Why does this flying bug UV light trap intermittently trigger my GFCI? - Page 1
Forum section: electronics / general

author: NeverDie
author_rank: Regular Contributor
timestamp: November 18, 2022, 09:32:29 am
content: The name of the product is DynaTrap. You plug into mains, whereupon it powers on four UV led's to attract gnats to it, and they then get stuck to a nearby sticky glue board when they land on it.https://www.dynatrap.com/dynatrap-dot-indoor-flying-insect-trapIt actually works, but the problem is that it intermittently trips my GFCI. I've tried it on two different GFCI circuits (a different GFCI in each case), with the same result.Why?Attached is an overview photo together with a photo of the circuit board inside.

author: timenutgoblin
author_rank: Regular Contributor
timestamp: November 18, 2022, 09:58:37 am
content: Check VR1 (varistor?), it looks like it might be damaged. Gnat's what I reckon.

author: Stray Electron
author_rank: Super Contributor
timestamp: November 18, 2022, 12:59:19 pm
content: My advice is to toss that thing. It's been proven over and over again that they attract more bugs into the area that you want to protect than they catch. It's also been shown that they catch far more beneficial bugs than they do pests, such as mosquitoes. Using one of these is a lose-lose situation as far as I'm concerned.

author: jonpaul
author_rank: Super Contributor
timestamp: November 18, 2022, 03:02:18 pm
content: Dangerous mains current leakage, Chinese junkj

author: tom66
author_rank: Super Contributor
timestamp: November 18, 2022, 03:39:49 pm
content: Since it only has L and N this is an interesting question as there can be no mains leakage unless you touch it.A device like this probably has a very cheap SMPS in it which is not compliant with the required EMC standards, and the conducted noise could be causing the RCD to detect a fault.But this does seem to stretch believability, as you would have thought an RCD would need to deal with a lot more EMC before a shitty ~1 watt SMPS would cause a hassle.Could there be a fault with the socket instead? Perhaps inserting the device into the socket is allowing a conductive path to form, like some kind of conductive gunk stuck in the socket. Or perhaps you have a swapped neutral somewhere, which means that the neutral current is bypassing the RCD, causing an imbalance and trip.

author: electr_peter
author_rank: Unknown
timestamp: November 18, 2022, 09:26:22 pm
content: I agree withtom66that these is likely something wrong with wiring to cause RCD trip with only L & N connections, not UV lamp itself.I presume that UV light is plugged into some remote socket on the outside of the house. Is that socket (or related wiring) properly wired? Is that socket is used for other things?I would suggest to test that specific socket as well as try plugging in other electrical devices (but be careful). Something is not quite right.

author: NeverDie
author_rank: Regular Contributor
timestamp: November 18, 2022, 10:48:40 pm
content: Just to clarify: this uv bug trap is an indoor device, not an outdoor device. So, for instance, there are no beneficial indoor insects to consider in this equation. The more kills the better, regardless of the insect type.I have used this GFI-501A GFI Receptacle Tester:https://www.google.com/imgres?imgurl=https%3A%2F%2Fdylbs6e8mhm2w.cloudfront.net%2Fproductimages%2F300x300%2F623-GFI-501A.EPS.JPG&imgrefurl=https%3A%2F%2Fwww.shoplet.com%2FGardner-bender-Ground-Fault-Receptacle-Testers-GFI-501A%2FSEPTLS623GFI501A%2Fspdv&tbnid=Lq_tCMxp21XVmM&vet=12ahUKEwiC4Pmt5Lj7AhXHrmoFHZ_BAVsQMygBegUIARC-AQ..i&docid=lfHvej8ZJYVhFM&w=300&h=300&itg=1&q=gfi-501a&ved=2ahUKEwiC4Pmt5Lj7AhXHrmoFHZ_BAVsQMygBegUIARC-AQand it does not indicate any wiring errors. With the bug light removed, GFCI also appears to test out correctly using the same diagnostic tool. That said, I don't know how good a tool it either is or isn't. Maybe there are nuanced conditions that it is not good at detecting, but I presume it should catch anything that's egregiously wrong.Another possible clue:the further away on the circuit this uv bug trap is from the GFCI, the lower the probability of it tripping the GFCI. The tripping effect is most noticeable when the uv bug trap is plugged directly into the GFCI receptacle.

author: tom66
author_rank: Super Contributor
timestamp: November 18, 2022, 11:42:06 pm
content: Is it possible to test the device on a circuit using a different RCD/GFCI? Perhaps the GFCI is just really sensitive due to a defect, and a minute imbalance is tipping it over the edge.

author: james_s
author_rank: Super Contributor
timestamp: November 19, 2022, 03:01:08 am
content: Are you sure it's a GFCI and not an AFCI? The latter is much more common for ordinary indoor branch circuits and since a bug zapper is using an arc to kill bugs it would not surprise me if an arc fault detector trips.

author: pcprogrammer
author_rank: Super Contributor
timestamp: November 19, 2022, 06:54:01 am
content: The device is not arcing according to the product advertising. It uses glue cards to hold the bugs. The UV light attracts them and then they land on the glue card. Kind off like these old fly catchers that you hung from the ceiling or so.The op also wrote that he tested the device on two different protected circuits indicating that the device is the most likely candidate to be the culprit.But the fact that it has no ground connection, it is not likely due to current leakage. Most GFCI's are 30mA which is a lot of current to be leaking through plastic. So what comes to mind is to much capacitive or inductive load, causing a large enough phase difference to trip the GFCI. But the circuit board does not show a lot of this.Basically a big mystery.

author: amyk
author_rank: Super Contributor
timestamp: November 19, 2022, 08:43:52 am
content: Trace out the schematic, it looks simple enough to be a capacitive dropper.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: November 19, 2022, 10:50:23 am
content: Quote from: timenutgoblin on November 18, 2022, 09:58:37 amWhat you did there. I see it.

author: rdl
author_rank: Super Contributor
timestamp: November 19, 2022, 11:04:12 am
content: I have bad gnat problems every year. I guess gnats, could be fruit flies or whatever. What works best to keep them under control is a bowl of vinegar with some water and dish washing soap added. I had a mini bug zapper with UV LEDs and it would kill a few every day, but they drown by the dozens in the vinegar bowl.

author: james_s
author_rank: Super Contributor
timestamp: November 19, 2022, 06:55:36 pm
content: Quote from: pcprogrammer on November 19, 2022, 06:54:01 amThe OP is in the USA, GFCI trip current is 5mA.

author: pcprogrammer
author_rank: Super Contributor
timestamp: November 19, 2022, 08:12:14 pm
content: Quote from: james_s on November 19, 2022, 06:55:36 pmWow that is low. Over here 30mA is common and comes in two types, slow and fast. There also used to be a 300mA or even 500mA version for a circuit with a washing machine or other type of inductive load, but not sure if they are still sold. Nowadays the slow type is used for the washing machine.But which such a low current it must trip rather easily.

author: james_s
author_rank: Super Contributor
timestamp: November 19, 2022, 08:16:50 pm
content: Quote from: pcprogrammer on November 19, 2022, 08:12:14 pmThat's the idea, they're meant to trip easily if for example you pick up the end of an outdoor extension cord with wet hands. They're only used for specific purposes, originally receptacles outdoors, garages and in bathrooms had them mandated by the late 70s, then in the 90s they started requiring them for kitchen receptacles and anything else near a source of water. We don't have the sort of whole house RCDs used in some parts of the world.

author: tom66
author_rank: Super Contributor
timestamp: November 19, 2022, 11:51:23 pm
content: Quote from: james_s on November 19, 2022, 06:55:36 pmI have read though that it's not unusual for such a GFCI to take several seconds to trip at its rated current.Whereas a 30mA RCD in the EU will trip in less than 40ms.The result is that while EU RCD will not trip <30mA, both types will trip within a similar amount of time (<100ms) at dangerous current levels (>=30mA, heart fibrillation usually occurs >40mA.)

author: james_s
author_rank: Super Contributor
timestamp: November 20, 2022, 01:16:31 am
content: Quote from: tom66 on November 19, 2022, 11:51:23 pmI can't say I've ever tested that. I do know from experience though that if you drop the end of an extension cord in a puddle on the ground outside the GFCI will trip instantly. I've never tried to actually measure it but maybe I will sometime if I get bored.

author: timenutgoblin
author_rank: Regular Contributor
timestamp: November 28, 2022, 01:15:00 am
content: Quote from: NeverDie on November 18, 2022, 09:32:29 amI think this type of circuit likely uses a dedicated LED driver IC and a bridge rectifier - both surface mount type and would need to be located on the back of the circuit board. Maybe it's just a pair of transistors (MOSFET or BJT) configured as a current limiting circuit. One of those electrolytic capacitors is likely to be a high voltage rated type of small capacitance. I can't see a fuse, but the resistor is likely to be a fusible type.I have seen something similar on BigClive and DiodeGoneWild.

author: tooki
author_rank: Super Contributor
timestamp: November 28, 2022, 05:07:02 pm
content: Quote from: tom66 on November 19, 2022, 11:51:23 pmRegulationsallowmulti-second reaction times for very low current, but in practice they practically always react in a fraction of a second. See e.g. page 6 ofhttps://www.westernautomation.com/wp-content/uploads/2016/03/GFCIs_For_AC_DC_Systems.pdf