Thread: What Cable size to run from a 160w Panel to a MPPT Solar Regulator?

Whats the 'high' voltage output of the panel? Assuming its around 18-20v?
At a guess, I'd use 6mm2 tinned copper solar cable, only because i have heaps of it. I only work with pv in the 240-1500v range so not 100% sure.

Hey Robmacca If it’s just to keep the batteries topped up a bit of 2.5mm2 would be fine
If your planning to keep a fridge running go the 6mm2

I use this web volt drop calculator

AC and DC Voltage Drop Calculator AS/NZS 3008 | jCalc.net

It’s quick easy and accurate, does ac and dc and has the Australian standards based cable selection for 240/415 volt ac

The higher the volt drop the less power (wattage) you’ll get at your battery
You can use the panels rated current as a guide to work out your wattage after working out your voltage



Gav

I'm no expert ... but isn't is about system efficiency?

If there is significant draw on the batteries when the car is parked up, then you want to maximise your efficiency and minimise voltage drop. Use the calculator - but I too would use 6mm2 solar cable as I have a supply on hand.

But if its just to keep you batteries topped up, then with a big panel like that it really doesn't matter if the system is inefficient, and a cable rated to carry the max amps of the panel will do - the voltage drop will not be important.

When selecting the panel for a fixed mounting position, you need to take into account environmental factors such as orientation and shading.
160watts sounds like a lot but that is in optimum mounting position, right angles at all times to the sun, temperature at 25 degrees C, sun producing 1000 watts per square meter of solar irradiance
If your not within these specifications you won’t be producing 160watts
Shading can drastically reduce the out put of the panel, even one cell can reduce the panel by 30-90% depending on the cell configuration

Facing NE-NW and around 20-30 degrees is about the best you can achieve

Lots more too it but themes the basics



Gav

i use 6mm auto (4.59sqmm) which is good for up to 50amp.

Hi Rob and this is just a suggestion but may not suit your needs.

If it was me, I would be making up a LONG lead using either 6mm2 marine twin or even 8B&S ( 7.5mm2 ) twin and fitting Anderson plugs to both ends.

This way you would have a heavy duty extension cable, which will cause very little voltage drop while being used on the solar panel and can be used for medium current drawing situations, like running a compressor and the likes.

Overkill on solar wiring is never a drawback, but this would give you other uses as well.

The system will mainly be for keeping the batteries topped up while the vehicle is parked. Currently when the vehicle is parked up for 3-5days, the battery volts drop to around 12.3>12.4v (2010 Puma Defender), so I need a way to keep the batteries topped up to maximise the battery's life. I'm thinking this is what contributed to me killing my good AGM AmpTech Aux battery only after 2.5>3yrs of service. The VSR that I'm currently using keeps both batteries connected down to 12.4v before disconnecting and I'm sure that even though the current draw of the VSR is minimal, over time it all adds up to discharging the batteries.

To solve this, I plan to do something similar that I did on my old Defender and install a Solar panel on the roof for travelling with a MPPT Reg mounted under the Cubby Box. When not travelling I'll use a spare 160w panel plugged into a anderson plug at the rear of the vehicle which runs up and also taps into the MPPT reg under the cubby box. Because of the trees around our place, etc the solar panel might only get about 5>6hrs of full sunlight which I hope will be sufficient when using a 160w panel...

Well, that's my thoughts atm...

(The specs of my VSR attached)

You need to perform math. Find the amperage of the panel at rating power and the length of the cables. Then look at voltage loss. You want to aim for below 3% of the panel’s voltage at rated power.