How to tune the power supply to the tube?

I got very little documentation (actually, none…) with my laser, so I don’t know how the power supply is set up compared to the tube. I don’t know if 100% means 100% to the laser, or a safer lower level, or if they didn’t even bother to set it and just went with some default.

So far, I haven’t gone above 60%, due to not knowing if it’s properly set.

Anyone knows if there is some good resource for how to set this properly?

There’s no way to tune it the way you’re meaning as the LPSU is not adjustable.
The best way to make sure you’re not overdriving the tube is to add a 0 - 30mA meter.
This way you won’t exceed the maximum mA rating roughly 15mA for a 35-40W tube in a k40. Once the maximum power is set, the rest of the power control should be configured in the LightBurn software.

What about a 130W tube?

I have no idea. I’m sure Google can help ya though.

Once you have a milliammeter installed and know what the max recommended current is for long life (not absolute max) then you should be able to adjust the power supply via a small trim pot.

On my power supply there is a small hole near the wire connectors, a small screwdriver is used to adjust. On my 130W Reci tube I used 28 mA as the max (I think - don’t recall the actual value) but normally would run at around 26 mA. Before adjusting the power supply, in order to achieve 26 mA I would need to set the power to about 80%. Which means that using 100% would have been overdriving the tube.

You don’t really need to adjust the power supply, as long as you set the power at a level where it does not push too much current through the tube you are okay - to know that you need a milliammeter.

Thanks! I’ll order one right away and check (or, possibly, if I get inspired, hook it up to my multimeter to get it done now…).

Does your multimeter handle tens of thousands of volts? Otherwise I’d avoid.

If you are measuring current, the resistance of the instrument is approximately 0, so there’ll be almost no voltage over the instrument.

If it doesn’t, it cost less than $10. I can get a new one.

I’ve done this and it’s benign - it certainly felt weird hooking up my trusty Radio Shack special to a HV supply, but if you’re measuring at the output side, there’s not enough residual to damage anything.

Current is equal everywhere in a series circuit, voltage however gets used up. There may be tens of thousands of Volts on the input side but on the ground side there is zero Volts. Just make sure you know which side to put the meter.

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I have seen PSupplies that could be adjusted to flatten out at the max ‘safe’ current by the vendor [Bodor]. The tube and PS were Reci, btw. And a Automation Tech laser I bought had a POT to decrease the tube power, altho I did not have time to explore how it worked, that one had a 100w Reci also but a Chinese mystery PS.

Current is equal everywhere in a series circuit, voltage however gets used up. There may be tens of thousands of Volts on the input side but on the ground side there is zero Volts. Just make sure you know which side to put the meter.

Not really used up, it’s more like divided. In this case, where with have an extremely high resistance in the tube, and almost now resistance in the ampmeter, it will be divided so that almsot all the voltage is over the tube. It doesn’t matter which side you put it on.

If you attach the multimeter to the positive side there will be tens of thousands of volts between the multimeter and ground. If you attach to the negative side there will be close to zero.

The voltage dropped across the multimeter will remain the same in either case.

Voltage is not really “divided” in a series circuit, it is dropped (used up) across each element. You can test this by measuring the voltage at various points in a circuit, place one side at ground and probe the other points to see the differences.

Really? “Voltage Divider” is an alternate name for a series circuit in literally every electronics textbook.

And if you place the probes on either side of the element in a series circuit you can see the divided voltage.

If you attach the multimeter to the positive side there will be tens of thousands of volts between the multimeter and ground. If you attach to the negative side there will be close to zero.

True, but you don’t measure to ground, you measure between the tube and the terminal on the PSU. That’s the same regardless of which side you are on, as long as you don’t stick your fingers in there.

The return terminal on the PSU is at ground level. If you install a milliammeter to the positive side of the tube then the electrical potential between the ammeter and the chassis will be at tens of thousands of volts.

Maybe you can make it work, but it is poor practice, and you will find no factories installing the ammeters on the positive side - there is a reason, I’ve tried to explain, perhaps I have failed.

Good luck.

No, you will see the amount of voltage dropped across that element. When you are measuring between two elements and ground then you are effectively “dividing” the voltage; you are measuring at a point where some of the voltage has been dropped (used up) by the upstream elements.

I’ve heard that if you go to the Vendor Settings in RDWorks, you can set the max laser power percentage; my thought is that if I know my tube shouldn’t exceed 25mAh, I can tune it down to have that as the max and then in LightBurn, if I set something to cut at 100%, I can safely know it won’t exceed 25 mAh. Does this sound correct and has anyone done this?

Yes, this is one of the things I have done. If you change power supplies you will need to repeat the process.

If you adjust at the power supply, then if you happen to have two power supplies then you can swap them back and forth with no need for changing settings in the software.

Either way, it is a really good idea to have an ammeter installed, and checking it during operation should be a normal thing.

Mine is, and most of the ones I’ve seen I The last 20 years or so have been,

I’ve yet to find a Chinese laser that isn’t.

From Bell Laser (I have a HY, not Reci, but the process is the same).

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