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Old 06-15-2021, 07:02 PM   #1
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Can I have 2 battery banks ?

Hi yall.
Ok I have 4 3.2v 100ah LI batteries connected in series(I believe that's correct) to become 12v 400ah LI. And I also have 2 200ah 12v gel batteries connected parallel.

I also have a dc to dc alternator/solar charge controller.
And a regular solar charge controller.

Oh and a 2000 w pure sine inverter charger
And a 3500 w inverter.
But they are different brands.

I was wondering how/if i can use both battery banks together. If I can how?
And if I can use both banks can I use bother charge controllers? What about the inverters?


Also
I sadly only have 300 watts of solar.
Do you think I should get more solar

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Old 06-15-2021, 07:23 PM   #2
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I think the issue would be that each bank of batteries is a different chemistry .. likely has a different charge and float voltage.. you definitely only want batteries of the same voltage and charging profiles together...
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Old 06-15-2021, 07:39 PM   #3
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I have my 'original' double lead/acid batteries linked in a bank behind an isolator and connected to the chassis batteries, but completely separate from the 280 AH LiFePo setup.

I researched linking up those two banks, but ultimately decided to leave the lead acid batteries in place but not connect them to anything. The charge requirements and controls are different and it just seemed silly to invest in more equipment to try and leverage that system. They function well as a jumpstarter setup (used it once when I flooded the engine).
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Old 06-15-2021, 08:21 PM   #4
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It IS possible to do this (combine chemistries), but itís not worth your time or the investment. Itís a mess, and generally a bad idea.

As KC says, they have different voltages, but thereís a way to deal with that. Itís always going to be a kludge.

300W isnít a lot, but itíll give you 1.5kWh on a sunny day. That may or may not be enough. Itís definitely not enough on overcast days or during the winter.

If you are hell bent on using both, get another few hundred watts of solar and have two parallel, unconnected systems.

If you have an abundant supply of used lead acid batteries in the future, use those. Otherwise, when the lead acids die, move the whole system over to LFP.

You have two battery banks, you have two inverters. Solar is cheap and so are charge controllers. Easy choice!
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Old 06-16-2021, 12:10 AM   #5
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Quote:
Originally Posted by Misfit_offroader View Post
Hi yall.
Ok I have 4 3.2v 100ah LI batteries connected in series(I believe that's correct) to become 12v 400ah LI.
No, ah doesn't add up when in series. You'll get 12v 100ah.
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Old 06-16-2021, 06:22 AM   #6
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Quote:
Originally Posted by Misfit_offroader View Post
Hi yall.
Ok I have 4 3.2v 100ah LI batteries connected in series(I believe that's correct) to become 12v 400ah LI. And I also have 2 200ah 12v gel batteries connected parallel.

I also have a dc to dc alternator/solar charge controller.
And a regular solar charge controller.

Oh and a 2000 w pure sine inverter charger
And a 3500 w inverter.
But they are different brands.

I was wondering how/if i can use both battery banks together. If I can how?
And if I can use both banks can I use bother charge controllers? What about the inverters?


Also
I sadly only have 300 watts of solar.
Do you think I should get more solar
When you connect in series, the voltage adds up, the current capacity remains the same. 3.2 *4 gets you the 12v at 100 AH.
Do you need more solar? Lol. We have 327W x 12 and we are thinking about finding real estate for four more.
We have 6 BYD 24V 220AH batteries in parallel for 24v x 1320 AH. Of course we would like 2 more.
You can have 2 separate battery banks of different chemistries, however not on the same solar array.
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Old 06-16-2021, 10:54 AM   #7
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I would not combine banks like others have said. However you could charge each battery bank, each using their own charge controller but the same PV array. For AC charging you'd need one charger per bank.

One pattern is to combine them with a battery selector:
https://www.amazon.com/Blue-Sea-Syst...3854907&sr=8-4

Use the lithium, then if that ever runs out on you, you can flip over to the lead acid. Nice little backup.

Another pattern is to put different loads on different banks. Inverter on lithium, sippy DC appliances on the lead acid. Same concept- two charge controllers, same PV array, or one AC charger per bank.

Could also use the lead acid for dedicated use cases like a winch or external lighting.


Also, put at much solar up as you have space, budget, need for.
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Old 06-16-2021, 01:18 PM   #8
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To further clarify what others have mentioned:

When you connect batteries in series, the voltage is multiplied, but the energy density remains the same.
ie - 4-3Volt 100Ah batteries wired in series = 12Volts 100Ah

When they are wired in parallel, the energy density (AmpHours) is multiplied, but the voltage remains the same.
ie - 4-3Volt 100Ah batteries wired in parallel = 3Volts 400Ah

Another example could be 2 pairs of the batteries wired in series, and then those 2 pair wired together in parallel (also known as 2S2P), which would = 6Volts 200Ah
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Old 06-28-2021, 03:17 AM   #9
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Quote:
Originally Posted by kazetsukai View Post
I would not combine banks like others have said. However you could charge each battery bank, each using their own charge controller but the same PV array.



OK, got lost here. 1 step at a time. How do the 2 charge controllers split up the time on the panels? Can they both use the panels at the same time?
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Old 06-28-2021, 12:45 PM   #10
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Quote:
Originally Posted by kidharris View Post
OK, got lost here. 1 step at a time. How do the 2 charge controllers split up the time on the panels? Can they both use the panels at the same time?
You can connect multiple MPPT chargers to the same set of panels, same as if you had multiple DC devices connected to a battery. Who will get how much power if there's not enough PV to fully satisfy both controllers is hard to say.



Lets say you have 200W of solar and two 12V 10A MPPTs connected. The MPPTs can in theory draw 240W total, but given there's only 200W available, that 200W will be split between the two MPPTs in some way. It could be 140W to one and 60W to the other, down the middle, or otherwise. Many MPPTs you can configure a rate limit to help facilitate this.



Also, the bank less used is more likely to remain (near) full and not need much to stay topped off.
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Old 06-30-2021, 03:20 PM   #11
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Our photovoltaic array is six 305-Watt panels for a total of 1,830-Watts.
These feed our AGM bank.
Our AGMs were new in 2003, and we rarely empty them past a couple-three percent.
.
Q -- Do I think you need a larger photovoltaic system?
A -- I think you could live with it a while as you learn to reduce your needs.
.
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One of my guilty pleasures is reading the posts at IRV2, a massive forum for owners of the equivalent of Shiny! BillionBuxBus conversions.
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