OMTech 60W Laser: Repurposing the HV Power Supply Water Protect Input

For reference, the input terminals on the OMTech anonymous 60 W HV laser power supply:

OMTech 60W HV power supply - terminals
OMTech 60W HV power supply – terminals

AFAICT, that’s the default layout for all similar power supplies.

The H and L pins are the High- and Low-active enable inputs that, when it’s working right, control the laser output. The KT332 controller (and, most likely, all RuiDa controllers) produce a low-active output, so you just wire the controller’s output to the L input and you’re done.

That was the original failure that got me to this point: the power supply ignored its L input and turned the beam on at whatever power the PWM signal on the IN terminal called for. Having that happen was surprising, having it happen with the cabinet lid open was … disturbing.

The P input is intended for the Water Protect signal from the flow sensor on the laser cooling plumbing. When the water is flowing, the IN terminal will be low and the power supply will pay attention to the L input.

The power supply arrived with a jumper between the P input and the G ground / common terminal:

OMTech 60W HV power supply - Water Protect jumper
OMTech 60W HV power supply – Water Protect jumper

The jumper holds the P input low = active, meaning the power supply thinks the water is always flowing.

It turns out that the Water Protect signal goes only to the controller. When it’s inactive = no water flowing, the controller will refuse to fire the laser and also sound an alarm. Running the signal directly to the power supply would result in a puzzling failure-to-fire with no diagnostic from the controller.

I removed that jumper and added a (green) wire from the Lid Interlock signal at the controller:

OMTech KT332 controller - Lid Interlock input - added wire
OMTech KT332 controller – Lid Interlock input – added wire

To the power supply’s P input:

OMTech 60W HV power supply - Water Protect as Lid Interlock
OMTech 60W HV power supply – Water Protect as Lid Interlock

In principle, if this power supply fails the same way as the previous one (with its L input always active), then at least it won’t fire with the lid up.

Believing that may display a childish naivety, but at least the thing seems marginally safer than it was before.

3 thoughts on “OMTech 60W Laser: Repurposing the HV Power Supply Water Protect Input

  1. The fda advocates passing the power supply to the power supply through a shunt in the lid. I’m paranoid enough to think that’s a damned fine idea … i’d never believe one logic level input to chinese garbage is more reliable than the other.

    1. Aye!

      I considered putting an SSR in series with the existing AC wiring to turn on the HV supply only when the lid is closed and everything else thinks the supply should be on. I’m not sure why I trust the lid interlock sensor more than I trust the HV supply’s guts, but I think requiring a double enable to fire the laser should suffice.

      Trust, but twist the key switch while fiddling inside …

Spam comments get trashed, so don't bother. Comment moderation may cause a delay.

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s