Simplest 3S or 4S lithium ion protection circuit?

[sam_sam_sam]

Re: Simplest 3S or 4S lithium ion protection circuit?

Here what I would try if I was doing this

I would find a micro controller that is easy to program if you have played with them before
that a plus

I would use a ac to dc converter ic chip ( unless your micro controller might have it built in ) and time clock ic chip ( I would not use a do loop to do this ) write code for each ic chip

Read start voltage
Start counting timer
Turn on load
Read voltage
In do loop until it gets to discharge voltage level that determine by cutoff voltage in parameters in your program
Turn off load
Read voltage
Stop counting timer

Display results at the end of test

If I start doing more used batteries I will probably build a controller to what I have above

When I had a above ground pool

I build a pool timer controller with a Parallax Basic Stamp 2

And here a sample of how I wrote this program

I use a time clock chip
I used LED as light sensor
( yea I know what you think you can not do this but yes you can with creative programming )

The program when like this

Start
Look and see if the sun is out playing
If so start timer turn on pool pump
If not go to start
Loop for 2 hours
Then turn off pool pump
Loop for 2 hours
Exit
Go to start

Or

If you do not want to use a micro controller to do this
There is another option but it takes a bit more work and you have to do some hacking

Find a kitchen timer and modify the start and stop buttons
Car headlight bulb
Relay
Zener diode at 3 volts

And set it up so that when you hit the start button that would start to the timer
Have the Zener diode setup so that when the voltage hits 3 volts turns off the timer and turn off load

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

That's the thing sort of, the cells need to be cheap, whatever the source is. The two packs I have that I've gutted so far for this project had the "right price" else I probably wouldn't even look into it.

I do have car lamps to use as dummy loads, though I was hoping to do away with the stopwatch and have a computer program deal with that along with measuring voltage and current.

the "right price" was that the packs were discarded trash picks

[sam_sam_sam]

Re: Simplest 3S or 4S lithium ion protection circuit?

There is another way to test batteries but it is not as accurate and is to use a MR16 50 watt light bulb and a volt meter and a stop watch and wait until the battery voltage get to 2.75 volts plus the time it takes to get to this voltage

Your amperage will start off at about 1.5 and drop down from there

I have done this before and results are decent on a scale of 0 to 10 and 10 being a brand new battery and 0 not testing the battery at all I give about 7

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

Thanks, but don't worry about it, I don't think I'll be buying any charger system, was planning on just depending on the protection board for the most part, then math for the rest. I was thinking I just need a mass number of not so great but passable cells and go on from there.

As for welding, yeah, I wish I had one. Plus the metal strips, but I think I will have to resort to solder, try to get it done as fast as possible to minimize damage.

[sam_sam_sam]

Re: Simplest 3S or 4S lithium ion protection circuit?

Give me a little time with that let me see what I can find for you

Do not buy this type of salvage bay I did this once and the results were that you get less than 30% useable battery for a lot of work

https://www.ebay.com/itm/99-SANYO-18...ry!32220!US!-1

Now the seller was nice enough to refund some of my money to make it worth while doing it
I have to be fair about it

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

No I don't. I'm just estimating by behavior with load and time, doing the math. Need to compensate for constant wattage, but only need to be close enough.

[sam_sam_sam]

Re: Simplest 3S or 4S lithium ion protection circuit?

Do you have a battery-charger-load-tester
Do you have something like this
This is what I use to check my battery with

https://www.ebay.com/itm/iMAX-B6-AC-...ry!32220!US!-1

If not you might want to think about getting one
This will tell you the status of the batteries that you are working with

When I do battery testing I only do one battery at a time and write the results on that battery and test the next battery and so on

I will weld battery packs for some one but

I will not do the battery testing this take to much time ( this could take any where from 2 to 4 hours to charge/discharge cycle depending on the condition of the battery )

I barely have enough time to do battery welding but you can see the end with battery testing you have keep eyes on the display screen most of the time

I setup the charger as follows 1 amp charging/1 amp discharging might be 1.5 amps ( or more so that your screen shows above 1 amp ) sometimes I set it to 2 amp if the battery voltage does not drop fast but if you do this setting then use the temperature sensors and put it on the cell that you are working on and set the temperature settings from 80* to 100* F ( this setting does work on this charger it stops when discharging and it also work when changing )

I also write down the amount of time when discharging voltage is above ( 3 volts @ 1 amp) (depending on how you want your parameters to be you might want to wait until it reaches 0.75 amps ) to do comparisons of each battery because some protection boards are very picky about voltages between cells

Yes it is very time consuming but your results are a lot better

Also if you are going to put battery pack together you might want to think about getting a battery spot welder for this under taking

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

Nah, I was just using the netbook as a "real world" load instead of using resistors or incandescent lamps. The netbook's battery isn't in great shape either (says about 60% of rated lifetime), but I think better than these cells in general by gut feel...

The netbook uses 2S3P config. I tore up a 3S2P pack from some random dead pack I had, as well as the 4S2P "base" pack to play with. Was hoping this 4S pack could be used for other purposes not specifically laptops, was planning on also feeding the output into a boost converter to 170VDC...

[sam_sam_sam]

Re: Simplest 3S or 4S lithium ion protection circuit?

Are your battery or batteries in your netbook bad if so why not replace them first and then work on the external battery pack because it might make a different in your results

The reason I point this out is I had a tablet that I tried to do this with an my results where not very good until I replaced the internal battery first then the unit worked with what ever external battery I would hook to it

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

Some more testing...trying to power my netbook with this 4S pack with a DC-DC converter. Much like before, it seems to cut off in several minutes and stay dead but if disconnected and reconnected, it will run for a while.

Not charging the internal battery, drawing about 12-18W I think. The condition of the cells are so poor it doesn't last long, but has similar characteristics where it will power a little longer after connection cycling and resetting the overdischarge.

Now I wonder if i should now hook up the cells from this other laptop pack...and break apart some other packs...

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

Yeah at first I was depending on the resistance of the power source, so the first couple of minutes of charging it was taking charge at 2+ amperes (!), and it was charging quite fast. But once voltage of the battery got high enough, it stopped and oscillated, much like the theoretical operation of my PoC relay protection circuit, so I guess I have something right...

After putting that resistor in series with the power supply, the oscillation stopped and charged normally until full. Yes, need to slow down current flow to operate correctly... or rather I should use a CVCC type charger for the pack.

[sam_sam_sam]

Re: Simplest 3S or 4S lithium ion protection circuit?

Interesting finding

Try lowering your charging current to like 250 milliamperes and see if that works better

I have some batteries that there milliamperes are all over place and wondering how I could use them but I do not have enough of any milliamperes value to make a battery pack that I can use

I guess I going to have to try what I was talking about earlier balancing the cell banks and see how this works in the real world

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

interesting... I shorted a prismatic cell for a second or so, which I guess it is sort of pouch, the wire got red hot real fast and I burned myself as I didn't notice... Bad me.

The first set of worn 18650s I'm using is basically from the same set of cells from a laptop. It's no magic - from a dead laptop to a custom pack, the battery isn't any better than before, but at least I can run fairly heavy loads without having to worry about cells overdischarging. I was able to power a 50W car headlamp, which is a bit high for the headlamp technically, but the cell condition was so crappy the voltage dropped down significantly. But the light did turn on for all of a good few minutes and the battery was consumed.

However not quite dead, after disconnecting, it will run the lamp a few more seconds after reconnecting. Also I was able to run my netbook with the pack and a DC-DC converter even with it partially discharged, but eventually it too could not power the DC-DC converter and shut down.

Eventually I need to recharge it of course. So, I tried charging it earlier today with +20V, it did not like it very much. It shut down fairly quickly once the batteries got up to voltage. I put a resistor in series and it charged much better, staying at voltage up until 16.8V or so as expected.

I will need to add more cells of course. As well as adding monitoring so I can do some pack analysis...

[sam_sam_sam]

Re: Simplest 3S or 4S lithium ion protection circuit?

I guess another good thing is that these expended old batteries have high internal resistance and thus cannot dump out all their energy fast, so one has more time before they immolate.

Let me know what kind of run time results you get with these type of batteries and if they are useful when you put your battery packs together

I am very interested in your results

[sam_sam_sam]

Re: Simplest 3S or 4S lithium ion protection circuit?

Pouch battery once you short it there is no going back it goes directly into cell failure right away

If you do this to a 18650 battery it might spark a little bit and hiss a little bit but does not go directly into cell failure

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

Fleabay... They haven't been so bad, most that have decent rep work well, it's the low overall rep that have problems. Just need to watch out the "too good to be true" vendors.

And no, water on lithium is not a good idea. Best to deal with batteries when they are discharged and don't shove metal into metal if you're not sure it's safe to do so. Then again, shorting for a short period of time (like milliseconds) shouldn't be a big deal. Just avoid it, whenever possible.

I guess another good thing is that these expended old batteries have high internal resistance and thus cannot dump out all their energy fast, so one has more time before they immolate.

[sam_sam_sam]

Re: Simplest 3S or 4S lithium ion protection circuit?

And ahh...got the protection board. Might need to get a few more for other uses...

Can you please post the link where you are getting them from

I once was real sloppy and some what of a hurry to get a battery case a part on a pouch battery using a metal prying device and the battery went violently into a fire ball hissing and sparking got it out of the house and near a water hose and put it out —> scared the crap out me

I have lot more respect for these batteries and lot more careful about how I take a part battery cases

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

IMHO it's either luck or sloppiness. If it's luck, it wasn't my fault and it is what it is. If it's sloppiness, it's my fault anyway.

I've shorted cells by accident and burned myself once, but luckily noticed before immolation.

And ahh...got the protection board. Might need to get a few more for other uses...

[petehall347]

Re: Simplest 3S or 4S lithium ion protection circuit?

them damn things get hot pretty quickly . last time i played at trying to rebuild a battery pack it ended up with it being thrown out of the door out of harms way . it didn't set on fire though as i expected it to .

[ChaosLegionnaire]

Re: Simplest 3S or 4S lithium ion protection circuit?

just a humble safety reminder here to members tinkering with lithium batteries. for high density lithium battery packs, once they catch fire, the fire can be impossible to put out and can burn for days. read the following articles on the dangers:

Why the Fire that Incinerated a Tesla Was Such a Nightmare to Put Out

Why Tesla's electric cars can burn hours after a crash

What First Responders Don’t Know About Fiery Electric Vehicles

stay safe, brothers! im not gonna be the one responsible for cleaning your ashes off the floor!! lol!