Top Balancing "How to"

[Horsefly]

I tried the step method tp parallel top balance my 8 EVE cells and it didn't work for me. I am attaching a photo of my 12 amp power supply set at 3.40 volts and it's only putting out 5.84 amps, and it's in CV mode. I used 12awg cables. The PS wouldn't put out the the full 12 amps until I set it above 3.50 volts. Then the PS went into CC mode and put out the full 12 amps. So I ended up setting it at 3.65 volts and cut the time it took to top balance in half.

After about 4 days of twiddling my fingers, the PS went into CV mode and it only took about 2 hours to finish the balance. I let the tail current drop to .100ma's. I was using the charging feature of the Riden and I had tested it on another battery before parallel top balancing so I slept while while it was doing it's thing. But I was happy to be awake when it was finishing up the charge so I could watch the end of charge.

There sre several methods to parallel top balance and in the end they all accomplish the same thing. I guess I am set in my old ways which is simply connecting all the cells in parallel, and setting the PS to 3.65 volts before connecting it to the cells. Of course using a traditional PS one should monitor the voltage and current of the PS and monitor the voltage at the cells.

Wow @Gazoo, that sounds like kinda strange behavior from your power supply. Have you seen anything documented about why it would limit itself to less than 6A @ 3.4V but put out 12A above 3.5V? You would think that if it were trying to limit power, it would be able to put out more amps at a lower voltage.

 

[Just John]

Wow @Gazoo, that sounds like kinda strange behavior from your power supply. Have you seen anything documented about why it would limit itself to less than 6A @ 3.4V but put out 12A above 3.5V? You would think that if it were trying to limit power, it would be able to put out more amps at a lower voltage.

Well, judging by the picture, his power supply was set to charge to 3.4v and it was measuring 3.39v. He was already above 95% there.
But I'll admit, that's just the one moment in time (the picture).
Like he does, I just set it to 3.65v and forget it until it is done. The Ridens work everytime.
I have 4 Ridens, so I can do a batch of 4 cells simultaneously, or use a 40 amp supply (my Ridens are the 18 amp models).

 

[Gazoo]

Well, judging by the picture, his power supply was set to charge to 3.4v and it was measuring 3.39v. He was already above 95% there.

The voltage of the cells delivered were 3.25 volts, and when I connected the PS. So there was some voltage drop as to be expected.

 

[Just John]

FYI, for anyone wanting to get 4 Riden supplies so you can charge 4 cells simultaneously, be warned to have more than one breaker circuit nearby. Generally near the high end (high voltage and high amps) you can't run more than one or two per circuit. Each of the 12 amp models has an 800 watt supply, the 18 amp models use a 1000 watt supply, and require a 1200 watt supply to get the full 60 volts at 18 amps.

 

[Substrate]

Gazoo - I'm not familiar with that supply enough to know if it is going into current limiting when using a low CV voltage, or if your cells were already in a high SOC - as compared to the 3.40 cv - and now you are in the tail-current part of step 1 where you just needed to be more patient.

Step 1, where you can take as long as you need is pretty cool because at 3.40v TIME is not a degradation factor. But you need to let the tail-current do it's job, to prepare for the next two steps where cumulatively, the time spent at relatively higher CV's and their tail-currents will be shorter.

Makes me wonder how many of the 10a supplies, when dropped to 3.40v do much the same as yours and appear to be current limiting, frustrating the owner so they just crank to 3.65 right from the get go.

I suppose it's not really worth debating what is best for anyone. I just know that from now on, my personal choice is to step it, because time has bit me in the ass before with LFP.

 

[RogerD]

Don't get me wrong - LFP has super charge-acceptance, but it wasn't designed to be trickle-charged. The major issue is that LFP was designed for rapid cycling, and spending the LEAST amount of time charging - as long as you stay within the specs.

When you say to stay within the specs ... what specs are you referring to stay within?

I'm starting with (8) 280 ah cells. The plan is to wire as 24v with overkill bms. I will more than likely buy a second set of 8 shortly after.

Wired as 24v / 280 ah bank. Using a charger that is 24v / 37.5a isn't quite .2C. Is this OK?

Should I initially wire as 12v / 280ah and charge 12v / 70a which would then be over .2C? I would have to buy a 12v bms just for doing this though.

Thanks for the advice.

 

[noenegdod]

FYI, for anyone wanting to get 4 Riden supplies so you can charge 4 cells simultaneously, be warned to have more than one breaker circuit nearby. Generally near the high end (high voltage and high amps) you can't run more than one or two per circuit. Each of the 12 amp models has an 800 watt supply, the 18 amp models use a 1000 watt supply, and require a 1200 watt supply to get the full 60 volts at 18 amps.

Please correct me if I am wrong but if you are charging cells in parallel you power supply is only going to supply 18 amps if you have 4 you will be at 72 amps, at 3.65 volts, which is only 262.8 watts, which at 120 volts is only 2.2 amps. You should be just fine running all 4 power sources off one circuit. No?

 

[Luthj]

There is no evidence of cell degradation from low charge rates. Full stop.

LFP does suffer accelerated capacity loss from high SOC, especially over 3.5V. This is cumulative over the life of the cell. Many users have performed capacity tests with full 100% charges before and after. A typical top balance does not appear to produce measurable (with our tools) capacity loss.

There are lots of folks wandering around with "truthy" ideas about what is good or bad for LFP. Much of it has no empirical data to back it up.

 

[Substrate]

@RogerD - problem solved for me. I'd say to FIRST follow the excellent advice already given by snoobler and others here.

Myself, since time spent on LFP charging is one of my main concerns, I'm augmenting this advice with a solution that works for ME when dealing with low initial charge current.

Found here in the Marine How-To. It's called Parallel Step-Method Top Balance.

There is a lot of good info there, so you may have to scroll or search for it on that long page.

DIY LiFePO4 Batteries On Boats - Marine How To

DIY LiFePo4 On Boats Last edit;3/26/23:The base of this article was written a number of years ago (2010) but this does not mean the information here is outdated. We have been keeping it updated and have added to it when ever we had the time. This article deals

marinehowto.com

This neatly solves a time concern I have with LFP by utilizing successive steps to accomplish the job - most notably no time penalty spent on step #1.

Works for me, but may not be to everyone's taste.

 

[Just John]

Makes me wonder how many of the 10a supplies, when dropped to 3.40v do much the same as yours and appear to be current limiting, frustrating the owner so they just crank to 3.65 right from the get go.

From reading on here, it seems at least half don't understand how much crummy wires and alligator clips affect their results (especially amp output).

I suppose it's not really worth debating what is best for anyone. I just know that from now on, my personal choice is to step it, because time has bit me in the ass before with LFP.

I use a 40 amp supply, but mainly due to the time factor. I think that getting these cells to 100% is as harmful as charging your phone, laptop, or tablet to 100%. Yes, it isn't good for them and you should avoid it during routine operation since it can be cumulative.

But doing it for a top balance is well worth the effort. For me, charging to 3.4v per cell and letting it absorb without a runner is the desired and obtained outcome. I have found the results when you let it absorb at 3.65v to be much more consistent. If anyone worries, they could of course buy a bigger supply (or multiple cheap ones). It's difficult to find a supply under $200 that puts out enough amps at 3.65v as well as your pack voltage. Most people are "beginners", and will be using solar or DC-DC charging in an RV. The last thing they want to do is drop $200 on something that will be used at most once a year. Even with 16 cells in parallel, with good cables they would spend at most 8 hours above 3.45v. Less with fewer cells.

 

[Gazoo]

Gazoo - I'm not familiar with that supply enough to know if it is going into current limiting when using a low CV voltage, or if your cells were already in a high SOC - as compared to the 3.40 cv - and now you are in the tail-current part of step 1 where you just needed to be more patient.

I posted above the cells were at 3.25 volts when I connected the power supply. I built my own cables and put ring terminals on one end and fork terminals on the other end. So cables were not an issue. I know of someone else who used 6awg cables and had the same results as I did.

Towards the end of charge, the Riden power supply switched to CV at 3.60 volts but was still charging at 11.98 amps. The voltage at the cell terminals was 3.391 volts. Voltage at cell terminals when the power supply displayed 3.65 volts was 3.443 but it did go into absorb mode meaning the current started to taper off. The total amp hours on the power supplies display was 1300ah's and the total watt hours was 4595wh's.

A few hours later the voltage on the power supplies display was fluctuating between 3.64 volts and 3.65 volts. The voltage at the cells was 3.65 volts and ocassionaly I got a reading of 3.651 volts. The current on the display at the tail end was fluctuating between 210ma's and 120ma's and acted that way for awhile. Finally when the tail current drop to 90ma's the power supply cut off. The final tally on the amp hours going into the cells as measured by the Riden power supply was 1305.59 ah's and the watt hours was 4614wh's.

Makes me wonder how many of the 10a supplies, when dropped to 3.40v do much the same as yours and appear to be current limiting, frustrating the owner so they just crank to 3.65 right from the get go.

I see it often. The person will try the step method and the power supply will be putting out much less current than it's rated output and be in CV mode. Once they turn up the voltage to 3.65 volts the problem is solved. This does assume one is not using the 18awg or whatever cable comes with these supplies and the banana plugs and alligator clips.

I suppose it's not really worth debating what is best for anyone. I just know that from now on, my personal choice is to step it, because time has bit me in the ass before with LFP.

IMO I don't understand why the step method is better then setting the supply to 3.65 volts from the starting gate. I don't understand the value of it and people using 10 amp power supplies become frustrated when they see the power supply is only putting out 4 amps and is in CV mode, even though they are using good cable and ring terminals.

I have no idea what the results are if using higher amperage power supplies. I can only post what my own experience was using a 12 amp power supply and what others have experienced using 10 amp power supplies. So in the end what works for you may not work for me and others...
At the time setting the voltage to 3.40 volts was my personal choice too but it wasn't working for me.

 

[Substrate]

Ah Gazoo, we're just coming at it from different application vectors. So we're both good.

Read his article - the point of doing this is to spend as little time in the upper-knee as possible. And, the charger is considered to be part of the system when buying large capacity cells, so he's running a 60A unit.

And the big deal is that he and his customers are out on the open sea, so there is the tendency to do it totally right from an engineering perspective.

Here, with casual sub-c non-critical use, time spent above the knee with lesser equipment is not a big deal from that application standpoint.

So we'll just have to agree to disagree. I'll do it my way, you do it yours, and we'll all live in peace!

 

[Just John]

I'm still wondering why a standard charge defined by the manufacturer is to charge to 3.65 and let rest for an hour, then discharge. Must be awfully bad for the cells.

 

[toms]

There is no evidence of cell degradation from low charge rates. Full stop.

There is plenty of evidence of cell degradation when the cell is continually charged when it is in a fully charged condition.

The chemistry doesn’t care that you don’t understand the lithiation process.

Do you not believe that when the lattice is full you will get permanent bonding of lithium ions?

I can assure you no manufacturer is going to spoon feed you a trial result - this level of cell degradation is difficult to test at accelerated levels due to the differing chemical reaction at different charge rates.

You can choose to ignore the chemistry and follow popular opinion, and you will be rewarded with reduced cell life.

 

[Luthj]

You can choose to ignore the chemistry and follow popular opinion, and you will be rewarded with reduced cell life

It's convenient how you take my quote out of context, create a straw man, and put words in my mouth. Them ignore the capacity tests done by others after a top balance. Pathetic.

Just because your can't be bothered to find a single source for your "feels right" conclusion is no reason to be an ass.

I literally stated that extended time at high voltage causes capacity loss, but that there is no evidence of measurable loss from a typical top balance.

So the question is, why do you feel the need to lie and attack me (again!)? Maybe we will get lucky and you will throw a tantrum after no one accepts your conclusions, and leave us alone for a bit?

 

[noenegdod]

It's convenient how you take my quote out of context, create a straw man, and put words in my mouth. Them ignore the capacity tests done by others after a top balance. Pathetic.

Just because your can't be bothered to find a single source for your "feels right" conclusion is no reason to be an ass.

I literally stated that extended time at high voltage causes capacity loss, but that there is no evidence of measurable loss from a typical top balance.

So the question is, why do you feel the need to lie and attack me (again!)? Maybe we will get lucky and you will throw a tantrum after no one accepts your conclusions, and leave us alone for a bit?

toms is pathetic. Period. Dont bother engaging.

 

[Horsefly]

Not wanting to enter a war - and hoping the warring can cool it down a bit - I'll throw in my perspective. I'm not claiming any level of expertise, but just describing my logic.

IMO I don't understand why the step method is better then setting the supply to 3.65 volts from the starting gate. I don't understand the value of it and people using 10 amp power supplies become frustrated when they see the power supply is only putting out 4 amps and is in CV mode, even though they are using good cable and ring terminals.

The reason I think some step method is best is that if you can get all the cells to 3.4V and have them fully absorb all the energy they can, you can be somewhat assured that they are at the same level of charge at 3.4V. Same thing when you step again up to 3.5V. Then when you go up to your final top balance voltage you are on the steepest part of the curve, and all the cells should be together. You won't have to leave it at that top balance voltage for as long, because they were all at the same place.

I think if you charge all the way from a resting 3.2V or 3.3V up to 3.65V for a top balance, the cells will all be at the same voltage, but not the same state of charge. So at 3.65V you'll have to wait for some cells to absorb more energy than others, so the current will not taper down as quick as if you do the steps. IF you believe that harm can be caused by having your cells held at 3.65V, the step method allows you to not keep them there for as long.

This is all based on my assumption (I admit it) that cells can be at the same voltage but not the same state of charge. This is certainly true for lead acid, as that is why the absorption phase is so important. So some cells at whatever voltage will not take any more current while others will still absorb more current, and so more energy. Once all have absorbed all the current they can at a given voltage, they are at the same state of charge. This of course presumes that the cells are fairly matched in terms of capacity.

I also don't think you have to top balance to 3.65V. As long as you are on the steep part of the curve, your final step should ensure that the cells are pretty well top balanced. So I think top balancing to 3.6V, 3.55V, and even 3.5V is nearly as good as top balancing to 3.65V.

Now, recall my obligatory caveat: I am not an expert, and do not claim to be. Just trying to give a logical explanation for why charging in steps can be better, even if it only two steps rather than more.

 

[Just John]

The manufacturer recommends charging to 3.65v as a "standard charge", then letting it rest for an hour before discharge. Using this method is how they calculate cell life.

I am not sure the manufacturer understands how damaging this is to the cells, especially repeated a few thousand times. Or maybe they do.

The vast majority of users will top balance once. After that, most will set 3.4 or 3.45v as their desired full charge. So, the manufacturer tests it in the "danger mode" a few thousand times and lets it sit. I really seriously doubt that anyone is going to see decreased cycle life.

Coming in and saying you are going to bloat your cells, or reduce cycle life is confusing to beginners, and counter to what the manufacturer says.

 

[toms]

Many beginners or novices will be reading this thread and following this forum.

It would be remiss of me to not share the knowledge i have regarding the pitfalls of parallel top balancing.

Just because a few hundred internet experts have decided they have found a great way to balance their cells and wish to glow in the conformation bias that comes with it, doesn’t make it right.

Yes - every time anyone says that holding a cell at full charge doesn’t cause cell damage i will correct them.

I also recommend that at all times cell level voltage protection is used.

Your petty personal attacks slide right off - they are nothing compared to what i received a decade ago when i dared to share information that charging regularly into the knee was causing cell damage. I wonder what happened to the hundreds of people that were recommending that was OK “because everyone is doing it”.

 

[Horsefly]

Many beginners or novices will be reading this thread and following this forum.

It would be remiss of me to not share the knowledge i have regarding the pitfalls of parallel top balancing.

Just because a few hundred internet experts have decided they have found a great way to balance their cells and wish to glow in the conformation bias that comes with it, doesn’t make it right.

Yes - every time anyone says that holding a cell at full charge doesn’t cause cell damage i will correct them.

I also recommend that at all times cell level voltage protection is used.

Your petty personal attacks slide right off - they are nothing compared to what i received a decade ago when i dared to share information that charging regularly into the knee was causing cell damage. I wonder what happened to the hundreds of people that were recommending that was OK “because everyone is doing it”.

Let's assume you are right. You seem to feel some passion about it. Do you really think the best way to save us all is to post individually and somewhat viciously on a message forum?

If you have that much expertise and really do feel it is important to change minds, there are two things I suggest:

1. Take the message to @Will Prowse or maybe even to some universities that are studying the chemistry, and encourage THEM to tell people the truth and save us all.
2. If there are some legit sources that point out the "pitfalls of parallel top balancing" then start your own thread about it and post links to them.

You are right that there are probably hundreds of people who encourage either top balancing or bottom balancing, and most of them associated with solar would argue for top balancing. As far as I know, you are the only one that feels it is a really bad thing to do. If you are really an expert on this, there simply has to be some other respected sources for the same argument.

I don't think you are a troll. However, by just tossing out ad hominem attacks at people and not siting evidence, you can be seen as a troll.

I love to learn. If what seems logical to me is wrong, I really want to understand that. Help me understand. Post links. Work with people who have some credibility to get your message out.