Top Balancing new Aliexpress Lifepo4 cells, 200ah, stuck on 3.32v, have I been scammed?

[tinkertaylor]

Hi all, its with a heavy heart I make my first post but im afraid I have to call on any of the many experts who frequent this excellent forum.......Purchased 4 new cells from Aliexpress and proceeded to try and top balance the cells, connected them in parallel and set my lab power supply to 3.65 volts, all the cells were well balanced prior to charging (checked with a multi meter) starting voltages were 3.23 volts. After 24 hours on charge the voltage had gone upto 3.282 volts.





I knew it would take time as the power supply can only provided 2A maximum so i decided to separate the cells and top balance individually. Over the next week I tried each cell for at least 24 hours but nothing would budge them from 3.319 - 3.323 volts, the confusing part was the power supply was still providing 2A to the cell, verified with a multi meter in series with the cells. Is there something i'm missing? I have read that achieving 3.65 volts per cell is not really desired but would have expected them to get closer than the 3.319v. I'm $600 invested in the cells and to say my ass is twitching is an understatement. Any Ideas?

 

[Steve_S]

I've just finished Top Charging 4 LFP 280's pushing 30A, between 3.2V & 3.4 took about 8 hours.
It will take longer at a lower amperage.
The main Power Curve for LFP os 3.0V to 3.4V and the majority of all of the juice is between 3.100 - 3.450.
Once the cells reach 3.4 V the charge to 3.65 does not take very long and finally reach top as the Amps Drawn drops to below 3.0A
It takes a LONG Time to fill these puppies up.

280A ÷2A = 140 hours ! if starting from 2.50.
EDIT TO ADD: Are you aware that you can push 3.65V/140A at one cell ? Yes, 140A which is 0.5C

PATIENCE !

 

[mzamaites]

Patience is huge, I got some 280AH cells from alibaba and it took 14 days to top balance charging at 3.65V. Might feel like forever but it'll eventually get there.

 

[tinkertaylor]

I've just finished Top Charging 4 LFP 280's pushing 30A, between 3.2V & 3.4 took about 8 hours.
It will take longer at a lower amperage.
The main Power Curve for LFP os 3.0V to 3.4V and the majority of all of the juice is between 3.100 - 3.450.
Once the cells reach 3.4 V the charge to 3.65 does not take very long and finally reach top as the Amps Drawn drops to below 3.0A
It takes a LONG Time to fill these puppies up.

280A ÷2A = 140 hours ! if starting from 2.50.

PATIENCE !

Thanks for the reply,I will persist, I have separated the cells, total 200ah, so one cell should be 50ah? Guessed this would reduce the hours but maybe more patience is needed. The appearance of cells didn't help tbh, with one cell being slightly different to the others and small marks on the faces of cells. Also some strange 'blotches' underneath the blue heat shrink, see picture.

 

[Maast]

Two things: at 3.2ish volts you just ran into the 'flat' charge/discharge characteristics of lifepo4 - it'll hit 3.25ish and stay there until almost full and it'll finally creep up to 3.3 and higher.

Second thing: At 2A that barely qualifies as a trickle charge and it'll take you about 100 hours to fill.

It'd be MUCH faster assembling it as a 12V pack and charging using a normal charger up to near-full (while monitoring the individual cells to prevent one from overcharging) then changing back over to parallel and finishing up with your trickle charge.

 

[upnorthandpersonal]

while monitoring the individual cells to prevent one from overcharging

With a BMS, please OP. Don't assume you can just do this while measuring once in a while. You'll miss it, guaranteed.

Also, as others have stated: patience. The amount of energy these guys store is not to be underestimated, and I guess many people new to this don't realize how little 2A going in really is.

 

[tinkertaylor]

Two things: at 3.2ish volts you just ran into the 'flat' charge/discharge characteristics of lifepo4 - it'll hit 3.25ish and stay there until almost full and it'll finally creep up to 3.3 and higher.

Second thing: At 2A that barely qualifies as a trickle charge and it'll take you about 100 hours to fill.

It'd be MUCH faster assembling it as a 12V pack and charging using a normal charger up to near-full (while monitoring the individual cells to prevent one from overcharging) then changing back over to parallel and finishing up with your trickle charge.

Thanks, I will change over to this method tomorrow after tonight (I'm UK based and its currently 19:30)

With a BMS, please OP. Don't assume you can just do this while measuring once in a while. You'll miss it, guaranteed.

Also, as others have stated: patience. The amount of energy these guys store is not to be underestimated, and I guess many people new to this don't realize how little 2A going in really is.

I will hover over the assembled pack and monitor closely, I'm waiting for a bms to come from China.

Thanks to everyone who has replied, you have helped calm my nerves.........at least until tomorrow.

 

[upnorthandpersonal]

I will hover over the assembled pack and monitor closely

You're going to miss it. Be patient, wait for the BMS.

 

[Reed Cole]

Thanks for the reply,I will persist, I have separated the cells, total 200ah, so one cell should be 50ah? Guessed this would reduce the hours but maybe more patience is needed. The appearance of cells didn't help tbh, with one cell being slightly different to the others and small marks on the faces of cells. Also some strange 'blotches' underneath the blue heat shrink, see picture.

If you have 4 cells @ 3.4v that are connected in series to reach 200ah @13.6v then each cell is also 200ah.

 

[Gazoo]

I will hover over the assembled pack and monitor closely, I'm waiting for a bms to come from China.

It's almost impossible to monitor 4 individual cells in series with a DMM because once the voltage gets to 3.4 volts the voltage starts creeping up ..faster and faster as it goes up. If you have a runner cell you may not catch it. Connect the cells in parallel and wait. Also make sure you set the power supply to 3.65 volts BEFORE you connect it to the cells. By my calculations it will take apx. 8 days to to top off the cells in parallel and it's only a one time deal. Totally worth the wait.

 

[DJSmiley]

Which BMS do you have?

If you can adjust its parameters, you can set HVD to 3.65V and serie-charge them. Goes a lot faster.
Once a single cell hits the HVD the BMS will stop. At that point at least 1 cell is fully charged, and very likely the others are pretty close also. (Depending on how much the are different)

Reconnect in parallel and do a proper top balance. With this method, you only have to topup the remaining cells to reach 3.65V. Even with only 2A this usually would take only a couple of hours, assuming the cells are pretty close in SOC when received.

Usually, cells are 50-70% SOC when you receive them. With 4 cells in parallel, you have 280x4 = 1120Ah. Assuming they are at 70% SOC, you still need to charge 336Ah. And with a 2A supply, that would take 168 hours.. (1 week continously charging).
If they are at a lower SOC it will take even longer.

By series-charging you have 280Ah, and with 70% SOC you need to charge 84Ah. Assuming you have a 10A charger that's about 8.5 hours to fully charge them (well, mostly). Once done you're probably at about 98% SOC for even the lower cells (the BMS disconnects on the first cell which hits 3.65V) so topbalancing them in parallel goes much faster

As said: without a BMS, don't even try. If you're reaching the top-end, its a matter of minutes between 3.5 and 3.65V, which you will miss when measuring individual cell voltages. And even if you did, you won't instantly stop charging most likely.

Personally, I won't charge the cells to 3.65V seperately, but leave them in parallel. Doing so, you're sure they are exactly identical balanced.

 

[wmills_92105]

Charging 8x60Ah cells at fixed 3.65v took a LONG LONG time in parallel. Like 50 hours or so with a 6A limit. The taper down once it came off the 6A peg was like 12 hours to get down to the .5 amp ballpark.

2 amps max for you but only 4 cells... with my same 60Ah batteries would be 50 x 3 / 2 or 75 hours ballpark. It just takes a long time.

 

[Bob B]

Just don't make the mistake of mis-adjusting the power supply others have made which results in damaged cells.

Always adjust the power supply voltage ..... then connect the batteries and don't touch the power supply again during the charge.

 

[Burke]

2 Amps is almost nothing for 4 large capacity cells. that is only a half amp per cell... Get a battery charger that can put out 20 or 30 amps, or more.

 

[Gazoo]

2 Amps is almost nothing for 4 large capacity cells. that is only a half amp per cell... Get a battery charger that can put out 20 or 30 amps, or more.

All that is going to do is speed up the charge and add to the overall expense. Since parallel top balancing is a one time deal, if one has something that will work without overcharging the cells I say go for it. 500ma's per cell is fine. It just requires more time and patience.

 

[tinkertaylor]

2 Amps is almost nothing for 4 large capacity cells. that is only a half amp per cell... Get a battery charger that can put out 20 or 30 amps, or more.

I'm tempted to get a larger charger (200A!) but until my bms arrives I'm going to stick with charging on the 2A lab supply....... I have persisted with charging the one cell (just to see if the cell is capable of getting to 3.65v) and I'm pleased to report that it has finally pushed through the 3.319v barrier and is storming onto a heady 3.35 volts. My impatient nature does not suit the 2A power supply. Once I have proven the cell is good (from a charge point of view) the pressure is off with complaining to the vender.
My van build is at least 3 months away from completion, that's another story. Thanks everyone, its been a great help. VIVA la Internet.

 

[Burke]

All that is going to do is speed up the charge and add to the overall expense. Since parallel top balancing is a one time deal, if one has something that will work without overcharging the cells I say go for it. 500ma's per cell is fine. It just requires more time and patience.

Yes, but please take the context of the OP into question. He wanted to know if he was being scammed because his voltages didn't come up quickly, and I was explaining that there isn't enough amps going into the cells at 2A to make much of a difference in the time period he is referring to. Also, if you are going to utilize large capacity LiFePO4 cell banks, you need to be able to charge them at more than 2A.

 

[Just John]

I'm tempted to get a larger charger (200A!) but until my bms arrives I'm going to stick with charging on the 2A lab supply....... I have persisted with charging the one cell (just to see if the cell is capable of getting to 3.65v) and I'm pleased to report that it has finally pushed through the 3.319v barrier and is storming onto a heady 3.35 volts. My impatient nature does not suit the 2A power supply. Once I have proven the cell is good (from a charge point of view) the pressure is off with complaining to the vender.
My van build is at least 3 months away from completion, that's another story. Thanks everyone, its been a great help. VIVA la Internet.

One question, I assume from 4 cells you are aiming for a 12 volt pack? Do you already have a 12 volt charger? I am looking at 24v packs myself, and a 12 amp at 24 volts victron charger is $175, but an 18 amp Riden is approximately $185. At 12 volts the output of the victron (25 amps) is much better, but the Riden can be used to top balance, charge individual cells, and a full pack charger. It is an economical investment if you don't already have a bench supply and a pack charger. It does however require advanced planning (Riden generally takes about 2 or 3 weeks to arrive in the USA).

 

[Burke]

I would keep a lookout on ebay for a high quality power supply like a server unit, i have two HP server power supplies hacked into a 24v 65 amp PSU i use for power for the battery charger when i am away from the bench. I have a great 24 v power supply used for CCTV mounted on my bench. If you routinely search ebay they come up as bargains i think i paid $45 for the CCTV supply and $15 each for the HP server PSUs. The server mods are simple but you should have a good base electrical skill set if you want to do that stuff.

 

[tinkertaylor]

One question, I assume from 4 cells you are aiming for a 12 volt pack? Do you already have a 12 volt charger? I am looking at 24v packs myself, and a 12 amp at 24 volts victron charger is $175, but an 18 amp Riden is approximately $185. At 12 volts the output of the victron (25 amps) is much better, but the Riden can be used to top balance, charge individual cells, and a full pack charger. It is an economical investment if you don't already have a bench supply and a pack charger. It does however require advanced planning (Riden generally takes about 2 or 3 weeks to arrive in the USA).

I have the offer of a quality 12 volt power supply that gives out 200 amps, It's an old car power supply for diagnostics when the car battery is flat. I have been using a 10 amp lab power supply brought from Amazon ,cheap, but the power button is knackered so it has to go back .