View Full Version : Can I use a 40w PSU with a 50w tube ?

12-07-2014, 10:35 AM
Can I use a 40w PSU with a 50w tube

I went for the 50w machine, as it seemed a good deal.

It stopped working.

I am noticing 40w spec's are almost identical, but MUCH cheaper !

So, I need to find out if it's the tube or supply that is broken.

Can I buy a 40wPSU and use it with the 50w tube ?
Then if it doesn't work, I will buy a 40w tube.

Also in the future, the 40w will be cheaper each time I need to replace the tube (or supply)

I plan on using the poor little machine, all day every day, once it's working again.

Thanks in advance for any advice :)


Robin Hewitt
12-07-2014, 11:05 AM
If you want the tube to last a long time, you run it below it's max power and keep it cold.
The sensible lower limit on cold is somewhere safely above the dew point because condensation and 25kV don't mix.
I do not think there is a sensible lower limit on power to extend tube life but...
Are we mice or men?

12-07-2014, 11:14 AM
so, is that a round about way of saying it will work ? lol !

I was running it at 70-80% and 15-20DegC

Do they need 'rests' ? since looking in to it, one source said about their machine to rest it for 30 mins every 2-3 hrs cutting ?

12-07-2014, 12:14 PM
It probably is...
In general if you have a device which requires 50W, but you're only using 70-80% (i.e. 35-40W) then you're operating within the rating of the power supply. So unless there's some other rating in the PSU that changes, it's fine.

Edit: Regarding rests, if you're talking about the laser then if it's just a thermal thing then switching off for 30mins every 3h is the same as running continuously at 83% power... which appears to be the case for you anyway.

12-07-2014, 12:50 PM
Yes, Jonathan, I'd usually agree with your logic.

However, this is how I understand it so far, the tubes have a recommended trigger and running voltage. The power is controlled by PWM, so the voltage doesn't change for a tube and PSU pair. But higher and lower power tubes require a matched PSU. The tube lengths are specific to each power level. The 40w and 50w seem to be very close, so I am assuming it will be ok. (you know what ASSUME means ! ).

I wondered if a lower trigger and working voltage in the 40w PSU would be enough to run the 50w tube ... think, putting a small engine in a big car ! ... if it does manage to fire the laser .. might it shorten the life of the PSU ?

Just picking brains, before I try it anyway ! lol

unless , of course, anyone has a valid reason why I shouldn't :)

16-07-2014, 09:15 PM
OK .. short answer is yes :)

My K3020 arrived today ... with a dead tube :(
but !
I wired up the PSU to my 50w tube and it fired up ok :)

I've ordered a 40w PSU 60 inc post ... and will report back further, when I test it.

25-07-2014, 10:35 PM
PSU 2 died today
PSU3 fitted today (another 40w)
PSU4 ordered (60w)

30mA panel meter hooked up to keep an eye on things !

26-07-2014, 09:19 PM
cut a full day ... no problems ..

obsevations ..

added a mA panel meter to observe tube power output .. stayed constant at 18mA throughout

PSU transistors were getting hot to the touch
Took side panel off the machine and pointed desk fan at it ... stayed cool
Will add extra cooling permanently :)

will keep you updated :)

29-07-2014, 09:20 PM
another update ... 40w suply worked ok, the short time it was installed.... and will keep as a backup :)

Fitted the 60w PSU that arrived yesterday ... very impressed with it ... fro Cole-Tech ... ordered fri, arrived Mon, and looks like a decent bit of kit ! :)

1st test output 25 odd mA ... so had to reduce output to 63% to get a safe 20mA (Which I guess , in theory is the max I should push through ? )

done several hours with it so far ... it's cutting approx 40% faster than the original PSU (but I didn't have a mA meter hooked up) ... so all goo so far :)

all happy here :)