200a Portable Lifepo + BMS + Balancing

[nebster]

Originally Posted by newhaul

finally you quantified your responses with " in my opinion."

Hey, buddy, there's no reason to try to beat me up on words here.

Everything I said before in this thread is my experience with ONE big battery bank in ONE real life production installation. And I peppered my statements with "I suspects," "probably", and as many other qualifiers as I could. I'm pretty confident in a lot of my conclusions, based on a lot of time spent reading and then a lot of time spent experimenting on my little test bench in my garage.

If you didn't read that into my long paragraphs with lots of details, I'm sorry. I'll try to do better.

Yes I will be in the lower range as far as charging is concerned however my cells are capable of charging at a 5C rate. As per manufacturer specifications.

I feel like you're getting defensive about your cells here, which is kind of weird.

If you try to continuously charge a large bank of lithium cells at 5C or 3C or probably even 1C, you will have a thermal problem and the pack will likely suffer as a result. You can use your cells, or my cells, or the 18650 NMCs in the Tesla modules, or whatever you want.

The physics is the arbiter in this "debate." I'm just reporting on my experiences and my observations.

If it makes you feel better that the sticker suggests your cells can tolerate 5C, great. But let's not kid ourselves (or mislead the next battery pack builder who wanders along and has to suffer through this thread). You can't actually charge those at 5C for any normal ESS application.

[nebster]

Originally Posted by newhaul

with enough money many things are possible .
For the 40ah Caleb cells you can just go to Amazon and order them .
https://www.amazon.com/SE40AHA-CALB-.../dp/B0063Z8AM6

Uh, are you missing the point, or do you just enjoy cluttering the thread? Or are you a troll?

[nebster]

Originally Posted by newhaul

as I said regulatory derated to 120kw.

It's quite a lot less interesting that someone can install a megawatt DC power supply in a parking lot somewhere. What's interesting from a battery point of view is when we start to see charging happening at higher rates. I believe they will come, but maybe not at 3+C with the technology we have today.

That 2 in the exponent makes life difficult.

[newhaul]

Originally Posted by nebster

It's quite a lot less interesting that someone can install a megawatt DC power supply in a parking lot somewhere. What's interesting from a battery point of view is when we start to see charging happening at higher rates. I believe they will come, but maybe not at 3+C with the technology we have today.

That 2 in the exponent makes life difficult.

it is reminiscent to the internet. Remember when you were max allowed to download at 56kbps and now it is measured in gbps. Deregulation will come as people demand it to .
As I see it the charging stations are not dc but AC with the dc inverter charger being built into the vehicle.

[john61ct]

Originally Posted by nebster

If you try to continuously charge a large bank of lithium cells at 5C or 3C or probably even 1C, you will have a thermal problem and the pack will likely suffer as a result.

Which is why your charge source needs to be controlled by temperature cutoffs, or ideally scale back current as required.

In ambient cool temps can charge faster than in the tropics.

Obviously if you just keep dumping charge current at whatever level as temps rise, you're getting into trouble.

If you don't have that sort of gear, then you're absolutely right, stay at .5C or lower. But do not claim that is a general limitation of the chemistry.

BTW CALB newer CA line is specifically designed to stay cooler at higher C rates.

And, are you suggesting the guy at ecpc - one-man shop, right? - is a credible vendor you recommend for ongoing supply?

And you would buy his generic unbranded cells? Really? Not for me.

Winston/Voltronix, CALB, GBS, A123 & Sinopoly

AFAIK that's it.

[john61ct]

Originally Posted by nebster

You're making no sense.

I was simply responding to your claim

Originally Posted by nebster

The vendor designs the cells to hold a certain amount of energy when charged to a certain voltage.

As if the correlation between SoC and voltage was something the mfg "controls" in designing the cells.

The only way to do so is to modify the chemistry formulation.

Yes the AH capacity is a function of mass.

And trying to get a (very insignificantly) higher capacity by going over 3.5Vpc to me is just foolish.

[Maine Sail]

Originally Posted by nebster

Yeah so you're in the normal reasonable range... not going to be an issue for you. If someone does try to run a house bank at higher rates, they are going to have a lot of trouble with heat and, likely, follow-on cell degradation. For practical purposes today, in my opinion 0.3C or lower is much better.

It's good to see someone in this thread who gets and understands the chemistry and it's nuances..

[Maine Sail]

Originally Posted by john61ct

I was simply responding to your claim


And trying to get a (very insignificantly) higher capacity by going over 3.5Vpc to me is just foolish.

As nebster has been attempting to shed some light on, charge rate plays a role too.

[john61ct]

Google just gave me this in my feed

https://www.sciencedaily.com/release...0216110525.htm

See all the "related" stories below the article to see how higher-C charge rates are a very important quest for the industry.

Heat being the limiting factor

But yes largely irrelevant for most sailors.

[john61ct]

Originally Posted by Maine Sail

As nebster has been attempting to shed some light on, charge rate plays a role too.

So if one has a potentially high output ICE charge source to run while living off-grid,

minimizing runtime being an important factor,

at what C rate would you estimate longevity to be unduly harmed?

assuming the precautions above (including overtemp cutoff and sub 3.5Vpc) are observed

[nebster]

Originally Posted by john61ct

Which is why your charge source needs to be controlled by temperature cutoffs, or ideally scale back current as required.

Another idea that sounds great in theory. Most large OTS chargers can't adopt an arbitrary thermal current curve. They might have a lead acid temp adjustment, though.

In ambient cool temps can charge faster than in the tropics.

Can't agree more.

Obviously if you just keep dumping charge current at whatever level as temps rise, you're getting into trouble.

Yep, exactly why "charge up to 1C, however you like" is impractical in real life.

If you don't have that sort of gear, then you're absolutely right, stay at .5C or lower. But do not claim that is a general limitation of the chemistry.

It is absolutely a property of the chemistry and the design of the cells. It becomes a limitation in the real world, when a closely-packed stack of cells is charged faster.

BTW CALB newer CA line is specifically designed to stay cooler at higher C rates.

Great. See below.

And, are you suggesting the guy at ecpc - one-man shop, right? - is a credible vendor you recommend for ongoing supply?

I don't know about the shop, but you can click on the data sheets, including for your beloved "higher temperature" CALB CA series cells. Did you go look at the C rate? Why does your concern about this vendor make it so that the datasheets are not convenient to look at on that site?

And you would buy his generic unbranded cells? Really? Not for me.

Irrelevant. Go look at the ratings on the cells you like. You can download the spec sheets, and if you actually do it and stop bloviating on this forum, you'll see that the ratings are very low.

AFAIK that's it.

Incredible: we've found a boundary of your "knowledge!"

What cells do you have, John? Why won't you tell us what you're using today?

[Paul_Carroll]

Ok, so conversation has gone far afield from the original posting, but I wanted to say that I have purchased 220Ahr LiFePO4 cells from the source originally asked about (Lithium Batteries, Chargers, Solar Storage | Electric Cars Parts Company). These turned out to be very good cells and the company president a very knowledgable and ethical man to do business with. All the LiFePO4 prismatic cells are made in China these days, and it is only a matter of whether they are made by a reputable factory or not. The owner actually goes to China at least once a year and inspects factories looking for new and better sources.

I did not purchase a "finished" battery as you are looking at, but just the cells and am quite pleased with my 24V bank. I have an electric propulsion boat and regularly discharge these at 100A and recharge at about 70A.

The BMS system is one I designed and built myself, because I wanted cell level monitoring of voltage and temperature and wanted to be able to control my charger and load disconnects. And for the record it does no balancing. I started with a bottom balanced pack, and it merely keeps me informed of the state of charge of each cell and then I can decide when to rebalance (meaning drain each cell down to 2.65 volts, then recharge the entire pack until any cell reaches 3.5 Volts)

There, now I have added my 2 cents.

[tanglewood]

Originally Posted by Paul_Carroll

Ok, so conversation has gone far afield from the original posting, but I wanted to say that I have purchased 220Ahr LiFePO4 cells from the source originally asked about (Lithium Batteries, Chargers, Solar Storage | Electric Cars Parts Company). These turned out to be very good cells and the company president a very knowledgable and ethical man to do business with. All the LiFePO4 prismatic cells are made in China these days, and it is only a matter of whether they are made by a reputable factory or not. The owner actually goes to China at least once a year and inspects factories looking for new and better sources.

I did not purchase a "finished" battery as you are looking at, but just the cells and am quite pleased with my 24V bank. I have an electric propulsion boat and regularly discharge these at 100A and recharge at about 70A.

The BMS system is one I designed and built myself, because I wanted cell level monitoring of voltage and temperature and wanted to be able to control my charger and load disconnects. And for the record it does no balancing. I started with a bottom balanced pack, and it merely keeps me informed of the state of charge of each cell and then I can decide when to rebalance (meaning drain each cell down to 2.65 volts, then recharge the entire pack until any cell reaches 3.5 Volts)

There, now I have added my 2 cents.

Thanks for sharing a real system. How did you make up the BMS?

[nebster]

Originally Posted by Paul_Carroll

Ok, so conversation has gone far afield from the original posting, but I wanted to say that I have purchased 220Ahr LiFePO4 cells from the source originally asked about (Lithium Batteries, Chargers, Solar Storage | Electric Cars Parts Company). These turned out to be very good cells and the company president a very knowledgable and ethical man to do business with.

I also found him to be genuine, and he seemed like someone I would be happy to buy from. He and his son run the business together, I think.

The BMS system is one I designed and built myself, because I wanted cell level monitoring of voltage and temperature and wanted to be able to control my charger and load disconnects. And for the record it does no balancing. I started with a bottom balanced pack, and it merely keeps me informed of the state of charge of each cell and then I can decide when to rebalance (meaning drain each cell down to 2.65 volts, then recharge the entire pack until any cell reaches 3.5 Volts)

Very nice. So, have you had to do that rebalancing yet?

[Paul_Carroll]

Tanglewood: my BMS is Arduino based, and once I have at least a full season of running it without making major changes to the design, I will likely make it available to the community.

Nebster: I have not had to rebalance yet. After more than 2 dozen deep discharge cycles, my cell voltages are still within 0.1V of each other.