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Forum Index : Solar : AGM 2 of 140am or a 330ah?
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hi Looking at replacing my battery bank and could use some feedback. I suspect my battery bank is on its last legs, will do a few tests this weekend. Its currently using 6v wet cells, 220Ah. A 48v system. Looking at Giant AGM batteries, good prices and dont see to many bad reports. I can either go for... 4 330Ah 12v AGM's in series. $2400 approx. Pro, more capacity. Con, really heavy, and if one battery dies, the bank will be offline until its replaced. 8 140Ah 12v AGM's in series parallel. $2160 approx. Pro, lighter, if one battery dies I can keep the bank online while its replaced. Con, less capacity. In theory this will give 280Ah ( or more ) capacity. Thoughts? I have no experience with AGM, but I've read they can be discharged much harder than wet cells, like to 50%. There is the thing with wet Lead Acid, if you parallel up two batteries, you get more than the combined Ah rating. Would this also apply to AGM? Would 2 140Ah batteries give more than 280Ah capacity? Yes I know Lithium is better, but my budget is $2500 max. Glenn Edit - bugger, cant edit the title. 140ah, not 140am. Edited 2021-04-23 15:55 by Gizmo The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Solar Mike Guru  Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
Glen, we opted for 8 x 6v 300AH sealed lead carbon batteries, rather than standard AGM, as they have a 15-20 year life and can be discharged flat many more times than AGM without suffering damage. Each bat weighs approx 56Kg. No idea what they cost in Aus, bound to be less expensive than here in rip-off NZ. Google 6REXC300. Lifespan Graph All LA batteries; lighter the discharge the more AH's can be extracted to a set low voltage point. Cheers Mike Edited 2021-04-23 19:27 by Solar Mike |
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| noneyabussiness Guru Joined: 31/07/2017 Location: AustraliaPosts: 512 |
Be careful with AGM's too as cycling them regularly will dry them out, with no way of topping them up, had heaps of times with mine having to " crack " the top and topping em up through those tiny holes.... prefer forklift wet cells now, more around the 3500 buck mark, but wayyyyyy tougher and easier to maintain... usually rated at 5c, so solar very easy on em.. If you interested try " CEIL " they have 2nd hand and new ones... they have looked after 4 off gridders I know ( not including me ) and all very happy... I think it works !! |
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sPuDd Senior Member  Joined: 10/07/2007 Location: AustraliaPosts: 251 |
Glenn, I use the Trojan 105 series 6V 225ah wet lead acids (1800ah total). I did all the calculations for cost per ah and life cycle and they always came out on top by a long way. And lithium was moon shot priced for new, and a major fire hazard if using old cells, plus the BMS would cost more than a lead acid pack alone. At the moment you can find the 105's locally for about $250ea. 8 of them would fit your budget. I water my set using a pump & dispenser about once every three months. Currently the bank only gets about 10% depth of discharge per night. My calculations show I have a 10-15 year life span at least. As others have said, they benefit from a good high current stir up, which a gel or agm bank would not handle from what will be 30kw of solar once I'm all done.  It should work ...in theory |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Thats an impressive battery bank Spudd. I'm a bit over the wet cell topping up thing. Some time last year I did the battery maintenance and forgot to put the caps back on, for a month they were open, collecting dust. I suspect its affected them in a bad way, looking very black in there, and voltages are all over the place, even with equalisation. So figured its time to start looking at options. The AGM's seam attractive because no maintenance, and I can discharge to 50%. I've been probably over discharging my wet cells, so going to 50% safely would be good. I had a look at the carbon lead cells SolarMike suggested. Nice, but out of my budget. Looked up the Peukert effect for AGM's, not as high as wet cells. So realistically 2 140Ah batteries in parallel would give 300Ah at max. But I really do like the idea of 2 strings, so I'm not left in the dark if one battery goes down. Plus I could add a 3rd bank later, but not to late. Glenn Edited 2021-04-24 14:06 by Gizmo The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
I am tempted to squeeze the budget and see if I can get a deal on 12 of the 140Ah batteries. That would give 420Ah, 3 strings, and a lot more redundancy. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| noneyabussiness Guru Joined: 31/07/2017 Location: AustraliaPosts: 512 |
Oh and forgot to add, most forklift batteries have a central watering system... mine get topped up about every 2 odd months... I think it works !! |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
I would be tending to go for forklift batteries. They have an 80% DOD rating so if you keep them above that and only do 20-30% most of the time, you'd be laughing for longevity. If you needed to dip deeper on occasion you could without any major problems. At 620 Ah, you would not be taking much out of these compared to what you have now which would be better all round. The lipo proponents talk about the charging current ability but these fork packs can take all anyone would be able to throw at them. As said, the watering systems make the job a non event. Here are some in Fleabay that would fit the bill. I Imagine there are places in brisvegas that could do similar pricing. pack 1 2 3 |
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Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1020 |
Been watching those batteries and other's for a long time, thought they would be selling faster, but some sit there on sale for a long time, probably scraps them if they don't sell within a certain time frame....Haggling opportunity there perhaps. Seems to be few forklift companies moving on to lithium anyway, probably be used in distribution centres for shops etc. You would have to check the price and availability of a replacement cell just incase one might be needed. Cheers Aaron Off The Grid |
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| noneyabussiness Guru Joined: 31/07/2017 Location: AustraliaPosts: 512 |
Just be careful with those ebay specials.. a good friend got bit hard with one ... why i ended up going ceil, they do 2nd hand ( when available) come with dod / capacity test sheet and 12 month warranty... I think it works !! |
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| greg199 Newbie  Joined: 03/11/2015 Location: AustraliaPosts: 39 |
I'd also go for AGMs. The depth of discharge, as you probably know, affects the lifetime so check the spec sheets carefully when comparing AH ratings and number of cycles before they "fail". I had a bank of AGMs in my boat for house use and they lasted over 8 years. Their charging regime was not perfect because my charging system failed a couple of times but they held up well. When designing an off grid house a few years ago I also decided to only use AGMs just to simplify the maintenance. (Never got to build it). Multiple strings is also good in my opinion - I like redundancy and ease of maintenance in systems when you need to rely on them. |
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pollenface Regular Member  Joined: 01/09/2020 Location: AustraliaPosts: 47 |
When pricing AGM I usually look at the lowest cost per Ah of differing battery sizes. Although it's not recommended, you can actually pry the sealed caps off and add a little bit of water. Although there's no "water level" per se, you will be able to tell if one cell looks drier than the others. Edited 2021-05-11 09:57 by pollenface Off grid man caver |
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| noneyabussiness Guru Joined: 31/07/2017 Location: AustraliaPosts: 512 |
Why i said after quote above, " crack " the top off em ( usually a bit of plastic to hold rubber valves on vents) and top em up, PITA but doable..... it amazes me how many AGM's used in solar are actually rated for " standby " use only, because of the above... I think it works !! |
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