balancing strategies as they relate to BMS

[ArthurEld]

Here is the new topo for pack charging

Generally you only do provisioning once.
It doesn't really matter if you charge them to 3.65 until they fully saturated.
You could leave full to the brim and exposed to 3.65 volts for a week and imo its not a huge deal.
Of course shorter is better.
If the 3000-5000 subsequent service cycles where you want to terminate on tail current.

I guess that's why Will just says set the charger to 3.65 and let it go.

 

[Gazoo]

Snoobler and smoothJoey told me that when you get to 3.65 you need to stop charging. These chargers don't just charge to 3.65 and stop.

Were they referring to a power supply or charger? When I charged my batteries using the Riden in charging mode the charger did stop when the batteries reached 14.6 volts at 100ma. My regular LifePo4 charger stops when the battery reaches 14.62 volts at 500ma.

I don't know how it's going to behave charging at 3.65 volts. I suspect it will behave the same way but I sure will be watching it. I might call it quits when the cells reach 3.55 or 3.60 volts.

They reduce the voltage before they get to 3.65 and they reduce the amps too.

But that was not my experience...not even close. Are you referring to the 120 amp power supply you have? Perhaps that is my misunderstanding.

We are trying to use the BMS shut off the charger when the cell gets to 3.65. That way I can charge full speed right to the target voltage and shut off charging.

Right and I understand. At this point I would remove the BMS, connect the cells in parallel then top balance them the traditional way. Better yet, leave them connected in series as @GXMnow suggested and let the BMS do it's thing with it's active balancers. I understand and respect what you and smoothjoey are attempting. And they are your cells and BMS. But you have a nice BMS and there is no point in risking damage to it. If you decide to proceed with your experiment, I will respect that too. Just be careful.

 

[John Frum]

When I charged my batteries using the Riden in charging mode the charger did stop when the batteries reached 14.6 volts at 100ma

Well if the riden has charge termination logic this hole exercise just got much easier.

 

[ArthurEld]

Were they referring to a power supply or charger?

I don't know why the Riden isn't called a battery charger. Where the wires are connected it says for charging batteries.
I'm sure there is some technical reason not to call it a charger. But the word charger pretty much explains what I am doing in one word. Power supply is two words and it doesn't explain what I am doing with it.

When I charged my batteries using the Riden in charging mode the charger did stop when the batteries reached 14.6 volts at 100ma. My regular LifePo4 charger stops when the battery reaches 14.62 volts at 500ma.

I don't know how it's going to behave charging at 3.65 volts. I suspect it will behave the same way but I sure will be watching it. I might call it quits when the cells reach 3.55 or 3.60 volts.

But that was not my experience...not even close. Are you referring to the 120 amp power supply you have? Perhaps that is my misunderstanding.

The Riden displays 3.65V but if you look at the coulomb meter or the BMS volts it's not at 3.65V. Then the Riden reduces the amps which technically isn't reducing the voltage but the battery never actually gets to the 3.65V. Besides that it hangs at the 3.65V area for too long. That is different than if I use the BMS to stop the charging. When I use the BMS it charges full blast until the BMS reads the battery is at 3.65V and then it cuts off the charging. There's no hanging around at the top. This is very hard to explain and I am just repeating what I heard someone else say.
I'm very inexperienced so I am not trying to say that I understand much. But this is the subject that has been in my mind for a long time.

The issue I am describing above is much worse with a 5A power supply.

Something else I realized is that 48V at 12A isn't really all that wimpy. Riden 48V x 12A = 576W Mean Well 3.3V x 120A = 396W
The Mean Well is more powerful for parallel configuration charging. Or charging single cells. But it is faster for me to charge 16 cells in series with the Riden than it is to charge them in parallel with the Mean Well. And I get the BMS when use the Riden.

At this point I would remove the BMS, connect the cells in parallel then top balance them the traditional way. Better yet, leave them connected in series as @GXMnow suggested and let the BMS do it's thing with it's active balancers. I understand and respect what you and smoothjoey are attempting. And they are your cells and BMS. But you have a nice BMS and there is no point in risking damage to it. If you decide to proceed with your experiment, I will respect that too. Just be careful.

As far as the risk to my BMS, of course I don't want to destroy it. But I am learning a ton. If I lose a BMS it's $200. That's the cost of 2 cells. I see people destroy 10 or more cells and they still don't understand the BMS. So, I'm not going to sweat it. Besides, it's pretty easy for me to connect my $24 4s BMS to 4 cells to check if the experiment is going to destroy the BMS. That piece of crap 4s BMS I bought has to be good for something.

I realize that GXMnow's suggestion might work. But I am enjoying what smoothJoey and I are doing right now. It is a challenge. Part of a challenge is risk. I will get to GXMnow's suggestion another time. I have watched Will's top balance video a few times and that is great info. But it will do that hanging around at the top of the knee thing even if I use the Mean Well in parallel.

 

[ArthurEld]

Well if the riden has charge termination logic this hole exercise just got much easier.

I'm still working that through my mind. The problem I see is that the Riden charge termination is based on Riden volts. Which isn't the same as battery volts.

 

[John Frum]

I'm still working that through my mind. The problem I see is that the Riden charge termination is based on Riden volts. Which isn't the same as battery volts.

Close is good enough.
How close is it?
Consistency matters more imho.
lifepo4 is more foregiving on the top end.
1st priority is to get these cells consistently fully charged(top balanced).
2nd priority is to minimize the voltage stress on the cells.

 

[ArthurEld]

Close is good enough.
How close is it?
Consistency matters more imho.
lifepo4 is more foregiving on the top end.
1st priority is to get these cells consistently fully charged(top balanced).
2nd priority is to minimize the voltage stress on the cells.

I will have to experiment to see if I can get some consistent results. The over voltage protection turns off the power supply as soon as the power supply reaches the voltage limit. That is way before the battery is up to that voltage.

 

[John Frum]

I will have to experiment to see if I can get some consistent results. The over voltage protection turns off the power supply as soon as the power supply reaches the voltage limit. That is way before the battery is up to that voltage.

Over voltage protection is not necessarily the same as charge termination logic.
What @Gazoo is describing sounds like tail current termination which would be great.
A tail current of 100 mA is low but fine for our purpose.

 

[ArthurEld]

Over voltage protection is not necessarily the same as charge termination logic.
What @Gazoo is describing sounds like tail current termination which would be great.
A tail current of 100 mA is low but fine for our purpose.

I tried the over voltage protection on the Riden. As soon as the Riden got to the limit it shut off the power supply. The battery was far behind in voltage.
I don't think that is tail current. But I will check it again to be sure I am not mistaken. And then I can give some solid numbers.

 

[John Frum]

phase 1 - constant current
better understood as current limited
the charger limits the current the battery can draw by adjusting the charge voltage down from the configured level.

phase 2 - constant voltage
The moment the battery draw is equal to or less than the charger's configured current limit the charger no longer
has to adjust the voltage down. So it supplies whatever current the battery draws at "constant voltage".
As the battery voltage converges with charger voltage current flow decreases accordingly.

The battery voltage never actually reaches charge voltage and current flow never stops.
This is how cc/cv charging works in the absence of charge termination logic.

I'm going to take a step back now.

 

[ArthurEld]

Sorry smoothJoey. I think I did misunderstand.
We were talking about so many ways to stop the charger and I didn't realize you were talking about just setting the voltage and letting it go until it finished. It will get very close to the target voltage if I do that.

I am fairly sure the Mean Well will does the CC/CV too. So, it will stay at the target voltage until the battery stops accepting current.

 

[John Frum]

Sorry smoothJoey. I think I did misunderstand.
We were talking about so many ways to stop the charger and I didn't realize you were talking about just setting the voltage and letting it go until it finished. It will get very close to the target voltage if I do that.

I am fairly sure the Mean Well will does the CC/CV too. So, it will stay at the target voltage until the battery stops accepting current.

As I said above the battery will never stop accepting current but it will appear to.

Asymptotic -- from Wolfram MathWorld

Informally, the term asymptotic means approaching a value or curve arbitrarily closely (i.e., as some sort of limit is taken). A line or curve A that is asymptotic to given curve C is called the asymptote of C. More formally, let x be a continuous variable tending to some limit. Then a real...

mathworld.wolfram.com

 

[ArthurEld]

So, back to the fuses. There was some disagreement about fuse amperage and I have thought about it more.
I am starting to think it would be best to use a fuse that is just above the expected amperage. When using the Riden it seems like 15A might be good. If more than 15A is going anywhere something is wrong.

I looked around and from what I could tell ATC/ATO fuses aren't meant for 48V. The only 15A fuses I could find that were rated for 48V are glass fuses. I'm going to have to pick something up today.

 

[ArthurEld]

As I said above the battery will never stop accepting current but it will appear to.

Asymptotic -- from Wolfram MathWorld

Informally, the term asymptotic means approaching a value or curve arbitrarily closely (i.e., as some sort of limit is taken). A line or curve A that is asymptotic to given curve C is called the asymptote of C. More formally, let x be a continuous variable tending to some limit. Then a real...

mathworld.wolfram.com

Sorry again. I assume the power supply stops charging when the amperage gets very low. But I haven't tried that yet.

 

[John Frum]

Sorry again. I assume the power supply stops charging when the amperage gets very low. But I haven't tried that yet.

You know what they say about assuming.

 

[John Frum]

So, back to the fuses. There was some disagreement about fuse amperage and I have thought about it more.
I am starting to think it would be best to use a fuse that is just above the expected amperage. When using the Riden it seems like 15A might be good. If more than 15A is going anywhere something is wrong.

I looked around and from what I could tell ATC/ATO fuses aren't meant for 48V. The only 15A fuses I could find that were rated for 48V are glass fuses. I'm going to have to pick something up today.

Fuses protect wires.
As I have said before the fuse is constrained by the wire it protects.
What is the smallest gauge wire in the circuit that the fuse will protect?
What is the temperature rating on the wire insulation?
Is the conductor pure copper?

 

[ArthurEld]

Fuses protect wires.
As I have said before the fuse is constrained by the wire it protects.
What is the smallest gauge wire in the circuit that the fuse will protect?
What is the temperature rating on the wire insulation?
Is the conductor pure copper?

I honestly don't understand a lot.
The wire is stranded copper THHN from the home improvement store. The temperature rating is 90 degrees Celsius.
It's 6 AWG and I already have a 100 amp fuse on the battery positive terminal.
The 100A fuse was in line but didn't blow when I burned up my coulomb meter and I have to wonder if a lower amp fuse would have stopped that from happening.

 

[John Frum]

I honestly don't understand a lot.
The wire is stranded copper THHN from the home improvement store. The temperature rating is 90 degrees Celsius.
It's 6 AWG and I already have a 100 amp fuse on the battery positive terminal.
The 100A fuse was in line but didn't blow when I burned up my coulomb meter and I have to wonder if a lower amp fuse would have stopped that from happening.

The display portion of the meter has tiny wires.
They should be a different circuit.
I suspect that was more a voltage problem then a current problem.
When I suggested another fuse I meant to protect the relay upstream and downstream.
There should be no potential on the relay downstream but just for an abundance of caution I always put a ~1 amp fuse in that circuit.
The upstream should be fused according to the relay doco.

 

[John Frum]

Anyway if the riden does charge termination the relay is not necessary.

 

[ArthurEld]

Ok, my meter arrived. $17.95 and free next day delivery. The meter uses smaller wires. I used 16 awg wire on that last time.
So, I need a fuse on that circuit. I might not be swift but I catch on eventually.