Wonky Dollar Store Night Light. Is this normal? Your thoughts... - Page 1
Forum section: electronics / general

author: edy
author_rank: Super Contributor
timestamp: July 23, 2017, 07:28:05 am
content: Hi everyone,My wife bought some night lights for the home and we have them in the kids rooms too (those cheap dollar store $1.25 types that comes with a bulb too). After a few months, one started to act funny. The switch wouldn't turn it off! I was concerned it may be a safety issue, and I didn't want to unplug it all the time either. So I decided to make a video teardown and see if I could fix it.To my surprise, the construction was very simple and I figured out why it wasn't turning off. The switch worked by pressing a metal tab against one of the plug contacts. After a few months, the metal tab stopped being "springy" and therefore wouldn't spring the contact open when the switch was in the off position. You'll see that in the video below (jump to 11:25 if you want the short version).It only uses a 4 W bulb, so the current running through is small.... according to my calculations, 33 mA based on a 120 VAC outlet. So looking back I don't think there is any safety issue with that tiny amount of current. The fact that the 4 W bulb is there definitely protects the circuit from having enough current to arc across, so I wouldn't expect any spark or arc-weld or burning to happen. Still, I am not too impressed with the construction of the switch and I was wondering if that was considered normal, something UL would approve, and/or if this compares to other night lights? Or do you think it is sub-standard? Please let me know your thoughts. I was just surprised... maybe I shouldn't have been.A few things about the video... I can't add annotations anymore (YouTube stopped it) so corrections... US CA is USA and Canada I presume, not California as I said in the video.Also near the conclusion of the video I also say some stupid things about spark-gap and short, which doesn't really make much sense in this context.Again, considering it is using only 33 mA, I don't see any real safety issue from electrical point of view... I am curious as to whether this is "normal" and what to expect from such a device as I haven't opened any others up so I have nothing to compare to. Also if you want to just jump to the conclusion go to time 11:25 in the video.

author: Zero999
author_rank: Super Contributor
timestamp: July 23, 2017, 08:39:58 am
content: I don't know about the approval being genuine or not but this doesn't seem dangerous, just cheap and nasty. I've seen similar things before.As with many devices with generic lamp holders, the greatest danger is user error: someone replacing the lamp with a more powerful one and it overheating, causing a fire.

author: edy
author_rank: Super Contributor
timestamp: July 23, 2017, 01:25:34 pm
content: Thanks. I understand now why the behaviour was sporadic and changed based on which outlet I used. Depending on the tolerance of some outlets it would cause the plug tines that insert in the socket to deflect just enough to open the tiny gap between the copper tab or not. The construction just seems very "how ya doing" although electrically will pass.

author: tooki
author_rank: Super Contributor
timestamp: July 24, 2017, 07:37:22 am
content: FYI, since it's AC, arcing isn't a huge problem, since the voltage is zero 120 times per second (on 60Hz AC), so any arc extinguishes on its own.

author: VK3DRB
author_rank: Super Contributor
timestamp: July 25, 2017, 02:00:10 pm
content: Quote from: tooki on July 24, 2017, 07:37:22 amInteresting. I wonder if the USA has more fires from thermal runaway in houses with arcing connections with their 110VAC that we do with our 230VAC in Australia. But with our 230VAC there is more risk of electrocution.So the choice is: Be electrocutedor burn to death.

author: tooki
author_rank: Super Contributor
timestamp: July 25, 2017, 02:37:17 pm
content: What are you talking about? Whether it's 50 or 60Hz, whether it's 120 or 230V, either way arcing is minimized because it's AC, and thus is at zero volts twice per cycle, so arcs self-extinguish in normal situations. So what thermal runaway from arcing are you talking about? (Also, all else held equal, higher voltages arc more easily.)P.S. USA is 120V, not 110. Hasn't been 110 for many, many decades.

author: VK3DRB
author_rank: Super Contributor
timestamp: July 27, 2017, 10:23:58 am
content: Current through poor contacts -> heat dissipation.Higher heat dissipation -> higher resistance.Eventually too much heat -> fire.I have seen a 30 year old mains outlet and 3-pin plug melt due to thermal runaway. It was driving a single phase saw bench for many years. As for arcing, you can HEAR it in some cheapo mains power boards with poor contacts. Arcing pits contacts. Pitted contacts -> increased resistance.But yes DC is more subject. But 230V RMS AC or 230V DC, it makes no difference to heat coming from poor contacts.

author: tooki
author_rank: Super Contributor
timestamp: July 27, 2017, 11:58:57 am
content: So again, where are you getting this whole "electrocution vs fire" deaths comparison with 120V vs 230V??

author: tablatronix
author_rank: Regular Contributor
timestamp: July 27, 2017, 01:34:17 pm
content: US electrical code requires AFCIs on certain circuits, most of the time they get installed on all breakers.