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

[Marqus]

Originally Posted by s/v Jedi

I'm at the point of pulling out my old PIC programmer :-)

Sounds promising but ...... when the rubber hits the road, software always seem to come up with hidden glitches/bugs. I'm not sure, but it would not be surprising if the Russian Mars mission is in trouble due to software rather than hardware issues; and they would do exhaustive prior testing (you'd hope).

So, there you could be mid-passage with your expensive House Bank's survival subject to Nick having found and removed absolutely every bug from his PIC program .... keen to roll the dice, anyone?

Absolutely no offence, Nick.

[T1 Terry]

recall Terry mentioning an RC Logger. Terry, can your Logger serve as an out-of-balance alarm, with user adjustable threshholds?

I use a Juni Cell Log 8, that is exactly what this little unit is used for. It gives a display of the voltage of each cell, how many milli volts difference between the highest and lowest, alarm set points for high cell voltage, low cell voltage, max out of balance and over and under total pack voltage although the other alarms would have gone off before that happened. each alarm point can be set to either just flash the error section on the display or sound an audible warning and power an alarm port that can be used to turn a relay on or off, be amplified to be sure it was heard, flash a light some where, what ever would be a useful extension of the unit. With the data logger model the record interval set from every 2 secs to minutes so it can record over a week or more worth of info, handy for back tracking where a problem started or just how well the system is balanced and coping. For their price they are very hard to beat. http://http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=10952 and http://http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=9282 for the data logging model. you do need to buy a plug to fit http://http://www.ebay.com.au/itm/130422865674?ssPageName=STRK:MEWNX:IT&_trksid=p398 4.m1439.l2648
at a glance you know what voltage the cells are at, handy when determining when to finish charging and a clear indication when 100% SOC has been reached.
We have found the easiest way to connect them through to the main control panel is the buy 2 X DB9 pin cables, one short, the other long enough to reach from the batteries to the control panel. Cut the short cable in half, wire one end to the battery terminals, connect the other end to the cell logger plug. Now the cell logger can be plugged in at the battery bank or the long cable an be connected at the batteries and the logger connected at the control panel, one unit to do both jobs, or you could lash out another $14 and buy a second unit and a double adapter cable from E bay and have a unit at each location.
Here is a link to just about all the BMS units available, http://http://liionbms.com/php/bms_options.php if you scroll down to the digital monitors, 2nd from the bottom Shenzhen Juni Electronics.

T1 Terry

[T1 Terry]

Another forum member reported use of simple "resistor boards that help balance the cells at the end of the recharge by burning off excess amps on individual cells". These boards are not classified as a BMS. Have you come across that approach and do you know how it works?

The resistor balance is just another form of BMS active management. They have a nasty tendency to overheat if they are not part of a master control that also turns the charger back to a few amps charging, so the resistor isn't over powered. If something goes astray or the whole system isn't used as a complete unit the chances of things going wrong increases, one of these little burn off resistor boards either goes up in smoke and therefore being non functional anyway or latching on and gradually dragging that cell dead. Often one unit fails and doesn't send a communication to the main control, the whole thing shuts down. At least this method saves the battery pack being destroyed but now you are in the middle of the big puddle and the charging system doesn't works. Now you realise you left your electronics and programming skills and certificate at home, so you’re stuffed. The postman can't deliver a replacement bit with a sorry note attached.

To be sure you can operate the system with the skill level you have it's best to keep it simple. Recharge to 98% or when the cell voltages hit 3.45v and stop as soon as one goes higher. When balancing time is convenient, sit down with a cool drink, a multi meter and a light bulb or 12v jug element in a bowl of water and connect up the load across the cell/s that are over 3.45v, pull them down charge a bit more, repeat till they are all 3.45 or higher, 3.45v to 3.55v, plenty of room to move. If it takes 2 cool drinks you either drink fast or it was a long time since you did it last time, it's that easy.

T1 Terry

[downunder]

Originally Posted by T1 Terry

I use a Juni Cell Log 8, that is exactly what this little unit is used for. It gives a display of the voltage of each cell, how many milli volts difference between the highest and lowest, alarm set points for high cell voltage, low cell voltage, max out of balance and over and under total pack voltage although the other alarms would have gone off before that happened. each alarm point can be set to either just flash the error section on the display or sound an audible warning and power an alarm port that can be used to turn a relay on or off, be amplified to be sure it was heard, flash a light some where, what ever would be a useful extension of the unit. With the data logger model the record interval set from every 2 secs to minutes so it can record over a week or more worth of info, handy for back tracking where a problem started or just how well the system is balanced and coping. For their price they are very hard to beat. http://http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=10952 and http://http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=9282 for the data logging model. you do need to buy a plug to fit http://http://www.ebay.com.au/itm/130422865674?ssPageName=STRK:MEWNX:IT&_trksid=p398 4.m1439.l2648
at a glance you know what voltage the cells are at, handy when determining when to finish charging and a clear indication when 100% SOC has been reached.
We have found the easiest way to connect them through to the main control panel is the buy 2 X DB9 pin cables, one short, the other long enough to reach from the batteries to the control panel. Cut the short cable in half, wire one end to the battery terminals, connect the other end to the cell logger plug. Now the cell logger can be plugged in at the battery bank or the long cable an be connected at the batteries and the logger connected at the control panel, one unit to do both jobs, or you could lash out another $14 and buy a second unit and a double adapter cable from E bay and have a unit at each location.
Here is a link to just about all the BMS units available, http://http://liionbms.com/php/bms_options.php if you scroll down to the digital monitors, 2nd from the bottom Shenzhen Juni Electronics.

T1 Terry

Those monitors particually the data logger look cool and well priced.
Does each cell in the bank need to be wired up to it.
I am not electrically minded and learning so please be kind.

[T1 Terry]

The wiring is straight forward, all explained in the PDF that comes on the disc. Basically, wire one to the negative cell 1, wire two to the neg cell 2, wire three negative cell 3, wire four negative cell 4 and wire 5 to the positive cell 4. The external alarm port can be switched to be normally open or normally closed and this is used to drive the 85 or 86 terminal of an automotive type relay or can be used to switch a solid state relay. If the external alarm port was used to turn the charging relay for high voltage cut off then a timer circuit would be needed because as soon as the charging stopped the voltage would drop causing the alarm to turn off and the relay on, and the whole thing starts again. A 10 min timer would be enough to allow the load from the hose power to drain the over voltage cell, no wasted charge, all used. Maybe one of the electronic clever people can design a simple timer circuit or point the right direction to buy one off the shelf.

The down side of these units, the alarm port is activated by any and all alarm signals, if this was used as the high cell voltage cut to drive a relay then a light would also need to be installed to alert the operator that the cell logger had recorded an alarm and look to see what alarm it was.

T1 Terry

[goboatingnow]

To be sure you can operate the system with the skill level you have it's best to keep it simple. Recharge to 98% or when the cell voltages hit 3.45v and stop as soon as one goes higher. When balancing time is convenient, sit down with a cool drink, a multi meter and a light bulb or 12v jug element in a bowl of water and connect up the load across the cell/s that are over 3.45v, pull them down charge a bit more, repeat till they are all 3.45 or higher, 3.45v to 3.55v, plenty of room to move. If it takes 2 cool drinks you either drink fast or it was a long time since you did it last time, it's that easy.

Terry, if you only ever charge to 3.45, why would any cell get over 3.45 ??? ( leaving aside sloppy cutoffs etc)

Dave

[T1 Terry]

Originally Posted by goboatingnow

Terry, if you only ever charge to 3.45, why would any cell get over 3.45 ??? ( leaving aside sloppy cutoffs etc)

Dave

When charging as a pack the target max cell voltages are added together, 4 X 3.45v is 13.8v. If one cell is ahead of the others it could reach 3.8v while the other tree cells were still at 3.33v, if they were only at 3.3v when the high cell reach 100% charged it could run away to 4.8v, seriously damaging the cell. By setting the HVC cut at 3.8v and the cut off timer for 10 mins the house discharge load will pull the runaway cell back to 3.4v or lower, this would required as little as 0.5 amp draw to pull the high cell down. 0.08Ah would have been discharged in the 10 mins at 0.5 amps, very little out of the low cells but enough out of the high cell to bring it back to a safe level. On the next charge cycle the other cells would be closer to the 100% full level either by the time the HVC was reached or enough to reach the 13.8v total before the run away cell reached the HVC of 3.8v. When the HVC cut function stopped the charging and set the alarm warning light the operator can make the decission to stop charging at that point or if things were calm and safe to do so, go down the the battery bank and connect the light bulb across the high cell so during the next charge period the other cells could catch up.

It is really only a safety thing to protect the cells from damage if a runaway was to happen, the safest way would be to stop charging when all the cells were approaching the 3.4v mark or at least have a look and see if they are all fairly close and decide it they should be allowed to charge till the 13.8v was reached. It's just to keep the operator informed of what's going on, something you just couldn't get with lead acid batteries unfortunately due to their construction. A lot of lead acid batteries die just because a cell has gone out of balance to the others and nothing can be done to recover it.

T1 Terry

[goboatingnow]

Originally Posted by T1 Terry

When charging as a pack the target max cell voltages are added together, 4 X 3.45v is 13.8v. If one cell is ahead of the others it could reach 3.8v while the other tree cells were still at 3.33v, if they were only at 3.3v when the high cell reach 100% charged it could run away to 4.8v, seriously damaging the cell. By setting the HVC cut at 3.8v and the cut off timer for 10 mins the house discharge load will pull the runaway cell back to 3.4v or lower, this would required as little as 0.5 amp draw to pull the high cell down. 0.08Ah would have been discharged in the 10 mins at 0.5 amps, very little out of the low cells but enough out of the high cell to bring it back to a safe level. On the next charge cycle the other cells would be closer to the 100% full level either by the time the HVC was reached or enough to reach the 13.8v total before the run away cell reached the HVC of 3.8v. When the HVC cut function stopped the charging and set the alarm warning light the operator can make the decission to stop charging at that point or if things were calm and safe to do so, go down the the battery bank and connect the light bulb across the high cell so during the next charge period the other cells could catch up.

It is really only a safety thing to protect the cells from damage if a runaway was to happen, the safest way would be to stop charging when all the cells were approaching the 3.4v mark or at least have a look and see if they are all fairly close and decide it they should be allowed to charge till the 13.8v was reached. It's just to keep the operator informed of what's going on, something you just couldn't get with lead acid batteries unfortunately due to their construction. A lot of lead acid batteries die just because a cell has gone out of balance to the others and nothing can be done to recover it.

T1 Terry

Sorry Terry , forgot your talking about series strings, I got so caught up in the discussion about parallel balancing, I forgot the normal is serial, yea fully agree,

BUT, don't you find ( as Ive found) with large prismatic Whinston cells, that aside from initial balancing, really no further balancing is needed, in typical fractional C environments like that found in boats, ie charging at less then 0.5 or even 0.25C. Thats my experience.

I fully agree cell monitoring is a good idea, especially on $$$$ Li cells.

Note your comments re runaway cells, while I agree there is a rapid increase in voltage on Whinston Cells, Theres no thermal runaway, the cell gets damaged alright. This isnt true for other LI technology where severe thermal runaway occurs.

Agree fully re your comments on Lead ACID.

[T1 Terry]

Note your comments re runaway cells, while I agree there is a rapid increase in voltage on Whinston Cells, Theres no thermal runaway, the cell gets damaged alright. This isnt true for other LI technology where severe thermal runaway occurs.

Lithium iron cells in general don't appear to suffer thermal run away but they are heat damaged easily from over voltage boiling the electrolyte. In the Lithium over view given by Jay Whitacre he mentions that the chemical makeup of the electrolyte can be altered to adjust the temp operating range up or down, but it couldn't be expanded i either direction. Perhaps when Li cells are made just for house battery use they will adjust the operating range higher although there would still be off the grid situations where batteries were exposed to seriously sub zero so maybe not. I'm thinking they will probably sacrifice some of the high rate charge and discharge characteristics for more Ah capacity in the same size casing by increasing the thickness of the active material sprayed on the plates. Seems the copper and aluminium sheeting used as the cathode and anode carriers is the part that is holding the price up.

As far as the cells going out of balance during use, mine are solar charged using PWM and they are discharged over 200Ah over night every night. They have not been rebalanced or required balancing since their initial conditioning charge, that was 5 mth ago. These cells cop a hammering because they are my test bed, they have been dragged down to inverter cut off a few times, had fast charging attempted ( melted the 6 B&S cable before any serious terminal voltage was noted) had cells added and removed to see the effects of capacity upgrades, they have behaved faultlessly.
For all the horror stories that abounded regarding using these cells and all the hidden traps and dangers if you didn't use special control equipment bought from the people who were telling the horror stories, these batteries have been by far easier to work with than lead acid. I have never heard of anyone who had a set of lithium iron batteries fitted say they regretted it and wished they'd stayed with lead acid, it's always been the other way, why did I wait so long to step into the 21st century.

T1 Terry

[Whimsical]

Originally Posted by T1 Terry

When charging as a pack the target max cell voltages are added together, 4 X 3.45v is 13.8v. If one cell is ahead of the others it could reach 3.8v while the other tree cells were still at 3.33v, if they were only at 3.3v when the high cell reach 100% charged it could run away to 4.8v, seriously damaging the cell.

T1 Terry

Small maths check. If your charging potential was 13.8 and one cell got to 4.8 then the other 3 would need to have an average of 3v each. That would be a huge imbalance. if the others were at 3.3v then the high one could only get to 4v.
Terry have u any info on the charge rate versus the charge potential. I am thinking of setting it to 13.6 volts then it would be almost impossible to ever get any cell over 3.8 but i wonder if the charge rate drops off much at that level. I haven't got my cells yet. Trying to get a group buy together for 12,000 cell amp hours to get a better price,CALB.
I was going to use 2 of the cellogs, 1 for high alarm and 1 for low alarm then i can can have seperate cutoffs. Only $14 each so why not.
To balance i was going to get a 12v to 3.5v dc to dc convertor, about 10 A, then just use it to lift a low cell if it was ever needed

Mike

[s/v Jedi]

Originally Posted by Marqus

Sounds promising but ...... when the rubber hits the road, software always seem to come up with hidden glitches/bugs. I'm not sure, but it would not be surprising if the Russian Mars mission is in trouble due to software rather than hardware issues; and they would do exhaustive prior testing (you'd hope).

So, there you could be mid-passage with your expensive House Bank's survival subject to Nick having found and removed absolutely every bug from his PIC program .... keen to roll the dice, anyone?

Absolutely no offence, Nick.

Wow, life must be tough for you.... Almost everything has software inside today... How can you even post on this board when you refuse to accept it? Modern cruising yachts don't operate without software anymore. Not even the wind instrument.

ciao!
Nick.

[T1 Terry]

Terry have u any info on the charge rate versus the charge potential. I am thinking of setting it to 13.6 volts then it would be almost impossible to ever get any cell over 3.8 but i wonder if the charge rate drops off much at that level. I haven't got my cells yet. Trying to get a group buy together for 12,000 cell amp hours to get a better price,CALB.
I was going to use 2 of the cellogs, 1 for high alarm and 1 for low alarm then i can can have seperate cutoffs. Only $14 each so why not.
To balance i was going to get a 12v to 3.5v dc to dc convertor, about 10 A, then just use it to lift a low cell if it was ever needed

Mike

Hi Mike,
You could charge to 13.6v but you would never get the cells to 100%, 0.05v over potential is required to over come internal resistance and create a current flow so charging at 3.4v per cell would bring the cell voltage up to 3.395v. Just how far short of 100% SOC that is I really don't know and I'm thinking that manufacturing tolerances being what they are it would be different between cells but I would say it would be definitely more than 90% and possibly close to 95%.
Lots of possible charging regimes.
You could use a 2 stage or even 3 stage charging regime, 14v boost charge, dropping back to 13.9v absorption charge and 13.6 float. This is the preferred charge settings for solar using a PWM controller although MPPT use PWM control for final charging anyway so the controller would need to have adjustable stage settings. The 13.6v float is for storage, 13.8v for a working system.
Another option is for combined generator and solar, fast charge with the generator to 14v and stop, let the solar finish the job off.
Another option and possibly the safest for charging between maintenance balancing is to charge to 13.6v like you have suggested and when in safe territory do a maintenance balance charge to 14v bulk then 13.8v to finish off. 14v is 3.5v per cell, still plenty of safety before a cell could run away into high voltage, it the cells were already at 3.95v from the 13.6v charging regime it wouldn't take long to get to the 14v or 3.5v per cell so the operator could stay with the batteries and keep an eye on exactly what is happening and be prepared to stop as soon as a cell started to run away. Using that charging method a high cell cut wouldn't be needed if you wanted to build a less complicated system, the alarm settings would tell the operator if any extremes had been reached.
As far as low cell cut, a handy safety device but the chances of a cell dropping below 2.5v without the whole cell pack dropping below 11v, the point an inverter shuts down, is highly unlikely. Once the high load of an inverter was removed to cell voltage would bounce back up a bit. The dull lights and the cell logger alarm telling you that the pack voltage was below 12v would let you know you had forgotten to recharge and if things are very busy trying to stay alive and up the right way then the batteries possibly being damaged is the last of your problems at that moment so you wouldn't want all the power to suddenly shut down just to save the batteries.
The DC to DC 3.5v converter, sounds good, do you know where to get one? You could use an inverter, most likely already part of the system anyway and a wall wart with the plug removed and alligator clips fitted.

In general 12v systems are very easy to work with, 24v system can be a little bit trickier, the safety margins aren’t as big so the 3.4v per cell (26v) could be a better general charging voltage. The Juni Cell logger can handle 8 cells but a link needs to be soldered internally to make the unit powered from all 8 cells, it’s only powered from the first 6 cells when it comes from the factory. The unit only uses a very small amount of power but over an extended time the top 2 cells start to get ahead of the other 6 cells, easy balanced out during a maintenance charge but still something to keep in the back of the mind.

T1 Terry

[downunder]

Originally Posted by Whimsical

Small maths check. If your charging potential was 13.8 and one cell got to 4.8 then the other 3 would need to have an average of 3v each. That would be a huge imbalance. if the others were at 3.3v then the high one could only get to 4v.
Terry have u any info on the charge rate versus the charge potential. I am thinking of setting it to 13.6 volts then it would be almost impossible to ever get any cell over 3.8 but i wonder if the charge rate drops off much at that level. I haven't got my cells yet. Trying to get a group buy together for 12,000 cell amp hours to get a better price,CALB.
I was going to use 2 of the cellogs, 1 for high alarm and 1 for low alarm then i can can have seperate cutoffs. Only $14 each so why not.
To balance i was going to get a 12v to 3.5v dc to dc convertor, about 10 A, then just use it to lift a low cell if it was ever needed

Mike

This thread has some seriously good discussion. Thanks guys, all.

Mike, I have been following your build and will be interested to follow and see how you a go about your battery bank setup.

Congratulations on your build so far, seriously good quality workmanship and practical ideas you have used.

Cheers

[Marqus]

Originally Posted by s/v Jedi

Wow, life must be tough for you.... Almost everything has software inside today... How can you even post on this board when you refuse to accept it? Modern cruising yachts don't operate without software anymore. Not even the wind instrument.

ciao!
Nick.

Ok Nick, caught me out pretty well - Gps, Epirb, autopilot, Ais, vhf, ssb, instruments etc. Also have a desktop computer, two laptops, an iPad and smart phone at home, so I should have phrased more tongue-in-cheek than I made obvious. Still, I remain quietly content there's no software (yet) in my diesel engine or anchor system.

Now, just to echo what Downunder said - I'm also grateful for the great contributions by Terry, Dave and others to this ongoing thread. Sincere thank you guys.

[TassieBloke]

+ 1 to Downunder & Marqus

I am a newbie to anything Li in a boat, so I am watching this thread very closely. The main point that is coming across loud & clear is the absolute sensitivity of Li to overcharging, and the necessary charging controllers to ensure this.

Like most here i guess, I am a firm believer in redundancy, and therein lies the conundrum. What happens when I am offshore and the electronics go pear shaped, and then my 20yr 120amp alternator run off my 30yr old diesel donk is cooking my battery bank?

I am not an early adopter, more a 2nd or 3rd gen adopter waiting that little bit longer to get the major bugs sorted. I know I will change my house bank over from Floodies to Li, but this charging controller issue has balked me. I do not want to cook my $5000 battery bank, so i guess i need to carry even more spares on board...or am i missing something here?

Thanks again for the very informative info from those who are experimenting at the moment.

Bloke