Ma readings.. Need help with analysis

[Pete Cyr]

Ma readings.. Need help with analysis
Quote
Post by Rich Decatur » Sun May 14, 2017 1:24 am

Ok, so i got my ammeter installed today.
I did power readings at 10, 11, 13, 15 and then in 5% increments thereafter.
What i saw was 100% repeatable. Unexpected but repeatable.
The only thing i can think is that it is in some form of pre-ionization phase before a coherent beam is created.

Laser%20Power.JPG

So the 2 questions that come from this are:
1. Is my assessment of the spike at 13% accurate? if not what is it.
2. If this is truly a 40 watt laser (only identifying marks on the tube state 800, which i assume to be mm) what is the max opperating current? I'm hesitant to go above about 14ma.

Thanks in advance to all.

-Rich

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Post by Pete Cyr » Sun May 14, 2017 9:34 am

I would say you power supply has issues at power below 25%pwr and or you are at the limit of your tubes capability.
Assuming you have a 50w system 25% pwr = 12.5w
Assuming you have a 40w system 25% pwr = 10w
Somewhere between 8w-10w output is pretty typical as a minimum output for many systems
I think a better test would be re-performing the testing you documented above pulsing for 2sec into a piece of acrylic. That will show you your useful power range in a real world example that can be compared and measured.

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Post by Dave gomez » Sun May 14, 2017 11:40 am

From Russ's stuff, he showed curves that where flattening paired with simple line tests in acrylic to show where your peak laser power is, i don't think your there yet.

Also the early ma peak maybe the transition point of when active lasing occurs, the Florida video where his companion talks show around that point voltage spikes hard to get over the hump, then it settles back down, and probably affects current draw. I thought I remember that at 10% power or lower, not much lasing going on.
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Post by Dave Kearley » Sun May 14, 2017 2:47 pm

My 50W will not fire below 11%

I'll be doing some curves soon, interesting stuff.
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Post by Kevin Johnson » Sun May 14, 2017 4:13 pm

Just to add my 2 cents worth - my 50W fires at 13%, won't fire at 12%. It all depends on your tube / power supply combination.

Edit: and my tube draws 18mA when set to 74%.
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Post by Rich Decatur » Sun May 14, 2017 5:40 pm

Thanks for the replies.
It gives me some things to work out. I'll need to order some thick acrylic first however.
For clarification, my laser does not fire at 10% but does at 11.

Pete, I need some clarification from your statement. Sadly i don't understand it.

"or you are at the limit of your tubes capability"

I've had the machine for 4 days. Are you saying that it's going bad?
If not, at what point on the graph do you see this happening, and how did you come to the conclusion. I'm obviously not getting something, which is very likely since this is a new world to me.
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Post by Robert Johnson » Sun May 14, 2017 6:06 pm

I'm going to speculate that he's saying you haven't yet seen the peak in your power curve as it is still climbing on the right. What is the max recommended operating current? Is it the 15mA where you stopped?

Here's the info you're looking for: viewtopic.php?f=104&t=3479
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Post by Rich Decatur » Sun May 14, 2017 6:50 pm

Thanks Robert. That is the data i was looking for. I'll finish out the data until i get to 18ma. Though i still may run it a bit lower because im paranoid and want to extend the life of the tube as much as possible
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Post by Pete Cyr » Sun May 14, 2017 8:04 pm

I don't think anything is wrong.
All equipment has min and max capability. Your data indicates you system's minimum capability to out put a laser beam is around 10w-12w.
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Post by Mike Audleman » Thu May 18, 2017 10:56 pm

I had time to build up my chart tonight. I took 10 readings at each point. Threw out the highest and lowest and averaged the remaining 8 points.
Here is the spreadsheet:
https://docs.google.com/spreadsheets/d/ ... edit#gid=0

Laser Tube mA vs % Power - Sheet1.pdf

For my readings, I took 10 samples at each power level. I discarded the highest and lowest reading and averaged the remaining 8 for that data point.

It doesn't look too far off from your chart. Shape wise anyway. However my lower peak is at about 20% not your 13% and its not as drastic as your 9.5ma.

Your 9.5ma is on parallel to approximately 48% on your chart. My peak at 4.68 is on parallel to approximately my 33%.

My tube is an 800mm from ebay labeled as 50w. However, given what I have been informed (there are no 50w tubes), I have limited my everyday use to 74% or approximately where 14ma occurs. With brief exceptions such as exploring the 74-85% with brief pulses to get readings for my chart.

The interesting thing here is that my pre-ionization area ends almost exactly where yours does. 25%. Go figure.