View Full Version : Is it safe to run laser tube with lower power supply?

Aras Balali
07-22-2017, 7:23 PM
We recently blow the tube on our laser cutter at our local makerspace. We are looking for option to replace it. The tube was rated as 119W and the power supply is rated for the same tube. We have found a 150W tube nearby, would it be safe to run a 150W tube with a 120W power supply?

Rich Harman
07-22-2017, 9:30 PM
I think it is "safe", as in you won't be increasing risk of injury.

The larger tubes require higher voltages (and current) so your power supply may not be enough. However, it could be that your power supply is appropriate for a range of wattages and depending upon how the tubes are rated, it may fit within spec. Such as your 119W tube - I've never heard of such a thing. Are you going by the test sticker on the tube? It is probably a 100W tube. If so I think it is unlikely that a power supply intended for 100W tubes would work for 150W/130W tubes.

However if you have a 130W watt tube that has been tested at 119W, and the new "150W" tube is actually a 130W tube (like mine) then maybe the power supply is exactly what you need. I doubt it though.

Some people will advertise tubes at their max output because it sounds more impressive. Others will market the exact same tube at the more honest max "recommended" output which is of course a lower number. My tube can be either described as a 150W or a 130W depending on how you look at it. Then of course there will be a sticker on the tube showing what it tested at, which is generally an even higher number.

Dave Sheldrake
07-22-2017, 10:31 PM
the 119 tube is a 100, if the other tube is a 150 (a real 150) then you will kill the psu using it on that tube.It will fire and run but the load on the PSU components will be too much. PSU's run in stages, a 150 watt tube requires a 150 - 180 PSU and will peak at 210 watts output

Joseph Shawa
07-24-2017, 5:53 PM
I just talked with a laser tube company in Ca. They said many people do this. My guess is that it's better than overpowering your tube and as long as you aren't running the amps at max output all the time the PS will be just fine.

Dave Sheldrake
07-24-2017, 8:19 PM
It will kill it, the components in a smaller PSU aren't rated or built to take the strain of running at the top end of their output for any length of time, there's a reason 80 watt PSU's have 2 current stabilisers, 120 watt have 3 and 150 watt have 4

John Lifer
07-24-2017, 8:35 PM
Trying to understand, Dave, if he were to take a 150 watt tube and a 100 watt ps, and run at say 50% max output, would this harm the ps?

Dave Sheldrake
07-24-2017, 9:28 PM
Nope not as such although the voltages are quite a bit different. It's one way some companies try to skin buyers, they fit a standard 80 watt PSU in a 130 watt machine and run the PSU at the top end of it's ability (32mA out of an 80 watt PSU built to max Q at 35 mA) rather than a 150 watt PSU that has a max setting of 50mA.

Chinese PSU's (generally) are built to give just enough for their given size and output and don't have much of a margin built in.

The strike current for a bigger tube is a LOT higher so to get a big tube to fire it still has to strike at a minimum current, that minimum is often above what can safely be obtained from a smaller PSU.

In effect you can *run* the bigger tube but you have no control over the strike current the tube needs to fire and that's what will end up killing the power supply