diy solar

diy solar

12vFacepalm

AmpD

New Member
Joined
Nov 12, 2022
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137
Hello everyone. Can't say I have any real experience with solar panels. I did drive an 8' ground rod in and have someone wire up a panel box for me once. I have been reading a lot this past week about amps, volts, parallel, series, and wire gauges.

I've realized my error a bit too late but hindsight is always clear. I could have done much worse. My first (well second) purchase was a 4Kw 12v Aims Inverter. It was a $500 discount amazon purchase. I'm honestly just hoping it arrives in functional order and I will be pretty tickled. It was "used very good" condition defined as "damaged packaging". According to terms the item might be slightly used but should be functional.

Now I need your help to build a system around it and avoid any more pitfalls along the way. My household usage is about 2kw/hour so in theory I could power my house from this inverter right? I don't want to go all that far just yet. For now I want to assemble the components for a 26' box truck to RV conversion power system.

I am thinking it should be capable of 500W an hour. I am looking at LiFePo4 batteries in the 300 Ah range. Most quality ones seem to have a 4 in parallel limit. Again I see now why my 12v choice really limited me in growth.

I have not done a true energy audit aside from the ahem *current* power bill. Okay that was a bad joke but I hope at least one person laughs.

Minimum I want to budget constant power for

150W Fridge
150W 2 laptops
50w networking
150w random (led lighting, usb equipment, inverter, water pump)

Surgewise I want to have the ability to pull larger draws like Powertools, Microwave, Waterpot, Airfryer, ect.


I've done some lurking this week to better understand what I am getting into. I've been "wanting too" for years. I finally made the plunge. So far I'm in it 1k. Hopefully won't regret my choice of an Aims PICOGLF40W12V120V Inverter too much in the next decade. I think where it will bite me the most is in batteries and cable. I doubt I will ever push this thing past half it's continual rating much less it's 12k surge. Which I'm willing to bet isn't too smart on a 12v system under any circumstance.

My first regret is wondering if I can ever get cables that will safely transmit 4Kw from banks to inverter at 12v. So before anything goes boom pop ouch maybe I can get some advice?


CABLES & FUSE(S)

2 sets of 4/0 cables ordered cut to length and precrimped. (WindyNation amazon)

24" 3/8 and 5/16 lugs (for inverter connection)

12" with 5/16 lugs on both ends

Originally I was thinking 500 amp inline fuse on the positive wire from bank to inverter. After reading more about wiring I am wondering if this is even safe. My Inverter documentation said 4/0 under 12 feet. I was reading more about wire gauge and amperage ratings. Now I'm confused between what my manual tells me and what wiring charts say. I understand that temporary short surge amps exceeding capacity are "safe" but sustained amps doing so are not cool. I don't see any proper length of 4/0 wire that will transfer 500amps at 12v.

What should I do? I already bought high end of low tier equipment as it has been described. What's next? Perhaps a fuse that burns before my wires? What size will keep my wiring safe but let me get the most of my inverter? 200amp? From what I understand that would limit me to about 2400W on the AC side before it blows right? For safety I must also shorten the wires down to 1ft correct?

Can I go any higher? 300Amps and 9" cables? It looks like I might have to find someone to cut and recrimp my cables but at least I'll have more cables. 6" seems really short to be trying to link components with but it would get me to 400A@12v safely if I did the calculator right. Does that mean all lengths need to be 6 inches including between each battery? Also would I be able to get away with a 6" from battery to fuse then 6" from fuse to inverter for a total of 1 foot between battery and inverter? How about the negative. Would I need to run a second fuse, shunt, or disconnect on that line as well?


I know I made some mistakes already. The best I can do at this point is recognize my limitations and work within them. I don't really see myself ever hitting over 3Kw draw at any one time but it would be nice to run a circular saw if I wanted. I can't believe they even get away with selling 4Kw12v inverters sheeesh!



Yeah a lot of questions already and I am just getting started. The more I read the more questions I have I'm afraid. So as I stroll down the facepalm path knowing I'm going to hit a huge wall at the end. That is now showing itself in the battery department. I'm going to need big ones. So specifically I would like help with branding. I saw some reviews where they claimed the LiFePo4 batteries they were sold were actually Li-ion 18650 cell banks when they cut into it. These brands were FLLYROWER and Mose. I noticed both these brands claimed "newer bms" tech that allowed for unlimited parallel connections. I'm not sure if it means they are junk or why they would misrepresent them. They seemed to be in the same cost brackets as the weize and other brands. As a person who knows nothing aside from trojan as a top brand help school me on the new LiFePo4's please.

What are the economy class batteries 300-400 ah LiFePo4? I was looking at some Weize, Vatrer, and Ampere Time. I wouldn't be opposed to 400Ah batteries if they aren't too cost prohibitive. Suggestions too help me build a bank between 12k-20K Ah@12v. What am I trading off buying economy batteries as opposed to high end. What price ranges am I looking at for these 2 sizes of batteries on the high and low ends?

Second battery question. How to accumulate them without saving up $6k for an all at once purchase. From what I understand unused they don't really deplete very rapidly. Could I in theory buy one every 2-3 months keeping them unused until I get 4 of them. Will this help me avoid the mismatched syndrome? I'm guessing they have some way of storing them in a warehouse before they get to me. What is the standard for long term storage if not using them?


Last question for now.

I want to test the inverter for basic functionality when it arrives. I don't think that will require a lot of amps or at least I hope not. I have a standard 12v car battery I'm not too attached to and it holds a charge. For testing purposes do you think it would be safe to wire up the 120ac output with an outlet and a 6 watt USB lightstrip on a surge protector? That shouldn't draw any massive amps to fry 4/0 24" cables on the 12v side of things should it? I know that sounds like pretty assinine question but I've never hooked up an inverter. There shouldn't be anything in there drawing massive loads if there isn't anything plugged into it asking for one correct?

Yeah I'm a newbie so what. At least I'm old enough now to ask for help lol! Seriously though thanks for any helpful advice on how to proceed without killing myself or my equipment. I'm hoping I didn't jump in over my head but when I saw an old hippy with alligator clips everywhere and multi-sized batteries stacked up on bookshelves in the bedroom I knew i could do worse. I'm usually pretty good at absorbing information. If anything I am prone to overanalyzing it. I should have read more about it but I was getting advice from an old hippy who told me 12v is just fine for 3-6Kw systems. Then I got home and saw the inverter on the steal of a deal shelf. Where I come from the high low end is about as good as it get after all. Sure beats a plug in car inverter and alligator clips. What I really need now is someone besides the hippy to give me a bit of advice and direction.


Edit: I don't have panels or any of the rest yet. My plan is to start with inverter and bank then move on to the panels. In an emergency this will at least let me use my genset efficiently until I get the full system built.
 
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1) So your utility bill shows power consumption of 2kWh per day?
2) That inverter has high idle consumption power (the unity is on but no AC load connected) according to the spec: idle Consumption: <3.47 amps DC which is about 42W, so if it is just on 24 hours, it will consume 42W x 24h = 1008Wh (1.008kWh)! that is a lot of wasted power.
You need for sure to do energy audit first.
4000W 12V inverter is not practical at all, I'm surprised that AIMS makes one.
 
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4000W 12V inverter is not practical at all,
Agreed!
4000W / 12V / .85 efficiency = 392A

You will need fusing and wiring for 500A (unmanageable!)

Do you think you will have a big enough LiFePO4 battery bank to be able to supply 400A? You'd need something like 4x LiFePO4 batteries with 100A BMSs. There are other combinations but pulling 400A from LiFePO4 at 12V is absurd.
 
1) So your utility bill shows power consumption of 2kWh per day?
2) That inverter has high idle consumption power (the unity is on but no AC load connected) according to the spec: idle Consumption: <3.47 amps DC which is about 42W, so if it is just on 24 hours, it will consume 42W x 24h = 1008Wh (1.008kWh)! that is a lot of wasted power.
You need for sure to do energy audit first.
4000W 12V inverter is not practical at all, I'm surprised that AIMS makes one.
Correct 2kWh is my daily home use. I want to set this up in a mobile system. My plan is setting up a 500Wh system and about a 16kWh capacity bank. The 50W constant draw was included in the 500wH projection in the energy audit I presented above. When it is time for panels there will be up to 26' x 8' of real estate to add them. I'm sure we can come up with something.

I realize it is inefficient and not able to safely produce its claimed values. At this point it is more or less a question of.

How much can I get out of it safely?
How do I wire it to do that?

I think I did that gauge/amp calculator wrong. 4/0 is 107 mm2 not 5 lol I don't quite understand that voltage drop 2% variable either.
It is now telling me up to 4.5 ft. is acceptable for a 500A@12V lead. (9.77ft for a 12v 500A loop 4/0 wire) If I understand it a 2ft 4/0 wire would handle the full 12kW 12v surge range of the inverter. Providing I have that 1kA fuse lmao! Having a little fun here of course.

Do ALL wires in the system need to be these lengths or just the ones from Bank to fuse to inverter? If I understand it just the power source (batteries) to load device (inverter). Is this correct?

I've already got the 500W inline fuse and the 2' 4/0wires. I'll get shorter ones before I put any massive loads on but it sounds like I will be alright using it as is. That even in it's inefficiency it will likely last me a long time and serve my needs. Again 2kWh is my household usage. In theory this thing should supply that and safely. I will not be using it for that. I want to get 500w per hour from it. I also want to be able to get a decent upper limit so I could run a rice steamer or other high draw appliances for up to an hour. Knowing I have the potential to power my whole house on the road is a comforting thought. I might not see myself hitting that 12Kw surge range it claims but ...

Can I expect to get 3.6Kw-4.8Kw "surge" draws safely If I was using short wire runs 2ft or less? For example running a 1500W rice steamer for an hour, while intermitantly using a 1500 microwave, and my normal 500W draw all at once without melting wires? a 400 amp fuse should let me pull 4800W before it blows right? That should protect the wiring and I can keep a spare on hand. Is this viable?

In reality the most constant draw I will probably see would be around 2500W for an hour while the rice is cooking. I still want to know what my limits are and what can be done safely. I realize I bought inexpensive but I didn't buy cheap. What I want is to maximize what I bought.
 
Agreed!
4000W / 12V / .85 efficiency = 392A

You will need fusing and wiring for 500A (unmanageable!)

Do you think you will have a big enough LiFePO4 battery bank to be able to supply 400A? You'd need something like 4x LiFePO4 batteries with 100A BMSs. There are other combinations but pulling 400A from LiFePO4 at 12V is absurd.
I'm likely going with 4x 300ah LifePO4 200A BMS style batteries. If I understand spreading it over 4 of them shouldn't be too stressful on things.
Am I better off with Gels?

Unmanageable. Please tell me more.
 
I'm likely going with 4x 300ah LifePO4 200A BMS style batteries. If I understand spreading it over 4 of them shouldn't be too stressful on things.
Am I better off with Gels?
This part sounds great but connecting them in parallel at 12V will be a huge regret having to manage 500A. Equipment to handle 500A will be hard to find and will be expensive.

If you can return or sell that 12V inverter and get a 48V one you would be on track to make a good system.

If you plan to be in this project for the long run, you will eventually get to 48V and it will be an expensive lesson.
 
what to you mean by manage them? I'm confused. Don't you just plug the charge controller to charge them and the inverter to draw them.

Here is one of the batteries I am considering.

 
Look up "sunk cost fallacy". You're getting ready to waste tons of money and time going down the wrong path because you bought the wrong inverter. Return / sell it and start from scratch, write it off as educational cost. Especially for an RV, use quality gear, the cheap stuff won't last.
 
If you really want to run lots of your house you will want to be at 48v - so make sure any purchases can handle both. That way you can reuse it if/when you convert. But 12v is much better (although still not idea) for RV/box truck applications.

Assuming you don’t want to return the inverter and start directly with 48v… (the inverter and wires will be where most of the lost money is if you change voltage).

So make sure the batteries you get can also be connected in series - up to 4s. If you add solar to your system - make sure the solar charge controller can do both 12v & 48v.

Don’t think of that inverter as a 4000w inverter- lots of stuff dies if it runs flat out - but it should run stuff well for one big item at a time.

Battery wiring, especially since you be adding batteries in the future, connect each battery to a bus bar. Use a high quality bus bar (I.e. copper not brass), Blue Sea makes great equipment, but I would really look at a Victron Power In.

You will need to know the power levels of the batteries (how much power the batteries have in them - are they at 90% or 20%). A shunt based battery monitor is the best. Look at Victron Smartshunt or BMV712. (I love and use Victron equipment- but there are other brands out there).

Finally, how will you be recharging the batteries? Solar/ Grid?

Fuse - look at a (Blue sea) class T 400a. That will let you run the inverter to 100% (400a * 13v = 5200w) because a surge lasts just a moment if you look at the spec sheet for the Class T fuses you will find you can use a fair amount of surge too.

Planning- draw up a diagram before buying- this group is really good about helping spot errors.

Good Luck
 
what to you mean by manage them? I'm confused.
Yeah, "unmanageable" probably not the best word. Perhaps "unworkable" is better.

500A is out of my realm of experience and waaaaay out of my comfort zone. I will step back from this thread, i've added all i could, hopefully for the better.

Good luck!
 
So I read something that enlightened me a bit further. In solar arrays 12v=1kW max output. Pretty much E.O.D.

As much as a don't want to hear the "you wasted your $ turn back now" advice it is well warranted. I was excited and received some bad advice without further research before I made a large purchase decision. It appears what this inverter is really suited for is Backup Power Grid Tied situations. The inverter itself can charge a decent bank if grid tied. Should I want to use it off grid I would need a really expensive generator. Sound about right?

Ok I get why I can't use this for a "solar" setup. At 12v the max charge rate I can hope to achieve will be about 1Kw hour and that will take some pretty expensive connections & boxes for solar input. That solar charging is more efficient at higher voltages allowing thinner cables. At 12v 1kW it would take 4 days to charge the bank and be a waste of money compared to a 48v setup charging it daily. That an even more realistic limit for 12v is 600w of panels.



I really appreciate Rocketman here. Realizing I am likely to proceed down the fools path you gave me some sound advice and working knowledge more in line with what I was aiming at. If I do want to proceed down the 12v road I am best off with a 48v end path mindset when making purchases. That until I replace this with something else treat it as a 1kW inverter with a high surge rating.

Curious what if I made 2 banks with a buck device between them. Would that allow the panels to charge the first bank at higher voltage then have it flow into the 12v bank at a slower rate but enough to satisfy the bms? Something like that would require a fuse between inverter and battery smaller than the amp rating of the buck to prevent it from frying out the buck yes? Wondering if that would allow me to setup up an higher voltage system and then limit myself safely with the inverter until I decide to replace the inverter.

I get it I really do. I'm better off returning it as soon as it arrives.
 
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Hey if you can provide the safety and have the money then why not be happy with your 4000 watt inverter. 12 volts is fine and there’s many gadgets that can fulfill your 12 volt dreams.
 
You can also have more than one solar array.

Even with a Victron 150/100 @ 12v that can handle about 1450watts of solar & deliver 100a of power.

The 150/70 are a “cheaper” unit per amp. It can handle 1000w of solar. The reason 48v is often better is that same 150/70 can handle 4000w of solar. It would take four 150/70’s to do the same 4000w @$589 each that can almost pay for the 48v inverter.
 
So I really appreciate the time and efforts here. I've tried to put amazon returns and cancellations in process. We'll see what I get stuck with. I really don't have a large budget for the project and am planning on investing over time.

So what parts are best to invest in first. I will start a new thread since this one is already a "lesson learned" and hopefully mistake avoided by getting in here before any of it officially arrived.
 
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