Need advice on replacing lead battery to AGM or Lithium? - Page 2 - Fiberglass RV


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Old 07-18-2019, 01:18 PM   #15
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Originally Posted by Techscott View Post
Faster solar charging means less panels necessary.
I'm afraid I don't understand this. How can you do faster charging with fewer panels?
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Old 07-18-2019, 01:50 PM   #16
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I'm afraid I don't understand this. How can you do faster charging with fewer panels?
Because lithium batteries charge at the full output of the solar controller until almost full. Lead acid battery controllers must switch to an absorption stage, limiting charging current when they reach 80% of full.

In other words, you can use panels with less output because all of the output goes to charging the battery until full. With lead acid you need higher currents during the bulk stage to end up putting the same # of amp hours back in the battery.
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Old 07-18-2019, 03:50 PM   #17
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Jon, I get that. But how does that relate to fewer panels? Having a longer bulk phase, at a lower peak, with fewer panels, doesn't seem like it would always reduce the overall charging time. Maybe, in some cases, but not as a general rule.

Often, the full power of the solar array is far below what the batteries are designed to accept. And rooftop solar systems only produce about 40% of their rated output if laid flat.

The absorption phase is not a step function that drops the amps to a predetermined lower value, it is a gradual tapering off. So even though it might be the last 20%, it could be nearly the same amperage as bulk for a large percentage of that phase, especially if the solar array is small.

I just don't get how one can claim, as a general rule, that faster charging means less panels are necessary. Aren't there too many variables to generalize in that way?

It's not fair to assume that all charging will be done from nearly dead to fully charged. That is not the real world, and especially if the system is a rooftop system that is always ready to go whenever there is sun. If power use is small overnight, and every day is sunny, the lead batteries will be in absorption most of the time, but a smaller array on lithium could equal the average amps of the absorption phase. If you had more collectors, you might only need half the day to recharge the lithiums.

I'm just trying to understand how a smaller system can always charge faster.
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Old 07-18-2019, 04:19 PM   #18
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Originally Posted by Raspy View Post
Jon, I get that. But how does that relate to fewer panels? Having a longer bulk phase, at a lower peak, with fewer panels, doesn't seem like it would always reduce the overall charging time. Maybe, in some cases, but not as a general rule.

Often, the full power of the solar array is far below what the batteries are designed to accept. And rooftop solar systems only produce about 40% of their rated output if laid flat.

The absorption phase is not a step function that drops the amps to a predetermined lower value, it is a gradual tapering off. So even though it might be the last 20%, it could be nearly the same amperage as bulk for a large percentage of that phase, especially if the solar array is small.

I just don't get how one can claim, as a general rule, that faster charging means less panels are necessary. Aren't there too many variables to generalize in that way?

It's not fair to assume that all charging will be done from nearly dead to fully charged. That is not the real world, and especially if the system is a rooftop system that is always ready to go whenever there is sun. If power use is small overnight, and every day is sunny, the lead batteries will be in absorption most of the time, but a smaller array on lithium could equal the average amps of the absorption phase. If you had more collectors, you might only need half the day to recharge the lithiums.

I'm just trying to understand how a smaller system can always charge faster.
One example - With my lead acid batteries at 85%, even with 480 watts of solar, the controller limits the current to a couple of amps (example is with a pair of 6V Interstate 232 amp hour batteries & a GoPower PWM controller). I'm using a very small percent of the available solar panel output.

A single 100 watt panel with a controller designed for lithium would produce 5-6 amps until the lithium batteries are full.

After switching to a pair of 100 amp hour lithium 12V batteries, with 320 watts of solar flat on the roof, I was getting 16 amps into a pair of lithium batteries that were at 80% this afternoon. It took about 2 hours to bring them to 100%.

I'm not suggesting that one switch to lithium for just the recharging capabilities, but is is certainly one of the advantages. Now if they only cost a bit less!
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Old 07-18-2019, 05:03 PM   #19
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Thanks Jon,

I'm surprised that your controller limited the absorption amps, at 85% charged, to only 2 amps. That is a very aggressive reduction during absorption.
The smart charger I had some experience with, regulated the current to maintain a battery voltage of 14.1 (during absorption) until the amps fell to 5, and then it went to float. It was a gradual taper from full amps, down to 5.

If your flat array was producing 16 amps at 14 volts, you were getting about 70% of it's rated output of 320 watts. That seems like very good performance for panels sitting flat. Of course we are near summer solstice.

So, I can see from your example that in your particular conditions, with your particular controller, quicker charging could occur with lithium. But don't cut down the collector array too much or the "quicker charging with fewer panels" theory will not hold. Do all solar controllers fall off on their absorption amps to that degree? If so, they are wasting power and lengthening charge times. The amps delivered should be driven by the voltage of the batteries and be a continuous curve.

My theory is that, for the most part, usage will rise to meet supply. The practical result of this is that most systems will spend most of their time in the bulk phase. If usage is small, the system will spend a lot of time in absorption, but if usage rises to near capacity, then the bulk phase will be mostly where the charging occurs. It's easy to get to this condition because the available real estate on the roof is limited and the collectors are flat. Plus, the convenience of having power means it can get used a lot.

We seem to be fairly heavy users of power, especially in the winter with the heater getting used. But on average, three to four days gets us to 50%, and that is with (4) T105, 6 volt, flooded batteries. Most of my solar charging has been done on other rigs I've had. I also lived on a 42' Ketch for many years and had to manage those batteries while charging with a dedicated alternator for that purpose. I had two 8D deep cycle house batteries there. Solar is much harder to arrange on a sailboat, and the power usage can be much higher with navigation lights, radar, autopilot and depth sounder always on, as well as the other loads similar to what trailers experience.
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Old 07-18-2019, 05:11 PM   #20
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Originally Posted by Byron Kinnaman View Post
Replacing a standard Lead Acid battery with a new one is whole lot cheaper than replacing with something else and it works just as well.
I am 100% with Byron , lead acid batteries are cost effective , work well and provide my trailer with 12VDC .
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Old 07-19-2019, 05:38 AM   #21
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+10 You are making it too hard.

The original question in the OP, what is cost effective?

Cost effective is replacing your battery with a lead acid battery. Cost will be under $100. Sounds like your battery wore out. That is what they do. When they wear out, you replace them.

Imagine the battery in your tow vehicle wore out. You would replace it.

Then buy a battery tender to charge your battery.

Is it cost effective to buy an AGM battery? No, that increases your cost to ~ $250, and won't give better battery life (and certainly is NOT going to last 2.5 times longer). Lithium is even more expensive, think $1000 +/- PER BATTERY. Yes, Lithium is a better battery, with longer life too. The question is whether you want to spend 10X the price of a lead acid battery.

One side advantage to Lead acid RV batteries is they are available everywhere. So if you are traveling, no problem picking one up at Walmart for example.

The lead acid in my Escape lasted 6 years, that's pretty decent. I recently replaced it with another lead acid battery.

At some point, if lithium batteries decline in price, the switch to lithium will become more cost effective. Full time off grid living? Lithium could make perfect sense already!
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Old 07-19-2019, 06:23 AM   #22
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Most power hungry thing I run normally is a small fan. I want to replace that with a 12 volt model to run directly from the battery instead of running the inverter because that is more efficient.
not to turn this into a discussion of fans, but...the 12v breeze box fan from the fantastic fan folks is great, small powerful and doesn't eat up a lot of volts.

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Old 07-19-2019, 06:44 AM   #23
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Originally Posted by thrifty bill View Post
+10 You are making it too hard.
..
Is it cost effective to buy an AGM battery? No, ...
I respectfully disagree.

First, figure $100 more for an AGM compared to an equivalent good quality true deep cycle battery. So if you have to buy a battery anyway, the difference is closer to $100. Second, cost is also measured in things other than the purchase price of the battery alone. Reduced maintenance on the battery, the wiring and the tongue (from corrosion) is worth something also. I had to repair the battery box mounting on the tongue after only three years because of the corrosion. AGM can handle the shock and vibration on the road better also. If you don't maintain the water / acid level in the wet battery then it dies and then the AGM battery would have been MORE cost effective. So if you're on a budget and dont mind the maintenance requirements and corrosion, then get a standard battery. But if cost effective to you means having all the aforementioned advantages, then go AGM.
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Old 07-19-2019, 08:18 AM   #24
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Originally Posted by gordon2 View Post
I respectfully disagree.

First, figure $100 more for an AGM compared to an equivalent good quality true deep cycle battery. So if you have to buy a battery anyway, the difference is closer to $100. Second, cost is also measured in things other than the purchase price of the battery alone. Reduced maintenance on the battery, the wiring and the tongue (from corrosion) is worth something also. I had to repair the battery box mounting on the tongue after only three years because of the corrosion. AGM can handle the shock and vibration on the road better also. If you don't maintain the water / acid level in the wet battery then it dies and then the AGM battery would have been MORE cost effective. So if you're on a budget and dont mind the maintenance requirements and corrosion, then get a standard battery. But if cost effective to you means having all the aforementioned advantages, then go AGM.
Doesnít toyota use an AGM battery in the sienna ?
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Old 07-19-2019, 09:03 AM   #25
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Thanks Jon,

I'm surprised that your controller limited the absorption amps, at 85% charged, to only 2 amps. That is a very aggressive reduction during absorption.
The smart charger I had some experience with, regulated the current to maintain a battery voltage of 14.1 (during absorption) until the amps fell to 5, and then it went to float. It was a gradual taper from full amps, down to 5.

If your flat array was producing 16 amps at 14 volts, you were getting about 70% of it's rated output of 320 watts. That seems like very good performance for panels sitting flat. Of course we are near summer solstice.

So, I can see from your example that in your particular conditions, with your particular controller, quicker charging could occur with lithium. But don't cut down the collector array too much or the "quicker charging with fewer panels" theory will not hold. Do all solar controllers fall off on their absorption amps to that degree? If so, they are wasting power and lengthening charge times. The amps delivered should be driven by the voltage of the batteries and be a continuous curve.

My theory is that, for the most part, usage will rise to meet supply. The practical result of this is that most systems will spend most of their time in the bulk phase. If usage is small, the system will spend a lot of time in absorption, but if usage rises to near capacity, then the bulk phase will be mostly where the charging occurs. It's easy to get to this condition because the available real estate on the roof is limited and the collectors are flat. Plus, the convenience of having power means it can get used a lot.

We seem to be fairly heavy users of power, especially in the winter with the heater getting used. But on average, three to four days gets us to 50%, and that is with (4) T105, 6 volt, flooded batteries. Most of my solar charging has been done on other rigs I've had. I also lived on a 42' Ketch for many years and had to manage those batteries while charging with a dedicated alternator for that purpose. I had two 8D deep cycle house batteries there. Solar is much harder to arrange on a sailboat, and the power usage can be much higher with navigation lights, radar, autopilot and depth sounder always on, as well as the other loads similar to what trailers experience.
I probably should have been a bit more specific. The 2 amp rate was at the end of the 2 hour (non adjustable) absorption phase, with the batteries at 85%. At the start of the absorption stage, it was drawing 6 amps or so. The problem with the fixed absorption time is it switches to float well before necessary.

The most recent version of the GoPower controller does have the ability to repeat the absorption cycle, but I have found it to be a very conservative controller.

I'm currently using a Victron SmartSolar 100/30 controller, far better suited to lithium batteries.

As to cutting down the size of the solar array, that won't happen. I dry camp in the Arizona desert for the winter, and even with the addition of a 160 watt portable panel to the 320 watts on the roof, a string of cloudy days has me limiting power usage (that was with the wet batteries; I hope that will be different with the lithium).

I do tilt the rooftop panels to match the Phoenix solar angle during January & February...
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Old 07-19-2019, 11:39 AM   #26
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Doesn’t toyota use an AGM battery in the sienna ?
Maybe now they do, but my 2015 Sienna came new with a standard battery, and as you can see in the photo, when its time to replace the OEM battery in the not too distant future, some additional work will be called for dealing with the corrosion. This is what I hope to avoid on my camper which now has a AGM battery.
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Old 07-19-2019, 04:48 PM   #27
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Maybe now they do, but my 2015 Sienna came new with a standard battery, and as you can see in the photo, when its time to replace the OEM battery in the not too distant future, some additional work will be called for dealing with the corrosion. This is what I hope to avoid on my camper which now has a AGM battery.
Looks like time for some baking soda and a tooth brush
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Old 07-19-2019, 05:12 PM   #28
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Looks like time for some baking soda and a tooth brush
Yea. but I would only use baking soda if the battery were removed first.. too much risk of some getting in the battery and neutralizing the acid.
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