I was trying to make a hv generator from an ignition coil. I bought one from the local mechanics, and put it in a circuit in series with a capacitor and a light dimmer connected to mains 240v. The capacitor was likely much too low of a value, around 5nf. The circuit didn’t spark at all, so (having no idea what I was doing) figured I had the wrong type of ignition coil, since I had the pencil type. I probably ran the coil for a combined total of around 2 minutes. Anyway, I went back to the mechanics to get a more traditional type, and they offered to swap it for me. I told them that I had used the coil, and they said that was fine, they would just test it. They said it tested fine, but I’m sceptical that they couldn’t pick up all the damage to the coil, since it would be internal. Anyway, I’m really worried that it’s in someone’s car now, and I will cause a horrific accident because I returned the coil. Am I being completely unreasonable? Will a mechanic be able to pick up internal damage to a coil? Is the coil even likely damaged?

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    \$\begingroup\$ This is an expanded repeat of your question from yesterday. You are again asking if you damaged the ignition coil, in a way which was not detected during testing. Please don't duplicate questions - it is against the rules here. If you have new information, the philosophy on Stack Exchange sites is that you edit the original question to improve it. Thanks. \$\endgroup\$ – SamGibson Jul 4 '19 at 12:54
  • \$\begingroup\$ Sorry, just very worried. I will delete yesterday’s question 👍 \$\endgroup\$ – Steve Jul 4 '19 at 12:58
  • \$\begingroup\$ "I will delete yesterday's question" You will probably not be allowed to do that, since your question from yesterday already has an answer. Deleting the question would remove the answer and therefore waste the time taken to write that answer - see here for more details. \$\endgroup\$ – SamGibson Jul 4 '19 at 13:06

5 nF has an impedance at 50 Hz of 637 kohm so it's unlikely that any damage will have occurred because the maximum continuous current (even into a short circuit) from 240 volts AC is limited to only 0.4 mA. This might rise to about 0.5 mA if your supply is 60 Hz.

Given that an ignition coil is used to having several amps applied to the primary in order to generate a decent ignition spark, I don't think you need to worry unless, of course, you may have done something that you are not mentioning.

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  • \$\begingroup\$ Thanks for the reply 👍. The only thing I think that could otherwise have damaged it is the fact that there was no spark. I think no spark means the secondary was open, and the hv build up has no where to go, which means it can short internally. Is this true? \$\endgroup\$ – Steve Jul 4 '19 at 12:48
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    \$\begingroup\$ No spark is probably due to the fact that the primary was driven with a current more than a thousand times smaller than the current used for normal sparking operation. \$\endgroup\$ – Andy aka Jul 4 '19 at 14:21
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    \$\begingroup\$ I thought I already answered this in your original question. The coil is probably fine, you didn't over-drive it. You under-drove it. \$\endgroup\$ – DerStrom8 Jul 4 '19 at 19:05

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