Entry level system for a small cabin

[Fireside]

Hey Xplode, thanks for your thoughts. Straight up, I just want to say I agree with everything you're saying.. But I guess I've been trying to save you guys from having to hear my whole lengthy and probably boring story lol. The key notes are.. Catastrophic life changing motor vehicle accident with spinal injury which caused a total financial implosion. Which leaves me largely broke, broken, unemployable and fighting anxiety. I've used up any favors I ever earned. Stretched every friendship I ever had and sold off every asset that is surplus to requirement. But I am nothing if not stubborn, and so I'm trying to put some sort of life back together piece by piece. I've learned how to walk again, which is handy.. And I have some tools and talents which I'm trying to position myself to take advantage of.

Right... So the assets are, A piece of rural land in a remote location that I own outright. A car which I own outright, that I'm just barely holding together. And a bunch of tools that I can use to dig myself out of this financial hole I'm in..... If I can just develop my setup enough to do so.. Which is where I'm at currently.

So, I've achieved Step 1. I built a camper, and assembled some basic tools for clearing brush and carving out a small livable patch. I have a serviceable 12v setup, which is barely.. but just enough to exist.

Being honest... And realistic about what I can and can't achieve.. I simply don't think taking a leap to the 48v system is do-able. Initially, I focused my efforts on developing a modular solar solution that I could build upon. But there are so many points of compromise.. like.. Battery banks. you can't just add more new batteries to your old ones over time. Well you can, but as we know, It's an expensive way to wind up with a half new bank that performs like an old one. The cost of 48v controllers is a big step up... The cost of 48v inverters is a bigger step up.. A whole lot of factors have combined to convince me that my best option is to install an interim 24v system for the cabin I'm building, which will be a big step up from my current camper on 12v.. The goal of Step 2 is some rudimentary level of comfort.

My reality is, I simply cannot afford the system I need, and I know it. Heck, friend.. I'm not even close... But I am getting very good at living within my means.. I am literally picking berries and hunting to eat here lol. And I guess the other thing is, in my part of the world Winter is coming.. And it snows here. So I guess I'm scrambling to get a better roof overhead and some panels on it. Because I know I can't afford to run the Genny that much.

On the plus side, If I build a nice little 24v system for now, and it makes life more comfortable for the next 12 months, allowing me to get my workshop built and to develop additional income streams, I can always sell the 24v system as a 1 year old going concern and invest whatever I can sell it for back into the bigger system.

Anyway, sorry for going on a bit.. I'm not angling for attention or sympathy lol.. I just can't think of any better way to explain the situation than the truth as such. I really will use whatever available power I can create.. And not a watt/hour more.

[Fireside]

Ok folks, I've been doing my homework. I researched the configurability of those EPever Upower all in one units and they are as configurable as the Tracer mppt controllers. Which means I can limit max charging amperage if required.

I haven't heard back from the guy who might have some 2nd hand batteries to sell. But I will follow up with him tomorrow. He's one of those, will get to it when he does kinda guys, and if pushed too hard, he'll just bail on the whole thing. It's kinda why I hadn't pursued that option as a preference. But in any case, I will still try to find out what he's got laying around. But I've taken onboard the advice about avoiding telco batts... FWIW, these ones come from remote, solar powered cell tower sites, which have been getting upgraded to include 5G infrastructure. But still I will approach with extreme caution. The ones from mines are usually big thin 150AH AGM's that have had a very short service life, if any..

I feel like I have a time crunch, as I need to head back to the bush tomorrow, and I still haven't ordered anything. The wheels turn slowly out here, so even if I do get something ordered soon, it will be weeks before things arrive.

So, if I may bring this back to the two controller/inveters I mentioned in the OP, I'm convinced that I can't buy separate controllers, inverters and AC backup chargers for the price of one of those Upower all in one units.. And given it's a brand I keep reading good reports about. I'm pretty much ready to push the button on purchasing one of those. Do I just grab the one with the smaller MPPT charger in it? or pony up the extra $200 for the bigger one with a view to hooking up more panels? The fact that I can safely attach more PV to the big one and limit it's charge Amperage as required is definitely making me lean towards that one.

[littleharbor]

With so much blatantly mislabelled rubbish flowing out of China these days, I did some extensive research. One of the reviewers I found particularly useful is Adam Welch on youtube. He buys cheap charge controllers, puts them through their paces and opens them up for a look inside. I must admit, I bought this one based on this review and though I do have watt meters, I've not bothered to do further testing. https://www.youtube.com/watch?v=1z5r3Yo6fmQ

I have another small system running as a standby charge/backup system on a 4x4 which I have on the property, it's using one of the little EPever landstar 10A PWM contollers, the fully sealed waterproof ones. Which I've been very happy with..

At any time the meters he has connected to the controller are showing the SAME current, in and out. Also you can clearly see that the watts in is higher than watts out.. This controller is acting like a PWM controller would. MPPT controllers take the incoming power, (watts), and convert the voltage and current to suit the batteries needs. Basically, watts in = watts out, minus a small loss for efficiency. PWM controllers are basically switches and

whatever current coming in is the current going out, no boost. This is exactly what I see happening on this video.

As to the incoming voltage being higher than charging voltage, The panels are producing their expected voltage and the lower voltage out to the batteries is being clamped by the batteries. There is no magic there. When the higher voltage is stepped down by a real MPPT controller the current should be proportionately stepped up.

[Fireside]

Lucky I didn't pay too much for it then huh... Oh well , all the more reason to get the new system up and move that little unit on to vehicle battery tending duties.

Sitting here trying to find what I read about not adding 12v AGM batteries in parallel, can anyone shed any light on that? If I could get my hands on say 4 of them, is there a reason to not have them wired 2x2 in series/parallel?

[Mike90250]

Wiring circuits in parallel is difficult to achieve perfect balance because of small differences in resistance, Bolt/Lug torque, Crimps, cable length and even Internal Battery Resistance.

AGM cells have very low resistance, so all the external factors will be the cause of current imbalance. then a couple of hot/cold cycles and stuff shifts and the resistance changes yet again !

Here's a long writeup about it http://www.smartgauge.co.uk/batt_con.html

[Fireside]

Awesome, thanks Mike. I've seen that page before and I think I'll study it till I know it back to front. I can see myself welding up a custom battery rack for this setup. Torquing down all the bus bars etc.

[littleharbor]

Here's a direct link to their Technical Info pages. There is a wealth of information throughout their site.

http://www.smartgauge.co.uk/technical1.html

[Sunking]

I have 11 good panels to work with.

11 Panels is a PRIME NUMBER and not going to work. Only PRIME NUMBERS that work are 1 and 3

With a Prime Number only gives you two panel configurations of all in Parallel or all in Series. You need to Gain or Loose a panel so you can wire as many panels in Series like 2S5P, 5S2P, 3S4P or 4S3P. 11 in parallel is just plain foolish and waste of money.

Budget is no object going off grid. By going off-grid you choose to spend a fortune.

[Fireside]

Hi Sunking, yep sadly there were 12.. But the guy selling them got them out on a windy day and just leaned them against the side of his shed for me to collect... With predictable results.. Honestly, I'm glad they all weren't shattered. Anyway, safe to say there was a renegotiation. Ideally, I've pictured trying to get up to 9-10 panels onto the cabin, leaving 1-2 to be installed on a pumphouse at a later date.

I hear you on the price of going off-grid. But I haven't really had a great deal of choices to choose between.. Just a guy trying to make things work with what he has. Australia has a massive housing bubble recently fuelled by Chinese property investors which have driven urban house prices through the roof. Even if I could find affordable rental accommodation with wheelchair access, I'd be spending every cent I could scrape together just to be there. So the short term discomfort of offgrid on a shoestring is something I hope to offset by building the workspace I need to start developing income streams which will give me a future..

If I'm honest, I think on balance I'm enjoying the challenge. Life isn't perfect and as an engineer, I've always dealt with degrees of perfection. In the real world, outside of a machine shop, things are rarely square or flat.. Solar systems are not as good as they could be.. You can't afford a million dollar tractor, so you make do with the 3k one you picked up from a salvage yard and welded back together lol. You use the power you've got, drink the water you collect and when it runs out, you go without or innovate. But I'm not afraid of hard work and I'm pretty good at saving, so the big perfect system will come.

I've made some decisions folks. I'm pushing the purchase button on the bigger of the two controller/inverters today. And I'm off to the bush so I will swing by the bloke who often trades in 2nd hand batteries place and see what he has. Thanks all for the input, I'll let you know how it pans out.

[Xplode]

Keep us posted, and if you can in sure we'd love to see done pictures of it coming together

[Fireside]

Hey Xplode, for the life of me, I couldn't get a stable enough signal to reply from the bush lol. But I'm back in town for a couple of days and excited to take delivery of this.
P_20190328_160346.jpg
It's funny, mostly when I buy things online, they arrive and I think.. huh.. Looked bigger than that in the ad. But this was the opposite. It's a beefy unit and will require a quick rethink as to where I will mount it lol. As well as the controller/inverter I also picked up a PC connect cable and a bluetooth link so I can mess about with an android tablet and see about making a nice little indoor control panel, as the batteries and electronics will likely live in a service hut nearby.

I'm going to do work on my panel maths and cable routing plans. And will post back to see if I'm on the right track.

[jpt]

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.

[jpt]

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

[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.

[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.