Current Settings for 40 Watt Tube

[Jonathan Bowen]

So I've been digging around for a bit and can't find anything definitive. So I replaced my blown power supply recently and it's capable of powering a 60 watt tube. I set the initial max power in Lasercut 5.3 to emulate similar cutting power/speeds that I'm used to. I procured a descent meter today and did some testing and was shocked to see it was at like 12mA. I hear numbers being tossed around a lot for 22mA-30mA for safe current levels. Does the tube wattage determine the amperage settings or are they all basically the same and a setting of 25mA for max power is good?

This is a production machine so I'd like to get close to full power while staying in the safe operating range. I also can't seem to find a datasheet or anything for the tube. It's a FanHua 40 Watt.

[Jonathan Bowen]

Should a laser tube be losing current during a job? I found some rough numbers of 15mA to 18mA for the tube and have been running at that but it's still not cutting right. I started at about 15.5mA and did a 30 min cut job. The current slowly dropped to about 14.3 by the end of the file. So I set it to 17.5mA and its still not cutting right. Random spots on the table have parts that are not cut correctly. Randomly like the issues I've been having. Focus checks out and so does table height. I suspect the tube is bad but it's only like 6 months old. Really getting cranky with Hurricane right now. I got my power supply from another vendor because they refused to work with me on price and I could get a better one for $200 cheaper. If I have to pay for another tube then I'm going to really blow a gasket. If it is the tube then I suspect it was an issue with the old power supply burning too hot and cooking both of the tubes we have had in it.

[Dave Sheldrake]

16Ma to stay safe Jon, FanHua are just above basic tubes but will cope with the odd overcurrent quite well. It sounds like the tube is getting hot while running, hot spots on the mirror cavity aren't unusual even when the water temp reads good.

It is quite possible the old supply was over driving the tube, if so then the electrodes in the tube errode but that results usually in the drawn current getting higher not lower.

I'd bet on heat, also be worth checking alignment if you are getting bad spots on the table.

Running tubes at higher than factory current will kill them quite quickly as well as generate a LOT of localised heat.Sure you get more power but the tubes just don't last.

cheers

Dave

[Jonathan Bowen]

The spots are random. It's not alignment or focus doing it. It's a power reduction at some point. I'm trying to figure a way to test the input voltage to the 5 volt analog input on the power supply. Just to rule out the controller being a problem.

It does feel like a heating issue but it seems independent of the amount of current I set it for now. I had this same issue in the last tube that hurricane replaced for free under warranty. It would just randomly loss power and get a perforated look to the cut then drop to the point that it doesn't cut all the way through. Right now its looking like the problem is occurring twice during the cut. A dip in power about the middle of the cut and then an increase till it gets towards the end and dips again. Depends on the length of the cut file. I'm really not happy with the problems we have had with this machine from the start.

How do I check for localized heat? Is the tube just going to feel hot in sections when running?

[Pete James]

Jonathan,
I have the same machine that you have. I am not sure what you are cutting or what you mean by perforations, but if you mean small, fairy evenly space ripples along the cut - this is not uncommon and is usually cause by the beam pushing the heated material ahead of it. I do not do as much cutting as you do and certainly no cutting runs that take as long as 30 minutes to complete. However, I have found the best way for me to get a really clean cut is to make 2 passes. I setup so that the 1st cut speed/power will just barely fail to cut the material completely out (but the piece can be forced free) then the 2nd cut finishes the job and smoothes out virtually all irregular edge conditions. My machine will start losing power if the temp approaches 30c. Since my runs are usually short, this rarely happens. If the water temp increases by more than 6 degrees c, there is usually an accompanying gradual loss of power.

[Dave Sheldrake]

Hi Jon,

Hard to check for localised heating in the mirror chamber unless you have access to FLIR equipment? but if you can keep your running water temperature to 16-23 degrees C that may well help. What happens when you get hot spots on the total reflector mirror is the surface changes from flat to a fractional radius, this causes a lot of the photons to scatter outside of the resonator train (basically miss the output coupler) so until the mirror cools you will get hit and miss cutting.

How are you cooling your system?

cheers

Dave

[Jonathan Bowen]

I'm cooling it with a cw-3000. So no control on the temp. I'm talking to Hurricane and hopefully they will replace the tube again. It's about 6 months old and the second tube to be damaged by it. We are suspecting the power supply of over currenting them but that is hard to test as it's been destroyed. I'm also at a loss for the reduction in current over time.

The error doesn't seem to be heat sensitive and I've run it at temps up to 27-30C with the same weird result. Not worse or better. I want to test the input voltage from the controller and make sure it's not fluctuating or over heating. I'm not sure how to hook that up right now. I can't find my alligator clips so I might need to run out and get some.

@Pete This is what I mean by perforations.

https://dl.dropboxusercontent.com/u/61862/2014-01-11%2014.39.36.jpg

It cutting fine and then little holes start to appear till finally it's not making it through the paper. It might still be caused by what you mentioned but it's hard to tell.

At this point I'm hoping for another tube but not holding my breath. I might just upgrade it to a 60W if I have to buy my own tube. I can find them cheaper then Hurricane wants for their 40Ws. I just need to see if I can get the longer side panel somewhere or rig something up. I'm really kicking myself for not getting an Epilog or Trotec. However my company was struggling to get off the ground then. Now I can afford it for the lack of headaches.

[Dave Sheldrake]

That looks like the tube is about to go Jon, called "sputter" usually caused by the trigger wire being loose or the tube about to go pop.

Moving to a 60 won't give much in the way of results so it may be worth looking at a fatbody 80 from EFR or RECI (they are the same length as a narrow 60 watt) Generic tubes can be very hit and miss, one of the dealers I know very well often had batches of cheap tubes come in that were 20% DOA and another 10% gone inside a week.

If you don't mind importing contact Bejing EFR direct, their tubes are only a little below GSI S series for quality but still at very good prices. Last I saw the ZX 80 watt was about $240 FOB. On my DC machines I won't use anything these days other than EFR or GSI as I can't have them unreliable.

cheers

Dave

[Jonathan Bowen]

The only issue with upping to 80 watt is that my power supply that I just bought only does up to 60W :) Speaking of the wires. How do you guys normally attach them to the tube? THe ones that came with it were a mess and when I replaced the tube I pulled them off and they are just loops of copper soldered to the wire and covered with a silicon filled boot. I couldn't get solder to stick to the pegs themselves but I did get it to create a better hold. Is there a better way?

[Dave Sheldrake]

it's not possible to get a true solder joint on the trodes Jon, they are tungsten :( two ways, Croc clips work or the brass cores from chocolate block connectors are also excellent (just don't murder the screws up too tight or you will crack the glass supports) A piece of 3mm wall 16mm diameter silicon tube over the joint will deal with most insulation needs on 40 to 80 watt units.

If your PSU is a 60, check the voltage spec on it, some 60's can be used with 40 watt tubes but some have too high a voltage. (some sellers will tell you they are all the same, then again some sellers will tell you that it's possible to cut 35mm acrylic on a 35 watt laser;))

cheers

Dave

[Jonathan Bowen]

Here are the specs.

Specification


Power (output): 60Watt Max

Triggering Voltage: 26KV
Operating Voltage: 22KV
Current: 26mA Max

Power (input): 110V or 220V (switch selective)
Dimension: 8.5"x7.5'x4"


I got it from here: http://www.lightobject.com/20W-40W-60W-PWM-CO2-Laser-Power-Supply-P72.aspx

I figured I could solder to it and didn't want to really try but I did wrap it tight and then solder it to make a snug joint. I did not however add more calk to it afterwards. It still has the boot that is full of silicon but I never reapplied it so it might not be completely encasing it. I might look at doing that or seeing if I have some of the block connectors laying around the shop.

[Dave Sheldrake]

22Kv T / 15Kv O for Fanhua 40 watts, it will run hot on that supply but so long as you adjust the current to 16Ma max you should be ok.(life will be reduced a little but not by huge amounts) might be good to improve your cooling system though.

cheers

Dave