FLA battery bank question

dbarnard67 · December 2019

Hi all, I have had a set of Crown 430ah FLA batteries on 48v set. These are 6 volt with 8 in the string. When I got them I asked the company what they recommended on the charge settings they told me. I then thought it seemed low from what I had researched and decided to reach out to crown. They gave me much higher settings. So, I waited a little bit and called them back up, and got a different charge parameter but was in the middle of the settings. I went with that and it was too low. Think these are toast because of undercharge. Is anyone using AGM's, pros/cons? Also, has anyone built a powerwall out of Nissan Leaf batteries, how are they performing. Thanks for any input, just trying to get some opinions.

Estragon · December 2019

What are the SG readings on the bank? When was the last EQ done, and were there some particularly weak cells?

People do use deep cycle AGMs. Generically (they aren't all the same)...
Pros:
- don't need regular SG checks and watering
- can usually be installed in any orientation
- easier to ship
- don't gas in normal operation
- lower self-consumption

Cons
- can't check SG or add water
- generally ~2x cost vs FLA
- permanently damaged if overcharged

To me, having to check SG and water is a feature as it helps me monitor battery health. For others, it's a bug.

Estragon · December 2019

People have used EV batteries, but in my limited understanding it's not something to be undertaken lightly.

One issue with any lithium battery is they can't be charged in freezing temps.

dbarnard67 · December 2019

The SG's are reading about 1.265, to 1.270 across the board. Tried to do and EQ on them just about 2 days ago and it aborted. Cells don't appear to be weak, just cannot get these things to go above 54.6 volts on the bank itself. Crown says that they need to be around 59.9 to 61.0 to gas and even with a generator running to help "bump" them they will not recover. The settings from crown are EQ 61.9, Absorb 58.1, and float 54. This is after getting to engineering. Before they had them at 58.4 for EQ, Absorb was 56.8, and float was 52.7. And yes had heard that about the EV's glad to see someone's had seen this as well. Good thing for me, I have it in a climate controlled garage it is usually 60-80 degrees F so they shouldn't freeze, but have heard they really need the BMS on each bank with a combiner module to charge them efficiently. What have you all heard about he DOD on the AGM's. I have been told up to 80% but obviously wouldn't want to do that to keep them from weakening up sooner than later.

Estragon · December 2019

SG sounds ok. Charging voltages are close to what I use for my L16s (Vabs=58.8). Lower charging voltage is sometimes a default recommendation for grid applications (eg floor sweeper) where absorb can be done for much longer than is usually possible using solar.

Not getting above 54.6v in bulk would be a concern though. Is charging done with a remote temperature sensor? Do any cells get warm/hot?

60-80°f should be fine for lithium. BMS is definitely not optional.

AGMs can go to 80%DOD (as can flooded), but at a cost of lower expected cycle life. In a standby application that's okay, because the bank is more likely to die of old age than cycling. In a daily cycling application like off-grid, more like 50% max is likely to be a better cost/watt proposition.

mike95490 · December 2019

Do not buy the expensive AGM's until you have the bugs worked out, and a bank of Flooded, last you 8 years.

dbarnard67 · December 2019

Yeah the 54.6 just seems a concern I would expect to be able to get them to 58 or so as a starting point before the sun went down. Thanks for the input Mike, agree to fry a lower price battery than a more expensive one. Being told a full river 200ah has more usable capacity than my 430ah FLA Can get a 48v setup of these for half the cost of my original FLA

706jim · December 2019

What is the size of your solar array? I agree that your original settings were low having gone through a similar quandary with low capacity.
I presently have my 24 volt system set to 29.8 bulk and 27.6 float and things are much better. SG runs about 1.25 which makes me wonder if you have a bad battery or cell.

dbarnard67 · December 2019

I have a 5.4Kw array. 18 panels at 305 watts

Estragon · December 2019

My array & bank are a bit smaller but in the ballpark. At this time of year (in Canada), generator charging is pretty much essential even on sunny days. Does running the genny get to absorb voltage?

mcgivor · December 2019

dbarnard67 said:

I have a 5.4Kw array. 18 panels at 305 watts

What is the array topography, series parallel arrangement and panel specifications? What charge controller is being used? Rationale being that perhaps the voltage headroom is not sufficiently high enough to achieve the target setpoint. Just a thought.

dbarnard67 · December 2019

Running the gen gets them close but it can run all day and when I shut it down the voltage drops to 52.6 to 53.1 on average. I am going to investigate each battery today to see what I can uncover. Panels are set up in Groups of 3 with 6 groups coming to a combiner box. From there they feed into the Schnieder XW+ 6848 with a midnite controller. Equipment seems to be good and on a good sunny day it can give them a good soak even in winter and get them to around 57.1, but once the sun goes down the voltage drops with very little load, 400 watts, and they are at 52.1 in a matter of minutes. I am suspecting it is a battery

Estragon · December 2019

Most 48v nominal banks have a "full" resting voltage of ~51.x. Above that, with no charge source, is a surface charge with very little power. A 400w load would take that off fairly quickly.

Below that resting voltage, a healthy bank should drop more slowly. With a 400w(~8a) load, I'd expect the bank to last about a day to 50%

Unless the bank is warmer than room temp (and assuming RTS is working) you should be getting to absorb voltage though. IIRC, the MN localapp shows the temp compensated target voltage somewhere. Maybe check to see if that's reasonable?

mcgivor · December 2019

When a lead acid battery has lost capacity the voltage will climb rapidly with current tapering off correspondingly, if there are internal shorts the voltage would be low with higher current accompanied with increased temperature in one or more cells/batteries, the energy has to go somewhere.

Going by description it would seem 3 × 305W in series would provide enough headroom voltage wise, when conducting an equalization it is generally recommend to disconnect all loads to allow maximum available voltage, I'm wondering if this may be a factor because the SG readings would correlate with such a situation, almost there but loads prevent competition.

Obviously the current/temperature information aforementioned is important to understand the dynamics.

mcgivor · December 2019

mike95490 said:

Do not buy the expensive AGM's until you have the bugs worked out, and a bank of Flooded, last you 8 years.

Actually I would suggest skipping AGM altogether and going LiFePo4, if temperatures can be controlled. For around 2× the price of FLA , which is comparable to AGM, it is a much simpler solution. No more anxiety regarding state of charge, absorption time, equalization woes, SG readings, watering, corroded terminals, overcharging, over dischargeing, short circuit protection, over temperature, cell ballancing, etcetera, etcetera, a good BMS will take care of the battery..

Lead acid batteries are dinosaurs of batteries , in all shapes and forms, they belong in the jurassic park of off grid, but just like the dinosaurs they don't tolerate the cold to well, so that has to be taken into consideration, I'm in a tropical location so naturally conditions favour the chemistry, your situation may differ.

dbarnard67 · December 2019

Good points McGivor. I am definitely looking at the LifePo4's. They also give you a greater DOD, which would allow for a small sized bank. By that I mean a 430ah FLA only gets 50% DOD, the LifePo4 could handle 80% so a 430ah bank could be replaced with a 240ah easily

mcgivor · December 2019

Although in theroy there may be some logic to reducing capacity however the better approach would be to replace with like capacity if that was working for you with LA. Keeping the discharge levels to ~ 20 SOC and maximum charging to ~95%SOC will extend cycle life significantly with LFP.
The most significant benefit is their ability to accept high current until charging termination, without the long absorption stage, meaning less time is needed, having more capacity than needed means a few days of marginal PV input would probably suffice as partial state of charge is not an issue.

Estragon · December 2019

Another point in favour of not reducing capacity by that much with LFP is although we try to limit DOD with FLA to 50%, we do still have the capacity available should it be needed. I like to know it's there in case the genny is being cranky or whatever.

My lithium drill battery invariably dies with the bit stuck in the work. My nickel one gives me a bit of warning.

FLA battery bank question

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