Aoyue 998 - dangerous product?? - Page 1
Forum section: electronics / general

author: tatus1969
author_rank: Super Contributor
timestamp: July 27, 2016, 06:55:07 pm
content: this is a hot air gun for SMD rework, and I opened it to replace the broken triac of this unit. Apparently that broke because the manufacturer saved the heatsink for that device, but that's another story.What scared me is how they intended to reach product safety. Look at the PCB, it is directly connected to mains. The potentiometer terminals carry lethal voltage. I checked the lower one, center tap goes to mains through a 270 ohms resistor.The potentiometers are metal can types. Of course the electrical parts are isolated from the can, and the can itself is also not electrically connected to the PCB. But they take this whole assembly and fasten it directly into the mounting holes that you see on the second picture.At least they did the earthing of this part of the unit's housing right. And if they do hipot testing in their fab, should I feel reasonably safe then?

author: SteveyG
author_rank: Unknown
timestamp: July 28, 2016, 01:28:58 pm
content: How do you think dimmer switches are made? The potentiometer is connected to mains and may be on a metal faceplate. There's nothing inherently dangerous about this if it is a Class I product and instructs you to ensure it is earthed.

author: tatus1969
author_rank: Super Contributor
timestamp: July 28, 2016, 02:39:19 pm
content: just looked at dimmers that I have. They all use potentiometers with plastic housings. My concern is not that the pot's terminals connect to mains, but that they have been using metal housing types. I didn't measure creepage/clearance but my rough estimate is that it is less than 1mm.I don't feel good with that although I think I can rely on our ground fault circuit breaker, but I decided to replace these with plastic types anyway.

author: Kilrah
author_rank: Unknown
timestamp: July 28, 2016, 02:42:24 pm
content: The pot case is isolated. The pot shaft is isolated. The case is properly grounded to catch any unlikely fault that might appear.Don't see the problem?

author: tautech
author_rank: Super Contributor
timestamp: July 28, 2016, 02:52:06 pm
content: Quote from: Kilrah on July 28, 2016, 02:42:24 pmPlus the knob is non-conductive also.There's been hundreds of thousands of CRO's built with metal pots with metal shafts for Intensity control @ 1kV or more and nobody bats an eyelid. Only the plastic knob and mains ground are between you and a shock.

author: ebclr
author_rank: Super Contributor
timestamp: July 28, 2016, 02:53:24 pm
content: I guess Aoyue isn't alone on this, The majority of stations use the same principle

author: tatus1969
author_rank: Super Contributor
timestamp: July 28, 2016, 06:58:14 pm
content: hmmm, I see it is maybe only my personal safety need. Although I stick to my objection that the 1mm clearance is not enough. I am not an expert in this, but wouldn't a class 1 / 230V device require >1.5mm clearance and >4mm creepage? Both is not given here.

author: ebclr
author_rank: Super Contributor
timestamp: July 28, 2016, 07:44:33 pm
content: Maybe this one match your needshttp://www.techni-tool.com/821SO9516

author: tatus1969
author_rank: Super Contributor
timestamp: July 28, 2016, 09:47:58 pm
content: Quote from: ebclr on July 28, 2016, 07:44:33 pmthanks, I have a decent Weller. This is about my hot air gun. I will either live (or die) with it, or replace the pots.

author: Refrigerator
author_rank: Super Contributor
timestamp: August 04, 2016, 07:51:12 pm
content: If you have it properly grounded then there's nothing to worry about.

author: tatus1969
author_rank: Super Contributor
timestamp: August 04, 2016, 09:14:52 pm
content: Quote from: Refrigerator on August 04, 2016, 07:51:12 pmagree, but it just doesn't feel good to know that I have a device with less than 1mm clearance between AC mains and my fingers, even knowing that my houses' RCD will detect those problems when earthing is interrupted, and I will only be shocked shortly.P.S. There are lots of Chinese power strips on the market that lack the PE conductor to save copper cost:http://www.eah-jena.de/~gitter/kabel_1.jpgDon't have one of these though O0Common saying in Germany: the devil is a squirrel.

author: Refrigerator
author_rank: Super Contributor
timestamp: August 06, 2016, 11:32:48 am
content: Quote from: tatus1969 on August 04, 2016, 09:14:52 pmA squirrel ? Here where i live devil is a goat.