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

[weavis]

Lets move on folks.

[john61ct]

Originally Posted by Q Xopa

However you have repeatedly shown to have gaps in what you believe and what actually is.

I don't doubt it, I do learn new things every day thank dog.

I have often stated that I welcome correction of issues of fact that I get wrong, any help in deepening my fundamentals etc.

So I'd really appreciate y'all sticking to the specific factors, conclusions etc of the topic being discussed.

But constant negging for no good reason, repeated speculation about my business, requests for more personal details than what I prefer to share etc

or just making flatout expressions of scorn about my opinions, without indicating which bits you think are wrong,

serve no useful purpose.

Perhaps think of me as a bot, an AI that is constantly updating its neural net algorithms, would that help reduce your agitation?

[john61ct]

Originally Posted by weavis

Lets move on folks.

Sorry, crossposted, will abide

[Cpt Pat]

Originally Posted by newhaul

pat I'm sure you understood that I only stated about the HVD as being in the bms control to protect from over charging as a safety feature not as a normal stopping point .

No, I missed that distinction. Now with a better understanding of your post, I agree. I treat my BMS HVD like an ejection seat handle: it's comforting to have - but hopefully will never be used.

I am charging at only 0.05C (average), and once the per cell voltage reaches 3.65 volts or above, the cells are seriously overcharged. The BMS HVD is there to prevent catastrophic consequences (cell bursting and fire). Operationally, I measure amp/hours in and out, and terminate charging at 80% SOC (I'm conservative - 90% SOC is safe enough). I can't use charge current taper to detect SOC since my charging sources aren't either constant current or constant voltage (solar panels and towed impeller generator). Every 10 cycles or so, I recalibrate the amp/hour counter with a current-limited constant voltage charger connected to shore power, and then utilize charge current taper to manually detect 100% SOC.

Since my recalibrations to 100% SOC occur fairly frequently, I haven't encountered any memory effects. At a charge rate of 0.25C, 100% SOC occurs at 13.9 volts every time I recalibrate.

[OceanSeaSpray]

Originally Posted by tanglewood

This memory phenomenon that you describe is interesting if for no other reason than you seem to be the first to identify it.

Wrong. Another contributor from Australia a few years go reported how he had to "service" all his RV installations every 3 years or so because they were running out of capacity. That was in excess of 100 of them if I remember correctly.

You need to measure capacity to identify issues and this requires doing a full controlled charge or discharge cycle. Most people never do that, or only at the very beginning, and then just keep claiming that everything is great and as good as new.

Originally Posted by tanglewood

To that end, can you provide some details on how you are assessing all this? All you've said is that you can only recharge to 70%, but how are you determining that?

I have already done that if you actually read the material, but the fine detail is that I started recharging with the pack very close to the bottom, 2.95V/cell or so, and recharged continuously until the termination condition was hit while metering the current. There are no "misconceptions". Within 1-2% of capacity at the very most, that is what it is.
After the charge, the cell voltage settled back down to a value abnormally low for fully recharged cells and in agreement with the charge supplied. This is a tell-tale of memory effects and precisely what prompted me to formally measure the available capacity. When a 4S pack has been fully recharged, the voltage under light load should hold above 13.3V for about 0.2C. If this doesn't happen, there is an issue somewhere.

[john61ct]

Originally Posted by Cpt Pat

I am charging at only 0.05C (average)

Wow. Big bank, or tiny panelage?

I don't recall if you've put up a build thread for the specifics of your LFP control systems?

If that's something you don't mind sharing, I'm sure would be very helpful, maybe not the rocket science you're used to but 8-)

[OceanSeaSpray]

Originally Posted by Checkswrecks

As for what OceanSeaSpray wrote, partial cycles really relate to depth of discharge and it appears there is use of the terms memory and capacity interchangeably.

This is not correct. Partial cycles in this context relate to incomplete recharge, because this is what causes issues. The depth of discharge doesn't matter. The terms memory and capacity are used for what they each mean and are not interchangeable.

Originally Posted by Checkswrecks

It's easy to think that reduced capacity is the cell or battery developing a charge memory and nobody here would be the first or last to do this.

Cell memory produces distinctly different symptoms (which I have described) than a battery that effectively becomes gradually smaller, but still behaves normally within that reduced capacity window.

I have operated this installation for 4.5 years in very adverse conditions to study what would happen, so it is not something that you are going to observe overnight while living in the sun and easily recharging every day, unless - like the guy in Australia with his RVs - you are not recharging properly due to an incorrect setup. And it will still take a long time before issues materialise.

As far as I am concerned, the bottom line is that unless you formally measure the bank capacity, statements about its performance and condition are null and void. That leaves very few statements!

[caipirinha]

Hi, my (very) own questions


I thought I'd read the whole thread but logging back in I found you guys kept talking so I browsed quickly through the recent pages / no specific answer for me.
My cat has twin diesels (own alternator & 12 V battery) driving each a 24 V alternator feeding a house bank. At present only starboard bank has batteries (Trojan T105, 4S).
Previously I had a double-output charger and separate inverters, this has recently been changed to a combined inverter-charger (Victron MultiPlus) connected to the (starboard) house bank.
I wish to install batteries in the portside bank and the first question is between T105 (same a starboard, easier to intergrate, but lead is dying....) and LiFePO4 (would likely be Winston)
Second question / confirmation is a Cyrix is probably the best way to charge the portside bank from the MultiPlus (using the starboard bank as primary). But does it make sense to also install a "reverse" Cyrix to allow charging the starboard bank from the portside engine / alternator ? (Note if motor-cruising I usually am running a single engine)
Third question is, if I change battery technology (having LiFepO4 portside), should I upgrade the alternator's regulators (Incharge Hearth, analogic), and if yes by which device ?


Thanks in advance for your (argumented) advices !

[john61ct]

Most of Victron's lines have a fantastic reputation

Cyrix is not one of them.

[Maine Sail]

Originally Posted by OceanSeaSpray

As far as I am concerned, the bottom line is that unless you formally measure the bank capacity, statements about its performance and condition are null and void. That leaves very few statements!

I have actually done that, every 50 cycles to 1000 cycles, and now doing it every hundred cycles as it really just got tiresome...

As we discussed in emails our pack shows no sign of memory issues but we are getting to 100% SOC at least every 20 +/- cycles and at the worst every 50 cycles... Our most frequent charge source is about .35C. I wonder if memory effect may also be related to low charge rates stacked on top of many months PSOC cycles?

[nebster]

Originally Posted by john61ct

Perhaps think of me as a bot, an AI that is constantly updating its neural net algorithms, would that help reduce your agitation?

I think the agitation comes because you insert your theories or opinions and fail to qualify them as such at any point. Every sentence you write is presented with equal weight, importance, and confidence.

I do kind of think of you as a bot. Particularly because you rarely express remorse and always have to "win", even when you are posting to acknowledge that what you said was blatantly false.

You basically troll us, week in and week out, even though you probably have good intentions some where in that neural net.

[nebster]

Originally Posted by john61ct

Would be nice if automation allowed that V setpoint to be varied by load's current level, but we're not there yet.

You might not be, but some of us are. There exist chargers that dynamically adjust their cutoff based on current.

[nebster]

Originally Posted by Don C L

The best recourse is to state verifiable facts, evidence and qualifications and let the readers decide whom they care to listen to. Everyone is free to stop following a thread if they find it less than useful or informative.

I agree that it's a recourse, but it fails to take into account the valuable time of the rest of us who feel we have to do that, again and again.

I can think of several other forms of recourse that would be very effective in this special circumstance.

[Cpt Pat]

Originally Posted by john61ct

Wow. Big bank, or tiny panelage?

I don't recall if you've put up a build thread for the specifics of your LFP control systems?

If that's something you don't mind sharing, I'm sure would be very helpful, maybe not the rocket science you're used to but 8-)

225 A/H, 4S pack. (One 100 A/H in parallel with one 125 A/H pack.) Normal load: 5 amps (0.02C), max stead-state load 12 amps (0.05C), sporadic load (HF SSB transceiver transmitting at 100 watts and 100% modulation) 25 amps (0.11C).

The 5 amp load includes VHF transceiver, one chart plotter (I have two), GPS receiver, AIS plotter and Class A AIS transceiver. Max load includes previous list plus autopilot, LED bow lights, second chart plotter, second AIS plotter, navigation lights, LED cabin lights, and HF transceiver and tuner in receive node.

Max charge from solar array: 12 amps (0.05C) and from water impeller generator 8 amps (0.04C).

Shore power charger: 56 amps (0.25C) rated, derated by me to 36 amps (0.16C).

Battery fused at its terminals to 50 amps.

External (operational) BMS: Victron model BVM-702 for SOC display and charge termination control. APO3 Automatic Power Off module set at 12.7 volts for discharge termination (which controls a high amperage relay). One 120 amp schottky diode for current steering. Definitely not rocket science. All off-the-shelf stuff.

(Heresy alert!) No cell balancers. I manually balance (rarely needed only to make me feel good). Balancers are just one more thing to fail (and drain a cell to zero). At my low C rates, I don't need them.

[john61ct]

Wow, super-essentials, love the minimalism there.