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

[Hkalan]

Hello,

Use a battery isolator from the alternator, and a relay from your LifePO4 BMS. I have a charge controller that cuts off at 28v to assure no overcharge of the LFP bank as well... Here is my system...

Attachment 87383

[roetter]

Originally Posted by Jd1

Has anyone come up with a safe way of keeping both flooded lead acid batteries and lithium batteries happy in an installation?
...

I have done just that on several boats. All charges to the LFP batteries (shore, alt, solar) go to a charge bus.
Between the charge bus and the LFPs is a solenoid.
The voltage of the LFP battery is measured by a programmable voltmeter

Once the voltmeter sees 13.8V the solenoid opens and ALL chargers are disconnected from the LFP. LFPs have a very simple charge needs compared to LA. Just charge to a certain safe voltage then stop. Start charging again one the voltage has dropped a bit. I chose 13.3V. 90% of ny charging is done by 1800W solar with the solar controller set to 13.75V so it does not trip the disconnect. The starter battery remains connected to the alternator when disconnecting the LFP and prevent damage to the alt as they absorb the "spike" until the alt regulator reacts.

I have a Junsi to check if the individual cells remain in balance. Should there be an imbalance, then I "short" the high cell(s) with a length of regular construction electrical cable that will give me about a 30A drain.

[goboatingnow]

The simplest way to do this is a battery to battery charger

Dave


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[Jd1]

Originally Posted by goboatingnow

The simplest way to do this is a battery to battery charger

Thanks Dave, I have not heard of such an animal before - I shall investigate!

[Jd1]

Turns out that yes, I had heard of them before but it had totally dropped out of my mind (old age is a terrible thing). Googling on this type of charger revealed plenty but none seem to include a litium charging profile or are adjustable. I thought I had hit the jackpot with Sterling but reading the manual showed that there was no lithium profile .... and I would really require something where I can adjust the charge voltage. It can be a real dumb box because it only needs a constant voltage output and no multi stage wizardry.
I will continue looking for that kind of a charger as that is exactly what I need.

Jens

[roetter]

Just to clarify LFP and LA in the same installation.

LA needs higher voltage (14.5) absorption, and float plus times and current detection to terminate absorption.
LFP does not need any of that and voltages are lower (13.8 -14.0V).
That makes it real simple.
Use your chargers with LA profiles and charge both LA and LFP from the same sources.
When the voltage reaches 13.8 to 14.0V (whichever is your magical number), disconnect the LFPs from charge automatically as I described before.

The simplest, best, and cheapest way to live with both battery type.


Rolf

[UnNamedBeneteau]

Thanks Eric,
I knew that mixing the two battery types was a no-go. I accepted that the lead acids would 'suffer', and was ok with it. (I just didn't expect ti to happen right away!) One solution I am considering is to simply remove the two lead acids as you mentioned. I think the lithium can handle my starting and bow thruster which I only use with the engine running anyway.
I'm not eager to add second alternator because I just bought the 160 amp one with a serpentine belt.
A likely first step should be to disconnect the cells, then charge them individually to ensure they are indeed top balanced - which I didn't do.
I have an alarm set to indicate low voltage at (from memory, I think) 11.99. The BMS would cut out independently at a lower value, but set to protect the lithium set up.
Thanks for your suggestions. I am just now back to dock after 29 days at anchor. So once I'm back to the boat I will start some fact finding.

[Jd1]

Originally Posted by roetter

Just to clarify LFP and LA in the same installation.

LA needs higher voltage (14.5) absorption, and float plus times and current detection to terminate absorption.
LFP does not need any of that and voltages are lower (13.8 -14.0V).
That makes it real simple.
Use your chargers with LA profiles and charge both LA and LFP from the same sources.
When the voltage reaches 13.8 to 14.0V (whichever is your magical number), disconnect the LFPs from charge automatically as I described before.

The simplest, best, and cheapest way to live with both battery type.


Rolf

The one part that I am bothered with is that everything hinges on the disconnect when the lithiums reach the magic voltage setpoint. I would feel much better if the charging source limits the charging voltage and the disconnect is a safety device that only activates if other things fail.
Thinking this over a bit, I guess I could have one contactor shut things down on a regular basis and have a second contactor with a completely redundant voltage sense system as a safety backup giving me the same level of protection. For reasons unknown though, I seem to be uneasy with this sort of arrangement (some kind of gut level uneasy feeling) .... Maine Sail, what is your take on this sort of charging regime ?
It certainly is a pretty straightforward way of going and eliminates a number of failure points.

[OceanSeaSpray]

Originally Posted by UnNamedBeneteau

Thanks Eric,
I knew that mixing the two battery types was a no-go. I accepted that the lead acids would 'suffer', and was ok with it. (I just didn't expect ti to happen right away!) One solution I am considering is to simply remove the two lead acids as you mentioned. I think the lithium can handle my starting and bow thruster which I only use with the engine running anyway.
I'm not eager to add second alternator because I just bought the 160 amp one with a serpentine belt.
A likely first step should be to disconnect the cells, then charge them individually to ensure they are indeed top balanced - which I didn't do.
I have an alarm set to indicate low voltage at (from memory, I think) 11.99. The BMS would cut out independently at a lower value, but set to protect the lithium set up.
Thanks for your suggestions. I am just now back to dock after 29 days at anchor. So once I'm back to the boat I will start some fact finding.

There a few useful suggestions for you coming through following JD1's question anyway.
I would definitely keep the starting battery as lead-acid (redundancy, always able to start your engine) and probably get rid of the bow-thruster one.

Do balance your cells, parallel them up, leave them for a few hours and then charge them up towards 3.55V or so. Best is using an adjustable DC power supply for this, so you can set the top voltage without risk of overcharging. If you use something else (not properly voltage limited for the job), you will have to watch like a hawk all the time for the rapid rise in voltage near the end - possible but not recommended.

Now remember that once a lithium cell leaves the 3.2-3.3V plateau, it is very close to fully discharged and when you run a top balanced system, the "smallest" one of your cells is going to suddenly drop in voltage first. You should alarm on low cell voltage (say 3.0V) primarily, bank voltage is not as meaningful. Also make sure that the BMS doesn't cut on a bank voltage limit either, but any cell dropping below a given level so it can protect it.

Your charging issues might originate from splitting diodes (isolator). Some voltage is lost over the isolator, typically around 0.6V (in fact it varies a bit with the amount of current flowing through, 0.4-0.9V). If you had set your alternator output voltage for 14.0V, then you might have been charging the lithiums at 13.3V or so only and this could explain the lack of capacity and frequent need to recharge.
But follow the wiring, find the isolator if any, and find where you are sensing the charging voltage, before or after the isolator and on what bank.

Your first step should be balancing, but don't stop there or try to use the system afterwards. You must make sure your protections are effective because at the moment you seem to be all set to lose cells on over-discharge.

[roetter]

Originally Posted by Jd1

The one part that I am bothered with is that everything hinges on the disconnect when the lithiums reach the magic voltage setpoint. I would feel much better if the charging source limits the charging voltage and the disconnect is a safety device that only activates if other things fail.

On my live-aboard boat solar (Outback) and shore charger (Victron) are set to the LFP max I want (I.e. 13.8V) so the solenoid is the "insurance" policy. Only the alternators go higher as per original internal regulator. They could be changed to LFP with an external Balmar, but I see no reason for that as I mainly charge of the large solar panels. The alternators are also the only ones charging the LA batteries. And LA needs a higher voltage to live a long and happy life.

When the engines are on I am always on the boat and the Junsi triggers a load alarm should anything be out of whack so I can attend to it right away. I assume this will never happen though.



Rolf

[goboatingnow]

Originally Posted by Jd1

Turns out that yes, I had heard of them before but it had totally dropped out of my mind (old age is a terrible thing). Googling on this type of charger revealed plenty but none seem to include a litium charging profile or are adjustable. I thought I had hit the jackpot with Sterling but reading the manual showed that there was no lithium profile .... and I would really require something where I can adjust the charge voltage. It can be a real dumb box because it only needs a constant voltage output and no multi stage wizardry.
I will continue looking for that kind of a charger as that is exactly what I need.

Jens

Use the battery to battery to charge the LA


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[goboatingnow]

When charging Li banks, you should definitely not rely on contactor actions to stop charging , as jd1 points out the Li charge profile should limit voltages , the contactors are a safety system and in real life should never activate

I see no evidence from your original post, to indicate the Li bank isn't charging, you mention the thrusters , but they are currently on the LA set.

Hence I'm not sure why everyone here is discussing Li issues.

Dave


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[roetter]

Originally Posted by goboatingnow

Use the battery to battery to charge the LA

So the battery-to-battery charger draws from the LFP and chargers the LA?

This means it has to be a charger that steps up the voltage from 13.xV to 14.5V or so.

What prevents the b-t-b charger to not completely drain the LFP when the LA has a short or any other problem on the starter circuit?

[Jd1]

Originally Posted by roetter

What prevents the b-t-b charger to not completely drain the LFP when the LA has a short or any other problem on the starter circuit?

That would be handled by the lithium battery protection system.

[rfadler]

Originally Posted by Jd1

The one part that I am bothered with is that everything hinges on the disconnect when the lithiums reach the magic voltage setpoint. I would feel much better if the charging source limits the charging voltage and the disconnect is a safety device that only activates if other things fail.
Thinking this over a bit, I guess I could have one contactor shut things down on a regular basis and have a second contactor with a completely redundant voltage sense system as a safety backup giving me the same level of protection. For reasons unknown though, I seem to be uneasy with this sort of arrangement (some kind of gut level uneasy feeling) .... Maine Sail, what is your take on this sort of charging regime ?
It certainly is a pretty straightforward way of going and eliminates a number of failure points.

Why are you bothered that everything hinges on the disconnect with the lithiums? Would you feel better if you had a BMS (such as the HPBMS) that was configured as a backup?

My understanding is that in a traditional LiFePO4 installation (if there is such a thing) a disconnect is a safety device if other things fail because disconnecting will most likely destroy the alternator. In Rolf's installation the LA battery is there to absorb the spike and protects the alternator.

Am I missing another reason that you would not want to use the disconnect as described by Rolf? It seems like a very elegant solution.