Constructing Janus, by Dirk

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Re: Constructing Janus, by Dirk

Postby StigOE » Sun Nov 27, 2011 10:11 am

Looks very nice! Is the vector file something you can share?
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Files for Leopard

Postby dirktheeng » Mon Nov 28, 2011 12:50 am

I'll post the files. The credit for this work goes to seyit. I found this art work posted on scrollsaw village. If you use it for any fo profit work you should contact them for copywrite.
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Leopard 8x10.zip
Files for the leopard
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Jaguire

Postby dirktheeng » Mon Nov 28, 2011 4:22 am

just a quick pic and that's it. I'm tired and going to bed. This turned out very nice:

DSCN4393.JPG
Jaguire
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Isolated weird usb problem

Postby dirktheeng » Sat Dec 03, 2011 12:47 am

All,

I figured out what was causing the issue with my computer loosing the USB every now and again. Somehow, the laser tube is leaking current to the water and it was showing up at the water pump. If you've been following my build at all you know that I am controlling the pump (and fans) with an arduino that is connected to Mach via the modbus. I happened to hear a "click" at the pump when I fired the laser via the PPI system. That got me thinking that it may be a shock, but I couldn't figure out how it was getting there. Anyhow, I checked by holding the ground and the 5V pin to the tip of my finger and having my wife turn on the laser... I got a good shock... it really kind of hurt. I suspect that the shock only makes it to the water when the high voltage capacitor in the LPS discharges to start the arc. I also suspect that this has been doing it since the laser was first built. I first noticed it as a random usb failure with the UNO that I use for the modbus. However, I think the shock has to be at the right time to make it fail. I suspect that the problem was made worse with the PPI rapidly turning on and off the laser and that just increased the chances of it happening. When the USB used to fail it happened so infrequently that I just wrote it off as a random fluke of the arduino. Anyhow, I fixed the problem by grounding the radiator. now it doesn't do it anymore. I don't think I can keep the laser tube from sparking to the water, so I think I have to deal with it by grounding the pump loop. I strongly suggest that others do the same thing.
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Re: Constructing Janus, by Dirk

Postby lasersafe1 » Sat Dec 03, 2011 3:41 pm

Pehaps a safety sticky is in order elsewhere on this forum. I've stuck my finger into my water reservoir many times to check temperature and never felt a shock. I guess mine is grounded through the pump impeller shaft or radiator already. Good catch, but it still seems quite unusual unless there was some sort of capacitive transfer of voltage. There should definitely be no real electrical contact between voltage components within the inner glass and the water loop.
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Re: Constructing Janus, by Dirk

Postby dirktheeng » Sat Dec 03, 2011 4:08 pm

The shock only seems to happen when the laser goes from off to on... not when the laser is running at constant on. I suspect that what is happening is the voltage needed to start the plasma when the laser turns on is high enough to overcome the dielectric insulation capacity of the glass in the laser tube and you get a short burst of current into the water at the cathode side. So unless you stick your finger in the water right at startup you won't feel a thing. Also, you would have to be touching ground somewhere else to actually feel the shock if your tube leaks current like this one did. This could be very dangerous as there is enough current supplied by the power supply to stop your heart... I think you only need 4mA. Further the voltage is high enough to break the dielectric resistance of dry skin to shock into your blood stream.

It may just be my tube that has thinner than needed glass at the cathode junction, but I don't immagine that this is an isolated incident as the quality control of the chinese lasers is probably not that high. Throw a stripped copper wire with a weight on it in the bucket and tie it to ground or ground your radiator. $0.30 of parts could save your life in the right situation (or rather terribly wrong). The worst thing would be touching ground with one hand and putting the other in the bucket when this shock happens.
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Re: Constructing Janus, by Dirk

Postby steppenshoe » Sat Dec 03, 2011 7:52 pm

4 ma to stop your heart? I would be dead many times over then. Its more like 100 ma . Currents from 0.03 to 0.07 amp "can" start to impair the ability of the person to breathe, but the most dangerous currents are actully from 0.1 to about 0.2 amp. Currents in this range can cause death by uncontrollable twitching of the heart(fibrillation) which stops the regular flow of blood to the body. Currents a lot bigger than 0.1 amp do NOT result in fibrillation . They do stop the heart completely though. If this happens and the the duration of the current is short, the heart will "usually"(not always) start to beat by itself after the current is removed.

Be safe and ground and read, flame all you want, but a lot of people actully have no busness building these lasers IMHO. I read things on lasersaur that scare me, people not knowing basic things about electricity, it seems here safety is more of a concern and rightfully so.
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Re: Constructing Janus, by Dirk

Postby dirktheeng » Sat Dec 03, 2011 9:05 pm

steppenshoe wrote:4 ma to stop your heart? I would be dead many times over then. Its more like 100 ma . Currents from 0.03 to 0.07 amp "can" start to impair the ability of the person to breathe, but the most dangerous currents are actully from 0.1 to about 0.2 amp. Currents in this range can cause death by uncontrollable twitching of the heart(fibrillation) which stops the regular flow of blood to the body. Currents a lot bigger than 0.1 amp do NOT result in fibrillation . They do stop the heart completely though. If this happens and the the duration of the current is short, the heart will "usually"(not always) start to beat by itself after the current is removed.

Be safe and ground and read, flame all you want, but a lot of people actully have no busness building these lasers IMHO. I read things on lasersaur that scare me, people not knowing basic things about electricity, it seems here safety is more of a concern and rightfully so.


Your right... I got my numbers mixed up. Anyhow, you should still ground it. I was just surprised to see current coming through the laser that way.

I'm not sure how to take your last commend though. I'm not sure what you mean by flame all you want. Are you saying that I have no buisness building a cnc laser? There is risk involved in a project like this and you can get hurt, but I believe I have addressed the safety issues and made people aware of potential issues to safe operation. Perhaps you are not talking about me/this community but just lasersaur?
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Re: Constructing Janus, by Dirk

Postby dirktheeng » Sat Dec 03, 2011 10:48 pm

steppenshoe wrote:4 ma to stop your heart? I would be dead many times over then. Its more like 100 ma . Currents from 0.03 to 0.07 amp "can" start to impair the ability of the person to breathe, but the most dangerous currents are actully from 0.1 to about 0.2 amp. Currents in this range can cause death by uncontrollable twitching of the heart(fibrillation) which stops the regular flow of blood to the body. Currents a lot bigger than 0.1 amp do NOT result in fibrillation . They do stop the heart completely though. If this happens and the the duration of the current is short, the heart will "usually"(not always) start to beat by itself after the current is removed.


I've been thinking about the current leak and again I think this is very dangerous without a ground. I think the LPS uses a capacitor that it charges to a high voltage (higher than the normal high it has during sustained on) and discharges it to form the arc that makes the plasma... so the question is what is the current discharge rate of a charged capacitor... well on the instant it turns on it is equal to ohms law... if the resistance is low enough it could be very high as the voltages are extreme... the capacity of the capacitor to sustain that current is direcly proportional to its size. So there is no way to know what that real current may be without scoping it because we can't know the true impedance of the system. The point is that there is a potential for the system to produce a high current maybe even tens of amps, if only for a nanosecond or two (ok maybe a few miliseconds). This isn't something to mess around with. Even if the LPS is only rated for 10ma, that current rating may not be the max it can dish out especially at transient start up.
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Re: Constructing Janus, by Dirk

Postby bill griggs » Sat Dec 03, 2011 11:17 pm

dirktheeng wrote:I'm not sure how to take your last commend though. I'm not sure what you mean by flame all you want. Are you saying that I have no buisness building a cnc laser? There is risk involved in a project like this and you can get hurt, but I believe I have addressed the safety issues and made people aware of potential issues to safe operation. Perhaps you are not talking about me/this community but just lasersaur?


I don't think he meant you. I think it was a generic "some people" not directed at an individual. I could be wrong. But that was the way I read it.

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