Newer 60W power supply went "bang" - now what?

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audiomath
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Newer 60W power supply went "bang" - now what?

Post by audiomath »

Hello,

I bought a 60W "Jupiter" branded power supply from LightObject 12/7 , and have since put perhaps 2-3 hours on it. Several nights ago I was running a job cutting 3mm acrylic @ 60% power. The supply made a loud "crack" sound and blew the mains fuse.

I had a spare (much smaller physically) supply from another vendor in the shop, also supposedly 60W, so this Saturday I replaced it. The machine is running fine now, although the new "spare" supply won't quite reach 22mA with the power set to 100%. (I normally don't run a 60W tube over 20mA, this was a test)

The reason I bring this up here instead of just contacting LightObject for warranty is because although the spare supply won't quite reach expected current, tests at different power levels show that the current tracks the power level much better than the Jupiter supply. For example, The spare supply runs 20mA @ 100% power, and 10mA @ 50% power. The Jupiter supply ran 22mA @ 100% power, roughly 15mA @ 50% power and roughly 10mA @ 25% power. The tube would also stop lasing below 15% power with the Jupiter supply, but I haven't tried that yet with the spare.

My question is: Is it normal for the Jupiter supply to be so non-linear in the output? It seems to be much better designed and built than the (cheap) spare supply I have installed now, but it did fail and the PWM duty cycle "power" vs output current is skewed toward the top.

Power supplies aren't cheap, but since I have to partially disassemble the laser to replace one I want the best quality supply I can get. I don't use the machine a lot, but I need it to be reliable. Any suggestions? I replaced the tube when I installed the Jupiter supply, so it only has 2-3 hours on it as well. (I bought the tube from a different vendor, LightObject was out of stock at the time and apparently still is)

Thanks,
--jim
Tech_Marco
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Re: Newer 60W power supply went "bang" - now what?

Post by Tech_Marco »

How did you control the current? How do you tune the output to 100% and 50%??
It is not quite possible to get linear output from a laser power supply.

BTW, our 60W should output more than 22mA at full power. I believe it output up to 25mA~26mA
There ware two POT built-in on the PCB board inside of the power supply; one used for setting 50% power and another one is used to 100% power output. Depends on what controller card and tube you have, it is not always to get 22mA from 100%. Most controller allow you to set max output without over driving a laser tube. For example, 75% may reach 22mA so we should set 75% as 'max' current on the controller.

A crack could happen if the connection to the laser tube or to the current meter got lose. So, make sure you tight it up before power up a laser power supply.


Marco
audiomath
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Re: Newer 60W power supply went "bang" - now what?

Post by audiomath »

Hi Marco,

I controlled the PWM duty cycle, not the current directly. The *average* of the current is measured with a cheap 100mA meter movement that I put in series with the cathode. I put a 3-conductor "shorting" type 1/4" plug in the back of the case to connect the meter. The sleeve (ground) connection isn't used, so the cathode isn't grounded. It isn't the best way, but it's the most direct way. The meter is only in the circuit when I'm testing, not in normal operation. I don't trust the jack, the cable or the meter that much. I could do better with a shunt, an integrator and a precision voltmeter, but I haven't wanted to work that hard and I haven't seen anyone else go to that much trouble. :-)

I understand it isn't possible to get perfect linearity, but I was surprised when the linearity of the cheap supply was significantly better than the Jupiter. Perhaps the Jupiter was misadjusted, but since no schematic or procedure is available I don't know how the end user would change that.

I suppose I wasn't clear. The Jupiter supply no longer functions. The "crack" it made wasn't an external arc - both the cathode and anode connections were good and showed no carbon traces, nor did the anode wire. I haven't opened the case, but since it has a burned smell and no longer operates it's pretty clear it failed. The tube still operates fine with the spare supply, although the output is slightly less with the cheap spare, as I mentioned.

If you have any other questions, please let me know. I am no expert with glass tube lasers, but I am a working electrical engineer with 35 years experience. If there's anything I can do to avoid this happening again I'll certainly look at it. I'm not unhappy, equipment breaks. I just want to make sure it doesn't break more than it needs to. My time is more valuable than the difference in price between "this" power supply or "that one".

Thanks,
--jim
audiomath
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Re: Newer 60W power supply went "bang" - now what?

Post by audiomath »

Correction, to my last post, sorry.
The meter I'm using is a cheap 50mA unit I bought on Amazon, not 100mA . I wouldn't be surprised if the average current wasn't actually 26mA. I haven't wanted to risk damaging one of my Fluke meters to find out, and the highest voltage divider probe I have is the standard 6KV
Fluke unit I bought with one of the meters, so I can't measure the voltage directly with any accuracy either,

Thanks,
--jim
Tech_Marco
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Re: Newer 60W power supply went "bang" - now what?

Post by Tech_Marco »

Hey Jim:

Sorry I don't have the schematic otherwise I'm more than happy to share with you. You know things in China. They keep everything in 'secrete' and worry that people are copy cat it. Even the basic drawing from the mirror/laser head are not disclosure which giving me so much trouble when I try to support my customers. They blame me not to share but it is not me who doesn't want to share. They don't understand that I don't make those parts but deal direct with the manufacturer. Yes, I know they have the right to suspect that I may copy cat it and find our supplier to 'make' it. Can't explain well enough to them, I guess.

Anyway, you may send the LPSU for repair. But if you feel that the linearity is so important, I have no problem to issue you a refund when return it. Again, I have no control how they implemented the circuitry. But one thing I know is that the components this supplier used to make the LPSU are better than others. They don't mass production in China like MY or HY in JInan which you will see the difference on those components if you have been in this field for long


Regards,
Marco
audiomath
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Re: Newer 60W power supply went "bang" - now what?

Post by audiomath »

I agree the Jupiter PSU is much better built than the cheap ones, so I'll stay with it.

I suppose what I should do is make a chart of the current at different duty cycle percentages, so if I need to change a LPSU I'll know at least approximately what to change in each job to get the same results. I was hoping that the LPSU operation would be consistent enough across units so that I could standardize my jobs, but if that's unrealistic I'll modify my expectations... Hopefully I can use the same logic with the tubes as they age.

I'll be in contact about the repair, thanks.

Regards,
--jim
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