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

[darylat8750]

What Third Day said.

[Highland Fling]

Originally Posted by SV THIRD DAY

Everyone has their own special way, heck I had a friend who used a potato clock to top balance.

Why tie them together in a 4 cell bank rather than separately...well I think you just hinted at it with your description of doing things manually and the potential fiasco that could cause you!

Connect them together, set your Max charge voltage and walk away. Charger hits max voltage set-point and no more amps go in....let them sit for a day all connected together without the charger on and then disconnect and verify individual cell voltage. Done...over....easy.

How easy is that compared to the kapookie dance you seem to be wanting to take watching paint dry?

Sometimes you just have to take the easy way out because it also turns out to be better.....

If there is ONE big thing that this thread has taught me is that people are always looking for their special way to do things. Rube Goldberg would be proud but why? Why make things simple more complicated and then debate and argue about how many electrons will fit on the head of a pin?

Well being on the boat it was easy to do this and no chance of a fiasco at all unless I could somehow bend the laws of physics.

BUT as I am off the boat for the next four days (during the daytime) racing in the Heineken I have set the Lab P/S to 3.65V and connected four cells in parallel and will just let things happen.

For sure I am NOT looking for a special way to do things as I deeply hate reinventing the wheel.

kindest regards

David

[Highland Fling]

Originally Posted by Jd1

There is nothing wrong with individually charging the batteries, with charging them in parallel or charging them in series. Do whatever turns your crank but be sure to monitor your cell voltages! You can not monitor your cell voltage with the charger if your cells are in series. You can set your charger to 3.5V and hook up all the cells in parallel but of course you will run into an issue where you will have very little current flow to each individual cell as that cell gets close to the charger voltage.
Because of the flat voltage vs SOC of lithium, the only way to know when SOC is equalized is when you get to the high voltage knee where the voltage starts to rapidly rise. Further, lithium does not like to sit at a high SOC for a long time (as in weeks or months). As a result, if you set the charger voltage and just let the batteries slowly creep up in charge you are doing them a dis-service.
It is better if you set your charge voltage higher but you MUST monitor the charging process because once you hit the knee things happen rapidly. You can't monitor this manually !!!
The closest equalization is only required in order to maximize capacity. If you are not worried about capacity you can cut down playing at the knee voltage.
The one thing you can not compromise on is monitoring cell voltage !!!
I hope this helps ....

Re My Bolding, was that a typo?, did you mean if the cells were in parallel?

kindest regards

David

[Highland Fling]

Originally Posted by Maine Sail

It his is a lab type power supply why not set it for 3.5V or even 3.6V? What happens when the cells get full and you're not there to shut off the 6 volts......?

I was there so that was a non issue, I was trying to maximise the current flow.....BUT I am not there today so i have set the Lab P/S at 3.65V

Question though. IF I use a Balmar external alternator controller with three or four 12V 200AH batteries I cant really use 'on' battery voltage monitoring unless I connect to the BUS BAR. Would you say that this is 'better' than non battery voltage monitoring and that I only need to tweak the Balmar regulator to 'accommodate' the small voltage drop between the batteries and the BUS BAR. and do you see any issues or problems in doing this?

thanks

kindest regards

David

[Maine Sail]

Originally Posted by Flying Scot

I was there so that was a non issue, I was trying to maximise the current flow.....BUT I am not there today so i have set the Lab P/S at 3.65V

You will not change the current output by setting the voltage at 6V. If the battery terminals are not at 3.6V or 3.65V then the power supply is in constant current mode and supplying all the power it can. It only reduces current when constant voltage mode has been attained and the battery can no longer accept full current so as to not over shoot 3.65V.

Originally Posted by Flying Scot

Question though. IF I use a Balmar external alternator controller with three or four 12V 200AH batteries I cant really use 'on' battery voltage monitoring unless I connect to the BUS BAR. Would you say that this is 'better' than non battery voltage monitoring and that I only need to tweak the Balmar regulator to 'accommodate' the small voltage drop between the batteries and the BUS BAR. and do you see any issues or problems in doing this?

thanks

kindest regards

David

David,

Setting aside the Balmar question for now I am at a complete loss as to why you would want three or four 12V LFP batteries on-board your vessel?

[Jd1]

Originally Posted by Flying Scot

Re My Bolding, was that a typo?, did you mean if the cells were in parallel?

kindest regards

David

Not a typo but probably a misunderstanding since you ended up putting the cells in parallel and not in series.

If you put the cells in series and set the charger to an appropriate voltage (say 4 cells in series, charger at 14V), the charger will only reduce output when it reaches 14V but you could easily have a single cell in that string being well above the allowed voltage per cell while other cells are still accepting current.
Hope that makes sense ....

[Highland Fling]

Originally Posted by Jd1

Not a typo but probably a misunderstanding since you ended up putting the cells in parallel and not in series.

If you put the cells in series and set the charger to an appropriate voltage (say 4 cells in series, charger at 14V), the charger will only reduce output when it reaches 14V but you could easily have a single cell in that string being well above the allowed voltage per cell while other cells are still accepting current.
Hope that makes sense ....

OK MISS understanding I am measuring the cell voltage with a DMM connected to the cells NOT just looking at the display on the P/S so in parallel I cant measure individual cell voltage BUT I can when they are connected in series

kindest regards

David

[Highland Fling]

Originally Posted by Maine Sail

You will not change the current output by setting the voltage at 6V. If the battery terminals are not at 3.6V or 3.65V then the power supply is in constant current mode and supplying all the power it can. It only reduces current when constant voltage mode has been attained and the battery can no longer accept full current so as to not over shoot 3.65V.



David,

Setting aside the Balmar question for now I am at a complete loss as to why you would want three or four 12V LFP batteries on-board your vessel?

WHY!!! Well I want 600AH or 800AH LIFEPO4 for electric cooking we have ATM two induction hobs and LA(AGM/GEL) and the inverter are not happy with the big loads and the big voltage droop under load.

The BMS I will be using comes as standard with a relay capable of handling 240A (from memory) so I am keeping things simple. and of course this is just going to be like building using Lego bricks, one done leads to two done and.........

So I will have three or four 12V 200AH 4S batteries which are easier to install and monitor in a nice progressive and simple manner. I was thinking of putting in two 12V 400AH 2P4S or one 12V 600AH 3P3S batteries but then with the need to handle a system of 400/600A then with bigger disconnect relays and the physical size of two 400AH or one 600AH batteries I decided to go for triple redundancy 3x 200AH and since I have 30 cells to play with why not quad redundancy and 800AH. Then I could IF I wished distribute the batteries closer to their loads...like the ANCHOR WINDLASS, and maybe a BOW THRUSTER and POWERED SHEET WINCHES had I got or needed such expensive toys.....though the powered winches are for sure somewhere in the future, we manage ATM with a 28V Milwaukee Right Angle Drill.

In order to get the Lab P/S to move into CC mode I had to set the no load voltage to 6V at 3.65V even 4V it was in CV mode, both CC and CV are adjustable

kindest regards

David

[Highland Fling]

OOOPS when updating my FS profile noticed the small number of post I had made....... THEN remembered about this one............OOOPS TWO

[Maine Sail]

Originally Posted by Flying Scot

WHY!!! Well I want 600AH or 800AH LIFEPO4 for electric cooking we have ATM two induction hobs and LA(AGM/GEL) and the inverter are not happy with the big loads and the big voltage droop under load.

The BMS I will be using comes as standard with a relay capable of handling 240A (from memory) so I am keeping things simple. and of course this is just going to be like building using Lego bricks, one done leads to two done and.........

So I will have three or four 12V 200AH 4S batteries which are easier to install and monitor in a nice progressive and simple manner. I was thinking of putting in two 12V 400AH 2P4S or one 12V 600AH 3P3S batteries but then with the need to handle a system of 400/600A then with bigger disconnect relays and the physical size of two 400AH or one 600AH batteries I decided to go for triple redundancy 3x 200AH and since I have 30 cells to play with why not quad redundancy and 800AH. Then I could IF I wished distribute the batteries closer to their loads...like the ANCHOR WINDLASS, and maybe a BOW THRUSTER and POWERED SHEET WINCHES had I got or needed such expensive toys.....though the powered winches are for sure somewhere in the future, we manage ATM with a 28V Milwaukee Right Angle Drill.

In order to get the Lab P/S to move into CC mode I had to set the no load voltage to 6V at 3.65V even 4V it was in CV mode, both CC and CV are adjustable

kindest regards

David

Design it how you want it, its your boat.....

[Highland Fling]

Originally Posted by Maine Sail

Design it how you want it, its your boat.....

Well on that point we are in total agreement

[darylat8750]

Originally Posted by Flying Scot

WHY!!! Well I want 600AH or 800AH LIFEPO4 for electric cooking we have ATM two induction hobs and LA(AGM/GEL) and the inverter are not happy with the big loads and the big voltage droop under load.

The BMS I will be using comes as standard with a relay capable of handling 240A (from memory) so I am keeping things simple. and of course this is just going to be like building using Lego bricks, one done leads to two done and.........

So I will have three or four 12V 200AH 4S batteries which are easier to install and monitor in a nice progressive and simple manner. I was thinking of putting in two 12V 400AH 2P4S or one 12V 600AH 3P3S batteries but then with the need to handle a system of 400/600A then with bigger disconnect relays and the physical size of two 400AH or one 600AH batteries I decided to go for triple redundancy 3x 200AH and since I have 30 cells to play with why not quad redundancy and 800AH. Then I could IF I wished distribute the batteries closer to their loads...like the ANCHOR WINDLASS, and maybe a BOW THRUSTER and POWERED SHEET WINCHES had I got or needed such expensive toys.....though the powered winches are for sure somewhere in the future, we manage ATM with a 28V Milwaukee Right Angle Drill.

In order to get the Lab P/S to move into CC mode I had to set the no load voltage to 6V at 3.65V even 4V it was in CV mode, both CC and CV are adjustable

kindest regards

David

Most of the people with LiFe experience agree that parallel first to the desired amperage and then series to voltage is the desired set up.

Are you going to build separate charge, monitoring and disconnect setups for each of your 12 volt batteries?

[goboatingnow]

A note , if your using a lab power supply, check that it has over voltage protection. Most don't like being connected to batteries otherwise


Sent from my iPad using Tapatalk

[matureee]

In engineering design there is a thing called "human factors engineering" for us this means that if you give a person a device capable of producing 20V and a cell which will only stand 4V one day he is going to put 20V on that cell, see Compass Marine´s site for evidence of this.

I am considering building myself a cell top balancer, this will bring one cell at a time up to a known state of charge. The known state of charge is defined as a fixed voltage somewhere on the steep dv/dSOC curve (upper knee) at a fixed charging current.

It will consist of a 5V wall wart capable of supplying 5-10A a constant current source a voltage sensor and a latching relay. Plug it in and led1 comes on (rule one in electronic engineering:- it does not matter what it does make sure it has plenty of pretty flashing lights) connect it to the cell and led2 comes on press the button which engages the relay and a constant current is fed to the cell (led3) when the cell voltage hits (insert favourite number here) V the relay disconnects and led 4 comes on and a buzzer sounds. Repeat with all cells. All in this is about $10 worth of electronics and is much easier to lose somewhere on my boat than a lab power supply.

Why one cell at a time?. When cells are paralleled we have no control over the current into individual cells the approach has been to hold the voltage until the current drops to close to zero then we know the current in each cell. I believe that holding a high voltage on these cells is detrimental to their health and want to minimize this.

This seems too easy have I missed any snags with this?.

[Maine Sail]

Originally Posted by matureee

In engineering design there is a thing called "human factors engineering" for us this means that if you give a person a device capable of producing 20V and a cell which will only stand 4V one day he is going to put 20V on that cell, see Compass Marine´s site for evidence of this.

I am considering building myself a cell top balancer, this will bring one cell at a time up to a known state of charge. The known state of charge is defined as a fixed voltage somewhere on the steep dv/dSOC curve (upper knee) at a fixed charging current.

It will consist of a 5V wall wart capable of supplying 5-10A a constant current source a voltage sensor and a latching relay. Plug it in and led1 comes on (rule one in electronic engineering:- it does not matter what it does make sure it has plenty of pretty flashing lights) connect it to the cell and led2 comes on press the button which engages the relay and a constant current is fed to the cell (led3) when the cell voltage hits (insert favourite number here) V the relay disconnects and led 4 comes on and a buzzer sounds. Repeat with all cells. All in this is about $10 worth of electronics and is much easier to lose somewhere on my boat than a lab power supply.

Why one cell at a time?. When cells are paralleled we have no control over the current into individual cells the approach has been to hold the voltage until the current drops to close to zero then we know the current in each cell. I believe that holding a high voltage on these cells is detrimental to their health and want to minimize this.

This seems too easy have I missed any snags with this?.

You don't need to hold it super high and it does not take all that long to attain bouncing between 0.0A to 0.1A on the PS.....