High Voltage Needle

[Jeng]

High I am working on a project to electrospin polymers. This project involves charging the needle on a syringe to 25kV-30kV and placing it about 6-8in away from a grounded collector. The charged needle creates a surface charge on the solution, the droplet on the end of the needle becomes stretched due to repulsion of the surface charges and at a critical voltage the charge repulsion overcomes the surface tension of the stretched solution and a jet forms which is directed at the grounded collector. What I am concerned with is the safety of charging a needle to this voltage in a lab. We are going to be building a plexiglass case around the entire set up for both safety and to vent the solvent that evaporates from the jet solution. I was wondering what sort of safe distances should be kept from the high voltage needle. Also we are building a bit of a makeshift syringe pump with a slow motorized actuator. Is there a safe distance I should keep electronic equipment from the high voltage needle?

[powerlabs]

Hi Jeng,

I am sure you realize that the voltage itself is completely harmless: on a dry day you can generate over 10 thousand volts by walking across a carpeted floor. Since you did not specify a current, I can't give you much in the way of recommendations, but I imagine that the current required for what you are trying to accomplish is very low; possibly 1-3 ma or so? At that current level the risk of electric shock would be non existant, provided your power supply is designed with safety in mind.
The equipment should be fine also, just try to not keep it in direct line with the needle, otherwise you will start to charge it up electrostatically and will need to deal with shielding and grounding.
Cool project by the way! It seems to me like you'd need a lot more than 25kV to produce a liquid spray into a target 8 inches away though...

[Jeng]

Ha, I can't believe I forgot to put that in the post. You are right the power supply is only rated for 3.5mA output. I know that it is the current that determines the danger of the application. I was wondering whether it is possible for power supplies to deliver more current then they are rated for? The power supply is an old 1994 Glassman LG series. I would think this shouldn't be an issue, I just wasn't sure since I have not worked with high voltage power supplies before (I just want to be precautious).

There has actually been some work with this sort of project and optimal voltage was about 25-28kV (I know, you would think it would be more but a lot of times syringe pumps are used to help it along.

[powerlabs]

It depends on the power supply; I would expect something like that to be current limited, but you should check; just connect an ammeter across the output and turn it on; it will either blow a fuse (it should have one: install one if it doesn't) or maintain a constant current... Anything below 10mA is considered "safe" (I.E. non lethal).

[zapitgood]

I realize this is an old post but the shock hazard is not the issue, the solvent ignition is. 3mA is plenty of energy to ignite certain solvent vapors is any oxygen is present . Not being familiar with the process or method maybe this is prevented somehow.

[cipher510]

wouldn't that depend on what the soulition is? what if its not flameable?