15 kV or 20 kV 1mA power supply - Page 1
Forum section: electronics / projects

author: kriswillems
author_rank: Newbie
timestamp: February 02, 2025, 01:06:21 pm
content: Does anyone know where I could get such a power supply. It should not give much more than 1mA current to reduce risk on electrocution (but also not less). It will be used in a school project in which we try to separate beach sand and micro plastics via electrostatic effects (corona effect). I tried cheap chinese igniter modules (20 kV), followed by a voltage multiplier, but the voltage collapse at very small currents.

author: geggi1
author_rank: Frequent Contributor
timestamp: February 03, 2025, 06:52:05 pm
content: You can look into a CRT voltage multiplier.They will not give alot of current but as you are relying on the electrostatic charge current will most likely not matter.

author: Benta
author_rank: Super Contributor
timestamp: February 03, 2025, 07:37:59 pm
content: Automotive ignition coil.But you'll need a way to limit the voltage, a spark plug could do the job. And you probably need to build your own 20 kV smoothing cap if you want pure DC.

author: DaJMasta
author_rank: Super Contributor
timestamp: February 04, 2025, 06:27:41 am
content: How much current do you actually need? 1mA at 20kV is 20W after the losses of the supply, which isn't a trivial amount. It's also absolutely lethal (can cause cardiac arrest, also if you charge anything up the momentary discharge current peaks much higher than your constant current) so while it is technically less lethal than 2mA or 20mA at 20kV, make no mistake that what you are working with can still kill you and appropriate precautions need to be taken.If this is an electrostatic application, less current than that is probably required, and maybe you need a series resistor chain or similar to just reduce the peak current draw when charging your plate from zero with the supply. It could also be a cleanliness issue as 20kV can cause a lot of surface contamination to break down and draw current where you intended for none.As for sources, there are dedicated low current HV supplies with current limiting as part of it, like a standard lab power supply - an older Spellman unit may not be that expensive. There are also likely surplus X-Ray tube supplies that meet similar requirements, but they'll typically have large, application-specific connectors that are there for safety and shouldn't generally be ignored (make doubly sure you know what you're doing), and you'd want to inspect any HV cables attached specifically before powering up in case they were damaged from removal or age.

author: Gyro
author_rank: Super Contributor
timestamp: February 04, 2025, 08:23:31 pm
content: Quote from: DaJMasta on February 04, 2025, 06:27:41 amEspecially as this is for a school project. As E=CV2, it takes very little capacitance to give you an unpleasant day. Any DC supply is likely to contain some output capacitance, so you need a well insulated high value, high breakdown voltage, resistor in series with the output to be reasonably safe (also try to avoid introducing any more stray capacitance than you need to). I would size the resistor to give ashort circuitcurrent of 1mA, ie. 20M ohms, that should provide reasonable safety.As DaJMasta says, this sounds like a basically electrostatic application (especially if you ensure that the sand is completely dry - basically silica). Note that the resistor would dissipate 20W in a continuous short situation, so would need to be large, however as long as it meets the voltage rating, a smaller wattage resistor could be used to protect against an accidental brief short or accidental touch.Edit: Just one other thought. Does the school possess a Van der Graaf generator? A wire from the dome, manipulated by attaching it to the end of an acrylic rod, would probably give you a much better effect than a 20kV PSU and also be relatively safe (but still painful).

author: tooki
author_rank: Super Contributor
timestamp: February 04, 2025, 08:35:24 pm
content: I support one project at work that uses a 40kV, 1mA lab power supply (Heinzinger PNC 40000-1). Bear in mind that such a thing is not a little toy -- it costs a lot of money and weighs a ton. And you need knowledge to work with that kind of voltage safely. Do not underestimate what DaJMasta and Gyro say about the safety, including capacitance. At that kind of voltage, just your HV power cable itself can hold a significant charge!