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Old 04-27-2023, 04:30 PM   #1
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THOR #16721
Discoveries on my lead-acid to lithium battery conversion

This is my opinion why lithium coach batteries should never be a "drop-in" replacement for lead-acid batteries.

My motorhome came equipped with a Trombetta CYH/603 relay and associated Precision Circuits Isolator Relay Delay module (IRD).

The following description uses general terms such as "fully charged" and "low voltage". There are specific voltages involved, but for the purposed described here - general terms suffice.

The Trombetta is merely a DC solenoid switch used to connect (parallel) two separate batteries. The IRD is the brains - it senses voltages between the two batteries and sends a signal to either open or close the Trombetta, effectively connecting/disconnecting the two batteries.

The function of the IRD is primarily to protect the chassis battery from being discharged by loads on the coach batteries. The Trombetta incorporates a "fail safe" emergency start switch which allows the two batteries to be temporarily connected - providing a "jump start" scenario of the chassis battery using available power from the coach batteries.

The original IRD setup has two shortcomings with LifePO4 batteries:

1) Overloading the chassis alternator.
When driving (using the alternator), if the chassis battery is fully charged, the IRD connects and "shares" the charging voltage with the house batteries. Due to the low resistance nature of LifePO4 batteries, they (by design) can potentially draw a very high current while charging, which can severely tax the alternator causing premature failure.

1) Overcharging the chassis battery.
When connected to shore power using the converter, the IRD is sensing the voltage from the house LifePO4 batteries. Since lithium batteries have a higher charging voltage range (charge profile) before BMS cutoff (fully charged), a potentially high current may be passed to the chassis battery - creating an inadvertent overcharging situation of the chassis battery.

There is a third problem not related to chassis/coach battery isolation... the charging profile difference between lead-acid batteries and LifePO4. The stock converter in most motorhomes is designed to charge lead-acid batteries. It will reduce current before LifePO4 batteries are fully charged - creating a continuous under-charged state. Your lithium batteries will never fully charge. Newer converters have a switchable profile to handle the different battery chemistries. OR - remove the existing converter and replace it with a lithium compatible charger... usually a combination inverter/charger.

Although not perfect, the Precision Circuits Li-BIM 225 Battery Isolation Manager (Li-BIM) provides at least some measure of protection:

According to Precision Circuits specs, with the engine running, if the chassis battery is fully charged the batteries are connected for no longer than 15 minutes, then disconnected. After 20 minutes (alternator cool-down) the voltages are reevaluated and the cycle repeats.

If the chassis battery is low, and the coach lithium batteries voltage is above 13.5 volts, the batteries are connected for one hour, then disconnected. After two minutes the voltages are reevaluated and the cycle repeats.

With many LifePO4 batteries, the charging is controlled by an internal Battery Management System (BMS) which prevents overcharging, prevents charging when below certain temperatures, and disconnects at a specified low voltage point. Lead acid batteries rely on these functions being provided by a smart charger - which ramps up/down voltage according to the battery charge state... something you DO NOT WANT with LifePO4 batteries!

With the low resistance of LifePO4 batteries, they can accept a much higher charge (amperage) which could damage a lead acid battery. Using a charger designed for this higher amperage is beneficial and allows the BMS to cut off the charge when the battery is fully charged.

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Old 04-27-2023, 04:40 PM   #2
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Thus, I will replace our FLA house and chassis batteries with AGM when the time comes. That time has very likely come for the house batteries.
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Old 04-27-2023, 04:53 PM   #3
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Thus, I will replace our FLA house and chassis batteries with AGM when the time comes. That time has very likely come for the house batteries.
Definitely a much more economical solution... and one that works for you.

For motorhomes with limited weight and storage capacity, a lithium conversion may make sense... but IMO only if needing the much higher amp hours. Lithium definitely has an advantage in amp hours to weight ratio. It's NOT for everyone though!
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Old 04-27-2023, 07:28 PM   #4
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Good analysis and I agree LiFePO4 batteries are never a "drop-in" solution.... but they can be very advantageous.


I've been running LiFePO4 batteries (850Ah BigBattery) for two seasons w/ the LI-BIM 225 and have had no issues.

My Magnitude does have two alternators and I also have 495W of solar so while I am driving during the day and there is ample sun I am getting charging support from the solar as well.

After the first season on LiFePO4's I moved from a Progressive Dynamics LI Converter / Charger to a Xantrex Freedom XC Pro 3000 Inverter / Charger that is configurable and provides much better charging capability than a Converter..... especially one that is located far from the battery bay with under-sized wiring. If I was running on my batteries and depleted them down to 10 - 20% SOC, I can use my generator to get the batteries charged to 80% very quickly and then let the alternator / solar combination continue the charging.

I'm very happy with my LiFePO4 conversion. I rewired the coach so the 3000W Inverter can power anything. I have run an A/C unit over night without any issues and still plenty of power to spare.

We are heading out on the Fantasy Tours 62-Day Alaska Your Way Caravan in a month or so and we were told by the Wagonmaster that we will have a few days where we will need to be on solid battery power. There are a couple campground with no or limited shore power and a few others that use generators to provide 30A service, which can be unreliable.

I have no concerns about running on my batteries through western Canada and Alaska with my setup but I would be a bit concerned if I only had wet or AGM batteries.
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Old 04-27-2023, 08:02 PM   #5
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Both excellent write-ups and information @Chateau-Nomad and @Judge. Thanks for sharing it.
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Old 04-27-2023, 08:23 PM   #6
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Excellent explaination.

Like many things these days, is situational to meet needs.

Rarely do we use our RV without being plugged into shore power or generator. My original house batteries date code 2015 are in boat.

I still use flooded batt in racecar as it has been reliable in conjunction with 100 amp alternator.

Newer tech is impressive but depending on application, may not be required.
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Old 04-27-2023, 09:20 PM   #7
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I'm reading and learning from posts like this.

I understand tires, oil, RV mattresses and washing our unit well enough to do OK. But running on batteries is still hocus pokus for me. Add Li and I'd rather plot orbit velocities. So Thank You!
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Old 04-28-2023, 12:56 AM   #8
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I'm crawling under the MH tomorrow to string 2/0 AWG cable from a rear storage compartment to the engine bay, which will connect the Victron Power In (using as a bus) to the Li-BIM... then another run across the firewall to the chassis battery.

Thor used 6 AWG for the lead-acid battery connections... so there's yet another consideration if converting to lithium. Thor tends to use bare minimum spec for components... probably assuming some people will never upgrade - so why install heavy over-gauge wire that serves no purpose? But 6 gauge battery cable would rarely fly on the most minimal lithium setup.

Has anyone else crawled under their rig to look in awe at the maze of wire loom encased cable and wiring? Thor must use ALL pre-cut lengths - then bundle the excess into MASSIVE gobs of zip-tied knots. There's probably 20 feet of wasted cable just tied up to the frame!!

Some aftermarket lithium installers go full Monty with 4/0 gauge cable. For my uses, calculations dictated 2/0. Pure copper cable is uber expensive now, so it's easy to waste a few hundred bucks on unnecessarily heavier gauge cables.

Another key point is keep the batteries and inverter/charger as close together as practical. My batteries to inverter run is less than three feet. This allows setting the 3k inverter/charger to a higher amperage for quicker charging without overheating cables.
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Old 05-05-2023, 01:41 AM   #9
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My experience with LiFePO4 coach batteries so far.

In Oct 2021 we “dropped in” a pair of LiFePO4 Group Size 31 12V batteries, resulting in a total of 210AH available stored energy, on our 2018 Vegas 24.1. Concurrently we installed the Precision Circuits Lithium BIM and swapped out the OEM WFCO 8955 converter for their Li-specific MBA, a two-level system, and added a Victron shunt to monitor the coach batteries.

Now, more than 18 months later, my impressions are:

1. I have yet to observe the input current from either the alternator, or the converter, or solar, or any combination of the above, exceed 50A, and normally the highest current is in the upper 30A range when starting with 210AH of LiFePO4 coach batteries SOC of below 50%.
2. In my opinion, discussion on the pros and cons on the ambiguous figure 80% in charging the LiFePO4 is unnecessary and distracting. I have observed the SOC obtained from the alternator input alone is normally well above 90%. Combined with roof solar input, the lithium batteries easily reach 100% SOC in a half-day’s worth of driving.
3. At least one LiFePO4 battery manufacturer is now offering lithium hybrid starting batteries. There is even one model offered with 560AH in a group size 31 case. Though expensive, RVs with standard battery cage space for two Group31 Deep Cycle batteries can theoretically drop-in 2 LiFePO4 batteries in the same space, totaling 1120AH of available 12V energy to the coach..
4. Suitable environmental protection of LiFePO4 batteries with a combination of insulation, air circulation, and heating is feasible today, and may be an opportunity for “drop-in” innovators. I have observed our batteries BMS shut off charging input because of well below freezing temperatures.
5. In my experience and research, LiFePO4 batteries often do NOT require 14.6V for charge charging, and sometimes the optimum bulk charging voltage is about the same or even less than AGM batteries. For our particular LiFePO4 batteries, the optimum charging voltage is probably between 14.3 and 14.4V, with anywhere between 14.2 and 14.6 good enough.
6. Many modern vehicles with smart alternators intentionally keep the chassis battery at 80% SOC, to provide capacity for regenerative braking. In my opinion, it seems feasible for near-future Ford or other MH chassis manufacturers to utilize a combination of sensors and ECU algorithms, to directly optimize alternator output for both chassis and coach electric systems, including the chassis and coach batteries, and provide coach/chassis battery isolation capacity, negating the need for a separate BIM.
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Old 05-05-2023, 02:06 AM   #10
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Are you referring to 80% state of charge in your #2 above? As for "drop in", I would think that refers to making no other changes to the system other than "dropping in" the LiFePO4 batteries in place of lead acid.

Please correct me if I'm wrong, but my understanding is that in a drop-in situation, you are using the factory WFCO converter which utilizes a charging curve optimized for lead acid batteries... meaning the voltage tapers as the battery reaches full charge. As I understand it, that's the issue with the converter... or shore charging.

Now, solar is a different issue... especially if you have an MPPT controller with adjustable charge profiles.

Being a new install, I wasn't sure what to expect from the alternator... that was my gray area. It's comforting to hear a real-world alternator charging experience. We boondock a lot, so it's likely the solar is going to be responsible for topping off the batteries, and the alternator won't even be a major player.
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Old 05-05-2023, 03:34 AM   #11
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Originally Posted by Korey & Tana Jackson View Post

……cut….

3. At least one LiFePO4 battery manufacturer is now offering lithium hybrid starting batteries. There is even one model offered with 560AH in a group size 31 case. Though expensive, RVs with standard battery cage space for two Group31 Deep Cycle batteries can theoretically drop-in 2 LiFePO4 batteries in the same space, totaling 1120AH of available 12V energy to the coach..

…..cut….

That much battery capacity in a size 31 case seemed high to me, so did a quick check and found one company, Dakota, that builds a 560 Ah battery; but it’s much larger — essentially two group 31 end-to-end.

Dakota also offer a 280 Ah in a group 31, which is more in line with other manufacturers’ batteries. What is different is that the BMS has very high current capacity for short period so battery can be used to start an engine.

I’d appreciate it if you could double-check the information. If there is a 560 Ah X 12 Volt battery in a size 31, that would be a huge improvement in battery density, a real game changer.
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Old 05-05-2023, 03:48 AM   #12
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That much battery capacity in a size 31 case seemed high to me, so did a quick check and found one company, Dakota, that builds a 560 Ah battery; but it’s much larger — essentially two group 31 end-to-end.

Dakota also offer a 280 Ah in a group 31, which is more in line with other manufacturers’ batteries. What is different is that the BMS has very high current capacity for short period so battery can be used to start an engine.

I’d appreciate it if you could double-check the information. If there is a 560 Ah X 12 Volt battery in a size 31, that would be a huge improvement in battery density, a real game changer.
I'm leary of single high capacity LiFePO4 batteries if it's the only battery I'm relying on. If the BMS were to fail, or an internal short compromised the battery...

Maybe I'm just being paranoid, but I'm going with multiples of 100Ah batteries. Starting with two, and room for one more. Besides, that's the only size case that fit under the bed... and they barely fit!
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Old 05-05-2023, 10:05 AM   #13
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Originally Posted by Korey & Tana Jackson View Post

Now, more than 18 months later, my impressions are:


1. I have yet to observe the input current from either the alternator, or the converter, or solar, or any combination of the above, exceed 50A, and normally the highest current is in the upper 30A range when starting with 210AH of LiFePO4 coach batteries SOC of below 50%.



5. In my experience and research, LiFePO4 batteries often do NOT require 14.6V for charge charging, and sometimes the optimum bulk charging voltage is about the same or even less than AGM batteries. For our particular LiFePO4 batteries, the optimum charging voltage is probably between 14.3 and 14.4V, with anywhere between 14.2 and 14.6 good enough.

In response to your two points above......


1) When I first converted to Lithium, I went with a 60A Progressive Dynamics LiFePO4 Converter / Charger I would typically only see charging currents in the 30A range. I attributed this to the fact my Converter was under the bed and and there was over 20' of wiring to the batteries and the wiring was sufficiently undersized for the length of the run.

A year latter when I upgraded to an Inverter / Charger capable of charging at up to 150A and disabled the Converter. The cable run from the Inverter / Charger to the batteries was under 4' and properly sized. I configured the Charger for 120A and I can now see over 100A of charging current when needed.



2) Technically Bulk, Absorption and Float charging do not apply to LiFePO4 batteries. I went with BigBattery for my LiFePO4 and their optimal charging range is 13.9V to 14.6V and the BMS will shut down charging if the voltage goes over 14.7V. I configured the Charger as BigBattery recommended below with the exception of setting the Float Voltage to 13.6V since that is 100% SOC for a fully charged cell at rest. I used 14.5 as the charging voltage and will see that voltage when charging.
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Old 05-05-2023, 10:09 AM   #14
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Originally Posted by Chateau_Nomad View Post
I'm leary of single high capacity LiFePO4 batteries if it's the only battery I'm relying on. If the BMS were to fail, or an internal short compromised the battery...

Maybe I'm just being paranoid, but I'm going with multiples of 100Ah batteries. Starting with two, and room for one more. Besides, that's the only size case that fit under the bed... and they barely fit!

I found BigBattery had the best $ per Ah value among the higher-end battery manufactures and their smallest capacity was 170Ah. Each battery has its own On / Off Switch, LED Voltage Readout and Quick Disconnect Battery Cable.

I have five of the 170Ah batteries and if one of them would have an issue I could either turn the battery off or just pull the quick disconnect from the battery.
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Old 05-05-2023, 12:03 PM   #15
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I went with SOK batteries... and I came very close to buying their 206Ah battery. For my starting target amp hours, I would have only needed one battery... but I got to thinking about critical failure... and two of them (412Ah) is beyond my needs (and budget).

So my logic brought me back to buying two of the 100Ah, with room to add one more later if needed. I never plan on running A/C from batteries, so more than 300Ah is nice insurance, but definitely overkill.
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Old 05-05-2023, 12:31 PM   #16
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Chance,

I stand corrected. 280AH in a GroupSize 31 case. Mea culpa.
And yes, I was referring to the oft-stated dictum that the alternator will only charge the coach lithium batteries to 80% SOC. That isn’t entirely bad, and in practice it isn’t entirely true.

Judge,

My two Dakota Lithium 105AH batteries are in the original coach batteries cage under the steps, using the original battery cabling. For 210AH I am satisfied with maximum alternator charging currents of 30-50A, which is in the same range as popular DC-DC chargers, is consistent with the charging current of the WFCO 8955, and within Dakota Lithium’s recommendation to maximize battery life by charging at roughly 0.3c. It is good enough.

Chateau Nomad,
yes, I probably strayed from a common understanding of “drop in”. I also propose that understanding will evolve by model year.
Your initial point about the battery isolation system, whether a BCC, B.I.R.D./Trombetta, or BIM is valid. In practice, if lithium coach batteries are dropped in while there is still a SLA chassis battery, the battery isolation system will detect a charging voltage on the coach side and connect coach to chassis…in essence there is no longer a battery isolation system.
However, what is the impact of the coach and chassis not being isolated? Will the chassis battery overcharge or its lifespan be significantly reduced? How does the impact of the lithium coach batteries long-term charging of the chassis batteries at about 13.2V differ so much than the extended charging from a battery maintainer, or a solar maintainer, or even the alternator input of long term driving?
I do acknowledge a lithium BIM or DC-DC charger (especially for large battery banks) should be used. But how bad is it on the coach if the original BIM160 is used and not replaced with the Li-BIM225?
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Old 05-05-2023, 02:04 PM   #17
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Originally Posted by Chateau_Nomad View Post
I'm leary of single high capacity LiFePO4 batteries if it's the only battery I'm relying on. If the BMS were to fail, or an internal short compromised the battery...

Maybe I'm just being paranoid, but I'm going with multiples of 100Ah batteries. Starting with two, and room for one more. Besides, that's the only size case that fit under the bed... and they barely fit!
It’s a valid concern, but to me a battery failure is not the end of the world, so losing 100% versus 50% capacity isn’t the end of the world, particularly since the more batteries there are the greater the chance of a failure.

A single large battery is often cheaper than two smaller ones of equivalent capacity, but unless covered by warranty, a failure could end up costing a lot more, though chance of failure is less. There is no 100% right or wrong.

Electric cars often have “one” battery made up of many cells wired in series (some parallel too on higher-capacity units) for really high voltage and lower current, so manufacturers are betting on reliability to a great degree.

A single RV battery could get pretty heavy depending on required capacity, so that needs to be considered as well.

I visited an RV plant in Elkhart recently, and the van I was interested in had high-capacity lithium battery option without generator, and they used a single battery. It was actually fairly compact and mounts under coach or bed inside van where it is protected and normally kept at ideal temperature.

It comes down to choices, but almost anything should perform well if engineered and installed right.
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Old 05-05-2023, 02:45 PM   #18
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Originally Posted by Korey & Tana Jackson View Post
Chance,

I stand corrected. 280AH in a GroupSize 31 case. Mea culpa.
And yes, I was referring to the oft-stated dictum that the alternator will only charge the coach lithium batteries to 80% SOC. That isn’t entirely bad, and in practice it isn’t entirely true.

…..cut…..

Thanks for clarification.

Regarding size, I see that there are now 300 Ah cells being used to manufacture lithium batteries. Dimensions are a little larger than Group 31 when used to build 12.8 Volt batteries, but may fit in some battery trays anyway.

In time I expect RV manufacturers will place lithium batteries inside coach so that temperature concerns are mostly eliminated. Let’s hope they have enough sense to locate batteries and inverter/chargers next to each other to minimize low-voltage wiring.

I agree alternators can charge lithium enough to be functional for the most part without requiring voltage boost. Solar can do final top off, and for those who don’t care for solar, campground shore power will certainly do it.

I think the issue is that as lithium batteries approach 90+ SOC and alternator is hot/warm from driving all day, voltage difference is so minor that charge rate becomes very low. With high battery capacity like 600 Ah or greater, that last bit could take hours of driving. I expect that’s why so many report not getting much more than 80~90 percent.

And in fairness (to be clear), most RVs with 600+ Ah from factory have a separate dedicated alternator, so voltage is regulated independent of chassis electrical system. It’s only with people like Judge that add large lithium banks that this is even a relevant issue. My son is upgrading to 600 Ah but is fortunate that his RV came with optional dual alternators with capacity to spare. Charging at 100 Amps while driving through DC-DC should be easy without having to add a dedicated alternator for house.
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Old 05-05-2023, 05:53 PM   #19
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We have a Chevy Bolt with a single 65kWh battery... rumored battery replacement cost is $15k. They are warranted through Chevrolet for 10 years.

I have no anxiety about Chevrolet honoring a warranty on a battery of such magnitude and expense... they replaced thousands of previously defective ones.

However... dealing with a Chinese consumer grade battery manufacturer is another story.
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Old 06-22-2024, 02:46 AM   #20
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Since it concerns LiFePO4 batteries, I'm reviving this thread as an extension of my recent "unscientific" refrigerator test.

I was interested in getting a baseline of how long I could run our absorption refrigerator (2-way 120v / propane) along with a couple MaxxAir fans on low to medium speed.

Unfortunately the temperatures here in Ohio spiked this week with daytime temperatures low to mid 90s, and night temps only dropping to mid to upper 70s. No rain in forecast with sunny hot days. Visiting niece from Florida said it feels worse than home in summer! Oppressive humidity.

Our preference is we avoid motorhome travel if we're forced to sit inside with A/C running. We are the hiking/outdoors type, so when temperatures climb we usually head to the mountains. We do use occasional A/C... but only if absolutely necessary. If it's THAT hot, we're moving on!

So... this test wasn't a good representative example. But I was already running with it so...

300Ah LiFePO4 batteries. 3,000 watt inverter/charger. 600 watts rooftop solar.

Started with batteries at 100% at about 9:00 am. Refrigerator empty. Two MaxxAir fans @ 30% speed.

Ran all day and night. Next morning the batteries were at 7%... refrigerator just above 32°, freezer 0°.

The solar only recovered the batteries to 35% the next day. The following morning (before sunrise) all batteries were 0%... dead. The refrigerator was just under 60°. Propane did not kick in because it requires 12 volts.

Although a fail, I learned a lot. First, (as we always do anyway) cool the fridge using electric hookup FIRST, then fill with cold items... frozen items in freezer.

Second, use propane at night to maintain temps... then revert to inverter during day with sun. With temperatures in 70s with sun, I'm confident the solar could easily maintain the refrigerator/freezer and two fans, plus various lights etc. The charge controller was indicating 30 amps from the solar mid-day.

I intend to do another trial when temps return to normal... usually around low 80s this time of year. I'll start with the fridge already cooled from electric... then let the inverter take over. Then after sunset plug in to shore power (to simulate propane)... the idea is to just maintain refrigerator temperature while no solar is available. I think that will give a better representative example.
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