PWM setting on Chinese lasers

[Vicki Rivrud]

Here is a question for the Chinese laser owners using Lasercut or if you have an answer as well.

The PWM setting on most Chinese lasers reads 20,000 and I was always warned/advised not to adjust this setting as it could damage the machine and/or controller and/or tube.

I am beginning to read here and elsewhere that Chines machine owners are using the PWM setting like the PPI setting adjusting the frequency to act like the PPI setting. AND nowhere am I ready about damage!

What say you??

Vicki

[Rodne Gold]

It does not act like a PPI setting , at least not on ours..its not called PWM (pulse width modulation) in our tube settings but is called frequency..changing it seems to have no effect , however I have not used VERY low values like 150.
I might be wrong , but I don't believe the glass tubes are pulsed anyway, PPI really only works on tubes that are pulsed
On my software , there is a "dot cutting" setting under the cut menu settings which emulates PPI.. IE cuts with "dots" , you can specify interval between dots , power of dots , how big the dot must be etc..actually a lot more powerful than PPI

[walter hofmann]

hi vikci
this all depends on what kind of board you got in your machine. if you got the moshiboard there is nothing what realy makes sence if you change the frequency.
if you got a DSP like the 6515 or the AW608 then the frequency setting could make a big difference, for instance if I wana cut I set the frequency to 15000 if I wana do ordinary engraving then I set it to 18000 and if I do detailed engraving I set it to 24000 my board is a AW608B the best on the marked right now and the software is lasercut V.6.47.
greetings
waltfl

[Vicki Rivrud]

Hi Rodney,
I have the Leetro MPC6515 using Lasercut 5.3 and yes I have used the "hole" setting for paper perforation, rhinestoning & decorative edges.

I haven't figured out how to use this function when cutting acrylic or as in another post here, paper. Although I have been able to achieve some nice cuts with my 150 watt tube I'm always looking to improve.

Thanks
Vicki

[Vicki Rivrud]

Hi Walter,
I have the Leetro 6515 using Lasercut 5.3 . . . I have looked at changing it out with Marco's AW608. I understand that this board specifically calls for a PPI setting as well as a better greyscale engraving.

What is your experience with this board? Did you replace the Leetro board? If so did you have to change out steppers or make any other modifications??

I am still a bit concerned with possible damage to the board,power supply or the tube by midulating the pwm but the more I research the more I am finding others making the frequency change.

I was hoping to hear from someone with the Leetro board.

BTW, where in Naples are you? I'm down in the Ft Myers Beach area alot to see the grand-kids - perhaps I could stop bye sometime??

All the best,
Vicki

[Vicki Rivrud]

I wanted to post the response I received from Leetro in case someone else does a search on this topic. The engineers have explained that the pwm setting is only for radio frequency tubes not CO2 analog tubes. So adjustments to the standard 20,000 pwm setting would have no affect. Furthermore they stated that if an in correct adjustment was set - especially too high, damage could occur to the power supply and/or tube. Well my enquiring mind needed to know :) Vicki

[Greg Holt]

Typical power supply for a glass tube laser has two main basic control inputs.

1. TTL 5v signal that turns the laser on and off.

This can be done very rapidly. Example high speed engraving.

The AWC608 has a PPI feature. Whereby it turns the laser on an off while cutting, to produce a pulsed cutting action. Adjustable and called "Pulse Per Inch"

2. The milliamp output of the laser power supply is controlled in one of two ways:

A. 0 to 5V analogue signal. With 0v signal resulting in zero milliamp power supply output. And 5v resulting in maximum milliamp output. This method is usually used with a manually adjusted potentiometer. (Or Laser Power Dial)

B. PWM or "Pulse Width Modulation", sometimes called "Pulse Duration Modulation". Magnitude being the TTL voltage level (5v). Recommended frequency for my power supply is 20khz. The percentage of "on time" controls the power supply output. 0% resulting in zero milliamp output and 99% resulting in maximum milliamp output. This method is usually used by controllers like the AWC608 etc.

This PWM should not be confused with frequency as it relates to RF excited laser tubes as used in major US made lasers. And neither should PPI.

Usually the PWM signal is smoothed internally by the power supply, with a little circuitry, to reproduce the 0 to 5v analogue signal.

Varying the PWM frequency of a glass tube laser power supply should have no effect on the cutting characteristics. Moving too far away from the recommended frequency, will just destabilise the level of power modulation control, that the laser controller has over the laser power supply.

So if you are adjusting the PWM frequency in the belief that you are legitimately adjusting cutting characteristics, then IMO you are fooling yourself.

Again this is all about DC excited glass tube lasers. Not to be confused with ULS, Trotec, Epilog, etc.

Greolt

[walter hofmann]

hi Vicky
sorry I just did see your respond because somehow the responds does not get back to me.
no I have mostly converted the moshi system machines with the AW608B and I helped many people to convert to the AW608 even if they are not from marco and they all are super happy.
I am in the process of moving to Lehigh acres.
what I write is all for the AW608 there it is proofen that changing the frequency setting gives much better results depending what is done cutting lower frequency or engraving higher frequency not over 25,000.
I am not familiar with your machine but if you got already stepper motors for X and Y axis, a PWM laser power supply and a 24V main powersupply what I assume then you don't need to change anythings else, except maybe two mechanical end switches.
the good part is that marcos AW608 brings real updates to easy implement with a download and believe me it is worth to convert.

greetings
waltfl