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

[newhaul]

Originally Posted by senormechanico

Newhaul,


What is the resolution of your meter? Does it change in hundredths of a volt?
The meter may have drift with temperature as well.
I wouldn't worry about it.

yes .001v resolution same 65℉ in the shop as always maintained . Unless doing fiberglass work then 75℉ .

[nebster]

Even 10degF is plenty to shift the cell a millivolt or so. I'd have to go look at my notes, but in testing on the bench I noticed that I could use my pack voltage as a pretty darn good thermometer when in steady state.

LFP do exhibit some self-discharge as well, and the amount you have measured is certainly not out of the question for six months.

[john61ct]

They were worrying it was **too little** of a drop!

As in I averaged over 790 on my SATs! Isn't that too high? 8-D

[scaredycat]

Mine have been offline for over two years and show a very similar result.
Of the twelve cells, all are the same reading (13.287), with the exception of two cells, which are slightly lower at 13.285 volts. Tested using a Fluke DVM.

[JmanC]

For setups that run an ACR with a side lead acid battery. Does diverting the charge sources back & forth with a solar controller cause it issues? I have always read that victron mppt chargers should be first connected to a rested battery before any solar is connected.


Also what is a good ACR that will work with the victron BMV 712's relay?

[CatNewBee]

Originally Posted by scaredycat

Mine have been offline for over two years and show a very similar result.
Of the twelve cells, all are the same reading (13.287), with the exception of two cells, which are slightly lower at 13.285 volts. Tested using a Fluke DVM.

I am not aware of 13V cells...

[CatNewBee]

Originally Posted by JmanC

For setups that run an ACR with a side lead acid battery. Does diverting the charge sources back & forth with a solar controller cause it issues? I have always read that victron mppt chargers should be first connected to a rested battery before any solar is connected.


Also what is a good ACR that will work with the victron BMV 712's relay?

That is true, do not disconnect the battery when solar cells are connected, you may kill the FET of the controller. Victron MPPT controller have a remote switch input to be propery shut down and stop charging.

If you only add a battery and disconnect it, you will be fine.

[Delfin]

Originally Posted by JmanC

For setups that run an ACR with a side lead acid battery. Does diverting the charge sources back & forth with a solar controller cause it issues? I have always read that victron mppt chargers should be first connected to a rested battery before any solar is connected.


Also what is a good ACR that will work with the victron BMV 712's relay?

I can't speak to the Victron, but the Blue Sea ACR is what I have used for years and it never disconnects from the house bank, if the house bank is wired as the primary.

FWIW, I have abandoned using the ACR as it dawned on me that its functionality in my use case isn't needed. I do not have solar, but I don't see how that changes anything. I already had two separate rotary switches for the LA starter bank and the house bank, now LFP, so using those and the BMS that allows me to disconnect the LFP bank from the positive buss and isolate it, I turn on and off the starter bank and BMS as follows:

State 1, LFP charging, or at anchor using the bank: First BMS on, then starter off
State 2, LFP not charging: First starter on, then BMS off

So, underway when the LFP bank is full, state 2. When it needs recharging, state 1. At the dock for days/weeks with the LFP at around 50% SoC, state 2. If I am at anchor for long enough to worry about the LA starter bank self discharging, I can turn the starter bank on, and it gets charged along with the LFP bank when the genset is fired up.

Pretty simple and it eliminates the whole issue of floating, which with a two bank setup like yours or mine seems pointless.

[mikedefieslife]

Originally Posted by Inkog

Who knows, but here is the Dometic version sold in Europe:

https://www.dometic.com/en-gb/uk/pro...12-40-_-152914

And Renogy in the US:

https://www.renogy.com/renogy-12v-dc...ttery-charger/

The outside cases differ slightly but the manuals are identical neither bothered to rewrite them.

The manual states there is a 60A version, but neither Renogy or Dometic sell it.

The Dometic charger is poor. You have very little control over the voltages and profiles. It’s dip switches with select profiles.

The Sterling charger does allow customisations but is done by playing around with a button or two and identifying things via blinking lights. It’s almost 80s user friendliness. Why they can’t just stick a Bluetooth module in there. If you have to have the instructions in front of you to change a basic setting it’s bad design.

[Inkog]

Originally Posted by mikedefieslife

The Dometic charger is poor. You have very little control over the voltages and profiles. It’s dip switches with select profiles.

The Sterling charger does allow customisations but is done by playing around with a button or two and identifying things via blinking lights. It’s almost 80s user friendliness. Why they can’t just stick a Bluetooth module in there. If you have to have the instructions in front of you to change a basic setting it’s bad design.

I have the Sterling 1260. I don't care for it much. Half the time it runs in low power mode because it generates so much heat (inefficient design) giving me an avg. of ~35A going into my bank. It only has to increase voltage by ~0.4V in my system, and its loud AF while its at it. I'd find something else if it wasn't now relegated to backup/emergency use now that my solar is in.

The configurable voltage profiles of the Dometic/Renogy B2B are fine for LiFePO4, at least on paper. I don't know how accurate they are in practice.

[newhaul]

Originally Posted by scaredycat

Mine have been offline for over two years and show a very similar result.
Of the twelve cells, all are the same reading (13.287), with the exception of two cells, which are slightly lower at 13.285 volts. Tested using a Fluke DVM.

do you recall what the reading was on the day of decommissioning ?

It would be interesting to see what others have experienced wrt stored banks.
It at this point appears that the self discharge is basically non existent
Another reason for conversion from Fla and its 10% per month self discharge.

[scaredycat]

Originally Posted by CatNewBee

I am not aware of 13V cells...

Sorry, you are quite right!!!!
Neither have I.
Delete the preceding "1".

[JmanC]

Originally Posted by CatNewBee

That is true, do not disconnect the battery when solar cells are connected, you may kill the FET of the controller. Victron MPPT controller have a remote switch input to be propery shut down and stop charging.

If you only add a battery and disconnect it, you will be fine.

thanks
I would just use a relay or dc breaker between the mppt & panels. One reason I thought the controller needs to be first connected to a battery before any solar is to get an idea of the voltage/state of battery. But now I think about it, that cant be true. It should just start charging when the sun shines.

Can you say if the same will happen for an AC charger? Something inside may blow if the battery disconnects during charging? I have done this on my sterling a good dozen or more times and it is still alive.

[JmanC]

Originally Posted by Delfin

I can't speak to the Victron, but the Blue Sea ACR is what I have used for years and it never disconnects from the house bank, if the house bank is wired as the primary.

FWIW, I have abandoned using the ACR as it dawned on me that its functionality in my use case isn't needed. I do not have solar, but I don't see how that changes anything. I already had two separate rotary switches for the LA starter bank and the house bank, now LFP, so using those and the BMS that allows me to disconnect the LFP bank from the positive buss and isolate it, I turn on and off the starter bank and BMS as follows:

State 1, LFP charging, or at anchor using the bank: First BMS on, then starter off
State 2, LFP not charging: First starter on, then BMS off

So, underway when the LFP bank is full, state 2. When it needs recharging, state 1. At the dock for days/weeks with the LFP at around 50% SoC, state 2. If I am at anchor for long enough to worry about the LA starter bank self discharging, I can turn the starter bank on, and it gets charged along with the LFP bank when the genset is fired up.

Pretty simple and it eliminates the whole issue of floating, which with a two bank setup like yours or mine seems pointless.

thanks
My interest with the ACR was purely to have an automatic means of cycling between 20-80%soc for max longevity, with monitor triggering a relay that diverts/turns off the charge sources alone, Rather than manually doing anything. But doing this I cant see anyway to auto start genny.
I now don't see the point in stopping to 80%soc instead of just going to full & floating, as floating is simply & automated. I think I can live with less cycle life.
The battery will only be floating for a few hours each day until loads draw it down & unless cycled almost everyday I dont see the worry in less life. Not with just 200-300AH anyway.
Same with dockside float voltage of 50%soc. I dont see why it really is bad as appose to letting the battery just sit there at 50%.

[john61ct]

Originally Posted by JmanC

One reason I thought the controller needs to be first connected to a battery before any solar is to get an idea of the voltage/state of battery.

That **is** true, hook up the battery first, and disconnect it last.

Even if it isn't "dangerous" for a given SC.

Good habit, like always*removing jewelry, or removing the battery's negative before positive, and reconnect negative last.