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

[CatNewBee]

Originally Posted by sparrowhawk1

https://youtu.be/DQeUYJoTpzg

All hail Lord Andy. Please please that was a joke. The bottom line is all his videos are experimenting . No one has said why it makes sense to put your float lower than your charge . no dogs in the game I have an old school controller and I've stated the drawbacks to it. works with my circumstances but if I could change the parameters life would be perfect LOL

All this videos and advise need to be taken with a grain of salt, the measurements of the voltage are done on a constant current, that affects the voltage. So conclusions on voltage settings without knowing / mentioning the current at this time are BS. Charge profile have CC /CV settings and especially CV (Absorption) terminates when the voltage is reached AND the currend is lower than the set threshold.

[hjohnson]

Originally Posted by sparrowhawk1

Well I guess that's the big question is it more harmful for them to sit full or to needlessly cycle. Also it's clear to me that it's best to either top balance or bottom balance and my BMS has I believe 200 milliamp balancing capability so I believe it's a good thing to keep the battery full for a couple hours every day so the balancer can do its thing.

I didn’t bother doing any balancing on my pack, and just let my BMS (REC Active BMS) take care of things. At this point, my cells are hovering within 0.05V of each other, no matter the SoC. I’ve taken the pack down to 25%, and all the way up to full.

If you buy good gear, there’s a lot less fooling around.

[Maine Sail]

Originally Posted by hjohnson

If you buy good gear, there’s a lot less fooling around.

yes and with premium cells and a BMS that can move more than a few mA.. You won't have issues..

Buy cells off Aliexpress and a cheap BMS that can only shunt a few mA and your system winds up useless like the guy below......Even at just 14.1V this BMS kept tripping on cell high voltage.. The BMS was incapable of correcting the cell to cell imbalance..


The problem becomes crystal clear once you properly capacity test the cells..These cells had a 6.6% variance in capacity... The Daly BMS stood no chance..

[newhaul]

Originally Posted by Maine Sail

yes and with premium cells and a BMS that can move more than a few mA.. You won't have issues..

Buy cells off Aliexpress and a cheap BMS that can only shunt a few mA and your system winds up useless like the guy below......Even at just 14.1V this BMS kept tripping on cell high voltage.. The BMS was incapable of correcting the cell to cell imbalance..


The problem becomes crystal clear once you properly capacity test the cells..These cells had a 6.6% variance in capacity... The Daly BMS stood no chance..

Question is were the cells top and or bottom balanced prior to commission? What was the cycle count what was the charge and discharge rate? How long in service without testing ?
Settings of charge sources? Was it set to top balance with every cycle? Or 5 years of rough use with no balance or even capacity test?

Yes he has serious but not uncorrectable issues atm.

Answers to above would give insights as to potential corrective/ mitigation measures .

[Maine Sail]

Originally Posted by newhaul

Question is were the cells top and or bottom balanced prior to commission? What was the cycle count what was the charge and discharge rate? How long in service without testing ?
Settings of charge sources? Was it set to top balance with every cycle? Or 5 years of rough use with no balance or even capacity test?

Yes he has serious but not uncorrectable issues atm.

Answers to above would give insights as to potential corrective/ mitigation measures .

Brand spanking new direct from China drop-in battery. Battery had to be destroyed to get to the cells. Even after top balancing the Daly BMS could not keep the cells in balance for more than 10-12 cycles...Charge rate was .1C discharge rate less than .03C..When you have that much variation cell to cell these shunting BMS's often cant keep up..

[newhaul]

Originally Posted by Maine Sail

Brand spanking new direct from China drop-in battery. Battery had to be destroyed to get to the cells. Even after top balancing the Daly BMS could not keep the cells in balance for more than 10-12 cycles...Charge rate was .1C discharge rate less than .03C..When you have that much variation cell to cell these shunting BMS's often cant keep up..

Definitely a problem with the cells . Sounds like a damaged cell. And not the fault of the bms . Definitely a quality control issue.

A good reason for using quality cells to start with .

[Maine Sail]

Originally Posted by newhaul

Definitely a problem with the cells . Sounds like a damaged cell. And not the fault of the bms . Definitely a quality control issue.

A good reason for using quality cells to start with .

The discharge graph should have made that clear...But we see these issues with the Daly BMS routinely where someone gets mismatched cells and the Daly does not have the balance current to keep up...

[CatNewBee]

Could be just a bad connection on the cell that causes the runoff under current.(high resistance).

[bill good]

Well here goes nothing!! Installed a DIY 12V 304A/H using 123 smart BMS yesterday. Not a big fan of BMS unit full of mosfets & fans to keep things cool & peak limits at the point of failure, so using a 300A bi-stable relay that can pass all the current needed continuity. Time will tell. May need more solar.

Regards

[sparrowhawk1]

Just curious how far out of balance do grade a cells get when the battery is at 14.2? Now I knew when I was buying my batteries from AliExpress I was taking a big risk. But I'm on a budget and the batteries I bought were literally half price so I thought it was worth the risk. And I am very happy with my choice but I would never recommend people take the same risk, but I also think telling people buying grade a batteries is the only way to go is (insert whatever negative term you want). I started out with a daily BMS so I didn't really know what was going on with the batteries and I've only had a BMS with Bluetooth for maybe 6 months. And when I first hooked them up they were out of balance so I manually discharged the higher cell until they were close by close I mean within .05 millivolts. We've had a lot of rain lately and for a week and a half or more I've never gone above 13 8 volts. first day of sunshine I went to 14.1. overnight my battery is discharged to 60% the next day my controller did not come on because I cannot change my float from 13.2 so if I was not here to put a load on my battery Bank it would have never started charging for the day, the panels would just have kept up with whatever loads are on. That would mean the next day my batteries would discharge to 20% capacity. now if I left my boat unattended it would fully charge the next day and go through this whole cycle again discharging my batteries to 20% in 2 days and then fully charging it. Over and over again. In my humble opinion this is bad. I know I've already explained this but I just am doing it again because I want to help people especially the ones that have helped me. My cells never go more than .05 milliamps out of balance and usually it's one cell is lower than the other three so my charge controller needs time to discharge the three other cells. Which is usually twice a week that my voltage is at 14.1 (14.2 setting) for 2 hours because I am aware of my amp hours and if I have them I use them,

[sparrowhawk1]

Okay maybe this will keep everyone happy. Because I swear he said earlier to keep the charging and float the same and pointed out the reasons it was bad to have the float lower but it makes sense now. 13.8 charge 13.4 float because a fully charged battery will not be above 13.4. https://youtu.be/xBu7ScAdKrg

[sparrowhawk1]

Or I should have said and more importantly a slightly discharged battery will drop below 13.4 allowing the battery to be recharged and not cycle needlessly.

[Na Mara]

I’m sure this has been asked and answered somewhere in this thread or elsewhere but how does one get an alternator to cease charging a bank of LFP batteries with internal BMS in the event of a problem?

Imagine a bank of 600Ah with 6 batteries all with their own BMS charging off a 200A alternator. Now if one BMS shuts down it’s battery it’s not a big problem as the alternator still has the other 5 to charge against. Indeed this is a positive feature of a system with multiple independent BMS’. But imagine a high or low temperature event that shuts down all the batteries at roughly the same time. Now with a single external BMS a signal is sent to the alternator regulator to zero the field on the alternator and all is peaches and cream, but no signal can be sent from the individual BMS’s to the regulator except for the battery voltage suddenly dropping to zero. Is that how the regulator knows to cease charging or am I missing something? Dumb question I know but I’d like an answer as at the moment I’m deciding on a lithium upgrade and getting the regulator to talk with the BMS is pushing me towards a more expensive solution.

[CatNewBee]

Originally Posted by Na Mara

I’m sure this has been asked and answered somewhere in this thread or elsewhere but how does one get an alternator to cease charging a bank of LFP batteries with internal BMS in the event of a problem?

Imagine a bank of 600Ah with 6 batteries all with their own BMS charging off a 200A alternator. Now if one BMS shuts down it’s battery it’s not a big problem as the alternator still has the other 5 to charge against. Indeed this is a positive feature of a system with multiple independent BMS’. But imagine a high or low temperature event that shuts down all the batteries at roughly the same time. Now with a single external BMS a signal is sent to the alternator regulator to zero the field on the alternator and all is peaches and cream, but no signal can be sent from the individual BMS’s to the regulator except for the battery voltage suddenly dropping to zero. Is that how the regulator knows to cease charging or am I missing something? Dumb question I know but I’d like an answer as at the moment I’m deciding on a lithium upgrade and getting the regulator to talk with the BMS is pushing me towards a more expensive solution.

Read about alternators, start battery, house battery, charge distribution blocks (diodes, FET). This is a perpetual topic asked from every new LFP convert, and the answers are always the same - from don't worry - a battery is a battery and the systems work as designed - to OMG I'm gonna kill the alternator if I don't sacrifice some thousend dollars for a (insert any expensive device like B2B charger, Wakespeed regulator, Balmar whatever).

[Na Mara]

My question is a bit more specific. How does the regulator know to stop charging without an ATC signal or other signal from the internal BMS’ ? Is it the voltage drop at the batteries or is this just a risk one lives with assuming all the batteries shutting off together when the engine is running will never happen?