Chinese 50w laser loosing power.

[michael croft]

Based on that then the tube we are talking of will be the RECI similar as those being sold on ebay?

[Kel Kodama]

I would recommend installing an ammeter to prevent overdriving the laser tube. I bought this one on Amazon:
85C1 DC 0-30mA AMP Current Panel Meter Analog Ammeter - Multi Testers - Amazon.com
It measures from 0-30mA.

I cut an acrylic plate (in purple!) to replace the metal end cap on the laser chamber. An Adobe Illustrator file for this plate is attached. If you buy a different ammeter, you may have to change the cutout and screw mounting hole sizes/locations.

I didn't have time to unscrew the plate to take a picture of the ammeter connections, but it is really quite simple. I purposely mounted the ammeter in this location because it is very close to the wire that you need to tap into.
-Needless to say, but I will say it anyway, turn off and unplug your machine.
-Unscrew the blue metal plate. To get access, open the electronics access door. Be careful, some of the screws have nuts, which you will want to reuse.
-Attach your ammeter to your acrylic plate. My ammeter required M3 nuts for both the mounting and the wire terminals.
-The laser tube has two wires going to it from the power supply, a red wire (caution, high voltage, don't cut this wire!) and a black wire. You want to cut the black wire.
-Connect the black wire coming from the power supply to the + terminal on the rear of the ammeter. I used a circular wire terminal and a M3 nut.
-Connect the black wire going to the laser tube to the - ammeter terminal.
-If you hook them up backwards, your ammeter indicator will rotate the wrong way (and possibly damage the ammeter if run this way for a long time, but a quick pulse shouldn't hurt it).
-Screw your ammeter acrylic plate onto the machine, making sure you don't pinch any of the wires or push the black wires too close to the red wire.

I found that a 65% laser power setting uses 20mA, which is supposedly the max you are supposed to supply to a 40W/50W tube to maintain a long life. So the ammeter has been very helpful so far. I would also recommend the SarbarMultimedia videos on Youtube (who also sets his maximum power to 65%). The whole series is extremely helpful for owners of this laser (although I am not completely convinced by some of his testing methods, they still serve as good food-for-thought).

Attached Files

[michael croft]

Hi Kel Kodma

That is really helpful and makes full sense Thank you, have ordered a meter of ebay.

Must say that the SarbarMultimedia videos on Youtube were as you say a mine of very helpful information.

Having watched the tutorials I thought I would retry cutting at a lower power setting 60% min 65% max at a speed of 5 with 3mm MDF the result was actually as he said which comes back to the statement anything over is putting unnecessary stress on the tube.

Most of the areas cut out fine but for some unknown reason there is still areas of the cut that are not going all the way through, can see the out line but not quite enough to just drop out.

Now is this the MDF or the laser settings, I doubt the MDF as it happens in the same places each time,

After an hours cutting it has now Finally given up the ghost water temp has gone from 17 at the start to 22 and it is just marking the surface of the mdf.

Disappointing as at first I thought the reduction in power had made the difference and I had saved a few £s but it hasn't the longer I use the weaker it became.

Shall run same test tomorow just to clarify but I reckon as Dave says the tube has died.

[Dave Sheldrake]

Having watched the tutorials I thought I would retry cutting at a lower power setting 60% min 65% max at a speed of 5 with 3mm MDF the result was actually as he said which comes back to the statement anything over is putting unnecessary stress on the tube.

Nope, tubes all have a maximum operating current, it is quite safe to go up close to that so long as you don't go over.

The 65% thing comes from badly adjusted supplies that put out 20mA at 65% rather than at 100%. Running a tube at lower power rather than closer to 85/90% means jobs take longer, longer jobs means the tube is stressed for longer so in many cases self defeating.(engraving stresses a tube far more than cutting as the tube has to strike at the beginning of each pass @ above the nominal operating current)
95% is the advisable max as this will allow for spikes in current on a well adjusted,quality PSU

Best way is to use the meter to find out what current you are pumping, then turn the small screw on the underside of the PSU to reduce current until you are at 1-2mA under the tubes working limit @ 100%, if you then run at no more than 95% you will be pretty safe

[michael croft]

Ok first of all thanks to Dave Sheldrake for the contact as in Chris @ HPC Laser, one could not ask for a better advice or service, Emailed my needs of a new 40w tube measurements etc this morning and by 4.30pm I had it in my hands, it so happened that Chris was down this way in the South and he had one in his van.
Tomorrow I will fit it and by evening I hope that production will be back up, running and the problem has been sorted.

One thing that has been pointed out by Chris was that a 40watt tube should not be run by anything higher than 17mA, logical i suspect but my concern will of course be performance, I was offered a slightly higher power tube(50Watts?!) but its dimensions would not fit my machine, but as I said we shall see tomorrow what the results are.

[Dave Sheldrake]

Ok first of all thanks to Dave Sheldrake for the contact as in Chris @ HPC Laser, one could not ask for a better advice or service, Emailed my needs of a new 40w tube measurements etc this morning and by 4.30pm I had it in my hands, it so happened that Chris was down this way in the South and he had one in his van.
Tomorrow I will fit it and by evening I hope that production will be back up, running and the problem has been sorted.

One thing that has been pointed out by Chris was that a 40watt tube should not be run by anything higher than 17mA, logical i suspect but my concern will of course be performance, I was offered a slightly higher power tube(50Watts?!) but its dimensions would not fit my machine, but as I said we shall see tomorrow what the results are.

your welcome Mike, Chris is a clever chap....not many people in the UK have his expertise or experience with lasers.

The performance issue is moot sadly, 40 watt = 17mA even if that's slower than a 50 watt or an over driven 40 watt at least it's not going to go bang anytime soon

[michael croft]

Well final part of the problem solved.
It was the tube. All up and running again 3mm MDF 15 speed @ 65% power on a new 40 watt tube.

Only problem I had was the fact that the length of the tube is bigger than the machine so had to remove the inspection plate and at present have the end of the tube protruding by about 100 mm, this will be resolved as my friend is fabricating me a cover for it using the original holes.

One thing I will recommend again for those of you with the Chinese eBay lasers in particular the Shenhui 350 50 watt is the series of video on you tube by SarbarMultimedia, I learnt a lot about my machine his videos certainly enthused and helped remove the stigma of owning what is normal termed inferior, they are not especially if you know how to tweak them.

[Scott Marquez]

Couldn't you make your own spacers for the side plate out of your wood, just start stacking them?
Scott

[michael croft]

Couldn't you make your own spacers for the side plate out of your wood, just start stacking them?
Scott

Confused what spacers are you meaning?

[Scott Marquez]

I'm assuming that there is a flat side plate that you were able to remove, and now your tube is extending out of the side of your machine. If that is the case you could use the end plate as a pattern and make multiple copies, with the center cut out to create spacers to extend the side of your machine beyond the tube.
Scott

[michael croft]

I'm assuming that there is a flat side plate that you were able to remove, and now your tube is extending out of the side of your machine. If that is the case you could use the end plate as a pattern and make multiple copies, with the center cut out to create spacers to extend the side of your machine beyond the tube.
Scott

Ah thanks for the suggestion

Yes that would be possible but as my friend is a fabricator he is making a metal one for me, plus I am fitting an ammeter onto the cover to give me more control and understanding of the lasers ability.

He is also doing me another job and that is to cut me an access inspection hatches at the left hand side of the machine as the manufactures did not do this.

That will give me access to the lenses so they can be stripped down and maintained easier.

Finally he is making a custom laser support bed which like SarbarMultimedia, uses but with a few adaptations of my own.