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Help Troubleshoot HeNe Laser

IsaacT

IsaacT

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So I got tired of replacing AA Batteries in my HeNe build, so I bought a wall wart that outputs 5VDC 2000mA to power my Power Supply. After installation, I plugged it in and it turned on for a few seconds and then turned off. I checked all the connections but I can't find anything wrong with it. Clearly it is turning on but no staying on?

I brought it up to my room and turned it on and it is staying on, but it is buzzing and the tube is slightly flickering like it did when my batte ries were low. Any idea what the issue is?
 





Cyparagon

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First rule of troubleshooting: thou shalt check voltages.

Do so, and report back.
 
IsaacT

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Speedy78 said:
Mine flickered when my ballast resistor was insufficient.
Click to expand...

And I thought about that, but it hadn't had problems when I was using 4 AA Batteries....

Of course, 4 AA's gives 6V and this new wallwart gives 5V....maybe it is voltage? I am not sure how old this tube is but according to Sam's Laser FAQ older tubes may require more and more voltage to do either wear and tear or gas pressure changes.
 
bloompyle

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The difference of a single volt can mean a lot. I'd check the PSU again with the 4x AA batteries, then check the wallwart.
 
LtKernelPanic

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Maybe not enough current? I know my Green HeNE's PSU would give off a high pitched whine when using one DC supply but not with another. Turns out the PSU was pulling 2.12A from the one PSU but could only get 1.98A from the other. Replaced the jury rigged supply with a 12v 5A supply and all is well.
 
IsaacT

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I hadn't been around it all day, sorry. I just dug out my terribly budget multimeter and:

Under Load: 5.26V
No Load: 5.49V

I tried to do current but I am not quite sure if I am doing it right. I put the wheel on 10A, and measured it.

Under Load: 0.88
No Load: .90

Does that mean my wallwart is only supplying the PSU with 900mA instead of 2000mA?
 
Cyparagon

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You measure current in series with the load. You cannot measure "no load" current, because it is zero. You must have shorted the output through your DMM, which is not good for the wart. Hook up your AA setup which you know works, and compare those numbers.
 
IsaacT

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Under 4xAA setup:

Voltage Under Load: 5.22V
Voltage No Load: 6.31V
Current: 5.30A

That is quite the current difference. I was under the impression that the PS I was using wanted 1.2A or so.... see HERE. I am surprised at how high the current draw is.
 
Sigurthr

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28W sounds reasonable for a HeNe, mine draws about that at 13.8V input.
 
Cyparagon

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I'm rather impressed the AAs only drop 1V under a 5A load.

I knew 1A sounded too low. That's only 5W input, and the tube itself draws at least 10W. Add in power supply inefficiency, and a 2A wart isn't going to cut the mayonnaise.
Time to go pick up a Chinese power supply off ebay or whatever. Shouldn't be much more than $10.
 
Last edited:
IsaacT

IsaacT

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Cool, thanks for the heads up! So 5A is not overpowering the power supply? I guess I could look for a 6V wallwart @5A or something. I don't really know what to look for in a power supply.
 
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