LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[sparrowhawk1]

Originally Posted by roetter

On my mono with 360Ah of LiFePo I currently have a 120W solar panel directly (no charge regulator) connected to the cells. I run a programmable voltmeter that triggers a solar cutouff relay (automotive relay) at 14.0V to cut the solar off. At 13.4V the solar is switched back on.

I do not use a BMS for the many reasons that have been explained on this thread.

This is like going back to school. Is automotive relay the same as solenoid. One of the problems with the many posts and many threads on the subject is its hard for someone that's trying to learn to keep track of everything and there a lot of different opinions. if you could explain in detail about your voltmeter that triggers the cutoff relay and what "models"they are that would be great. And almost forgot how much does it cost?

[ele2014]

Originally Posted by sparrowhawk1

This is like going back to school. Is automotive relay the same as solenoid. One of the problems with the many posts and many threads on the subject is it hard for someone that's trying to learn to keep track of everything and there a lot of different opinions if you could explain in detail about your voltmeter that triggers the cutoff relay and what "models"they are that would be great

I do not think is a good idea to use any type of Lithium battery including LiFePO4 without a BMS.
I do understand why people want to do that since there is no good option available.
I needed to work over 6 month already to design my own BMS see details in my signature and some details in the post before yours.
One reason is that the cells will become unbalanced even if not by much is enough to exceed 3.6V and if that is the case for LiFePO4 the battery life will suffer even if probably nothing else will happen up to much higher voltage.
Cell balancing maybe not as important in energy storage applications as individual cell monitoring. You can if you chose do a manual balancing once every one or two months capacity loss do to imbalance will not be that high.
14V /4 cells is 3.5V/cell if cells will be perfectly balanced but they wont at least not for to many cycles even a small less than 1% imbalance will push one cell over 3.6V
LiFePO4 is at about 3.3V over 95% charged so you can have 3 cells at 3.3V and the forth one needs to get to 4.1V to add to 14V and stop the charging . Even with 3.4V for rest of the cells 99% charged one of the cell will get to 3.8V before charge stops still to high and that cell will have a reduced life.

[sparrowhawk1]

Originally Posted by electrodacus

I do not think is a good idea to use any type of Lithium battery including LiFePO4 without a BMS.
I do understand why people want to do that since there is no good option available.
I needed to work over 6 month already to design my own BMS see details in my signature and some details in the post before yours.
One reason is that the cells will become unbalanced even if not by much is enough to exceed 3.6V and if that is the case for LiFePO4 the battery life will suffer even if probably nothing else will happen up to much higher voltage.
Cell balancing maybe not as important in energy storage applications as individual cell monitoring. You can if you chose do a manual balancing once every one or two months capacity loss do to imbalance will not be that high.
14V /4 cells is 3.5V/cell if cells will be perfectly balanced but they wont at least not for to many cycles even a small less than 1% imbalance will push one cell over 3.6V
LiFePO4 is at about 3.3V over 95% charged so you can have 3 cells at 3.3V and the forth one needs to get to 4.1V to add to 14V and stop the charging . Even with 3.4V for rest of the cells 99% charged one of the cell will get to 3.8V before charge stops still to high and that cell will have a reduced life.

Thanks for the very clear explanation of the importance of keeping the cells balanced. I've read your posts on several threads and watched your YouTube videos, they are a little too technical for me to understand. I've watched videos with mini BMS between the positive and negative of each cell and the explanation that the LED's are showing that this battery(cell) is at the voltage point where current is being shunted but they don't show how. And I understand that there is high voltage cutoff for charging circuits and low voltage cutoffs. but I've yet to find any drawings or schematics or videos on how exactly it's done. Thanks again and good luck with your project.

[ele2014]

Originally Posted by sparrowhawk1

Thanks for the very clear explanation of the importance of keeping the cells balanced. I've read your posts on several threads and watched your YouTube videos, they are a little too technical for me to understand. I've watched videos with mini BMS between the positive and negative of each cell and the explanation that the LED's are showing that this battery(cell) is at the voltage point where current is being shunted but they don't show how. And I understand that there is high voltage cutoff for charging circuits and low voltage cutoffs. but I've yet to find any drawings or schematics or videos on how exactly it's done. Thanks again and good luck with your project.

Sorry if things I explain are not to clear. I try to simplify things as much as possible but I do not always succeed.
Hi and low voltage cut off is quite simple for charging you stop the charging when any of the series connected cells gets to the set high voltage point let say 3.6V.
You need to monitor each individual cell in order to be able to do that.
Low voltage cut off at discharging is the same way when any cell gets under that point say 3V you just cut the load.
You never care about the total battery voltage just the individual cells.
Not sure exactly about what mini BMS you are talking about but individual cell monitors is common on large battery banks like those on electric vehicle.
There you have individual monitor on each cell and those are linked together using a serial communication protocol to transmit voltage data to a main unit that reads what each individual monitor is sending and takes the decision to cut the power (usually using external relays) if any of the cell has an Hi or Low voltage condition.
For cars they have large voltages even over 100V so they need a large number of series connected cells so it makes sense to have individual monitors and a two wire serial linked communication to minimise the number of wires going to the main monitoring unit.
For small number of cells like is my case with Solar BMS max 8 cells is easier and more economical to have monitor wire from the main unit to each individual cell just 9 wire for 8 cells.
I'm sure there are some diagrams out there on how to connect everything I must admit I did not do a diagram for my Solar BMS as of now.
I target a more knowledgeable crowd at first do to the nature of my product. Is more a dev board and extremely flexible with fully programmable parameters (over 30 different parameters) so an understanding of each individual parameter is needed else if you introduce even just one wrong parameter you can damage the battery.
Is flexible so that it can be used with any type of existing and future Lithium cells not just LiFePO4 and can even be used with supercapacitors like I do during development.
I can of course set custom parameter for LiFePO4 or even lock the parameters to work only with LiFePO4 but depending on application most of those parameters need to be different for optimum use.
But I'm starting again to go in to complicated details.
In the end a BMS is quite simple it just need to know voltage of each individual cell and keep those cells between a high and a lo level.

[sparrowhawk1]

Well like I said I understand the theory but I'm having a hard time getting specific details.

[ele2014]

Originally Posted by sparrowhawk1

Well like I said I understand the theory but I'm having a hard time getting specific details.

Probably what is confusing is that larger systems have a lot of separate modules and components.
My Solar BMS is as easy as it can be is made as a replacement for those 12V / 24V solar charge controllers that you know for Lead Acid batteries.
Those have only 6 connectors two for + - PV panels two for + - Battery and two for + - Load nothing more is needed for Lead Acid.
My Solar BMS has the same connectors just arranged a bit different.
There are 10 power screw connectors since one can only support 20A all are just for the positive connections the negative are common and connected external.
From left to right first two for + PV panel next four are for + Battery and the last four are for + Load up to here the same as Lead Acid controller.
The difference is another 10pin smaller connector on the right of this power connector (there is another 6 pin connector I will explain latter)
This small 10 pin connector had 2 GND pins and 8 pins one for each cell and is used to monitor voltage on each individual cell and do cell balancing this connector is the only difference compared to a Lead Acid solar controller.
The 6 pin connector has a serial opto isolated port to communicate with external devices or for computer data logging 3 pin and the other 3 pins are for an external temperature sensor to measure battery temperature (optional for LiFePO4 in storage applications since they are used at low discharge rate they will not get hot).
But this two futures serial port and external temperature can be found on some Lead Acid solar controllers also.
So the only difference is that small 10 pin connector for individual cell monitor and balancing nothing else.

[deckofficer]

Originally Posted by electrodacus

Probably what is confusing is that larger systems have a lot of separate modules and components.
My Solar BMS is as easy as it can be is made as a replacement for those 12V / 24V solar charge controllers that you know for Lead Acid batteries.
Those have only 6 connectors two for + - PV panels two for + - Battery and two for + - Load nothing more is needed for Lead Acid.
My Solar BMS has the same connectors just arranged a bit different.
There are 10 power screw connectors since one can only support 20A all are just for the positive connections the negative are common and connected external.
From left to right first two for + PV panel next four are for + Battery and the last four are for + Load up to here the same as Lead Acid controller.
The difference is another 10pin smaller connector on the right of this power connector (there is another 6 pin connector I will explain latter)
This small 10 pin connector had 2 GND pins and 8 pins one for each cell and is used to monitor voltage on each individual cell and do cell balancing this connector is the only difference compared to a Lead Acid solar controller.
The 6 pin connector has a serial opto isolated port to communicate with external devices or for computer data logging 3 pin and the other 3 pins are for an external temperature sensor to measure battery temperature (optional for LiFePO4 in storage applications since they are used at low discharge rate they will not get hot).
But this two futures serial port and external temperature can be found on some Lead Acid solar controllers also.
So the only difference is that small 10 pin connector for individual cell monitor and balancing nothing else.

Welcome to CF and our overgrown LiFePO4 thread. I used to design for off grid homes long before lithium and I used 6 volt golf cart batteries and L16 for the small systems, the larger systems were based around a 48 volt inverter and banks of single 2 volt cells.

Now with LiFePO4, lead is dead to me.

[ele2014]

Originally Posted by deckofficer

Now with LiFePO4, lead is dead to me.

Thanks. I wish more people understood the benefit of LiFePO4.
It will happen eventually but it seems slow.

[Hkalan]

Hello Everyone,

If I may cut in and ask input from those having LifePO4 banks.

After researching what is available around me... Is $5,400 USD for 8 cells of 3.2v 500Ah including delivery.

I just can't find listed prices for 3.2v 500Ah cells.

Appreciate your input.

Alan

[ele2014]

Originally Posted by Hkalan

Hello Everyone,

If I may cut in and ask input from those having LifePO4 banks.

After researching what is available around me... Is $5,400 USD for 8 cells of 3.2v 500Ah including delivery.

I just can't find listed prices for 3.2v 500Ah cells.

Appreciate your input.

Alan

That seems like a decent price. What brand is that?
I payed about 1200$ + some sipping don't remember exactly for my 8 cells 100Ah GBS but that was two years ago.
I don't think prices have changed much maybe the quality of some batteries has improved and there are a bit more options now.

[deckofficer]

Originally Posted by Hkalan

Hello Everyone,

If I may cut in and ask input from those having LifePO4 banks.

After researching what is available around me... Is $5,400 USD for 8 cells of 3.2v 500Ah including delivery.

I just can't find listed prices for 3.2v 500Ah cells.

Appreciate your input.

Alan

With you being in Hong Kong, I would think you had access to the best prices. I bought from Balqon but they seem to only have the 700 and 1000 a-hr cells. Here is another retailer, - CALB (USA Stock!)

From what I've seen the sizes jump from 400 a-hr to 700 a-hr.

[Hkalan]

Hello,

There are several factories within a 1 hour train ride from me making the LifePO4 cells, but I am receiving so many different prices. The 3.2v 500Ah cells fluctuate from $625 per cell to $760 per cell (without shipping).

I would assume that buying factory direct, should be a fantastic savings. That's how it works for all the other goods I buy. Just picked up a 110v AC cyclone vacuum cleaner factory direct for $22 that is on the Bertram 46.6, that retails in the USA for $160.

Perhaps I am being a bit selfish here LOL...

Alan

[deckofficer]

Originally Posted by Hkalan

Hello,

There are several factories within a 1 hour train ride from me making the LifePO4 cells, but I am receiving so many different prices. The 3.2v 500Ah cells fluctuate from $625 per cell to $760 per cell (without shipping).

I would assume that buying factory direct, should be a fantastic savings. That's how it works for all the other goods I buy. Just picked up a 110v AC cyclone vacuum cleaner factory direct for $22 that is on the Bertram 46.6, that retails in the USA for $160.

Perhaps I am being a bit selfish here LOL...

Alan

Not at all. Most all these cells are made in China, your in China, I would say shake the bushes locally and if they need a quanity order, come back here and dig up some buyers.

[sparrowhawk1]

Balqon didn't answer my phone message or my email but they have a 700 amp hour battery for $700 and a 400 amp hour for $440. Free shipping, 6 week lead time.

[Maine Sail]

Originally Posted by sparrowhawk1

Balqon didn't answer my phone message or my email but they have a 700 amp hour battery for $700 and a 400 amp hour for $440. Free shipping, 6 week lead time.

I have Balquon cells and got very lucky with my order. Some on here have waited over six months and I know some that finally cancelled orders...

I have one customer I was doing a consult for who never got his Balquon cells. He bought CALB, and had them in 8 days.

Sorry but Balquon runs the company like it is in your best friends moms back yard, and like it is run out of a tree fort by some six year old kids. Completely unprofessional, communication is HORRIBLE, and they focus more on on-line chat with "chatters" who know nothing, than actually running a good company, at least from a retail perspective...

I have left three messages in the last year and not had a single return phone call. I also suspect the 700Ah and 1000Ah stock they still show is OLD stock.

Unless there is a MAJOR turn around at Balquon, not seen it yet, I will never and could never recommend them to anyone... Do yourself a favor and find USA stock of CALB, Hi Power, GBS etc........ Caveat emptor with Balquon....

My last quote from these guys was within $16.00 per cell of Balquon, when delivered, and they were shipping within two days of order. Personally I think the CALB cells are a better cell than Winston too. Not just me, Genasun chooses CALB due to the consistency of the product..

- CALB (USA Stock!)

You need to look at the total delivered bottom line price not just the purchase price. Balquon shipping is rather STEEP.......