1kv DC variable power supply on a budget
August 28, 2024 11:59 AM Subscribe
1kv DC variable power supply on a budget, where do I find one for cheap?
I have a high schooler who is looking to build her own Milikan Oil Drop experiment. The tricky part is looking to be finding a 1kv variable power supply that doesn't cost an arm and a leg. At this point we're thinking of wiring one up ourselves to save money. Any tips on a cost effective purchasable model? We don't need much power output at all, just a nice high voltage to float tiny little beads with a couple extra electrons.
I have a high schooler who is looking to build her own Milikan Oil Drop experiment. The tricky part is looking to be finding a 1kv variable power supply that doesn't cost an arm and a leg. At this point we're thinking of wiring one up ourselves to save money. Any tips on a cost effective purchasable model? We don't need much power output at all, just a nice high voltage to float tiny little beads with a couple extra electrons.
An old neon transformer (I was offered one for free last weekend, they are out there in number), a variac and a couple of high voltage diodes is my first thought, if you can deal with very bumpy DC. Using a lower voltage transformer of a helpful ratio but way out of spec/backwards would also work but you run the risk of its insulation failing.
A kV is rather hazardous, and while I very much support kids being allowed to do dangerous things, so go ahead, do take precautions.
posted by deadwax at 2:27 PM on August 28
A kV is rather hazardous, and while I very much support kids being allowed to do dangerous things, so go ahead, do take precautions.
posted by deadwax at 2:27 PM on August 28
9v batteries aren't too expensive and I'd reckon you need around 130-140 of them assuming some loss. That's probably ~$150 and a lifetime supply of fire alarm batteri3s afterward.
https://hackaday.com/2012/12/18/244-9-volt-batteries-in-series-arcing-ensues/
posted by chasles at 4:29 PM on August 28
https://hackaday.com/2012/12/18/244-9-volt-batteries-in-series-arcing-ensues/
posted by chasles at 4:29 PM on August 28
To be clear this is somewhat silly but a teachable moment about series v parralell. Proceed with utmost caution and lots of videos being taken while testing.
posted by chasles at 4:30 PM on August 28
posted by chasles at 4:30 PM on August 28
9v batteries aren't too expensive and I'd reckon you need around 130-140 of them assuming some loss.Such a setup could easily kill someone when mishandled. 9V batteries can easily deliver 200 mA pulses for short periods. Those pulses, placed through a human heart, will kill someone easily.
Please do not do this suggestion.
posted by saeculorum at 6:18 PM on August 28 [1 favorite]
9V batteries can easily deliver 200 mA pulses for short periods.
And it's impossible to remove power from such a setup if it's going wrong, I also would not go here. A kV is serious think about everything twice territory. Maybe three times.
posted by deadwax at 10:40 PM on August 28 [1 favorite]
And it's impossible to remove power from such a setup if it's going wrong, I also would not go here. A kV is serious think about everything twice territory. Maybe three times.
posted by deadwax at 10:40 PM on August 28 [1 favorite]
For this to work properly you need a very stable supply of DC power that is adjustable over a certain range, otherwise you will not be able to get measurements that are remotely usable. Also, depending on how your highschooler wants to set this up, you need the ability to flip the polarity instantly (or to turn it off without adjusting it down first).
Please, do not use batteries as suggested above, that would be very dangerous as saeculorum wrote.
If you buy a power supply, look for one that has a smoothed DC voltage. Cheap ones often just flip half of the AC sine curve and no way to know what the exact voltage is that keeps the drops floating, but you need an accurate measurement if you want to calculate the charge of the droplets.
posted by amf at 11:31 PM on August 28
Please, do not use batteries as suggested above, that would be very dangerous as saeculorum wrote.
If you buy a power supply, look for one that has a smoothed DC voltage. Cheap ones often just flip half of the AC sine curve and no way to know what the exact voltage is that keeps the drops floating, but you need an accurate measurement if you want to calculate the charge of the droplets.
posted by amf at 11:31 PM on August 28
You definitely need a regulated, smoothed and adjustable DC voltage for this.
Surplus HV supplies can be found; I have one that does up to 1kV at well over lethal currents, and I use it with extreme caution.
For a setup I once built that required a somewhat lower voltage at a few mA I took two transformers, a small one doing mains to 24V at 10mA, and one doing mains to 6V. That second one got its low-voltage windings hooked up to the 24V AC, and its mains windings now provided about 4 times mains voltage. Rectify and smooth with two antiparallel single diodes and you have twice the voltage (and a bit) again. Put a variac in front or a beefy variable resistor between the two transformers to regulate the HV DC.
And build it all into a suitable isolating enclosure.
posted by Stoneshop at 1:01 AM on August 29
Surplus HV supplies can be found; I have one that does up to 1kV at well over lethal currents, and I use it with extreme caution.
For a setup I once built that required a somewhat lower voltage at a few mA I took two transformers, a small one doing mains to 24V at 10mA, and one doing mains to 6V. That second one got its low-voltage windings hooked up to the 24V AC, and its mains windings now provided about 4 times mains voltage. Rectify and smooth with two antiparallel single diodes and you have twice the voltage (and a bit) again. Put a variac in front or a beefy variable resistor between the two transformers to regulate the HV DC.
And build it all into a suitable isolating enclosure.
posted by Stoneshop at 1:01 AM on August 29
As a parallel option, if you are near a college with a good-sized undergraduate physics department there's a decent chance they already own this setup for their students to use and many folks who run teaching labs are surprisingly open to sharing (I am one such person but I don't run a physics lab, but I have several friends who would probably say yes).
If you do DIY this it's really an opportunity to work through safety philosophies generally. One thing I talk over with my students is if "being careful" should be what keeps you alive, as opposed to building a system that cannot kill you unless multiple safety features fail at once. In other words, it should be impossible for "operator error" to lead to death or serious injury. Or worst case, implementing a set of N procedures where any one of them will keep you away from 1kV, so if you forget to do N-1 you're still alive. (So for example, before touching anything internal: turn off switch, unplug power cord, place unplugged cord end where you can see it, test power supply output with meter.)
posted by range at 5:03 PM on August 29
If you do DIY this it's really an opportunity to work through safety philosophies generally. One thing I talk over with my students is if "being careful" should be what keeps you alive, as opposed to building a system that cannot kill you unless multiple safety features fail at once. In other words, it should be impossible for "operator error" to lead to death or serious injury. Or worst case, implementing a set of N procedures where any one of them will keep you away from 1kV, so if you forget to do N-1 you're still alive. (So for example, before touching anything internal: turn off switch, unplug power cord, place unplugged cord end where you can see it, test power supply output with meter.)
posted by range at 5:03 PM on August 29
(And really, I should say, if this is in a school setting then the bar really needs to be "designed so it can't kill you" PLUS "redundant procedures." The consequences are just too dire for classwork.)
posted by range at 5:18 PM on August 29
posted by range at 5:18 PM on August 29
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eBay also for used
I would spec out the one I want and then google that part number.
posted by St. Peepsburg at 12:19 PM on August 28