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

[Robmacca]

Guys... for those Electrical gurus...


I currently have an MPPT solar regulator mounted under the centre Console & a 160w Solar panel mounted on the roof. This car doesn't get driven too often and is parked under a Carport making the roof solar useless.


To solve this, I'm thinking of buying a separate Solar Panel to leave out in the sun to charge the batteries in the car during the day. To do this I was thinking of installing an Anderson plug at the rear of the car where the cable would also run up into the Solar inputs of MPPT Solar Reg under the Centre Console and plug the Solar panel into the Anderson Plug to keep the batteries charged.





Now, my question is what size cable should I run from a 160w Panel up to the MPPT Solar Reg mounted under the centre Console?




I'm assuming as long as the cable is rated to carry the current of the panel it should be sufficient? Voltage drop shouldn't really be an issue due to the high volts output of the Solar Panel - Would this be correct?

[Vern]

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[emoji1]. I only work with pv in the 240-1500v range so not 100% sure.

[Gav 110]

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 (https://www.jcalc.net/voltage-drop-calculator-as3008)

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

[emoji481][emoji481]

Gav

[towe0609]

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.

[Gav 110]

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

[emoji481][emoji481][emoji481]

Gav

[loanrangie]

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

[drivesafe]

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.

[Robmacca]

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)

[Red90]

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.

[Robmacca]

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.

I realise that, but with the Regulator being mounted under the cubby box near the batteries under the seat, so the voltage drop is not a huge factor as the voltage output of the solar panel is a lot higher than 12v so if there is a small voltage drop from panel to MPPT, I don't think will make a big difference, as long as the cable can carry the required current... or unless I'm looking at this in the wrong way...

[Red90]

The voltage drop from the panel to the charge controller is important. Every percentage lost is loss of output. It is simple math. Do the math and design your system correctly.

[Red90]

Post up the spec sheet or model for the panel and the charge controller.

[Vern]

I realise that, but with the Regulator being mounted under the cubby box near the batteries under the seat, so the voltage drop is not a huge factor as the voltage output of the solar panel is a lot higher than 12v so if there is a small voltage drop from panel to MPPT, I don't think will make a big difference, as long as the cable can carry the required current... or unless I'm looking at this in the wrong way...Correct. Panel output before it gets to the regulator will be well over 12v. 160w panel will be overkill to keep you batteries topped up too, but if you already have it, use. I'd still just go with 4-6mm2

[roverrescue]

A 160W panel with a half decent MPPT in vague sun for “some” hours a day will keep an Engel running indefinitely

I am certain you could link it with end to end coat hangers, electrical tape and cable ties and keep a battery topped off !!!

I agree with Tim however

No one ever made up a heavy duty Anderson-Anderson extension cable and said
“Geez I wish I went with smaller cable”

Steve

[Robmacca]

A 160W panel with a half decent MPPT in vague sun for “some” hours a day will keep an Engel running indefinitely

I am certain you could link it with end to end coat hangers, electrical tape and cable ties and keep a battery topped off !!!

I agree with Tim however

No one ever made up a heavy duty Anderson-Anderson extension cable and said
“Geez I wish I went with smaller cable”

Steve

I understand that but I'm only looking at the wiring from the Anderson Plug up to the MPPT under the Cubby Box. I've already got 12v extension leads that are of a good size.

[drivesafe]

Hi again Rob and as you are only intending to maintain your batteries during long periods of non use, then even thin cable/wire will do the job.


With that huge panel being used for nothing more than maintaining, then even with light wire, your batteries will be fully charged in less than an hour after the sun rises each day.

[d2dave]

I would use 6mm auto cable which is actually about 4.9mm squared.

A small amount of voltage drop, not that you would get much, is fine between panel and regulator as the panels out put somewhere between 19 to 21 volts.

I run this size cable when camping with 160 watt solar and cable 25 metres long and it works fine.