Need help with solar setup

My system includes 2 240w panels, 40a mppt solar charge controller, 1500 pure sine wave inverter, 2 105ah agm batteries, 250a breaker, gland, y branch connectors, mc4 extension cords, on/off switch. Will be connecting system parallel.

What size wires do I need to connect the batteries to the inverter, and to the charge controller, also battery to battery? The batteries will be less than 1 1/2 feet from the inverter. Everything will be less than 1 1/2 feet apart.
Where do I connect the on/off switch and the breaker?
What else am I missing?
Do I need to add fuses anywhere?

All help is very appreciated. Thank you

Everything that connects to the battery needs a fuse or breaker. There are special DC breakers by midnite solar that I have used a lot. Make sure you wire them with the + facing towards the source of the power you are trying to interrupt. Since a solar panel has a fixed output, you will align your breakers to the battery. Fuses do not care about polarity. Customarily, you would put fuses or breakers on the positive lead. You size the fuse based on the amp carrying capacity of the wire that is connecting to the load. You can put a smaller fuse on bigger wire, but never the reverse.

A 40A controller should use something like 8ga or bigger wiring. It would be fine to wire it with a 40A fuse or breaker. You should also fuse the wires running to the solar panels. That is generally thinner wiring, like 12 ga, so put a 20A fuse between the controller and the panels to be thorough.

The 1500Watt inverter will depend on your system voltage. At 12v it will pull 125 amps (1500/12) at its rated output. Since it also likely has a surge capacity, I suspect they included the 250A breaker for the inverter. If you use that breaker though, you will need to size the wire for the full 250A. 2/0 would probably be okay even though it falls a little short at 195.

The connections between the batteries do not need to be fused, and will likely be fine with 2/0 cable. I would highly suggest looking for welding cable, as it is much easier to work with than the stiffer stuff you would get from Home depot. You will also need lugs to connect the wiring to the battery/inverter/breaker posts. The little screw-terminal types work just fine. You can also get an anvil-style crimper and some copper lugs for not too much money. I want to say I paid 20 bucks for one on amazon.

Anyway, if you have any other questions, feel free to ask

Thank you very much.  

I purchased the 250a breaker separately. This is the breaker I have. Should I use another fuse instead?
Should I use a 20a inline fuse for panels?

Where would I put the on/off switch?
And what size wires should I use to connect the batteries in parallel to each other.
I was going to purchase the wires that have the lugs already connected.

Ki Hd wrote:Thank you very much.  

I purchased the 250a breaker separately. This is the breaker I have. Should I use another fuse instead?
Should I use a 20a inline fuse for panels?

Where would I put the on/off switch?
And what size wires should I use to connect the batteries in parallel to each other.
I was going to purchase the wires that have the lugs already connected.

Hi Ki,
Usually you would use a 4x0 or 0000 guage wire for your connection from the battery to the inverter if you plan on using a 250 amp breaker and fuse. That is overkill for the 1500 watt inverter but a thicker gauge is always better when using 12 volt as the surge amps are huge.if you don't mind me asking what is the model of the charge controller? I ask because the Y connectors should not be necessary unless it's input voltage is really low and you might be throwing away the mppt advantage of cloudy day charging.
Cheers,. David

If I don't use the y connectors how will I connect the panels together in parallel.

Should I use a fuse instead of the breaker?

What size wires should I use to connect the batteries together in parallel?

Ki Hd wrote:If I don't use the y connectors how will I connect the panels together in parallel.

Should I use a fuse instead of the breaker?

What size wires should I use to connect the batteries together in parallel?

wires between paired batteries would usually be the same guage as the mains if you were building to code. Small mobile setup often use a thinner guage but that is cutting corners.
Breakers tend to be more forgiving then fuses and you get a second chance so if budget allows I say breaker.
That controller is not really an mppt controller. It's a pwm controller that mimics a mppt. It's what I suspected. You will for sure need those y connectors and hook up your panels in parallel as you planed. If you want the functions of an mppt and have not already purchased the controller I would suggest another unit. Basically you get charging out of your panels earlier in the day, later in the day and on cloudy days. It balances out the charging better.

Thank you David, I don't know why they false advertise those.

Should I use a 20a inline fuse between the panels and charge controller?

Where would I put the on/off switch?

For fusing the panels, look on the nameplate for the Isc (short circuit current) which is the max that the panels can produce. If you are going to run them in parallel, then double that value. This is how much current your wire will need to carry from the Y to the controller. If it is less than 20A (and it should be) then you can use 12 ga wire and a 20A inline fuse on the positive. Depending on how far the panels are from the controller, you might need to size up the wires to prevent too much voltage drop - but you can stick with a 20A fuse. You are really just trying to protect those wires from a double fault - the controller getting fried and the panel wiring short circuiting - since in that case the fuse for the controller would be too large for the smaller wires. It is also convenient to have a way to disconnect the panels if you need to work on other parts of the system.

As for an on-off switch ... for what? The controller will always be connected, and the inverter will have a switch on it to turn it on and off. A more complicated system might include a disconnect between the battery and a main bus if you wanted a way to shut off power while working on the wiring or something. I am not sure what good it would do you. You can always just disconnect the battery at the terminal to power it down fully.

And David's suggestions of using 4/0 cable is likely a good one. Bigger cables are better, but also bear in mind that you only have about 1200Wh of actual usable capacity in your battery bank - so running a full 1500W load will flatten them in 48 minutes.

I read to have an on/off switch if you need to work on the panels or other parts.
I have a few generators and shore power to use also.

Hi Ki

I'm sorry, but I have bad news for you.  You've been scammed.  The controller you bough is a fake MPPT, that is frequently circulating around Ebay and Amazon.  The name of the company is "MPPT Solar".  It is actually a low-budget PMW controller.  So, when you see on the label it says "MPPT Solar Charge controller", what they are legally stating is that it's a PMW charge controller made by MPPT Solar.

I would immediately complain and try to return it.  Otherwise just throw it in the garbage and start over.  It would work marginally if you wire your two panels in parallel instead of series, but the too high voltage is likely to damage your batteries if left too long.  Look for a more reputable company, like Epever.  A good rule of thumb for a real MPPT is the shipping weight.  If the shipping weight is 8lb, it's real.  If it's 8oz, it's fake.

What size wire and lug is this?

Ki Smith wrote:What size wire and lug is this?

Ki, I could show it to Hubby, but without something like a ruler or coin or known size bolt right beside it, he'd simply have no safe way to make a useful suggestion.

A ruler and dime on the wire and lug

Hubby says he can't say just from the pictures, but here are some tests you can do:
1. Some lugs are all copper, and some are copper-plated steel and the way to tell is with a magnet.
2. Some wires are all copper, and some are copper-plated aluminum. The way to tell that is to strip off a bit of the insulation at one end, spread out the strands of the wire, and hold a lit match under it. Copper will be fine. Aluminum will melt. Pure copper wire will have a larger current carrying capacity.
3. Carefully look at the wire to see if the gauge or square millimeters of size is stamped on to the insulation anywhere. You can't tell the conductor size by the outside measurement because you don't know how thick the insulation is.
4. If you're buying any electrical equipment or parts online from a discount provider, you need to derate it by 50%. As Michael suggested with one product that you posted, weight can be one indicator you can check.

This positive wire came with my inverter just didn't want to buy more unnecessary wire for my system. I need to purchase 8 awg cables

Ki Smith wrote:This positive wire came with my inverter just didn't want to buy more unnecessary wire for my system. I need to purchase 8 awg cables

From past experience from entry level inverters it's probably 6 gauge or the better ones 4... So rated for 60 or 80 amps max. A little more that that in air. The problem usually happens when you try to run something big. The wire can't handle the initial inrush of current so the voltage collapses and your inverter turns off. That 250 amp breaker will serve no purpose except as an off switch as it would still chug along as the wire melted so if you want safety add a correctly sized breaker to it. You can use it and probably be fine but those wires are for occasional use in a mobile application and are meant to get you to buy the inverter not to meet any kind of standard.
The wire and breakers cost money but gives a lifetime of peace of mind.

My application is going in my bus, I'll just purchase the 8 Guage and 4 Guage wire

4 ga will be adequate for running your inverter, and like David says, put a smaller breaker on it. 125A to 150A would be about right.

Ok thank you

Minor suggestion. For the more mundane items -- cables, lugs, fusing, etc. Go to McMaster-Carr. They are THE industrial maintenance supplier for US industry. The products they offer are top notch.

In case this is helpful to anyone there is an awesome eBook for setting up a solar station:

https://permies.com/wiki/137968/ebooks/Solar-Station-Construction-Plans-Ben

Just throwing it out there, perhaps this is a solution for someone.