replacement battery pack

[janderson]

Hi All,

Years ago, I assembled a system with 3500 watts of PV, a Magnum Inverter, Midnight Classic charge controllers and 24 volt battery pack. The battery pack is comprised of 12 Rolls S550, 6-volt batteries in a 4S3P config (I think). Each battery is rated at 554 amp @100 hr rating. So, if my math is correct, this pack should supply 24 volt @1650A or 39.6 KW.

This system has been running around 7 years flawlessly but I'm concerned with the future life span of the batteries. Replacement cost of the battery pack today would be around $4800 with the upgraded replacement for the S550. I've been looking at various battery technologies, but it does not appear that that I can get anywhere near that capacity in better battery chemistry for the same money. Am I missing something? I sure would like the lower maintenance and deeper discharge rate of LiFePo if that were a viable option. Or perhaps another battery chemistry?

Any observations, thoughts and ideas would be appreciated......

 

[sunshine_eggo]

Hi All,

Years ago, I assembled a system with 3500 watts of PV, a Magnum Inverter, Midnight Classic charge controllers and 24 volt battery pack. The battery pack is comprised of 12 Rolls S550, 6-volt batteries in a 4S3P config (I think). Each battery is rated at 554 amp @100 hr rating. So, if my math is correct, this pack should supply 24 volt @1650A or 39.6 KW.

Math checks out. Consider that half if it is usable capacity for longevity.

This system has been running around 7 years flawlessly but I'm concerned with the future life span of the batteries. Replacement cost of the battery pack today would be around $4800 with the upgraded replacement for the S550. I've been looking at various battery technologies, but it does not appear that that I can get anywhere near that capacity in better battery chemistry for the same money. Am I missing something? I sure would like the lower maintenance and deeper discharge rate of LiFePo if that were a viable option. Or perhaps another battery chemistry?

Any observations, thoughts and ideas would be appreciated......

IMHO, Rolls are bulletproof. Have you been maintaining them, keeping SG on spec and equalizing as needed? If so, I would expect at least a few more years of reliable service. I keep trying to kill my 2S2P S-605, and they won't die.

Considering that you have 20kWh usable, that could be accomplished with about the same amount of DIY LFP 300Ah cells for a little less than the replacement cost of your Rolls. 23kWh of ~300Ah cells would run you about $3500-4000. You would have 3X 8S batteries in parallel with 300A total output.

 

[janderson]

Considering that you have 20kWh usable, that could be accomplished with about the same amount of DIY LFP 300Ah cells for a little less than the replacement cost of your Rolls. 23kWh of ~300Ah cells would run you about $3500-4000. You would have 3X 8S batteries in parallel with 300A total output.

I'm just getting started on my solar re-education -- any chance you have a link for those 300AH cells?

 

[Steve_S]

I decommissioned my Rolls Surette 22kWh(gross) S-550 Bank on January 1 as I hadn't used it other than put charge to it in over a year. I'm now running on only LFP (LiFePO4) and just love the result. Faster & Deeper charge, use up to 90% without a blink, Paralleled packs balance up nicely and share the load & charge very well. I was considering replacing the S550s with others and doing the math alone was the winning option.

I started with a single 24V/400AH Prebuilt which was a Scam with used batteries (16x175AH internally) & junk dumb BMS which almost caught fire (I felt the heat (really hot) and cut it off. That is the ShunBin Disaster. After that point I rebuilt it as 2x 24V/175AH and a good BMS. After that I built my 1st 24V/280AH and well... Now with 3x 24V/280AH + 2X 24V/175AH for 30.4kWh (1190AH)... Rural & Remote offgridder can be snowed in for days, so reserve up here is important.

Im also using a Midnite Classic-200, Samlex EVO-4024 Inverter/Charger.

LFP (LiFePO4) is the Safest and least expensive of all the Lithium Batteries out there. It's not hard to build a pack and set it all up. Configuring the Classics are a wee bit tricky but not crazy to do. These are Millivolt & Milliohm Sensitive so some extra care is needed when setting parameters.

One of our Best Known Vendors here is Luyuan Tech, owner Amy Wan does all communications and is great. Lot's written up about them.

Shenzhen Luyuan Technology Co., Ltd. - Lifepo4 battery, LTO battery

Shenzhen Luyuan Technology Co., Ltd., Experts in Manufacturing and Exporting Lifepo4 battery, LTO battery and 0 more Products.

szluyuan.en.alibaba.com

NOTE, to get a proper quote with Shipping to your home, you MUST open a Chat/Messenger session and provide teh info. The Shipping Guestimator is Way Off !

A SPECIAL NOTE ON Matched Cells.
Every vendor wil tell you that is what they sell. BUNK !
Virtually all of them get cells from Brokers not direct from the manufacturer.
These are Matched using a simple Battery Tester for Voltage & IR (Internal Resistance) at teh storage voltage, This is NOT Matched !
A Few like Luyuan do sell Properly Matched & Batched cells with complete test reports from the cycle.
Matching & Batching run charge/discharge cycles at different C-Rates and tests IR at each point, cells with match acroos the board are Batched, the ones that do not comply goto BULK or B-Grade.
ALSO: Matched cells will rate 10% Higher Gross Capacity than Non-Matched cells.
IE a 280AH Bulk cell may test out between 270-280AH Gross while a Matched Cell will test out at 282-290+AH Gross.
Gross AH is from 2.500V-3.650V per Cell (Full allowable Voltage Range.
Net AH is from 3.000-3.400V per cell which is LFP actual Working Voltage Range +/-0.050V.

WARNING !!!
Many terms used with Lead are also used with Lithium BUT it's not the same. We do not say DOD it is SOC for example and so there is a Learning Curve to put everything into the LFP Context. Everyone trips over this stuff at first.

Please see the links in my Signature, there is a LOT in there that can hellp you. If you cannot see signatures, check your user settings or ask for the links and I'll post them. The Luyuan Assembly guide has detailed voltage charts & more.

Good Luck, hope it helps.

 

[sunshine_eggo]

I'm just getting started on my solar re-education -- any chance you have a link for those 300AH cells?

What @Steve_S said.

I purchased my 280Ah cells from Amy at his link. It was a good experience, and I was happy with the cells as I have the ability to test them. These were "Bulk" cells that tested ~270Ah. This was BEFORE they were offering their current "matched" cells.

 

[janderson]

Considering that you have 20kWh usable, that could be accomplished with about the same amount of DIY LFP 300Ah cells for a little less than the replacement cost of your Rolls. 23kWh of ~300Ah cells would run you about $3500-4000. You would have 3X 8S batteries in parallel with 300A total output.

8S3P for 25.6V(840 A) = 21.5 KW?

Those prices from Amy are really great.

 

[sunshine_eggo]

8S3P for 25.6V(840 A) = 21.5 KW?

Those prices from Amy are really great.

Yep.