Chinese tube trigger voltage built into power supplies?

[Joe Walmer]

Reading up on the Chinese tubes and power supplies I am assuming the power supplies themselves take care of the triggering voltage each time it fires internally?

[Rich Harman]

Reading up on the Chinese tubes and power supplies I am assuming the power supplies themselves take care of the triggering voltage each time it fires internally?

My guess is that since the power supply is only controlled via a pwm signal that it is up to the controller to send the correct signals to the power supply. I don't think the power supply "decides" the voltage, other than it is making whatever voltage it is capable of. I think this is why you cannot use a 150W power supply on an 80W tube - even if you limit power. The voltage is just wrong.

In the vendor settings area there are several options for specifying the way in which the laser is fired. It makes sense that the mainboard is handling the timing and amplitude of the triggering.

[Joe Walmer]

Yes but there is a 5v signal to tun the laser on and off then an analog 5v that can be pmw or controlled with a potentiometer but that pmw is still converted to an analog signal. So a potentiometer is not capable of saying for at 100% then real fast 84% or what ever the ratio is for the operating voltage is. If you have pmw also then you would have to say 100% is the trigger voltage and 84% operating etc but then using it at low power wouldn't work because you run out of room. I think it must be handled internally because otherwise the k40 lasers that are adjusted with a potentiometer straight to the laser wouldn't be able to do it.

If you were going to use a pwm signal it would be turing it on and off for engraving at different ppi etc.

[Rich Harman]

Yes but there is a 5v signal to tun the laser on and off then an analog 5v that can be pmw or controlled with a potentiometer but that pmw is still converted to an analog signal... If you have pmw also then you would have to say 100% is the trigger voltage and 84% operating etc but then using it at low power wouldn't work because you run out of room.

On mine there is only the one signal line. There is a potentiometer used for adjusting the power supply but it is not used for varying the power. Not sure how the K40 is set up. Are you saying that there are two signal lines coming from the mainboard to the power supply? One to turn on/off the beam and another to set power?

There are many ways it could work. Don't know which, if any, is the correct way. Could be that 100% is always the trigger voltage and 0 to 90% is working voltage - so you would never run out of room. Could be a cap in the power supply that dumps the extra current needed each time it is switched.

A way to find out would be to put a logic analyzer on the signal line, if there is no variation to the signal then you know that the power supply is handling the trigger voltage.

[Joe Walmer]

The way most power supplies work is there is a 5v ttl signal either low or high terminals to trigger the laser to fire. there is an analog 5v terminal that can be shorted to 5v for full power and you can hook up a pot to it by its own 5v- 5v+ and the 5v analog read is the wiper or middle pin on a pot. That is just turning the 0-5v analog read for 0-100% laser power. pwm this with 5v from an arduino or control board at the recommended frequency and the power supply converts that into a 5v analog signal to be read in the end.

I will definitely hook up my scope when I get a tube. I just got a 4 channel rigol ds1054 for $399 and its great. I actually plan on having a cheap graphic lcd based equalizer built into one of my future lasers I already have a nice https://www.matrixorbital.com/ display and will use at least one external arduino (Yun) to run all that stuff and let the control board handle only stepper and laser commands. I cut acrylic at one size/power/speed etc. so it will handle the laser power also as to not waste cpu cylces for pwm interrupts.

The lack of trigger voltage settings in laser firmwares I have been looking into and the way I have seen all the instruction booklets is there is an internal circuit that has a very fast discharge before each firing automatically. That is why these power supplies are somewhat specialized I imagine and the stories of people trying to make their own don't turn out well.

How many mm/sec are you doing to cut say 1/8 acrylic with that 160watt tube? do you have to turn down the power?

[Joe Walmer]

I pretty much found out its just like a neon sign power supply and it has an auto trigger voltage. Found it on Sams laser FAQ and a few other places. I just wanted to be able to test a laser when I get one and make sure its not overpowered hyped tube and make sure is not firing at 34mA etc. like some stories I have heard.

[Keith Colson]

Laser power supplies are a "constant current power supply", the voltage rises quickly until the current (mA) is reached. The trigger voltage is variable and is not important so long as your system in the ballpark. The voltage will vary depending on the current you set. You can put a resistor in place of the tube if you wish to adjust the power supply before connecting it to the laser tube.

Cheers
Keith