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Some time ago I winded a high voltage coil. It used to measure 2.55 kohms. Today I finished another one, 2.76 kohms, 210 more ohms. The first one my multimeter reads as 12 point something Henry. The second one, reads nothing. I'm suspecting the extra resistance made it hard for the multimeter to work. At first I thought these things used the full 9V from battery to generate the "measuring signal ", then I connected to another multimeter in Volts scale. It uses 222mV on the highest scale, the one I need, some 70mV on middle scale and 300 in the lowest setting. Weird. I just don't know how to be sure my coil has no short circuit inside.

Then I did 2 "dumb" tests. First I got a big coil which I could temporarily short some turns. It stills measure, but less "Henry". Then I connected a 9V battery to my coil and when I disconnected it, I got zapped. Should I proceed to the vacuum and insulating varnish or is my coil bad?

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  • \$\begingroup\$ Try L=V*dt/dI with a battery measure I after 1 second, open with a safe arc and compute L \$\endgroup\$ – Sunnyskyguy EE75 Jan 18 '18 at 2:39
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    \$\begingroup\$ @Sparky256, the comment about needing serious schooling is rude and out of place, he is obviously not a native speaker. I'm also not sure how you worked out that he is using toys, as he doesn't say anything about one of the meters. \$\endgroup\$ – replete Jan 18 '18 at 2:51
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Inexpensive multimeter 'L' functions may not be reliable or you may have exceeded the maximum range. Inductance increases with turns squared so a 10% increase in turns would result in more than 20% higher inductance.

Try connecting it in parallel with a known inductance and calculate the inductance

\$Lx = \frac{1}{\frac{1}{Lm} - \frac{1}{Lk}}\$ where Lk is the known inductance and Lm is the measured inductance.

Eg. if known is 10H and measured inductance is 6H the unknown is 15H.

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