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Forum Index : Solar : AGM batteries series parallel thoughts.
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| Davo99 Guru  Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
I agree Tony. Much as I have played with alternate power generation, This little blink this morning was good in how it got me thinking and how naieve I have become. Because the power was down, the net was also. No problem, I was able to link my tablet to my phone ( Oh how modern and teenage tech savvy I am!) and lookup that there was in fact an outage and they knew about it. It made me appreciate that this little play thing I have had on my desk that is a cheap controller on a couple of little 9Ah batteries attached to a little 190W panel on the roof could be a very valuable asset in a grid down situation. Least I can power my phone and charge different lights I have that are battery powered and that little thing is a lot better than nothing. I also thought about what if the net and the Mobile towers are out? Person is virtually screwed. Might have radio but trying to get any real news off that is a waste. Remember that when the fires were around 3 years back. Useless. If for some reason the population was really wanted to be kept in the dark...... That's the way to do it. Maybe I should buy and learn to use a short wave or CB radio? I have already thought of the fuel situation. I believe if there is not a shortage of that may be too exy to buy. Already hearing of better than $2.00 prices round here. Might pay to buy another drum of petrol exy as it is before it gets worse and I have already to stock up on the veg oil and make an effort to go after that and put it away. Someone smart here referred to IBC's of veg as their 10K kwh battery's and that hit home much as I have had to do with veg over 20+ years. That is an excellent term for exactly what it is. THAT I can stock up on and be prepared with for very little cost and something I am going to do. Even a 44 is a 2000Kwh battery and that's an energy density no amount of money can provide by any other means than a liquid fuel. I have already asked the Mrs to start stocking up on food and am looking for another freezer to buy. Lot of things I can put in that and rotate as well as long term store. I had the idea of freezing rice to stop damage by weevils I know it usually contains when you get it. Looked that up and seems a well regarded thing. supposed life of 10-20 years. Tins are also said to last well beyond their use by dates and they are more an Optimum" date than that of good and bad food. Yes, already have that covered. been accumulating a bit of cash of late and stashing it. No damn point having it in the bank to get .5% interest now anyway and if things go down, they won't be giving out money or taking cards. I am definitely going to prioritise my self sufficiency power setups. Might start with that 150A 24V alternator I saw advertised and enquired about last week. That's good for 4KW through an inverter and I certainly have plenty of engines to hook it too. Couple of small batteries for ballast and I can hook solar to and I have another minimal but very helpful system to fall back on. Might be an assett for others to have something similar as a fall back if their grid or offgrid systems fall over as well. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Could someone Decipher the info of this battery for me please? I have tried to work out the AH capacity but I keep coming up with numbers that disagree with what it as advertised at or anywhere near it. Can someone tell me what the AH is and if there is a chart one can work out what the state of discharge is based on voltage. Cant copy the info because of characters but it's a 6 cell battery with each cell rated at 280W data PDF LINK The voltage points to me seem to be very low and indicate very deep DOD. What would be the sensible limit for these AGM's? 50%? I notice on the data sheet they specify 260, 100% discharges in cycle use. Seems very resilient. If they take than then 50% of less ought to give them a good long life. I'm looking at these more for ballast than real capacity for a small backup system to be solar and genny powered. Are there any problems with these being mainly floated with the occasional minor exercise? Edited 2021-12-15 11:12 by Davo99 |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Well, 97 watts for one hour is roughly about 8 amps. So maybe 8 amp hours or something like that when its brand new. Its a small motorcycle "type" battery. If you try fast charging this, its going to gas and dry out very quickly. Its really for very slow trickle charging overnight, then using in something like a high powered photographic flash, where the loads are quite heavy, but of short duration. I suspect ballast operation with serious charging current would kill it pretty quickly. Cheers, Tony. |
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Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 961 |
They seem to be very heavy, much too heavy for a motorbike battery, so I had a better look. I think that is per cell and and with 6 cells that would be 582Wh. Cheers Aaron Off The Grid |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Its all extremely confusing Aaron, they mix up single cell data, and data for six cells. One cell 97watts for one hour, six cells 582 watt hours. 582 watt hours at 12v nominal is 48.5 amp hours. Car battery size for six cells. Edited 2021-12-15 12:30 by Warpspeed Cheers, Tony. |
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| Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 961 |
Yes, good point, car battery size. Depending on the price of these, a set of large truck batteries would work as a ballast as well, provided they where used during the day not over night, they will still be useful for other things, some have deep cycle rating although it is very low for the size. Cheers Aaron Off The Grid |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
If YOU are confused Tony, Imagine how a pleb like me felt trying to make head and tail of it all! Far as I can determine, it's 6 cells @ 280W ea. That's what the manufacturer on the sheet I linked to which hopefully worked specifies. They are -supposed-to be 100Ah but I came up with about every number bar that. I figured 100Ah x2 @ 50% DOD would have about a KWh reserve and handle a decent charge rate. In reality, I would envisage using them where the solar or a generator kept the things near float level and provided the used power. Might get drained a bit for a fridge or something and be recharged in the morning. If these are a viable unit, I might also go 4 of them. Trying to flog a few bits of machinery and things I'm not using so figure I could re invest a little in something like this and a decent inverter. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Using your calcs, 280W x6 = 1680 /12 = 140Ah. Would this be correct? Was how I worked it out too but couldn't figure why they would be sold as 100AH if they are so far over... unless the guy selling them has trouble working it out as well? They are supposedly new and being offered for $80 ea. |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 379 |
Davo, if you plan on using the batteries for backup, then using 50% of their capacity is not a great plan. Like the blurb on the battery says, they can supposedly withstand 260 cycles of 100% discharge. In a stand alone solar setup that is less than one year. Pretty expensive way to use batteries. My batteries are Valve Regulated Lead Acid types. The manufacturers give expected life cycles for different discharge levels. The figures they give are that if I were to discharge them to 80% state of charge ( use only 20% of the capacity) then they should last 12 to 15 years. If I were to take them down to 50% state of charge then they will only last about 8 years or so. Taking them any lower will significantly lower their life. I make it a rule never to go below 80% charge. I don't like paying out money unnecessarily. I would suggest treating AGM the same as VRLA if you want a long life from them. Seems that many solar companies these days rate their batteries in KWH ratings, I guess it is easier for customers to understand, being that there are many different voltages of banks about. Pete |
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| Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 961 |
on the data sheet, Rating 280W at 15 minute-rate to 1.67V per cell 140Ah would be around 50kg battery. Looks like they they rate them like this for UPS use, not seen anything else written up like that. So I still think its 48.5Ah. Well I have learned something different about batteries for UPS, will have to check the one in the ups on the computer. Got the Error "Only ASCII characters allowed in Message, no special characters ( emojis, etc ) Turns out it was the Celsius sign.  Ok I Have Revised my answer, going to 1.67V per cell would make it 53AH Battery, But you wouldn't want to discharge it all the way to get that much.I Checked the Batteries in the Belkin UPS, 12v x2 And surprised to see they too are rated 34W per cell @ 15min , no AH figure anyway to be seen, I worked it out to be about 4.2AH. (Exact same size as the Bugler alarm battery) I was sure the other old ups had An AH rating on the battery's, just shows me that one has to be really careful looking at the advertised figures. I prefer AH or KWH measurement, less confusing. Edited 2021-12-16 12:14 by Revlac Cheers Aaron Off The Grid |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
If I could get 8 years out of these I'd be stoked! I get your point though and from what yourself and others have said, seems my question has been answered and I'll pass on them. I normally see batteries rated in AH but you did mention solar particularly and that's not something I specifically look at. Anything on fleabay or whatever I don't even concern myself with given the pure and outright Fraud that goes on there with most things solar/ electrical. What I see is mainly AH but watts per cell was new to me and it seems other more knowledgeable and experienced people as well. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
I think you have hit the critical point here. The rating of the battery is the devil in the detail. The 1.67 is probably squeezing every last drop out of them and at a very low voltage point. Conversely though, it is a 15Min rating where a lot of others are 20 hours or 5 hours. the lower draw rate may elevate the capacity but pulling them down that far is still an issue. You are better than me. I stuffed around for about 10 Min trying to work out what it was and gave up thinking it was the formatting. You found it, I certainly didn't. I certainly agree. Still 53 Ah over 48 is not of significance and it's certainly not the 100Ah advertised. Perhaps why they were a relative bargain. Should have known. I Checked the Batteries in the Belkin UPS, 12v x2 And surprised to see they too are rated 34W per cell @ 15min , no AH figure anyway to be seen, I worked it out to be about 4.2AH. (Exact same size as the Bugler alarm battery) Those are the standard brick batteries as I call them and some I have are rated at 34w and specced at 7.2 Ah at the 20 hour rate. I also have some the same physical size that are rated at 9Ah. That seems to be right and they are definitely heavier. Seen a few brands like this. You could compare the size but what I have seen, the 4.2 Ah cells are a definite square shape where the 7.2's are a Definite rectangular, undersized brick. Just looking at one I have on the bench, it too is specced as 34W/ 1.67 15 min but it's definitely the 7.2/ 9 ah physical size. I used to use UPS units in a trailer I had for doing onsite work. Was filled with servers and printers and had a tent out the back with another 20 or so laptops. We would do events and someone would ALWAYS just pull the plug where we were connected without considering what it might be attached to and the old servers could take a good 10 Min just to reboot which was a major Pain in the arse especially when you had a line up of people and trying to go flat out. I hooked some cables into the UPS units and then ran them to a couple of large car batteries. That saved us SO many times and I was surprised at the run time I could get out of them which at the longest test, was an hour. I don't know what I ran those batteries down to and frankly didn't care. They lasted a couple of seasons till I sold the setup so Damn good value to me. Some of the more profitable places we went had no power other than dodgy generators so I bought one of my own which was a good move because we were no longer tethered by a Cord and could go where we wanted as well as have reliable power. Couple of times the event hosts tapped into my genny when theirs went down and a mate and I that used to go to these things did running repairs on their gennys more than once. I have often thought how I'd do it now. Probably cover the trailer with panels and I do mean cover. Sides as well as roof and probably have some I could set up on ground mount. Ran 20 Laptops as well as the servers so I don't know would cover all those particularly as we often were still there at night fall but might save running the genny through the middle of the day..... although that was when we were quiet so probably more batteries would help. All up the setup used very little power despite the ancient servers having 3 Power supply's all with 15A plugs on them and being rated at 3000W. I think the 15 Fans or whatever they had used more power than the 8 processors. Wonder if the difference in the ratings that gives 4.2Ah for the little batteries instead of 7.2 applies to the other ones in question? Still don't see them being 100Ah though. I can get the 9ah batteries for $10 ea new. I was thinking about buying 20 or so of those and series/ Paralleling them as a battery bank. Connecting them all up would be a serious pain though. Yeah, I always Convert AH to KWH then I know what it is regardless of voltage in packs. |
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| Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 961 |
A big setup of series parallel batteries is not out of the question, I did this with a heap of those 18650 cells. There will be a lot of parallel wiring and yes it is a pita to do. Not sure about there quality but the old man got some old used ones from the dump that were thrown out after a years service or whatever it was, they where Yuasa brand, made in Japan, got years of life out of them and the plates where thicker than what trojan had in there so-called deep cycle battery. Just for curiosity see how many you would need for this to be viable at a happy discharge rate and amount, then see what the total cost works out to be, would probably use them to half the rated capacity to keep them happy, it might be a a way to keep your fridge and freezer going (with inverter) during a blackout, the food value alone is worth more than those little batteries. Cheers Aaron Off The Grid |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I think this would be a real challenge even with brand new batteries. With a mixed bag of batteries in unknown and possibly questionable condition, the odds are really stacked against you. Batteries in parallel mean that if one dies, it will likely kill its neighbors too. Separate series strings, with the strings individually fused before being connected together might be about the best you can do. Cheers, Tony. |
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| Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 961 |
With small 18650 cells, they usually have fuses between parallel cells, can be 100's of cells, usually if one cell has a short it has never blown the fuse, it just heats up, it would need something catastrophic to blow the fuse, yes it can drag the others down a little if it has a small short, it could take weeks or months to do that. With lead acid you would notice something is wrong before it gets too far as the voltage would drop faster and more than usual under load, then fix the problem if possibly. If in series a battery can will also heat up if something is wrong, not likely to have a fuse in series batteries anyway for lead acid in this situation. Without the batteries in parallel there will be destruction of cells overtime due to unbalance issues, I learned the hard way. Different battery types will react differently, often FLA will fail open circuit or high resistance, I did have one deep cycle FLA on its own with a solar panel charging it every day and running a fish tank, that battery just produced a lot of heat, be noted that the battery had failed to hold charge and was stuffed 2 years earlier, just left it sitting there as to take power from the panel and the fish tank pump takes the left over power. If a heap of small batteries is all that is available there will be a lot of parallel strings, don't see any other way for it to work. Plenty of trucks running around with 4 to 8 batteries in the carriers. Ideally the best way to go (as always) is to use large single battery cells.   Cheers Aaron Off The Grid |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
You could always do something like this :   Three batteries in parallel, but they cannot discharge into each other if one craps out. It could be done very easily with a standard six diode three phase rectifier diode pack. Six, nine or any number of batteries could be connected up this way. Edited 2021-12-18 10:02 by Warpspeed Cheers, Tony. |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1125 |
This is how we have wired our 48 volt 900 AH bank:  Each bank has its own 60 amp charger, all cables back to the inverter bus bar common connection are same length. When I worked installing large banks of telecom batteries at micro-wave sites, where there were maybe 6 x 48 volt banks all in parallel, this was the method of wiring; never had any issues with uneven charge\discharge. Cheers Mike Edited 2021-12-18 11:18 by Solar Mike |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
Warpspeed I think you would need some bleed resistors across the input diodes so the charge regulator can measure the battery voltage, and get power, after dark. Plus the diodes would need to dissipate some serious watts. My batteries have arrived and its all assembled. The leads are equal lengths for each series. I have a 100amp circuit breaker per series.  I'll keep an eye on it and check the currents for each string under charge and under load. A difference in current between strings will be a good indicator of uneven batteries, something a microchip with wifi could monitor. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
With my system the inverter is fed from three diodes, from three separate sources. Straight from the panels, from the battery, and from a grid powered rectifier (when its switched on). Yes the particular diode doing the work gets hot, but its only about 1% of the total power being lost in the heat sink. I only have one battery, and the solar controller is connected directly to it, so the problem does not arise. If I had multiple batteries, I would probably fit multiple solar controllers fed from the same panels and no charging diodes. But you are quite right, the charging diodes could (should?) be shunted with resistors. The current required to run the solar controller at night will be very small, and voltage measurement not of any importance at night. Cheers, Tony. |
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| bob.steel Senior Member  Joined: 27/02/2020 Location: AustraliaPosts: 188 |
I'm getting 340 Ah @6 volts cost $5K for 48 or $105 per battery? LFP only 1/4 capacity needed = 85Ah but 8 of 100 Ah in series gives 96 volts . at an ebay cost of $360 per battery = $2880.. Hmm ! Some notes oon LFP . Buying individual cells has become quite dicey. You cannot buy new cells from China . Its illegal for them to sell them under original patents with USA and Japan. The cells you can buy are refurbished by the military and have had at least 2 years prior use . Usually they meet the stated capacity but you can be unlucky and get duds . Getting three in the same batch though seems unlikely and I'm wondering about the veracity of that claim.Ive had one die after the first charge but otherwise in probably 100 cells now thats the only one I've been unable to bring back to life and I cut it up to have a look and the burning on the plates was obvious . Ill see if I can attach a pic here. Lately the Russians have been scamming in the ali express market and the cells are offered dirt cheap and don't arrive! You must fight to get your money back and they will keep it if you are slack. One way the patent agreement is overcome is to value add in China so by building cells and constructing them into plastic cases with BMS installed they can sell to the world. Chinese firms are also setting up warehouses in destination countries that they bulk ship to by sea and then sell locally. As I've posted elsewhere Digi-Marker have 200 Ah LFP 12 volt batteries for $780 in Australia on ebay delivered and they use their own alloy walled cells in that battery and their own cylindrical cells in the smaller battery versions.  Edited 2022-02-13 09:11 by bob.steel |
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