[mizlplix]

I have chosen a different cell strategy, one I'm sure that will ignite many critics and cause a lot of "You're a dummy" posts. I don't care. It works for me. I only present it here as an abstract idea and mental exercise.


I named it -Middle balanced-:

I paralleded my pack in their as-is delivered state. I do not much care as to their real charge state just as their not full 3.9 or 3.0

I left them for a week. After disconnected another week, they were all 3.310

They were installed, series, and brought up to full charge. (recorded)

I had one wild cell, #12. I put a cell voltmeter on it. It was 3.90

Driven, recorded, charged, driven, charged....4 complete 35-40 mile cycles.

The figures all repeat, every-time accurately.

The same cells charge and drain in an accurate, predictable manner.

The basis of my "middle charging" idea is that when it charges it only gains 50% of the deviation of a bottom balanced pack. It also drains at 50% of the deviation of a top balanced pack.

In short, It uses a 50% median line to limit the deviation to 50% above or 50% below instead of the full 100% as of top or battom balanced.

The top charge is repeatable and "watched by the charger. The problem cell that will drain first has a cell monitor on it and will give me a really obvious red light on the dash.

Yes, it has been only 4 cycles so far, but it has repeated accurately.

Miz

[onegreenev]

So what is your end of charge target? That one cell could have been 5 AH out of whack from the others and could very well be exactly the same AH in the cell as the others and would be sitting happy with the others if you had lower balanced your pack. If you even take your pack to 3 volts per cell you know your not on the bottom but pretty much on the down swing. All should easy be within an AH or so from each other. Then on the upper charge your swing won't be so far as long as you stay off the very bottom which is pretty easy to do with a smart controller and AH counter. I would not just do a middle because it is hard to KNOW what the MIDDLE is. It is easier to do the balance on the upswing or downswing. Downswing being the safer but either works if you so choose. My last balance is more in the range of 2.7 volts rather than 2.4 volts like I did before. Still no cell goes over 3.8 by the time the charger cuts off. All cells just before termination are 3.7 and lower. I now use 3.55 volts as a cutoff voltage since I can choose any termination voltage with my controller when its used as a charger.

Pete

I might suggest you bring your one cell down a touch to better match the others so your not charging it to such hight voltages. 3.9 is in the range where you may not want your cell to live and if it has the capacity you surly don't want to leave it there.

The purpose of balancing is to also find which cell is the lower capacity one or ones and to find out by how much. If your termination voltage is like 3.7 and lower for your highest voltages your doing well.

[onegreenev]

No matter how you set up your pack your still charging in series single cells so each will charge accurately and repeatably every time. That is not in question. The question is how well balanced is your pack of cells to each other cell in the pack. The closer together they are the better. Top, Bottom, or Middle. Just harder to balance accurately in the middle vs the top or bottom swing.

[mizlplix]

For the last 4 cycles, my pack has done the exact same thing. They all come back to .014/volt of each other when in that mid-balanced area. Even that high one.

I do not intend to further alter any even if I lose that strange one. That is the premise of this method.

I am aware I am leaving some capacity on the table with the way my charger is set, but that is another story.

When I get my transmission put back in, I will get some lower discharged cycles on them. If that follows predictions, it will bear me out. If not then I will just top balance like everyone else and keep them that way.

In my world, when a cell tops out first AND bottoms out first, it is lower in capacity than the rest. I have 14 that deviate from the rest of the pack when on the top end. I still need to check them on the bottom end to say for sure.

The problem with this forum is that there are too many different opinions. All state they are right, making it very confusing for anyone seeking knowledge.

Miz

[onegreenev]

The problem with this forum is that there are too many different opinions.

The information given is factual and I see no opinions. Information is already out there that supports what is said, including mine. Believe it or not some still do things based on what has been done and not what is done on a typewriter.

If you don't know where the top or bottom truly lies then how do you propose to properly balance the pack in the MIDDLE.

[DIYguy]

Originally Posted by mizlplix

I have chosen a different cell strategy, one I'm sure that will ignite many critics and cause a lot of "You're a dummy" posts. I don't care. It works for me. I only present it here as an abstract idea and mental exercise.


I named it -Middle balanced-:

I paralleded my pack in their as-is delivered state. I do not much care as to their real charge state just as their not full 3.9 or 3.0

I left them for a week. After disconnected another week, they were all 3.310

They were installed, series, and brought up to full charge. (recorded)

I had one wild cell, #12. I put a cell voltmeter on it. It was 3.90

Driven, recorded, charged, driven, charged....4 complete 35-40 mile cycles.

The figures all repeat, every-time accurately.

The same cells charge and drain in an accurate, predictable manner.

The basis of my "middle charging" idea is that when it charges it only gains 50% of the deviation of a bottom balanced pack. It also drains at 50% of the deviation of a top balanced pack.

In short, It uses a 50% median line to limit the deviation to 50% above or 50% below instead of the full 100% as of top or battom balanced.

The top charge is repeatable and "watched by the charger. The problem cell that will drain first has a cell monitor on it and will give me a really obvious red light on the dash.

Yes, it has been only 4 cycles so far, but it has repeated accurately.

Miz

I did exactly this when I got my pack new over a year and half ago. I wanted to get driving and didn't want to take the time to bottom balance accurately. I never even go below 50 -60% so, it worked fine and never drifted or had any issues until I got around to bottom balancing.
After my rebuild, I re-did everything, so I decided to redo the bottom balance a bit lower. I used the Power Lab 8 and discharged each cell to 2.7 volts. It took a bit of time, but I did it while I worked on other things.
After seeing that the finish charge in CV at 3.45 volts per cell did not cause any shooters at the top above 3.6, I upped the charger to 3.5 vpc. I have 3 cells that I watch with slightly lower capacity . . about 1% is all. They climb to about 3.65 and interestingly enough, they start to go back down before the charge clicks off. It's perfect.
So, ya, it can work and perhaps if you have a pack that is not so perfectly matched, maybe is a good compromise.

[ricklearned]

Originally Posted by DIYguy

I did exactly this when I got my pack new over a year and half ago. I wanted to get driving and didn't want to take the time to bottom balance accurately. I never even go below 50 -60% so, it worked fine and never drifted or had any issues until I got around to bottom balancing.
After my rebuild, I re-did everything, so I decided to redo the bottom balance a bit lower. I used the Power Lab 8 and discharged each cell to 2.7 volts. It took a bit of time, but I did it while I worked on other things.
After seeing that the finish charge in CV at 3.45 volts per cell did not cause any shooters at the top above 3.6, I upped the charger to 3.5 vpc. I have 3 cells that I watch with slightly lower capacity . . about 1% is all. They climb to about 3.65 and interestingly enough, they start to go back down before the charge clicks off. It's perfect.
So, ya, it can work and perhaps if you have a pack that is not so perfectly matched, maybe is a good compromise.

I have a very similar situation with my pack, although I only have one shooter. So now there are three of us that "middle balance". Another description I have heard is ragged ends, to reflect the fact that on either end there is some uneveness. I stay away from the ends and my cells are within 10mv of each other at various states of charge.

[EVfun]

Are you sure they vary by "about 1%" DIYguy? I ask because the 6 cells I had there where getting a little high near the end of charge (3.61-3.99 volts) only needed 0.2 amp hours removed to knock them back in line, now finishing between 3.46 and 3.51 volts. I have put a second cycle on them since pulling the newer 6 down and got the exact same finishing numbers.

It is a shame nobody makes a simple 100 milliamp 3.5 volt shunt reg (no BMS function, simple shunt reg.) That would be more than enough for slight variation, even for added cells of the same type. A red LED would make inspection easy.

[DIYguy]

Originally Posted by ricklearned

So now there are three of us that "middle balance".

Just to be clear, I only did this for a few months. I have been bottom balanced since then. Thanks.

[dougingraham]

Originally Posted by mizlplix

The problem with this forum is that there are too many different opinions. All state they are right, making it very confusing for anyone seeking knowledge.

There is the right way, the wrong way, and the military way.

Here is a helpful (or not) guide for grading opinions.

1) If the opinion comes from a manufacturer or vendor it is suspect. They want you to spend your money and will tell you what they have to to get you to do so. There are exceptions to this rule.

2) If the opinion comes from a product user their opinion will be against if they have had problems with a product but will be in favor if they have had no problems even if the product does nothing of value for them. So their opinion cannot be trusted. There are exceptions to this rule.

3) If the opinion comes from an "Expert" it is suspect. You don't know what they do and don't know and what is just their opinion. Experts are good at "typing themselves smart". There are exceptions to this rule.

4) If the opinion comes from a noob then who cares. But it doesn't mean their opinion is wrong. It just doesn't mean much.

5) If the opinion comes from me then it isn't an opinion, it is a fact! There are exceptions to this rule. (I usually, but not always, will tell you I don't know when I don't know.)

So whats the answer? There is no correct answer. There is only what works for you.