# How to properly pre-equalize/balance new LiFePO4 cells?



## frodus (Apr 12, 2008)

NEVER EVER charge lifepo4 to 4.2V. Max voltage should be under 3.7V. 4.2V charge voltage is for LiPo, not LiFePO4.

You've definately overcharged them.....They're likely comprimised and I would never trust them again.

Start over, build the pack, and get a RC charger that has taps for balancing. That way once or twice a year, you can balance charge the pack.


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## dougingraham (Jul 26, 2011)

If after resting overnight your cells are much above 3.4 volts then they are overcharged. You aren't doing them any favors leaving them there.

Get one of the hobby chargers, a Power Lab 6 or Power Lab 8 or an iCharger 3010b and use that to charge each cell if you want to top balance or discharge each cell if you want to bottom balance. There are lots of threads about this.


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## frodus (Apr 12, 2008)

You don't need a hefty charger like the PowerLab or iCharger for a 4-cell pack.... they're overkill and expensive and they don't run on AC, so you need a 12V power supply.

Something like this:
http://hobbyking.com/hobbyking/stor...2_6S_Battery_Balance_Charger_AC_DC_w_PSU.html
Or this:
http://hobbyking.com/hobbyking/store/__6478__IMAX_B6_AC_Charger_Discharger_1_6_Cells_GENUINE_.html

Both are balancing chargers and can easily do 4-cell lifepo4 battery packs. Just make sure you program them for lifepo4, and not lipo or some other chemistry. The current doesn't need to be high since you're not balancing them all the time.... just once in a while to keep them healthy.

Just get a JST 4s connector and connect to your 4-cell pack (B+, B- and each cell-tap).


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## Electron Power (Jan 2, 2013)

All I can say right now are curse words. But for the sake of our "discretionary" readers [not to mention the moderators], I will refrain from typing them out. But after spending104 (82+22) bills on the dozen of them, I will NOT be a very happy camper if they won't start the bike, after I solder (or would it be better to weld?) them together into the required 13.2V (4x3) configuration. It definitely beats messing up on 100 40Ah cells though.

Right now, voltage on the12 of them in parallel is up to 3.32, with 166mA being fed to them, so it does appear that they are taking charge, in what at least appears to be, an acceptable fashon. I'll adjust the top-off point to 3.7V on the small power supply that is charging them. When that voltage is reached, I'll end the charging and wait 2 more days, at which point they will be separated apart and given 2 more days to find where they stabilize out to, on an individual basis. Finally, I will slap them together into the final 4x3 configuration, with the goal being that the 4 final sections (with each section consisting of 3 cells) be as equally matched as I can get them to be. 

Maybe later I'll consider investing in a decent balancing charger. But right now, I don't want to waste any more time in getting the pack into the bike so the electrics [mainly the headlight] work properly so it will pass state inspection, and I can ride it without fear of getting fined, This year's riding season is ticking away...


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## Ziggythewiz (May 16, 2010)

The current usual definition of 'full' is 3.65 vpc @ C/20 and I would only take them that high for the initial top balance. The further you are from the ends the longer they will last, and the less you need to worry about just how balanced they are.

CALB recommends charging to 90% full, which gives a resting voltage ~3.33. How high you need to charge to reach that would depend on your charge current, I cut mine off @ 3.4 VPC.

If your daily charge is lower than the balance charge, you don't have to worry about the balance being an issue, unless a cell has been damaged. In your case I'd check them all near and at the top of the charge for a week, then check up on them once a week for a bit, then once a month.


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## dougingraham (Jul 26, 2011)

Electron Power said:


> Right now, voltage on the12 of them in parallel is up to 3.32, with 166mA being fed to them, so it does appear that they are taking charge, in what at least appears to be, an acceptable fashon. I'll adjust the top-off point to 3.7V on the small power supply that is charging them. When that voltage is reached, I'll end the charging and wait 2 more days, at which point they will be separated apart and given 2 more days to find where they stabilize out to, on an individual basis. Finally, I will slap them together into the final 4x3 configuration, with the goal being that the 4 final sections (with each section consisting of 3 cells) be as equally matched as I can get them to be.


At 166ma you are already well below the CV finish point so set your power supply to no more than 3.45volts or you will overcharge them. Resting fully charged after a few days you should see near 3.4 volts. At 3.45 volts for the CV it will takes weeks to do any noticeable damage.


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## frodus (Apr 12, 2008)

They might hold up if they're decent cells, but they will likely be compromised as far as life-cycles go. Just don't trust them 100%.


Go unplug them NOW... you've already overcharged them, and 0.166A is 0.05C, which is basically charged fully. Don't just let them sit there on the charger... they're done. Just disconnect them and let them sit in parallel, they'll equalize themselves over the next day or so. Once they're equalized, just assemble the pack, they're good to go.

If you're using a power supply, adjust the 3.7V output BEFORE you connect the cell. Just a hit for future charging.

What cells did you buy? Do they have tabs already? I wouldn't solder them unless you have a super hot soldering iron that you can melt solder on first, then touch the ends and remove quickly. High heat is another enemy of lithium batteries. If you have access to a tab welder made for batteries, that may be your best bet. Don't use a normal welder for this, it's got to be made for batteries.


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## Electron Power (Jan 2, 2013)

With the PS set at 3.70V, the all-paralleled cells were reading 3.33V, because the PS is so tiny small, only allowing 166mA maximum. Upon [disconnecting and] re-setting the PS to 3.45V, now the voltage on cells is 3.31 [upon re-connect], with current @ 150mA (will continue to drop as voltage increases, I assume). With PS disconnected, the cells drop to 3.28V. I'll keep checking the disconnected voltage every few hours until I see it top 3.33, at which point I will let them rest [connected together] for a day or so, then separate apart to find where each settles to.

This is where purchased: http://www.ebay.com/itm/12-PCS-Life...e_Batteries&hash=item2ec87abcb5#ht_1226wt_725

I don't see any brand specified, or anything at all printed on the outer shrink-plastic coverings either. That does kind of make me wonder - why they measure 26x700, instead of the standard 26x650, for 3.3Ah cells. I just hope that they aren't 5mm longer because I got stuck with a set of those dreaded re-caps. The implications of that would be that they have been re-purposed (which implies used). And that would imply not-new, with new being what I was led to believe I was paying for. But at this point in time, I have no legit reason to accuse anybody of making any less-than-honerable transaction.

As can be seen from the link, they DO NOT have tabs. But I do have an old weller 240/320 watt soldering gun, which you can't even get anymore. It should allow me to melt the silver based solder onto the battery contacts very quickly. I also have a compressed air blowgun @200psi to quickly cool them. But I only want to have to do this one time. That's why I'm being so anal about getting them correctly matched, the first time around.


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## frodus (Apr 12, 2008)

You're already charged at this point. 0.166mA is 0.05C and isn't doing anything to charge those cells measurably. Just remove it, they're charged. Let them sit a while and equalize.


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## PStechPaul (May 1, 2012)

You may be lucky to get 1500 or even 1000 mAh from these cells. You paid about $0.90/Wh for these cells. I purchased and tested some 18650 LiFePO4 that were rated 1800 and I measured just about 1100. I paid about $0.73/Wh according to spec, but more like $1.19/Wh as measured.

My 18650 LiIon cells were rated 3600 mAh and I measured about 960. I paid about $0.26/Wh according to spec, but for actual capacity they were closer to $0.90/Wh.


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## Electron Power (Jan 2, 2013)

Ah, I just checked on the cells and noticed 2 things. First off, I was incorrect in stating that the shrink covering on them has nothing on it. It shows the following::

1st line: BTJ -10.6Wh-3.2V
2nd line: 26700Fe 2VW11B23 24113
3rd "line" is a barcode

The other thing is that the wooden jig that originally held them all very tightly is now very loose, whith some of the cells not even making contact. I cn tell because when i squeeze it tightly with my hands I can see the voltage drop down. The harder I squeeze, the lower it goes, meaning that more cells are making contact. This one caught me off guard, probably due to insufficient drying out of the wood after I cleaned it and assmbled the pieces. I'll try to fix it and leave the the cells in together one more night before removing.


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## Electron Power (Jan 2, 2013)

Here it is> Since that last post [that was NOT made by me] had put me under a great deal of pressure to find out exactly what the truth is regarding these cells, I finally broke down and did do what I had to do. I started out by bumping up the the feeble charge current by 2 orders of magnitude (that's 100x, for those non-scientific types) to about .5C, until voltage reached 3.65V (I wanted to git-er-done, so the discharge test could get under way, with minimum delay) After resting them for several hours, the no-load reading showed 3.35V. 

FYI - the discharge test used a load that consisted of a double filament halogen automotive headlight bulb, with both filaments connected. Current is stable at just a tad over 4 amps, using that type of load load on LiFePO4 cells. And visually speaking, it is very easy to tell when the cell(s) is starting to poop out. In my case, using 12 3.3Ah cells in parallel, it comes out to .1C, or 10 hours for 100% discharge. But keep in mind that 1 or more of the cells could have been loosing connection without me knowing it, or even being able to check.

Final result: My call, based on a score of appoximately 90% (9 hours), the come up CLEAN!


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## PStechPaul (May 1, 2012)

I'm glad that you were able to run the test and find the cells to meet specification. Thanks for your effort. They are a different brand from what I purchased, so maybe they are being more careful with their suppliers and specs. The worst performers in my case were the Li-Ion cells which tested at about 27% of rated capacity, and some NiMH cells that were 23% of rated capacity. Their LiFePO4 cells tested at 62% of rated capacity, and now that I look back at the data I realize that I did this test "as received" and I had not topped off the charge, so they may have been OK. There is a website where many of these "off-brand" cells were tested and many of them were as bad as, or worse than, what I found.

http://lygte-info.dk/review/batteries2012/Common18650Summary UK.html
http://www.lygte-info.dk/info/indexBatteriesAndChargers UK.html


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## Electron Power (Jan 2, 2013)

Here is the update:

The 12-cell (4 groups of 3 cells per group) battery has been in service for a little bit of time now, and is working fine. BUT - 3 of the cells WERE REPLACED less than 1 week after the pack went into service.

Remember the cell I was talking about which wanted to go higher than normal on the charging voltage, and also read lower voltage when being discharged? Well, it appears to have failed. And it also took the 2 other cells in the group down with it. 

In my haste to give them a "pass" rating based on 90% performance for 12 cells in parallel, I failed to take the following into account: What if the 90% was NOT due to all cells making the minimum spec of 3.0Ah, but rather 1 bad CELL bringing down the other 11 that were each near the normal spec of 3.3Ah? That is what now appears to be the case. 

When I finally decided on which cells to go in parallel with each other, I put the pack into service. But within a week it failed to start the bike. Within a couple days after first noticing that my cranking power was dropping, it did not have enough to crank at all. In my attempt to manually charge it, I saw that the voltage on that group was like 4.7V, maybe even higher. So basically, all 3 in the group were toast now, It just happened that I had 3 other, 5mm shorter & different color, that I was able to replace the 3 now-bad ones with, so it is currently working - with 9 out of the original 12 cells.


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## PStechPaul (May 1, 2012)

It seems like the cell or cells that were higher voltage during charge and lower during discharge had high internal resistance. That may have indicated a manufacturing fault such as a bad connection, but as long as it did not have internal leakage it would probably not damage the other cells in parallel. The high resistance would just cause it to remain undercharged when the others became full, and likewise it would limit the discharge current. The series resistance is fairly easy to measure, but the leakage resistance would probably require monitoring the voltage for a period of time after charging.

If one out of 12 cells was bad as received and initially tested, it might just be bad luck, or it could mean they were not all properly tested, or it might indicate poor manufacturing processes that may eventually cause deterioration and further failures.


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