Better wire for solar panels -> charge controller?

[rossvtaylor]

Or, similar to the shipboard cable zelatore recommended, but available at any Lowes or HD, is an (essentially) equivalent cable sold in the "by the foot" section where they cut it for you. Ask for SOW or SOOW cable, in the wire gauge you want. It's got a durable EPDM outer jacket and is oil and water resistant (proof, more realistically). It's like super heavy duty extension cord. We use it in wind turbine installations in remote areas, some of which are exposed to the elements for years. Really durable stuff and it coils easily.

 

[Herbie]

I use 12AWG Speaker wire, paired inside a single rubber jacket "for in-wall installation": http://www.monoprice.com/product?c_id=102&cp_id=10239&cs_id=1023902&p_id=2816&seq=1&format=2

This stuff is nice because the single cover makes it behave like one wire, and it is VERY flexible. (I keep it coiled in about a 7" loop when the panel is not deployed). I have Anderson PowerPole 30A connectors at both the panel and at the connection to the controller, so I can swap in longer/shorter cables as needed. I've found the cover to be very tough and easy to clean when it gets dirty, which is a nice feature too, since the cable comes inside the van after deployment.

I originally bought the single-jacket stuff specifically because I wanted to run it through a cable gland (and I will eventually do that) - "zippered" paired conductor or two separate jackets don't seal well in a single pass-through.

 

[4RunAmok]

How many amps are your solar panels delivering?

Why the thick PITA wires? 10 Amps will carry over 16 gauge wire for 25 feet without voltage loss.

Head to Amazon and pick up the 25' 14 gauge wire with SAE plugs on it and you can even pick up a surface mount SAE plug on Amazon and have a handy plug on the side of your vehicle that connects directly to your charge controller.

 

[LandCruiserPhil]

How many amps are your solar panels delivering?

Why the thick PITA wires? 10 Amps will carry over 16 gauge wire for 25 feet without voltage loss.

Head to Amazon and pick up the 25' 14 gauge wire with SAE plugs on it and you can even pick up a surface mount SAE plug on Amazon and have a handy plug on the side of your vehicle that connects directly to your charge controller.

▲This▲

 

[IdaSHO]

How many amps are your solar panels delivering?

Why the thick PITA wires? 10 Amps will carry over 16 gauge wire for 25 feet without voltage loss.

Head to Amazon and pick up the 25' 14 gauge wire with SAE plugs on it and you can even pick up a surface mount SAE plug on Amazon and have a handy plug on the side of your vehicle that connects directly to your charge controller.

It has little to do with amps, and everything to do with voltage and voltage drop.

For those running 12V panels with their 12V system, they need every bit of voltage they can muster.

Especially in non-peak sun. A 12V array on a long undersized cord may not produce enough voltage to even provide a charge.

Running larger conductors helps fight that battle, making non-peak sun more productive.



For instance, a 12V panel producing 10amps at 15V using 25' of 14G wire would see a voltage drop of 8.4%

Bump that same setup to 12G and you see a voltage drop of 5.3%

And again to 10G and you see a voltage drop of just 3.3%



Again, that's for the 12V panels.

For simplicity, you can cut those voltage drops in half if running a 24V array

 

[dwh]

For this application I wouldn't care about voltage drop.

With a pwm controller the entire charging loop (battery, wire, solar panel) will be operating at battery voltage anyway.

With mppt the solar side loop will be at vmp.

I'd just want thicker tougher wire laying on the ground, getting stepped on and, in my case, probably tripped over.

 

[verdesardog]

Voltage drop is inversely proportional to wire diameter and directly proportional to current flow.
20 feet of #12 wire @ 10 amps = .32 voltage drop
20 feet of #10 wire @ 10 amps = .2 volts

So you can see there is really not much to worry about when sizing wire unless you have hundreds or thousands of feet to run.

 

[verdesardog]

It has little to do with amps, and everything to do with voltage and voltage drop.

Amps has everything to do with voltage drop, keeping wire the same size, double the current you will double the voltage drop. I=E/R . In other words E=IR where I is current, R is resistance and E is voltage. Simple basic electrical theory.

 

[dwh]

Voltage drop is a theoretical construct that often doesn't actually exist.

I.e.: Battery is at 12v. With a pwm controller the solar will be operating at 12v. Doesn't matter that the solar has a potential Vmp of 18v, it will be operating at 12v.

With the entire loop - battery, wire, solar - at 12v, no matter what size wire, voltage drop doesn't actually exist.

 

[verdesardog]

Voltage drop is a theoretical construct that often doesn't actually exist.

I.e.: Battery is at 12v. With a pwm controller the solar will be operating at 12v. Doesn't matter that the solar has a potential Vmp of 18v, it will be operating at 12v.

With the entire loop - battery, wire, solar - at 12v, no matter what size wire, voltage drop doesn't actually exist.

You don't have a clue what you're talking about. All conductors have some resistance, any current flow through a resistance will cause a voltage drop. As stated in my previous two posts you can see that 10 amps through a 12 or 10 ga wire will have a voltage drop of somewhere around 2/10 of a volt. A pwm controller can not increase the voltage any more than the panel is putting out unlike an mppt controller which can increase the voltage output higher than the solar cells thus negating the small voltage drop from the wires. It is the internal resistance of the cells that will keep the voltage at battery voltage. The voltage on the battery side of the system will be battery voltage, a voltage drop from the wires will cause a lower current to charge the battery. I=E/R there is no way to change the laws of physics. The higher the R the lower the end voltage and/or current. The voltage measured at the cell will always be lower than the voltage at the input to the controller depending on how much resistance the wire has and the voltage the cells can produce which will determine how much current can flow. How much lower? Depends on the resistance of the wire and how much current is flowing. More current flow = more voltage drop which limits current flow. Now if you could super cool your wires..........that's another story.

 

[IdaSHO]

Amps has everything to do with voltage drop, keeping wire the same size, double the current you will double the voltage drop. I=E/R . In other words E=IR where I is current, R is resistance and E is voltage. Simple basic electrical theory.

Nowhere did I ever say that amperage has nothing to do with voltage drop.

Re-read my post.

What I did say (with respect to the post I responded to) is that running a larger conductor in this situation has more to do with voltage drop than it does actual conductor amperage limits.

Which is 100% true.

 

[dwh]

On a phone...which I hate. But I'm doing it just for the hell of it. It does enforce brevity and that's an interesting experiment for me.

(The peanut gallery snickers and mumbles jokes about incorrigible pedants.)

So no deep detailed explanation is forthcoming.

But I do know exactly what I'm talking about.

Q:,Why is mppt good?
A: Because it allows the pv to operate at vmp rather than at battery voltage.

The existence of Internet voltage drop calculators misleads people into thinking that resistance always manifests as voltage drop. Not true...sometimes it manifests as current drop.

 

[dwh]

All conductors have some resistance, any current flow through a resistance will cause a voltage drop.

And the battery is the big resistor limiting the voltage on the circuit.

unlike an mppt controller which can increase the voltage output higher than the solar cells

That is wrong.

It is the internal resistance of the cells that will keep the voltage at battery voltage.

Also wrong.

The voltage on the battery side of the system will be battery voltage

And with pwm the voltage of all sides of the system will be at battery voltage.

a voltage drop from the wires will cause a lower current to charge the battery

No. Resistance causes a lower current. OR a voltage drop. Pick one, but not both. Use the formula you posted.

I=E/R there is no way to change the laws of physics. The higher the R the lower the end voltage and/or current.

And/or. Exactly.

The voltage measured at the cell will always be lower than the voltage at the input to the controller

A) That's backwards and B) it's wrong anyway.

 

[4x4junkie]

You don't have a clue what you're talking about. All conductors have some resistance, any current flow through a resistance will cause a voltage drop. As stated in my previous two posts you can see that 10 amps through a 12 or 10 ga wire will have a voltage drop of somewhere around 2/10 of a volt. A pwm controller can not increase the voltage any more than the panel is putting out unlike an mppt controller which can increase the voltage output higher than the solar cells thus negating the small voltage drop from the wires. It is the internal resistance of the cells that will keep the voltage at battery voltage. The voltage on the battery side of the system will be battery voltage, a voltage drop from the wires will cause a lower current to charge the battery. I=E/R there is no way to change the laws of physics. The higher the R the lower the end voltage and/or current. The voltage measured at the cell will always be lower than the voltage at the input to the controller depending on how much resistance the wire has and the voltage the cells can produce which will determine how much current can flow. How much lower? Depends on the resistance of the wire and how much current is flowing. More current flow = more voltage drop which limits current flow. Now if you could super cool your wires..........that's another story.

×2
One only needs to measure the voltage at the battery with a meter, then measure again at the solar panel, and clearly observe the voltage at the battery will always be lower than at the panel (panel in the sun of course). If this difference in voltage is great enough, the panel can actually end up operating above Vmp (resulting in operation below Imp) due to the fact a panel's Vmp drops considerably with temperature in the hot sun. This most certainly would cause reduced charge current going into your battery.

The heavier gauge/shorter length your wire is, the smaller this difference in voltage will be (the closer the panel will be to battery voltage), lessening the likelihood your hot panel(s) will operate above their Vmp (below Imp).


It is correct however that a MPPT controller can't step up voltage, it can only step up current when it steps down a panel voltage that is higher than battery voltage (if I'm not mistaken, most if not all MPPT solar controllers are simply DC-DC buck converters).

 

[dwh]

×2
One only needs to measure the voltage at the battery with a meter, then measure again at the solar panel, and clearly observe the voltage at the battery will always be lower than at the panel (panel in the sun of course).

Measurement error.

PV to meter to pv. That is a different circuit than the pv to battery to pv circuit and operates at a different voltage (no battery in that circuit, less resistance, higher voltage) than the pv to battery to pv circuit.

Since you are measuring the voltage of a short, low resistance circuit, you'll see the full *potential* of the pv.

But that has nothing to do with what is happening over on the other circuit where the battery is.

In other words...easy to fool yourself that way.