this is wrong this is so wrong
when I was a little kid in the 1980s electric clocks which ran on the full AC line voltage
and had a continuously sweeping second hand were a common sight in fact many homes had a special
recessed outlet mounted high up on the wall for powering one but by the 1990s more and more of
them started being replaced by Quartz clocks which have a ticking second hand and consume
so little power that they can run for years on a single 1.5 volt AA battery
so for most people the inconvenience of needing to replace the battery every once
in a while is more than outweighed by the benefits of not having to plug it
into an outlet and not having to reset the time every time the power goes out
so as a result AC powered clocks have pretty much disappeared from the consumer market
you do still see AC powered clocks in commercial and institutional settings
like schools hospitals and train stations but for everyday household use they've pretty much
disappeared and it's almost impossible to find a new one today except for this one it's made
by a company called Chicago Lighthouse it costs about $33
and it says on the box it's an electric wall clock it's the model 67801103
14 and a half inch electric wall clock and if I open up the box
there it is
says the Chicago Lighthouse electric quartz assembled in USA
and it's so big I can't even fit the whole thing on camera but the unusual thing is
it runs on AC power and has an ordinary 120 volt AC power cord on it it's definitely a
new product this one was made in May 2023 but it doesn't use an old-fashioned AC motor to
run the clock it uses the same kind of quartz clock mechanism as battery powered clocks it
even has the space for where a double A battery would go but instead it says no battery required
and instead right into that quartz clock mechanism which normally runs on a 1.5 volt battery
it has the power cord feeding 120 volts ac how does that work
here's one of those standard quartz clock mechanisms which I took out of a broken
clock it says young Town quartz made in Taiwan no jewels unadjusted as model 1288 you can still buy
these today for around five dollars for just the mechanism or for around ten dollars for a complete
kit including the hands to make your own clock and there's where the 1.5 volt double A battery goes
there it is with the cover removed and all you really see is a bunch
of plastic gears and a big coil of wire but if I disassemble it
further which will probably result in all those gears spilling out
you can see the electronics and there is the quartz crystal which pulses 32,768
times a second and if you divide that by two 15 times you get a pulse every second
and that pulse Powers this coil which kicks the Second Hand by one second and that's why
these clocks tick instead of having a continuous movement of the second hand
in addition to that quartz crystal there's also an integrated circuit under this blob
and really that's about it you have the crystal the integrated circuit the coil
of wire and the whole thing runs directly on 1.5 volts DC from a single double A battery
now the question is how can you take one of these designs and run it on 120 volts ac
here's the mechanism in the new Chicago Lighthouse clock and it doesn't have any
terminals for where the battery would go but that's clearly where it was originally
designed to hold the double A battery but they put a sticker saying no battery required
it says Quartex USA engineering and quality made in China and there's clearly not enough
room in this little plastic box to fit a Transformer you can see how thin it is
before I possibly destroy it in the process of trying to figure out how
it works I thought I should show it working so here it is I'm going to plug it into AC power
that's interesting it stayed still for a couple seconds before it started moving
almost like it's charging up a big capacitor or something otherwise
it makes the same standard ticking noise there's no AC hum or anything
now I'm going to unplug it and I'll see if it stops instantly
or if it keeps running for a few seconds Beyond when I unplug it
no it stopped pretty quickly I'll plug it back in
and this time there wasn't that long delay before it started moving
just one thing I noticed is that unlike most old-fashioned AC motor wall clocks which have
an externally adjustable time adjustment knob usually on the bottom this one does not so you'll
have to take it off the wall to adjust the time and they give you this very tiny little thumb
wheel which takes a lot of rotations to move the time so if the time indicated on the clock
is far away from the actual time you're going to spend quite a bit of effort trying to adjust it
now I'll try to open it
without destroying it wish me luck
[Music]
okay well it mostly looks the same we have the same bunch of plastic gears and coil
of wire but instead of the double A battery we have the 120 volt AC coming in right here
then there's four diodes which form a bridge rectifier and a smoothing capacitor
one thing I do know is that because this runs on rectified DC instead of directly on the AC
that means the frequency of the AC doesn't matter it does not use that as a timing reference unlike
the old-fashioned electric clocks which used an AC motor to run the mechanism so
we can run this on either 50 or 60 hertz AC power and it'll keep accurate time either way
and I was also able to look up the battery powered version of this mechanism and everything inside
this clear plastic box is identical it's only the circuit board it's mounted onto that's different
so I'm gonna need to disassemble this further to
try to see the bottom of this to figure out what's going on
but before I go that far I left it running overnight and it is keeping accurate time and I
noticed it just barely getting warm to the touch around here so there's definitely something in
this mechanism which is dropping down the voltage and producing a little bit of heat in the process
thankfully I was able to disassemble it non-destructively
but there's just so many things wrong with this first of all there's no strain relief
on the power cord you can see where it's kind of been crimped by the plastic casing and that's it
the two wires are just split apart and the case goes on top of it and that's it
now if we take a closer look here one side of the AC line goes directly into
a surface mount resistor I've never seen that before I mean are these little tiny
resistors even rated for 120 volts because normally they only run it five volts or less
it's so small you probably can't read it but it says 203 on it which means it's a 20K resistor
and I noticed on the case here it says 120 volts ac 60 hertz 0.4 Watt so if they're drawing almost
half a watt through this little resistor it's no wonder it's getting warm and you'd think
that dropping resistor would be connected to the hot side of the AC line but if I connect one of
my multimeter probes to the hot terminal on the plug which is the smaller blade but if I touch
it with the other probe we get nothing the hot side of the AC line is actually coming in here
which seems like it should be the ground plane because it has all this connected to it
and if we follow the path of continuity from coming in there we go all the way over here
and look how close that is to the screw holding together the clock mechanism right
here is connected directly to the hot side of the AC line and that's the screw holding the
thing together there's like what two millimeters of clearance there if we follow the path around
here that's hot go down here that's hot right next to this integrated circuit and then we go
down here which would have been the battery terminals if this was the battery version
that's connected to the AC line so it's a good thing they didn't
put any battery terminals in it otherwise it could reach in and touch the AC line directly
and if I connect my multimeter probe to the neutral side of the AC line which is
the wider blade on the plug that is connected right here which goes to that dropping resistor
and that's where the continuity ends because it's going through that resistor so you'd think
this would be the hot side and this would be the neutral side but they reversed it
these are all the diodes forming the bridge rectifier and here is the smoothing capacitor so
if we follow the output of that it goes around here directly into that integrated circuit
so I'm going to try to carefully measure what is the voltage coming out of that smoothing
capacitor into the integrated circuit because you can see it's designed to run on batteries with
these terminals so you think this would be 1.5 volts DC coming in on this side approximately so
they're going to be dropping a lot of voltage to go down from 120 volts ac to 1.5 volts DC
okay right now it is plugged in and connected to AC power so I'm going to be very careful
and if you're going to do this you should be too the multimeter is set
to measure ac voltage so we're going to probe across the AC line right here
yep 120 volts approximately coming in now let me see what's coming out of that dropping resistor
what 2.3 volts ac it really is dropping all the way from 120
to 2.3 volts that's a lot of drop to put on that little surface mount resistor now the
multimeter is switched to measure DC voltage and I wasn't even sure where it would be a safe place
to measure it but then I realized what about these battery terminals so if I go across that
about 1.8 volts so if this actually was connected to a battery it would charge the battery so yes
they're definitely running that chip on about 1.8 volts which seems okay that's probably
within the tolerance of what it was designed for but the vast majority of that dropping down from
120 volts to approximately 2 volts is through that tiny surface mount resistor that's amazing
so what a weird design to be fair it's completely encased in plastic
when it's installed so there's no shock hazard to the user but still
you're putting a lot of faith in that little service Mount resistor
well it's all back together except for the plastic cover I want to make sure
I got all the clock hands properly aligned before I put this back on
and thankfully it's still working and I don't mean to imply that this is in any way
a dangerous product because like I said earlier I left it plugged in overnight and it only got
mildly warm to the touch near where that dropping resistor is but it's definitely a very weird and
unconventional design which seems to break a lot of rules about electronics and the way it works
so if you want a new AC powered wall clock this is pretty much your only choice from Chicago
Lighthouse and it is assembled in the USA and in this case it was reassembled in the USA as well