Intermittent 50W Laser Issues - Stops but still firing

Community Laser Talk
1

Hi there -

I have a Chinese 50W blue and gray laser that I use with a rotary attachment.

Recently I have had some intermittent issues. I am able to run several jobs just fine and then randomly the laserhead will stop in the middle of the job, ruining the cup…however it is still firing and the control panel shows that the head is still moving back and forth.

Once the job runs through and thinks it is finished, the laserhead will not move using the arrows on the controller at that point.

If I turn it off and start over, same thing…several jobs fine and then randomly stops while still firing. The lights on the driver are green and then when the laserhead stops they are both red.

Additionally, my air assist motor has become very loud, and it just doesn’t sound right. Is there any chance that this could be causing the problem? I am assuming no, but just trying to provide as much information as I can.

Is there anything you can suggest for me to try to determine the problem? I ordered new drivers, but I don’t feel confident that is the actual issue (or only issue.)

Any advice would be greatly appreciated!

Thank you,

Katsie

1 Like
2

A picture would help.

If that is one of the stepper motor drivers, then knowing exactly which driver model you have will help find the manual, which will then explain what the indicator LEDs mean.

For example, this is a DM545A stepper driver:

PXL_20221112_000202110 - DM545A Motor Driver A
PXL_20221112_000202110 - DM545A Motor Driver A1125×1500 250 KB

If it is powered from the 120 VAC line, it is likely unrelated.

If it is powered from the 24 VDC power supply that also powers the stepper motor drivers, then it is definitely related.

With the power turned off, trace the input cable from the air pump until you either reach the 24 VDC supply or the 120 VAC power line.

Again, photos will help.

3

Mine was 120V… Might want to be a bit more specific.

:smile_cat:

4

I have the same drivers DM545A. Here are pictures of the driver.

I will trace the input cable now…

IMG_7123
IMG_71231920×1440 299 KB

image0 (16)
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5

This is where the line goes

IMG_7197
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6

OK, that’s as expected.

The DM545A manual says:

  1. , the status on light’s indication
    PWR: green, normal work light.
    ALM: red, failure light, the motor with phase short-circuit, overvoltage and under-voltage protection.

So:

  • Green LED = on → the 24 VDC power is good now
  • Red LED = on → something bad happened earlier

I assume the red LEDs on both stepper drivers are lit, along with both green LEDs, as shown in your picture.

It is unlikely they both have hardware failures and even more unlikely both motors have hardware failures, which suggests a problem with the 24 VDC power supply.

The DIP switches set the peak motor current to 3.31 A. I have an uneasy feeling the power supply has a 6 A rating (the machine looks a lot like mine), and that may be the root cause of the problem.

The power supply will have a data plate label with the output voltage & current ratings. The data plate will (probably) be on the side of the power supply that’s jammed against the wiring channel where you (probably) can’t read it. With the power off, look back there and see what you can see.

Take a close look at the assist air pump. If has a label, then it should tell you what voltage it’s running from. If not, trace the wires from the pump to either the 24 VDC supply you just found or the 120 VAC line.

I’d expect the latter, in which case the wires may end up at the terminal block just to the right of the supply that looks like it handles the AC power.

But ya never know, so all this poking around and peering into hidden places is just to find out what’s going on.

7

I think this is the data plate you referred to….working on looking at air assist next

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IMG_7221
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8

Your agility is second to none! :grin:

So here’s what I think is going on

  • The two stepper drivers are set to deliver 3.3 A each to the motors.
  • The Ruida controller requires maybe 1 A for all its functions; this is not documented anywhere I can find
  • The power supply is rated for 6 A maximum, but must deliver something over 7 A

This works most of the time, because power supplies can deliver somewhat more than their stated maximum current. Machine designers, at least good ones, don’t abuse that margin and, indeed, specify a slightly larger supply than absolutely required. Obviously, supplies with higher current capacity cost more, so there’s a powerful motivation to use the cheapest supply that doesn’t fail immediately.

In point of fact, my laser has a third stepper driver for the Z axis motor, set to 5.1 A peak, so the “6 A” supply must deliver nearly twice its rated current. That the poor thing doesn’t fail continues to amaze me, but, as the old song goes, it’s living on reds, vitamin C, and cocaine.

With that long-winded explanation in mind, I think the power supply in your laser is at the other end of the spectrum: it can deliver just a little more current than its specified 6 A, but eventually the overload causes a voltage glitch that trips the stepper driver under-voltage error. When the stepper drivers turn on their red LED they shut the motor off, thus eliminating the overload on the power supply, which promptly resumes normal operation.

If that’s what’s going on, perhaps reducing the motor current will improve things. Reducing it too much will cause other problems, but you can probably get away with a little tweak.

The DIP switches are identified by number, with switches 1 2 3 controlling the current. Right now they’re set OFF ON OFF which calls for 3.3 A peak.

With the power off, flip switch 1 on both stepper drivers from OFF to ON, so they are ON ON OFF. That will reduce the current to 2.8 A peak, which might be juuuust enough to unload the supply.

Then see what happens during a few runs on a scrap mug …

1 Like
9

lol! I literally had to jam the phone down in there to get that picture.

You are awesome! I will give this a shot and let you know! I truly appreciate you taking the time to help (and teach) me!

10

Made the change you suggested and so far so good!! I have run the same job about six times with no issue.

Thank you!! I really appreciate it!

My last question is about the air assist motor….does it just get louder with age or could that be an issue sometime soon?

1 Like
12

Tah dah!

The correct solution is to buy a supply with more current capacity, as overburdening that poor thing can’t be a good long-term strategy. However, “more current” means “bigger case” and it likely won’t fit in the same spot, not to mention the same screw holes.

Soooo: keep this in mind, drive it until it drops, then wedge a larger supply in there somehow.

Note that it’s a dual supply with both 24 VDC and 5 VDC outputs, which somewhat limits your choices and suggests labeling the wires so you don’t mix them up.

It’s most likely getting louder as the bearings grind themselves into dust, so you’ll want a replacement for that, too. Searching the discussions here for the obvious keywords (“assist” / “compressor” / “air pump” / “aquarium”) will occupy you for hours.

FWIW, this pump came with the laser and works fine for me:

The hulking lump on the left is the Z axis stepper motor.

Happy hunting …

1 Like
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Thank you! I will start the hunt!

14

I knew you had issues… such a clean machine… sign of a sick mind :crazy_face:

:smile_cat:

15

Well I just tried working on some jobs and it happened again :(. Stopped right in the middle of a job. Any other suggestions?

16

Assuming I’ve diagnosed the problem correctly, which may not be the case, the solution is a new supply.

You can reduce the stepper motor current again, although this will eventually cause the motors to stall.

Set DIP switches 1 2 3 to OFF OFF ON, which requires flipping all three from their current position. That reduces the peak current from 2.84 A to 2.03 A, which might get it through.

However, the “peak current” is the maximum current in a single motor winding. At certain points in the motor rotation, both windings will carry 0.7× that current for a total of 1.4× the “peak current”, so with the driver set for 2 A “peak current” the power supply must provide 3.2 A for each motor.

When the stars misalign, that means it must provide well over 6 A for the whole machine. All you’re doing by reducing the motor current is trying to find a setting that will allow it to (barely) continue working, even though it’s inadequate.

Good luck …

17

Could water protection. If wp is connected to the ps and not the controller laser will stop if low or no water flow (or bad switch) but motion will continue.

18

Which is not the symptom: the laser continues firing with both stepper motor drivers hard-stopped on an internal error condition.

If the failure were due to a protection failure, the controller would turn off the laser as well as the motors and the drivers would not show an error.

19

The controller will stop the motors only if WP is wired to the controller and the controller is set with the correct polarity for the Water protection. Some systems (like mine) only have WP wired only to the laser power supply and not the controller. The laser will stop firing and the controller (gantry) will continue as if it is lasing.