Battery Bank Expansion Question

[Juliet 15]

Greetings, all. Thanks to all for providing correction and suggestions to my last post ("Possible?"). I more appropriately named this one, and have a new idea/proposal for expanding my current battery bank.


I have a house bank of four 6v/230Ah FLA batteries, with each of the 2 pairs connected in series (to produce 12v) and the two 12v pairs connected in parallel (460Ah) to my inverter.



I want to add a 2nd almost identical bank of four 6v/415Ah AGM batteries, connected identically (two 12v pairs in connected in parallel for 830Ah.


Looking at my scribble-gram, I'm thinking I could use of of the large battery selector knobs to separate the banks. Does anyone see problems doing this? Essentially, I'd use one house bank, say the FLA bank (bank 1), down to its 50% limit, then switch to the AGM bank (bank 2) which allows use down to approx 80%.


Thanks again in advance.

 

[SteveK]

I see this working.
Before you start, determine how you will charge each independantly

 

[ranger58sb]

I have a house bank of four 6v/230Ah FLA batteries, with each of the 2 pairs connected in series (to produce 12v) and the two 12v pairs connected in parallel (460Ah) to my inverter.

I want to add a 2nd almost identical bank of four 6v/415Ah AGM batteries, connected identically (two 12v pairs in connected in parallel for 830Ah.

Why all that work? Why separate banks?

If space is available, why not make one big bank of 6x L16s? If AGM service advantages are part of your goal, Lifeline makes L16 AGMs...

-Chris

 

[DavidM]

From my reading, normal AGMs don’t have very different discharge limits than FLAs. Firefly AGMs are touted as having lower discharge limits but I doubt you are talking about them.

So why not wire them as one big 1290 Ah bank? Yes AGMs and FLAs have slightly different charging parameters, but IMO not enough different to matter. Sure makes managing the battery bank easier this way.

David

 

[tiltrider1]

The concept will work.

Before you get going, there are many important details that must be done correctly.

Recharging is an issue but it can be handled. Your wiring diagram is not correct as drawn, it suggests an out of balance wiring concept. You show no safety fuses.

While a manual system like this can work, you will be leaving your self wide open to human error which could lead you to two dead battery banks.

 

[Juliet 15]

Thx, all. Some.answers below.
1. I have an existing FLA 460Ah system. Theu are less than 2 yrs old, but their too little Ah.

2. I want a larger Ah system, so I bought the AGMs as they have near double the Ah.

3. I'd planned to pull out the current low-Ah batteries, and replace them with the new ones.
4. Then I realized, hmm, why not keep them and make one big bank.
5
So I asked on this forum if I can mix Ah batteries. Answer: no, I should not.

6. So, I'm thinking about doing it this way.

Lastly, I left out all the fusing and stuff. I'll have a marine electrician give me the safety stuff before I do it. I just wanted to see if it could be done this simply.


As for charging, I believe (but may be wrong?) that the bank selected on the selector switch will be charged. If I Empty both banks, I'll have to charge 1, then the other. I know, thats a potential forgetfulness hazard...


Once my smaller Ah batteries are due replacement I'll probably get 4 more of the larger Ah batteries and make it one big bank. Just didn't wanna throw the away.



Thoughts?

 

[SteveK]

As for charging, I believe (but may be wrong?) that the bank selected on the selector switch will be charged. If I Empty both banks, I'll have to charge 1, then the other. I know, thats a potential forgetfulness hazard...

If the charger is connected to the output line then it will want to charge the active bank. But it is the other bank that needs the charging, that is why you switched banks.
Charging unequal banks with one charger, I don't think will work.

 

[Portage_Bay]

Charging unequal banks with one charger, I don't think will work.

Wouldn't a multiple output charger work? I have a Sterling charger that handles 3 banks. In my case house, main engine and generator. Each receives the charge current it needs.

AGM and FLA have slightly different charge profiles. The Sterling can only be set for one charge profile for all 3 banks. For OP I'd use one of the AGM profiles or custom program the output.

 

[Bacchus]

Don't forget to research and consider proper fusing for large batty banks.
ABYC and best practice requires protection for fault current (dead short) for the batty bank installed. That is very different that protecting wiring for ampacity.
Many fuses under dead short / very hi amp simply weld them selves and don't offer protection.
CMS Marine How To and Steve D Antonio both have good articles with better explanation than I can offer. It's not a trivial matter and can save your boat if done correctly.

 

[SteveK]

Wouldn't a multiple output charger work? I have a Sterling charger that handles 3 banks. In my case house, main engine and generator. Each receives the charge current it needs.

AGM and FLA have slightly different charge profiles. The Sterling can only be set for one charge profile for all 3 banks. For OP I'd use one of the AGM profiles or custom program the output.

I have one that does 4 banks. I have not yet determined if it is 60 amp/4 or 60amp per bank. yes a multi bamk charger will work.

 

[Flatswing]

Greetings, all. Thanks to all for providing correction and suggestions to my last post ("Possible?"). I more appropriately named this one, and have a new idea/proposal for expanding my current battery bank.
I have a house bank of four 6v/230Ah FLA batteries, with each of the 2 pairs connected in series (to produce 12v) and the two 12v pairs connected in parallel (460Ah) to my inverter.
I want to add a 2nd almost identical bank of four 6v/415Ah AGM batteries, connected identically (two 12v pairs in connected in

I thought in your “possible” post, you added L16 FLA, but now the new batts are AGM which adds potential charging issues.
Check with the manufacturers web sites for the charging parameters for your L16 AGM & your FLA GC batts. Per Rod Collins (Marinehowto.com) optimum battery life is obtained by customizing the charger settings rather than using the stock “FLA” & “AGM” settings. I expect these may be significantly different for the 2 types you have.
Here are 4 choices:
1) customize your inverter/charger’s charge settings to your new $$$ AGM’s, use the manual switch to deplete/charge each bank accepting that the charge profile will be low for the LA batts and they will not last as long.

2) customize your inverter/charger’s charge settings to your new $$$ AGM’s but add a battery to battery charger to charge the FLA from the AGM’s. Manual switch set on AGM will only deplete AGM bank, manual switch set on FLA will deplete AGM bank until very low SOC then will deplete FLA, switch to AGM to charge both.

3) customize your inverter/charger’s charge settings to you new $$$ AGM’s. Add a good quality 3 or 4 stage battery charger to charge the FLA bank, manually switch to deplete each bank, switch to AGM to charge both banks. This will be a faster charge.

4) scrap/sell the GC15 FLA batts. Add 2 more identical L16 AGM’s to your existing 4 as others have already suggested and make your life much easier. Of course, customize your inverter/charger’s charge settings to your AGM’s, and add an appropriate sized JLLN type fuse to your new large bank.

Since you have already ponied up for the big AGM’s, option 4 is not that much more than the cost of additional chargers, wiring & fuses in options 2&3 but will be much more user & battery friendly since all the batteries will be essentially the same age-not to mention easier to integrate with additional charging sources like solar, additional battery charger or a second (paralleled) inverter/charger in future as your needs dictate.

 

[Bacchus]

I have one that does 4 banks. I have not yet determined if it is 60 amp/4 or 60amp per bank. yes a multi bamk charger will work.

AFAIK most chargers state the total out it is capable of. Could be conne Ted to one bank where that bank gets full A capable or multiple where it is divided depending on SOC / V of each bank and divides the output accordingly.
Also any I've looked at only have one profile setting.

 

[ranger58sb]

Thx, all. Some.answers below.
1. I have an existing FLA 460Ah system. Theu are less than 2 yrs old, but their too little Ah.

2. I want a larger Ah system, so I bought the AGMs as they have near double the Ah.

3. I'd planned to pull out the current low-Ah batteries, and replace them with the new ones.
4. Then I realized, hmm, why not keep them and make one big bank.
5
So I asked on this forum if I can mix Ah batteries. Answer: no, I should not.

OK, so why not sell off the smaller batteries after all (your #3, @Flatswing #4), use that to partially fund two additional 415-Ah AGMs? No need to leap through so many hoops, elegant outcome...

-Chris

 

[Juliet 15]

"OK, so why not sell off the smaller batteries after all (your #3, @Flatswing #4), use that to partially fund two additional 415-Ah AGMs? No need to leap through so many hoops, elegant outcome...

-Chris"



Yeah, I know,and those are good points. Bottom line, the new batts are $3200 for 4 ($500 was shipping), and I don't wanna spend another 3.2k right now. I'm hoping this is a relatively easy add-on. After my smaller batts die in a few years I'll replace them with big batts.

 

[Flatswing]

Bottom line, the new batts are $3200 for 4 ($500 was shipping), and I don't wanna spend another 3.2k right now. I'm hoping this is a relatively easy add-on. After my smaller batts die in a few years I'll replace them with big batts.

If you do this, you will want to keep them as 2 separate banks to preserve the life of the new ones rather than combine old and new (albeit same type/brand). If you prefer to consolidate into 1 large bank, consider adding 2 new (same AGM) now despite the $$$