[0:00] I’ve encountered an interesting problem
[0:02] with my string of LED lights I’ve
[0:04] converted them to run on a rechargeable
[0:06] lithium battery in a previous video and
[0:09] it looked like everything was working
[0:10] fine I charged up the battery and ran
[0:13] the lights for a couple of hours with no
[0:14] problems but the next evening when I
[0:17] tried to turn them on again nothing
[0:19] happened checking the battery it was
[0:22] completely flat so flat that the battery
[0:24] protection circuit had cut in
[0:26] I thought maybe I hadn’t charged the
[0:28] battery properly or there was an issue
[0:30] with the charging itself so I thought
[0:32] I’d better do some investigation
[0:34] checking the voltage when we’re charging
[0:36] it works fine and the battery charges up
[0:39] to 4.17 volts but a few hours later when
[0:43] I checked the voltage it’s dropped
[0:45] significantly so I started to suspect
[0:47] there might be an issue with the wiring
[0:49] maybe the switch was broken or there was
[0:52] some other issue so I stripped off the
[0:54] connections to the lights then I checked
[0:56] the switch there’s nothing wrong with it
[0:58] it’s turning off and on properly and
[1:00] putting the multimeter in series with
[1:01] the circuit there’s no current flowing
[1:03] when the switch is off so the wiring
[1:05] seems to be completely fine
[1:07] next I thought maybe the PCB is faulty
[1:10] and it’s draining the battery but when I
[1:12] measured the current flowing from the
[1:13] battery it was only 98 microamps nowhere
[1:16] near enough to drain the battery
[1:18] so my next thought was that is the
[1:21] salvage battery maybe it’s just a bit
[1:23] broken so after charging it up again I
[1:26] swapped it for a fresh off the shelf
[1:28] battery I left both of these overnight
[1:31] the new battery connected to the PCB and
[1:34] the old battery disconnected from
[1:36] everything
[1:37] checking in the morning the old battery
[1:39] held its charge perfectly it’s
[1:41] completely fine but the new battery is
[1:44] almost completely dead
[1:45] I measured the current flowing out of
[1:47] the battery again and everything seemed
[1:49] fine there was nowhere near enough
[1:51] current to drain the battery this was
[1:53] getting really strange
[1:55] so I charged up the battery once again
[1:58] and this time I left the multimeter
[2:00] wired up to see if there might be an
[2:02] occasional fault
[2:03] when I removed the charging cable I
[2:06] noticed that there was six milliamps
[2:08] flowing out of the battery but here’s
[2:10] where it gets even more strange if I
[2:13] break the connection between the battery
[2:14] and the board the current returns to a
[2:17] much more normal amount
[2:18] so my conclusion is there must be
[2:21] something wrong with the tp4056 chip on
[2:24] this particular board if I charge the
[2:27] battery and leave it connected it will
[2:29] slowly drain the battery but if I
[2:31] disconnect and reconnect the battery
[2:32] everything is fine
[2:34] looking at the block diagram of the IC
[2:37] the fault must be somewhere around here
[2:39] maybe this mosfet is somehow getting
[2:41] latched into a slightly conducting State
[2:43] and when you disconnect the battery and
[2:45] reconnect it it resets it at this point
[2:47] I decided to try another board it is
[2:50] exactly the same but I figured the chip
[2:51] on the first board might be faulty so I
[2:54] swapped the battery over and monitored
[2:56] the current the charging looks good and
[2:58] when I disconnect the cable the current
[3:00] drops down to a much more normal 2.5
[3:02] microamps
[3:04] so I charged up the battery with a new
[3:06] board and left it the voltage did drop
[3:08] down to 4.07 volts after a few hours
[3:11] which made me think maybe this battery
[3:12] wasn’t actually as good as my salvaged
[3:14] one but even after leaving it overnight
[3:16] the batteries still had 4.07 volts it
[3:20] held its charge perfect so in the end it
[3:23] looks like there was something wrong
[3:25] with one of the boards and I just
[3:26] happened to use the faulty one I even
[3:28] found someone else online mentioning
[3:30] this issue it could be that there’s a
[3:32] bad batch of tp4056 chips floating
[3:35] around that don’t work properly either
[3:37] way it was a very curious and
[3:38] interesting problem to solve
[3:40] since I’ve made my own little power
[3:42] board I thought I should probably double
[3:44] check that it doesn’t have a similar
[3:45] problem as well the board was made by
[3:47] PCB way as always check out a link to
[3:50] them in the description as they’ve
[3:51] always done a good job for me
[3:53] this board is a little bit more
[3:54] complicated it does use a slightly
[3:56] different chip for charge control it’s
[3:58] using the
[3:59] tp4065 chip I’ve also added a low
[4:02] voltage indicator for this I’m using an
[4:05] stm1061 low power voltage detector this
[4:08] has a built-in voltage reference and
[4:10] when the battery voltage drops below a
[4:12] set voltage it will pull its output low
[4:14] I’ve just connected an LED to this with
[4:16] a fairly High resistor so it will light
[4:18] up when the battery is low I chose 3.1
[4:21] volts as my threshold I could have also
[4:23] used the output to disable the rest of
[4:24] the circuitry maybe something for
[4:26] version 2 of this board there’s also a
[4:28] low Dropout regulator which should give
[4:30] us a stable 2.8 volts on the output
[4:33] for this PCB I wanted to be able to
[4:35] power the end device directly from USB
[4:37] if the battery was flat so I’ve added a
[4:40] direct path from a USB 5 volts to the
[4:42] voltage regulator and I’m controlling
[4:44] where the power comes from using these
[4:46] two shock key diodes if the 5 volts is
[4:48] connected then it will override the
[4:50] power coming from the battery and the
[4:51] ldo and if the five volts is not
[4:53] connected then the power will come
[4:55] straight from the battery and the ldo I
[4:58] things up so I can measure the
[4:59] current when we’re charging everything
[5:01] looks good and if I disconnect the 5
[5:03] volt Supply then the current drops down
[5:05] to a very low value down to about 77
[5:08] microamps it is higher than I’d like but
[5:10] our battery should last for a very long
[5:12] time if we leave it connected to the PCB
[5:14] so that’s great thanks for watching and
[5:17] I’ll see you in the next video