2013 Shenhui 350 losing power already?

[Arjen Abbestee]

Hi, Last year I bought a Shenhui 350 (50W). I use it mainly for hobby purposes, so it has not been running more than a couple of hours in a row. In fact, after about a year it has 97 laser-hours on the clock (info from Laswerworks).
Lately Ive noticed a large reduction of power. Cutting 3mm light plywood used to cut easily at 18mm/sec, my last try was at 10 mm/sec and still not cutting through the whole job. Lens and mirrors are clean and well aligned.
I checked the tube for a manufacturing date, but of course all text is in Chinese, I could not even make out if it is indeed a 50W tube. There is however nothing handwritten anywhere on the tube so I doubt there has ever been a date on it...
I have no way of measuring the output power from the tube, the only thing I can do is measure the current going through the tube by placing a mAmp meter in the return wire. With this 50W tube, what would be the 'normal' current when cutting at 100% power?
And if the current is off, what does this tell me? Dying power supply or dying tube?
So many questions...

Thanks,

A

[Bill George]

Just went through the same thing with a laser purchased this spring. I used for engraving and never for cutting. When I did try the vector cutting as 3mm ply it would not cut even at 1 mm/Sec 90% power (35 watt tube). My MA meter still showed 22-24 ma, but no real power out.
Now with my new tube which is rated at a full 40 watts plus and tested I can cut 3mm ply at 15 mm/Sec at 80% power. I looked at the old tube and saw it was Mfg March 2014 and tested at only 32 watts, yet sold as 35 watts! A good honest look at the measurements of CO2 glass tubes shows to get a full 40 watts you need a tube 850 mm long. A true 50 watt tube would be a full meter long.
Some venders will put a 40 watt tube in a machine and then over drive it to make it seem like a 50 watt tube and call the machine a 50 watt model. That is one reason they don't put meters on the machines. If its only 850 mm long chances are its only a 40 watt tube and when you over drive them with more current than design, they will fail early.
I got my new tube from LightObject dot com.

[Clark Pace]

Are you sure it's loosing power? I have a 350 also , and I lost power also, but it just became un aligned. After I re aligned them, my power was back. Do you have a laser meter? If not you might want to get one. They cost around $60 on ebay.

[Lucy Lee]

For a normal CO2 laser tube, even you not use it ,just in stock, there is little leakage, but it maybe not loose power suddenly, except there is some broken

[Arjen Abbestee]

Thanks for your replies.
Mirror alignment is OK. Checked all four corners of the bed, less than 0.5mm. difference from the center on the final mirror, so no problem there. I've got two lenses, both appear to be clean but no difference in power.
I just checked the specs, it is supposed to be a 40/45 Watt tube. Don't know Why I thought it was 50. A 50W tube would not fit in the housing.
@ Clark: I searched on ebay, but did not find a meter for less than a couple of hundreds of $$. What should I look for?

Thanks,

A

[Arjen Abbestee]

I just put my meter in the return line from the laser tube. At full power cutting it reads 17.2 mA. That seems to be a bit low. But of course the question remains, is it the tube or maybe the power supply...

[Bill George]

I just put my meter in the return line from the laser tube. At full power cutting it reads 17.2 mA. That seems to be a bit low. But of course the question remains, is it the tube or maybe the power supply...

Seems low but how accurate is your meter? I had good mA readings but the tube still did not have power. Did you check the high voltage connections to the tube and the input wiring to the power supply?

LightObject sells mA meters and even the digital one is less than $20. I see your in the Netherlands so shipping from US to you would be expensive. But he might be able to arrange shipping direct from China to you from his sources.

Measure the length of your tube, that will tell you more about the rating. My new 40 watt tube measures 850 mm end to end and diameter is 51 mm.

[Arjen Abbestee]

Funny thing is I asked Shenhui more than once what the power of the tube is but never got further than 40/45. My tube is also about 850 mm long, but 50 mm diameter. So it's most likely a 40 watt. Lightobjects lists a 40W tube (on ebay) that is 830 long and 55mm diameter. But that could be a typo because it also says 2inches, which is closer to 50mm of course. What's interesting is that it also states a max current of 18 mA, making my 17.2 quite normal. But tech support at Shenhui said it should be between 20-25 mA.
The meter I use is a Fluke digital multimeter. Connected in the return wire from the tube.
All connections appear to be OK. The power drop did not occur overnight but gradually over the past month or so. Last couple of day it seems to go more rapid though.

[Clark Pace]

Thanks for your replies.
Mirror alignment is OK. Checked all four corners of the bed, less than 0.5mm. difference from the center on the final mirror, so no problem there. I've got two lenses, both appear to be clean but no difference in power.
I just checked the specs, it is supposed to be a 40/45 Watt tube. Don't know Why I thought it was 50. A 50W tube would not fit in the housing.
@ Clark: I searched on ebay, but did not find a meter for less than a couple of hundreds of $$. What should I look for?

Thanks,

A

I can't find them on ebay either,but here is the one I have. You can get it on amazon also

http://www.amazon.com/Laser-Engraving-Cutting-Machines-microns/dp/B00EOMTSOO

[Bill George]

My LightObject 40 Watt tube measures as I stated above, his ad copy is wrong. On his forum it says 40W tube should be 22~24 mA but those are the Max ratings, I run this one never over 20- 22 mA. I would say your Fluke should be right on the money for a reading. The sellers all want you to run at lower power (18 mA) so they at least make it past the warranty period before they fail :)
Your going through the same decision making process that I did. They only thing different is I had slightly higher mA readings. But given the track record of Chinese glass tubes I think I made the right choice by replacing. He is giving a 6 month warranty on the tube they sell, but I'm sure it has conditions. I have found Marco more than fair on my dealings with his company.

[Dave Sheldrake]

Arjen,

I'd say it is the tube, the resistance in DC tubes increases as they die so the PSU has to work a lot harder to strike an arc (remember you are measuring the return current, not the current applied). Even a 40 watt laser PSU can pump 35 - 40 mA when required, that and the gradual decline of the power suggests the tube is on it's way out. Even a new machine can on occasion have a tube that is nearly 2 years old in it when it arrives from China.

Bill is quite right about over driven tubes, seem it many times even to the extent of 80 watt supplies being used to pump 130 watt tubes from one of the well known makers.

In a perfect world a 50mm diameter reservoir is able to pump 80 watts per Meter, that doesn't mean much though as the controlling factor is the diameter of the resonator tube and size of the electrodes (design) (as well as a whole load of more complex factors).

The tube and PSU are the very heart of the lasing operation, get the best you can afford and you won't have many problems. Cheap Chinese tubes are often cheap for a reason.

cheers

Dave

[Arjen Abbestee]

Looks good pity it's not available in Amozon Europe. Sending to the Netherlands often costs alnost as much as the device itself...

[Bill George]

Looks good pity it's not available in Amozon Europe. Sending to the Netherlands often costs alnost as much as the device itself...

The tube or power measuring meter?

I think Marco can have the tube drop shipped to you via China if needed.

I had a power supply circuit board for a Samsung flat screen shipped to me via DHL air from Hong Kong to Iowa cost was $25 USD and three days in transit. The tube weighs less than 8 lbs and that's double boxed with lots of packing.

[Arjen Abbestee]

The meter. I'm not decided about a tube yet...

[Dave Sheldrake]

Thermo meters aren't very accurate Arjen, they are in effect a cooking thermometer with a block of aluminium on them.

Have a look at this by Lindsey Wilson (http://imajeenyus.com/optical/20130423_measuring_laser_power_thermally/index.shtml) Lindsey isn't a garage hick with a few tools, he really IS the real thing (It's Dr Lindsay Wilson to use his proper title) and a nice guy with it.

He lists the numbers you would need to perform the calculation as well. Cooking thermometer is about $5 in just about any store and works using the exact same principles.

cheers

Dave

[Arjen Abbestee]

So many good things to learn on the www. This certainly is one of the best recently!
Thanks a lot for this link.

[Arjen Abbestee]

Yes, I'm afraid it is the tube. But finding a replacement is no easy task. Shenhui wants to sell me a new tube only if I take the full risk of breakage during transport. So that's not an option.
I'm in the Netherlands, so buying from the US or Chine does not make much difference in shipping costs. Any recommendations? The current tube is 45W (according to Shenhui), but I would not mind a 60W. There is an opening in the case to accommodate longer tubes. Of course I will also need a new power supply, but I'd rather pay a little more for a good quality combo than replace the tube and find myself in the same situation a year from now...

[Dave Sheldrake]

Try the UK Arjen, we aren't too far away from you?

cheers

Dave

[Arjen Abbestee]

True, any pointers?

BTW, I saw the post about the house you're working on. Wow!