Question about mA Meter on Chinese Laser (With Video)

[Matt McCoy]

So I could previously cut through 1/8" plexi at 85% power and 6mm speed. Now I can cut through it at 85% power and 9mm speed. Same piece of plexiglass. I have done nothing since the first cut except for changing the cooling liquid.

That is dramatic. How confident are you that you're conducting this test under the same exact conditions? You mention that you're in an unheated/unconditioned space. For instance, was the original test in the summer after some time messing around on the laser and then your current test was first thing in the morning when it's cool? Did you align or clean your mirrors/lens? Were your numbers really dialed-in? Appreciate you sharing.

So this would back the previous statements that the RV coolant robs some power and conducts some electricity.
By changing to distilled water the tube seem more stable (less arching) and you have a bit more power.

But unfortunately doesn't coincide with the previous two statements by Jerome and Bill.

[Brian Leavitt]

That is dramatic. How confident are you that you're conducting this test under the same exact conditions? You mention that you're in an unheated/unconditioned space. For instance, was the original test in the summer after some time messing around on the laser and then your current test was first thing in the morning when it's cool? Did you align or clean your mirrors/lens? Were your numbers really dialed-in? Appreciate you sharing.

I didn't do anything with the mirrors or lens other than remove one mirror and the lens, measure them, and put them back in.

Both tests were done immediately after turning on the machine for the first time that day and the temperature in my garage at the time of testing was was in the 50's both days. Test one was the night of December 1st. Test two was the night of December 7th. For both tests I cut two 1" x 1" squares out of plexi at each speed setting until it cut all the way through, starting at 10mm/sec and lowering by 1mm/sec for each test. Both times the testing was done around 8:30pm, which is when I usually have a short window of time to get out to the garage.

There was one difference besides the coolant being used that I just thought about. The temperature of the water was probably different. For test one, the RV antifreeze would have been close to the temperature of the garage, so maybe around 55 degrees. For test two the water was probably closer to 65. I don't know if that makes a different or not, but it's the only other variable I can think of.

[David Somers]

Brian....if you are looking for a quick check on the accuracy of your mA meter, do you have a multimeter handy? That will do the same thing for comparison purposes.

[Matt McCoy]

I didn't do anything with the mirrors or lens other than remove one mirror and the lens, measure them, and put them back in.

Both tests were done immediately after turning on the machine for the first time that day and the temperature in my garage at the time of testing was was in the 50's both days. Test one was the night of December 1st. Test two was the night of December 7th. For both tests I cut two 1" x 1" squares out of plexi at each speed setting until it cut all the way through, starting at 10mm/sec and lowering by 1mm/sec for each test. Both times the testing was done around 8:30pm, which is when I usually have a short window of time to get out to the garage.

There was one difference besides the coolant being used that I just thought about. The temperature of the water was probably different. For test one, the RV antifreeze would have been close to the temperature of the garage, so maybe around 55 degrees. For test two the water was probably closer to 65. I don't know if that makes a different or not, but it's the only other variable I can think of.

Cool. Water temp definitely affects cutting on a laser. How much and to what degree it might have had with you, in addition to switching to distilled water, I'll have to defer to someone like Sheldrake, when he swings by. Thanks for the info.

[Kev Williams]

There was one difference besides the coolant being used that I just thought about. The temperature of the water was probably different. For test one, the RV antifreeze would have been close to the temperature of the garage, so maybe around 55 degrees. For test two the water was probably closer to 65. I don't know if that makes a different or not, but it's the only other variable I can think of.

Big fat YES! I'm running an 80w machine with 3000 'radiator' cooler, which means I can watch the temp go up pretty quickly when cutting. With only a 5 degree temp rise, what was a 2 pass cut in 1/8" plastic will require a 3rd pass. I run into this mid-job all the time, where the beginning cuts are great but the ending cuts are .030" light...

you had a 10 degree swing, so that likely had some to do with your testing...

[Brian Leavitt]

OK then I'll do a third test tonight and see what happens. It'll probably be about 10 degrees colder in the garage than it was for either of the other tests. It's 38 degrees outside now and has been that cold or colder since the sun went down yesterday. I'll get a water temp before I start. What is the optimal temperature for the incoming tube water anyways? I see the active chiller on LightObject is supposed to keep it between 64.4 and 86. That seems like a big swing if temperature makes that big of a difference.

If 65 degree water resulted in more power than 55 degree antifreeze, then 45 degree water should be even worse than the first test. I will report back with whatever happens.

[Bill George]

OK then I'll do a third test tonight and see what happens. It'll probably be about 10 degrees colder in the garage than it was for either of the other tests. It's 38 degrees outside now and has been that cold or colder since the sun went down yesterday. I'll get a water temp before I start. What is the optimal temperature for the incoming tube water anyways? I see the active chiller on LightObject is supposed to keep it between 64.4 and 86. That seems like a big swing if temperature makes that big of a difference.

If 65 degree water resulted in more power than 55 degree antifreeze, then 45 degree water should be even worse than the first test. I will report back with whatever happens.

I think you have it backwards. The cooler the water (within limits) the more effective the laser tube operation. Unless your tube has defective glass as much thinner in one area, I don't see how tap water vs distilled water makes any difference. If the power was being magically drained off, the mA meter would show it.

[Kev Williams]

Thanks for the reminder Bill, I forgot to mention this about rising water temps-
as my water temp goes up, my mA meters also read lower. At 70% power and 20c water my mA meter is usually just under 28, but at 25c it's usually at 26. I'm assuming the warm water creates some sort of resistance which shows up on the meter as well as the work--?

[Brian Leavitt]

I know the performance of the tube is reduced if the water gets too warm, but I had warmer water in test two than test one and cutting performance increased, and it was suggested that the water temperature affected the power between the two tests, so from that I deduced that water that is colder than optimal will also reduce power. If that is not true, then the change to distilled water, from antifreeze, is what affected performance.

[Brian Leavitt]

44 degree water and still cut at 9mm/sec and 85% power. It actually cut through at 10mm/sec, but not clean so I don't count it. Changing my optics now.

[Brian Leavitt]

Got the new mirrors and lens installed. Not 100% aligned yet but I was impatient so I ran another test. This time I was able to cut through the same piece of acrylic at 85% power and 21mm/sec speed. As I said - I still need to finish alignment, and I also need to find the optimal focal point (I used the focus "tool" that came with the machine for this test), but I'm happier than a pig in slop. I also made an order from Macken for their 100 watt power probe. This is mostly because I think my X2-600 is losing power, but also to monitor the health of all the laser tubes.

Photo of old mirror vs new mirror. The old lens didn't look too bad, but I don't think it was focusing very well. Couldn't get a very small spot size with it.

[Scott Marquez]

I also made an order from Macken for their 100 watt power probe.

A power meter is worth the money for tracking your tube health, and will also be useful on your other lasers.
I made an acrylic bracket to hold mine in the different parts of the laser path.
http://www.sawmillcreek.org/showthre...r-meters/page4
Keep us informed of your future findings.
Scott

[Brian Leavitt]

Yeah I've been wanting one for a while. I just never pulled the trigger. In the past I have rented one before, but I decided that's just a waste. If I had bought one in the first place, it would have paid for itself by now, avoiding the rental fees. Should be in Friday. Then I'll get a measure on all the machines.

[Dave Sheldrake]

It's not the loss of current that conductive coolant causes, it's destabilisation of the actual plasma it causes leading to a loss of power. It's something I looked into in great depth about 5 years ago when I decided to fill a tube with UV reactive coolant just for giggles and stuck a UV light in the cabinet, it dropped 30% power and the beam profile when measured on a decent quality profiler went all sorts of insane.

[Bill George]

I was thinking it was more like a capacitance effect instead of current flow or voltage arcing. In my Chinese glass tube laser I could not see any difference, RV , automotive anti freeze or plain tap water.