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

[toddedger]

Originally Posted by nixsee

On a related note, one of my cell boards for my HPBMS doesn't seem to work properly. When all cells are above 3.55V(as verified by my multimeter and Junsi CellLog), 3 of the boards are shunting but the 4th only does so intermittently. It therefore attains a higher voltage/SOC. I generally keep below this voltage anyway, but it is a nuisance when I'm trying to periodically top off the batteries.

Also, the shunting and HVC levels seem to trip about 20mV too high (3.57 and 3.62) indicating a calibration issue. Anyone else have any similar experiences?

Otherwise it has been working nicely.

Could there be resistance in the connections? Have you tried swapping the boards around?

[44'cruisingcat]

Well, I bit the bullet!


Just replaced my 6 year old 600 a/h AGMs with 310 a/h of Winston LiFePO4's.


Cost about 25% more than the AGM's would have, weigh about 100kg less, (about 1/3) and take up about 1/2 the space.


Hopefully they'll last twice as long....

[senormechanico]

Congrats on your upgrade.
Let the gushing about your system's improved performance begin !

[downunder]

Originally Posted by 44'cruisingcat

Well, I bit the bullet!


Just replaced my 6 year old 600 a/h AGMs with 310 a/h of Winston LiFePO4's.


Cost about 25% more than the AGM's would have, weigh about 100kg less, (about 1/3) and take up about 1/2 the space.


Hopefully they'll last twice as long....

Congratulations. Would appreaciate some detail of your installation once finished.

Cheers

[isaacchacon]

Hi all. THis is my second post in this great forum, this time i want your help to get feedback about my electrical diagram. I am building a van conversion with 200AH LIFEPO4, since very few resources online, I come here hoping to get responses even though i don't have a boat.

Please help and tear apart my design!!!!!

I decided to buy Elite power solution's 200AH battery + BMS system, and am just planning the main system. I will later buy a 3000 watt victron inverter / charger. but for now i will bear with the 15A charger provided. I have not yet used / tested the battery. The package included a charger, a video screen for monitoring SoC, BMS, the battery, and a shunt. (all of them shown in the diagram below).

Contrary to many opinions that i've seen, I decided to go with a latching relay for switching the main loads (BLue sea 7700, 500 amp) , and will be controlled by relays and the BMS. THis latching relay can be manually switched without power, saving me the need to buy a switch.

My installation is somehow inspired on the mar azul boat blog, and i slightly modified the relays to control the under voltage. There are also very helpful manuals that were provided by elite power solutions, and of course learned some from this forum.

The below diagram is a reduced version that omits some components of the BMS package (FUSES, Ground connections, video screen, and others), hoping to give a good understanding for controlling Under VOltage and Over Voltage Conditions:

Attachment 124317

THe BMS has ( Black biggest central component) , among other, these outputs:
- OV : Over voltage, +12V normally, GND if any cell >3.6V
- UV : Under voltage , +12V normally, GND if any cell <2.5V

(note) both OV and UV go to GND for other errors like over temperature or BMS sensing failure

For OV control, it is directly connected to the sense cables of the charger, and i am adding a buzzer ( utilizing a relay on the right side), so I can hear when there's an OV condition. This should make the charger stop charging in an OV event.

For UV control, i decided to connect two relays ( to the left of the BMS system) and then the latching relay: One Normally Closed Relay that, when actuated, it opens the circuit. If there are normal conditions on the BMS, this relay would be OPEN. IF there is an Under Voltage condition, this relay would close the circuit and activate the 2nd relay (a flashing relay), which would send the signal OPEN for a few seconds ( to the orange connection) to the latching relay. THis would OPEN the main connection


All the relays, bms, and all loads are connected after the latching relay, if an Under Voltage event occurs, all the loads get disconnected, including BMS, RElays, and everything. I added to the diagram a couple of override switches to manually connect the bms and the main latching relay for diagnosis / repairs.

Please let me know your feedback, below is the complete diagram ( i ommitted fuses and ground connections for the sake of simplicity), including all the components that would need the bms to be operable.
Attachment 124318
I welcome your feedback on every error / issue / pottential issue that you see in my design.

Several thanks in advance for your kind help!!!!!!

[Maine Sail]

Externally Rectified...

Yet another experiment. This time I am trying to get a cooler running alt and better performance by removing the rectification from the back of the alternator and moving it out of the engine bay.

In just one year charging the LiFePO4 bank the magnet wire coating is severely darkened due to pushing the alternator too hard. I don't have room for a large frame alternator so tweaking a small case alt is my best option.

The math seems to predict that I should be able to drive this alt at nearly full bore and not over heat it. I will report on performance once it is installed and up and running..

[senormechanico]

That definitely makes a lot of sense.
I always wondered why mfr's. didn't already do that.

[lagoon100]

Hello for a 1200ah bank i have the following question:

1. Would you make 2 Banks of 600ah each and parallel them each whit its own BMS, or would you do 1 Banks of 1200ah and one bms (each cell is 200ah)?
Some say its better to have a big bank as cells are more stable and is difficult to reconnect the Banks if even just out by a few mili V as the current for equalizations would be to big.
Others say its better to have more Banks in parallel so as it is easier to identify a week set of cells and finally the weak cell, i tend to go that direktion, but not sure?

2. Would you fuse whit-in the Bank, in the parallel strings (3P or 6P), some suggest that, i’m unsure as how much to fuse and if would it reale work if one cell ges bad as the current from the bad cell would have to be quite big in the failure … would it reale be big enough to pup a fuse.

Would be nice to get an answer, thank you so much

cheers

[fallingeggs]

Originally Posted by Maine Sail

Externally Rectified...

Yet another experiment. This time I am trying to get a cooler running alt and better performance by removing the rectification from the back of the alternator and moving it out of the engine bay.

In just one year charging the LiFePO4 bank the magnet wire coating is severely darkened due to pushing the alternator too hard. I don't have room for a large frame alternator so tweaking a small case alt is my best option.

The math seems to predict that I should be able to drive this alt at nearly full bore and not over heat it. I will report on performance once it is installed and up and running..

It will be very interesting to see your results. Along with the MC-614, you've removed half the guts from the alternator.

On that point, curious how this would change the MC-614 wiring. My wild guess is not by much... the red/power, blue/field and the alt temp sensor wires still go to the alternator. Hmm.

[OceanSeaSpray]

Originally Posted by Maine Sail

Externally Rectified...

Yet another experiment. This time I am trying to get a cooler running alt and better performance by removing the rectification from the back of the alternator and moving it out of the engine bay.

In just one year charging the LiFePO4 bank the magnet wire coating is severely darkened due to pushing the alternator too hard. I don't have room for a large frame alternator so tweaking a small case alt is my best option.

The math seems to predict that I should be able to drive this alt at nearly full bore and not over heat it. I will report on performance once it is installed and up and running..

It will help keep the alternator a bit cooler overall for sure. The windings will still dissipate the same heat however, but the air reaching them won't have gone through the rectifiers first, so should be a little better.

I wouldn't expect a massive difference in continuous output capability... the heating power in the windings varies with R x I^2. There is no substitute for keeping the current below a sensible limit.

The heating power in the rectifiers is VF x I only where VF is the forward voltage drop in the diodes (say 0.4-0.9V depending on current). This is not the one getting out of control at high output, but rectifiers certainly get hot.

[ColdEH]

What alternator temperatures are considered hot when driving your Lithiums ?

Just looked it up Balmar says 90 Celsius is hot , Echo-Tech says 93 Celsius which mine runs at .

Does anybodies alternator get hotter then that ?


Regards


Sent from my iPhone using Cruisers Sailing Forum

[OceanSeaSpray]

Alternators have been running hotter and hotter in recent years with the development of rectifier diodes that can handle much higher temperatures, but for continuous operation it is not very helpful.


I like to still just be able to touch them briefly, so about 90-95degC. I have seen some that climbed to 120-130degC and over while charging lithiums (you need to measure against the laminated stator) and I cut them back.
Heat always seems to get the windings before the rectifiers, so it seems that the most meaningful fraction is resistive heating of the stator.
Because this varies with R x I^2, reducing the current to 90% gives 81% of the heat only and 80% of the current gives 64% of the heat. You don't need to give up on a lot of current to keep them much cooler.

[bill good]

Diodes exist with much lower forward drop & this translate to much lower heat losses.(Heat generated). Extra cooling for the windings/controlling field for power generation may help. Newer designed alternators suitable for the LIFE batts will be the future. Using too larger alternator on the small 1GMS on my boat resulted in actually bogging the RPM & stopping the engines if trying for more engine power with belt slipping as well with the lower range of RPM until the alternators were prevented from charging the LIFE until above 1800 RPM. (Stopped the belt slippage as well) LIFE charging is CC/CV so the alternator size to provide the CC part has to be selected to be within the alternator limits. Time limits can be short times @ the max rated O/P changing, some as little as 5 minutes to approx 1/2 rated current O/P for continuous running.

Regards

[evm1024]

It will be interesting to see MailSails results after removing the diodes. I see a number of factors that will come into play.

Firstly will be the increased cooling that the diodes will have by being out on their "own" with a larger heatsink and a clear air path. Keeping the diodes cooler will increase their MTBF. Of course todays diodes don't often fail so this in not a big gain in general.

Secondly is the temp in the alternator - by removing the diodes he will remove a source of heat in the alternator but more importantly I suspect is that the air flow pattern (the diode assemble will not be blocking the air flow) will create a more efficient transfer of heat out of the alternator.

The end results will be an alternator that can deliver more current for a given temp (or a lower temp for a given current).

The heat is the limiting factor of an alternators output to the greatest extent. Sure, over current or heat the diodes and they die. By the same token over heat the windings and they bake the insulation off and short out. Kills bearings too.

With unlimited cooling we could pull current out of an alternator right up to the magnetic saturation point.

[OceanSeaSpray]

Good luck finding magic diodes. Schottkys can give 0.3-0.4V drop, but not at huge currents unless they are also huge and hugely expensive... practically, you lose close to 0.9V at peak current. It is a matter of balancing the heat and economics.


When it comes to the magnetic saturation point, yes, sure, but that is not far away either because making the stator unnecessarily large adds little else than cost as well.


Dreaming up new technology doesn't do much for today's problems. I want superconducting windings in my alternator too.