Power % to mA

1n2
Posts: 113
Joined: Tue Jan 29, 2013 10:46 am

Power % to mA

Postby 1n2 » Wed Feb 20, 2013 8:50 am

Hiya people

Having successfully updated my cheapo laser I set about working out what % setting on the power equates to what mA.
I started at 50% which seems to equate to 11/12 mA... it was at this point my Milliamp meter decided to die (typical :roll: )
Has anyone made such a chart? just to put me in the ball park, or for more help, what would (roughly) the power % be for 17mA (ie full power)
As I read you can "overpower" the laser and cause damage (although this would seem a bit silly as for a power supply designed for a 40 watt tube surely would not allow the tube to be fritzed?)

Thanks

John

aram
Posts: 12
Joined: Wed Jan 16, 2013 12:14 pm

Re: Power % to mA

Postby aram » Wed Feb 20, 2013 9:47 am

Hey John,

I'd be interested in the answer to this question as well. If you're running the PWM power supply from lightobject (http://www.lightobject.com/40W-PWM-CO2- ... y-P71.aspx), the specs are as follows:
Power: 40Watt
Triggering Voltage: 25KV
Operating Voltage: 22KV
Current: 18~20mA

according to the specs for the replacement lightobject sells, the tube specs for the k40 are:
Power: 40W (45W peak)
Triggering Voltage: 20KV
Operating Voltage: 15KV
Current: 16~18mA.

It seems to me that the power supply is not designed for a 40w laser, per se. It falls into the correct power output range for one, and therefore is appropriate to use, but can, if set incorrectly, overpower the tube.

If the power supply puts out 18-20mA, 90% would never be over 18mA. However, 90% puts it at about 19.8KV operating voltage, and the tube is rated at only 15KV operating voltage, but in that particular set up we still only have aprox. 34 watts. We've set ours to 68% max (15KV is 68% of 22KV), just to stay safe. The problem with this set up is that we're actually only getting 19.5 watts out of a 40 watt machine.

This is the part I have no real understanding of. I can do the math and figure out what the numbers are, but I don't really know what they mean. My knowledge of electronics is pretty limited. So maybe someone can take the info I've put out and make a good analysis of it and what it means for adjusting the power to operate safely and get the best performance out of the machine.

Tech_Marco
Posts: 4328
Joined: Mon Jun 15, 2009 3:00 pm

Re: Power % to mA

Postby Tech_Marco » Wed Feb 20, 2013 11:53 am

There is no way you can control the high voltage from 20kv to 15kv. The goal is not to limit the voltage but the current. Use a current meter say 0-50mA or 0-100mA will do the job

Marco

1n2
Posts: 113
Joined: Tue Jan 29, 2013 10:46 am

Re: Power % to mA

Postby 1n2 » Wed Feb 20, 2013 12:05 pm

Tech_Marco wrote:There is no way you can control the high voltage from 20kv to 15kv. The goal is not to limit the voltage but the current. Use a current meter say 0-50mA or 0-100mA will do the job

Marco

LOL I was until it decided to show full power (20 mA) at a setting so low the laser wasnt firing

1n2
Posts: 113
Joined: Tue Jan 29, 2013 10:46 am

Re: Power % to mA

Postby 1n2 » Wed Feb 20, 2013 12:09 pm

aram wrote:Hey John,

I'd be interested in the answer to this question as well. If you're running the PWM power supply from lightobject (http://www.lightobject.com/40W-PWM-CO2- ... y-P71.aspx), the specs are as follows:
Power: 40Watt
Triggering Voltage: 25KV
Operating Voltage: 22KV
Current: 18~20mA

according to the specs for the replacement lightobject sells, the tube specs for the k40 are:
Power: 40W (45W peak)
Triggering Voltage: 20KV
Operating Voltage: 15KV
Current: 16~18mA.

It seems to me that the power supply is not designed for a 40w laser, per se. It falls into the correct power output range for one, and therefore is appropriate to use, but can, if set incorrectly, overpower the tube.

If the power supply puts out 18-20mA, 90% would never be over 18mA. However, 90% puts it at about 19.8KV operating voltage, and the tube is rated at only 15KV operating voltage, but in that particular set up we still only have aprox. 34 watts. We've set ours to 68% max (15KV is 68% of 22KV), just to stay safe. The problem with this set up is that we're actually only getting 19.5 watts out of a 40 watt machine.

This is the part I have no real understanding of. I can do the math and figure out what the numbers are, but I don't really know what they mean. My knowledge of electronics is pretty limited. So maybe someone can take the info I've put out and make a good analysis of it and what it means for adjusting the power to operate safely and get the best performance out of the machine.


strange thing is I utilised the milliamp meter in my digital multi meter but it really didn't like it......showing meaningless results.
I have a dedicated digital meter coming I will make a chart up ..ok it wont be the same for everyone but it will get us in the ball park...maybe...but the way my luck is going LOL :roll:

John

Tech_Marco
Posts: 4328
Joined: Mon Jun 15, 2009 3:00 pm

Re: Power % to mA

Postby Tech_Marco » Wed Feb 20, 2013 12:13 pm

It looks like that you have feedback issue. Make sure to power the current meter from an isolated power sources. Also, make sure it's connect to the negative side, not the HV or it will blow the meter.

Marco

1n2
Posts: 113
Joined: Tue Jan 29, 2013 10:46 am

Re: Power % to mA

Postby 1n2 » Wed Feb 20, 2013 1:36 pm

Tech_Marco wrote:It looks like that you have feedback issue. Make sure to power the current meter from an isolated power sources. Also, make sure it's connect to the negative side, not the HV or it will blow the meter.

Marco

thanks Marco
I am sure the meter was connected correctly on the neg side...I think it was the meter I had thrown it away and retrieved it for the purpose of the experiment!

will report further when I have a known to work ammeter...

John

waltfl
Posts: 674
Joined: Thu Sep 08, 2011 5:29 am

Re: Power % to mA

Postby waltfl » Wed Feb 20, 2013 1:41 pm

maybe I tell you my story,
I believe after conversion with all of marcos part that the DSP would protect the current to be at settings of 95% max 18maand I tell you what a surprise that the current at 70% pn cutting at 5mm/s was allready more then 23mA.
and then I made my own max settings up what is around 48% for 16mA. but sometimes even with this setting I get more then 20mA.
just my experience
greetings
waltfl



1n2 wrote:
aram wrote:Hey John,

I'd be interested in the answer to this question as well. If you're running the PWM power supply from lightobject (http://www.lightobject.com/40W-PWM-CO2- ... y-P71.aspx), the specs are as follows:
Power: 40Watt
Triggering Voltage: 25KV
Operating Voltage: 22KV
Current: 18~20mA

according to the specs for the replacement lightobject sells, the tube specs for the k40 are:
Power: 40W (45W peak)
Triggering Voltage: 20KV
Operating Voltage: 15KV
Current: 16~18mA.

It seems to me that the power supply is not designed for a 40w laser, per se. It falls into the correct power output range for one, and therefore is appropriate to use, but can, if set incorrectly, overpower the tube.

If the power supply puts out 18-20mA, 90% would never be over 18mA. However, 90% puts it at about 19.8KV operating voltage, and the tube is rated at only 15KV operating voltage, but in that particular set up we still only have aprox. 34 watts. We've set ours to 68% max (15KV is 68% of 22KV), just to stay safe. The problem with this set up is that we're actually only getting 19.5 watts out of a 40 watt machine.

This is the part I have no real understanding of. I can do the math and figure out what the numbers are, but I don't really know what they mean. My knowledge of electronics is pretty limited. So maybe someone can take the info I've put out and make a good analysis of it and what it means for adjusting the power to operate safely and get the best performance out of the machine.


strange thing is I utilised the milliamp meter in my digital multi meter but it really didn't like it......showing meaningless results.
I have a dedicated digital meter coming I will make a chart up ..ok it wont be the same for everyone but it will get us in the ball park...maybe...but the way my luck is going LOL :roll:

John

daveman
Posts: 15
Joined: Wed Jan 09, 2013 10:07 am
Location: Frankfort, Kentucky

Re: Power % to mA

Postby daveman » Wed Feb 20, 2013 6:32 pm

waltfl wrote:maybe I tell you my story,
I believe after conversion with all of marcos part that the DSP would protect the current to be at settings of 95% max 18maand I tell you what a surprise that the current at 70% pn cutting at 5mm/s was allready more then 23mA.
and then I made my own max settings up what is around 48% for 16mA. but sometimes even with this setting I get more then 20mA.
just my experience
greetings
waltfl



I believe that there is quite a bit of randomness when it comes to the quality control around these inexpensive (I won't say cheap because after all the mods I have done to mine, I don't consider it cheap anymore :) ). Here is my experience, I never drive mine above 60% and it stays between 16-17mA consitently on straight cuts. I don't want to push the tube to far and honestly most work I have done with it never needs more than 35%. The bigest stuff that I have cut though is 5mm acrylic which cuts well for me at 3mm/s at 35%. What I have seen from other posts though is that what may yield 16-17mA on mine will prove quite different on someone elses machine with the very same power supply.

My thought on why the power supply can over drive the tube is that they are probably not truly matched in all reality. Your power supply can drive a 40W tube, unfortunately these inexpensive "40W" lasers don't actually have a 40W tube in them. I think Marco has also indicated here in other posts that the tube is more along the 30-35W range. This makes sense based on what I have researched. The length of the tube is directly proportional to power output. For example 80W = 1600mm, 60W = 1200mm, true 40W = 850mm, these laser tubes are only 700mm which kind of confirms for me what Marco has said.

aram
Posts: 12
Joined: Wed Jan 16, 2013 12:14 pm

Re: Power % to mA

Postby aram » Wed Feb 20, 2013 10:28 pm

So if i understand this correctly, the voltage is a constant at 22KV operating voltage isfrom the power supply, and the only thing adjusted by limiting the power in the manufacturer parameters is the amperage?

1n2
Posts: 113
Joined: Tue Jan 29, 2013 10:46 am

Re: Power % to mA

Postby 1n2 » Wed Feb 20, 2013 11:50 pm

daveman wrote:
For example 80W = 1600mm, 60W = 1200mm, true 40W = 850mm, these laser tubes are only 700mm which kind of confirms for me what Marco has said.


Looks like the next mod is a hole in the end so a longer tube can stick out :lol:

I agree that there must be LOTS of non uniformity I was showing 12mA ay 50%.

John

waltfl
Posts: 674
Joined: Thu Sep 08, 2011 5:29 am

Re: Power % to mA

Postby waltfl » Thu Feb 21, 2013 2:31 am

maybe some other point of experience I did find out setting the PWM frequecy to 16,000 instead of 20,000 gives a much more consistend, stable and more cutting power. By the way in regards to longer tubes a friend of mine did it he cut a square hole in the housing and made a cover with some selfcutting screws and put a 850mm tube in it and after his tests the cutting power is pretty much doubled on plywood.
greetings
walt



1n2 wrote:
daveman wrote:
For example 80W = 1600mm, 60W = 1200mm, true 40W = 850mm, these laser tubes are only 700mm which kind of confirms for me what Marco has said.


Looks like the next mod is a hole in the end so a longer tube can stick out :lol:

I agree that there must be LOTS of non uniformity I was showing 12mA ay 50%.

John


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