Category: Electronics Workbench

In the process of replacing the laser cutter’s OEM 24 V 6 A power supply with a 15 A supply, one of the two screws holding it in place remained stuck in the underlying sheet metal plate:

You can’t see either of the screws from that position, but they’re in the upper-left and lower-right corners. The offending screw is, of course, on the top, tucked between the top of the supply and the wire raceway. The bottom screw came out easily and I could maneuver the supply out of the way.

Vigorous persuasion involving a bent-nose pliers and muttering got the screw out and revealed the problem:

The reason why the screwdriver didn’t get much traction in the head also became obvious:

Folks on the LightBurn forum seem astonished when they discover their fresh-from-the-factory has loose screws, missing screws, and occasionally the wrong screws.

I always wondered where the switch pointed to by the conspicuous label might be:

Unlike most supplies, it’s inside the case:

After you spot it, you can also find it just below the tip of the arrow in the previous picture. I suppose putting it inside the case prevents it from being inadvertently flipped, but somebody had to dismantle All. The. Supplies. to flip that switch for the USA-ian market.

The dataplate also became visible:

You’ll recall the 5 V 2 A output was dedicated to the red-dot pointer drawing about 20 mA.

In contrast, the 24 V 6 A output handled:

• X axis stepper driver: 3.5 A peak
• Y axis stepper driver: 3.5 A peak
• U axis stepper driver: 5.1 A peak
• KT332N controller &c: 1 or 2 A
• Gantry LED strip: 0.25 A

The stepper drivers are set to drop the motor current by half when they’re idle, which means their load would be only around 6 A. That’s as delivered to the motor windings, with the power supply’s average current being lower by roughly the ratio between the motor’s rated voltage and the power supply voltage. The instantaneous peak current, however, is the sum of all those currents.

At some point I must measure all that, but for now I want to shoehorn a bigger supply in there to take care of the additional load of the rotary stepper driver, plus the existing platform lighting and improved electronics bay blower.

The OMTech 60 W laser has a 24 V + 5 V power supply for the stepper motors and, I had always assumed, the feeble LED strip light on the gantry:

The stepper motor driver settings, plus a few amps for the controller and suchlike, added up to something over 12 A, far more than the 24 V supply’s 6 A spec should produce. When I added the COB strip lights around the platform, I dropped a 24 V wall wart into the electronics bay to avoid abusing that poor supply:

For reasons to be described later, it’s now time to upgrade that 24 V power supply to a 15 A supply that’s been on the shelf for far too long. However, it does not have a 5 V output, so it’s also time to figure out how much 5 V power the laser really needs.

A quick measurement suggested the 5 V output delivered 20 mA to something. After convincing myself the multimeter was working and that the gantry LED strip was still lit, I finally tracked the wire pair to the red-dot pointer:

Yeah, a whole dual-output power supply for one red-dot laser module.

Conveniently, the KT332N controller has several 5 V outputs and the LIMIT terminal block even has a GND terminal on the other end:

Prying off the hot melt glue, extracting the red-dot pointer wiring from the raceway, crimping ferrules on a couple of jumpers, and deploying a pair of Wago connectors:

I am still not accustomed to the color code:

• Black = signal
• Brown = power
• Blue = GND

But it’s like that and that’s the way it is.

The red dot lit right up, the gantry LED strip obviously uses 24 V power, and I must shoehorn a slightly larger 24 V supply into the space currently occupied by the old supply.