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Author Topic: Solar charging voltage question  (Read 866 times)

jrclen

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  • John
Solar charging voltage question
« on: June 14, 2020, 09:14:05 PM »
With no load other than the propane detector, I am reading 14.1 volts at the brand new group 27 lead acid battery. Is that to high? On a normal day of camping with shore power and solar, and light loads the battery reads 13.7. When I bought the camper the old battery was very low on water and refused to hold a charge. I don't want to boil the water out of the new one or harm it with to much voltage.

I have a LMS2430 solar controller which I know nothing about. I have a blinking green light and a constant red light.

I read through this link and still know nothing. And I'm an electrician. :)

https://solarpanelskit.us/shop/energy-system/lms-series-intelligent-solar-charge-controller-1224-vdc-30-amps-with-lcd-display-2-usb-ports-and-load-controler-model-lms2430/
2006 Jay Feather 19h hybrid

Gene50

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Re: Solar charging voltage question
« Reply #1 on: June 14, 2020, 09:45:25 PM »
With no load other than the propane detector, I am reading 14.1 volts at the brand new group 27 lead acid battery. Is that to high? On a normal day of camping with shore power and solar, and light loads the battery reads 13.7. When I bought the camper the old battery was very low on water and refused to hold a charge. I don't want to boil the water out of the new one or harm it with to much voltage.

I have a LMS2430 solar controller which I know nothing about. I have a blinking green light and a constant red light.

I read through this link and still know nothing. And I'm an electrician. :)

https://solarpanelskit.us/shop/energy-system/lms-series-intelligent-solar-charge-controller-1224-vdc-30-amps-with-lcd-display-2-usb-ports-and-load-controler-model-lms2430/

I’m not sure about the lights but the 14.1 volt is not high.  And the 13.7 under load is not low. 

Maximum charging voltage is normally in the range of 14.4v - 14.8v on an RV solar system (most toward the lower number).

Depending on the level of monitoring information you wish to have, there are several setups that will give you the exact amount of amps you have used in a time period and also how many charging amps have been provided.  That gives a very accurate state of charge indication. 

You haven’t told us what size solar panel array you have.... 
2011 F350 Lariat 6.7PS
2015 Dutchman Denali 262RLX

Kevin Means

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Re: Solar charging voltage question
« Reply #2 on: June 15, 2020, 02:31:38 AM »
Sounds about right. That's a three stage 30 amp PWM controller, and I found this about it on someone's blog. "When it reaches a full charge of 14.1 volts then it will be steady." So it seems like that's a programmed charging voltage for that controller.

Kev
2011 Winnebago Tour 42QD
Towing a Jeep Rubicon Unlimited LJ
RVI Brake 2, TST 507 TPMS, 960 watts of solar, SolaRVector tilt
Lakeside, California

Ex-Calif

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Re: Solar charging voltage question
« Reply #3 on: June 15, 2020, 05:56:55 AM »
It's very complicated to answer the float question accurately. To get true float you need to basically have the battery disconnected from every load. It is also ambient temperature dependent as well as battery temperature dependent.

14.1V is actually too high for a float charge for AGM at standard temps.  But you probably are never getting to float state anyway because you are using that battery constantly (like everyone does) - The bigger issue is repeated over discharging.

The only comment I would make is that there should be a battery type selection on any decent controller. Looking at the tech data on that controller the write up is horrible. I wouldn't throw it away but there is no way I would "buy" a controller if they can't even explain the basic functions in plain English - LOL...
"Marvin" - 1997 Georgie Boy Pursuit 3150 - P30 Chev 454
Various classic MGBs
Ex-liveaboard boater - Class A newbie in sponge mode

jrclen

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Re: Solar charging voltage question
« Reply #4 on: June 15, 2020, 09:01:15 AM »
Thanks Kevin. I will keep an eye on the water level. But it is nice to have the battery maintain a charge between using the camper. The problem with disconnecting it is my gas detector then goes off and I need to disconnect that too.

Ex-Calif - the battery is a lead acid, not agm. Is the voltage to high for one of those? I agree about the clear as mud instructions. That's why I'm here asking. LOL I did see something about adjusting the maximum charge. Just wondering if I should look closer at that and try to adjust it downward.

But if it sounds "about right" I'll just leave it alone and keep an eye on things.
2006 Jay Feather 19h hybrid

Isaac-1

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Re: Solar charging voltage question
« Reply #5 on: June 15, 2020, 10:19:37 AM »
14.1VDC is fine for charging, but is high for floating, without knowing the state of charge of your batteries, it is hard to know if 14.1VDC is ok with your system.  Do you have a solar disconnect, if so can you disconnect the solar, and check the battery voltage after the surface charge has bled off (disconnect all significant loads for an hour, then check voltage, you can leave LPG/CO2 detectors, etc. connected, just no lights, appliances, etc.).    This would give us a better idea of what is going on at the point in time of that snapshot.
2002 Safari Trek 2830

PJ Stough

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Re: Solar charging voltage question
« Reply #6 on: June 15, 2020, 10:26:49 AM »
I would look at the charging parameters for the battery because that is what matters. If your charge controller is adjustable as far as charging and float voltages, set them for what the battery manufacturer recommends.
PJ Stough   Iowa
2005 Winnebago Voyage 38J

“Those who can make you believe absurdities, can make you commit atrocities.”--- Voltaire

Gary RV_Wizard

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Re: Solar charging voltage question
« Reply #7 on: June 15, 2020, 10:52:05 AM »
The generally accepted range of voltages for charging a lead-acid battery is roughly 13.3-14.4, though some solar gurus give a wider range, maybe 13.1-14.8.  What is "right" depends on the details of battery type, temperature and the current state-of-charge.  Quality chargers manage amps as well as voltage, so a voltage that might be excessive under some circumstances may be fine if the charger is limiting current (amps) as well.

There are some good articles available that explain charging without going overboard on the tech stuff. Try one of these:
http://www.chargingchargers.com/tutorials/charging.html

https://www.batterystuff.com/blog/3-stages-of-smart-chargers.html


In my opinion, 14.1v is high for "float charge" to keep a battery at 100% but not for the earlier stages of charging that get it to 100% in the first place (bulk and absorption charging). Most battery experts agree that 13.3-13.6 is the target to holding a battery at full charge.

For the record, lead-acid refers to the battery internal chemistry; floodedcell, AGM and Gel are types of lead-acid battery design. Flooded cell batteries are the ones with a loose liquid electrolyte and can be either open or sealed. AGM places the electrolyte in a sponge made of woven glass may and Gel uses a thick gel electrolyte. All, however, are lead-acid batteries.
« Last Edit: June 15, 2020, 10:58:01 AM by Gary RV_Wizard »
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Mark_K5LXP

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Re: Solar charging voltage question
« Reply #8 on: June 15, 2020, 06:13:23 PM »
The controller manual says "All of control parameters could be set and modified" but I saw a few that couldn't.  I've come to expect that with the low end controllers.  The thing to do is match, line by line, as best you can the operating parameters of the solar controller and the charging requirements of the battery.  What I see is that this controller is probably better suited to "intermittent" use than "daily" use an RV might see but it will "work".  When you factor the vagaries of solar panel input and loads, the precision of the solar controller isn't the longest pole in the tent.  For sure, you've got a platform to play with and study cause and effect going forward, with which you can better understand what you'd want to change "next time" to suit your application.

Mark B.
Albuquerque, NM

jrclen

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Re: Solar charging voltage question
« Reply #9 on: June 15, 2020, 08:49:31 PM »
Okay. Thanks everyone. I talked with a local battery shop owner and he told me the 14.1 was fine. I'll keep an eye on things and I still plan to disconnect the battery when the camper is not being used. I bought the battery from Walmart and have no idea what the specs for charging are. I could and might do a search to see if I can find them.
2006 Jay Feather 19h hybrid

jrclen

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Re: Solar charging voltage question
« Reply #10 on: June 15, 2020, 09:54:50 PM »
Gary, I'll look at those links.
Isaac, I don't have a solar disconnect that I know of.
I'll try to look up the battery manufacturer to ask them about it.
2006 Jay Feather 19h hybrid

Ex-Calif

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Re: Solar charging voltage question
« Reply #11 on: June 16, 2020, 05:25:24 AM »

Ex-Calif - the battery is a lead acid, not agm. Is the voltage to high for one of those? I agree about the clear as mud instructions. That's why I'm here asking. LOL I did see something about adjusting the maximum charge. Just wondering if I should look closer at that and try to adjust it downward.


Monitor your fluid levels for a while. 14.1V float is a little high for flooded wet batteries. 13.3-13.5V is preferred - nothing bad will happen but it can gass off ore quickly so if you find you need to service it a lot see if there is a 13.5V float setting.
"Marvin" - 1997 Georgie Boy Pursuit 3150 - P30 Chev 454
Various classic MGBs
Ex-liveaboard boater - Class A newbie in sponge mode

jrclen

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Re: Solar charging voltage question
« Reply #12 on: June 16, 2020, 08:01:14 AM »
Thanks, I will look for a setting. I noticed when we are camping the voltage stays at 13.7. The 14.1 is when nothing is on other than the propane detector and it is not connected to shore power.
2006 Jay Feather 19h hybrid

Gary RV_Wizard

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Re: Solar charging voltage question
« Reply #13 on: June 16, 2020, 09:39:02 AM »
Most modern converter/chargers manage float voltage to 13.6v, so your 13.7 when on shoe power is pretty much normal.  It seems your solar charge controller is a bit higher, but its not much different than a car alternator.

It appears you have a common automotive-type 12v battery. Those aren't very fussy about charging voltages - they are designed to take high inrush and outrush currents and relatively high alternator voltages.  Assuming its not a sealed (maintenance free) battery, just keep an eye on the electrolyte level in the cells. If it goes a few months without needing to add distilled water, you probably have nothing to worry about. However, if you see a loss of liquid or a lot of wetness on nearby surfaces, I'd be looking to dial that voltage down.
Gary
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Isaac-1

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Re: Solar charging voltage question
« Reply #14 on: June 16, 2020, 06:04:46 PM »
My only suggestion at the moment is to upgrade to a better solar controller, after all this is a $20 30 amp solar controller, at that price for that many amps I suspect it has more than one shortcoming.

Victron makes a nice 30 amp MPPT solar controller that should drop right in https://www.amazon.com/Victron-Energy-BlueSolar-Charge-Controller/dp/B076N5PTBN  though the price is considerably higher , it could also be rewired for higher panel voltage and better off peak performance from your existing panel setup, this assumes you have around 400 watts of solar panels now which would be the limiting factor for a 30 amp solar controller, if less solar panels a smaller one would also work.
« Last Edit: June 16, 2020, 06:07:44 PM by Isaac-1 »
2002 Safari Trek 2830

jrclen

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Re: Solar charging voltage question
« Reply #15 on: June 16, 2020, 06:36:01 PM »
Here is the battery I bought.

https://www.walmart.com/ip/EverStart-Lead-Acid-Marine-RV-Battery-Group-27DC/164242687

I will keep an eye on the electrolyte level. So far it is still right on the mark. But it's only been a couple weeks. Thanks Gary.

Isaac, that controller is kind of pricey. So far it seems our camping will be at sites with shore power, so the solar at this point is just something that came with the camper. My concern is basically not trashing my new battery.
2006 Jay Feather 19h hybrid

Mark_K5LXP

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Re: Solar charging voltage question
« Reply #16 on: June 16, 2020, 09:11:46 PM »
I have a LMS2430 solar controller which I know nothing about. I have a blinking green light and a constant red light.

The flashing green light means the controller is still in bulk mode so that voltage could be totally normal (even higher in absorb or equalize mode - green LED on solid).  The red light means the external load is enabled but that may not matter depending on how you have it hooked up.

What I see with a lot of controllers is that they default or are permanently set to overly conservative values, and tend to undercharge batteries that see a lot of use.  So while your concerns are valid I think they probably lie with the converter and not the solar controller.   The converter stands a much greater chance of overcharge and water dissolution since it can be on for days, weeks or months on end where solar is really only "on" a fraction of the day.  Watch voltages and water levels and over time you'll determine what the values for your system need to be.

Mark B.
Albuquerque, NM

Ex-Calif

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Re: Solar charging voltage question
« Reply #17 on: June 17, 2020, 06:47:41 AM »
That sure looks like an AGM battery not a flooded cell but either case you are fine, IMO.

I am suspecting you don't have 400W of solar panels - Maybe one 100W panel?  So the controller you have is "adequate" and I would definitely not buy an MPPT controller. I had 400W on my boat and used a PWM controller for years. Above 400W I would definitely do MPPT but that's a whole nuther conversation.

If you only have this one house battery and as I am guessing, one solar panel you are OK.

Keep in mind that what is more likely to kill your battery 10 to 1 is not overcharging by 1/2 a volt - it is deep dishcharging cycles. Even 50% discharges can cut battery life in half.  I personally like to target 30% discharges and you can make a deep cycle battery last 10 years or more.

1 - Size the battery bank for the consumption you expect. It is easy to burn though 30 amps in 12 hours... Your battery is 109 a/h
2 - Size the solar and other charging to fill that 30amps each day

A 100w panel makes 8 amps in full sun. Conservatively you plan for 70% efficiency so 6amps and then plan for 7 ours of sun = 40amps a day. If you have a couple days of rain you will likely be depleting your battery.


Here is the battery I bought.

https://www.walmart.com/ip/EverStart-Lead-Acid-Marine-RV-Battery-Group-27DC/164242687

I will keep an eye on the electrolyte level. So far it is still right on the mark. But it's only been a couple weeks. Thanks Gary.

Isaac, that controller is kind of pricey. So far it seems our camping will be at sites with shore power, so the solar at this point is just something that came with the camper. My concern is basically not trashing my new battery.
"Marvin" - 1997 Georgie Boy Pursuit 3150 - P30 Chev 454
Various classic MGBs
Ex-liveaboard boater - Class A newbie in sponge mode

jrclen

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Re: Solar charging voltage question
« Reply #18 on: June 17, 2020, 09:24:21 AM »
Thanks Mark and Ex-Calif. As we are always plugged in to shore power I consider the solar a good way to keep the battery charged between camping trips (no significant loads) which this summer will be every other week. When we dry camped (I think that's the term) with the old pop up, I monitored the battery voltage and charged it every day with the generator (with the converter).

The battery is flooded cell. And it's the only one. I will watch the battery and monitor the electrolyte as well as the voltage so as not to overly discharge it. 30% sounds like a good number to me.

Thanks for the info on the green and red light Mark, that's helpful to know. As it the tip about the converter.

Thanks to everyone for the information.
2006 Jay Feather 19h hybrid

Gary RV_Wizard

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Re: Solar charging voltage question
« Reply #19 on: June 17, 2020, 09:40:16 AM »
Quote
That sure looks like an AGM battery not a flooded cell
Not an AGM.   An AGM is totally sealed and would not have the removable caps on top.  That is a basic Marine/RV flooded cell, which is a slightly modified car starting battery design.    In RV Use, it has a useful life of about 3 years if lovingly cared for and as little as 16-18 months if not.
Gary
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Ex-Calif

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Re: Solar charging voltage question
« Reply #20 on: June 17, 2020, 10:34:07 AM »
Not disagreeing that it is a flooded wet cell battery but it is designed to be maintenance free - That is it is not vented and you should no remove the cap.  It does have a vent for when the battery does get overcharged and it will vent.

And not trying to be argumentative but these batteries (and I have used many) will last 10 years if properly maintained with <30% discharging.

I agree 100% that if used as a "deep cycle" ~50% + discharges you can expect to buy new ones every 3-5.  On boats where you can have an 8 battery bank, battery life is a really hot topic. Boat guys freak out when they have to spend >$1,300+ for a new set of Trojan t105s.

But again - I am learning the expectations of the RV world are a lot different.

Not an AGM.   An AGM is totally sealed and would not have the removable caps on top.  That is a basic Marine/RV flooded cell, which is a slightly modified car starting battery design.    In RV Use, it has a useful life of about 3 years if lovingly cared for and as little as 16-18 months if not.
"Marvin" - 1997 Georgie Boy Pursuit 3150 - P30 Chev 454
Various classic MGBs
Ex-liveaboard boater - Class A newbie in sponge mode

Mark_K5LXP

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Re: Solar charging voltage question
« Reply #21 on: June 18, 2020, 10:22:43 PM »
And not trying to be argumentative but these batteries (and I have used many) will last 10 years if properly maintained with <30% discharging.

Right, but you only get to use 30% of the capacity you paid for at a time.  So you paid for and are hauling around 3 times as much battery as you're using.  There's no overhead associated with that? 

Calendar time isn't the only measure of life.  If the goal was to get them to last as long as possible you'd put them in a cool, dark place and never use them at all.  Batteries run your stuff.  If you run them twice as hard they last half as long but you still got everything you paid for.  Unless I missed it you don't get a prize for limping these things along for the better part of a decade.  Given the typical use model most RV's have you'd be doing really well to cycle them hard enough to actually use them up before they expired.  You can get anything to "last longer" by not using it.  Why would I do that?  I buy batteries to run my stuff, and that use costs me money.   It's hard to picture a use scenario with an RV (or a boat) where a bank replacement is but a drop in the bucket in overall acquisition, operation and maintenance costs.   I don't see any discussions about maintaining a certain speed to optimize oil or tire life.  Batteries are no different in terms of a consumable.  I *want* to have a bank sized so I wear it out, if it's any bigger than that all I've done is paid more for it at the front end and lost out on use in the back end.  The DOD and cycle life discussion would be different if this was a large off grid storage bank powering a house.  RV's aren't that.

Mark B.
Albuquerque, NM

Ex-Calif

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Re: Solar charging voltage question
« Reply #22 on: June 19, 2020, 05:06:15 AM »
Life cycle cost can get complicated but here is the basics.

Let's say one consumes 50 amps a day. One buys a 100 ah battery and cycles it to 50%. It lasts 3 years so over 9 years you buy 3 batteries.

Another buys 2 batteries and cycles it to 30%. It lasts 9 years and you bought 2 batteries. You also have 100 extra ah in case of a dry spell. One could argue about the up front investment cost but opportunity cost these days is like 2%...

One issue is do you have room on an RV to double the battery space?

The bigger issue is how do you use the RV. If you are plugged in 100% of the time, you should just have an AC powered RV. So if you are plugged in 90% of the time even 1 battery is probably enough. The more one decides to boondock the more important the plan becomes.

I am already thinking to add a second layer of batteries to my rack (4 total & plenty of space) and 400w of solar on the roof.  With this setup I can basically boondock full time as long as propane holds out.

I know I have only been here a nano-second but I am pretty shocked at all the solar and battery discussions. RV folks may think batteries lasting 3 years is great but it's really not in my opinion.

Right, but you only get to use 30% of the capacity you paid for at a time.  So you paid for and are hauling around 3 times as much battery as you're using.  There's no overhead associated with that? 

"Marvin" - 1997 Georgie Boy Pursuit 3150 - P30 Chev 454
Various classic MGBs
Ex-liveaboard boater - Class A newbie in sponge mode

Mark_K5LXP

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Re: Solar charging voltage question
« Reply #23 on: June 19, 2020, 01:33:00 PM »
Part of the problem with the RV application is the wildly varying and disparate use of batteries and chargers.  Many have grown to accept that their batteries will expire quickly because the way they're used, that's all you can reasonably expect.  Even if the use model is carefully understood it's usually not practical to optimally size a bank for a given user.  So even with proper care and charging you can end up with a wide range of mild to severe cycling under one owner.  Compounding the problem is the idle time.  These things can sit for months at a time and there are all manner of hazards that cause early battery death, from inadvertent draw through parasitic loads to improper float voltages to stratification damage.  While I wouldn't consider the application itself severe there are plenty of opportunities for problems that a lot of folks aren't aware of and don't have the experience or knowledge to mitigate.  Compound the problem with lowest common denominator charging and monitoring equipment most RV's come with and it's a train wreck in the making.  I'm guessing few spend weeks on end studying battery data sheets and charge profiles, then deploy a temperature compensated battery management system to cover all the bases.  Most folks buy an RV to travel or go camping, not to become an electrochemical engineer.   The usual progression of events is you run the thing, the batteries crap out for some inexplicable reason, you buy new batteries and move on.  If it weren't for my past life working with these things I'd probably be right there too.

Your idea of doubling the Ah and extending the life works only when the cycling is that neat and predictable, and even then the benefit is slim.  Most days of the year the DOD is zero, some number 20%, some number run all the way down and maybe left that way for a while.  Often recharges are just bulk from day to day, then there might be a period where they're floated for an extended time.  On and on, the variables are far too mixed to forecast any kind of lifespan and when compounded with the storage issues the chances of a battery surviving more than a few years of that isn't likely.  So my premise is to use them up before the other cumulative trauma takes it's toll.  Which isn't as easy as it sounds, you mentioned a 50% duty cycle in your example lasting only 3 years. That's three years straight of daily cycling - who does that?   Guessing that even full timers would plug in for some percentage of that.  While I believe a storage battery's potential life is greater than 3 or 4 years in my experience they're showing decline at 6 and by 7 they're pretty much done.  That's under controlled conditions, which would be tough to pull off that long in an RV.  Then we're back to service life.  The service life - delivered Ah - between 80% DOD and 50% DOD is only a small percentage different.  So it becomes a race between using up the battery before age and all the other factors does it in.  So doubling the Ah is sound in terms of operating margin but it's my position you'll never have that bank around long enough to recoup the small percentage service life advantage that configuration offers.  Folks are welcome to try but all it takes is a few operational insults over a span of a few years to negate that incremental efficiency margin. 

Mark B.
Albuquerque, NM

Ex-Calif

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Re: Solar charging voltage question
« Reply #24 on: June 19, 2020, 02:22:19 PM »
I agree fully that the duty cycle for an RV can be very difficult to predict. I agree that "most" RV owners just want to "use" their RV for their particular purpose. I agree there are hazards to the duty cycle inherent in how an RV is used.

The area where we diverge is the relative harm of a 50% vs. 30% discharge - By most all measures and data battery cycles are halved compared to 30% duty cycle.

So for the RV owner who just wants to "use" his RV, peace.  They can live with whatever they get.

I am of the opinion that a diligent owner who wants to learn a bit and mitigate the hazards, and yes probably add some better battery monitoring equipment can have significant savings over someone who does not. For the vast majority who travel from site to site plugging in every day?  You don't even need solar. But something as simple as a SoC device would alert the owner to run the generator for a while if SoC approaches 40%...

At the other end the more one plans to boondock, the more one can save by planning the entire DC system better.

I spent many years off shore racing, sometimes up to 10 days at a time. I spent a lot of time "vacationing" in my own boat "on the hook" - DC self sufficiency was/is critical for off-shore boats but admittedly with 800ah of batteries, 400w+ of solar and a 150 amp daily energy budget it's a whole nuther financial model.

So if someone here asks, "Why do my batteries only last 3 years?" I feel compelled to lay out at least the major factors.
"Marvin" - 1997 Georgie Boy Pursuit 3150 - P30 Chev 454
Various classic MGBs
Ex-liveaboard boater - Class A newbie in sponge mode

Mark_K5LXP

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Re: Solar charging voltage question
« Reply #25 on: June 20, 2020, 11:35:20 PM »
The area where we diverge is the relative harm of a 50% vs. 30% discharge - By most all measures and data battery cycles are halved compared to 30% duty cycle.

Define "harm".  Batteries are "harmed" by any degree of use, including non-use.  The more you use them the quicker they die, just like anything else.  Like tires they have a "best by" date that no matter how many miles, or "cycles", they will no longer be serviceable.  If you wear a tire out before it ages out, you got all the service you could ever get from that tire.  Same exact thing can be said for batteries.

The measure of a battery's service life isn't cycles.  Cycles are a measure to quantify the effects of depth of discharge to be sure, but the measure of performance is how many Ah it delivers.  That is a function of cycles and DOD, how many amps it delivered to the load.  When you create a graph that factors Ah delivered then the cycles becomes much less significant.  Depending on the battery and how it's used it usually shows that 30% DOD is no better in terms of delivered Ah than 80% DOD.  There is usually a small "bump" in efficiency somewhere between 40 and 60% DOD, about 5 to 7%.  So all this whizzing about the 50% rule is all to gain a single digit percentage net in delivered Ah.  That would be under ideal conditions.  Throw in the above vagaries of storage and use and I would offer that target would be difficult or impossible to achieve.

Going back to the cycle life graph we should look at the 80% DOD point.  I recall with T105's that number is around 600 cycles.  Most folks will never come close to 600 cycles on their batteries, ever.  3 weeks a year plus some weekends is only a couple hundred at most before the clock runs out.  If you're full time then you would probably want a bit more operating margin and only go to 50% on a new pack since as it ages you will be drawing into it deeper and deeper and at some point you'll be hitting the 80%DOD capacity limit.  But this is still many hundreds of cycles which represents years and years of use, all at 50% DOD or greater.  If you don't get years and years it's not DOD, it's some other operational factor.

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So if someone here asks, "Why do my batteries only last 3 years?" I feel compelled to lay out at least the major factors.

There are many but way down on the list is DOD.  Way high on the list is improper charging, storing and maintenance.  These effects are cumulative and folks just don't get that the ongoing subtle operational insults to the battery affect longevity.  People treat them as an "energy bucket" they empty and fill back up which works for a while but if you really want them to last you have to pay attention to temperature, absorption time and voltage, and float voltage.  Plus electrolyte if they're flooded.  Batteries don't complain and operating parameters complicated to interpret, so they will work to some extent under marginal conditions until they don't.   With so many offering the advice "don't run your batteries below 50%, you'll kill them very quickly" the first assumption when batteries crap out is yep, I ran them low last year, that must've done it.  When more likely their converter is marginal or they were run dead in storage, left partially charged for an extended time, or who knows what.  DOD is not the enemy, not by a long shot and there should be no anxiety running them right down to 10.5V if that's what the situation demands.  They're made to do that or the manufacturers wouldn't spec them for it.

Mark B.
Albuquerque, NM

Ex-Calif

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Re: Solar charging voltage question
« Reply #26 on: June 21, 2020, 06:23:01 AM »
Peace brother... I think you can have you opinions and they’ll work for you but you can’t have different science. I have have a lot of experience with batteries lasting 8-10 years. There’s a ton of battery science out there.  3 years or less is a terrible life for a battery....
"Marvin" - 1997 Georgie Boy Pursuit 3150 - P30 Chev 454
Various classic MGBs
Ex-liveaboard boater - Class A newbie in sponge mode