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

[transmitterdan]

Originally Posted by lagoon100

Hi floks,



Can this noise form the Chargers not be eliminated by "just" adding few big Capacitors in Parallel? How big would they need to be for 1000ah bank?

Anybody has experience whit the noise of the Victron 24V/5000/100A combo?



Other topic:

For the Alternator and other peack induced Voltages, has anybody used big current Z Diodes to limit peace Voltages like 18V or 36V for 12 or 24V systems, they can pull up to 100A for short periods whit in nanoseconds, so few of those at critical points should do the job in order to prevent the V to run away in case your

Bank disconnects, and before the Alt. Regulator kicks in.

I do have a normal lead acid Bank in Parallel via a bipolar diode that gives me 0.7V drop, maybe i even put 2 of those in so 1.4V drop, so there should not be to much drain current from that, it's the bow truster batt anyhow so i need it (has sep. Charger).



Any comments on that?

Many thx.

Lagoon

A single filter capacitor has to be huge to do any serious filtering. A good filter will use a combination of inductors and capacitors. The designers of these chargers most likely know how to design the right filter but the customers will not pay the increased cost. In this market price is the #1 consideration. And lead acid batteries don't seem to care about the noise.

Putting in voltage or current limiting diodes would just generate more waste heat.

Splitter diodes waste power and may lead to chronic battery undercharging. A better solution is the automatic charge relay. Very low loss and keeps all the batteries at the proper (and same) voltage.

[senormechanico]

Originally Posted by OceanSeaSpray

As long as the battery still loads the charger properly, voltage ripple is usually not much of a concern, the battery itself keeps it down. Problems can start when the current tapers down.
This is how cells can get completely destroyed even by very small chargers.

If I get a chance today, I'll repeat the test when battery gets to acceptance (13.8) I've set float below battery voltage, so there's a slight negative current flow.

[OceanSeaSpray]

Originally Posted by lagoon100

Hi floks,

Can this noise form the Chargers not be eliminated by "just" adding few big Capacitors in Parallel? How big would they need to be for 1000ah bank?
Anybody has experience whit the noise of the Victron 24V/5000/100A combo?

Other topic:
For the Alternator and other peack induced Voltages, has anybody used big current Z Diodes to limit peace Voltages like 18V or 36V for 12 or 24V systems, they can pull up to 100A for short periods whit in nanoseconds, so few of those at critical points should do the job in order to prevent the V to run away in case your
Bank disconnects, and before the Alt. Regulator kicks in.
I do have a normal lead acid Bank in Parallel via a bipolar diode that gives me 0.7V drop, maybe i even put 2 of those in so 1.4V drop, so there should not be to much drain current from that, it's the bow truster batt anyhow so i need it (has sep. Charger).

Any comments on that?
Many thx.
Lagoon

The noise is only a problem when it gets too high and then you are dealing with a junk charger. The lower the frequency and the higher the current, the more expensive it is to filter.

Units like Victron AC chargers etc are in fact high-frequency switch-mode power converters. The output will have a ripple, but it should be modest and the spec might even elaborate on this.
The problems with some of these units is that they keep doing stupid things in terms of charge management and hopelessly overcharge lithium batteries, because they were only ever intended for lead-acid.

If you measure your charger output with a multimeter on the AC range, you might get an idea of how noisy it is, but keep in mind that this doesn't show peak values. If you want peak, use a fast diode and a capacitor before the meter on DC range and you should see much better how high the voltage peaks actually are.


I have never seen a zener diode that would be able to take a direct hit from a disconnected alternator. I use some all the time in power switches that can take a 3-5kW spike, but it better be over really quick because they won't hang in there longer than a millisecond, if that much. Alternator regulators are very, very slow to react in comparison. Also, the voltage still rises quite a bit at peak current, like 30V for a 18V zener.

My preferred design is splitting the alternator output over blocking diodes and routing it to both the SLA start battery and the LFP bank, sensing at the LFP output of the isolator (NOT the battery, which is past the disconnector!). It fully takes care of the matter.
Also, while you charge the LFP at full current and the SLA with (usually) much less, the voltage drop over the diodes is also imbalanced and results in a higher voltage at the SLA, which is exactly what we want. This naturally disappears as the LFP current tapers down at the end. The additional absorption the SLA needs at higher voltage can be obtained using auxiliary methods - solve the big problem first and then deal with the small stuff.

So far I have thrown out every single VSR I have run into. They are bad news already with lead-acids and never seem to lead to anything acceptable with LFPs. Paralleling switches and VSRs are in the no-go zone with dual DC bus systems in particular.

[lagoon100]

Originally Posted by transmitterdan

A single filter capacitor has to be huge to do any serious filtering. A good filter will use a combination of inductors and capacitors. The designers of these chargers most likely know how to design the right filter but the customers will not pay the increased cost. In this market price is the #1 consideration. And lead acid batteries don't seem to care about the noise.

Putting in voltage or current limiting diodes would just generate more waste heat.

Splitter diodes waste power and may lead to chronic battery undercharging. A better solution is the automatic charge relay. Very low loss and keeps all the batteries at the proper (and same) voltage.

Heia,
Thx for your answer, the Z diodes only come to affect if we have short peak voltage from the alternator in case of failures, so is just a last line of defense and very simple, that is why the Voltage would be 18V or so, save the nav and other equipment.


Yes the condenser would need to be big, but wold it not cut the peaks at least abit ..... anybody done test on the ripple of viltron chargers, i won't be able until before 2 months or so.

For the split diodes, it is basically a bag up battery and also a big condenser for the above in case of system failures, as said it has its own charger, so no worries that the bow truster battery (bag up) will be undercharged.

regards

[lagoon100]

Thx OceanSeaSpray!

what is a VSR?

cheers

[lagoon100]

ok, have it --> voltage sensitive relay,

agreed! relays fail and are not fast enough, for every relay in my system i order a spare one, i try to have as few as possible and only whit little switching.

Thx for your comment's, guess i check the ripple whit a oz. first before i go further.

thx

[transmitterdan]

A VSR (or automatic charge relay) is not for the purpose of protecting against over voltage. It is for connecting battery banks in parallel only when the charging source is on. They are quite reliable. Some of them are solid state with no moving parts so they last decades without failure.

[Merc83]

Hello,

I am interested in using LiFePO4 in our RV and am reading all the info I can lay my hands on. I must say that this is by far the most comprehensive and informative thread I have come across, thanks to everyone for supplying their knowledge, even if it means reading 350+ pages.

I would like to know when charging a pack of 4 series cells, in my case 260Ah Winstons, do you stop charging at say 14 volts when the pack is loaded? Wouldn't that voltage reading alter depending on how much load is present on the cells at that particular time?
In our situation be it a yacht or RV, our battery bank is never really at rest and always has a load so does that alter when charging should stop?

Your thoughts would be appreciated as my research has not provided very much information on loaded volts and charging.

Thanks,
Les

[SV THIRD DAY]

Originally Posted by Merc83

Hello,

I am interested in using LiFePO4 in our RV and am reading all the info I can lay my hands on. I must say that this is by far the most comprehensive and informative thread I have come across, thanks to everyone for supplying their knowledge, even if it means reading 350+ pages.

I would like to know when charging a pack of 4 series cells, in my case 260Ah Winstons, do you stop charging at say 14 volts when the pack is loaded? Wouldn't that voltage reading alter depending on how much load is present on the cells at that particular time?
In our situation be it a yacht or RV, our battery bank is never really at rest and always has a load so does that alter when charging should stop?

Your thoughts would be appreciated as my research has not provided very much information on loaded volts and charging.

Thanks,
Les

Welcome to Cf Les...
Many cruisers hit the RV Circuit when their days on the water are over and the 12v systems are pretty similar. While living aboard you never really have a "resting voltage" that's just the reality of how the batteries work in the real world. We have been living aboard full time for 2 years now with our 400AH LiFePO4 bank and we simply set our charging sources to a top voltage of 13.8v ...Solar...wind...battery charger and set it and forget it. I started out at 13.4v and just have slowly walked it up a bit as I have learned more and developed a comfort and confidence in the battery bank. Now every once in a while I mess with things and up the voltage, but at the end of the day the amount of capacity I am losing (at least to me) just isn't worth the hassle or extra control needed to get more fancy. Two years of doing this and I have not seen a measurable drift in cell voltage or any measurable loss of capacity.

Now I love the techy guys in this thread that have this computer, that control, this fancy-dancy measureabob...I really do love them and in no way at all say this to disparage them. But you have to remember who these early adapters of a new technology are...they are tinkerers...guys that want to play and design and have fun doing it. These new LiFePO4 batteries are as much of a fun science project as it is just a way to power their boat. So when you get advice from some of these VERY smart guys, they are going to give you the "I'm flying this ship to the moon baby" type of answers. Because baby...everything they do is first class and proudly over-engineered. Again...I love them, but I personally think so much of the advanced monitoring with auto this...auto that is just overkill. When I talk to the folks that sold me my battery at Lithium Ion Storage he keeps asking me back, "Why the heck are you boaters making it so complicated? These batteries are much more bullet proof, relax and don't worry as much."

So back to your question, yes, you will never really get to full charge...but SO WHAT? Do you want to build or buy a NASA control scheme and mission launch computer to get that last 5-10% or just enjoy life? I vote for enjoying life and letting others panic.

[Merc83]

Hello and thanks for your reply.

So you do not take any notice of what load may be on the cells when charging, just set it to turn the charging off at 13.8 volts? Perhaps that is my problem - over thinking it. I do plan to use a simple system to end all charging sources when a voltage is reached, I just didn't know if the load at that charging time would effect the level of SOC. I think you are correct.
Some do seem to go to extreme lengths with computer monitoring and logging and that is fine for those who can do it but I would prefer the less complicated way. I do not intend to run air conditioners and other high powered items so I think that helps too.
Again, thanks for your thoughts.

Les

[senormechanico]

Third Day's post could just as easily have been written by me.
13.8 works for my single bank 200 aH boat as well (very well appointed with electrical goodies).

[BigBeakie]

Along the line of Third Day's recommendation to "keep it simple", does anyone use or have looked at the Super B LFP's from Netherlands? Did a search but not getting a hit on CF about these drop in replacement type.

And I have read this whole thread,and must admit that I am still quite daunted to try and put together an LFP bank, with BMS, and get into balancing/monitoring etc etc.

I have heard very good things about these Super B's & how the BMS works, so would appreciate anyones feedback or thoughts.

Here is their site although there is not really detailed info on how the BMS works: SB12V160E-ZC Lightweight Lithium Ion energy / traction battery, 28 kilogram. | Super B

In simple sentences, what would the major deficiencies of this BMS be??? What are the questions I should be asking the vendor?

Thanks muchly

[BigBeakie]

Super B LFP info:

Apologies, neglected to attach the tech info re BMS. Here 'tis

I guess the central question is, as long as charging system is well monitored and controlled for over voltage, do these seem like a viable house bank LFP solution or not?

[BigBeakie]

Sorry, the PDF info sheets were too big for the CF upload limit

The Super B tech book & manual are in the downloads area FYI.

[evm1024]

Originally Posted by Merc83

Hello and thanks for your reply.

So you do not take any notice of what load may be on the cells when charging, just set it to turn the charging off at 13.8 volts? Perhaps that is my problem - over thinking it. I do plan to use a simple system to end all charging sources when a voltage is reached, I just didn't know if the load at that charging time would effect the level of SOC. I think you are correct.
Some do seem to go to extreme lengths with computer monitoring and logging and that is fine for those who can do it but I would prefer the less complicated way. I do not intend to run air conditioners and other high powered items so I think that helps too.
Again, thanks for your thoughts.

Les

If you are charging your batteries they are not under load....

Which is to say if there is current going into your batteries (more current is being generated that the loads (lights etc need) are using then the loads are being supplied current from your charging sources. The difference in charging source current and load current is the current available to charge your batteries.

The charging/load voltage will stabilize at the point where E=P/I (E=voltage. P=power available from the charging sources and I = current). Of course there are a number of limits (charge voltage regulation, supply current limits etc) that get in the way.

Ohm's law rules - voltage, current, resistance always balance out.

tossed in for reference: Voltage current resistance and electric power general basic electrical formulas mathematical calculations calculator formula for power calculating energy work equation power law watts understandimg general electrical pie chart electricity calculation