Timeline for Old Variac -- chassis ground? is it safe?
Current License: CC BY-SA 4.0
15 events
| when toggle format | what | by | license | comment | |
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| Mar 30, 2021 at 2:35 | comment | added | BZo | You may be interested in what I discovered after having another go at this: electronics.stackexchange.com/questions/557212/… | |
| Mar 28, 2021 at 18:40 | vote | accept | BZo | ||
| Mar 28, 2021 at 18:40 | comment | added | BZo | Well I'd rather keep that to a minimum, so points taken. :) I appreciate your helping me understand this. | |
| Mar 28, 2021 at 18:39 | comment | added | Spehro 'speff' Pefhany | In a word, "yes". A single short would not affect the output voltage, just the electrocution risk. | |
| Mar 28, 2021 at 18:37 | comment | added | BZo | Thanks, good catch. I guess what I'm taking away from this enlightening discussion is that not only can I not earth the chassis, I shouldn't use this thing at all, because even if I add a polarized plug something has gone wrong. There are no moving parts in the core which seems tightly bonded together, and so assuming there's no intentional connection-- maybe that doped fabric insulating mat has somehow decayed over time and become conductive? I remain somewhat confused as to how it even works (produces the expected output) if it is really damaged in some fundamental way like this. | |
| Mar 28, 2021 at 18:27 | comment | added | Spehro 'speff' Pefhany | The fact the connection board markings say you can ground either end of the winding 2/4 indicates that it's intended to be isolated. Also the non-polarized plug which would be an unacceptable safety hazard even in 1950. Sorry. | |
| Mar 28, 2021 at 18:19 | comment | added | BZo | Not as far as I can tell. Smells normal & no visible charring that I can see anywhere. I added yet another photo showing the rear coil side. There some sort of doped plastic insulating mat between the coils and the backside of the mount plate, and the inner tubular aluminum core (which runs through to the front) doesn't contact anything at rear when assembled (the rotating spindle from the front knob is not conductive). So if you're just eyeballing it, it sure looks like it's not supposed to have continuity to the chassis. But it also doesn't appear damaged at all. ¯_(ツ)_/¯ | |
| Mar 28, 2021 at 18:08 | comment | added | Spehro 'speff' Pefhany | Any indication of damage, like burnt smell? | |
| Mar 28, 2021 at 18:07 | comment | added | BZo | The whole mount panel of the core is in contact with the chassis. My expectation would be to see no continuity between the taps and that mount panel (because there's some other evidence of isolation on the coil side) but there seems to be some internal connection within that block? (I have added a new pic showing this best I can) | |
| Mar 28, 2021 at 18:05 | comment | added | Spehro 'speff' Pefhany | Can you find a deliberate connection to the case or the frame of the variac? | |
| Mar 28, 2021 at 18:05 | comment | added | BZo | Thanks again, for the info & ideas. The plug is not, in fact, polarized-- and it seems original. (The socket on the Variac is polarized, interestingly.) In an effort to figure out where the chassis connection actually happens, I removed the transformer core, and it sure looks to me like somewhere inside the sealed internals the wiring is connected to the chunky front aluminum mounting plate which gets bolted directly to the chassis. (See new photo). I'm getting a bit out of my depth as to what the ground-to-line stuff is doing above, but I don't know if I can disconnect this? :-| | |
| Mar 28, 2021 at 17:46 | history | edited | Spehro 'speff' Pefhany | CC BY-SA 4.0 | added 230 characters in body |
| Mar 28, 2021 at 17:41 | history | edited | Spehro 'speff' Pefhany | CC BY-SA 4.0 | added 230 characters in body |
| Mar 28, 2021 at 17:37 | comment | added | BZo | Thanks. With the power off, unplugged, I attached the meter measuring resistance between each input plug prong and the exposed metal switch on the case. When the switch is off, infinite resistance. When the switch is on, I see 1-2 ohms. I'm not expert so I might be misunderstanding you, but that seems like continuity to the case. I added a photo to the question showing this configuration in case that helps. | |
| Mar 28, 2021 at 17:20 | history | answered | Spehro 'speff' Pefhany | CC BY-SA 4.0 |