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diy solar

Top Balancing "How to"

Thanks, that’s what I figured but thought I would ask in case I was missing something.
 
Pyke13 said:
I should get my 8x 272ah cells in the next week, I’ve read loads on how to top balance but have a question. I’m planning on running 4s2p using 2 bms’s. 2 12v batteries in parallel
do I top balance as a pack of 8 or do I top balance as 2 packs of 4?
I will assemble the packs as 2 separate 4s packs with bms and charge to 14.4v the disassemble to connect in parallel to top balance. Using a bench top cccv 30v 10a power supply. Set to 3.65v cv and allow it to finish balancing the pack.
Click to expand...

If you want to do it as fast as possible, that means drawing as many watts as possible from your supply.
You have 10A max available and you have 30V available
30V/3.65V = 8.22
You can connect 8 cells in series, in which case each cell can be charged at 10A, until BMS disconnects at your setpoint of 3.65V for any cell.

Then, connect in parallel to top balance.

(or to continue the initial approach, put the full cell at the end so BMS still sees 8 cells, but charge the remaining 7 in series until one hits 3.65V
...
"And then there were none."

After all cells have hit 3.65V with series charging, connect in parallel to top balance.
 
I’ve also got a 80a charger with adjustable voltage, I will use that to get the battery with bms up as close as possible to fully charged then just finish of the balance with the small charger. Saves waiting days at 10a
 
Steve_S said:
Just to toss a monkey wrench into the works.

I've just received 4x EVE 280's to build a 12V pack. Before doing so, I figured on top charging each cell and doing a capacity test on them, curiosity got the better of me. I'm only using one of those 180W / 20A load testers, so it's 14 hours run per cell... talk about tedious. Charging though is why I'm popping in.

I've been charging these 280's with a TekPower 1540E power supply and doing one cell at a time. Starting with 3.60V/30A CC which eventually flips to CV mode and slowly the amps decrease as the impedance changes. The DOCS say 0.05 of the C-Rate which is 14A is fine but as I am doing per cell, cutting off at 1.5A taken. That sets the cells to 3.650. and they settle out to 3.62-3.63 within an hour. At one point I allowed the cells to sit a couple of days after that charge level and they independently settled between 3.51-3.56 "Without Paralleling". The Capacity tests are showing between 276 & 278AH but I am cutting off at 2.65V and starting from 3.60V after being charged & rested for an hour. A Side benefit of doing this, is being able to charge each cell from 2.65V with the same CC-CV charge, helps get things balanced up.

An observation: While it may be a PITA to do a single cell charge (not so bad with 4 but) it is quite a bit faster per cell. It's also easier to top that single cell down to 1-2A taken. Once I've completed my current charge run per cell, I'll tie them together in parallel, let sit a few hours (overnight) and then apply a topping charge to 3.60 to the parallel set until the Amps drop down to 4 or so. Then it's reconfigure & BMS Time.

Remember, the cells can take 0.5C Charge rate, the more amps you can put behind the charge the faster the cells will top off.
Click to expand...
I wish I would have a purchased a bigger power supply now...I got a 10 amp CV/CC to do balancing not realizing how slow this same charger would be to use to just "charge". My EV cells were all sitting at around 3.2 when I got them...now it's taking me forever using the 10amp. The TekPower 15/40 is $190. The 15/60 is $290 so I may pick one up. I'm also realizing buying an RV-style charger is not that great of an option either and most of which are a compromise, and or they include an Inverter/Converter or shore power switching. For bench use, these TekPower or similar supplies seem to be the best solution.
 
Dogsareloud said:
Inverter/Converter
Click to expand...
Is an RV-ism. In Solar Land we call those Inverter/Chargers which can take "shore power" AC for charging a battery system. Some are capable of also accepting Solar Input from a Solar Charge Controller. Alternately there are AOI's (All in Ones) with Solar, Inverter & Charger all built into one modular unit.

I used a Tek Power 15V model because I am only bench Charging cells and not full packs with that. I run 24V-8S battery packs so a 15V charger is of little use there. I will have ONE 12V LFP pack with it's own SCC & Panels (presently it is a huge AGM) which is strictly for the RV-Furnace (Suburban-NT20S) in my Powerhouse but then I can bypass that to power the furnace from my normal battery systems if required.
 
Steve_S said:
Is an RV-ism. In Solar Land we call those Inverter/Chargers which can take "shore power" AC for charging a battery system. Some are capable of also accepting Solar Input from a Solar Charge Controller. Alternately there are AOI's (All in Ones) with Solar, Inverter & Charger all built into one modular unit.

I used a Tek Power 15V model because I am only bench Charging cells and not full packs with that. I run 24V-8S battery packs so a 15V charger is of little use there. I will have ONE 12V LFP pack with it's own SCC & Panels (presently it is a huge AGM) which is strictly for the RV-Furnace (Suburban-NT20S) in my Powerhouse but then I can bypass that to power the furnace from my normal battery systems if required.
Click to expand...
Yep...I've got an RV and will eventually have to update the converter/charger in the WFCO panel - so that it can handle a LiFePo profile and is more compatible.
 
Dogsareloud said:
I wish I would have a purchased a bigger power supply now...I got a 10 amp CV/CC to do balancing not realizing how slow this same charger would be to use to just "charge". My EV cells were all sitting at around 3.2 when I got them...now it's taking me forever using the 10amp. The TekPower 15/40 is $190. The 15/60 is $290 so I may pick one up. I'm also realizing buying an RV-style charger is not that great of an option either and most of which are a compromise, and or they include an Inverter/Converter or shore power switching. For bench use, these TekPower or similar supplies seem to be the best solution.
Click to expand...
The new Riden power supply at 18 amps is very useful, especially for bigger packs up to 48 volts. I have both the Tekpower and Riden, obviously the Tekpower is faster, but the Riden does tell you how many amp hours you put in the battery or cell. Just set the voltage and it will stop charging as well.
 
Pyke13 said:
I should get my 8x 272ah cells in the next week, I’ve read loads on how to top balance but have a question. I’m planning on running 4s2p using 2 bms’s. 2 12v batteries in parallel
do I top balance as a pack of 8 or do I top balance as 2 packs of 4?
I will assemble the packs as 2 separate 4s packs with bms and charge to 14.4v the disassemble to connect in parallel to top balance. Using a bench top cccv 30v 10a power supply. Set to 3.65v cv and allow it to finish balancing the pack.
Click to expand...
I would definitely top balance both sets of cells in parallel, that way both battery packs are in the same state of charge when hooked up in parallel.
 
MisterSandals said:
You need to connect the + and - leads to opposite ends of the parallel bank. Put the black lead onto cell 4 and leave the red lead on cell 1.
Click to expand...
Putting the power supply leads on opposite ends is good practice to do anytime you have parallel cells or batteries. However, I don't think it matters much for top balance. Yes, with the power supply leads on the same cell, it will see a higher voltage and take more current initially. Yes, this cell will get charged faster. However, as the cells get charged and the current goes down, the voltage differences will diminish. Eventually all the cells will be charged, the current will be zero and the voltages will be the same on all the cells.

This brings me to a warning about top balance: If you see voltage differences between cells during the top balance process (and you often will), don't worry about it. Don't try to adjust your charge voltage to take care of it. Just be patient. The cells will all eventually get to the target voltage.

As @Just John said: "Just have patience". Patience is the most important tool to have for top balancing.
 
FilterGuy said:
This brings me to a warning about top balance: If you see voltage differences between cells during the top balance process (and you often will), don't worry about it. Don't try to adjust your charge voltage to take care of it. Just be patient. The cells will all eventually get to the target voltage.
Click to expand...

However, voltage differences between cells could be a yellow flag that the connections at a terminal may not be as tight as you think. That happened to me.
 
HRTKD said:
However, voltage differences between cells could be a yellow flag that the connections at a terminal may not be as tight as you think. That happened to me.
Click to expand...
Fair point..... particularly if you are seeing a large voltage difference.
 
I ordered 0-30v 10a power supply from Ali ...and my friend give me this power supply bml 351041/1 ( 48 vdc 12.5 a ) it's adjustable from 40to 59 v ,675w I was thinking of using this supply to charge my 16s 280ah up to 3.5 with bms and finish it with cheap Ali in paraller ...do i need to use trough MPPT bml power supply or directly to batteries which is better approach ?

​

 
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