I recently got a new project to work on, an Electrospray Deposition setup. Basically, it consists of a needle that contains a liquid, a electrode and a high voltage source. The needle is positioned at a distance to the electrode and the source is connected to both the needle and electrode. Because the needle is charged by the source, the liquid inside is also charged, up until the moment where the liquid disperses into little droplets. These droplets are then accelerated towards the electrode placed under it.

The source for this is a DC Voltage supply ranging from 5kV to 35kV, which also brings me to my question, how dangerous is it working with this kind of setup and what safety measures should be taken? Once the supply is turned of and the experiment is over, the electrode and needle are still going to be charged, which is why I thought a discharge stick would be necessary, do any of you have experience with this?

I will link the voltage source, which was already bought without my influence and gives me not the best impression if I am honest. HV350CC/GRA80 is the one I have at my disposal.


From papers of other setups I figured I'd need about 5-20kV range for my setup, but I'd prefer it to be safe for the whole range. Do any of you have tips on how to choose the resistors for the discharge stick or what other measures to take?

  • \$\begingroup\$ Are we talking one needle, or ten thousand? Because the current requirement will scale with the number of needles. One needle would only need a tiny current. \$\endgroup\$
    – rdtsc
    Apr 9, 2021 at 15:24
  • \$\begingroup\$ There's more to it than just 'high voltage'. High voltage in and of itself is not dangerous. When you rub your feet on a carpet and build up static, that literally is somewhere from 3kV-20kV of voltage. But it doesn't kill you when you touch a doorknob and get a shock, right? That's about what's going on in your system. Very high voltage, almost zero current. Basically what a "taser" is also. The real danger from low-current HV systems is if you touch one, your muscles may contract and become uncontrollable, then you fall off a ladder. Keep one hand in your pocket.... \$\endgroup\$
    – Kyle B
    Apr 9, 2021 at 15:36
  • \$\begingroup\$ It's really just one needle and one round electrode \$\endgroup\$
    – rohulla
    Apr 9, 2021 at 16:33
  • \$\begingroup\$ Yeah I guess that's why so many of those setups look pretty homemade and without much safety precautions. The current should be limited by the source to 200uA so I guess I should be good on that part. What I am concerned about is the stored charge afterwards and that I am hardly able to get a good reading of the voltage as the source is pretty scuffed. \$\endgroup\$
    – rohulla
    Apr 9, 2021 at 16:36
  • \$\begingroup\$ I've worked with smaller electrospray devices for LCMS, but at very low flows. Depending on your flow, you may be able to limit the current to a lower value. 1uA is not too scary (will hurt tho), 100uA needs full respect IMO. Careful with the fluid lines as a conduction path. A ground point can be added to the fluid path, but will cause larger current draw. Discharge into the atmosphere from time to time as you adjust the settings is likely, maybe issue if high solvent %. If anyone else is going near it, carefully designed safety covers with interlock are required. \$\endgroup\$
    – Pete W
    Apr 9, 2021 at 17:48

1 Answer 1


TL;DR short answer

To protect PSU’s that failed catastrophically during Hipot tests in factory, I modified the HV supply probe to insert a string of 1/4W Resistors so if it failed the xx uA limit the capacitance would not dump amps into the device. You ought to consider doing the same at exit after parasitic capacitance, and use static dissipating material to safely discharge until to get experience.


There is not enough detail known on the leakage resistance of the medium, effects of humidity and air contaminants that affect leakage resistance nor the volatility of an organic paint.

What is interesting is that Electrostatic Spray Deposition shares the same abbreviation as Electrostatic Discharge, namely ESD. Spraying nano particles of paint while the volatiles evaporate during air travel sounds like an opportunity for combustion if the current is too high. But like Hydrogen the explosive limits LEL (4% fact) and UEL (lower and upper) determine the probability of explosion. For concentrated organic paint, I would hope the concentration is above the UEL.

However you question is limited to the residual charge of the HV paint gun, and again this is unknown due to ambient conditions of humidity and dust that determine the decay time constant of some unknown purity of a dielectric insulated paint.

If in doubt use a sheet of CMOS carbon black foam or other static dissipative material and any charge will bleed slowly..

It is also interesting to note that powder coating version of ESD use a grounded nozzle to spray and a UHV charged conductive target that can easily be dissipated using ESD dissipative material or controlled humidity.

I recall not too long ago doing UHV 100 kV DC insulation tests on a 5MVa transformer to determine that the inception voltage for Partial Discharge or PDIV was around 18 kV which was below the HV primary side and resulted in H2 generation in the oil filled transformer. The fascinating part was as we were guarded by a Faraday wire cage that was grounded standing outside 3m from the massive transformer in the factory, the epoxy paint on the transformer tank and the Safety cage both got electrically charged like a nylon carpet and gave vigorous impulse shocks just rubbing or touching the paint everywhere on the surface for a couple minutes. It also made any dry hair and the backs of our neck “literally” stand up.

I don’t have any powder coating experience, but have never heard of any issues, but I’ve given you some variables to think about, like charging the target instead of the sprayer and grounding the nozzle for safe neutralizing and direction control. As well variables that cause charge decay ( air contaminants and humidity)

I think monitoring the HV current level and a AM radio to listen for paint PD discharges on a quiet AM band will give you the best feedback for charge control in your ESD paint research.

There are also thousands of articles on this subject to follow, more often focused on nano-deposition for semiconductors. So Socratic filtering of your re-searches is necessary.

Also read about ESD protection with 1Meg resistor to shoes, and static dissipating lab coats to see if this applies to ESD Painting.




  • \$\begingroup\$ For the liquids themselves, I am considering a mixture of 1:1 Water and Methanol but the quantity is also very slow for this kind of setup, so even in the case of a spark I believe it should be rather save, if the setup is enclosed. So you would recommend a dissipative material to discharge the components? So instead of a resistor with a certain resistance you use this material to limit the current and rate of discharge? As for the monitoring of the HV source I am also a little concerned with the setup. Is the best way to setup a voltage split or how would you approach this? \$\endgroup\$
    – rohulla
    Apr 9, 2021 at 16:47
  • \$\begingroup\$ Measure groundcurrent with a current limiting string of hiV R’s . Methanol burns low temp.? Use sheet material for discharge \$\endgroup\$ Apr 9, 2021 at 18:25

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