Power Supply Question...

[Mark Taylor2]

My laser (a Chinese 40W) has a MYJG40W PS. When I go look it up on Google, the specs say 30kV Trigger and 20mA. Which is 60W. Is it that the actual voltage drops after triggering? Or the components aren't rated higher?

I'm thinking of making an upgrade with a 40W tube (820mm long) as opposed to the 32W (730mm, I think). I just cut hardwoods, it's for a hobby and not a business. I'm thinking I add parts a lot cheaper than buying a bigger machine.

Thanks in advance.

[Lee DeRaud]

Does Not Compute: 30kV * 20mA is 600W, not 60W.

In any case, when I looked it up, I saw 23V x 20mA max current (460W). Overcurrent protection cuts in at 130% of max, or 26mA.
(http://www.ecvv.com/product/3458558.html It's listed as a "40W Laser Power Supply", but it is not a 40W power supply.)

[Scott Marquez]

There are a few places to buy laser tubes from, just ask them to sell you the appropriate power supply for that tube.
Scott

[Dan Hintz]

My laser (a Chinese 40W) has a MYJG40W PS. When I go look it up on Google, the specs say 30kV Trigger and 20mA. Which is 60W. Is it that the actual voltage drops after triggering?

Yes, but not enough to meet those numbers. The strike voltage may be 30kV, but the running voltage will drop down to around 20kV+. As Lee said, the running power is significantly more than 60W. You definitely want to size your supply to the tube you plan to use, particularly the strike voltage. Too high of a strike voltage will burn out a small tube, and too low will not reliably lase (if it lases at all).

[Dave Sheldrake]

40 watt 55mm diameter tube = 16mA MAX run current

[Mark Taylor2]

That's weird.. I had to recheck my math and a missed decimal point.. that is 600W at trigger and 400 at run.. WTF? I'm assuming the Chinese screwed up the conversion on the mA or there's something else amiss. The various sales droids I've talked to insist these numbers are correct for a 40W supply and as the links in the next para down, are right for the tube.

I'm looking at one of these tubes: http://www.lightobject.com/SPT-850mm-CO2-Sealed-Laser-Tube-40W-P977.aspx http://www.lightobject.com/SP-45W-CO2-Sealed-Laser-Tube-1M-P751.aspx Their figures seem to be off also. I can fit the 45W with a minor mod to the mounts. I know I'll have to put a housing extender. I'm just debating on the Power Supply. I'd rather give the longer 40W a shot as right now I have the 720mm tube. All things considered, I'd rather have more than what I need then less.

I tested with what I have (the 720mm tube) and 16mA seems to be the max... running the amperage above that (per the meter and assuming it's correct) doesn't get the cut any deeper just wider at the top so I'm probably overpowering the tube. Not a good thing. I'm testing with 1/4" thick Castello Boxwood. I also don't see an improvement in depth if I cut at 12mA instead of 16mA.

I'm really hating talking to the sales droids.. Luckily, I'm under no pressure as I'm not needing the 1/4" wood until the next project, but why wait until I need it. :) OTOH, if I win the lottery... there will be a bigger and hopefully better machine.

Sorry for being disjointed in my approach... I'm just very puzzled.

[Bert Kemp]

Laser tube (40W): (Length=1010mm, Diameter=51mm)
Expected Life: 2000+ hours
Laser Tube, 40 Watt (48 Watts MAX, 40 Watts


That's weird.. I had to recheck my math and a missed decimal point.. that is 600W at trigger and 400 at run.. WTF? I'm assuming the Chinese screwed up the conversion on the mA or there's something else amiss. The various sales droids I've talked to insist these numbers are correct for a 40W supply and as the links in the next para down, are right for the tube.

I'm looking at one of these tubes: http://www.lightobject.com/SPT-850mm-CO2-Sealed-Laser-Tube-40W-P977.aspx http://www.lightobject.com/SP-45W-CO2-Sealed-Laser-Tube-1M-P751.aspx Their figures seem to be off also. I can fit the 45W with a minor mod to the mounts. I know I'll have to put a housing extender. I'm just debating on the Power Supply. I'd rather give the longer 40W a shot as right now I have the 720mm tube. All things considered, I'd rather have more than what I need then less.

I tested with what I have (the 720mm tube) and 16mA seems to be the max... running the amperage above that (per the meter and assuming it's correct) doesn't get the cut any deeper just wider at the top so I'm probably overpowering the tube. Not a good thing. I'm testing with 1/4" thick Castello Boxwood. I also don't see an improvement in depth if I cut at 12mA instead of 16mA.

I'm really hating talking to the sales droids.. Luckily, I'm under no pressure as I'm not needing the 1/4" wood until the next project, but why wait until I need it. :) OTOH, if I win the lottery... there will be a bigger and hopefully better machine.

Sorry for being disjointed in my approach... I'm just very puzzled.

[Dave Sheldrake]

Efficiency fellas, DC pipes pump 10 - 12% of input ;)

[Lee DeRaud]

That's weird.. I had to recheck my math and a missed decimal point.. that is 600W at trigger and 400 at run.. WTF? I'm assuming the Chinese screwed up the conversion on the mA or there's something else amiss. The various sales droids I've talked to insist these numbers are correct for a 40W supply and as the links in the next para down, are right for the tube.I suspect when they say "40W Laser Power Supply", they mean "Power Supply for 40W Laser Tube".

I don't recall the efficiency specs for laser tubes in general, but they're quite low. My ULS 25W has a 500W (48V, 10.3A) power supply for both the laser and the motion system, and the steppers for the X and Y axes are probably only pulling about 1A each, leaving ~350W to run the 25W tube. (In my case, "tube" includes a big cooling fan and the internal high-voltage supply.)

[EDIT: thanks, Dave, kept me from having to look it up. :-)]

[Bill George]

That's weird.. I had to recheck my math and a missed decimal point.. that is 600W at trigger and 400 at run.. WTF? I'm assuming the Chinese screwed up the conversion on the mA or there's something else amiss. The various sales droids I've talked to insist these numbers are correct for a 40W supply and as the links in the next para down, are right for the tube.

I'm looking at one of these tubes: http://www.lightobject.com/SPT-850mm-CO2-Sealed-Laser-Tube-40W-P977.aspx http://www.lightobject.com/SP-45W-CO2-Sealed-Laser-Tube-1M-P751.aspx Their figures seem to be off also. I can fit the 45W with a minor mod to the mounts. I know I'll have to put a housing extender. I'm just debating on the Power Supply. I'd rather give the longer 40W a shot as right now I have the 720mm tube. All things considered, I'd rather have more than what I need then less.

I tested with what I have (the 720mm tube) and 16mA seems to be the max... running the amperage above that (per the meter and assuming it's correct) doesn't get the cut any deeper just wider at the top so I'm probably overpowering the tube. Not a good thing. I'm testing with 1/4" thick Castello Boxwood. I also don't see an improvement in depth if I cut at 12mA instead of 16mA.

I'm really hating talking to the sales droids.. Luckily, I'm under no pressure as I'm not needing the 1/4" wood until the next project, but why wait until I need it. :) OTOH, if I win the lottery... there will be a bigger and hopefully better machine.

Sorry for being disjointed in my approach... I'm just very puzzled.

I have dealt with Lightobject on a couple different items. they have always been fair and the specs they publish are correct. One was a laser tube. Don't buy or make the extender for the tube until you get it, my new tube was a tad under the 850 mm and it went in just fine. My old 40 watt supply worked fine. The OEM tube was sold as 35 watts, agreed watts was 32 as marked on the label. The new tube worked great.

[Mark Taylor2]

Dooh..... yer right. DC efficiency is "different"..324321 Thanks Dave, for the head slap. Been too long for me on the electronics and all the calculations. Thanks for setting me straight. I think Lee hit it with "it's for a 40W tube". Ok.. that I can work with.

Thanks Bill... I'll recheck the space before ordering. I was looking hard and there's a thread over there about using the 45W with a 40W supply but holding the power down to 90% of max along with some other pitfalls. So I'll continue to give this some thought as there's no rush at this point.

[Dave Sheldrake]

The underside has a Pot on it Mark,do the usual output mA test and adjust the pot down. The difference between a 40 watt and a 60 watt on voltage isn't enough to worry about :)

[Bill George]

I don't think anyone runs at 100% anyway.

[Mark Taylor2]

Thanks Dave. I wondered where that adjustment was.

Bill, as I understand, doing so kills the tube life.

[Dave Sheldrake]

So long as the PSU pot is adjusted to stay within the tube maximum it's safe to run at 100%, thing is most chinese supplies aren't that stable (the cheaper ones anyways) so over current is always a risk , the 90% rule is to keep the tube ticking over at a safe(ish) margin from Max in the event the PSU is badly adjusted

[Mark Taylor2]

Thanks again, Dave. That makes sense given the nature of these things and the uneven quality control. I'm going to tweak that pot today for the tube I have just in case.