Solar panel set up and cable specs

[tchierici]

Here is my planned set up: I have two domestic batteries in series. Then two 25w panels wired to a single charge controller and a another 40w panel wired to another charge controller. The first set of panels will be connected to one domestic battery and the other one wired to the second domestic battery.
My questions are:
1) is this the most efficient way to wire panels with different wattage.
2)I need extension cables. What size and specs do the cables need to be? The distance from the panels to the batteries is approximately 5m.

 

[geem]

Are your domestic batteries wired in parallel? If they are then you need to treat those batteries as a single bank and connect the panels through their controllers to the bank of batteries not the individual batteries

 

[LadyInBed]

I have two domestic batteries in series

Is that 2x6v to give 12v or 2x12v to give 24v?

 

[Boater Sam]

Here is my planned set up: I have two domestic batteries in series. Then two 25w panels wired to a single charge controller and a another 40w panel wired to another charge controller. The first set of panels will be connected to one domestic battery and the other one wired to the second domestic battery.
My questions are:
1) is this the most efficient way to wire panels with different wattage.
2)I need extension cables. What size and specs do the cables need to be? The distance from the panels to the batteries is approximately 5m.

Not separate feeds to 2 batteries, you will not equalise the charge when they are suppling power in series. If the panels and controllers are the same voltage as the 2 batteries in series, connect them both to the ends of the battery bank. Else whys you need different panels and controllers.

 

[VicS]

Here is my planned set up: I have two domestic batteries in series. Then two 25w panels wired to a single charge controller and a another 40w panel wired to another charge controller. The first set of panels will be connected to one domestic battery and the other one wired to the second domestic battery.
My questions are:
1) is this the most efficient way to wire panels with different wattage.
2)I need extension cables. What size and specs do the cables need to be? The distance from the panels to the batteries is approximately 5m.

Do you really mean in series ?

Last year you had a a 40 watt panel charging a 100Ah domestic battery and were considering increasing the amount of battery power.

Surely you must mean that you now have two domestic batteries in parallel

 

[tchierici]

Are your domestic batteries wired in parallel? If they are then you need to treat those batteries as a single bank and connect the panels through their controllers to the bank of batteries not the individual batteries

Do you really mean in series ?

Last year you had a a 40 watt panel charging a 100Ah domestic battery and were considering increasing the amount of battery power.

Surely you must mean that you now have two domestic batteries in parallel

View attachment 131621

Sorry I meant to say they will need to be in parallel (ie 12v)

 

[tchierici]

Are your domestic batteries wired in parallel? If they are then you need to treat those batteries as a single bank and connect the panels through their controllers to the bank of batteries not the individual batteries

Sorry I meant to say in parallel. The issue I have is that the two 25w panels are connected to a controller from which a negative and positive cable are coming out from. The other panel also has a controller with an another set of neg and pos output. Can I just connect the two sets to a bus bar to the battery bank?

 

[tchierici]

What about the specs of the extension cables? There are quite a few different types around

 

[geem]

Sorry I meant to say in parallel. The issue I have is that the two 25w panels are connected to a controller from which a negative and positive cable are coming out from. The other panel also has a controller with an another set of neg and pos output. Can I just connect the two sets to a bus bar to the battery bank?

25w panels are tiny. What is the rating of the controllers? You might be able to use a single solar controller for the two 25w panels. In parallel connections all positives connect together and all negatives connect together. You could do this at a busbar neatly

 

[William_H]

The currents involved will be quite small such that you could use quite small cables. However just for the sake of long life and physical robustness you should use decent sized cable as might be claimed to be 15 amp. Get tinned copper if you can. Do fit a fuse in the wire controller to battery near the battery. ol'will

 

[VicS]

What about the specs of the extension cables? There are quite a few different types around

I'm not sure what you are asking here.
Taking the question of cable size (cross sectional area) first.

Although, as William says, the currents involved are quite small the cable run distances are sufficient to cause significant volts drop.
My calculations suggest that 2.0 mm²will be sufficient but that 2.5mm² would be better. If the 25 watt panels are wired individually to the controller 1.0mm² or 1.5mm² could be used for them. If the wiring can be protected from physical damage and UV thin walled, preferably tinned, cable can be used. Other wise cable designed for solar installations wold be preferable.
You might find not all cable types are readily available in the sizes I have suggested.

There is no problem in connecting two controllers in parallel to the same battery bank but if your existing controller can handle all 90 Watts you could connect all the panels in parallel to it (assuming all are the same nominal voltage). If the controller is an mppt type the closer the panels' maximum power voltages are to each other the better.

If all the panels are connected to one controller increase the cable size between it and the batteries to 4.0 mm² or 4.5mm² unless the distance between the two is very small.

As William says fit fuses as close to the batteries as possible. 5 amp if two controllers are used., 10 amp if all is routed through one

 

[tchierici]

I'm not sure what you are asking here.
Taking the question of cable size (cross sectional area) first.

Although, as William says, the currents involved are quite small the cable run distances are sufficient to cause significant volts drop.
My calculations suggest that 2.0 mm²will be sufficient but that 2.5mm² would be better. If the 25 watt panels are wired individually to the controller 1.0mm² or 1.5mm² could be used for them. If the wiring can be protected from physical damage and UV thin walled, preferably tinned, cable can be used. Other wise cable designed for solar installations wold be preferable.
You might find not all cable types are readily available in the sizes I have suggested.

There is no problem in connecting two controllers in parallel to the same battery bank but if your existing controller can handle all 90 Watts you could connect all the panels in parallel to it (assuming all are the same nominal voltage). If the controller is an mppt type the closer the panels' maximum power voltages are to each other the better.

If all the panels are connected to one controller increase the cable size between it and the batteries to 4.0 mm² or 4.5mm² unless the distance between the two is very small.

As William says fit fuses as close to the batteries as possible. 5 amp if two controllers are used., 10 amp if all is routed through one

Can I just connect up all panels in parallel using a Y branch parallel adaptor then run a single 5m cable sized 4mm to the controller, which is close to the batteries?

 

[rotrax]

That is what I am shortly going to do when I install 400W's of solar through an Epever 30A controler. My cable runs will be less than 5metres.

You will need two cables from the solar, the + and - .

4mm2 cable should be perfect.