Entry level system for a small cabin

[Mike90250]

Batteries in parallel = race to the bottom (with cycle use. Data centers in standby are fine)

Batteries in series, all batteries see the same charge/discharge, and if matched well ( from the same batch ), age much more gracefully. This is where the flooded EQ cycle comes in and compensates for the outliers. AGM can get a extended absorb for an extra hour and that helps keep those balanced.

outboard balance systems, the more parts you have, the more that can go wrong. There are established techniques to have a long life bank with proper sized cells. Or you can roll your own and hope it works.

[Fireside]

Ok so the more I read, the more questions I end up with. Using the search function I've scoured this site back to 2012, and I've gathered a few more pieces to the puzzle. For instance, the issue I'm facing is one of daily cycling. So the reason data centers get away with large arrays of parallel strings of AGM batteries is they sit for long periods on float waiting for that rainy day emergency use. And according to an old post from SunKing, if left alone on a float charge for a few days, my bank would find equilibrium and be happy for years. Effectively the less I use it the less harm I'm doing it. So I've got all the pieces for a great backup bank. Or armed with this information, perhaps even a dedicated bank for some of my larger cnc machines in the workshop that I use no more than once or twice a fortnight for a few hours at a time.

But it seems there may be a couple of mitigation strategies worthy of investigation and I wondered if you hadn't mentioned them due to them being disproven or just a lack of positive evidence to support?

Testing all my batteries internal resistance to make strings that match each other. If, from my 6 batteries I can put two strings together with internal resistance that is equal to each other within a fine tolerance.. Will that largely address the issue of current differential?

The other thing is battery balancers.. Now that I have some basic understanding of the problem, I can't help but think it sounds like an easy problem to solve. I can measure resistance in real time and apply resistance where needed. through a relatively simple logic circuit. Then on further investigation I find that there are of course products on the market that do that very thing, from reputable companies like victron, with the usual copies from fangpusun and the gaggle of no brand contenders below that. I've scoured the site for discussion but never really found one. I found a few guru's saying nope, don't work, move along... And suggestions that external balancing was too expensive for what you get.. But perhaps the price point has fallen because it doesn't look like too much to spend to make my system perform as I'd like it to. And I'm not aware of Victron peddling hokum. So why would they not do what they say on the tin?

One last thing.. AGM in series.. Everything I'm finding seems focussed on FLA in series. And as I read it.. The way FLA in series achieves charge balance across the string is the batteries which achieve full charge first overcharge and off-gas while passing surplus current on. But that sounds like it would be terrible in an AGM string. Which makes me circle back to.. What about these battery balancers?

[Mike90250]

With AGM batteries, keeping the current (amps) balanced is critical. Otherwise, it's a race to the bottom - the battery with lowest resistance path, does all the work, and starts to wear out, and then as it's internal resistance increases, the next lowest one takes over and over and over again.

Changing to a higher voltage system keeps the same watt hours, but cells are in series and not parallel/

[Fireside]

Hey Mike, or any of the gurus. I've been trying to get my (apparently thick) head around the significance of low battery internal resistance and it's likely impact on my system. And once more I find myself drowning in a world of information and maths, yet not 100% sure I have achieved a fundamental laymans understanding of the issues and possible mitigation strategies.

Here's what I think I get. AGM in parallel is bad.. Just always. Because it's all but impossible to achieve a perfectly balanced bank and therefore some batteries will quite quickly become undercharged (improperly charged?) And fail sooner than they might under ideal conditions. This problem being amplified by the low internal resistance of AGM and it's relationship to the current draw at a given terminal voltage for the bank....?..

So.. If that part is correct. I guess I find myself not understanding what actually kills the batteries young.. Is it that the one in parallel with the lowest resistance is taking more amps in and charging faster than the one beside it.. Leading to the digital charger to consider the bank charged then clicking over to float before battery 2 is ready? And battery 2 never catches up, getting further away from ideal condition.

Solutions/mitigation strategies:
If I'm on the right track up there.. What can I do about it.

I have multiple buildings, Cabin and workshop. So, a mid to longer term solution might be make do for now but save up for a 48v charge/inv with a view to splitting 4 batteries from the 6.. Ending up with two systems, one pair of 12vAGM in series for 24v and the other 4 in series for a 48v system in my workshop..

But for the meantime. Is there anything I can do manually to support better battery condition. I get that regular checks of terminal torque and cable condition is one thing. But is there value to say, isolating pairs periodically and giving them a day to themselves on the system? And/or is there anything I could change about my proposed wiring config to help them?

Thanks heaps in advance for any knowledge you can impart. I promise I do go and try to learn what I need to know before pestering you guys.

[Ampster]

Good to know. I have been using Noalox primarily on aluminum buss bars.

[Fireside]

Thanks guys, I'll grab a tube of No-OX-id for now. Fair chance I will get some of the aluminium anti-oxidant sometime too. I can think of a bunch of applications for it.

[Mike90250]

The conductive grease I have been using is called Noalox and sold at electrical supply houses and home centers.

Ideal 30-030 Noalox Anti-Oxidant Compound, Squeeze Bottle, 8 oz https://www.amazon.com/dp/B000LDE7V4..._9XwwDb3MR6WTG

Thats a anti-ox & grit for aluminum cables. No-OX-id A is for any metal connection and is the better product, IF you are not using aluminum cables


edit add:

"The Ideal 30-030 is an anti-oxidant compound. This anti-seizing compound improves efficiency and service life to aluminum-to-aluminum and aluminum-to-copper electrical connections, provides additional interstrand and inter-conductor current paths for improved conductivity and cooler operation. This compound contains suspended zinc particles to penetrate and cut aluminum oxide, also know as aluminum rust, as well as carrier material that excludes air to prevent further oxidation."

[Ampster]

...
One last thing before I place orders.. Carbon Grease or No-OX-id "A special"... Do you have a preference?

The conductive grease I have been using is called Noalox and sold at electrical supply houses and home centers.

Ideal 30-030 Noalox Anti-Oxidant Compound, Squeeze Bottle, 8 oz https://www.amazon.com/dp/B000LDE7V4..._9XwwDb3MR6WTG

[Fireside]

Figure B

3 parallel AGM is tough and bad. the batteries have such low internal resistance, the cable lug crimps and nut torque, will be major factors

Ok thanks, I'll lock in Figure B.. I'm planning to pull out all the stops on my cable shunt crimp terminations. With conductive grease and torqued fittings.

I'm having great difficulty locating supplies of Larger than 50mm AWG 0/1 cable and lugs. So I'm hoping they will suffice.. According to specs they should be up to the job from an amps point of view. I assume I need to keep any shunts I make as short as possible and all the same length where possible for minimal and matched resistance right?

One last thing before I place orders.. Carbon Grease or No-OX-id "A special"... Do you have a preference?

[Mike90250]

Figure B

3 parallel AGM is tough and bad. the batteries have such low internal resistance, the cable lug crimps and nut torque, will be major factors

[Fireside]

Thanks for the info. Too bad to hear about your leg, I hope it heals well.

There are a couple of other solutions available. Victron is out of my price range. Then there are MPPSolar units and rebranded ones and copies. I'm under the impression that Epever might be of slightly higher quality. Of course, I could buy separate units but it would be more expensive and would take more space (not too much of that in the habitation box).

Which unit did you end up buying?

I went with the UP3000-M6322 : 3000W,max pv input 150V,Max. PV charging current 60A,Max. PV input power 1500W. Spent a little extra over the next one down due to higher PV voltage and input power, which I felt gave me better expansion options so I can max out this 24v installation.

FWIW, the unit is not small. When I read your first post it actually crossed my mind that this beast would dominate some precious wall space. Where separate controller and invertor could offer more flexible mounting options. But I certainly do like the idea of having everything in one box with one software solution to monitor and manage my use. And I hear what you're saying with the Victron. After an absolute ton of research I concluded that Victron has joined the majority of Western companies in manufacturing offshore, with their "Designed in Europe" marketing and factories in India, China and Malaysia. Sure makes it hard to pay double for something that likely came out of a factory in the same industrial district using the same parts.


Hey folks, just finalising my thoughts on placement and wiring of the battery bank.. Done a pile of reading here and various recommended links. Wondering if some of the experienced members could check my working and give thoughts on option A vs B..

12v AGM batteries for a 24v bank.

battery_bank_1a.jpgbattery_bank_1b.jpg

And while I read that 0AWG cable should be sufficient, I thought I'd ask if people agree with that for my connecting cables and hookup to inverter/charger.

[jpt]

Thanks for the info. Too bad to hear about your leg, I hope it heals well.

There are a couple of other solutions available. Victron is out of my price range. Then there are MPPSolar units and rebranded ones and copies. I'm under the impression that Epever might be of slightly higher quality. Of course, I could buy separate units but it would be more expensive and would take more space (not too much of that in the habitation box).

Which unit did you end up buying?

[Fireside]

Fireside, what are your experiences with the unit so far? I'm thinking about putting one into my overland truck, but I cannot find much info on them.

Hi jpt. Sorry for the tardy reply. I'm based in a remote location and don't get to town as often as I might like. Sadly, I can't help just yet. I broke my leg and haven't been able to get up on the roof and install panels, so the unit remains safely in the ample packaging it arrived in. I suspect I will be unlikely to get it installed much before next season. All I can really say about it until then is that it was very well packaged, feels solid, weighs a lot. And has good documentation with it. Not Engrish that requires a translator and a good sense of humor to read. No doubt you will have selected something before then, but I will be sure to give plenty of feedback on the unit when I can.

On the broader subject of my system. I made a battery purchase. Having scoured nearby parts of the world for serviceable 2nd hand golf cart batteries or literally any well priced deep cycle lead acid offerings and coming up empty, I went against good advice and picked up half a dozen Exide J-Series AGM JTT 12V 215Ah Lead Acid Battery

Model No	JTT12V4800
Description	GNB JTT12V4800 Powerfit JTT Series 12V 215Ah
12V
215Ah
Length(mm)	522
Width(mm)	240
Height(mm)	221
Weight(kg)	72.5
Brand	GNB - CLASS 8

BattsOnUte.png

Weighing in at 165lb each They are no joke to move around. So the to-do list now includes build a storage solution for 1/2 a ton of lead and make some super duper cables to hook them up as efficiently as possible.

A bit more detail on the batteries. They are ex data center. Were in service for just shy of 2 years. The seller offered them with a 1 year warranty, and I paid around $300 AUD each for them, which is about $20USD.. Give or take.. lol.

[sdold]

Hi jpt, welcome to Solar Panel Talk. We don't have private messaging, so just wait and see if he responds. It's only been five days since your first message.

[jpt]

Apparently Fireside isn't reading the forum anymore. What do I need to do to be able to send private messages?