48v lifepo4 battery only charging upto 50v

john61ct said:
harper said:
Rassy said:
No harm adjusting the voltage of an individual cell group like you are doing, but I have no idea why one group has a higher voltage. At one time you reported all cell groups were at 3.35v to 3.37v. I am still inclined to think that your BMS has some strange operating characteristics, but it seems to me that you are on top of it and should get as good of service as is possible from your battery. Good luck with it! :)
Click to expand...

cells does not even getting closer to bms trigger voltage for balancing(3.65v).may be i should charge each individual cell upto 3.65v and connect them back :idea:

hope this will work! i will try it soon if this remains the same.

thanks for clearing my doubts my friend.

hoping the same :wink:
Click to expand...
Manual balancing is easy and with quality LFP may only need doing once a year, or every 50 cycles or. . .

Put them all in parallel no BMS, charge to 3.6 and hold until current drops to 0.01 or 0.02C

Then let them sit in parallel for at least 24hrs, 48 even better, will perfectly naturally self-balance.

Diagnostic - atomize isolated, see if any drop lower / faster than the others.

If so likely weak links, capacity testing only way to quantify for sure.

Replace if needed, reassemble pack, fresh BMS of better quality recommended.
Click to expand...

hello,

i don't think the cells are new because i got it only for 1.80$US per cell.most of them are used and imported from china.

and i have to desolder the pack to keep every cell in parallel for balancing..(doesnt the 0.01v difference in cell is balanced :?: )(mine is with 0.01v difference from cell to cell (ex:3.34v for first and 3.35v for second)after removing from charge after 3hrs)

i dont have spot welder. so, i have soldered the cells with fusible copper wire at 4amps max. but, i have not checked the internal resistances :( :( .

i have seen someone telling that internal resistance will play a vital role in charging and discharging the cells.

(last cell pack which is at (-)terminal is discharging to 2.9v as every cell is at 3.2 when load connected)

i am with a confusion :| .

i will discharge the battery again and notice the mileage today. i will update it soon.

thanks for helping a noob and teaching new things.

thankyou so much everyone.
 
Soldering cells can easily have damaged them.

If used, resistance will vary a lot.

If the charger is cutting out at 3.3V, you are far from fully charged, replace it.

So how are you getting to over 3.4?

Yes 10mV is reasonably balanced, but if you get a better balancer that starts at say 3.3V with 1+A balancing current, shoot for 3mV if you can get there in say 20min.

 
After following more of your conversation, I would change my position on tweaking your charger. If you choose to do so, you have to adjust it while it is on and the pack is fully charged. Very carefully adjust the potentiometer while watching the total pack voltage. If you can raise the final voltage you might not need to get a new charger, and if you ruin the charger, well you needed a new one anyway!

Good luck. :D

Edit: Private message sent
 
All cells need 3.6 v for BMS. I charge to 3.5v per cell.with no BMS for 1,480 cycles 6.5yrs old. So no lll effects as a poeple get lifepo4 and the stress and iill affect on 18650 is very different chemistry.
Get a single cell charger and charge low string to 3.5v don't walk away when monitoring sit and stay Do Not walk away. If you go to the bathroom on plug it. Please give us the voltage of your charger just to be clear. you could have one or two bad cells in your parallel group that are leaking a little bit or a low quality. You might have to buy another parallel group of cells and replace them ?
 
I think you might have some weak cells in your pack. If you didn't capacity check the cells before putting them together, some weak cells might have got into the pack.

Thats what happened to me and my 220ah pack. Since they were 5.5 mah cells and 32650 (wouldn't fit in my opus) I just check for voltage and put them together. The cells were new straight out of the box but were old stock. All my cells were at 3.31 volts when first tested. So I put the cells together, it wasn't easy, the cells were next to impossible to solder, I had to buy a tab welder.

I had nothing but balancing problems, and the pack would never fully charge, even when using a balance charger, the balance charger would stop charging and give me error warnings.

The only way I fix the pack so it would fully charge was by using active balancers. Now I get all cells up to 3.65 volts without tripping the bms early. The only correct way to fix your problem is take it apart and capacity check every cell, since you are using it in high drain bike I would also check the IR of every cell and get rid of the high IR cells.

Active balancers work for me because I don't have any high drain devices. The pack is going on 3 years of daily use, I also charge the cells to 3.65 volts every day.


picture of the lifepo4 32650 (next to 18650) that I use on my 220ah pack 160 cells. I paid 150 dollars for 80 cells.
32650 with 18650.jpg
 
john61ct said:
Soldering cells can easily have damaged them.

If used, resistance will vary a lot.

If the charger is cutting out at 3.3V, you are far from fully charged, replace it.

So how are you getting to over 3.4?

Yes 10mV is reasonably balanced, but if you get a better balancer that starts at say 3.3V with 1+A balancing current, shoot for 3mV if you can get there in say 20min.
Click to expand...

have you watched youtube channel with name (jehugrecia) :?:

he also did the same 2 years back...but balanced cells with an external balancer.

soldering cells will not get them damaged alot.

after observing the cells for more then 4 days.. at last i get to know that the problem is with the BMS..
most of the bms's in the market starts balancing at 3.6v but they are not facing the same issue..

thanks for your replay and thanks for being here to solve problems.. :)
 
999zip999 said:
All cells need 3.6 v for BMS. I charge to 3.5v per cell.with no BMS for 1,480 cycles 6.5yrs old. So no lll effects as a poeple get lifepo4 and the stress and iill affect on 18650 is very different chemistry.
Get a single cell charger and charge low string to 3.5v don't walk away when monitoring sit and stay Do Not walk away. If you go to the bathroom on plug it. Please give us the voltage of your charger just to be clear. you could have one or two bad cells in your parallel group that are leaking a little bit or a low quality. You might have to buy another parallel group of cells and replace them ?
Click to expand...

as we are in quarantine there are no shops available.

i have charged every cell upto 3.6v by removing the bms from battery.. some of them got upto 4.1v with a total voltage around 54.2v. and then i have rested them for 2 hours connecting the bms. after that i checked the voltage, and got around 51.2v in total..
 
Rassy said:
After following more of your conversation, I would change my position on tweaking your charger. If you choose to do so, you have to adjust it while it is on and the pack is fully charged. Very carefully adjust the potentiometer while watching the total pack voltage. If you can raise the final voltage you might not need to get a new charger, and if you ruin the charger, well you needed a new one anyway!

Good luck. :D

Edit: Private message sent
Click to expand...

bro!!! i have tested the pack with my tadpole trike and got around 37km in a single charge and a top speed of 55kmph
the fuses which i have soldered to cells were blown and i have reconnected to test it with my trike..
now, my battery is charging upto 51.2v (hope this 1v will give me some extra range) :)

thanks bro.. :) :) :flame:
 
Do **not** allow any cells to go above 3.6V, even that is harmful to longevity, why would you do that?

Pack voltage is irrelevant, stop before the first cell / group hits 3.6V, 3.45V best maybe 3.50V OK.

4.1V is actually dangerous, as in can burn the house down!
 
I agree with John that 4.1 is too high for the cells. However, this is LiFePO4 and it will not self ignite when abused, like many other chemistries do. They also operate at a higher voltage than many other chemistries. Ping chargers cut off at about 3.7V max per cell, or 59V for a 48V 16S pack. These Ping packs last for many years being fully charged and balanced on a regular basis with the BMS doing all the control work for you.

One reason I like LiFePO4 packs is their relative safety compared to most other chemistries.
 
Yes, but that is only relative safety.

A high voltage charge source left feeding an LFP pack indefinitely can start a major fire for sure.

Even lead banks can explode if not cared for properly.
 
Just to be clear, I am not advising that any batteries be abused, but the voltage for a 48V 16S LiFePO4 pack is a little higher than for other 48V Lithium chemistry packs, with the added plus of the chemistry not being as volatile when abused. A do encourage the use of a proper BMS at all times and not using hobby equipment to charge individual cells or to bulk charge. I believe the original poster was encouraged on this thread to bypass the BMS and balance his battery manually, and that is when he overcharged one of his cell groups. In my opinion that was bad advice and his battery did not need to be subjected to that abuse since it was not seriously out of balance.

Just my two cents. End of rant!
 
Rassy said:
Just to be clear, I am not advising that any batteries be abused, but the voltages for LiFePO4 are a little higher than for other Lithium chemistries, with the added plus of the chemistry not being as volatile when abused.
Click to expand...

I hope you mean lower voltage?
 
Rassy said:
Nice to hear it is working out for you. Were those fuses that blew just too small for the current that was required at the higher speeds?
Click to expand...

i think so.i have soldered thin fuses which only meant for 3 amps max(one fuse blown and one fuse disconnected). now, i changed them to 6amp max ones..
 
john61ct said:
Do **not** allow any cells to go above 3.6V, even that is harmful to longevity, why would you do that?

Pack voltage is irrelevant, stop before the first cell / group hits 3.6V, 3.45V best maybe 3.50V OK.

4.1V is actually dangerous, as in can burn the house down!
Click to expand...

i have charged them for once with bypassing BMS to know the problem and got these voltage variation. :(

but after connecting bms it balanced them to safer voltages (3.4v to 3.5v ). :)
and after resting it for around 2 hours the pack got down to 50.7v as usual :(
 
i have checked the battery again yesterday and got around 50.1km of range :D :flame: with average speed of 28 and max speed of 55kmph.
and the pack still contains so much juice (47.7V) but bms triggered because of voltage sags below 46v (bms low voltage trigger :lowbatt: )

my bms is not common port one so it is showing 43.5v at discharge terminal after low voltage cutoff, but the juice in cells is around 47.7v.

then i stopped the ride. :|

will discharging below 47v effect the pack :?:
bypassing bms and using it again in emergency :confused:
 
What is your highest C-rate that lasts for more than say 4sec?

What is your highest "continuous" rate?
 
john61ct said:
What is your highest C-rate that lasts for more than say 4sec?

What is your highest "continuous" rate?
Click to expand...

its around 28 amps at max speed of 55kmph for some time (max 7 sec ). that's what i have noticed till now.
cells i have used are of 3c and have 5c max rating.
 
john61ct said:
Ask again, this time using V per cell.
Click to expand...

my battery is of 15s and per cell voltage is 3.1v after bms got cut off(v 47.7v in total).

bms out voltage is showing 43v but the cells are at 47.7v

will discharging below 3.13v by bypassing bms will effect the cells :?: (as my controller is rated to work from 42v)

the voltage sag is around 1 to 3v for the battery pack.
 
harper said:
my battery is of 15s and per cell voltage is 3.13v after bms got cut off.

will discharging below 3.13v bypassing bms will effect the cells :?:
Click to expand...

Yes, of course what really matters is the Vpc after recovery, say a full hour isolated at rest.

Going that low may not "damage" as in render the pack scrap in a few cycles

but you're going to get a **very** short lifespan drawing them down so low on a regular basis.

You need newer/better quality cells, or higher Ah pack capacity.

 
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