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Oct 08, 2019, 05:30 PM
Quadaholic
--Oz--'s Avatar
I was a little embarrassed to show my lipo killer until I found this thread, lol. Most just toss their battery and thats it, why waist the time to build something to throw away your lipos?

I normally just connect a resistor across the pack (~500Ω for 4S) and set it in a coffee can outside in a safe place for a few days, takes it down to zero volts. This seemed to work well for ~30 packs, well until one day a pack had a bad cell, of course that cell went to zero voltage first, then the others start to recharge it with reverse voltage (yes, this is what happens), till it swelled, then popped and a lot of smoke, no fire. So the more out of balance your pack is and the higher the discharge current, the harder (faster) it is reverse charging the weakest cell(s). this is what my circuit protects against.

So I decided to make a safer lipo killer.
It does single cell discharge at ~55mA, for each cell (80Ω/cell), so when that cell goes to zero volts, that it is not being reverse charged, there is a led for each cell, the leds turns off around 1.7v, this semi shows the balance of the pack, if they all go off together it is balanced, if one or more turn off before the others, its not balanced.

Setup for 1 to 6 cells:
Basically 80Ω between each cell (I used 320Ω x4),
1 led + 500Ω between each cell,
1 led + 4KΩ across 6 cell.

Ready for the laughing/heckling.

EDIT: soldering is easy work for me, but not for everyone, so I made a simpler version, no LED's, using though hole resistors and no circuit board, about 10 cents worth of components (80Ω 1/4W x6 and 7 pin header). Next add a small piece of heatshrink.
Last edited by --Oz--; Oct 21, 2019 at 01:27 PM.
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Oct 10, 2019, 12:15 PM
Registered User
ccpdx's Avatar
Oz,
I really like this and would like to own a couple or more. You should market it. It looks difficult to solder. I also appreciate the term "lipo killer" because that's what I call this kind of thing too. (not sure if that's what most people call a zero-voltage lipo discharger?)

Charles
Oct 10, 2019, 01:48 PM
Registered User
simple and good design Oz. Wish I woulda stumbled on this before spending too much on one myself lol.
Oct 10, 2019, 03:46 PM
Quadaholic
--Oz--'s Avatar
Quote:
Originally Posted by ccpdx
Oz,
I really like this and would like to own a couple or more. You should market it. It looks difficult to solder. I also appreciate the term "lipo killer" because that's what I call this kind of thing too. (not sure if that's what most people call a zero-voltage lipo discharger?)

Charles
Thanks. When I raced rc on-road cars from 1981 to 2003 we used nicd and nimh 6s batteries. Most racers used a 10 to 20 car tail light bulbs in parallel (10~25A) to discharge the battery after running, this was common practice. I decided to look at the cell voltages when this was happening and when the bulbs turned off. Holly $h!t, cells were 0v and even worse some were negative voltage, I knew this was not good, so in early 90's I came up with single cell ballance discharge. Simply a resistor (usually 0.5Ω) in series with a silicon diode across each cell, then I added LED (5 of them for 6S) that was connected 1 led across 2 cells and resistor, I put them in a bar graph format, when the pack was discharging, you could see the capacity balance of the pack. When the discharge was done, each cell was ~0.6 volts and current stopped flowing, I sold quite a few of them in the 90's.

So the lipo killer is simply the same without the diode to take them down to zero volts without any reverse charging.

EDIT:
Quote:
Originally Posted by Darunion
simple and good design Oz. Wish I woulda stumbled on this before spending too much on one myself lol.
thanks
Last edited by --Oz--; Oct 10, 2019 at 10:06 PM.
Oct 17, 2019, 10:23 PM
Quadaholic
--Oz--'s Avatar
Quote:
Originally Posted by Darunion
simple and good design Oz. Wish I woulda stumbled on this before spending too much on one myself lol.
Out of curiosity, what did you buy? link?
Oct 18, 2019, 11:34 AM
Registered User
https://www.racedayquads.com/product...-disposer-xt60

$10 with shipping and takes forever, due to the small load. Not a huge amount, just hurts when you know its 50cents worth of parts.

I do like the idea of discharging from the balance leads better. Should have made one
Oct 21, 2019, 01:26 PM
Quadaholic
--Oz--'s Avatar
I made a simpler version for easy soldering, no LED's, using though hole resistors and no circuit board, about 10 cents worth of components (80Ω 1/4W x6 and 7 pin header). Next add a small piece of heatshrink. See my post #31 above.
Oct 21, 2019, 02:13 PM
The Other Side of Your Screen
SilverSport's Avatar
Nice .... miss Radio Shack to go pay twice the price for the parts but get them when needed in my neighborhood.
Oct 26, 2019, 09:55 PM
Quadaholic
--Oz--'s Avatar
Quote:
Originally Posted by SilverSport
Nice .... miss Radio Shack to go pay twice the price for the parts but get them when needed in my neighborhood.
In the 80's, there was a military issue, they backtracked the issue to radio shack, some company (raytheon/grumon/etc) bought radioshack components (because they needed them now to fulfil a project) and was later found out to be 90% faulty for military specs. So there was a saying, buy a dozen to get a good one from Sh!tShack, lol.
Oct 28, 2019, 08:07 AM
Registered User
Quote:
Originally Posted by --Oz--
In the 80's, there was a military issue, they backtracked the issue to radio shack, some company (raytheon/grumon/etc) bought radioshack components (because they needed them now to fulfil a project) and was later found out to be 90% faulty for military specs. So there was a saying, buy a dozen to get a good one from Sh!tShack, lol.
I remember that. It was the Missile Defense Project. Nothing consequential.

You sir are a skilled solderer. Do you use a magnifier while soldering? Would you mind showing your soldering setup? I have a soldering station but need some kind of magnifier and something good to hold stuff to keep my hands free. I do a lot of soldering but would have trouble with those boards above.
Oct 28, 2019, 08:16 AM
ancora imparo
jj604's Avatar
Thread OP
This might be useful

https://www.rcgroups.com/forums/show...or-tiny-joints

It is for very small solder joints however.

John
Oct 28, 2019, 11:36 PM
Quadaholic
--Oz--'s Avatar
Quote:
Originally Posted by AnotherMember
You sir are a skilled solderer. Do you use a magnifier while soldering? Would you mind showing your soldering setup? I have a soldering station but need some kind of magnifier and something good to hold stuff to keep my hands free. I do a lot of soldering but would have trouble with those boards above.
Those two versions of lipo killers are just soldered without aid, these resistors are huge relativity 0603 components.

Since I am over 50, I am needed help starting at 0402, and smaller 0201, 01005, and lately we been using 008004 (because of the high freq pam4 data rates, 58Gbaud). I use a Leica stereo zoom 6 scope, two metcal irons and a $70 hot air rework station. I can solder bond wires back on the pcb that need rewiring.
Oct 29, 2019, 09:40 AM
Frankenstein recycled packs
rampman's Avatar
Quote:
Originally Posted by --Oz--
Those two versions of lipo killers are just soldered without aid, these resistors are huge relativity 0603 components.

Since I am over 50, I am needed help starting at 0402, and smaller 0201, 01005, and lately we been using 008004 (because of the high freq pam4 data rates, 58Gbaud). I use a Leica stereo zoom 6 scope, two metcal irons and a $70 hot air rework station. I can solder bond wires back on the pcb that need rewiring.
My god, OZ. I can't imagine soldering the 01005 components.
My new Lipo ESR Mark II meter uses 0603 SM components and that is as small as I like to go...but the 30 pin connector is at .1mm spacing so I guess I am doing smaller. For all but OZ, that is 30 pins in about an inch.
Lucky for me, even at 62, I don't shake. Well, as long as I have my 1 cup of kawfee in the AM.

Here is my solder station at work. I mostly do through hole here but the lit magnifier is a must for us old guys as well as the 2x / 4x microscope for the smallest of jobs. At the least, a well it area is required but the lit magnifier is an option for most of the RC related soldering projects.

The pistol grip tool on the far right is a tool made by a company called DIC and it is a solder sucker. Guess what I call it?

Rick
Oct 29, 2019, 09:52 AM
The Other Side of Your Screen
SilverSport's Avatar
Wow .... it's bigger than I thought it would be! As long as it does the job satisfactorily I guess it doesn't matter.
Oct 29, 2019, 10:39 AM
pull up -- PULL UP!!!
Like OZ said, I just use a big power resistor to drain the lipo before disposal. And like him, I occasionally have one back-charge and get ugly.

I live in the desert and don't care if it sometimes gets all smokey and obnoxious. But for those who do, but don't want to do all the fabrication, why not just attach a couple of alligator clip leads to the resistor...clip the first two leads off the balance pigtail and drain one cell. When dead proceed to the next cell. etc. Obviously this takes longer, but is a quick and simple build. Trade-offs.

BTW, I use the big aluminum cased power resistors rated 100 or 200 watts. And much lower resistance, hence higher current than OZ. Only a buck or two from ebay. Stay to about 50% power rating or these things get smokin' hot. Which is okay, but sometimes painful.


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