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# Posted: 5 Sep 2023 12:05

Looking for thoughts on how to increase my electrical storage capacity. I currently have a 24V system with about 10kWh of storage in AGM batteries that are almost 10 years old (but still running strong). I don't want to mix old and new batteries, but could use additional storage capacity. I am considering adding a new battery bank (probably lithium) that I could charge from the original bank and use as a dedicated source for my refrigerator (which is a fairly consistent draw on a daily basis) and possibly for satellite internet (which I don't have yet but may be getting). This would also require a second (but smaller, less expensive) inverter. Typically I have significant excess charging capacity when it is sunny, so the electrical source end of the equation is not a problem.

Any thoughts on this multiple-bank idea? Is it stupid? Is there a better solution, short of a complete new (costly) system? I really don't want to jettison/replace the existing batteries, as they are working well, as is the original inverter.

# Posted: 5 Sep 2023 13:22

I originally started with Rolls Surette Heavy Lead but it just barely did what I needed. I then began to implement LFP in a parallel bank which I had setup using a BlueSea Switch which allowed for 2 banks.

Given that standard FLA & LFP have very similar charge profiles, it only took a bit of tweaking on my equipment: Midnite Solar Classic-200 solar controller & Samlex EVO-4024 Inverter/Charger.

I maintained my FLA Bank in Parallel with the LFP for 2 years as I built out my LFP Bank which is now at 1470AH / 36.7kWh. The lead was sent to recycle last year...

The only thing to remember is that with LFP there is NO EQUALIZATION! Strictly only Bulk/Absorb & Float, all of which are within the same charge profile for FLA or AGM pretty much. Also LFP takes charge Much Faster than Lead/AGM.

There is no need to use a separate SCC or Inverter....
My 24V LFP profile is as follows:

Midnite Classic Charge Controller Settings (Effective since Finalized build June 2022)
All equipment MUST BE Voltage Corrected & Calibrated (VERY IMPORTANT)

Divide Values X2 for 12V. Multiply X2 for 48V.
Absorb: 27.6 for 45 minutes (3.45vpc) (some call this boost) *I run a Bank of 5 packs, but never actually runs the full 45mins because of EndAmps
Equalize: OFF
Float: 27.5V (3.437vpc)
Min Volts: 21.2 (2.650vpc)
Max Volts: 28.6 (3.575vpc)
Rebulk Voltage: 25.6 (3.200vpc)
End Amps: 8.7A (*1) (** Using WizbangJr Smartshunt to control) (*** Allows for full Saturation at set Float Voltage)
(*1): End Amps is calculated from the LOWEST AH Battery Pack in a Bank. IE: (100AH X 0.05 = 5A 280AH X 0.05 = 14A. My Smallest 174AH is 8.7A)
NB: Victron Forum discussion says EndAmps = TailCurrent
Coulumbic Efficiency / Battery Status Meter Efficiency for LFP = 99%.
This gets the bank charged to full with high amps (Constant Current) and then float (Constant Voltage) tops off so the cells are at 3.47Vpc. I am running 7/24/365 so float is used up by the Inverter + provides whatever the packs will take to top off. (which is minimal)
* Do Not forget to adjust for Voltage Offsets between Actual Voltage @ Battery Terminal & at Solar Controller.

Very Special NOTE: Floating & Saturating to 3.437vpc, accounts for the Voltage Settling post Charge of any kind which actually brings the cells to just below 3.400Vpc.

When you start setting up an LFP Battery Bank, you can do it over time by adding packs in Parallel. They DO NOT suffer the aging degradation issues like FLA/AGM mainly due to how the chemistry works and the Battery Management Systems that control the cells. *Suggested* While you can even add different capacity packs (ie: 100AH & 200AH) without issues, it is best to try and stay close to same size packs. DO NOT PLAY THE Series & Parallel game, stick with 24V LFP Batteries, don't "do 12V in series for 24V" it only results in issues.

If you wish to make your own battery packs, I can provide a guide/manual more if needed.
The Distributor I use (and have for yrs) is a very known good vendor/supplier.

FYI on Weights...
LFP is much lighter than lead but it is heavy. A 24V Battery pack requires 8 cells.
105AH cell = 2.0kg ea
280AH cell = 5.4kg ea
305AH cell = 5.6kg ea

The supplier I put, supplies the busbars etc with the cells and all other components you need to assemble a pack. They also offer prebuilt units. Just peruse / browse and see what's there.

Hope it helps, Good Luck.

# Posted: 5 Sep 2023 19:46

10yr old AGM and looking for more capacity. Its prob time to replace them. Coming from a FLA user.

Lithium has come down and any lead based battery has gone up in the last few years. Granted you could just get a proper sized charger and charge them via a generator for a bit longer. Some times $10 worth of fuel a weekend is cheaper in the long run for a bit.

# Posted: 5 Sep 2023 20:22

Yeah that, my agm's lasted about 10 and started failing one by one, each fail brought down the bank's performance (the best the bank can do is to the worst battery). Futzed around the last year continuing to lose performance while deciding what to do.
Went LFP and wont look back
Fwiw, my target was use only the top 30% off the LA/agm, with LFP you can use 90% so each LFP is worth 2-3x the amp hrs/watts of LA to me and my use profile.

# Posted: 5 Sep 2023 23:02

Thanks all for the thoughts. Especially Steve for the detailed charge profile. I built my own LFP battery for my camper so may consider going that route - nice to have a recommendation for a decent supplier. I may get back to you for your suggestions on building up a pack. Seems that a swap over a couple years might be the ticket.

As of now, my AGMs (Rolls-Surrette) still seem to hold a charge almost as well as new. I have been very careful to keep the discharge below 20% for most of their life. They are only used 4 months of summer, and I have a maintainence solar panel on them over the winter (obviously I could not do that for the LFPs since temps here get well below zero in winter, but LFPs seem to hold charge longer than lead batteries).


# Posted: 23 Sep 2023 18:12

Steve S,

I'm back where I have better connectivity. Would like your input on redoing my battery bank, specifically sizing the BMS. Probably should do this off-site, so would appreciate if you could text me at your convenience: Seven75Seven62Seven550.

If you would rather keep it online, that is ok as well.


# Posted: 23 Sep 2023 19:15

Btw, one of the things I discovered in my degrading LA bank was poor connections. Pulled them all apart, cleaned and re-did; surprise, performance improved!
I got a season 'extra' than what I thought I would.

# Posted: 24 Sep 2023 05:42

I'm always happy to help if I can.
Building an LFP Battery Pack is not that hard and the sector is changing (for the better mostly). A 24V system is quite capable of a lot, my home runs off 24V Battery Bank system without issues.

BMS' systems for LFP vary a lot and TBH there is some great stuff & equally crappy stuff out there. Part of my "excursion" into this was evaluating several BMS and you really do not want to know how much cash was spent, that is now sitting in boxes. Simply put, enough for a couple of more battery packs (complete)... The JKBMS with Active Balancing, BlueTooth app (Droid & IOS) and interconnectivity between BMS & Smart Inverters + are actually a really good value and DO WORK AS INTENDED. They've just released a new family of BMS' based on suggestions from some of us which incorporate a lot of things previously not avaiable, like Upgradeable Firmware for one, as well as Open Connectivity to multiple devices.

In general terms, the BMS chosen (to handle a specific amperage) has to be able to support constant 1C output but also handle the surge demands. LFP can handle 2C surges without issue (at cell level). I will NOTE that once you want a battery pack to deliver over 200A constantly, then a Relay/Contactor based BMS is really the only option.

My system as a use case. (24V)
As of "today" I am running 2x174AH, 2x280AH, 1x105AH. By end of next week there will be my final 280AH Pack put into place. All of my BMS' are JKBMS with 2A Active Balancing and rated for 150A Continuous. (The 105AH is adjusted slightly different of course). Now that will be 6 Battery Packs capable of delivering 900A Continuous if required (has never happened)... The Beauty of Packs in Parallel !

Cells: So much pallaber on the cells and what things mean... Cutting to the chase and skipping dogmatic feelings... There are many vendors and marketters who flog stuff and misrepresent a lot. So a KISS response.

I will recommend a Vendor I have used numerous times as have a LOT of others in Europe, North America who is also shipping to our folks in Africa & Downunder with excellent results. They are NOT the cheapest out there but you do get exactly what you paid for... Complete with Factory cell test reports on each cell you get. I have used Direct Transfer and VISA with them and never ever an issue.

Contact Amy Wan on their Chat/Messenger, she is the owner of Luyuan, I'll drop her a note to expect you, just give her your name ATLINCABIN and she'll get you organized.

ProTip to save Cash !
If ordering cells, consider ordering the BMS' and additionals from one place, which in turn gets put into the packaging and sent at once. This does cut $hipping because there is a min charge for any box + weight/destination fees... you'd be shocked at how fast that adds up.

If you would also like a nice Steel Case that makes packs stackable, Luyuan has now made available Boxes for 8S/24V Batteries that can take 200-300AH cells. These are actually a good deal (especially when looking at the competitors prices).

Lastly, they can even assemble & test everything if you want for an extra fee, but when you work out the cost of X# of boxes shipped and do the math, it actually ends up cheaper on the bottom line as in a sense you get one heavy box with everything already put together instead of several boxes that cost too much to ship.

There are suppliers in the USA for Battery Cells, BMS etc but I have not personally dealt with them. While their "material" may be already in the US and available quickly, I have to say, they have a Generous Premium for the convenience.

# Posted: 24 Sep 2023 05:46

ATLINCABIN : I just sent a headsup to Amy to expect your contact.

# Posted: 24 Sep 2023 06:59

Some information for anyone who wants it.
Links below are various resources I put together over the last couple of years.

Basic guide to assembling an LFP Battery Pack (PDF)

LFP Voltage Chart with Curves. (PDF) 12-24-48v.109/download

Supplemental Voltage Chart- handy to have at hand (JPG)

# Posted: 25 Sep 2023 11:25

Steve S,

Thanks again for the info. I'll be in touch with Amy.

My biggest question is regarding how to set up battery banks with a BMS. A summary of my setup: Magnum inverter, 24V, 4000W. I rarely (if ever) draw a full 4000W but want to cover myself in case I ever do. 1000W of solar panel for input.

It sounds like you have set up several banks in parallel, each with their own BMS. If that works, then I could probably do similarly using two straight banks (per page 10 of the basic guide), each with a 100A or 120A BMS. That would allow me to draw 100A x 24V = 2400W from each bank and be limited by the capacity of my inverter. The alternative is to set up the system as a 2P8S block, which would only require a single 200A BMS. Is there an advantage of one over the other? In my mind, the pro for two-bank system is that one bank could be disconnected if there is a problem and I would still have power. The pro for the 2P8S system is that it is integrated and has only a single BMS, thus keeping all the cells equalized better. If there are no other considerations, then I would likely opt for the two-bank system. And if parallel banks work ok, then it would be easy to add capacity if desired.


# Posted: 25 Sep 2023 12:03 - Edited by: Steve_S

A bit of clarification.
Bank = a Collection of complete batteries operating as one power source. These can be any battery type.

Independent standalone batteries in parallel provide redundancy & fallback. They also divide & share both Load & Charge reducing stress in a sense. If one fails for any reason the other continues.

My own system has 1 Bank of Batteries.
2x174AH, 3x280AH (soon to be 4) & 1x105AH.

Paralleling Cells within a battery pack is tricky and NOT recommended unless you have fully Matched & Batched cells. These cells will have the same IR (Internal Resistance) throughout the working voltage range. Unmatched / will lead to imbalances and faults over time. This is a simple fact. Consider that any EV built must have perfectly matched & batched cells for proper longterm operation and safety.

Below is my current system more or less, it is the last revision of my logical diagram which I will update after I am done with the final changes.
Each battery has a JKBMS B2A24S15P BMS'. They have 2A Active Balancing, and handle 150A, BlueTooth, RS485/RS232 (These are the older models) My Bank is so large because of my location and I wanted 10 Days Reserve because in winter it can be dark for some time... I only use 3.5-4.0 kWh per day year round and I am FT here.

I use a Samlex EVO-4024 Inverter/Charger. I charge @ 80A from Genset when required (rare). I have taken it out to 4000W which pulled 155A +/- from the bank and even pushed it past that by using my MIG welder... Never pulled more than 220A from the battery bank. I have also pushed 250A Charge into the bank from Solar + Inverter/Charger + Supplemental charger...

My final config incorporates another Midnite Classic-150 in Parallel & 2300W of panel which will provide a total of 170A Solar Charge at peak... Of course that is being setup to compensate/offset for winter generation so it's not actually going to work out that way.

My last logical diagram

More info on my system (as is before final changes to be finished) here... There is a LOT more info here, just scroll through it... -120vac.1484/

# Posted: 25 Sep 2023 12:13

Damn it... this forum won't let me include images from outside anymore... Well look at my last link there and more will become clear.

I use a BlueSea Switch which allows for 2 Battery Banks but as 1, or 2 or both used at once. Simplifies my life for maintenance and control and also because of my busbar/fuse setup... each battery pack is connected to a 200A MRBF fuse at the busbars.

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