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Charging Circuit
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I am working on a Sabre Flashlight/Tazer combination.? The LED has shorted but that is not the reason for this post.? The charging circuit is very simple.? The line voltage goes through a 684nFd cap to one side of a diode bridge rectifier.? The other side of the bridge is connected to the other side of the line.? The output of the bridge goes directly to a 4 pack N size Nicad battery pack.? During the testing of the cap,? the bridge lead to the cap broke. I have found replacements for the LED and bridge.
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I checked the value of the cap by using my function generator and scope to make a divider with a resistor and calculated the cap value.? It calculates to 730 nFd.? A little more than 20% low.
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My question has to do with the limiting of the bridge output. Since there is no voltage or current? limit, what provides these two limits?? Also should this cap be replaced due to its low value.? There are no markings on the bridge other than the input sine wave and the output +/-.? I will replace this with a 1A 1000V bridge.? I have selected a 1 Watt 3.4 volt 20 mm heat sink LED since this was the original connection configuration.
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I am considering adding a 5 volt zener and resistor on the bridge output just to limit the bridge output.
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Any thoughts?
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Regards,
Dan Kahn
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wn4isx
Capacitors act like lossless resistors at AC. It's called capacitive reactance.
covers both capacitive reactance and inductive reactance.
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This web page does the calculations for you if you enter capacitor value and frequency.
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With the exception of the situation where the circuit is connected at the peak of the AC, where the inrush current can be extreme, a capacitor is like a resistor and will only allow X amount of current at Y frequency.
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The original LEC AC bulb replacements used a series capacitor, a current limiting resistor for inrush current at peak AC waveform and full wave bridge and a string of white LEDs.?
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In your circuit, the NiCad and LED would normally limit the voltage, although you can easily cook a NiCad to death with 24/365 charging at as low as 1/20 C (C being amp hour) and N cell NiCads have a very low amp hour rating. I suspect it'd be extremely easy to cook them to death.
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I'd be tempted to use a wall wart and build a real regulated power supply. The circuit you describe is simple, maybe too simple to be reliable.
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On Friday 10 January 2025 08:52:00 am Dan Kahn via groups.io wrote:
I am working on a Sabre Flashlight/Tazer combination.? The LED has shorted but that is not the reason for this post.? The charging circuit is very simple.? The line voltage goes through a 684nFd cap to one side of a diode bridge rectifier.? The other side of the bridge is connected to the other side of the line.? The output of the bridge goes directly to a 4 pack N size Nicad battery pack.? During the testing of the cap,? the bridge lead to the cap broke. I have found replacements for the LED and bridge.Is that uF or nF? That's higher than the 680nF you mention above... My question has to do with the limiting of the bridge output. Since there is no voltage or current? limit, what provides these two limits??The capacitor limits the current. Also should this cap be replaced due to its low value.? There are no markings on the bridge other than the input sine wave and the output +/-.? I will replace this with a 1A 1000V bridge.? I have selected a 1 Watt 3.4 volt 20 mm heat sink LED since this was the original connection configuration.Big Clive has done teardowns and reverse engineering on a lot of this kind of circuit. A few things you might want to add are a discharge resistor across the cap (470K-1M or around there, value is not critical) and an inrush limiting resistor in series with the input to the bridge (10-470 ohms, again not critical) which can also act as a fuse. A zener across the output of the bridge is also pretty common. While I've seen a great many of these circuits online, and a version of that was also posted to this list a while back, I tend to prefer the use of a wall wart because of isolation from the power line... -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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On Friday 10 January 2025 09:53:33 am wn4isx via groups.io wrote:
In your circuit, the NiCad and LED would normally limit the voltage, although you can easily cook a NiCad to death with 24/365 charging at as low as 1/20 C (C being amp hour) and N cell NiCads have a very low amp hour rating. I suspect it'd be extremely easy to cook them to death.Yeah, there is that. I have a Simpson DVM that uses four fat nicads to power it, and I'm on my second or third set of them so far. And they're not in good shape. The original charger for that was a wall wart that was supposed to put out 7.5V, fed through a resistor and that's it. I also have a cordless screwdriver that sits in its stand most of the time, with three nicads in it, and they're not holding a charge all that well these days either. I'd be tempted to use a wall wart and build a real regulated power supply. The circuit you describe is simple, maybe too simple to be reliable.I've pretty much given up on using nicads these days, but if I did I think I'd prefer to use a circuit that would stop charging them at a given point, coming back on only when needed. Like those TP4056 modules I use for the lithium cells... -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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Thanks for getting back to me Roy. Yes all values for the cap are nFd. I like the additional resistor on the bridge input. I can probably find a place to add this without taking up too much area. Calculating the Xc at 60 Hz it is around 3500 ohms. That works out to about 35 ma input current. My concern is the output voltage of the bridge and will it overdrive the battery pack. Dan On Friday, January 10, 2025 at 10:56:48 AM EST, Roy J. Tellason, Sr. via groups.io <roy@...> wrote: On Friday 10 January 2025 08:52:00 am Dan Kahn via groups.io wrote: > I am working on a Sabre Flashlight/Tazer combination.? The LED has shorted but that is not the reason for this post.? The charging circuit is very simple.? The line voltage goes through a 684nFd cap to one side of a diode bridge rectifier.? The other side of the bridge is connected to the other side of the line.? The output of the bridge goes directly to a 4 pack N size Nicad battery pack.? During the testing of the cap,? the bridge lead to the cap broke. I have found replacements for the LED and bridge. > > I checked the value of the cap by using my function generator and scope to make a divider with a resistor and calculated the cap value.? It calculates to 730 nFd.? A little more than 20% low. Is that uF or nF?? That's higher than the 680nF you mention above... > My question has to do with the limiting of the bridge output. Since there is no voltage or current? limit, what provides these two limits?? The capacitor limits the current. > Also should this cap be replaced due to its low value.? There are no markings on the bridge other than the input sine wave and the output +/-.? I will replace this with a 1A 1000V bridge.? I have selected a 1 Watt 3.4 volt 20 mm heat sink LED since this was the original connection configuration. > > I am considering adding a 5 volt zener and resistor on the bridge output just to limit the bridge output. > > Any thoughts? Big Clive has done teardowns and reverse engineering on a lot of this kind of circuit.? A few things you might want to add are a discharge resistor across the cap (470K-1M or around there,? value is not critical) and an inrush limiting resistor in series with the input to the bridge (10-470 ohms,? again not critical) which can also act as a fuse.? A zener across the output of the bridge is also pretty common. While I've seen a great many of these circuits online,? and a version of that was also posted to this list a while back,? I tend to prefer the use of a wall wart because of isolation from the power line... -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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Here is a schematic I reverse engineered. On Friday, January 10, 2025 at 11:01:52 AM EST, Roy J. Tellason, Sr. via groups.io <roy@...> wrote: On Friday 10 January 2025 09:53:33 am wn4isx via groups.io wrote: > In your circuit, the NiCad and LED would normally limit the voltage, although you can easily cook a NiCad to death with 24/365 charging at as low as 1/20 C (C being amp hour) and N cell NiCads have a very low amp hour rating. I suspect it'd be extremely easy to cook them to death. Yeah,? there is that.? I have a Simpson DVM that uses four fat nicads to power it,? and I'm on my second or third set of them so far.? And they're not in good shape.? The original charger for that was a wall wart that was supposed to put out 7.5V,? fed through a resistor and that's it.? I also have a cordless screwdriver that sits in its stand most of the time,? with three nicads in it,? and they're not holding a charge all that well these days either. > I'd be tempted to use a wall wart and build a real regulated power supply. The circuit you describe is simple, maybe too simple to be reliable. I've pretty much given up on using nicads these days,? but if I did I think I'd prefer to use a circuit that would stop charging them at a given point,? coming back on only when needed.? Like those TP4056 modules I use for the lithium cells... -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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Le 10/01/2025 6:45 pm, Dan Kahn via groups.io a écrit?:
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Just checked again and the cap is 684nFd and the 730 nFd that I calculated is within 10%. Close enough for normal EE. I must be showing my 84 years, Dan On Friday, January 10, 2025 at 10:56:48 AM EST, Roy J. Tellason, Sr. via groups.io <roy@...> wrote: On Friday 10 January 2025 08:52:00 am Dan Kahn via groups.io wrote: > I am working on a Sabre Flashlight/Tazer combination.? The LED has shorted but that is not the reason for this post.? The charging circuit is very simple.? The line voltage goes through a 684nFd cap to one side of a diode bridge rectifier.? The other side of the bridge is connected to the other side of the line.? The output of the bridge goes directly to a 4 pack N size Nicad battery pack.? During the testing of the cap,? the bridge lead to the cap broke. I have found replacements for the LED and bridge. > > I checked the value of the cap by using my function generator and scope to make a divider with a resistor and calculated the cap value.? It calculates to 730 nFd.? A little more than 20% low. Is that uF or nF?? That's higher than the 680nF you mention above... > My question has to do with the limiting of the bridge output. Since there is no voltage or current? limit, what provides these two limits?? The capacitor limits the current. > Also should this cap be replaced due to its low value.? There are no markings on the bridge other than the input sine wave and the output +/-.? I will replace this with a 1A 1000V bridge.? I have selected a 1 Watt 3.4 volt 20 mm heat sink LED since this was the original connection configuration. > > I am considering adding a 5 volt zener and resistor on the bridge output just to limit the bridge output. > > Any thoughts? Big Clive has done teardowns and reverse engineering on a lot of this kind of circuit.? A few things you might want to add are a discharge resistor across the cap (470K-1M or around there,? value is not critical) and an inrush limiting resistor in series with the input to the bridge (10-470 ohms,? again not critical) which can also act as a fuse.? A zener across the output of the bridge is also pretty common. While I've seen a great many of these circuits online,? and a version of that was also posted to this list a while back,? I tend to prefer the use of a wall wart because of isolation from the power line... -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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My sent messages shows the pdf file sent. Dan On Friday, January 10, 2025 at 12:48:56 PM EST, F1CHF via groups.io <f1chf@...> wrote: hello where is the file ? tks Le 10/01/2025 6:45 pm, Dan Kahn via groups.io a écrit?:
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On Friday 10 January 2025 12:53:48 pm Dan Kahn via groups.io wrote:
My sent messages shows the pdf file sent.Yeah, but this group doesn't accept attachments and will silently strip them from messages... -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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Le 10/01/2025 6:45 pm, Dan Kahn via groups.io a écrit?:
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So much for showing the diagram. D On Friday, January 10, 2025 at 12:57:13 PM EST, Roy J. Tellason, Sr. via groups.io <roy@...> wrote: On Friday 10 January 2025 12:53:48 pm Dan Kahn via groups.io wrote: >? My sent messages shows the pdf file sent. Yeah,? but this group doesn't accept attachments and will silently strip them from messages... -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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Done! D On Friday, January 10, 2025 at 01:04:07 PM EST, F1CHF via groups.io <f1chf@...> wrote: Le 10/01/2025 6:45 pm, Dan Kahn via groups.io a écrit?:
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Uploaded to /Sabre Zapper.pdf. D On Friday, January 10, 2025 at 01:04:07 PM EST, F1CHF via groups.io <f1chf@...> wrote: Le 10/01/2025 6:45 pm, Dan Kahn via groups.io a écrit?:
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wn4isx
On Fri, Jan 10, 2025 at 01:37 PM, Dan Kahn wrote:
Sabre diagramDid you leave out a series resistor for the LED? While you can power a LED from a button lithium cell because of the high internal resistance will limit the current, 3 or 4 NiCads will dump a lot of current, I've spot welded with 4 D cell NiCad, N cells would provide a lot less current but still enough to put a LED at serious risk of "burning" out.
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I fought NiCad's every working day from October 29, 1979 until May 23, 2003, lost more battles then I won.
Our Sony electronic TV field gear used 12V NiCads with ~"C" cells. Sony electronics had a hard, absolute lower voltage cut out of 12V. Not 11.8 but 12. Perfect for creating memory.
I used a Rat Shack PC DVM, spare PC, printer port to drive a relay with a resistor to draw 2A, the PC would record the number of minutes a battery would stay above 12V. This allowed me to weed out failing cells.
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While Sony's batteries were obscenely expensive, that cost was less then a busted video production.
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I have serious doubts, as in "there is no way on earth to make that circuit work, if will fry the NiCads and there is no easy fix."
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Perhaps you could use PIC or PICaxe to monitor the NiCad voltage and charge when needed.
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On a personal note, I was very active in the 1980s, early 1990s, with SkyWarm, a system that used amateur radio as tornado spotters. My wife and I used iCom IC-2AT that came with NiCad battery packs. They had active charge control that sort of almost worked....but we switched to alkalines because NiCads were not worth the hassle.
Intersil (or some company) made a smart IC designed to charge NiCads. A friend swore by it and had great success. I was too busy with work and home life to etch a board and play with the IC. Sadly my friend passed in August and I'm not sure of the manufacturer.?
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There are opamp based smart NiCad chargers but, even with surface mount parts, I doubt you could squeeze it in the original case.
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A stun gun is nice, a can of bear spray will stop a raging bull. Personal experience. Dropped the sucker to jis knees and I skedaddled over the fence.
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If your stun gun uses NiCad, how old is it?
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It might be time to upgrade to a system with NiMH or Lithium-ion batteries.
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A friend of my wife has a stun gun with a damn bright LED with a "dazzle" function.
Press the flashlight button 2 (or 3) times really fast and the LED flashes in a "random" pattern that will disorient you if it used in the dark.
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BTW, I have a no name "made in West Germany" personal alarm that uses 6 AA cells, and has a battery powered siren. I found this pretty small metal box about the size about the size of a paperback with a pin, I pulled the pin and the resulting sound was so loud I couldn't think. No one in the thrift store could.
I managed to push the pin back in and the shop owner begged me to take it away.
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I worked at a facility that frowned on firearms (as in we'll fire you on the spot). We backed up to an economically distressed area, I had to work really late several nights, I wore ear plugs on the way to my car, one night I was confronted by a group of yutes and pulled the pin.?
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To quote a song from my childhood....
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Yeah, they ran through the briers and they ran through the brambles
And they ran through the bushes where a rabbit couldn't go? ?
A NIST reference calibrated sound meter says the unit produces 130dB.
You might consider an audible deterrent.....
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On Friday 10 January 2025 03:18:30 pm wn4isx via groups.io wrote:
BTW, I have a no name "made in West Germany" personal alarm that uses 6 AA cells, and has a battery powered siren. I found this pretty small metal box about the size about the size of a paperback with a pin, I pulled the pin and the resulting sound was so loud I couldn't think. No one in the thrift store could.That reminds me of a device brought to me a while back, the circuit board contained 6 or 8 MOSFETs, and it hooked up to a horn-type tweeter. The guy that brought it to me told me that the battery had been hooked up backwards one time, and the unit refused to work after that. Looking at the board, I could easily see where one particular trace had opened up, acting as a fuse. My thought was to bridge that with a rectifier diode, and see if it still worked. It's somewhere in my "pile of stuff" and maybe if I run across it I'll give that a try... :-) Six AA cells oughta work, I'd guess. -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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Roy, I received the LEDs yesterday. I selected a 1 watt mounted on a 20 mm heatsink. Today I put 3.2 volts to the LED and measured the current at 200 ma. I am going to wait for todays mail for the bridge rectifiers and do the re-assembly tomorrow. I am still torn about adding some kind of overvoltage protection to the battery. I think I have some 5 volt zeners stocked somewhere in my stuff. I might just put it across the battery terminals and use the Xc of the cap to limit the current. Dan On Saturday, January 11, 2025 at 11:24:11 AM EST, Roy J. Tellason, Sr. via groups.io <roy@...> wrote: On Friday 10 January 2025 03:18:30 pm wn4isx via groups.io wrote: > BTW, I have a no name "made in West Germany" personal alarm that uses 6 AA cells, and has a battery powered siren. I found this pretty small metal box about the size about the size of a paperback with a pin, I pulled the pin and the resulting sound was so loud I couldn't think. No one in the thrift store could. > I managed to push the pin back in and the shop owner begged me to take it away. > > I worked at a facility that frowned on firearms (as in we'll fire you on the spot). We backed up to an economically distressed area, I had to work really late several nights, I wore ear plugs on the way to my car, one night I was confronted by a group of yutes and pulled the pin. > > To quote a song from my childhood.... > > Yeah, they ran through the briers and they ran through the brambles > And they ran through the bushes where a rabbit couldn't go > > A NIST reference calibrated sound meter says the unit produces 130dB. > You might consider an audible deterrent..... > That reminds me of a device brought to me a while back,? the circuit board contained 6 or 8 MOSFETs,? and it hooked up to a horn-type tweeter.? The guy that brought it to me told me that the battery had been hooked up backwards one time,? and the unit refused to work after that.? Looking at the board,? I could easily see where one particular trace had opened up,? acting as a fuse.? My thought was to bridge that with a rectifier diode,? and see if it still worked.? It's somewhere in my "pile of stuff" and maybe if I run across it I'll give that a try...? :-) Six AA cells oughta work,? I'd guess. -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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Update on my repair. It's NOT! I replaced the diode bridge and LED and connected the battery after "charging" for about 5 minutes. I stopped when I noticed the battery voltage was approaching 10 volts. Further investigation shows a bad cell in the 4 pack. The open circuit voltage on one cell is 1.12 volts but if I put my power supply across this cell it will not take any current. Even though it has a voltage it must have an open circuit internal to the chemistry. Trying to replace this 4 pack will cost about $32. A new light/zapper is $34.95 so it is a no brainier that a replacement battery is not worth it. Since I already purchased the LED and bridge for $15, no more investment will be made. Dan Kahn On Friday, January 10, 2025 at 01:04:07 PM EST, F1CHF via groups.io <f1chf@...> wrote: Le 10/01/2025 6:45 pm, Dan Kahn via groups.io a écrit?:
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wn4isx
NiCads can have some odd failure modes, yours is fairly common, under no load the cell will produce ~1.2V, place any significant load and the voltage drops to zero, and the cell won't take any charge current at any sane voltage.
I've had some success using a car battery and connecting the NiCad cell reversed, Bat V+ to car battery V-,, Bat V- to car battery V+. Just a touch, wear safety goggles, use thick gloves.
Another option is to charge a 100uF capacitor to 160ish volts and connect + to +, - to minus.
I restored an original iCom 2-AT battery back this way and the revived cell lasted a bit over a year before it went total open circuit.
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There are applications where NiCads thrive, watchman flashlights that are used ever night, charge each cell individually the next day at 1/10, use two sets of NiCads and you can (or could in the 1960s) several years use out of the NiCads.
Our next door neighbor's son was a watchman at IBM and he used this scheme.
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As I've said, I really distrust and dislike nicads....except for the big ones rail road companies used at crossings.
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NiMH are much better behaved but a @itch to charge.
Lithium Ion are better energy density wise, but draw too much current or charge wrong and you have an instant incendiary grenade.?
A friend had one of the troubled Samsung 'catch on fire' phones and his went up on a picnic table.
It was a bit too exciting. Hint, do not use water on a lithium fire, that made it more exciting. And knocking it into a bucket of water was beyond exciting.
Think "Extreme thermal event."
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F1CHF
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