AGM vs Flooded. weight & longevity

landyacht.318
landyacht.318 Solar Expert Posts: 82 ✭✭✭✭
in General Solar Power Topics #1
Why are AGM batteries significantly heavier than similarly sized flooded batteries?

I'm looking to replace the 3 115 a/h Everstarts in my CamperVan which have only lasted 11 months of daily cycling 3 to 12%. They are 14 months old and outside the free replacement warranty. One developed a bad cell and the remaining 2 fall below 12 volts overnight using only around 20 a/h.

I don't think I'd benefit from having AGM's at significantly more than twice the price. Unless the extra weight means that much extra lead and at least twice the number of discharges cycles.
I only have one 130 watt panel and the heaviest load of any duration will be an air compressor of <25amps.

I'm looking at some Crown deep cycle flooded batteries (20 minute drive, 105$ each) but I've noticed:
The Crown 27dc24 (105 a/h) weighs 51 LBS.
The Crown 27dc36 (115 a/h) weighs 59 LBS. Same exact size as above battery
My slightly smaller 27 sized Everstarts (115 claimed a/h) weigh 50.8 lbs.

Lifeline AGM:
Weight: 65 lb
Rated Cap. Amp. Hrs. – 20 Hr Rate: 100
Length – in: 12.01
Width – in : 6.60
Height – in : 9.25

The slightly smaller AGM has 5 to 15 less a/h but weighs up to 14 more lbs.

Are AGMs less prone to develop bad cells? Will they recharge any faster with my small panel?

Since I have no concerns with ventilation or ease of access, or excessive vibration, are the AGM's worth it?
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    Re: AGM vs Flooded. weight & longevity

    The AGM's have a better charging efficiency, about 95%, compared to the flooded cells 80%.

    BUT, you need to have an accurate charge controller with remote battery temperature sensor, and adjustable 3 stage charging, as the AGM's will NOT tolerate any overcharge, they vent, and you loose water, that cannot be replaced.

    I'd suspect that your 130W panel is not sufficient to recharge your batteries in 1 day, and that sitting 3/4 charged overnight, is sulfating them early. I'd hold off on getting AGM's till you have a batch of flooded cell batteries that last you 4 years. Otherwise, you will kill the AGM's quickly too.

    You didn't mention what your charge controller is either, maybe adding another panel, and a MPPT controller is required.

    With a bank of 3 batteries, you should look into the diagonal wiring methods explained and diagrammed here:
    Connecting on the "diagonal" will extend the life of the batteries by helping share the loads.
    http://www.smartgauge.co.uk/batt_con.html
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: AGM vs Flooded. weight & longevity

    agms are prone to bad cells too as i know of no battery that is safe from that dilema. if you didn't blow up from those everstarts you won't need to worry about any other batteries outgassing either and i'm not being a smartbut about it either. get whatever is priced best per ah and try to narrow down, if you can, find out what may be at fault being excessive loads or insufficient charging current to the old ones. unless you know everything is fine with your system it could make the same thing happen to the agm batteries.:cry:
    agms do charge up more efficiently, but may not offset enoughly any problems in your system or usage that could've caused those everstarts a premature death.
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  • blwncrewchief
    blwncrewchief Registered Users Posts: 17 ✭
    #4
    Re: AGM vs Flooded. weight & longevity

    landyacht,

    My first advice would be to get away from the marine/RV type batteries. At least go to a gc2 (golf cart/t105 etc) battery as these are pretty much considered the first level of "true" deep cycle. I do not know what room restraints you have but according to your numbers you gave a pair of 6 volt golf carts would give you about 220ah @ 12 volts. So your number of 20ah per day would be less than 10% - good. 130w panel would be about 10 amps charging, 4-5% of ah - good. 3 days no sun would be less than 30% dod - good. By generally accepted numbers with only one 130w panel you should not have more than 220-250ah of batteries. Good bang for the buck is to go to Sam's Club and for $70.00 a battery grab a pair of their GC2's and give them a shot. I have a bank of them and have been very happy with them for the 1 1/2 years I've had mine. They have been flawless, still averaging 89% charge efficiency, and have had no week cells or failures. I load tested them last week to 50% dod and they still tested at same as when they were new. And I have 32 of the batteries. After 1 1/2 years of cycling them 15-20% per day, 30%+ weekly they have seen a lot of use. Just my advice.
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  • landyacht.318
    landyacht.318 Solar Expert Posts: 82 ✭✭✭✭
    #5
    Re: AGM vs Flooded. weight & longevity
    mike90045 wrote: »

    I'd suspect that your 130W panel is not sufficient to recharge your batteries in 1 day, and that sitting 3/4 charged overnight, is sulfating them early.

    You didn't mention what your charge controller is either, maybe adding another panel, and a MPPT controller is required.
    http://www.smartgauge.co.uk/batt_con.html

    I've got a Blue Sky 2512i MPPT charge controller with the IPN pro remote monitor. Most days by 2 o'clock it is in float mode.

    When I first got the system running it was not staying in acceptance, but going from bulk to float. It did this for the first 2 months while I was in Baja. It probably started the sulfation and premature death.
    When I came back, Crewzer recommended I lower the float current and that worked, it stayed in acceptance. Every month I set the acc and float to 16 volts for equalization(15.6 at battery).

    As the batteries became weaker the fridge cycling would knock it from acceptance back to bulk. Since I was using almost no water I raised the float current to 14.6 and set float current 3a per 100a/h and let the batteries decide how much they could accept. They still were using almost no water. Voltage at the battery and the monitor are within .2 volts, higher at the monitor.

    The 2 remaining everstart batteries will crank the 5.2 liter v8 engine over no problem first thing in the morning. The monitor will record a 10.4 or .6 voltage during this. With 3 new batteries this number was from 12.4 to 11.9.

    At this time, I can't afford the AGM's. My question was if the AGM's are that much heavier for their size than flooded, which probably means more lead, I'd think they'd have more capacity or at least that much more longevity.

    I don't have the room to deal with the height of t-105s or equivalent. I do realize a third battery is more than should be added to my panel, but I am able to isolate the third and use it solely for engine starting when boondocking or many days of expected cloud or fog, but have wound up just keeping all 3 in parallel most of the time so they age the same. For these reasons I'm sticking with 12 volt batteries.

    I was thinking the Crown DC flooded batteries would be of good quality as they are among what the host sells. Anything has to be better than a dual purpose made to wally world cheap standard everstart.

    Thanks for the responses.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #6
    Re: AGM vs Flooded. weight & longevity

    Question that comes to my mind,,, Why the .2v drop between the battery and the monitor? Where are the two in relationship to one another. .2v sounds like a huge drop if they are close to one another. Is there a drop between the controller and the batteries, or between the panels and the controller?

    I have a system that the meter is 125' from the battery. Under no load I have less than .1v drop (12v system) between the battery and the meter.

    Tony
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  • landyacht.318
    landyacht.318 Solar Expert Posts: 82 ✭✭✭✭
    #7
    Re: AGM vs Flooded. weight & longevity
    icarus wrote: »
    Question that comes to my mind,,, Why the .2v drop between the battery and the monitor?
    Tony


    The monitor actually reads higher compared to multiple different dvm readings taken at the battery when above ~12.8 volts. Below this they are within .05 volts of each other.

    14.6 v according to the monitor = ~14.38 v at the battery

    12.8 v according to the monitor =~12.78 v at the battery

    12.2 v according to the monitor = ~12.23 v at the battery

    They are about 8 to 10 feet from one another over 10awg.
    Actually with Bluesky's sb2512i and IPN pro remote, the monitor gets it's power from the charge controller over a phone like cable. Mine phone cable is 1 foot long. 6 feet of twisted pair wire goes to the shunt from the monitor.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #8
    Re: AGM vs Flooded. weight & longevity

    I have this vague memory of some of the bluesky controllers needed calibration with a special calibration tool, which I think was a resistor if memory serves. Sounds like your controller may need a tweek. I think the Bluesky web site has instruction as to how to do it. (PS the Bluesky website says that your controller does NOT need calibration) (http://store.solar-electric.com/chvocato.html)

    It also sounds like you may need to find out which if any of your dvms are accurate.

    The 12.2 vs 12.28 or the 12.8 vs 12.78 wouldn't bother me, but 14.6 vs 14.38 would cause me to scratch my head.

    Tony
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  • landyacht.318
    landyacht.318 Solar Expert Posts: 82 ✭✭✭✭
    #9
    Re: AGM vs Flooded. weight & longevity
    icarus wrote: »

    It also sounds like you may need to find out which if any of your dvms are accurate.

    Tony

    I talked with a Bluesky rep at the solar expo in San Diego last week or so and found his answers to my specific questions to be very politic, meaning he talked a lot without answering the question. Got a free hat though.:D

    I did not trust the accuracy of my cheap DVM so I borrowed some of my friends quality ones and found them all to read within .03 or .05 volts of each other. Current flow was quite a different story when testing computer fans.
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #10
    Re: AGM vs Flooded. weight & longevity
    Why are AGM batteries significantly heavier than similarly sized flooded batteries?

    The slightly smaller AGM has 5 to 15 less a/h but weighs up to 14 more lbs.

    I believe the objective answer is that VRLA batteries (AGM and gel) contain less acid per cell than flooded-cell batteries due to the matte or gel content. For a given battery size, the VRLA battery's energy storage density is therefore lower.

    So, for similar size batteries, the VRLA models will typically be rated at a lower Ah spec than flooded-cell variants, and the VRLA modles may be heavier.

    Another issue is that manufacturer's capacity ratings are not necessarily uniform. Trojan Battery manufactures flooded-cell, AGM, and gel batteries, so comparing like-size batteries from Trojan (i.e., all Group 27's) might be a better controlled exercise.

    See: http://www.trojanbattery.com/Products/RecreationalVehicle.aspx

    Hey, we missed you at Solar Power in San Diego!

    HTH,
    Jim / crewzer
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  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    #11
    Re: AGM vs Flooded. weight & longevity
    mike90045 wrote: »
    With a bank of 3 batteries, you should look into the diagonal wiring methods explained and diagrammed here:
    Connecting on the "diagonal" will extend the life of the batteries by helping share the loads.
    http://www.smartgauge.co.uk/batt_con.html

    Mike:

    It seems "diagonal wiring" requires a common terminal where all positives are joined, and another terminal where all negatives are joined; and then, from those two terminals you connect the cables to the inverter. Am I right?

    If my interpretation is correct: Will voltage remain the same? Where can I find such kind of "terminals"?
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #12
    Re: AGM vs Flooded. weight & longevity
    JESSICA wrote: »
    Mike:

    It seems "diagonal wiring" requires a common terminal where all positives are joined, and another terminal where all negatives are joined; and then, from those two terminals you connect the cables to the inverter. Am I right?
    No, that's a buss bar.

    JESSICA wrote: »
    If my interpretation is correct: Will voltage remain the same? Where can I find such kind of "terminals"?

    no, you just need to attach one of the battery cables to the other end of the bank:
    http://www.smartgauge.co.uk/images/batt_new.gif

    They show 4 batteries, but don't let that throw you.
    quote from their site:



    All that has changed in this diagram is that the main feeds to the rest of the installation are now taken from diagonally opposite posts.

    It is simple to achieve but the difference in the results are truly astounding for such a simple modification.

    The connecting leads, in fact, everything else in the installation remains identical.

    Also, it doesn't matter which lead (positive or negative) is moved, Whichever is easiest is the correct one to move.

    The results of this modification, when compared to the original diagram are shown below. Only that one single connection has been moved.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    #13
    Re: AGM vs Flooded. weight & longevity

    Ok, Now I am really lost.

    Can you take a look at this diagram and tell me if what you recommend is the same thing? Or will achieve the same results?

    http://www.solarseller.com/readypower_emergency_and_standby_power__trace_drop_shipped_prices.htm
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #14
    Re: AGM vs Flooded. weight & longevity

    "Jessica",

    The link you posted shows connecting each battery to a bus bar/common point... The drawing would be a 100% accurate way of doing it if each and every wire was the same length (or, at least, the "path an electron would need to travel from +bus to -bus, through the battery harness/battery, is the same length).

    What Mike is suggesting is another way of connecting batteries... It also works because the path of that imaginary electron is the same no matter which battery path is taken from + to - bank connection...

    Either of the above is perfectly acceptable--just depends on which works best for you.

    Imagine Mike's drawing where the Negative bank connection is moved "down" in the drawing to connect to the same battery as the Positive bank connection...

    You can see that the bottom battery has the lowest resistance connection to the load/charger connection. The top battery has to connect through three sets of interconnects (and the lead/connection resistance of each set) to the load/charger bank connection...

    Basically, the bottom battery will be first to supply/accept current and the top battery will be the last... So the bottom battery will "age faster" than the top battery in the string...

    What we are looking for is to reduce/balance resistance between all of the batteries and battery connections within the bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #15
    Re: AGM vs Flooded. weight & longevity

    technically they are the same thing when dealing with that many batteries. we recommend taking power from the opposite ends of a battery bank to help keep some symmetry and thus even charging and discharging. when a battery bank is long it introduces extra resistance on the interconnections for the batteries in the middle for our normal recommendation. in your example jessica, the middle has less resistance and the ends more as wiring would be longer to reach the common buss connection. in a simple 2 battery arrangement the resistance will be equalized between the batteries with our opposite battery/post connection method. you can make it equal in a 2 battery arrangement if the battery interconnects are equal in length to the leads coming off of the opposing battery connections to a buss connection and the power is taken from the buss.

    the key to either way it's to be done is to try and keep equality to each of the batteries so that one battery may not have to work harder than another and thus have a premature failure on some batteries. this is why i like recommending heavier wire and heavier busses with keeping of good connections. this keeps resistances low and more equal. yes, this is very small amounts of resistance, but when dealing with high currents the effects are much more pronounced.

    i like to recommend moving the batteries around occasionally so as to re-equalize all batteries electrically from a physical standpoint. middle batteries to end and end batteries to middle. equalizing charges from a controller or charger help in the mean time, but this essentially sends an over charge to some batteries to allow others to catch up and eventually takes it toll on batteries too imho.
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  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    #16
    Re: AGM vs Flooded. weight & longevity
    niel wrote: »
    ...we recommend taking power from the opposite ends of a battery bank ...

    Thanks, now I understand.

    I have another question, though: In the configuration proposed, do I still connect the mx60 (I mean, the charge controller) to those same "opposite ends" (posts) from which power is taken? In other words: Will I still use the same battery terminals both for the input charge and for the output cables to the inverter?
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #17
    Re: AGM vs Flooded. weight & longevity

    Jessica:

    Yes!


    For the same reasons as well,

    T
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #18
    Re: AGM vs Flooded. weight & longevity

    you can attach to the same terminals as your loads or if it makes connections easier you can attach to the opposite free terminals. if connecting all batteries using a buss this only allows connecting to the buss of course.
    hope you can see this attachment ok as it's been awhile since i've done this.
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  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    #19
    Re: AGM vs Flooded. weight & longevity

    I don't know how do you feel when you participate in this Forum, but I have to admit this is not only instructive, but also “divertido” (in Spanish, “divertido” means “fun”).

    I never thought I would learn so much.

    Thanks to all of you.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #20
    Re: AGM vs Flooded. weight & longevity

    i think i'll agree with you that we consider this as fun. strange aren't we?:roll::p:D
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