OMTech 60 W Laser: Replacement HV Power Supply Waveforms

While I had the hatch open, I thought it would be interesting to look at the HV supply’s current waveforms:

HV laser power supply - current probe setup
HV laser power supply – current probe setup

The Tek current probe over on the right measures return current through the cathode wire, the point in the circuit where you might be tempted to install an ordinary analog (moving-coil) panel milliammeter, oriented so (conventional) current returning from the tube will produce a positive voltage.

Unfortunately, an analog meter isn’t up to displaying anything meaningful for this nonsense:

HV laser power supply - 5 mA-div - 50 ms 10 pct pulse
HV laser power supply – 5 mA-div – 50 ms 10 pct pulse

Admittedly, that’s a 50 ms pulse, during which an analog meter would barely twitch. The vertical scale is 5 mA/div, so the highest peaks exceed 35 mA, more than twice the tube’s recommended “14-15 mA”.

A closer look at the pulse startup waveform:

HV laser power supply - 5 mA-div - 50 ms 10 pct pulse - detail
HV laser power supply – 5 mA-div – 50 ms 10 pct pulse – detail

It sure looks like the chaotic current through a forced neon-bulb relaxation oscillator. Remember neon bulbs?

An even closer look:

HV laser power supply - 5 mA-div - 50 ms 10 pct pulse - tight detail
HV laser power supply – 5 mA-div – 50 ms 10 pct pulse – tight detail

That’s at 10% PWM, close to the threshold below which the laser just won’t fire at all. The power supply must ramp up to produce enough voltage to fire the tube while simultaneously limiting the current to prevent the discharge from sliding down the negative resistance part of its curve.

Apparently this supply isn’t quite up to the task.

A 10 ms pulse at 50% PWM gives the supply enough time to stabilize the current:

HV laser power supply - 5 mA-div - 10 ms 50 pct pulse
HV laser power supply – 5 mA-div – 10 ms 50 pct pulse

The 14-ish mA at the tail end of the pulse (note the baseline offset) matches my previous 13 to 14 mA measurements as closely as seems reasonable. That 2 ms of hash on the leading edge suggests the start of each cut or engraving line will be a bit darker than you might expect.

Another 10 ms pulse, this time at 99% PWM:

HV laser power supply - 5 mA-div - 10 ms 99 pct pulse
HV laser power supply – 5 mA-div – 10 ms 99 pct pulse

The peak 24-ish mA matches the previous measurements. Note that the peaks in all the previous pictures exceed the 99% PWM current level.

AFAICT, all PWM values below about 25% produce equivalent results: random current spikes with unpredictable timing and amplitude. Changing the PWM value does not affect the (average) tube current or laser output power in any predictable way.

Some samples to illustrate the point, starting with a different 50 ms pulse at 10% PWM than the first one up above:

HV laser power supply – 5 mA-div – 50 ms 10 pct

A 50 ms pulse at 15% PWM:

HV laser power supply - 5 mA-div - 50 ms 15 pct
HV laser power supply – 5 mA-div – 50 ms 15 pct

A 50 ms pulse at 20% PWM:

HV laser power supply - 5 mA-div - 50 ms 20 pct
HV laser power supply – 5 mA-div – 50 ms 20 pct

A 50 ms pulse at 25% PWM:

HV laser power supply - 5 mA-div - 50 ms 25 pct
HV laser power supply – 5 mA-div – 50 ms 25 pct

Now, that last one is different. After the hash during the first 8 ms or so, the power supply actually produces a stable 5 mA beam current, which is roughly what I measured using the power supply’s meter.

However, the other three are pretty much identical: the 10% PWM pulse does not delivers half as energy as the 20% PWM pulse. The waveforms may be different, but not in a meaningful or consistent way: the two 50 ms 10% pulses are different, but you’d (well, I’d) have trouble separating them from the 20% pulse.

To summarize:

  • The first several millisconds of any pulse will consist of randomly distributed spikes with very large tube currents.
  • For PWM values greater than 25%, the tube current will settle down to the corresponding current after 5 to 10 ms. Before the current settles down, the tube will be firing those random spikes.
  • For PWM values less than 25%, the tube current never settles down: the entire pulse, no matter how long, will be short, high-intensity spikes, without a consistent DC-ish level.

No matter what an analog meter might show.

I have no way to know if this power supply is defective, but I’ll certainly ask …

Smashed Glass vs. Epoxy

Just to see what happens, I laid some smashed glass in puddles of epoxy:

Smashed Glass vs epoxy - samples
Smashed Glass vs epoxy – samples

Backlighting with the LED light pad reveals more detail:

Smashed Glass vs epoxy - backlit samples
Smashed Glass vs epoxy – backlit samples

The chunk on the left is the proof-of-concept shot glass coaster with a form-fit black acrylic mask atop a clear epoxy layer on a clear acrylic base. The chunk at the top is raw shattered glass fresh from the pile. The two chunks on teardrop acrylic scraps are bedded in transparent black and opaque black tinted epoxy.

A look through the microscope at all four, laid out in that order, with the contrast blown out to emphasize the grain boundaries:

Smashed Glass vs epoxy - magnified comparison
Smashed Glass vs epoxy – magnified comparison

You may want to open the image in a new tab for more detail.

The raw chunk has air between all its cuboids, so it’s nicely glittery. All the others have much of their air replaced by epoxy.

Clear epoxy produces an essentially transparent layer where it fills the gaps, because its refractive index comes close enough to the glass. The stretched contrast makes the gaps visible again, but the backlit image shows the unassisted eyeball view.

Transparent black dye sounds like an oxymoron, but it fills the gaps with enough contrast to remain visible. The overall chunk is not particularly glittery, but it’s OK.

Opaque black dye produces a much darker tint; the slightly tapered thin layer between the glass and acrylic (the small white circles are air bubbles) cuts down on the transmitted light. The gaps remain nearly as prominent as in the air-filled chunk, although with very little glitter.

Bedding the glass in epoxy against an acrylic sheet should reduce its tendency to fall apart at the slightest provocation, although the proof-of-concept poured coaster showed the epoxy must cover the entire edge of the glass sheet to bond all the slivers in place.

Onion Maggot Flies vs. Sticky Traps: Round 2

Mary decided the second round of sticky traps had collected enough Onion Maggot Flies (and other detritus) to warrant replacement, so this season will have three sets of cards.

The two sides of each card after about a month in the garden:

  • VCCG Onion Card A - 2022-07-17
  • VCCG Onion Card B - 2022-07-17
  • VCCG Onion Card C - 2022-07-17
  • VCCG Onion Card D - 2022-07-17
  • VCCG Onion Card E - 2022-07-17
  • VCCG Onion Card F - 2022-07-17

There are many flies that look (to me) like Onion Maggot Flies, in contrast with the first round of cards which had far fewer flies after about six weeks in the bed.

Some could be Cabbage Maggot Flies, but my fly ID hand is weak.

One of the frames screwed to a fence post suffered a non-fatal mishap, so I made and deployed a seventh trap. We’re pretty sure the garden has enough flies to go around.

Lawn Chair Re-strapping: Countdown Hold

I planned to replace the vinyl straps on our set of (salvaged) lawn / patio chairs and made a pair of rivets for one long-missing strap:

Lawn chair strap rivets
Lawn chair strap rivets

The overall project is on indefinite hold, as a Steel-blue Cricket Hunter (*) has decided at least one of the chairs is an ideal place to start a family:

Lawn chair - wasp nest under construction
Lawn chair – wasp nest under construction

The patio under the chair is littered with blades of grass and twigs that didn’t quite fit through the 5 mm vent hole in the tube, but that long stem went in just fine:

Lawn chair - wasp nest grass stem
Lawn chair – wasp nest grass stem

We have seen the wasp airlifting crickets near the chair, so provisioning has begun. The cricket seemed not only larger than the hole, but also larger than the wasp; we assume the wasp knows what she’s doing.

The new wasp will hatch this year, pupate over the winter, then hatch and emerge next summer, but I plan to replace the straps after the construction season ends.

I have no idea how to clean out whatever’s accumulating in there …

(*) I learned them as Steel-blue Cricket Killer, but the crickets are just paralyzed, not completely dead.

Gentec ED-200 Absorber Surface Damage

Having grossly exceeded the Gentec ED-200 maximum power spec, I wasn’t surprised to see this when I finally tucked it back in the drawer:

Gentec ED-200 surface damage
Gentec ED-200 surface damage

The 0.5 mm scale suggests the damage came from a defocused 2 mm beam or the hot central part of a larger beam, but I obviously wasn’t paying enough attention at the time.

The rest of the surface seems undamaged, so this may have been one of those inadvertent long-duration pulses or several shorter shots in one spot.

BatMax vs. Newmowa NP-BX1 Camera Batteries: 2022

Two years ago, a quartet of new BatMax NP-BX1 batteries performed about as well as could be expected and, by last fall, had deteriorated about as much as expected:

Batmax NP-BX1 - 2021-09 vs 2020-03
Batmax NP-BX1 – 2021-09 vs 2020-03

In round numbers, the total capacity declined from 3.25 W·hr to 2.5 W·hr, which means a single battery can’t quite power the camera for the duration of our normal hour-long rides. I do not know what voltage trips the camera’s decision, but the batteries definitely shut down sooner.

So, based on their previous track record, I bought another quartet of Batmax batteries. Being that type of guy, I tested both the old (2020) and new (2022) sets:

NP-BX1 - BatMax 2022 vs 2020 - used-new
NP-BX1 – BatMax 2022 vs 2020 – used-new

The blue traces are the C/D batteries from the as-new tests back in early 2020, the green traces are C/D after two years of use, and the red traces are the “new” quartet after their first charge in the Official BatMax Charger.

It looks very much like BatMax is selling used batteries repackaged as new items, because they are indistinguishable from my used ones. They definitely are not the “Premium Grade A cells” touted in the description.

I returned them for a refund and sent the test results to BatMax; they sent “new replacements” even though I said I would not pay for any future shipments. The batteries had a slightly different wrapper, but the test results were still indistinguishable from used batteries. I offered to return the package and was told that would not be needed.

Just a few more batteries for the blinkies.

So I bought a trio of NP-BX1 batteries from Newmowa, an Amazon supplier with a few more vowels than usual, and repeated the exercise:

NP-BX1 - Newmowa 2022 ABC - 2022-06-29
NP-BX1 – Newmowa 2022 ABC – 2022-06-29

It seems three good batteries now cost about as much as four crap batteries, under the reasonable assumption chargers are essentially free.

Three batteries isn’t quite enough for my usual rotation and, for unknown reasons, one cannot buy only batteries, so in short order I will have two chargers and six batteries.

The consolidated test results:

NP-BX1 - Newmowa Batmax 2022 comparison
NP-BX1 – Newmowa Batmax 2022 comparison

The color code:

  • Newmowa: red
  • BatMax 2020 new: blue
  • BatMax 2020 used: orange
  • BatMax 2022 new: green + lime

I stopped writing Amazon reviews after having a few detailed-writeups-with-graphs rejected for the usual unspecified reasons. As the Finn put it, “You wanna download, you know the access code already.”

Please Close The Gate Signage: Painted

It seems two months of sunlight will fade laser charred MDF down to its original state:

Please Close The Gate - unpainted faded
Please Close The Gate – unpainted faded

That’s through a thick layer of indoor urethane sealant slathered over MDF without any surface prep. Obviously, not removing the char had no effect on the outcome. On the upside, the urethane did a great job of protecting the MDF from rainfall.

So. Back to the shop.

Lacking wider masking tape, two strips of tape laid along a cut-to-suit slab of fresh MDF will serve as a paint mask:

Please Close The Gate - masked engraving
Please Close The Gate – masked engraving

Belatedly I Learned: cut the tape close to the edge, then fold it under so the autofocus pen can’t possibly snag it en passant.

Shoot the entire surface with a couple of black enamel rattlecan coats:

Please Close The Gate - masked paint
Please Close The Gate – masked paint

Yes, the engraved areas look reddish, most likely due to another complete lack of surface prep. Perhaps brushing / vacuuming / washing would remove some of the char, but let’s see how it behaves with no further attention.

Peel the tape, weed the letters / antlers, slather on a coat of urethane, and it looks downright bold:

Please Close The Gate - sealed
Please Close The Gate – sealed

Of course, if those two tape strips don’t exactly abut, the paint produces a nasty line:

Please Close The Gate - mask gap
Please Close The Gate – mask gap

Should you overlap the strips a wee bit to ensure cleanliness, the engraved surface will then have a noticeable (in person, anyhow) discontinuity due to the laser losing energy in two tape layers, which wouldn’t matter in this application. We defined the few paint lines as Good Enough™ for the purpose; a strip of absurdly wide masking tape is now on hand in anticipation of future need.

Burnishing the tape might have prevented paint bleed around the engraved areas:

Please Close The Gate - paint creep
Please Close The Gate – paint creep

But, given that I was painting raw / unfinished MDF with an unsmooth surface, burnishing probably wouldn’t produce a significantly better outcome.

By popular request, the new signs sit a few grids lower on the gates:

Please Close The Gate - fresh painted
Please Close The Gate – fresh painted

Perhaps these will outlast the garden season …