[shobley]

What's the protocol for verifying a CO2 laser PSU without a tube.

I have a Coletech 80W that's just come out of storage, need to verify it's still good, but have no tube to test with.

Steve

[john-100]

Hi Steve ,

I've not worked with lasers,
but I'd not run the supply without a load to avoid damage to the insulation
a 5W to 10W load could be a good start

if the voltage across a working tube is about 20000 to 25000 volts
you may be able to use a number of high voltage resistors as a dummy load
and use an EHT meter , as used to test the EHT supply to CRT

the EHT probe I have contains a single 8" long 990M ohm resistor

combined with the 10M ohm input resistance of my multimeter , divides the voltage being measured by 100

it so happens in the April edition of EPE magazine one project is for an EHT
probe

EPEMag Online

John

[cinematic2]

Just set anode and cathode cables close to each other (about 10-12mm spacing) and fasten. Far from any metal objects.
Stand aside and switch PSU on for short time. No more than 1-2 sec.
You may check using 50-90% power if you know how to set it.
Or just 100% for short time.
There must be an arc.
Do not worry about the load. Laser PSU can stand few seconds without load.
Do not touch anode cable (red wire) for 10 min after that or connect both cables together before touching.

[Exsecratio]

Just set anode and cathode cables close to each other (about 10-12mm spacing) and fasten. Far from any metal objects.
Stand aside and switch PSU on for short time. No more than 1-2 sec.
You may check using 50-90% power if you know how to set it.
Or just 100% for short time.
There must be an arc.
Do not worry about the load. Laser PSU can stand few seconds without load.
Do not touch anode cable (red wire) for 10 min after that or connect both cables together before touching.

You are kidding right?? Your telling the guy to run a dead short through a 22,000 volt system to test it without a ballast?

[cinematic2]

You are kidding right?? Your telling the guy to run a dead short through a 22,000 volt system to test it without a ballast?

Yes, this is normal way of quick testing DC excited laser PSU.
Of course you must stay away of cables.
The arc is only between anode cable and nearest ground.
Only few centimeters max.
Any real ballast cost more than new laser so nobody uses it.
Arcs are normal things in DC laser machines.
This is not a danger as long as you do not touch cables.
Everyone who works with such lasers knows that.

[Exsecratio]

Absolute and complete crap!

No professional in the laser or electronics industry would suggest running a direct short through an unknown quantity PSU that may or may not be faulty.

Such advice is between ill advised at best to plain bloody stupid at worst.

Such a "test" will only show that voltage is running through it, it won't tell you how much or at what current.

It's like testing grenades by pulling the pins out.

[cinematic2]

Your posts shows that you know nothing about chinese lasers.
Maximal distance between anode cable and ground when arc starts will tell about current. For me will tell everything.
And this is not professional way of testing.
This is immediate way of testing without spending hundreds $ for f... "ballast".
And shobley knows how the current works.
And it looks to me he knows much better than you, "professional".

Electricity and lasers are not a MAGIC.
Some knowledge makes it really easy.

[Exsecratio]

Your posts shows that you know nothing about chinese lasers

It's got nothing to do with Chinese / Russian / German or laser from the planet Zob! it's all about high voltage electric current.

Maximal distance between anode cable and ground when arc starts will tell about current. For me will tell everything.

Again, total crap, even air resistance isn't constant, it depends on humidity levels as a very basic. Gauging current by the distance an arc can jump is like weiging gold using a lolly stick and a packet of peanut M&M's.

And this is not professional way of testing.

We agree there, it's not professional...it's not safe either. You have no idea about the skill level of the chap you are telling to jump his PSU, he could be a university professor or a high school reject with an IQ of 25 and yet you are telling him to do something that could easily end badly for both him and his equipment.

And shobley knows how the current works.

Quite how you deduce that from a couple of lines of text is amazing.

Electricity and lasers are not a MAGIC.
Some knowledge makes it really easy.

Ever heard the saying "A little knowledge is dangerous, a bit more knowledge can be lethal"?

Maybe you can explain in detail the protection circuit in the Chinese power supplies? is it just safe against thermal run away? does it have feedback control? what's the design parameter for earthing in the event of arcing?

Cinematic, this is not the first time you have posted inaccurate or dangerous information. I'd quit while your ahead before somebody gets injured or killed.

[shobley]

Thanks for the replies.

I was looking for some kind of suitable load that I could test with. I don't have any 25K resistors to hand, but I might have some in storage.

From reading the docs it seems like the laser PSU is doing some kind of current/voltage sensing - the initial "strike" voltage is higher than the run voltage.

I'm used to testing neon sign transformers with arcing, but they are internally current limited, just didn't know the best way to verify the laser PSU.

Thanks,
Steve

(Who does know a bit about current, voltage, lasers 'n' stuff ;-) )

[john-100]

Hi Steve ,

I've had a quick look
and high voltage 7 M ohm to 8 M ohm power resistors ( 80W)
are too expensive for a one off test

but a 30 M ohm 20 W resistor made from a number of smaller resitors
could be the answer
e.g. a 30 M ohm , 25W resistor made from 25 X 1M2 resistors looks like a possiblity

MGRF1WJ0125A10 - MULTICOMP - RESISTOR, 1W 5% 1M2 | Farnell United Kingdom

John

[Exsecratio]

(Who does know a bit about current, voltage, lasers 'n' stuff ;-) )

Tweakie's the man for this kind of thing

best wishes

Dave

[Asynchronism]

... while holding each lead in one hand, have a friend power the unit on ...

I right prefer my fancy meters and stuff, but the sparks and electric shock way sounds fun, too.

Having zapped myself a few times without damaging the power supply, I suspect you could safely substitute a large piece of meat for the resistor bank and have a go at that. Maybe a large ham or roast.

Dave

[Exsecratio]

... while holding each lead in one hand, have a friend power the unit on ...

I right prefer my fancy meters and stuff, but the sparks and electric shock way sounds fun, too.

Having zapped myself a few times without damaging the power supply, I suspect you could safely substitute a large piece of meat for the resistor bank and have a go at that. Maybe a large ham or roast.

Dave

all while standing in a bucket of water Dave

[Anthem]

When the Red Anode HT wire deterioates with age they sometimes start to spark through to any metallic ground before it reaches the tubes Anode terminal . This does not seem to do any damage to the supply.

There is a test done to check tube or PSU by Weike
They put a 50mA meter in series with a supplied resistor with the G Weike Lasers. Google Youtube video : Laser tube problem or Laser powersupply problem
The meter here deflects 30 - 40mA. If the power supply is 180W then that means R = P/I**2
For Maximum power
So R = 180 / (30 X 30) Mohm = 0.2 Mohm = 200 kohm (180W)

or 1/2 power out (I think you'd have to put a 5V input pulse with a 50% mark/space ratio into the IN pin on the power supply)
R = 90 / (30 X 30) Mohm = 0.1 Mohm = 100kohm (90W)

This is still quite big, but 10 X 10W resistors with a 10k resistance are easily available and should be linked in series for the 90W option
or 18 X 10W at 12 kohm each linked in series should about make the 200kohm test resistance.

Don't forget to put the 50mA Ammeter on the Cathode HT- side of the wire, since it's voltage is normally 0V relative to ground.

[Anthem]

Additional Info:

The IN could more easily be adjusted using an analogue input using a pot, say 10Kohm linear with sweeper connected to IN and minimum solder tag of the pot wired to G (= 0V) with maximum wired to the other pot solder tag connected to the +5V terminal.

The WEIKE video shows a test button, which my WEIKE power supply does not have. So just wire WP (or P) to G and use a push button or short TL momentarily to ground G. If the pot sweeper is put in the mid position about 50% of the power supply output is available. Should you have a digital PWM signal available to use for the IN rather than analogue signal then this signal requires to be at a frequency of over 20 kHz. They don't specify how much over. I'd set it at 25kHz. Much easier to just use the pot.

Setting everything lower would enable 5W resistors to be used which are cheaper and easily available. It is only a momentary test so even if double the power were to go through the resistors they would not get hot enough to fail. My calculations were based on a powerful 180W supply, but all the values could be changed to suite a lower wattage supply.

[Anthem]

Aha ! Just noticed.

G Weike use a 20K ohm 100W resistor to test their 80W Laser engraver and a 50mA Ammeter. The 20K is thus sufficient for the power supply current limiting to be effective at the 38mA current limit.

[jimmmi]

Aha ! Just noticed.

G Weike use a 20K ohm 100W resistor to test their 80W Laser engraver and a 50mA Ammeter. The 20K is thus sufficient for the power supply current limiting to be effective at the 38mA current limit.

Hello Anthem, still in this thread? I have a question

[jimmmi]

Anyone confirmed what resistor is needed to test laser Power Supply without the laser tube?