Ballast Tubes

[Muticraft]

I was wondering if any one could help give a clearer picture on ballast tubes, what they actually do in the HV cabinet, do they need preventive maintenance and safety concerns. Thanks,

 

[krugtech]

The ballast tubes control the current in the plasma tubes. There are 2 major things to make them last long- one is to make sure the cooling system is working properly, the other is to make sure the voltages are at the right level. Ballast tubes need to have a certain voltage drop across them to work, if it's not enough, your current will be down and you loose laser power, if it's too high, the tubes will run hot and this shortens their life.

I do not recommend handling the tubes unless it's absolutely necessary. Some techs like to pull the tubes and clean them. Over the years I'd say maybe 1 in 8 of the customers who had a tech pull the tubes had a tube failure a week or 2 after the service call. When you pull the tube, it puts a lot of stress on the pins and the hermetic seal starts to weep and the tube fails.

I gently blow the loose dirt/dust off the tubes while they're cool. I don't pull them and wipe them. I then make sure the cooling system and fans are all good and the cabinet is sealed properly to keep dust out, and that's it.

Also, despite what the "experts" say, there is no reason to wear gloves to handle them, they're tubes, not halogen bulbs. Some of the techs I know will do crap like that anyway in a lame ass attempt to look reaaallllllyyyyy prufeshinal!

It's all about the cooling and the voltage drop, keep these in line and the tubes last a long time. I've seen people cook them in a week, I've seen some run 20+ years.



Chris Krug

http://krugtech.com/

Maximum Up-time, Minimum BS

 

[Muticraft]

Thanks Chris for the advice and better understanding

 

[krugtech]

Glad you liked it. What a lot of people don't realize is a 10% increase in line voltage going to the laser can make roughly a 50% increase in the wear and tear on the ballast tubes.

Lets say my HV source is 16,000 and my tubes run at 13,000 volts. The drop across the tubes is 3000v which is pretty good. Now a 10% increase in line voltage will bump my HV source 10% or 1,600 volts +16,000v = 17,600v.

That 10% bumped my voltage drop over 50%- lets say the laser runs at 80 millliampers- .08 x 4600= 368 watts each tube pisses away as heat where before the 10% increase the tubes only generated 240 watts of heat. There are ways to address this.

Brand new tubes can be set up to work well with a lower voltage drop, they will run nice and cool for a long time like this, once they get some wear and tear you have to increase the voltage drop which increases heat which shortens the tube life.

The tubes are not very efficient when compared to a solid state system and more care must be exercised when setting them up, but the good part is, if you get fairly close on the setup they'll run great for a long time and when they fail it's usually a very slow and predicable performance loss. They take a beating and when they had enough they usually give plenty of warning.



Chris Krug

http://krugtech.com/

Maximum Up-time, Minimum BS