Power percentages & maximums query

[Ian Stewart-Koster]

I've read things here and there about so-many-milliamps being right and others being wrong for Chinese tubes.

I finally discovered a PDF file today that belongs to this 130 watt 1300x700 Golden Laser we got not long ago. (Reci tube, I think)

In it is says in Chinese english that if you run it at 100% power too much you'll minimise its expected life by an awful lot.
The book also says the tube is set for maximum 28 milliAmps.

I was running a file this morning, and testing power and speed options, and found that there is an ampmeter beside the tube power supply.
At 99% power, the ammeter read 22 mA.
At 97%, it was 20 mA.
At 92% it dropped to about 18 mA.

My question is that because 99% was using 22 milliamps, which is a fair bit under the 28 mA max listed in the manual, is it Ok for me to use 99%, or 100% power in the software, knowing there is a shortfall off reality and it's not a true expected 28mA 100% ?

I mean 22 mA happening at max power, out of 28 mA expected, is actually a 78% reduction. (or am I over thinkiing things, spoiled by the ULS and American brilliance ;) )

[Dave Sheldrake]

Always go by mA NOT percentage, the story going round the net about percentages being safe (65%) is ignorant rubbish and will kill tubes.

Stay 10% under the tubes maximum operating CURRENT and you will be fine

[John Lifer]

On my system, I can overdrive the 100 watt tube if I were to run at 99%. something around 32 mA. I stay below 28 mA which is supposed to be max continuous. It is about 70% on my scale. It does sound like your power has been turned down most probably in the software, but your power supply may be under rated. And the at the 100% setting the 22mA is all it really will put out. think of the percentage is just a setting with no interrelated scale between machines. One thing for sure is that at this output, your tube is safe!

[Doug Fisher]

FWIW, there was a recent discussion in the Ruida forums suggesting that it is possible to program the controller so that 100% on the controller is actually limited to a maximum safe power threshold (e.g. 100% showing on the display is really 65% of the true output from your power supply) . If true, maybe your manufacturer did this programming already in order to prevent you from being able to overdrive your tube?

[Kev Williams]

that's what I was thinking ^^^

because my Triumph nails a solid 26mA (tops for an 80w tube I believe) when 70& power is entered. I've found that cooler tube water can cause the mA's to raise slightly, so I do watch the meter.

As to the 70% figure, when engraving wood for example, using 35% power is very close to half of the 70% figure, so I just calculate that way..

But, I don't cut much, I mostly engrave, and these meters are useless while engraving ;)

[Ian Stewart-Koster]

Thanks Folks, those answers were the understanding that I was hoping for.

I had an idea there was a potentiometer in the tube PSU that you can tweak - maybe the serviceman the last owner had, did tweak it so it would be impossible to overload the tube to maximum current point.

[Mark Canada]

Very true about the '65% max power' being sheer ignorance. All that matters is current.

Every chinese laser power supply has a hole on the side or next to the terminals you can use to tune the power output. A single power supply module usually works for a range of wattages so it needs to be set by the installer.

Set your max power for what the tube is rated to for max life. Run a several second full power cut in a straight line to watch the current consumption.