAC mains. The output on it is rated at 0-24 but under no load conditions it will put out a maximum of 29.4VDC.

 Not much to say about the back of it, made in Taiwan, is marked as RoHS compliant and has two relatively decent quality output connectors.

 Having a quick look at the top of the unit, there's a small axial fan located on top, and that's about it.

Time for a peek inside, from here we can see the mains input socket to the bottom left, DC output at the top left, switching devices, heatsink and fan in the center. On the heatsink a fan speed control board can be seen, so it will run according to temperature. The two capacitors down the bottom are for mains input filtering after the rectifier, and the metal can on the front houses all the control circuitry, and analog meters.

Here's a look at the solder side of the circuit board, which is only single sided containing all through hole components. One thing that we notice instantly is the lack of major isolation between the mains input and DC output, only being an earth trace separating the two. The mains input is the three pin connector towards the left side of the bottom of the board, and the DC output lugs are the two large traces to the bottom right of the board.
The main transformer is just above top center of the board, being driven in a half bridge configuration by the two switching devices just under the top center of the board. This lot gets controlled by the TL494 in the controller mounted behind the voltage and current meters.

Not to say PowerTech is purposely lying about the RoHS status of the power supply, but those touched up solder joints on that rectifier look a whole lot shinier than the lead free solder around it. A little deceptive if that is in fact lead solder, but hey, can't expect everything from a cheap supply.

There's a small (presumably some manner of control transformer) ferrite cored transformer mounted to a vertical PCB along with a few other components. I'd say it's to simply save space, but this could also be a source of damage if the power supply were dropped as the board isn't secured anywhere apart from the solder joints.

Quick look at the terminations of the output connectors, there is no solder connecting the terminals directly, rather they rely on the connection between the nut and the board. The nuts are held in place with Locktite so chances are the connection will remain strong. 

There's also a 470uF 25V rated capacitor on the output. For reference, this supply puts out a max of 29.4V unloaded, so that capacitor is under rated for the voltage it will be seeing. I'm surprised it has yet to die.

Included on the +DC wire is a small ferrite choke, as to reduce interference the power supply passes. No output waveforms though, sorry.

The rosin/flux in the solder used to solder the boards (presumably also lead solder) wasn't cleaned from the output spade connectors, assuming the flux is no clean it won't pose any metal being eaten away risk.

The back of the controller/display looks pretty ordinary, with a shield added as the controller IC is hiding away in there.

The status LED's are to the right (POWER and WARNING), with the voltage adjustment potentiometer to the left.

The back of the controller/display looks pretty ordinary, with a shield added as the controller IC is hiding away in there.

And last but not least, the backlight of the current and voltage meters. To be honest I would have expected LED's would have been used, but for the price these small lamps were used instead to eliminate the need for a diffuser.

Overall, for the price I'd say the powersupply is a relatively decent build for the price, being very useful if you need variable voltage that doesn't need to be accurate or current limited. There are a few things I noted such as the lack of notable isolation between mains and the output, as well the lead solder used under RoHS, but hey, for $150 you can't expect much more. 

Cheers for reading, 

Drop a comment below if you have any questions!