Solar cable size (1 Viewer)

[GKD]

I'm looking 20 install 2 x 220W panels and I believe in parallel is best. What size cables to the controller is required. The panels have the following characteristics.

• Max Current (Imp) 10.7A
• Maxes Voltage (Vpm) 20.5V
• Short Circuit Current (Isc) 11.5A
• Open Circuit Voltage (Voc) 24.8V

If the cables are 5m long from the 'Y' piece connecting the panels together to the controller (voltronic 440 duo) , what size cables are recommended please. Max cable length from a panel to the 'Y' piece is 2m. cable dia 4mm

 

[Raul]

From Y piece to the controller, you can go 6mm2 cable. If you use solar cable it will have a very low resistance, double insulated so pretty robust for outside weather.

 

[Gromett]

I always go with 6mm² for solar. Simply because the lower the resistance the lower the losses.

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[autorouter]

5m of 6mm2 cable with a current of 21A gives a voltage drop of 5.5%. You need to be less than 3 - 4%. And that's without the 2m of 4mm2 at 10A giving a voltage drop of 1.5%.

If you can cut the 4mm2 length to 1m, then 6m of 10mm2 would give a voltage drop of 3.8% which is just about OK, although 16mm2 (2.7%) would be better. Try it for yourself using this calculator.

Voltage Drop Calculator | 12 Volt Planet

Use our Voltage Drop Calculator to select the correct Cable for your campervan, motorhome or boat wiring application. Auto and Marine Electrical Components from 12 Volt Planet - Cable Size Calculator

www.12voltplanet.co.uk

 

[Derbyshire wanderer]

5m of 6mm2 cable with a current of 21A gives a voltage drop of 5.5%. You need to be less than 3 - 4%. And that's without the 2m of 4mm2 at 10A giving a voltage drop of 1.5%.

If you can cut the 4mm2 length to 1m, then 6m of 10mm2 would give a voltage drop of 3.8% which is just about OK, although 16mm2 (2.7%) would be better. Try it for yourself using this calculator.

Voltage Drop Calculator | 12 Volt Planet

Use our Voltage Drop Calculator to select the correct Cable for your campervan, motorhome or boat wiring application. Auto and Marine Electrical Components from 12 Volt Planet - Cable Size Calculator

www.12voltplanet.co.uk

6mm is fine for the panel to controller as your calculations are for 12v not 20.5v panel voltage

 

[Lenny HB]

I always work it at 17v which is the minium the panel voltage drops to under max load.

So volt drop with 6mm sq will be about 4% at max output. Although a bit higher than recommended 3%, panels rarely achieve max output when flat on the roof and a long way north of the equator.

Also in summer with high output a small volt drop will not worry you and in winter with much lower output the volt drop will be negligible.

So 6mm sq will be fine.

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[autorouter]

6mm is fine for the panel to controller as your calculations are for 12v not 20.5v panel voltage

Yes, I was thinking of the solar controller output side, not the input side.

 

[Raul]

Oh dear, it’s 440w sent from splitter at 20v minimum ish (it can be 24v), to the controller. Over 5m DC unipolar copper conductor up to 30C deg, with a 6mm2 you will have a delta voltage 0,755v 3.77% drop. Use solar cable and voltage drop is even less. This applies only when panels are peaking max power. A 6mm2 copper conductor it’s good up to 34A.
You will have no real benefit with10mm2 in this scenario.
Before the splitter don’t cut any wires, you have 4mm2 for each 220w total 8mm2, for 2m run. Pis of pis.

 

[GKD]

Thanks for all the advice

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[3crispies]

check controller terminals, struggled with our victron terminal size. Use crimp ferrules too..

 

[Carpmart]

Output side to battery, 10mm2 will be okay, 16mm2 even better. This will be higher amps and lower voltage post MPPT magic.

 

[Sandancers]

Output side to battery, 10mm2 will be okay, 16mm2 even better. This will be higher amps and lower voltage post MPPT magic.

Is this correct? Yes if there was a step down transformer, but the mppt uses solid state components to regulate the output voltage to that needed by the battery at the time.

How could any extra current above the maximum provided by the solar panel be generated ?

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[Carpmart]

Is this correct? Yes if there was a step down transformer, but the mppt uses solid state components to regulate the output voltage to that needed by the battery at the time.

How could any extra current above the maximum provided by the solar panel be generated ?

You have 20v 10A x 2 panels delivering to the MPPT, that output voltage will drop to say 14v out to batteries with a corresponding increase in amps.

 

[Sandancers]

You have 20v 10A x 2 panels delivering to the MPPT, that output voltage will drop to say 14v out to batteries with a corresponding increase in amps.

So if 20A, which is the max the panels can provide, is going in to the mppt controller where do you get extra amps from ? The solid state voltage regulators will not generate any extra amps.

 

[Insider]

Is this correct? Yes if there was a step down transformer, but the mppt uses solid state components to regulate the output voltage to that needed by the battery at the time.

How could any extra current above the maximum provided by the solar panel be generated ?

W=A.V
Watts=Amps x Voltage

Watts is the amount of energy and doesn't change in any instance(so watts into and watts out of the MPPT will be equal) so if voltage is stepped down post MPPT then current must go up.

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[Sandancers]

W=A.V
Watts=Amps x Voltage

Watts is the amount of energy and doesn't change in any instance(so watts into and watts out of the MPPT will be equal) so if voltage is stepped down post MPPT then current must go up.

Not in the case of a voltage regulator. It is regulating the voltage down to 14v, but the max current is already being supplied, 20A, the voltage regulator cannot generate any extra current

 

[Lenny HB]

Not in the case of a voltage regulator. It is regulating the voltage down to 14v, but the max current is already being supplied, 20A, the voltage regulator cannot generate any extra current

Nope incorrect, 20amps @ 20 v =400 watts, 28.6 amps @ 14 v = 400 watts.

 

[StitchUp]

check controller terminals, struggled with our victron terminal size. Use crimp ferrules too..

I agree, terminal size on Victron is painfully small!!

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[Sandancers]

Yes, in a standard resistive circuit, but now you have solid state electronics in the way.

Totally different kettle of fish.

Nope incorrect, 20amps @ 20 v =400 watts, 28.6 amps @ 14 v = 400 watts.

 

[Lenny HB]

Yes, in a standard resistive circuit, but now you have solid state electronics in the way.

Totally different kettle of fish.

That is what the electronics does converts the input power to max output power .
Why do you think a Victron 30 amp controller (30 amps is the output power) is rated for max solar of 440 Watts.

Signed,
Electronics engineer in former life.

 

[Carpmart]

Sandancers - You mentioned in your earlier post you are going to run these in parallel. Series can also work well for solar and big arrays will have a mixture of both.

Series gives you more cumulative voltage, which is then converted to the voltage of the storage you’re using.

In your example, your panels in series may give you 40v and 10A (so smaller diameter wiring can be used) but exiting the MPPT, you get 14v and that may well give you up to mid 20A into the cells.

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[Sandancers]

Ok, so I looked at my manual for my controller and it specifies the same cable size on the input and the output on mppt controller. Would that be the case if there was greater current coming out as going in ?

I can photo the page if you want, but it won't be till next week as we are away right now.

I could also draw a circuit which has voltage regulator and ask you to show where the extra current comes from if you like.

 

[autorouter]

I could also draw a circuit which has voltage regulator and ask you to show where the extra current comes from if you like.

But it's not just a standard voltage regulator. There are electronic techniques to increase voltage or current. In this case the current is increased. The solar controller decides the voltage output required, based on the charge profile, and increases the current as much as it can within the limits of the total input power. Its ordinary electronic engineering wizardry.

For example, this device changes 48V to 12V with an efficiency of 94%. Its maximum output is 12V 10A. For that it requires an input voltage of 48V, and an input current of just over 2.5A, about 2.7A actually. So this will definitely increase the current from input to output.
Amazon product ASIN B07Y6DH4W9

 

[Lenny HB]

Ok, so I looked at my manual for my controller and it specifies the same cable size on the input and the output on mppt controller. Would that be the case if there was greater current coming out as going in ?

Quite likely as the input cable run is probably 5 m where the output cable is probably only ½ a meter. When calculating cable size it is a product of votltage amps and cable resistance, resistance of the cable is determined by its length and it's CSA.

A 6mm sq cable on the input side with a 5m cable, 20v at 20 amps would give a volt drop of approx 3%.
If the output cable was ½m, 14v at 30 amps the cable would only need to be 1.5 mm sq for a 3% drop.

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[Sandancers]

Quite likely as the input cable run is probably 5 m where the output cable is probably only ½ a meter. When calculating cable size it is a product of votltage amps and cable resistance, resistance of the cable is determined by its length and it's CSA.

A 6mm sq cable on the input side with a 5m cable, 20v at 20 amps would give a volt drop of approx 3%.
If the output cable was ½m, 14v at 30 amps the cable would only need to be 1.5 mm sq for a 3% drop.

The table made no allowance for length of cable run. If you look at post #11, which is the one which I originally replied to, that posting is calling for cables to battery of 10 or 16mm sq.

 

[Sandancers]

But it's not just a standard voltage regulator. There are electronic techniques to increase voltage or current. In this case the current is increased. The solar controller decides the voltage output required, based on the charge profile, and increases the current as much as it can within the limits of the total input power. Its ordinary electronic engineering wizardry.

For example, this device changes 48V to 12V with an efficiency of 94%. Its maximum output is 12V 10A. For that it requires an input voltage of 48V, and an input current of just over 2.5A, about 2.7A actually. So this will definitely increase the current from input to output.
Amazon product ASIN B07Y6DH4W9

That's a different electronic device altogether.

 

[Lenny HB]

The table made no allowance for length of cable run. If you look at post #11, which is the one which I originally replied to, that posting is calling for cables to battery of 10 or 16mm sq.

I give up you really don't understand it do you.

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[peterc10]

My Victron app shows me the voltage and current in and out of my Victron MPPT regulator at any one moment The output figures clearly show me that it reduces the input voltage to a figure suitable for the state of my batteries and increases the current flowing, such that the power used (W=VxA) remains approximately the same, allowing for a small loss. I neither know nor care how it does that, but it clearly does.

 

[autorouter]

That's a different electronic device altogether.

It's the simplest example that I could find of a device that reduces DC voltage and increases DC current. No extra bells and whistles like maximum power point tracking and multistage charging profiles like you find in a solar controller.

 

[headlight]

Sandancers my solar is producing 2.8amps at 18.83v but my MPPT is putting 3.7amps at 13.77v into my batteries. So it is putting 0.9amps more into the batteries than the panels are producing.

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