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Old 07-22-2021, 11:16 AM   #29
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Originally Posted by Mark_K5LXP View Post
'Routinely' it doesn't either. In the case of T105's the difference in service life between 40% to 80% DOD is a few percent. Not material by any practical definition.

Mark B.
Albuquerque, NM
The OP stated 20% not 40%. That will make a difference.

Enjoy,

Perry
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Old 07-22-2021, 11:25 AM   #30
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Originally Posted by BCam View Post
Two comments:

1. Running your FLA batteries below 50% state of charge on an occasional basis isn't going to have a material effect on their lifespan, only if you routinely do so.

2. I would put solar ahead of LiFePO4 batteries in terms of priorities. Solar will extend your boondocking or dry camping capability regardless of your battery type, so spend your money first on solar and then, should you decide to do so, on LiFePO4 batteries.

Totally agree!
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Old 07-22-2021, 12:41 PM   #31
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Originally Posted by Perryb67 View Post
The OP stated 20% not 40%. That will make a difference.
The post I responded to he said below 50%, so that implies 50% DOD to 80% DOD. I added some margin in there by going even less to 40%. Across the entire DOD range of best case around 30% DOD to worst case 80% DOD the difference in service life is only about 10%, so the idea of drawing any line in the sand in the interest of practical battery longevity is incremental at best.

Mark B.
Albuquerque, NM
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Old 07-22-2021, 08:17 PM   #32
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As an additional data point to how low DOD affects a FLA battery.... The problem is that sulfate insulation can grow on the plates with low power - but this takes time to happen.
Certainly draining them down (or allowing them to drain with inattention and something left connected) and then LEAVING THEM LOW is bad news for battery life.

BUT.... What about "actively" using the batteries, such as drawing them down overnight with something like a fan running..... And they hit 10 volts (under load, so basically 80% DOD) just before sunrise when the solar starts working again and they are immediately charged all the way up to full?

I have 1020 watts of solar on my roof and even while in storage, the Victron system is fully active. While using the RV though, I have inadvertently drained it down overnight to the inverter's cutoff point... But that has happened right before the solar started charging again (I've seen the logs) and they only sat at 10 volts for around an hour before they were getting power back in.

How much damage do you think I've done? I tend to think that if they weren't left at a dead level for long, the answer is probably "not much"
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Old 07-22-2021, 09:38 PM   #33
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We would be considered in the weekend warrior class by most people. However, we dry-camp, and boon dock frequently. We also have a 14 year old that wants to watch movies at night (often late at night). Plus many camp grounds we frequent, have limited generator hours. We have also camped in below freezing weather and have learned how thirsty the furnace is on the batteries.

For us Lifepo4 lithium batteries and a inverter is the ticket. We have estimate that we need about 300AH of lithium, and a 2000 watt inverter. That will pretty much cover 80% of what we do. For the rest we have the generator. We also have switched to a newer 12V converter to handle various charge characteristics.

To extend our dry-camping we do want a DC to DC charger for the alternator, and 250-300 watts of solar.

The lithium cost barrier is getting smaller every year, both with name brands like Battleborn, SOK and others. Solar has also gotten more affordable. As another poster mention, Will Prowse on YouTube has good advice, and has built a number of DIY lithium battery systems. Definitely worth watching, even if your have someone install your system. At least you will have a better idea of what to ask a dealer/instraller.
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Old 07-22-2021, 09:51 PM   #34
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If you build your own lifepo4 battery you can build a 280ah battery for under $700. It would take 6 lead acid batteries to give you the same capacity. So $600 + for lead acid.

Lead acid last 3 to 5 years. Lifepo4 for last 10 years.

So you can DIY your own lifepo4 batteries for the same cost per usable ah as lead acid. And get twice the life.
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Old 07-22-2021, 10:14 PM   #35
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Just as people buy different types/makes/models of RVs for their very varied life styles, I think that power storage/generation needs vary equally.

There are those folks in the lithium and FLA camps that will argue their point all day long. For them it may well be the perfect power solution. I have looked at switching to lithium batteries but have never identified a real problem I have with my current setups that would be solved by making the switch. My 5th wheeler has 1050 watts of solar, 460 AHrs of FLA batteries, a generator (hardly ever use it, 20.4 hrs in 5 months of road time) and 115 amps of converter, now turned off for four years since the solar was installed. I have no weight issue; lowest SoC for batteries was 84% one time, usually hit 92 to 93% in the morning; the solar nearly always has the SoC back at 100% by 10:00 am, I have a Flow-Rite watering system and watch the battery health monthly. I do not have a problem waiting to be solved. Thus no reason to spend money switching to lithium batteries.

We also have a Coach House Class C RV. There is no internal place to move the batteries to for a lithium switch and we do spend significant amount of time in boon docking with temperatures well below 27F. FLA is the only real solution for us in that rig as well.

For someone else the switch to lithium would make lots of sense. It's not just question of cost, longevity, usable AHrs, weight, recharge cycles, recharge times, etc. Some posters seem to think that their RV type is the only RV of consideration here. Our forum readers have every type, size , age, etc of Rv perhaps ever made.

The information here and other similar threads is good, but one solution does not fit all needs. The configuration on our 5th was done to meet some very specific requirements of where and when we travel. Like north of the Arctic Circle. Not everyone does that.
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Old 07-23-2021, 05:06 AM   #36
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If you own a TT, switching to Li/Solar maybe is more compelling. In our limited experience with this setup, it has been clear that the switch was the right choice for us. The battery weighs only 25% of the weight of two FLA. That’s significant if you’re nearing GVWR on trailer and tow vehicle. The cost of charging to 100% SOC with a generator is only 20% of FLA. By my calculations, if you have 200ah FLA and a Honda eu2200, it will cost $2.88 to charge from 30% to 100%. With LiFePo4, the cost is $0.72 because the charge profile is linear, and we charge at 80amps. That’s with gasoline @ $3.00/gal. Our actual cost are marginally higher because we use a propane generator. Using our limited portable solar of 110w, we could never go from 30% to 100%, but it’s so simple and easy to just plug it in, and get some quiet juice, further lessening the need to run the generator. The new ETFT folding panels are lightweight (7lbs) and efficient. It’s true you have to babysit portable solar, lest it walk away while you’re gone, but the same is true for your generator if you have a TT. People keep saying that LiFePo4 is too expensive compared to AGM. Well, my initial cost for Li was $4.70 per amp hour. After 200 generator charge cycles, the LiFePo4 cost will be exactly the same cost as AGM based on fuel savings. For us, that’s about 4 years. Probably would have gone with AGM if we had a MH, but for TT, the Li/solar combo has many advantages. If you spend most of your RV time with hookups, you don’t need any of this stuff.
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Old 07-23-2021, 07:02 AM   #37
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Originally Posted by geordi View Post
draining them down ... and then LEAVING THEM LOW is bad news for battery life.
Yep.

Quote:
What about "actively" using the batteries,
That's a "cycle".

Quote:
How much damage do you think I've done?
An important point here is to define "damage". Using something within it's rated specification isn't "damaging" it. So cycling a battery within it's ratings is no different than driving on a properly inflated tire. Each will exhibit "wear" which I guess in the strictest sense of loss of material or capacity might be considered "damage" but it's a known, expected and understood degradation. But a better description of that event would be "wear" and not "damage". Damage is when something is operated or an event occurs outside the rated specification that causes an irreversible change in the serviceability or rated performance of the unit. Example, overloading a tire or overloading a battery. So to answer the last point, there was no damage done at all to discharge a battery and restore the charge within it's specification. That's a cycle as defined by the manufacturer and a perfectly acceptable way to use a battery.

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Albuquerque, NM
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Old 07-24-2021, 07:30 AM   #38
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Originally Posted by Mark_K5LXP View Post
The post I responded to he said below 50%, so that implies 50% DOD to 80% DOD. I added some margin in there by going even less to 40%. Across the entire DOD range of best case around 30% DOD to worst case 80% DOD the difference in service life is only about 10%, so the idea of drawing any line in the sand in the interest of practical battery longevity is incremental at best.

Mark B.
Albuquerque, NM
I suggest you read depth of discharge vs life cycles. This article by Federal Batteries is a good start. A flooded battery only taken to 20% DOD is good for 1,200 cycles. That same battery taken to 50% DOD is good for 450-500 cycles and one taken to 80% DOD is good only to less than 300 discharges. That's not 10%, and is the reason many here have large battery banks. Lithium has massively changed that life cycle curve though.

Yes, you can take a lead acid battery to 20% DOD a couple of times, but the chemistry at that point is cumulative. Cumulative degradation is the killer of standard lead acid batteries. Took a couple of failed batteries to realize that actual practice trumps a theoretical chart, but a chart is only created for a perfect world, not the world we actually camp and draw power.

I'm dyslexic so excuse me if my numbers on DOD are reversed.

Enjoy,

Perry
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Old 07-24-2021, 08:11 AM   #39
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I used to have two DC24 FLA batteries in my 5th wheel, total capacity 130 Ah. That was barely sufficient to run the furnace fan through a cool night. And what capacity was left did not run the microwave or espresso machine in the morning for a minute because the voltage got too low for the inverter.

I could have added 2 more FLA batteries which might have done the trick but a total of 180 pounds was too much for my load situation. Instead I got a 300 Ah LiFePO and have more than enough capacity for my needs at 70 pounds. At $1200 I think the price was not too bad and worth it for me.
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Old 07-24-2021, 08:35 AM   #40
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I suggest you read depth of discharge vs life cycles. This article by Federal Batteries is a good start.
That's not a technical paper, it's a salesman's tip sheet. But we'll take it at face value.

Quote:
A flooded battery only taken to 20% DOD is good for 1,200 cycles.
...taken to 50% DOD is good for 450-500 cycles
...taken to 80% DOD is good only to less than 300 discharges.
For the purposes of their example that may be true, but if you read the data sheet for an actual deep cycle battery like a Trojan T105 and most any other deep cycle battery, the cycle life numbers look very different.

Irrespective of that, not covered at all in this brief is that cycles don't run things, amp hours do. When you factor the ever increasing Ah delivery over those seemingly precipitously falling cycle numbers with increasing DOD, you find that the energy delivery from the battery over it's cycle life range changes very little. That's what you buy a battery for, delivering Ah. The next trick is to use those Ah before the battery expires from time or injury. Most folks never come close to using all the Ah their batteries potentially have yet still obsess over DOD and cycles, and not the present factors that contribute to reliable operation and long service life.

Quote:
Yes, you can take a lead acid battery to 20% DOD a couple of times
Guessing you really meant SOC. So is Trojan lying when their data sheets show around 650 20% SOC cycles are possible with their batteries? Are they or you measuring SOC differently? The difference between 2 cycles and 650 is quite a significant disparity.

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Old 07-24-2021, 09:12 AM   #41
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That's not a technical paper, it's a salesman's tip sheet. But we'll take it at face value.
Just like one should take Trojan's paper at face value.


Quote:
Originally Posted by Mark_K5LXP View Post
Guessing you really meant SOC. So is Trojan lying when their data sheets show around 650 20% SOC cycles are possible with their batteries? Are they or you measuring SOC differently? The difference between 2 cycles and 650 is quite a significant disparity.
You said "possible." Possible is salesman talk too. Nobody runs their cycles like the charts imply. So tell me how do you stop at 20% SOC? Do you have a BMS for your flooded batteries? And that is how actual practice trumps charts.

Enjoy,

Perry
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Old 07-24-2021, 09:49 AM   #42
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This battery/solar panel stuff sure is complicated. Pushing the generator start button is easy. Plus since it came with the RV, there’s no additional purchase costs or figuring out how to install. And I never have to worry about shade, clouds, or rain degrading my battery charging ability. But we all have different needs and tolerances, I appreciate everyone sharing their knowledge of other ways to have power around the clock. Thank you.
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