# Forum Home Renovation Solar Electrical Systems  how to hook up solar

## warnie100

Hi folks this is all new to me i have a caravan and 2 x 120 amp hr agm batteries a 200 watt panel and 12 volt 3000 watt inverter and am trying to assess how to join the two batteries to get 12 volt at it s best regards wayne

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## John2b

Are they 12 volt batteries? If so connect (+) to (+) and connect (-) to (-). This is called a parallel connection and will give you 240Ah at 12 volts. Use 2 gauge wires (35mm cross-sectional area). 
You'll need a charge controller to connect the solar panel to the batteries  (+) to (+) and (-) to (-), and use a 20A fuse in at least one wire near the battery. Use 10 gauge wire if the panels are more than a few metres away. 
Connect the inverter to the to the batteries with a 250A fuse (if the inverter is not fused). Keep the inverter close to the batteries to keep the wire short and use 2 gauge or bigger wire. 
If you want to make it pluggable, use Anderson connectors with appropriate current ratings (same as the fuse or bigger). 
Make sure all of the connections are securely tightened up, or they will get hot and may burn. 
Below is a simple 12 volt system for a vehicle - pretend the box labelled "large short term loads" is actually the second of your two batteries.  You can ignore the car accessories, battery and voltage sensitive relays in the bottom left of the diagram, because you don't have a starter motor battery in your system. 
You can also see there is an "load" connection from the battery charge controller. This can be used to control a small 12 volt load, such as lighting, and often has some basic built in functionality such as turning on lights at night. You may want to use this feature or not, depending on your own setup. If not, just ignore that section as well. 
The website this drawing came from has a lot of useful info. See: https://outbackjoe.com/macho-diverti...and-inverters/

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## John2b

Re-reading your post I realised you asked a simpler question than I answered! As far as how to connect 2 batteries together in parallel, there is a right and wrong way to match the load on both batteries. Using 2 gauge cables as I suggested goes a long way to keeping them matched by minimising voltage drops in the connecting wires, however below is the correct way to keep the voltage across the terminals of both batteries identical:    https://caravanchronicles.com/guides...s-in-parallel/

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## phild01

Be sure your batteries are equal age, type and charge capacity.

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## chunky59

How would you connect 3 batteries up to a charge controller? 
the batteries are 10  amp hr, 12v, 31/900 Delkor Calcium battery that i got for free when they were pulled off a back up generator system 
i am going to charge them from 2 off 250W solar panels (30.43 V8.23A

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## John2b

Three batteries in parallel (+) to (+) to (+),  and (-) to (-) to (-). In the drawing in post #3 above, put the third battery in between the two shown. Keeping all the four jumper cables the same gauge and the same length will even the load between all 3 batteries. The two leads to the charge controller can be different lengths to suit, but keep them all as short as practicable. 
The two panels should go in parallel too, ie (+) to (+) and (-) to (-). That keeps the voltage the same as one panel, but adds the current of each to give you double current into the charge controller. 
Ideally the wires from the panels the same gauge and  two (+)s go the charge controller panel (+) terminal, and the two panel (-)s go to the charge controller panel (-) terminal. Then the (+) lead from the battery bank goes to the charge controller battery (+) terminal, and the battery bank (-) lead to the charge controller battery (-) terminal. 
Choose an MPPT charge controller, not a PWM one, or you'll only get half the power from the panels into the batteries, or less. And make sure the charge controller is rated at 20A or more with max input voltage of 40 volts or more to allow for panel tolerances and temperature effects on the panel outputs. 
Don't forget to select the appropriate settings for battery type in the charge controller. The settings can usually be found on the battery manufacturer's website. Make sure you look up the settings for the model of battery you actually have, not a different model as most manufacturers have models with different chemistries that need different settings. 
Connect the leads to the inverter on the same battery terminals as the charge controller. They can be different lengths to suit, but use the thickest leads you can and keep them as short as practicable. Double up the leads if the inverter has double sets of terminals, because at 3kw there will 250A in the cables, continuously, not just for a few seconds like an engine starter motor.

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## chunky59

John2b 
Thanks for that info it is great 
I am starting to install them this weekend so that will help greatly 
I am thn going to install approx 10-15 12 v Garden lights in my front yard that i will use the power from the batteries to run at night 
i need to run a cable from the batteries in my garage at the back yard all the way to the front yard to a junction box where it will spli to different some sections of the garden to run some 12 LED garden lights 
See plan attached 
Could anyone provide some help on the wire size i need to do this

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## John2b

Would need to know the amperage of each light to be able to work out voltage drop. If not specified on the light fitting, the amperage can worked out from the wattage with the formula Amps = Watts / 12 volts. So if a lamp is 5 watts, then 5/12 = ~  0.42 amps, and 15 lamps would be 6.25 amps total. 
The lamps might work fine down to 10 volts, so you could get away with 2 volts drop on the cable. To be safe, work on 10% drop, or 1.2 volts. Let's say 50 metres of cable. Then you need to look up what gauge will drop less than 1.2 volts over 50 m with 6.25 amps. Google for a wire size calculator. Don't forget to allow for the copper each way - 50 m of two conductor cable has a return path of 100m total. 
With my example numbers you'd need a seriously thick cable, 10mm2 or more, so you migh want to think about reducing the length by moving the battery closer. To keep the cable cost reasonable, you should aim for a length where you can work with 4mm2 which I think is a common size cable sold for low voltage garden lights. I would use the same size cable throughout as it is harder to make good joins with unequal cables.

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## chunky59

Ok why does it have to be so hard 
i purchased a Fangpusun 30 amp MMPT charge controller then purchased some good thick 15 mm wire to run from the battery to the charge controller 
now i find out the charge controller can only take 13 mm wire 
Can i put some type of connector on the end of the 15 mm wire that has a 13 mm plug/pin on it, that can fit into the charge controller? 
something like the MB in the pic below if it fits 
or is there some other way?

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## John2b

Yes, you can downsize the cable. It might be difficult to find a crimp connector like above for 15mm2 of copper as the largest ones in your picture (yellow) are for 6mm2 max, and larger crimp terminals usually require specialist crimping tools. You should be able to find a terminal strip that can accommodate 15mm2 on one side (=an entry hole >5mm wide), and then join a smaller cable on the other side to fit the charge controller terminals.

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## chunky59

Ok after talking to the supplier of the wire he said it should fit into the controller, it was just a bit fiddly buy eventualy it went in
Now i am trybing to connect the solar panels to the controller
i have two panel that i have joined using some Y connectors
i have check the y connector with a muti meter i am getting about 35 v from it
i purchased some 6 mm wire to run from the y connector to the controller
i then nott thinking purchased some MC4 connectors  that i tried to crimp the 6m wires to MC4 connectors and i am not getting any volts at the other end of the wire
So was thinking it must have been my poor connection attempt, but tried to crimp it a few times and it still gives me no reading
is it the fact that i am trying to crimp a 6m wire in a 4 mm connector and so will not connect properly? 
or is just my poor crimping?

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## chunky59

Ok i solved the problem with my sola MC4 connectors and am now charging the batteries up 
As i may have said before i want to run power from my back yard to the front to power approc 10-15 lights
to avoid voltage drop i wss thinking, to save some money on the thick garden type power cable to run over 30-40  mtrs that i would do the following
- Run a standard double insulted twin cable, from a fuse box, running off my batteries, to the front yard, a distance of approx 30 mtr.  this cable would be running under my house and i would attach it to the bearers under the house
- this would run into 2 off bus bar type units, from there i could feed the power off on a few runs to various parts of the front yard with 3-4  lights on each run, with a smaller cable (this cable would be smaller type cable and therefor cheaper to buy)
- My question is what size of standard double insulated cable would i need would 6mm bo ok? This is much cheaper than garden wiring cable $500.00 down to $180.00 
chunky59

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