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We're planning a (6th-8th grade) student take-apart day, with small non-functioning items like hair dryers, clock radios, coffee makers, etc. (no microwaves, TVs, monitors.) Even though items have not been in use/plugged in for quite some time, I feel like I should research parts like capacitors.

Students will wear safety glasses and gloves. I'm wondering if someone could offer additional tips, especially with safety in mind.

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    \$\begingroup\$ Search teardown videos for examples of each item. Learn to identify parts. And how to use a DMM \$\endgroup\$ Commented Mar 5, 2022 at 12:18
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    \$\begingroup\$ That first jolt really speeds up the learning process :) \$\endgroup\$ Commented Mar 5, 2022 at 12:38
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    \$\begingroup\$ Most items mentioned obtain power from AC mains. Ensure every item has its power chord severed, so that it cannot be plugged-in. Some items may have an internal back-up battery - upon opening up, this should be removed first. Any water-damaged items may have residue which is chemically active. \$\endgroup\$ Commented Mar 5, 2022 at 14:19
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    \$\begingroup\$ I suggest you teach them the flaws of elementary textbooks amasci.com/miscon/elect.html \$\endgroup\$ Commented Mar 5, 2022 at 14:55
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    \$\begingroup\$ Discharge any X capacitors for hair dryers and the like. Don’t disassemble magnetrons from really old microwaves with beryllium oxide isolation. \$\endgroup\$ Commented Mar 5, 2022 at 15:13

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You've already done a good job identifying that microwaves and old TVs are not the safest devices to take apart. Devices operating with low voltages are fairly safe to tinker with. That would mean devices that come with a mains adapter that drops the voltage to 5/12/24 V(AC/DC) and are not directly connected to mains.

Nevertheless, any device might have an input capacitor that should be discharged before touching the terminals, as a safety precaution.

SMD capacitors might be tricky to make contact to both terminals. One easy way would be to take a cable like a 4 mm "banana" cable, that's usually attached to multimeters and put sharp probes to each end of the cable and use it to penetrate PCB solder mask (and possible protective coating) and short any traces that seem to be in power input or near large capacitors.

Through hole components are easier to short out. In both cases it may be difficult to know if you have made good contact or not, so solder pads are a good target in short circuiting. That way you haven't at least penetrated the PCB copper.

In all likelihood the input capacitors in a low-power device are minized due to cost reasons and are safe. Usually they also have a "bleedout" resistor, rendering them safe after disconnecting from mains for a while.

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    \$\begingroup\$ Is any SMD capacitor big enough to store a dangerous amount of charge? Seems improbable. \$\endgroup\$ Commented Mar 6, 2022 at 2:15
  • \$\begingroup\$ I think there's no danger at all. Practical SMD caps usually hold less energy, but there's nothing stopping making a high energy SMD cap. And they can withstand high voltages, just as the through hole ones. \$\endgroup\$ Commented Mar 6, 2022 at 10:48
  • \$\begingroup\$ Contact spacing sets a practical voltage limit on SMD devices. They need special attention to avoid creepage. \$\endgroup\$ Commented Mar 6, 2022 at 15:08
  • \$\begingroup\$ 500 V rated SMD caps are available from any major supplier. \$\endgroup\$ Commented Mar 6, 2022 at 17:30
  • \$\begingroup\$ Thank you all so much for taking the time to respond to my post. It was so helpful! \$\endgroup\$ Commented Mar 11, 2022 at 0:40
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CD and DVD players are fun to take apart. Same thing with VCRs (if you can find one these days.)

If the gear hasn’t been powered on in a while there’s no significant risk from charged-up caps in the power supply.

Related: I would like to disassemble a dvd player. Is it safe?

Flatscreen LCD monitors and TVs (small ones) are relatively safe to take apart, aside from the motherglass breakage possibility. Big ones are unwieldy and would be a big dangerous mess if they got broken in the process.

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    \$\begingroup\$ On the subject of TVs - old plasma sets had relatively high voltages running around in them, on the order of 400 V IIRC. So need to make sure you know where those voltages are and discharge any suspect caps. \$\endgroup\$ Commented Mar 5, 2022 at 17:08
  • \$\begingroup\$ Same thing would apply: the charge would bleed off both through capacitor leakage and by an explicit bleed resistor. \$\endgroup\$ Commented Mar 5, 2022 at 18:31
  • \$\begingroup\$ Some CRT televisions and monitors had flat screens. Lightweight, flat, thin screen TVs and monitors are relatively safe. \$\endgroup\$ Commented Mar 6, 2022 at 2:16
  • \$\begingroup\$ Thank you all so much for taking the time to respond to my post. It was so helpful! \$\endgroup\$ Commented Mar 11, 2022 at 0:40

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