Weller WTHA1 ground leak - Page 1
Forum section: electronics / general

author: orcinus
author_rank: Contributor
timestamp: February 12, 2020, 06:57:23 pm
content: Anyone have any experience with the Weller WTHA1 "entryish level" hot air stations?Just unpacked mine, and it looks like it's not grounded properly.Touching/rubbing a finger on the hot air tool hose produces a very noticable 50Hz buzz feel.The hose is conductive and *should be* grounded to common ground (for ESD safety), but it looks like there's a current grounding through the hose and my finger when touching it. Haven't measured it yet, so have no numeric data to offer yet.This occurs even with the station switched off at the main switch, just plugged into mains, which is a bit worrying.And yes, i'm using grounded plugs (schuko).A JBC connected to the same outlet exhibits no similar "surprises".PS:no grounding screw on the station either, so the only way to ground it is through the euro plug.

author: orcinus
author_rank: Contributor
timestamp: February 12, 2020, 07:39:46 pm
content: Nevermind, tried wiggling the plug, and that made it come and go.Looks like the earthing contacts of the plug are a bit crappy.In the bin it goes, replacement works fine.

author: orcinus
author_rank: Contributor
timestamp: February 12, 2020, 07:51:50 pm
content: Nope, it's back with a different plug.GAAAH.

author: Monkeh
author_rank: Super Contributor
timestamp: February 12, 2020, 08:04:22 pm
content: Perhaps your socket is what's crap..

author: orcinus
author_rank: Contributor
timestamp: February 12, 2020, 08:07:51 pm
content: Entirely possible, but why is the JBC iron fine on the same socket?

author: wraper
author_rank: Unknown
timestamp: February 12, 2020, 08:27:02 pm
content: Quote from: orcinus on February 12, 2020, 08:07:51 pmEither slightly different plug dimensions or you simply didn't notice earth problem due to lack of Y noise suppression capacitors within JBC station or their small value. Measure resistance from JBC iron to earth in other nearby socket. It should be a few Ohms max.

author: orcinus
author_rank: Contributor
timestamp: February 12, 2020, 11:59:39 pm
content: Measuring less than an ohm for both.

author: wraper
author_rank: Unknown
timestamp: February 13, 2020, 12:04:28 am
content: Quote from: orcinus on February 12, 2020, 11:59:39 pmMaybe you are loosing earth connection to socket itself.

author: orcinus
author_rank: Contributor
timestamp: February 13, 2020, 02:33:43 am
content: Could be, although i probably would've noticed that on other tools and equipment by now.I'll try around a few other outlets tomorrow.Interestingly, while i was poking around and measuring the resistance, the unit ended up in some weird nether-state where it would turn on fine, display the temperature, but was completely unresponsive to any button presses. This persisted through turning off and on again, unplugging it etc. Almost like i turned the key lock on, which i didn't (and which doesn't quite behave like that anyways).Resetting to factory settings fixed it.Bizarre.

author: orcinus
author_rank: Contributor
timestamp: February 13, 2020, 02:48:31 am
content: And while on the subject of weird things...The manual is rubbish (both quick start and "full" one), and as if that weren't enough, it confusingly mentions a settings menu item that doesn't exist (preset temperatures), and that uses a temperature sub-display that's completely unused on this unit.Among other bizarre design choices, there's an output power meter, but no actual measured temperature (only the setpoint) so you have to watch the 5 segment power meter to know when you've reached the setpoint. There's THREE digital readout sections on the display. They're using one. And a 5 segment graph.The whole thing's a bit of a mess, looks like.At least it does its primary job well - it blows hot air, and reflows in seconds.They should've stuck with the two physical dials for a UI like on WHA900.

author: orcinus
author_rank: Contributor
timestamp: February 13, 2020, 04:56:08 pm
content: Getting similar results on all outlets.But now i'm getting paranoid and i think i've felt a 50hz buzz on a kettle this morning too.I'm getting convinced the whole building's earth wiring might have started rotting away.

author: orcinus
author_rank: Contributor
timestamp: February 13, 2020, 04:58:35 pm
content: On topic of weird UI...It *does* show actual current temperature on the subdisplay - but only when it's in the cooldown mode, which inexplicably has to be initiated manually, by pressing + and - together. And to top it off - the cooldown mode is not forced air cooling, it just... well... turns everything off, dims the display, shows the temperature and flashes "COOLING" on the display.Was someone drunk when designing this unit?

author: wraper
author_rank: Unknown
timestamp: February 13, 2020, 06:56:10 pm
content: Quote from: orcinus on February 13, 2020, 04:56:08 pmMeasure voltage between earth and active wires. One of them is neutral and should have the same potential as earth, so measurement should be near zero. And on line wire you should measure nominal mains voltage.

author: orcinus
author_rank: Contributor
timestamp: February 15, 2020, 02:51:48 am
content: There's about half a volt to a volt AC between earth and neutral.Resistance between earth and neutral is a few ohms.Edit: I think i'm going slightly crazy. I can't feel the 50hz on the WTHA 1 anymore all of a sudden.

author: orcinus
author_rank: Contributor
timestamp: February 15, 2020, 04:56:48 pm
content: For what its worth, the firmware bugs are definitely not in my head.I've just figured out what the mysterious lockup is.If you leave the unit in the phantom "cooldown mode", and then switch it off, when it powers on, it's still in the cooldown mode, but doesn't indicate it anywhere. You have to blindly press + and - keys, with no indication that you've really done anything besides all the controls becoming unlocked again.Someone, somewhere, forgot an if/then on power-on.

author: orcinus
author_rank: Contributor
timestamp: February 16, 2020, 12:51:48 am
content: I'm not crazy after all.I'm also not sure why i haven't checked this earlier.Voltage across earth and the hose:Voltage across earth and tool tip:

author: wraper
author_rank: Unknown
timestamp: February 16, 2020, 02:14:42 am
content: Quote from: orcinus on February 16, 2020, 12:51:48 amNow do the same with cable from JBC iron.

author: wraper
author_rank: Unknown
timestamp: February 16, 2020, 11:34:27 pm
content: OK, maybe you don't see higher voltage since it uses low voltage for iron, try touching any mains cable. In any case, what you have measured, has nothing to do with supposed tingle what you felt.

author: orcinus
author_rank: Contributor
timestamp: February 17, 2020, 12:07:31 am
content: I'm measuring the same (respective) voltage on both, whether they're turned on or off.So voltage to the tool should be irrelevant, unless switching occurs in the tool itself (which it doesn't).