DIY 24v 340Ah LiFePO4 Battery Boxes

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AlBargey
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Re: DIY 24v 340Ah LiFePO4 Battery Boxes

#21

Post by AlBargey »

Well I thought I'd give a little update on how the LFP is doing compared to our old Pb bank.

Firstly I will disagree with @Stinsy: LFP is not boring, it is very interesting! :ugeek: But yes, I can now charge harder and faster without watering and with fewer losses.

I have had a few issues with my communication and driver mods to show everything on the Victron system, but that's more me being a bit obsessed with making the integration provide data and keeping a closed loop control system all up to date on Victron VenusOS.

As I didn't top balance the cells, thinking they were close enough after first charging them to just under my target 28v (3.5v p/c) before just using them, I then found it took two months during winter to properly balance them all to around 5mV at the end of every absorption. I also found I had to ramp down the final charge current as the voltage increased to stop a few runners from hitting 3.5v before the rest, and they tended to be the cells that had a lower SOC but would start to balance down as their voltage was higher, but then the others caught up and the first runners were now lower from from earlier balancing.

I use Dbus-SerialBattery driver for Victron VenusOS to set the charging algorithm and closed loop controls, It's the most comprehensive charge control parameter set I've seen, all configurable too. As I have three JK BMS's I also use Battery Aggregator to allow them all to be aggregated and able to send charging parameters and alarms to VenusOS on the CerboGX (the central brain) and then to the mppt's / inverter.

It all works well, and you can see in my signature a link to the live data, or even select the advanced tab and look at different date ranges for the graphs I've set up.

It can go wrong though, like last night when I decided as everything was running so well, why not update it all... :idea: and quickly found the updates broke the BMS communication, and Victron in their wisdom has decided: if a BMS loses coms it will shut down the Inverter! :head-bang: then I'm scrabbling around in the dark trying to figure out how to sort it.. :oops:

Reminder: We're off grid with a diesel generator backup, so not ESS as most here are, but thought I'd compare the efficiencies of our flooded Lead (Pb) batteries this time last year, with the 26kWh of LFP. here are our updated efficiencies of both the batteries themselves and the system efficiencies, taken a few days ago:

Last 90 days on LFP:

Solar = 657kWh

Generator = 302kWh

Consumption = 758kWh

758kWh / 959kWh = 79% System Round Trip Efficiency

With Pb over the same 90 day period last year:

579kWh / 891kWh = 65% System Round Trip Efficiency


LFP:

SmartShunt 100% to 100% SOC - Discharged: 687kWh - Charged: 717kWh = 96% Battery Efficiency

Pb: (Old Bank)

SmartShunt - Discharged: 4,453kWh - Charged: 5,684kWh = 78% Battery Efficiency


So a 14% System efficiency gain from Pb to LFP, or 18% battery only efficiency gain from Pb to LFP. 14% of last years 90 day 891kWh generation = 125kWh lost due to Pb inefficiency, or 14% less diesel needed with LFP! - That's all quite exciting. :)

Obviously there are many variables if anyone is comparing theirs to ours, and we don't have an ESS setup that may have more AC-DC losses vs our DC MPPT's and only self consumption, but it's still an interesting comparison of LFP vs the old Pb.

TLDR: It works well (normally) :D
Last edited by AlBargey on Sat Mar 23, 2024 5:03 pm, edited 1 time in total.
38m Barge, Solar (10.6 kWp), 26 kWh of LFP, 50kWh Akvaterm Thermal Store (750l)
Victron Quattro 8 kVA, CerboGX, 3,500L STP, 57kVa Perkins
Our live data: https://vrm.victronenergy.com/installat ... e/c76c4bf6
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nowty
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Re: DIY 24v 340Ah LiFePO4 Battery Boxes

#22

Post by nowty »

I concur, I used to get about 67% full round trip on forklift LA and now I'm around 80% with lithium. Interestingly I used to get 90% DC to DC round trip out of my LA, so much higher than yours but they were probably newer than yours at the time.
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AlBargey
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Re: DIY 24v 340Ah LiFePO4 Battery Boxes

#23

Post by AlBargey »

nowty wrote: Sat Mar 23, 2024 12:29 am I concur, I used to get about 67% full round trip on forklift LA and now I'm around 80% with lithium. Interestingly I used to get 90% DC to DC round trip out of my LA, so much higher than yours but they were probably newer than yours at the time.
That is very similar!

Yes my OpZs Pb were probably well used, they were giving a higher round trip efficiency in the beginning, but I was the 3rd owner, they've now gone to their 4th, also it's the total lifetime efficiency since I got them until sold them.

I think the figures will vary throughout the year, I'm going to try and keep a note of it.
38m Barge, Solar (10.6 kWp), 26 kWh of LFP, 50kWh Akvaterm Thermal Store (750l)
Victron Quattro 8 kVA, CerboGX, 3,500L STP, 57kVa Perkins
Our live data: https://vrm.victronenergy.com/installat ... e/c76c4bf6
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Joeboy
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Re: DIY 24v 340Ah LiFePO4 Battery Boxes

#24

Post by Joeboy »

Might be worth investing in a battery operated motion sensor/low light led flood for the battery room Al? You won't need it until you really do!

I have a few LED's hooked onto my batteries so I don't do full stumble in the dark. Also a couple of led striplights tagged back to 12v batts. Looks like it's worked out well for you. Hopefully genny off soon for the Year? Does your solar setup max out the battery charge on a good day?
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AlBargey
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Re: DIY 24v 340Ah LiFePO4 Battery Boxes

#25

Post by AlBargey »

Joeboy wrote: Sat Mar 23, 2024 7:59 am Might be worth investing in a battery operated motion sensor/low light led flood for the battery room Al? You won't need it until you really do!

I have a few LED's hooked onto my batteries so I don't do full stumble in the dark. Also a couple of led striplights tagged back to 12v batts. Looks like it's worked out well for you. Hopefully genny off soon for the Year? Does your solar setup max out the battery charge on a good day?
I do have a rechargeable LED in the battery chest, but fortunately the Cerbo is in my workshop and the GXtouch display is in the living room close by, so I can scratch my head sitting on the sofa with laptop, headtorch and candles / camp LED lights if I need to.

We haven't had to put the genny on since the 25th Feb! The batteries have been fully charged a fair bit recently and I've been putting on extra electric radiators and all the washing etc when the suns out!

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38m Barge, Solar (10.6 kWp), 26 kWh of LFP, 50kWh Akvaterm Thermal Store (750l)
Victron Quattro 8 kVA, CerboGX, 3,500L STP, 57kVa Perkins
Our live data: https://vrm.victronenergy.com/installat ... e/c76c4bf6
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