Is my 12v LiFePO4 Battery dead?

[joelshort]

I can monitor the battery throughout the day, just not constantly.

Thanks for the compliment regarding my astro images! I've been doing it for nearly 17 years and have gradually upgraded my equipment over the years.

the best place I've seen (based on stuff here on the forum and some of my own experiences) to get "matched" cells is from "totalled" EVs, or otherwise from EV packs. Since the BMSs in those EVs generally are not going to allow the EV to overcharge or overdischarge the cells, and even not let them outside a very narrow range of SoC, the cells dont' really get run very hard, relative to what they *could* do, and so they're usually still very good cells by the time they're scrapped out. As long as you can use them in some of the "blocks" they already come in, they can be really easy to use, and can be easy enough to use in smaller sections if necessary (like for lower-voltage packs like yours), and just parallel them for greater capacities.

Is this the place you mean: http://evwest.com/catalog/

 

[999zip999]

Yes 2.8v to 3.1v is a lot faster then 3.1 to 3.4v then 3.45v to 3.6v goes fast because of where capacity compared to a voltage number. If you found a 3.4v charger you can fill really safe but still not totally safe. As keep an eye on it. Good luck.

 

[amberwolf]

Thanks for the compliment regarding my astro images! I've been doing it for nearly 17 years and have gradually upgraded my equipment over the years.

You have a few years on me for that.

Is this the place you mean: http://evwest.com/catalog/

I just meant used EV (electric Vehicle) batteries in general. There's actually a lot of threads around here about them. EIG's NMC packs, Leaf packs, Tesla packs (though those are harder to work with htan the first two), and others I can't recall ATM.

I use old EIG NMC cells to run my SB Cruiser trike, both for the traction pack and the "12v" lighting pack.

The one catch with the non-LiFePO4 packs is that it's a bit harder to get a "12v" pack that has good margin around that voltage. A 3s pack is about 10v+ minimum, and about 12.3-12.6v maximum depending on the cell and how full you make them. It'll be around 10.8-11v for most of it's discharge curve. A 4s pack will be about 13v minimum, and around 16.4-16.8v full, and around 14.4-14.8v for most of it's discharge curve.

Since automotive "12v" is generally within the latter range, that's actually pretty good reason to use a 4s (non-LiFePO4) pack, but only if you don't fully charge it, because over 15.something volts is beyond specs for a number of "12v" things I've seen. Not fully charging it does actually help increase it's lifespan, especially if you tend to keep it charged and ready to use all the time. With a 3s pack, you may not be able to use the lower end of it's range, because devices may only operate reliably down to 10-11v or higher.

LiFePO4 is a much closer range of voltage to the "12v" lead-acid profile most automotive electronics (and things based around that standard) expect.

LTO also works for that, becuase it's a much lower voltage cell, and IIRC 6s of that would be equivalent. It's become a more common cell to see for certain applications, especially those that need fast charging and abuse tolerance.

 

[999zip999]

I read LTO has long life and can be discharged to zero ? If true it would make it ssafer for recharging and one end of a possible battery problem ? Lifepo4 is perfect for 12v so many things made for sla devices. So ez.

 

[flippy]

I read LTO has long life and can be discharged to zero ? If true it would make it ssafer for recharging and one end of a possible battery problem ? Lifepo4 is perfect for 12v so many things made for sla devices. So ez.

they can be discharged to zero but they dont like it, especially when its cold.

LFO is fine for automotive but if you have a 24 (trucks) or 48V (UPS) system you are better off with a regular 7S lipo battery.

i built a few batties for trucks are replacement for their massive 220Ah 12V lead's to reduce the gross weight. some trucks have well into the 500lbs or more worth of lead batteries. in one application the weight was reduced by 400lbs and the smaller battery meant they could carry a custom shaped 1000 liter fuel tank without increasing the total weight. you cant manage that with LFO due to the size of the cells.

 

[joelshort]

Man it is taking a LOOOOONG time to charge/balance these cells with a 5v charger. I started with the lowest block, and after about 32 hours it has gone from 3.14v to 3.28v.

 

[joelshort]

you can "donate" a usb charger in the mean time.

just cut a usb cable, make sure the polarity is right and hook it up to the lowest block. do connect ALL the same cells in that block together as i see that all the cells are disconnected. keep the cells of blocks connected.

leave it running for 2~4 hours until the voltage matches the next lowest block and connect that one up as well. continue this until you connected all 4 blocks as one big one running at 3.65v.

Charging the first block now. When it comes time to add the second block, I assume I connect the blocks in parallel (+ to +, and - to -)?

 

[flippy]

Man it is taking a LOOOOONG time to charge/balance these cells with a 5v charger. I started with the lowest block, and after about 32 hours it has gone from 3.14v to 3.28v.

you are right in the zone where are all the energy is so it will stay there for a while.
still, its free. a half-decent supply does only 5A or so so it would still take many hours to fill these.

 

[dustNbone]

It will take some time for sure. That block was well under 1/2 full and it's 80Ah. You USB charger I would guess is 2A maximum, so you're in for a haul. Just beware once they get past 3.4V or so the voltage rises much faster. That flat charge/discharge curve is one of LiFePo4s best features but it does make judging state of charge a bit difficult.

Also make sure the voltages are near identical (ideally within .01V) when you connect more cells in parallel. If they're too far apart there will be an unregulated rush of current from high to low, which isn't good for them. They're pretty beefy cells so a little bit shouldn't hurt them.

I'm thinking being that it's the last group in the chain the BMS might have been pulling power from that cell group (vs the entire pack) to power itself. They are famous for this.

 

[joelshort]

The highest output USB charger I had was 3.5A. At least I'm seeing progress now. For like 15 hours I didn't see it move off of 3.22v. Now I'm seeing steady (but still slow) progress.

 

[flippy]

once you reach the voltage of the next block you can connect that one as well and continue until you have all 4 blocks connected and have reached 3.65V.

then disconnect the blocks and leave them for a day or so and see if they keep their float voltage identical without being connected.

 

[joelshort]

Does anyone know of a USA source for PVC shrink tubing? I'm not finding anything and I need a large diameter. Speaking of which I also could use some help figuring out what size shrink tube I'll need. Originally the battery bank measured 10Lx6Wx5.5H inches.

 

[Electroddy]

The only place I have found, is China by way of eBay. That said, I have some 450mm and 500mm that I could spare a couple feet of. Hit me with a PM. The stuff is measured flat so the dims to use are one side and top either direction.

 

[999zip999]

Luna cycle had some. Try ebike.ca
I have 3 voltpheaks for lifepo4 stop at 3.6v 2 amp.I have put 3 together. For 6amp on a 20ah A123 high quality battery cell. I cant find them anymore.

 

[joelshort]

The only place I have found, is China by way of eBay. That said, I have some 450mm and 500mm that I could spare a couple feet of. Hit me with a PM. The stuff is measured flat so the dims to use are one side and top either direction.

PM sent.

 

[999zip999]

Big battery with moving parts if 4 cells or less you could go 12v 60ah if needed ? Just saying you are lucky with opinions. Lifepo4 has long life if given a dose of what it lives on. Electricity. As said before the VMS can be parasitic to one or three cells in a big pack and is used to run the BMS bored. Happy is at 2.8v - 3.5v. Can take 3.7v or ? Don't do it - haha.

 

[joelshort]

I'm starting to get a little impatient After nearly 70hrs of charging the first block has reached 3.30v. The next block is at 3.34v

Is there any other low cost way to charge/balance these cells? Short of buying a desktop adjustable power supply...
If not I'll just try to be patient but this is taking way longer than I ever thought it would.

 

[amberwolf]

You could use separate USB chargers on each cell. Then each one will get more current and it'll go faster. But then you also need separate voltmeters on each cell, to constantly monitor them.

It *might* be possible to parallel several USB chargers on the paralleled cells...but:

Depending on their designs (which you can't know without reverse engineering them) it may not be a good idea to parallel the USB chargers, because they may not all be the same voltage, and some of them may fail when current flows into them from a higher voltage source (when disconnected from teh battery but still connected to the other USB chargers).

Putting (anodes of) diodes in series with each separate USB charger's positive output, and then tying all the diode cathodes together, (and just tying all their negatives together) would prevent any backflow from one into the other, but those that are higher voltage may end up supporting more of the load than the rest. It'd still make charging go faster, as long as you have the USB chargers to spare (in case they break).

Just remember that the faster you charge it, the more you have to keep an eye on it, so that it doesn't suddenly end up overcharged. (probably not going to happen with that size pack, but still watch out).

 

[dustNbone]

If you find yourself servicing batteries on any kind of a regular basis, I highly recommend one of these

https://www.amazon.ca/Genuine-SKYRC-Power-6Amps-50Watts/dp/B01MZ1ZZ7Z

It's not a huge charger, but it's highly configurable and not too expensive. You could connect balance leads to each bank of cells and just plug it in and forget about it. It will bring each group to a perfect 3.6V (or whatever it's set for), as well as telling you how many Ah went in to get there.

Just a nice tool to have, I'm surprised how many things I've used it for over the years.

 

[joelshort]

You could use separate USB chargers on each cell. Then each one will get more current and it'll go faster. But then you also need separate voltmeters on each cell, to constantly monitor them.

One question, if I use one USB charger and connect each cell block when the first reaches the same voltage, does that mean that adding each cell block with increase the time it takes to charge the same amount. In other words, if it takes 10hrs to charge the first block 0.1v when all four blocks are connected will it then take 40hrs to charge 0.1v?

Of course I thought of using separate USB chargers on separate cell blocks, and if the above is true then I'll be cutting those USB cables and charging each individually. Otherwise it would take weeks.

 

[joelshort]

If you find yourself servicing batteries on any kind of a regular basis, I highly recommend one of these

https://www.amazon.ca/Genuine-SKYRC-Power-6Amps-50Watts/dp/B01MZ1ZZ7Z

It's not a huge charger, but it's highly configurable and not too expensive. You could connect balance leads to each bank of cells and just plug it in and forget about it. It will bring each group to a perfect 3.6V (or whatever it's set for), as well as telling you how many Ah went in to get there.

Just a nice tool to have, I'm surprised how many things I've used it for over the years.

That does look like a handy device. But I don't anticipate doing this kind of thing very often or even ever again if I can help it. :lol:

 

[flippy]

You could use separate USB chargers on each cell. Then each one will get more current and it'll go faster. But then you also need separate voltmeters on each cell, to constantly monitor them.

One question, if I use one USB charger and connect each cell block when the first reaches the same voltage, does that mean that adding each cell block with increase the time it takes to charge the same amount. In other words, if it takes 10hrs to charge the first block 0.1v when all four blocks are connected will it then take 40hrs to charge 0.1v?
Of course I thought of using separate USB chargers on separate cell blocks, and if the above is true then I'll be cutting those USB cables and charging each individually. Otherwise it would take weeks.

no, because most of the charge is already in once you have the final block connected. once you go above 3.35v it will start rising faster and faster.

but yes, it will take some time. unless you buy a bench power supply.

 

[999zip999]

Best to kerpas one big 80ah 3.3v block to charge as it will act as 3.3 battery because they're all parallel just put a higher charge on it your battery could take 10 amps or more
Mistake corrected 3.3v not 13.3v. Sorry

 

[joelshort]

Alright guys, I'm making progress. Yesterday I started to suspect that perhaps the USB charger wasn't actually putting out 3.5A like the charger says. So I found another USB charger that says it outputs 4.8A (2.4x2) max. I hooked that one up and I saw an immediate difference in charging rate. I now have 3 of 4 blocks charging/balancing, and as has been said the pace is increasing.

Question, once the set of 3 blocks reach the voltage of the final block (in this case 3.50v), can I reassemble the battery pack (so 12v w/ BMS) and finish charging with my 14.6v 10A charger, or is it better for the battery if I finish out with the USB charger and take it to 3.65v?

 

[flippy]

No, it is very important you finish out at 3.65v.

Then disconnect the block and leave them for 24h.
Then measure the voltage on each block. If they are identical you are good.