On my morning walk with my technical advisor (Myka) we decided it was time to purchase a piece of hipot test gear. We have several pieces of kit from the 1970s that we use daily, as well as the pieces I have built in our home lab. Why not be absolutely certain all this kit does not present a hazard? It should be absolutely clear that a hipot tester is a potentially lethal device. No one should attempt to use one without full knowledge of how it works and how to use it safely. Understand that most American homes have guns "for protection". No need to go into how well that works for us, but the admonition to learn how to use one safely still applies. Back to the point of properly testing equipment one builds for themselves: if one isn't willing to really learn and understand what makes for a safe piece of equipment (not only shock hazrd but fire hazard as well), and actually verify that you have achieved that (even though the testing involves both cost and risk), you probably should not do it. Just grounding the chassis isn't really sufficient.
If the test is more dangerous than the equipment you want to test, it gets counterproductive. Can't you test insulation with equipment with a very low current limit?
Highpot testing is potentially lethal to the tester, hence the admonition to both understand what you are doing and how to do it safely. The test is dangerous because it uses high voltage: 2120 volts peak is typical. The technician performing the test must not come in contact with that voltage.
All equipment that gets plugged into a mains outlet and bears the mark of a Safety Agency will have undergone hipot testing (100% production line testing). So it can be done safely by a properly trained technician. If the equipment fails the test it was not ruined by the tester: it was already defective.
All equipment that gets plugged into a mains outlet and bears the mark of a Safety Agency will have undergone hipot testing (100% production line testing). So it can be done safely by a properly trained technician. If the equipment fails the test it was not ruined by the tester: it was already defective.
Off topic, but not completely: in the late 18th and early 19th century, a gentleman called Martinus van Marum did all sorts of experiments with a huge electrostatic generator at Teylers Museum here in Haarlem. One thing he was interested in, was checking the effect on human heart rate. Fortunately he had the common sense not to connect the Leyden jars during this experiment, otherwise his test subjects would probably not have had any heart rate at all after the test.
The conclusion of his experiment was that the heart rate after the shock was normal, but the test persons had a remarkably high heart rate just before the electric shock, particularly John Cuthbertson, the man who had built the generator for him.
The conclusion of his experiment was that the heart rate after the shock was normal, but the test persons had a remarkably high heart rate just before the electric shock, particularly John Cuthbertson, the man who had built the generator for him.
For button batteries, I suspect the written warning is useless for the intended target. I've seen more and more buttons that now come with a really bad tasting coating to prevent ingestion. (no, I did not try, I took the packaging labelling at its word)
Same applies with the little neo magnets used as toys.
For hipot, we have two machines. The old analog one has an upper limit of 2 mA, so worst case is capacitive storage.
The newer digitally programmable one has a hard limit of 6 mA, capacitive storage again the player. But the newer unit also has a built in GFI and shuts off if the return current doesn't match the send current.
edit: The paper written by Dalziel (GFCI inventor) had some hilarious pictures in it. One I used for a safety lecture had a pic of a subject grimacing with a wire in his right hand, and the researcher holding his left hand down on a wet electrode on a table. The really funny thing was the smile on the researcher's face while the subject was in pain. It was all research for the let-go current thresholds for humans. While they gave the subjects some kind of stipend, you couldn't pay me enough..
In my hypot training class, I teach the limits:
Below 50 volts, limit is 100 joules (89,000 uf at 50 volts)
50-400 volts, limit is 1 joule (12.5 uf at 399 volts)
over 400 volts, limit is .25 joules. (3 uf at 400 volts)
The 400 volt line in the sand is the decision that human skin breaks through at 400 volts, so the much lower resistance across the capacitor provides much higher currents.
Not sure where the numbers originated, maybe NFPA 70E?
Edit 2: what scares me is that the newer AED units start in the 120 joule (or so) range, and the smart ones go up with successive pulses to about 300 joules it the patient doesn't respond. Man, when the unit says "clear", holy mackeral, everybody better well be.
John
Same applies with the little neo magnets used as toys.
For hipot, we have two machines. The old analog one has an upper limit of 2 mA, so worst case is capacitive storage.
The newer digitally programmable one has a hard limit of 6 mA, capacitive storage again the player. But the newer unit also has a built in GFI and shuts off if the return current doesn't match the send current.
edit: The paper written by Dalziel (GFCI inventor) had some hilarious pictures in it. One I used for a safety lecture had a pic of a subject grimacing with a wire in his right hand, and the researcher holding his left hand down on a wet electrode on a table. The really funny thing was the smile on the researcher's face while the subject was in pain. It was all research for the let-go current thresholds for humans. While they gave the subjects some kind of stipend, you couldn't pay me enough..
In my hypot training class, I teach the limits:
Below 50 volts, limit is 100 joules (89,000 uf at 50 volts)
50-400 volts, limit is 1 joule (12.5 uf at 399 volts)
over 400 volts, limit is .25 joules. (3 uf at 400 volts)
The 400 volt line in the sand is the decision that human skin breaks through at 400 volts, so the much lower resistance across the capacitor provides much higher currents.
Not sure where the numbers originated, maybe NFPA 70E?
Edit 2: what scares me is that the newer AED units start in the 120 joule (or so) range, and the smart ones go up with successive pulses to about 300 joules it the patient doesn't respond. Man, when the unit says "clear", holy mackeral, everybody better well be.
John
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Assuming the test is properly conducted, hipot testing is rather boring. If the insulation does not hold up to the required test voltage the tester just clicks off. No sparks, fire or shrapnel.
The Safety Agencies also conduct what are called “Abnormal Tests” on product samples and that can be much more fun. Basically, any component can be shorted or opened and any trace can be opened. For example, a 400V bulk cap is shorted. To pass this test there must be no fire or exploding shrapnel and the integrity of insulation must remain intact. Hopefully a fuse opens and it is over. A proper development group will perform these tests during product development such that there are no surprises when the product is tested by a Safety Agency. It’s the failures that make the job exciting: balls of plasma fire and so on.
The Safety Agencies also conduct what are called “Abnormal Tests” on product samples and that can be much more fun. Basically, any component can be shorted or opened and any trace can be opened. For example, a 400V bulk cap is shorted. To pass this test there must be no fire or exploding shrapnel and the integrity of insulation must remain intact. Hopefully a fuse opens and it is over. A proper development group will perform these tests during product development such that there are no surprises when the product is tested by a Safety Agency. It’s the failures that make the job exciting: balls of plasma fire and so on.
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The hipot that 100% tested GE Appliance at end of assembly and before crating when I was Quality Information Equipment engineer was 10 ma @ 20000 volts. AC current from a GE neon transformer through a number of resistors 3" long each. The operators sometimes got shocked from the probe. No deaths or injuries, but they did not like it. They had to snap two AMP Mate-N-Lock connector blocks in a recess of a textolite (garolite, Nema C composit)probe with a start button on it. Were red & green lamps for test result on the probe. Was a sit down job, a big plus for older operators. We kept photos of articles in journals that demonstrated that it took 25 ma to kill a pig. Also let go current from experiments proved to be about 25 ma.
The AC let go we use is listed as 5 mA. The DC let go is 40 mA.
Dalziel's number for a 90 lb woman was 7mA AC, so a standard of 5 mA was chosen just to make sure.
I didn't look at the stats for bigger guys in Dalziel's graphs, but 25 mA AC doesn't seem too far off.
John
Dalziel's number for a 90 lb woman was 7mA AC, so a standard of 5 mA was chosen just to make sure.
I didn't look at the stats for bigger guys in Dalziel's graphs, but 25 mA AC doesn't seem too far off.
John
Standard transformers are expensive enough.
I wasn't thinking of either PSRR or crosstalk.
…And if wired correctly also be free from ground loops. But many common architectures that LOOK pretty lend themselves to the most awful ground loops.
When I worked for an industrial instrumentation company back in the 1980s and early 1990s involved in intrinsic safety instruments, we hipot tested to 2.5kV. That’s pretty tough on a small HF pot core transformer. For mains power transformers and opto isolation stuff, the test was 4 kV IIRC. All of the designs were certified by the national central standards bureau before going into production and being allowed to be sold. This stuff ended up all over petrochemical plants and down mines. Zero tolerance for failure.
My shiny new hipot tester arrived and I put it to the test with a very old transformer that powered a 60 watt per channel amp from my college days. No idea what standard it would have been built to, and I pretty much decided to pitch it for that reason, and because of its age. However, I was able to validate its integrity using 1500V for both primary and secondaries to its core, and 3000V primary to secondary (for 60 seconds). I think it will find a home now as a bench supply for amplifier boards. I should repeat the warning not to play with such a tester without knowledge and training. As Uncle Duke once said in a Doonesbury strip: “don’t try this at home kids: Unless you’re a professional, it can only come to grief”. He was talking about some hallucinogenic drug, but its the same...
I agree and strongly recommend that you not use your high pot tester while using LSD or similar drugs no matter how pretty the display can be!