Battery Question

[tpbrady]

I have 6 FireFly batteries arranged in 2 banks that are performing strangely.
Under a 20 amp load on a single bank with a theoretical capacity of 348AH, after about 4 hours drawing around 20 amps (81 amps on the Smart Shunt), I start getting low voltage alarms and the voltage under load has dropped to 11.57. After removing the load the voltage recovered to 12.57V in just a few hours indicating greater than 80% SOC.

This morning I continued the recommended recovery procedure which involves drawing down a fully charged battery to 10.5v and fully charging it. I put a 12 amp load on one bank which should draw the batteries down to 10.5v resting in around 30 hours. To speed the process up, I switched the bank over to running the inverter putting a 20A load with the starting voltage of 12.5v while running the 12A load already on the bank. With combined load of 32A on the bank, the inverter switched off within 20 minutes when the battery voltage reached 11.5v. The battery voltage quickly returned to 12.3v with the 12A load attached.

It seems that a load greater than 20A but less than 32A pushes the battery bank over a cliff where the voltage drops quickly. I have not seen this before. The batteries are 3 years old.

Tom

 

[DavidM]

I suspect having two banks is the root cause of your problems.

David

 

[BruceK]

I suspect having two banks is the root cause of your problems.

David

How does that work?
I don`t know the answer, or the type of battery involved but, batts are 3 years old, issue appears new, suggesting something new arising. Or maybe battery age is involved.

 

[Delfin]

I have 6 FireFly batteries arranged in 2 banks that are performing strangely.
Under a 20 amp load on a single bank with a theoretical capacity of 348AH, after about 4 hours drawing around 20 amps (81 amps on the Smart Shunt), I start getting low voltage alarms and the voltage under load has dropped to 11.57. After removing the load the voltage recovered to 12.57V in just a few hours indicating greater than 80% SOC.

This morning I continued the recommended recovery procedure which involves drawing down a fully charged battery to 10.5v and fully charging it. I put a 12 amp load on one bank which should draw the batteries down to 10.5v resting in around 30 hours. To speed the process up, I switched the bank over to running the inverter putting a 20A load with the starting voltage of 12.5v while running the 12A load already on the bank. With combined load of 32A on the bank, the inverter switched off within 20 minutes when the battery voltage reached 11.5v. The battery voltage quickly returned to 12.3v with the 12A load attached.

It seems that a load greater than 20A but less than 32A pushes the battery bank over a cliff where the voltage drops quickly. I have not seen this before. The batteries are 3 years old.

Tom

It would certainly appear that the batteries have lost a lot of capacity. Carbon foam is supposed to be resistant to capacity loss due to undercharging, but that doesn't seem to be the case here, or perhaps there is another cause. Twere me, I guess I would put a load on them to drain them completely, recharge and repeat a few times to see if capacity can be recovered. Check with Firefly to verify that driving the bank to 5 vdc or so won't cause some issue with that chemistry.

 

[tpbrady]

Delfin,

That's what I am doing one bank at a time. It acts like batteries that have developed a high internal resistance. Once the load reaches a certain point more energy is consumed in the battery than it is providing to the load.

Tom

 

[Delfin]

Delfin,

That's what I am doing one bank at a time. It acts like batteries that have developed a high internal resistance. Once the load reaches a certain point more energy is consumed in the battery than it is providing to the load.

Tom

It might just be one battery, but I suppose if both banks act the same way independently, the problem is systemic. PITA, but you may have to do the recovery and test one battery at a time to see if there is a single culprit.

 

[tpbrady]

Delfin,

I am pretty sure it is systemic as my first troubleshooting was to isolate each battery for a few hours and measure the resting voltage. In that test they were all within .2v of one another, so I ruled out a single battery. I then tested each bank isolated and saw identical performance on each bank isolated. After that I started the recommended recovery procedure from Firefly. It's taking a little while as I can only put a 10-12 amp load on the isolated bank. I'm still trying to come up a way to put a bigger load on the batteries to speed the process, but inverters are out due to low voltage disconnects. I learned one thing about a Victron Multiplus in the Inverter only mode when connected to shore power. In that mode, it ignores the shore power and only provides AC through the inverter from the batteries. I would have thought it would have passed the AC power through from the shore. I am going to look at the Victron documentation and see if it is a setting issue.

Tom

 

[Gordon J]

I have 6 FireFly batteries arranged in 2 banks that are performing strangely.
Under a 20 amp load on a single bank with a theoretical capacity of 348AH, after about 4 hours drawing around 20 amps (81 amps on the Smart Shunt), I start getting low voltage alarms and the voltage under load has dropped to 11.57. After removing the load the voltage recovered to 12.57V in just a few hours indicating greater than 80% SOC.

This morning I continued the recommended recovery procedure which involves drawing down a fully charged battery to 10.5v and fully charging it. I put a 12 amp load on one bank which should draw the batteries down to 10.5v resting in around 30 hours. To speed the process up, I switched the bank over to running the inverter putting a 20A load with the starting voltage of 12.5v while running the 12A load already on the bank. With combined load of 32A on the bank, the inverter switched off within 20 minutes when the battery voltage reached 11.5v. The battery voltage quickly returned to 12.3v with the 12A load attached.

It seems that a load greater than 20A but less than 32A pushes the battery bank over a cliff where the voltage drops quickly. I have not seen this before. The batteries are 3 years old.

Tom

The problem is most likely that while at dock you are keeping the charger on float. Firefly's don't like that. To get you capacity back discharge batteries to 10.5 volts. Recharge fully at .4C, discharge back to 10.5 volts. This should restore you back to 100 percent or better. You can find a full write up on line. Bottom line, don't use a float charge. Charge fully and periodically recharge.

 

[Jeff F]

How is each bank charged? There's a root cause here somewhere.

IIRC the low voltage cutoff on the inverter is adjustable. You should be able to run down to 11v or maybe lower.

Hope you can recover the batteries.

 

[JAllen]

Last year we discharged our batteries to 4 volts.
I was put in contact with a real engineer who helped me recover our batteries. I asked him about the charge profiles. He indicated that you can keep the batteries in float mode and don’t have to charge them up and draw them down.
I checked the updated manual on line and the verbiage about no float had been removed. I am curious then if they have gone back to the position of “No Float."

 

[SailorGreg]

Last year we discharged our batteries to 4 volts.
I was put in contact with a real engineer who helped me recover our batteries. I asked him about the charge profiles. He indicated that you can keep the batteries in float mode and don’t have to charge them up and draw them down.
I checked the updated manual on line and the verbiage about no float had been removed. I am curious then if they have gone back to the position of “No Float."

I have Firefly as well. I doubt there is any new guidance coming out regarding float for these batteries as the company went out of business a year ago. The 2020 and 2021 versions of the manual say float is not necessary, but don’t suggest float is harmful, although I think it is. ( my experience, so admittedly not definitive)
That said, I have had enough experience with ours to suggest they do not like to sit on float for extended periods. I have compared performance with and without sitting on float for long periods. At the dock, I fully charge them, which means achieving the required tail current, leave them on float for 24 hrs, and then disconnect them. I can’t completely eliminate all battery loads, but can get to -3A or so, which allows me to go a week or so between charges.
I don’t know Victron, we are Mastervolt, but I suspect you can select shore power pass through so you can keep your AC systems running while the batteries slowly drain.
For the deep discharge restorative cycle to work, you need to be able to charge at .4C ( or close to that) and achieve a tail current of about 2-3A ( I am guessing at that value, based on your configuration). Not sure how a Victron charger handles the absorb to float decision and how much control you have.
Two years ago, with one year on the battery bank, I thought my batteries were toast, as they behaved like yours. I added charging capacity, switched from Balmar to Wakespeed regulators ( because the Balmars could not hit the tail current reliably), and avoided float for extended periods. If I am at anchor for extended periods I do a full charge every two weeks, one way or the other. And I do a restoration charge every 6 months or so.
Not to be impolite, but I would ignore any guidance that doesn’t begin with “…I have Firefly batteries also….” . These batteries behave somewhat uniquely, compared to other AGMs.
Good luck

 

[JAllen]

I am surprised they went out of business. A few knowledgeable people liked the product. One of the reasons I went with these. I am hoping these hold on until some of the newer technology trickles down. Come on solid state batteries.
This is a response I got this afternoon from the engineer after I asked again about a float profile.

"Hi Pat - The manufacturer recommended the 14.4v bulk /absorp and the 13.4v float. However, very early on, one of their engineers also said that the battery really did not need a float - so fully charging it, and then simply letting it sit or discharging until the next charge cycle.
So likely, either approach is valid.
BTW - Firefly has gone out of business, but we are still supporting our clients who purchased them.
Regards, Tom & the OPE Team."

 

[Don L]

My FireFly batteries did something similar to the OP last year and then in a matter of weeks could not even run the freezer at night. Meaning they were near death after only 2.5 years! Of of course this was after I had left staying in the marina a the start of a 6 month trip. Sp I replaced them.

If you batteries suddenly start acting different/bad it means they are drying and the best you can do it replace on your terms not theirs.

 

[tpbrady]

I did the restoration procedure on one bank. It seemed to take forever using a 10A load, something like 23 hours after I drained them down with the inverter until the inverter disconnected. I would characterize the problem as not capacity, but voltage drop on anything other than a light load. When draining the bank with the 10A load, the voltage would be down to 10.5 under the load and then when disconnected jump back up to 11.9 after resting. It took quite a while to get them to the point where the resting voltage was under 10.5.

I will go through the rest of this year with these but then probably replace them with 2 or 3 200AH LFP batteries meeting UL1642. I can do that for less than what I paid for the FireFly's and my charging system is already half way there.

Tom

 

[twistedtree]

It's too bad to hear that Firefly batteries aren't holding up over time. I know a lot of people who went that route because LFP products weren't mature enough at the time.

 

[Jay N]

tpbrady -


Hi Tom.


How are you doing with your Firefly bank/Victron inverter? Any followup conclusions?


WESTERLY has 7+ years on her Firefly bank, a capacity test in January of this year indicated the bank of 6 Group 31's still has around 94%. Yes, I float full time at 13.4v.


Overall, service has been good with about 135,000 Ah taken from the bank since install in April 2016.


Cheers, Jay

 

[tpbrady]

Jay,

I don’t think it is a loss of capacity as all metrics of consumption versus standing voltage after rest indicate 95% plus capacity. The problem is the operating voltage under an 18A load on 3 batteries in parallel is 11.9-12 volts with a standing voltage of 12.3 volts after rest with no load. Basically when I drop below 70% SOC the inverter is right on the edge of shutting down due to low voltage. I lowered the low voltage disconnect on the inverter to 11.5 volts and that has made things better. I am running the inverter much more this year to keep the Starlink on line. It just seems the voltage drop under load seems excessive.

Tom