New cells arrive today! Spend 100 hours top balancing...

[kc130up]

I've setup my "lab" for top balancing my new batch of 280ah cells. :D


After my first experience using the "crappy" power cords that come with the chargers, I made new leads using old PC power cables. Used all 3 wires from each to create one lead each.

While I impatiently wait for Fedex to deliver, I'm doing napkin math and 36w into a 4S pack of 280ah cells is like 13 hours (assuming they are 1/2 charged). I am somewhat impatient so I got 4 chargers to prepare for today, but still, that is days and days.

So I'm thinking, why not use a 12v charger with high current to get the cells "higher", then top balance from 3v to 3.65?

The cells can take .5c so no issues with too much current.

Brilliant idea, bad idea, or something worse than a bad idea?

 

[Tulex]

Pretty sure that's a bad idea, believe there are threads on here as to why.

 

[kc130up]

I've been looking in the "up in smoke" section. I see people that used higher than 3.6v trying to charge an individual cell faster, but 4 cells in series would be ~12v.

I'm searching the threads to see how using a 12v charger on a 12v battery is an issue.

 

[Q-Dog]

Some folks build the battery with a BMS, charge until BMS cutoff, then break down the batteries and top balance the cells.

 

[BentleyJ]

The problem with putting cells in series and charging at higher voltage is that the first cell to reach 100% will "Run" up very fast. Unless you plan on using a 4S BMS on each set of 4 cells in series I would recommend NOT doing the 12V fast charge method. Reason being you really don't have any idea the SoC of the new cells and voltage measurements are only an approximation.

I've done a fair amount of bench testing and can attest to being surprised at how fast the cell voltage runs up and can get into dangerous territory within minutes or even seconds depending on current.

 

[kc130up]

I feel an important piece of the conversation is missing

The plan wasn't to overvoltage charge. The plan was to build a 12v battery (4x 3.2v) then charge that with 12v 20a charger.

 

[Q-Dog]

I feel an important piece of the conversation is missing

The plan wasn't to overvoltage charge. The plan was to build a 12v battery (4x 3.2v) then charge that with 12v 20a charger.

and if one of the cells is at a higher charge rate than the other 3, it can be over charged before the entire group of cells reaches 12 volts.

 

[kc130up]

and if one of the cells is at a higher charge rate than the other 3, it can be over charged before the entire group of cells reaches 12 volts.

Gotcha! Without a BMS to protect each cell, a cell could be different since its in series.
I will use the BMS to protect the individual cells.

Thanks for the sanity check.

 

[Tulex]

My first build was 2 batteries. I purchased a cheap 10A power supply and topped off each set one at a time. Then I built one more battery later on. Didn't care that it took a long time, had other things to get done. A year later I built 3 more batteries. Started charging all 48 cells in parallel, days later nothing seemed to be happening. So I broke it down to 3 sets and still nothing on a single set. Determined that the power supply wasn't working properly, so ordered a larger one.
15V 60A ( was a bit less when I bought it) and some heavy leads for back connection.
Connected all back in parallel. Charged in no time. I've also used it to charge other batteries, so the cost was worth it.

 

[frankrudis65]

Hi there, i've spend quite some time precharging(i hate the word top balancing,as everyone seems to understand something different) every single cell of my 17s 2p lifepo4 banks....There are advantages and disadvantages....Charging every single cell gives you emediately an idea of the quality of the cell:the capacity and if the cell holds the power....The disadavantages are the time,if you havent't got a lot of chargers and you best have to build yourself a small compressing shelf which contains rods,nuts and boards like the big one you would use to eventually get them all in place.....Swelling will happen at about 50% charge,not at as much at full charge! So it is adviseable to compress the cells from the first precharging onwards....I have never had any problems since precharging the cells,could compare from the start onwards the quality of every single cell and my cell off balance is between 3 and 6 mV.I would do it again this way,if i had to....Frank

 

[kc130up]

Hi there, i've spend quite some time precharging(i hate the word top balancing,as everyone seems to understand something different) every single cell of my 17s 2p lifepo4 banks....There are advantages and disadvantages....Charging every single cell gives you emediately an idea of the quality of the cell:the capacity and if the cell holds the power....The disadavantages are the time,if you havent't got a lot of chargers and you best have to build yourself a small compressing shelf which contains rods,nuts and boards like the big one you would use to eventually get them all in place.....Swelling will happen at about 50% charge,not at as much at full charge! So it is adviseable to compress the cells from the first precharging onwards....I have never had any problems since precharging the cells,could compare from the start onwards the quality of every single cell and my cell off balance is between 3 and 6 mV.I would do it again this way,if i had to....Frank

I actually had this in my cart at one time and opted for 2 smaller 10a chargers instead.

My theory was it was "faster" to charge 8 cells at 10a in parallel vs 16 cells at the same time.

 

[Brett V]

I just finished my 5th battery. Sixteen 230Ah cells. All in parallel at 3.65 volts and 10 amps, it took about 12 days. I’ve done all my batteries this way. Even with this method, they go from nothing is happening to all done very quickly.

 

[kc130up]

So 4x 10a chargers each with 4 cells @ 3.65v parallel, it should take 3 days right...haha.

 

[BarracudaBob]

I connect all 16 up and charge them up with 58.4V and everybody comes up to 3.650 and holds.

Do the same for a 4S at 14.6V

What is the issue? Simple.. Just do this

 

[S Davis]

I have done eight 4s batteries with lf280N cells using a 10amp power supply and each one took between 72-76 hours, I have packs with the same cells that I didn’t spend the time and they do not stay as balanced through the charge curve.

 

[BarracudaBob]

I have done eight 4s batteries with lf280N cells using a 10amp power supply and each one took between 72-76 hours, I have packs with the same cells that I didn’t spend the time and they do not stay as balanced through the charge curve.

That is why I use my 15A active balancer on every new battery. It does all the work for me.

 

[S Davis]

That is why I use my 15A active balancer on every new battery. It does all the work for me.

I don’t need them, less crap to go wrong.

 

[time2roll]

Build the battery. Let the BMS protect and balance the cells while in use. If the BMS cuts off... reduce the charging voltage.

 

[kc130up]

Cells did not arrive yesterday. They were due by 1P, then at 2P got an email saying "Updated Delivery" now tomorrow...
They got here today, so the LFP balance lab got underway.



Ran into 2 issues:

1) My little plastic folding table looked like it was going to snap from the weight of 16x cells.

2) I forgot to order more bus bars. I forgot from the last battery i made that I needed more bus bars to put them in parallel, vs series.

I put a piece of 1/2" shelving under the cells so the plastic table didn't sag in the middle.



I used some M6 nuts & bolts and connected two of 50a bus bars I had and made "longer" bus bars (just for balancing).
I know they only handle 50a, but the PSU only puts out 10a so I should be fine.

The crappy bus bars are limiting the current more than expected. This will do for a day or so.
I used the Flir to make sure there was not any excess heat.

Even with the bus bar workaround, I still only had enough hardware to balance 15 cells connected together.

There is 1 cell connected to its own charger and I am using the EBC-A20 to charge a cell by itself. Its only 5a, but better than letting the cell sit idle while I wait on the Amazon to bring more bus bars.



Side note, 5 fans running is louder than expected.

I am seriously considering a 60v 10a charger. Justification? I don't have the capability to charge a battery that isn't connected to an inverter. When a battery is being built / repaired / diagnosed, the only way for me to charge one is connected to the inverter or I have to remove a cell and charge it individually, which messes with the balance.

I plan on making 3 more batteries this year. Having a backup way to charge an entire 48v pack seems logical.

One can justify anything though :D

 

[Tulex]

Pay a little more and get a 15v 60 amp.

 

[BarracudaBob]

Pay a little more and get a 15v 60 amp.

Link?

 

[fnnwizard]

Lookup Toolkit M8P. Its a very capable 8S hobby charger. For less than $30, including buying some balance connectors, you'll have an excellent way to charge up to 8S cells at 20A with appropriate power supply.

 

[kc130up]

Pay a little more and get a 15v 60 amp.

A 15v charger doesn't allow me to charge a 48v battery. Even if i split the battery in half, that's still 24v.

Also (correct me if I'm wrong) but it would only ever be 60a if the battery was 100% dead. Otherwise the current would be less and less as the voltage approached the max.

 

[42OhmsPA]

I'd buy a 3KW 57V rectifier for ~$100 delivered, use that to bulk charge then use the power supplies you already own to bring up low cells while it's in pack form.

 

[740GLE]

What BMS are you planning to use in the final build?

IMO all this top balancing with leads and individual chargers to perfectly charge the cells is absolutely pointless.

I’m sure it’s fun to play around and check the current and voltage of each pack. Jot down and log the voltage rise over time.

But for me, build the battery with BMS and charge it, let the JK 2a active balancer do its thing.

The battery is there for solar storage, charging it from the grid just feels dirty.

My second battery I built was an 8s 280k ver3, after fully assembled, I only tossed maybe 30ah at it with my cheap 30v 10a charger, to verify things were working. I then just connected it parallel with my 80% SOC, voltage delta was maybe .10v 3.40 vs 3.30. Initial inrush was only about 200w into the new battery. After about a week or so both batteries were nice and balanced and fully charged to 3.45v/cell.