[RE-wrenches] Switching to LiFePO4

Tue Sep 17 09:28:39 PDT 2024

I have found that some of the older Outback FX, MX, and even some older FMs
don't like how the voltage rises; this can cause them to shut off charge
prematurely. I have found that the products made in 2008 and newer can be
configured with some tweaking to make it work, but the Lithium battery must
have its own BMS, and you have to be able to monitor SOC and Voltage.
 This applies to many products; I wouldn't be surprised if many older
legacy chargers struggle to charge LFPs. Many legacy inverters can have
issues charging LFP batteries, so when you install them, make sure you
commission them fully and check on them repeatedly to ensure that they are
charging correctly.

As for discharging, yes, try to keep them above 20% SOC, as going lower
will shorten cycle life. Many LFP manufacturers flat-out lie about them or
build them with a buffer to accommodate the deeper discharge.   Discharging
below 20% SOC will shorten the LFP lifecycle by up to 50%...

If you have parallel LFP batteries that are not connected in closed-loop
communication, make sure you balance them periodically, at least every 9-12
months. Failure to do so can lead to imbalances and over-discharge of the
unbalanced battery, which could "brick" the battery. Having a bit longer
absorb timer (20-30 min per parallel string) will help with this, but
programming short absorb timers will lead to balancing issues.   What
happens here is the voltage of the battery drops unevenly, and a large load
surging could draw the imbalanced battery below the minimum voltage,
causing the BMS to shut off to prevent cell damage due to discharge.
 Balancing is as simple as separating all parallel strings and charging
each battery independently until SOC is 100% across all parallel batteries.

Don't get cheap on connections. Install a positive and negative bus and
wire each battery to the bus with cables of equal size and length. Be sure
to use OCP on the positive conductors. This will make separation and
balancing periodically much more manageable and is an excellent idea
(Code requirements are going this way anyway) to prevent battery-to-battery
shorts in case someone drops a wrench or tools...  Trying to wire these
like you would three parallel strings of Lead with cables will induce
balancing/connection issues.

I have found that many customers buy LFPs expecting them to operate like
Lead. This is a huge mistake. Whatever you do, do not allow a 12v or 24v
LFP battery to go below its nominal voltage (10v or 20V for 12/24v
operation).  With lead batteries, namely flooded lead acid, you can do
this, and harm in the short run is minimal, but with lithium, doing so can
"Brick" the battery. At that point, your only hope is to place a regulated
power supply on the battery for a few days in hopes of recovering it.   We
make an S-Series battery that you can pull the cover off and apply a power
supply voltage to wake up the BMS. Still, you must be very careful doing
this because if cell damage occurs and you note higher than normal
temperatures when charging, the cells have been damaged. It's not a good
idea to continue using the battery.   This is a very costly lesson that
some have had to learn the hardway.

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On Tue, Sep 17, 2024 at 8:51 AM Todd Cory via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> I always read that lithium batteries were not compatible with Outback FX
> inverters... something about their limitations on voltage parameters.
>
> Todd
>
>
>
> https://forum.outbackpower.com/viewtopic.php?t=17565
>
>
>
>
>
>
>
> On Tuesday, September 17, 2024 8:42am, "jay via RE-wrenches" <
> re-wrenches at lists.re-wrenches.org> said:
>
> HI Dave,
> A whole new world.
> I didn’t realize how expensive the backwoods are, wow.
> There are many out there for around $1200 but not a lot in 24v.
> I have used many of the EG4 LL batteries, which at this point is one of
> the larger brands.
> I greatly prefer and only recommend batteries that have an active display
> that shows %, volts, amps, cell voltages, temperature.
> And I prefer ones that have a built in breaker.
> I don’t like ones with bluetooth as I’ve seen that fail when there is an
> issue and then you can’t see what’s going on as the bluetooth is down too.
> you’ll be really impressed once you get the hang of how differently they
> work.
> And as to size, to me its all based around days of autonomy.  Is 65%
> enough and to what DOD are you doing that?
> I usually only recommend running them down to 20%, sure you can go to 10%
> but anything less than that you’re in the zone of how accurate the % meter
> in the battery is.
> I’m sure you’ll get a whole lot of advice,
> good luck
> jay
>
>
> On Sep 17, 2024, at 9:19 AM, David Palumbo via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
> Wrenches,
> I have a nice little rental house here in my off-grid neighborhood that
> after 40 years is ready to transition to LiFePO4 batteries.
> I have no experience with any lithium home power storage batteries. I'm
> looking for advice, so I can avoid mistakes as a rental house with battery
> problems is quite the pain in the ass. The last tenant was my daughter so
> life with older lead acids wasn't a huge issue, but now I want something I
> won't have to enter the house to monitor and operate. I'll bullet what I
> think I know and my questions.
>
>    - The house has four 11-year-old Trojan Industrial IND 17-6 for 925 AH
>    @ 24V that are amply sized for the houses loads.
>    - It has a newer TriMetric meter that I was supposed to be able to set
>    up for web access using their WIFI module, but I have had no success with
>    being able to monitor battery state of charge remotely.
>    - I really need something that will give me battery state of charge
>    information without entering the house.
>    - The system has a single OutBack VFX3624. PV array is 2.5kW.
>    - System also has a Iota 40A charger so charging with my 6 KW genset
>    is typically in the 100Amp range with the OutBack and Iota.
>    - We are in northern Vermont, so we rack up significant generator (NOT
>    auto-start) run time in the winter months.
>    -  I'm looking at Eclipse LiFePO4 24V 200AH. Three of these will give
>    me 600AH @ 24V which is 65% of the rated Amp Hrs of the Trojan Industrials
>    now in use. Is this enough?
>    - My battery box can easily handle up to four of the Eclipse 24V 200AH
>    batteries. I see that Backwoods recommends that only three of the Eclipse
>    are connected with battery cables. If I opted for four (for 800AH) I would
>    need to use a busbar.
>    - Are there other distributors of Eclipse batteries other than
>    Backwoods Solar that I should consider? I haven't used my dealer account
>    with them for a number of years and I'm not sure that I'll get a good price
>    from them.
>    - What is the lead time for getting these batteries shipped out?
>    - Are there other LiFePO4 batteries I should consider?
>    - Is 600AH of LiFePO4's enough to replace 925AH of LA's?
>
> Dave Palumbo
> Retired from running Independent Power, but active in off-grid solar.
> Hyde Park, VT
> 802-371-8678 voice or text.
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