OK.. well shoot.. I just put one on the power.. its set to 3.5v. It's been on for 6 hours, started at 3.30 its at 3.36. I guess these 74ah take about 40+ hours or so to charge just one up. It's only at 2a and it's barely moved from v. I assumed from the videos it wouldn't take this lone for one cell. At this point if I put the rest in parallel I am guessing about 6 months to charge them from 3.3 to 3.5 LOL. What a pain in the butt to get this initial state so you can assemble the cells in to the 12/24/36/48 batteries. When I started down this path I thought the BMS would handle all this, didn't know there was the super long process to charge up the cells.
48v 16 cell.. do i need to charge individual cells before I put in series and charge?
- Thread starter beowulf
- Start date
Thank you for that SOC bit.. actually helped. So I don't know if I have bad batteries or it really does take a few days to charge one from 3.3 to 3.5v? I let it go all day, checked it multiple times too. Just one single cell, 30v/10a bench supply, using the battery terminal grips it came with (not the cheap alligator clips the other PS came with). From 3.0 to 3.3 took a couple hours. From 3.3 to 3.37 (where it was at last night) was 8 hours. Single battery. Is it REALLY this long to charge one to 3.5? I know a few tutorials including one linked here says "dont give up, it will eventually get there". But holy crap.. in no video or reading did I see it should take a few months of top charging to get 16 cells ready to be used in a 48v battery.
I would be down to buy a more expensive option to charge faster as I do plan on building other packs down the road as well.. either LFP or Sodium (or whatever else comes along). But man.. this is killing me how long this is taking. If I put all 16 in parallel and charge at 3.5v (the max the battery allows for).. will that seemingly charge much faster to all 16 than charging one at a time? I just assume that individually would charge 1/16 as slow as all 16 in parallel. But I read multiple places and videos to charge them up fast to like 3.4v or so using your BMS/inverter/charger setup then top charge. Too late for that though since I have them at diff states now.
If you tell me yup.. it's going to take 2 to 3 days per cell to go from 3.3 to 3.5 so they settle around 3.45 or so, so be it. But from the things I read, watched, etc nobody said it would take that long. Even in Prowse video he said when you connect in parallel they are going to charge up pretty fast. so that is why I am now wondering if I just have really bad cells, or my cells maybe top out at 3.35 and wont reach 3.5? Like is there any way to know if they are 95% to 100% charged? I am hoping the specs didn't lie and they are not able to get to 3.5.
Assuming I SHOULD put them all in parallel.. with the one battery at 3.37 and the rest around 3.28 to 3.31.. is that going to now be a problem? I can put 15 in parallel.. but then what happens with that last one? Keep checking till the rest are at the same, then add that one in at that time?
I would be down to buy a more expensive option to charge faster as I do plan on building other packs down the road as well.. either LFP or Sodium (or whatever else comes along). But man.. this is killing me how long this is taking. If I put all 16 in parallel and charge at 3.5v (the max the battery allows for).. will that seemingly charge much faster to all 16 than charging one at a time? I just assume that individually would charge 1/16 as slow as all 16 in parallel. But I read multiple places and videos to charge them up fast to like 3.4v or so using your BMS/inverter/charger setup then top charge. Too late for that though since I have them at diff states now.
If you tell me yup.. it's going to take 2 to 3 days per cell to go from 3.3 to 3.5 so they settle around 3.45 or so, so be it. But from the things I read, watched, etc nobody said it would take that long. Even in Prowse video he said when you connect in parallel they are going to charge up pretty fast. so that is why I am now wondering if I just have really bad cells, or my cells maybe top out at 3.35 and wont reach 3.5? Like is there any way to know if they are 95% to 100% charged? I am hoping the specs didn't lie and they are not able to get to 3.5.
Assuming I SHOULD put them all in parallel.. with the one battery at 3.37 and the rest around 3.28 to 3.31.. is that going to now be a problem? I can put 15 in parallel.. but then what happens with that last one? Keep checking till the rest are at the same, then add that one in at that time?
S Davis
Solar Enthusiast
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They hold a lot of energy, I have top balanced eight 12 volt 280ah packs and each set of four parallel took between 72 and 76 hours with the 30 volt 10 amp charger.
They came about 35% charged. I have short cut on four of the packs by charging fast and finishing the top balance with the 30 volt 10 amp charger and those packs are not as balanced through the charge cycle as the packs I took my time on, same batch of cells.
They came about 35% charged. I have short cut on four of the packs by charging fast and finishing the top balance with the 30 volt 10 amp charger and those packs are not as balanced through the charge cycle as the packs I took my time on, same batch of cells.
OK.. and I am OK if it takes a few weeks.. I'd MUCH rather have my cells in tip top balanced condition before I assemble the 48v battery. But it's odd to me that none of the videos seem to talk about this one step. Like.. I would preface ANY new battery setup with "BTW.. you need to top balance these and expect that to take about 3 weeks or more for 16 cell setup". It's just something I accidentally came across and was like what's this. Now I am reading all the responses and just like.. damn. This is a LONG chunk of time just to get the 16 cells ready to be used. Like I assumed buy the kit, batteries, plug it all in and go.
How did you charge fast? To what level did you go to before you top balanced with the 30v/10a charger? So I assume you put 4 x 3.2 in parallel? Did they charge all the way to 3.65?
S Davis
Solar Enthusiast
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I set them up with the BMS and used a 75amp 12 volt charger to get them to about 95% SOC then changed back to parallel and finished the top balance to 3.60 with the 30v/10 amp charger.
But I also set up my batteries like they are in parallel and then run my custom buss bars diagonally. I just pull off the factory buss bars and install mine and I don’t have to reconfigure the cells.
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Hedges
I See Electromagnetic Fields!
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3.5V x 10A = 35W that your power supply can deliver when parallel balancing.
16 x 3.5V x 74ah = 4144 Wh
4144 Wh / 35W = 118 hours to charge if completely empty. 5 days. I think someone said about 4 days.
That's a reason for the suggestion to connect all 16 in series, with BMS, and charge to the point of (cell) high voltage disconnect.
If you have a higher wattage source, e.g. an inverter/charger, it will go much faster.
First make sure your BMS has correct settings for your cells.
At that point, with all cells near full, you can reassemble in parallel and finish off with 3.5V (or maybe 3.65V) 10A supply.
Or, leave them in series and charge each cell individually to target voltage.
As you say here.
But I think people normally do this to 3.65V, one time to top balance.
After that, operate system to a lower voltage. If you only balance to 3.45V, you'll have to operate system lower, because one will run away above that.
And by the way, they will "settle" lower. Charge each to a particular voltage, then after all have sat for a while, confirm they are same voltage. If any are much lower than the rest, try charging it again. Others here had that due to poor contact.
If you use skinny wires and alligator clips, it will take longer and possibly be uneven. Use heavy wires, at least 12 awg or preferably heavier, as short as possible, and with ring terminals not clips.
16 x 3.5V x 74ah = 4144 Wh
4144 Wh / 35W = 118 hours to charge if completely empty. 5 days. I think someone said about 4 days.
That's a reason for the suggestion to connect all 16 in series, with BMS, and charge to the point of (cell) high voltage disconnect.
If you have a higher wattage source, e.g. an inverter/charger, it will go much faster.
First make sure your BMS has correct settings for your cells.
At that point, with all cells near full, you can reassemble in parallel and finish off with 3.5V (or maybe 3.65V) 10A supply.
Or, leave them in series and charge each cell individually to target voltage.
As you say here.
But I think people normally do this to 3.65V, one time to top balance.
After that, operate system to a lower voltage. If you only balance to 3.45V, you'll have to operate system lower, because one will run away above that.
And by the way, they will "settle" lower. Charge each to a particular voltage, then after all have sat for a while, confirm they are same voltage. If any are much lower than the rest, try charging it again. Others here had that due to poor contact.
If you use skinny wires and alligator clips, it will take longer and possibly be uneven. Use heavy wires, at least 12 awg or preferably heavier, as short as possible, and with ring terminals not clips.
