r/AskElectronics • u/o_blake • 1d ago
Can I use my multimeter to make sure this flash capacitor is no longer charged?
Battery has been out for about two weeks now. I would like to NOT shock myself again.
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u/JohnStern42 1d ago
Personally I just put a screwdriver across the terminals to make sure
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u/Lasse_Bierstrom 1d ago
I'd do the same in something which isnt sensitive or expensive. Measuring is good, but measure really well.
Shorting really empties most of the charge, but it does hurt your capacitor a bit. Better would be using a resistor.
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u/riverturtle 1d ago
Put a big resistor across the leads. That’s what I generally do. Agreed, getting bit by one of those caps hurts.
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u/Shot-Classic7398 1d ago
I'd be really shocked if the cap still has charge after 2 weeks, But if you probe across it with the multimeter you can check. Theoretically, your multi should have infinite impedance but realistically the cap will slowly discharge as you probe it. Echoing the other comment that I can't see any caps in this pic, but I guess it could be on the other side of the board but accessible from this side through a through hole via or something.
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u/Fallwalking 1d ago
Z50? Capacitor is in the grip. They show how to do this in the repair manual for the Z50ii.
What’s the issue with the camera?
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u/1310smf 1d ago edited 1d ago
In HV capacitor banks we used a shorting stick which was a long piece of plastic pipe or lucite rod (an insulating handle to keep your hand 3-6 feet from the business end) with a big power resistor (50W or more) on the end, connected to a copper braid connected to ground. I was advised that if the things had not been mostly discharged before we safed them we should expect the power resistor to blow up. Never happened to me as things were not sloppy in that lab.
For bitty things like this, you can use a 1/4W or so 1 MΩ resistor (good to 500V) with clip leads, and after you give it a minute or 10 to draw down, just short it with a test lead. If the capacitor is larger, clip in a 100K and then a 10K or just give it more time. If the flash cap might be 1000V, perhaps move up to 1/2 watt, though at that sort of voltage going series with two 500K or three 330K will keep the voltage-per-resistor and power-per-resistor down if the thing is juiced when you connect. If you have a lot of need for faster dischage or higher voltages, you can build things like a string of 50 2W resistors in series, or buy an expensive 50W+ power resistor.
If you're already willing to wait two weeks, the 1M resistor will do the job a lot faster than that for any capacitor you can easily pick up in your hand.
If your multimeter has a high enough DC range, yes you can use it to check the voltage on the capacitor.
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